Energy Recovery

ENERGY RECOVERY No part of this digital document may be reproduced, stored in a retrieval system or transmitted in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services. ENERGY RECOVERY EDGARD DUBOIS AND ARTHUR MERCIER EDITORS Nova Science Publishers, Inc. New York Copyright © 2009 by Nova Science Publishers, Inc. All rights reserved. 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LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA DuBois, Edgard. Energy recovery / Edgard DuBois and Arthur Mercier. p. cm. Includes index. ISBN 978-1-61728-402-1 (E-Book) 1. Waste products as fuel. I. Mercier, Arthur. II. Title. TP360.D82 2009 662'.87--dc22 2009024627 Published by Nova Science Publishers, Inc.    New York Herrero Martín Chapter 9 Energy Recovery Systems from Industrial Plant Waste: Planning of an Industrial Park Located in the South of Italy Silvana Kühtz.CONTENTS Preface vii Chapter 1 Biogas Recovery from Landfills Sherien A. Concept Overview and Environmental Evaluation Francesco Cherubini and Gerfried Jungmeier Chapter 4 Pinch Technology for Waste Heat Recovery Applications in Oil Industry Mahmoud Bahy Noureldin 1 69 97 141 Chapter 5 Treatment of Secondary Sludge for Energy Recovery Chunbao (Charles) Xu and Jody Lancaster Chapter 6 Energy Recovery from Waste: Comparison of different Technology Combinations Lidia Lombardi and Andrea Corti 213 Energy Recovery from Waste Incineration: Linking the Systems of Energy and Waste Management Kristina Holmgren 229 Chapter 7 Chapter 8 Experimental Analysis of a Combined Recovery System R. Elagroudy and Mostafa A. Warith Chapter 2 Landfill Gas: Generation Models and Energy Recovery Lidia Lombardi Chapter 3 Energy and Material Recovery from Biomass: The Biorefinery Approach. Sara Bellini and Giovanna Matarrese Index 187 253 289 311 . Francesca Intini. . The gases produced in solid waste disposal sites. The most important gas produced in this source category is methane (CH4). The priority for control of the gases is to protect the environment and prevent unacceptable risk to human health. In addition to CH4. pyrolysis/gasification) is used for another purpose such as to generate steam. direct liquefaction.. the gas may form explosive mixtures. Gas can migrate from SWDSs either laterally or by venting to atmosphere. and the potential to utilize the energy content of the gas. pyrolysis. including incineration. causing vegetation damage and unpleasant odors at low concentrations. solid waste disposal sites can also produce substantial amounts of carbon dioxide (CO2) and non-methane volatile organic compounds (NMVOC).Disposal of municipal wastes can produce emissions of most of the important greenhouse gases (GHG). Solid wastes can be disposed of through landfilling. Approximately 5-20 per cent (IPCC 1992) of annual global anthropogenic CH4 produced and released into the atmosphere is a by-product of the anaerobic decomposition of waste. and . can be a local environmental hazard if precautions are not taken to prevent uncontrolled emissions or migration into surrounding land. The several routes that energy recovery can follow from waste are looked at as well. In landfills. while at concentrations of 515 per cent in air. A major source of this type of CH4 production is solid waste disposal to land. Energy recovery in air conditioning systems to promote energy saving and improve environmental quality is also explored in this book. An overview of a variety of secondary sludge post treatment methods for energy recovery is given. of which the most common is waste direct combustion associated with conventional energy recovery in a steam turbine cycle. gasification. the modern landfill site is designed to trap the gases for flaring or use in energy recovery systems. This book examines the energy recovery technologies which use landfill gas to produce energy directly. supercritical water oxidation (SCWO) and anaerobic digestion. Both are considered here as solid waste disposal sites (SWDSs). With the recognition of the formation of landfill gas and its associated hazards. This chapter will deal with emissions resulting from landfilling of solid waste. fuel or electricity generation. Chapter 1 .PREFACE Energy recovery occurs when the energy that is released from a resource recovery process (i. particularly for the landfilling of biodegradable municipal solid waste in non-hazardous waste landfills. incineration or waste-to-energy. recycling.e. methanogenic bacteria break down organic matter in the waste to produce CH4. Landfill gas is known to be produced both in managed “landfill” and “open dump” sites. particularly CH4. The selected model is based on first-order decay equation and considers as basic inputs the years of landfill operation.viii Edgard DuBois and Arthur Mercier a landfill gas control system is therefore required. moderately and slowly biodegradable. energy conversion and environmental impact. In particular. These models will be presented in the chapter. One of these models has been selected for application to some study cases. collected and combusted landfill gas and recovered electric energy avoided emissions. Because of the on-going price increase of fossil resources. Therefore. the behaviour of a landfill where leachate is recirculated was observed. One of these methods is a default base method which all countries can use to estimate CH4 emissions from different types of SWDSs. The obtained configuration for energy recovery was evaluated also from an energetic and environmental point of view. It will then describe two methodologies for estimating CH4 emissions from SWDSs. Finally. implemented and compared among themselves and with data collected from existing landfills. but the energy recovery system definition and sizing. this section discusses sources of uncertainty associated with any estimates of CH4 emissions from SWDSs.and reproduced by means of adapting the landfill gas production model. control mechanisms are required to minimize the risk of migration of the gases out of the site. is a crucial and tricky issue. Further.A great fraction of worldwide energy carriers and material products come from fossil fuel refinery. the selection of an appropriate combination of engines has been carried out with the aim of obtaining the maximum profits from selling the produced electric energy. the feasibility of their exploitation is predicted to decrease in the near future. have been considered dividing the material categories into rapidly. In addition. the uncertain availability. estimating the overall contribution to Greenhouse Effect from escaped landfill gas. the environmental concerns and the fact that they are not a renewable resource. This chapter will describe the processes that result in gas generation from SWDSs and the factors which affect the amount of CH4 produced. alternative solutions able to reduce the consumption of fossil fuels should be promoted. in reference to biodegradation rate. The landfill gas production and energy recovery for the conventional landfill and the landfill with leachate recirculation were compared from different points of view: economic evaluation. It is recommended that countries which have adequate data also estimate their emissions using the second method presented. in order to investigate the management possibilities to enhance energy recovery. in particular the availability and quality of data required. the amount of municipal solid waste landfilled per year. Three different behaviours. Moreover. also in reference to its economic convenience.In this chapter different landfill gas production mathematical models have been analysed. the landfill with leachate recirculation shows better indicator values both for the overall energy conversion efficiency and for Greenhouse Effect specific emission. The landfill gas energy recovery by means of reciprocating engines is a quite widespread practice in modern landfills. reciprocating engines were considered for energy recovery purposes. recording a more concentrated landfill gas production in a shorter time than in conventional landfills . For this reason. Electricity and heat can be provided by a variety of renewable alternatives (wind. Chapter 3 . . Chapter 2 . the municipal solid waste component characterisation and biodegradability. The economic analysis showed that the specific disposal cost is lower for the landfill with leachate recirculation with respect to the conventional landfill. The model has been used to predict the landfill gas production of a case-study landfill in order to properly size the energy recovery system. Chapter 5 . is reported. fumaric acid and oxygen as chemicals and hydrogen. economic allocation) are therefore used and final results compared. is still the most widely used method for energy integration in oil industry. This together with record high oil prices have contributed to a need to examine methods of converting secondary sludge waste into energy. Secondary sludge waste management issues are a continuing challenge. and dewatering challenges. Different allocation procedures (substitution method. The first application is showing the effect of heat integration on both energy consumption and GHG emission reduction in an oil-gas separation facility. This chapter describes the emerging biorefinery concept and provides an overview of the most important biomass sources.Preface ix sun. In this chapter. almost all the types of biomass feedstock can be converted to different classes of biofuels and chemicals through jointly applied conversion technologies. and energy. water. Sludge disposal has become a worldwide problem for many reasons including rapidly shrinking landfill space.g. and in the second application an evolutionary approach to crude distillation pre-heat train design is introduced. exergy and C conversion efficiencies. electricity and heat as further energy carriers. after almost three decades of its emanation in the late seventies for a reason or another.This chapter addresses the problem of waste heat recovery via presenting an introduction to the pinch technology and two industrial applications of heat integration for waste heat recovery in oil and gas business. The biorefinery system is compared with a reference system based on fossil sources. System performances are also investigated with calculations of product yields and mass. In this part. 2. more stringent environmental standards governing the disposal of sludge. biomass). besides fossils. The second part introduces two important applications for heat integration in oil industry [5]. biomethane. authors have overviewed a variety of secondary sludge post treatment methods for energy recovery. The replacement of oil with biomass as raw material for fuel and chemical production leads to the development of “biorefinery”. the only C-rich material source available on the Earth. a LCA of a biorefinery system based on a lignocellulosic feedstock (e. Unlike the primary sludge. Pinch technology is now well documented in several literatures and the refernces 1 to 4 at the end of this chapter are only few main examples. In biorefinery. selection of utility mix and heat exchanger network synthesis using pinch design method [1. The advantages of biorefinery systems over conventional fossil systems are outlined by means of Life Cycle Assessment (LCA): in the second half of this chapter. authors will show how authors can use pinch technology for energy utility targeting. . wood industrial residues) and producing bioethanol and methyltetrahydrofuran (MTHF) as transportation biofuels. the first part introduces some aspects of Pinch technology in brief. increased environmental awareness. an allocation issue must be addressed. The evaluation of the environmental performances reveals that relevant environmental benefits can be gained with a shift from oil refinery to biorefinery: almost 89% of GHG emissions and 96% of fossil energy demand can be saved. Results focus on greenhouse gas (GHG) and energy balances and estimate the possible GHG and fossil energy savings. the secondary sludge as byproduct of the biological treatment is far more difficult to dewater and to be disposed. Pinch technology. furan resins. energy. exergy. conversion technologies and platforms (or intermediates). while the fossil resource alternative for production of fuels and chemicals can be just biomass.Primary and secondary sludges are produced as a result of primary and secondary wastewater treatment in municipal wastewater plant or pulp and paper mills. 3 and 4]. Chapter 4 . The chapter comes into two parts. a relatively young concept in the scientific literature. Since the biorefinery system co-produces many high value products. Chapter 6 . Through this process a biogas with elevated content of methane can be produced and supplied to engines for energy recovery. These processes require being fed by a homogeneous combustible fraction obtained by mechanical sorting and supply as output one or more combustible streams.The present work is found in the field of energy recovery in air conditioning systems to promote energy saving and improve environmental quality. various models are often used as decision support tools. gasification. A critical comparison between these methods is presented with respect to their net energy efficiencies. The combustion can be applied directly to Municipal Solid Waste or can be applied to a stream of selected waste obtained by means of mechanical sorting of Municipal Solid Waste. together with trading in waste and electricity and how this impacts waste incineration in Sweden. When making investment decisions. Some models for assessing waste incineration/ management are therefore described together with strengths and weaknesses when dealing with the dual function of waste incineration.x Edgard DuBois and Arthur Mercier including incineration. to push energy recovery also from this stream.Energy recovery from waste can follow several routes. using several technologies for the combustion. which can be applied through different technologies (wet and dry digestion). Besides the direct combustion of waste. A conflict is also that increased waste incineration can decrease production of combined heat and power in the district heating systems. consisting of a ceramic semi-indirect evaporative cooler and a heat pipe device to recover energy at low temperature in air conditioning systems. besides the combustible fraction stream. making investment decisions or designing policy instruments. Since policy instruments in Sweden are dependent on the common legislation of the European Union this will be addressed. is biological anaerobic digestion. available for energy recovery. pyrolysis. the most common of which is mobile grate combustor. The combination of schemes will be analysed in this chapter in reference to a study case characterised by an average waste material composition. direct liquefaction. Chapter 8 . The above-mentioned technologies can be combined in several schemes to optimise the overall energy recovery. but another option. The comparison will be carried out using some indicators of the overall energy recovery for each scheme. At present the fate for this stream is biological aerobic stabilisation. The most common one is waste direct combustion associated with conventional energy recovery in a steam turbine cycle. This chapter addresses the importance of taking this into consideration when e. When Municipal Solid Waste mechanical sorting is applied. Chapter 7 . Conflicts between the internal market in the European Union and waste management goals are shown. a humid fraction is also obtained. The advantages and drawbacks of each treatment option are also highlighted in this chapter.Energy recovery from waste incineration has a double function as a waste treatment method and a supplier of electricity and/or heat. The design of two policy instruments will be described as examples of the conflicting goals in the two systems. supercritical water oxidation (SCWO) and anaerobic digestion. a design of experiment (DOE) and an analysis of variance (ANOVA) were applied with the aim of .g. alternative possibilities for thermal treatment are gasification and pyrolysis. Waste incineration thereby links the systems of waste management and energy. For characterization purposes. characterised by a high presence of organic biodegradable fraction. Experimental research has been carried out whose aim is the characterization of combined recovery equipment. Chapter 9 . The authors present the results of a research study that authors are conducting on an Italian firm that produces polyethylene terephthalate (PET) supports for waterproof membranes from plastic bottles. A cost-benefit analysis is then carried out to plan how the whole industrial park can use the industrial waste to produce the energy it needs. The combined system built allows a feasible energy exchange between the supply airstream and the return one. An estimation of the energy saved by the combined system was carried out. A factorial design was performed by analysing how the factors used affect the characteristics analyzed. authors compare environmental and technological aspects of some innovative energy recovery systems from industrial waste. The authors first compared a traditional thermal waste treatment with a molecular dissociator and then with a specific gasifier.In this chapter. improving the operation in air-conditioning systems. . and can produce electric and/or thermal energy. The contributions of the single factors and their interactions were presented by carrying out a variance analysis. All three technologies can be fed with basically every type of waste. It is a new alternative device for use as a recovery system. In particular. The characterization of the system was carried out by employing experimental design methodology. showing the possibilities of implementing this solution to save energy and also to improve the indoor air quality by means of increasing the ventilation rates. For this firm (and all of the firms in the same industrial park). the waste represents only an undesired cost rather than a potential energy source.Preface xi better understanding the energy behaviour of the combined device. with economic and environmental benefits for all. The configuration chosen (crossed flow) is the most adequate from an operational point of view. The superiority of the evaporative cooling device under the operating conditions was clearly shown. the latter two produce syngas that can be burned after depuration to produce energy. . and Center for Environmental Engineering Research & Education (CEERE). can be a local environmental hazard if precautions are not taken to prevent uncontrolled emissions or migration into surrounding land. A major source of this type of CH4 production is solid waste disposal to land. Approximately 5-20 per cent (IPCC 1992) of annual global anthropogenic CH4 produced and released into the atmosphere is a by-product of the anaerobic decomposition of waste. 350 Victoria Street. Fax. Manshiett Elbakry. Patrick A. In addition to CH4. The most important gas produced in this source category is methane (CH4). methanogenic bacteria break down organic matter in the waste to produce CH4. the gas may form explosive mixtures. 403-282-7026. PEng. Egypt. Canada. In landfills. particularly for the * J. Alberta. Civil Engineering Department. jhettiar@ucalgary. Toronto. Cairo. Associate Head of Undergraduate Studies. Both are considered here as solid waste disposal sites (SWDSs). Solid wastes can be disposed of through landfilling. incineration or waste-to-energy. With the recognition of the formation of landfill gas and its associated hazards. Professor of Environmental Engineering. Department of Civil Engineering. The gases produced in solid waste disposal sites. M5B 2K3. 11341 2 Ryerson Polytechnic University. PhD. 13 El-Makreezy Street. Elagroudy and 2Mostafa A. Calgary. while at concentrations of 5-15 per cent in air. This chapter will deal with emissions resulting from landfilling of solid waste. Gas can migrate from SWDSs either laterally or by venting to atmosphere. Chapter 1 BIOGAS RECOVERY FROM LANDFILLS 1 Sherien A. solid waste disposal sites can also produce substantial amounts of carbon dioxide (CO2) and non-methane volatile organic compounds (NMVOC). causing vegetation damage and unpleasant odors at low concentrations. Tel. ON. recycling. 403-220-5503. Inc.In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers. the modern landfill site is designed to trap the gases for flaring or use in energy recovery systems. University of Calgary. Canada. Heliopolis. Landfill gas is known to be produced both in managed “landfill” and “open dump” sites. Hettiaratchi.ca . particularly CH4. and the potential to utilize the energy content of the gas. ABSTRACT Disposal of municipal wastes can produce emissions of most of the important greenhouse gases (GHG). Ain Shams University Univeristy. Warith* 1 Civil Engineering Department. for instance. Clean Air Act (CAA) requirements. most of this waste is deposited in municipal solid waste (MSW) landfills.2 Sherien A. Resource Conservation and Recovery Act (RCRA) solid and hazardous waste management requirements. Wastes that are generally considered unsuitable for landfilling include volatile liquids or solvents. control mechanisms are required to minimize the risk of migration of the gases out of the site. modern purposebuilt landfill sites normally incorporate a system for the extraction of landfill gas (arising from the decomposition of biodegradable wastes). More recently. and a landfill gas control system is therefore required. from which energy can be recovered. this section discusses sources of uncertainty associated with any estimates of CH4 emissions from SWDSs. there is a strong reliance on disposing of waste in landfills. 99% (around 90. although the estimation is subject to a great deal of uncertainty. It will then describe two methodologies for estimating CH4 emissions from SWDSs. In 1997. As MSW decomposes. including methane (about 50%). Furthermore. In addition. I. Finally. Regulations addressed in this section include the European Landfill Directive [1999/31/EC]. increasing attention has focused on the role of CH4 in global atmospheric change. or about 5 per cent to 20 per cent of the total estimated emissions of 375 Tg/yr (IPCC 1996) from anthropogenic sources globally. INTRODUCTION Throughout Europe and the United States. One of these methods is a default base method which all countries can use to estimate CH4 emissions from different types of SWDSs.000 tons per day) of Brazil's collected waste was being landfilled or simply dumped. In addition. which is nearly 1 ton per year. Section 4 . Methane from SWDSs contributes a significant proportion of annual global CH4 emissions. Elagroudy and Mostafa A. The types of wastes suitable for landfilling include biodegradable wastes. Landfilling is the oldest and most widely practiced waste disposal option. There are eight sections in this chapter. The priority for control of the gases is to protect the environment and prevent unacceptable risk to human health. Again. An overview of the different types of bioreactor landfills as a development to sanitary landfills is provided in Section 3 along with bioreactor features and advantages. Warith landfilling of biodegradable municipal solid waste in non-hazardous waste landfills.5 pounds of waste per day. and certain special wastes that would not pose toxic threats. wastes that would introduce unacceptable contamination into the leachate. US EPA 1994). it produces a blend of several gases. Section 2 discusses environmental regulations as they pertain to landfill gas emissions. Each person in the United Staes generates about 4. Modern landfill sites have developed from uncontrolled dumping sites to be an advanced treatment and disposal option designed and managed as engineering projects. It is recommended that countries which have adequate data also estimate their emissions using the second method presented. and Clean Water Act (CWA) requirements associated with landfill emissions. inert wastes. conditions for waste disposal are still rudimentary. This chapter will describe the processes that result in gas generation from SWDSs and the factors which affect the amount of CH4 produced. Estimates of global CH4 emissions from SWDSs range from less than 20 to 70 Tg/yr (Bingemer and Crutzen 1987. aqueous liquids in limited amounts. in particular the availability and quality of data required. and wastes that would interfere with the biological processes in a landfill site. in many developing countries. LFG mainly consists of methane and carbon dioxide. Several models are available for estimating the LFG generation rate using site-specific input parameters. often malodorous or toxic gases. Revenue from the sale of LFG or electricity generated using LFG as a fuel can offset costs for landfill environmental compliance and/or closure. anaerobic bioreactor. It also discusses gas-generation mechanisms and gas-transport mechanisms and factors affecting both mechanisms. LFG hazards including explosion. Landfill gas may form an explosive mixture when it combines with air in certain proportions. These models vary widely. a positive side to LFG control is energy recovery. The LandGEM model is one of these models and was developed by the US Environmental Protection Agency to estimate landfill gas emissions and to determine regulatory applicability to CAA requirements. LFG must be controlled to protect property. and public health and safety. composition. LFG production and methods of enhancement. Anaerobic decomposition of organic solid waste in the landfill environment produces landfill gas (LFG). Since methane presents a fire or explosive threat. and gas yield. Section 6 discusses LFG generation models. and Clean Water Act (CWA) requirements . LFG regression models using sitespecific data are also discussed in this section along with mathematical models. but also in their complexity. engineered solutions are needed to efficiently and safely monitor. II. many jurisdictions require landfill owners/operators to reduce reactive organic gas emissions to improve regional air quality. Also. REGULATORY CONSIDERATIONS This section discusses environmental regulations as they pertain to landfill gas emissions. not only in the assumptions that they make. The energy recovery technology is based around the gas collection system and the pre-treatment and power generation technology. It is a unique facility where the three processes. Resource Conservation and Recovery Act (RCRA) solid and hazardous waste management requirements. Section 5 focuses on LFG movement and generation and LFG monitoring programs. aerobic bioreactor and mining are sequentially applied in one cell. Clean Air Act (CAA) requirements. and in the amount of data they require. Section 8 covers the Calgary biocell as a full-scale case study that is constructed in Calgary. As noted. Gases generated in the landfill will move throughout the mass of waste in addition to movement or migration out of the site. Section 7 provides an overview of landfill gas energy recovery system. Today's technology allows a landfill owner/operator to recovery the energy in LFG while reducing gas emissions. Thus. Each of those three systems is explained separately in details in this section. Canada. Regulations addressed in this section include the European Landfill Directive [1999/31/EC]. both of which are odorless. collect. Trace constituents of other volatiles. The Intergovernmental Panel on Climate Change (IPCC) methodology for estimation of CH4 emissions from the landfills is based on First-Order decay (FOD) method. There are other LFG emission models in use by industry that also work very well. are also found in LFG. and process landfill gas. LFG can migrate through soil into structures located on or near landfills. asphyxiation hazards and odor are also discussed in this section.Biogas Recovery from Landfills 3 provides a broad overview on Landfill gas (LFG) characteristics. The stages of operation of the cell and the LFG data collected over 2 years from the cell are provided in this section. These 2 models are explained in details in this section. It is important that personnel know the regulatory framework under which the LFG control is being done (e. In addition to the Landfill Directive. to provide for measures. This chapter is not intended to stand in place of any applicable law.4 Sherien A. negative effects on the environment. regulation. The reduction of the biodegradable fraction of municipal waste going for landfill disposal is given specific targets in the Landfill Directive. soil and air.) in order to determine which. operation. groundwater. U Landfill Directive 1999/31/EC The EU Landfill Directive [1999/31/EC] became law on 16 July 1999 after a protracted drafting process. Warith associated with landfill emissions. A brief summary of these regulations applicable is presented in the following section. Regulations affecting LFG management are addressed under various legislations including: • • • • Landfill Directive 1999/31/EC The RCRA which regulates solid and hazardous waste management such as the landfill itself.g. and on the global environment. The aim of the Directive is "by way of stringent operational and technical requirements on the waste and landfills. the 16th July 2001. A. or standard and may not reflect the current standards embodied in law and regulation. Many of the regulations discussed below apply to currently operating or recently closed landfills and may not be appropriate for landfills that stopped receiving wastes prior to 1987. in particular the pollution of surface water. and Liability Act (CERCLA) remediation. during the whole life-cycle of the landfill. closure and aftercare of landfills. RCRA Corrective Action. regulations and administrative provisions necessary to comply with the Landfill Directive not later than two years after its entry into force i. The CAA which regulates air emissions. or reduce as far as possible. as well as any resulting risk to human health. including the greenhouse effect. Compensation. 1999) The Landfill Directive sets requirements for the authorization. The CWA which regulates discharges of water such as LFG condensate and storm water runoff. It was published in the Official Journal of the European Communities on the 16th July 1999. from landfilling of waste.e. procedures and guidance to prevent.." (Waste Landfill Directive. Elagroudy and Mostafa A. design. Comprehensive Environmental Response. etc. Member States were required to bring into force the laws. Some wastes may no longer be accepted in landfills and only wastes that fulfill certain acceptance criteria may be disposed of in the appropriate class of landfill. the . Statutes and regulations are the controlling rule of law and should always be consulted to determine how they apply to a particular set of circumstances to assure compliance before action is taken. The discussion of applicable regulations and legal requirements in this section is only meant to make the reader aware of some of the many requirements that may potentially apply to landfill gas emissions and disposal of condensate. if any of the following requirements must be met. WAC. Primary RCRA requirements pertaining to LFG emission and condensate disposal are found in the following regulations: • • • • 40 CFR Part 258 [regulations for LFG emissions from MSW (non-hazardous) landfills] 40 CFR Parts 260-261 [regulations for characterization and disposal of condensate] 40 CFR Part 262 [regulations pertaining to generator requirements] 40 CFR Part 268 [regulations for land disposal restrictions] C. Personnel need to be familiar with the specific requirements of each regulation prior to deciding whether or not the requirements apply to their project. and Control and Monitoring.Biogas Recovery from Landfills 5 Council Decision 2003/33/EC established the criteria and procedures for the acceptance of waste in landfills (commonly referred to as Waste Acceptance Criteria (WAC)). Up to 4 years' derogation from this is possible for countries currently landfilling more than 80% of wastes. the equipment and type of operations conducted at the site. CAA Regulations Since passage of the Federal CAA in 1970. The Directive has 19 Articles and 3 Annexes covering General Requirements. to 35% of 1995 levels by 2016. compliance and enforcement of operating permits. RCRA Regulations Under RCRA. fee payments. compliance schedules. monitoring data needs. Personnel involved in designing LFG control systems . Central to the Directive is the requirement (Article 5) that all Member States shall introduce measures to reduce the quantities of biodegradable material going to landfill. The Directive also requires Member States to set up a national strategy for the implementation of these targets. Potentially applicable CAA regulations include: • • • • New Source Performance Standards (NSPS) found at 40 CFR Part 60 National Emission Standards for Hazardous Air Pollutants found at 40 CFR 63 Title V Operating Permits found at 40 CFR Part 70 State and local air quality regulations The Environmental Protection Agency (EPA) designed the Title V operating permit program as a central mechanism to regulate emissions. RCRA requirements may have to be met. B. if LFG is emitted or condensate is treated and/or disposed of. size of the facility. and other conditions associated with the issuance. and the emissions from these operations. It also covers the technical requirements for landfills covered by the IPPC Directive (Council Directive 96/61/EC). many rules and regulations have been adopted that could potentially affect LFG operations. The applicability of these rules and regulations are governed by specific factors such as the implementation schedule of the rule. The Directive encompasses the requirements of Articles 3 and 4 of 75/442/EEC (The Framework Directive). substantive requirements such as numerical discharge limits may still have to be established and met at these sites. Other analyses may be required if other pollutants are expected to be present. landfills have become highly engineered facilities with sophisticated containment systems. SANITARY AND BIOREACTOR LANDFILLS A. CWA Regulations Under the CWA. especially when condensate is discharged via a point source to Waters of the U. and there was little effort to control storm water runoff and downward migration of water that had come into contact with the refuse (Barlaz 1997). However. Elagroudy and Mostafa A. sometimes it was burned for volume reduction. a landfill often represented little more than an open hole or mash where refuse was dumped. if LFG condensate is disposed of by treatment and effluent discharge to Waters of the United States. environmental monitoring. This information is important to the customer who is ultimately responsible for determining the need to obtain a Title V operating permit or to revise an existing permit. discharge permits may be required and effluent concentrations/limits may be required to meet a state's water quality standards.S. Effluent analyses required for all discharge permits can include: • • • • • • • • Biochemical Oxygen Demand (BOD) Chemical Oxygen Demand (COD) Total Organic Carbon (TOC) Total Suspended Solids (TSS) Ammonia Temperature pH Flow Response actions taken under CERCLA are not required to obtain discharge permits. III. The refuse was often not covered properly. . sewer effluent conditions will be imposed by the local POTW as regulated by local ordinances or federal requirements. Warith should ensure that the customer is made aware of calculated LFG emissions and what control devices will be used to control them. With the implementation of increasingly stringent regulations. If the condensate is disposed of by indirect discharge through a publicly owned treatment works (POTW). D. and improved operational practices. Any questions regarding the need to obtain an operating permit for the LFG control system should be discussed with the customer and the project team. Development of Sanitary Landfills In the past.6 Sherien A. spread out. aerobic bioreactors. However. For aerobic bioreactor landfill. the condition appeals to investigators to make efforts to make landfills more economically sound and environmentally friendly (Stessel and Murphy 1992). Therefore. primarily through the addition of leachate or other liquid amendments. Bioreactor Landfills There are three types of bioreactor technology: 1. Reinhart et al. 2002). 2002). and nutrient supplementation (Reinhart et al. a typical dry landfill has an impermeable bottom liner. (2) a reduction in the volume of leachate. The “bioreactor landfill” provides control and process optimization. until a planned depth is reached. Nowadays. conversion rates and process effectiveness over what would otherwise occur within the landfill (Pacey et al. Based on waste biodegradation mechanisms. A bioreactor landfill is a sanitary landfill that uses enhanced microbiological processes to transform and stabilize the readily and moderately decomposable organic waste constituents within 5 to 10 years of bioreactor process implementation. possibly in excess of the life of the landfill barriers and covers. and (3) significantly reduced methane generation and “anaerobic” odors. The bioreactor landfill significantly increases the extent of organic waste decomposition. Liner failure could happen in conventional dry landfill sometime in future. Consequently. The environmental barriers such as landfill liners and covers exclude moisture that is essential to waste biodegradation. B. Generally. and (4) make more potential benefits from increased methane generation in anaerobic bioreactor landfill. Beyond that. then the waste is covered with an impermeable cap. Anaerobic Bioreactor Landfills 2. syndrome. Aerobic Bioreactor Landfills 3. there were over 130 leachate recirculation landfills in USA (Gou and Guzzone 1997. but also because the public opposition.Biogas Recovery from Landfills 7 As a generality. 1999). wastes are contained in a “dry tomb” and remain intact for long periods of time ranging from 30 to 200 years. Costs for continuous supply of air are excessively high for municipal solid waste treatment (Hanashima. (3) accelerate waste stabilization and avoid long-term monitoring and maintenance and delay siting of a new landfill. there are four advantages for employing bioreactor landfill technology comparing to conventional dry landfills: (1) contain and treat leachate. compacted and covered at the end of the day with a thin layer of soil. or not in my back yard. this often called the NIMBY. there are three other advantages: (1) significant increase in the biodegradation rate of the MSW over anaerobic processes. the “bioreactor landfill” is one idea that has gained significant attention. bioreactor landfill operation may involve the addition of air. siting new landfills has been very difficult and costly not only because landfills can threaten the environment. the wastes are delivered to the landfill. Aerobic-Anaerobic Bioreactor Landfills . temperature control. which can cause serious groundwater and surface water contamination (Warith 2003). According to the survey conducted by the Solid Waste Association of North America (SWANA) in 1997. the addition of sewage sludge or other amendments. different kinds of “bioreactor landfills” including anaerobic bioreactors. and aerobic-anaerobic (hybrid) bioreactors have been constructed and operated worldwide. Today. 1999). (2) rapidly recover air space. CO2) as end products. Moisture is typically added in the form of leachate through a variety of delivery systems. the amount of leachate produced at many sites is insufficient to achieve optimal moisture conditions in the waste. 2005). Groundwater monitoring occurs at monitoring wells situated around the perimeter of the landfill (U. the duration of gas production is significantly shorter. The waste in typical landfills contains between 10 and 25 percent water. and organic acids as intermediate products. The landfill gas that is collected is used to generate energy. Because of this accelerated production. 2. Additional sources of moisture such as sewage sludge. The anaerobic biodegradation of MSW follows three sequenced biochemical reactions involving three different groups of anaerobic bacteria which are: (1) Fermentative and hydrolystic bacteria. which requires significant quantities of water. Figure 1 shows a cut-away view of an anaerobic bioreactor with elevated levels of ammonium in the leachate. As the moisture content of the waste approaches optimal levels. Leachate is removed via pipes from the bottom of the landfill and piped to an on-site biological leachate treatment facility. One consequence of this is that aerobic degradation can proceed faster than anaerobic degradation. or about 35 to 45 percent moisture. this in turn leads to an increase in the amount of landfill gas produced. acidogenesis. gas generated by the decomposing waste rises through the landfill. aerobic organisms can grow more quickly than anaerobes because aerobic respiration is more efficient at generating energy than anaerobic respiration. Aerobes require sufficient water to function just as anaerobes do. are required. At the same time. In landfills. Aerobic bioreactor landfills The Aerobic Bioreactor seeks to accelerate waste degradation by optimizing conditions for aerobes. While the rate of gas production in an anaerobic bioreactor can be twice as high as a normal landfill. However. The treated leachate and other liquids are then reinjected into the landfill. It is generally accepted that to optimize anaerobic degradation moisture conditions at or near field capacity. storm water. Warith 1. Anaerobic bioreactor landfills The Anaerobic Bioreactor seeks to accelerate the degradation of waste by optimizing conditions for anaerobic bacteria. In aerobic respiration. the rate of waste degradation increases. Aerobes are organisms that require oxygen for cellular respiration. there are four steps involved in the bacteria groups to convert waste into biogas (CH4. (2) Acidogenic bacteria and (3) Methanogenic bacteria. In landfills aerobic activity is promoted through . and other non-hazardous liquid wastes may therefore be necessary to augment the leachate available for recirculation. Also observed is an increase in the density of the waste. gas collection systems at bioreactor landfills must be capable of handling a higher peak volume but need do so for a shorter period of time. and is collected by pipes within the waste and on top of the landfill. Elagroudy and Mostafa A. In the anaerobic stage.S EPA 2004). The four steps are hydrolysis. Another consequence is that aerobic respiration can generate large amounts of metabolic heat. Anaerobic conditions develop naturally in nearly all landfills without any intervention.8 Sherien A. consortia of anaerobic bacteria are responsible for the conversion of organic wastes into organic acids and ultimately into methane and carbon dioxide. energy is derived from organic molecules in a process that consumes oxygen and produces carbon dioxide. However. acetogenesis and methanogenesis (Jin. It is also possible to apply a vacuum to the waste mass and pull air in through a permeable cap. Anaerobic Bioreactor Landfill (U. From the tank. with the need for additional sources of moisture even more acute than for anaerobic reactors. Figure 2 shows a cut-away view of an aerobic bioreactor. where it is released to filter down through the landfill to be collected again. The aerobic process does not generate methane. Leachate is removed from the bottom layer of the landfill and piped to a liquids storage tank. Groundwater monitoring occurs at wells situated around the perimeter of the landfill (U.S EPA 2004) Figure 2.Biogas Recovery from Landfills 9 injection of air or oxygen into the waste mass.S EPA 2004). Liquids are typically added through leachate recirculation. the leachate is piped across the top layer. Figure 1.S EPA 2004) . Aerobic Bioreactor Landfill (U. A blower forces air into the waste mass through vertical or horizontal wells located in the top layer of the landfill. liquids. Horizontal wells that are installed in each lift during landfill construction are used convey the air. Added benefits include an expanded potential for destruction of volatile organic compounds in the waste mass. In this system the uppermost lift or layer of waste is aerated. Bioreactors often need other liquids such as stormwater. The objective of the sequential aerobic-anaerobic treatment is to cause the rapid biodegradation of food and other easily degradable waste in the aerobic stage in order to reduce the production of organic acids in the anaerobic stage resulting in the earlier onset of methanogenesis. Landfills that simply recirculate leachate may not necessarily operate as optimized bioreactors. Figure 3. and landfill gas. wastewater. Aerobic-anaerobic bioreactor landfills The Aerobic-Anaerobic Bioreactor is designed to accelerate waste degradation by combining attributes of the aerobic and anaerobic bioreactors. Features Unique to Bioreactor Landfills The bioreactor accelerates the decomposition and stabilization of waste. and wastewater treatment plant sludge to supplement leachate to enhance the microbiological process by purposeful control of the moisture content and differs from a landfill that simple recirculates leachate for liquids management. C. Figure 3 shows a cut-away view of an aerobicanaerobic bioreactor. At a minimum. while the lift immediately below it receives liquids.S EPA 2004) . Landfill gas is extracted from each lift below the lift receiving liquids.10 Sherien A. Aerobic-Anaerobic Bioreactor Landfill (U. Warith 3. The principle advantage of the hybrid approach is that it combines the operational simplicity of the anaerobic process with the treatment efficiency of the aerobic process. leachate is injected into the bioreactor to stimulate the natural biodegradation process. Elagroudy and Mostafa A. Some studies indicate that the bioreactor increases the feasibility for cost effective LFG recovery. it could provide over 270 billion cubic feet of methane a year. Research indicates that the operation of a bioreactor may generate LFG earlier in the process and at a higher rate than the traditional landfill. The microbes can be either aerobic or anaerobic. A side effect of the bioreactor is that it produces landfill gas (LFG) such as methane in an anaerobic unit at an earlier stage in the landfill’s life and at an overall much higher rate of generation than traditional landfills. Currently. which in turn would reduce fugitive emissions. Landfill volume may also decrease with the recovered airspace offering landfill operators an extension for the operating life of the landfill. This presents an opportunity for beneficial reuse of bioreactor LFG in energy recovery projects. The moisture content. combined with the biological action of naturally occurring microbes decomposes the waste. when captured. The bioreactor LFG is also generated over a shorter period of time because the LFG emissions decline as the accelerated decomposition process depletes the source waste faster than in a traditional landfill.Biogas Recovery from Landfills 11 Moisture content is the single most important factor that promotes the accelerated decomposition. Potential Advantages of Bioreactor Landfills Decomposition and biological stabilization of the waste in a bioreactor landfill can occur in a much shorter time frame than occurs in a traditional “dry tomb” landfill providing a potential decrease in long-term environmental risks and landfill operating and post-closure costs. which is equivalent to one percent of US electrical needs. The net result appears to be that the bioreactor produces more LFG overall than the traditional landfill does. . Leachate quality in a bioreactor rapidly improves which leads to reduced leachate disposal costs. Potential advantages of bioreactors include: • • • • • • Decomposition and biological stabilization in years vs. The bioreactor technology relies on maintaining optimal moisture content near field capacity (approximately 35 to 65%) and adds liquids when it is necessary to maintain that percentage. decades in “dry tombs” Lower waste toxicity and mobility due to both aerobic and anaerobic conditions Reduced leachate disposal costs A 15 to 30 percent gain in landfill space due to an increase in density of waste mass Significant increased LFG generation that. can be used for energy use onsite or sold Reduced post-closure care Research has shown that municipal solid waste can be rapidly degraded and made less hazardous (due to degradation of organics and the sequestration of inorganics) by enhancing and controlling the moisture within the landfill under aerobic and/or anaerobic conditions. the use of LFG (in traditional and bioreactor landfills) for energy applications is only about 10 percent of its potential use. D. The US Department of Energy estimates that if the controlled bioreactor technology were applied to 50 percent of the waste currently being landfilled. LFG emitted by a bioreactor landfill consists primarily of methane and carbon dioxide plus lesser amounts of volatile organic chemicals and/or hazardous air pollutants. a mixture of 10 percent hydrogen and 90 percent carbon dioxide. For example. while a mixture of 60 percent methane and 40 percent carbon dioxide.8 30 ppm Toluene 3. Elagroudy and Mostafa A. Landfill Gas Characteristics Constituent Relative Specific Gravity Concentration in Landfill Gas Air 1 NA Methane 0. UEL 15% in air Forms weak acid.5 50 ppm Odorous Notes Source: US Army Corps of Engineers (2008) LEL = lower explosive limit. such as might be produced during the methanogenic phase of decomposition. Asphyxiant Forms strong acid Toxic: PEL = 10 STEL = 15 Forms acids with hydrogen sulfide and carbon dioxide Flammable Toxic: PEL 1. LEL 5% in air. Table 1 shows characteristics of some of the typical components of landfill gas.12 Sherien A.62 100% Saturated Benzene 2. and nonmethanogenic organic compounds. LFG production. will be slightly lighter than air.1 300 ppm Organic Acids Organosulphur Compounds GT 2 Traces Forms explosive mixture with methane Explosive. Table 1. LANDFILL GAS (LFG) This section covers LFG characteristics.529 30-60% Hydrogen Sulfide 1. Some typical values for density and viscosity at 00C and atmospheric pressure are given in Table 2. composition. and gas yield. such as might be produced in the first stage of anaerobic decomposition. It also discusses gas-generation mechanisms and gas-transport mechanisms and factors affecting both mechanisms. Landfill Gas Characteristics Landfill gas is typically a combination of methane.19 800 ppm Water Vapor 0. carbon dioxide. PEL = permissible exposure limit. Density and viscosity The density of LFG depends on the proportion of gas components present. Warith IV.0 ppm STEL 5 ppm Toxic: PEL 100 ppm STEL 150 ppm Odorous GT 1. . 1. UEL = upper explosive limit. A. STEL = short-term-exposure limit.554 40-70% Carbon Dioxide 1. will be heavier than air. 5.03 × 10–5 1.000 ppm according to research from the EPA. Water vapor Gas created during the decomposition of organic compounds typically includes between 4 and 7 percent by volume water vapor. 50 percent carbon dioxide. particularly during the initial anaerobic conversion of mixed organic acids to acetic acid. This value is about half that of natural gas. ethane. the type of landfill cover. and many other factors.6 MJ/m3 under good conditions. the gas produced will consist of approximately 50 percent methane.17 × 10–5 Source: US Army Corps of Engineers (2008) 2.9 1. 3. Heat value content During the methanogenic stage. LFG can be expected to have a heating value of 18. During the design phase of a landfill closure. in air.19 Viscosity (Pa*s) 1. 4. and vinyl chloride.29 0.39 × 10–5 1.71 × 10–5 1. 52. Others Hydrogen is produced during waste decomposition. Hydrogen is flammable between 4 and 74 percent. increasing the evaporation of water into the LFG. Non-methane organic compounds If a landfill contains a significant amount of municipal solid waste. The presence of CO2 affects these ranges although little significant change occurs near the lower limit of the range .Biogas Recovery from Landfills 13 Table 2. The most frequently detected compounds reported were trichloroethene. historical records or word of mouth information should be obtained as to the type of wastes that were placed in the landfill and the potential for these wastes to create off-gas emissions. The actual water vapor content of LFG will depend on the temperature and pressure within the landfill. and trace amounts of non-methane organic compounds (NMOC). Temperatures are typically elevated over ambient during biological decomposition. In the EPA study. toluene. Significant amounts of hydrogen are later consumed in the formation of CH4. The concentration of NMOC can range from 200 to 15.21 × 10–5 1.72 1. respectively. Typical Values for Gas Density and Viscosity at (00C) Gas Air Methane Carbon Dioxide 50% CH4+ 50% CO2 60% CH4+ 40% CO2 Density (kg/m3) 1. by volume. and methylene chloride were found at the highest concentrations in landfill gas with average reported values of 143. The actual heating value of the gas from a landfill is a function of the type age of the waste. benzene. and 20 ppm.35 1. 01 – 0.6 . It is 21 times more potent as a GHG. kilogram for kilogram.. 1993). Methane is a short-lived GHG with an atmospheric lifetime of approximately 12 years compared to over 100 years for carbon dioxide. whereas Table 4 shows the concentration of various VOC in landfill gases (Tchobanouglous et al. Landfill Gas Composition LFG is the product of microbiological decomposition of land-filled garbage.55% of LFG. The balance of the input rate and the removal rate determines atmospheric concentrations of GHG. There will be a greater impact by concentrating on methane in the medium-term because it is short lived in the atmosphere and has a high global warming potential (GWP).2 0. mainly volatile organic compounds (VOC) (Tchobanouglous et al. (2) minor components which consist of ammonia. no further conversions to simpler organic molecules are possible once methane has been produced. hydrogen sulfide. when present above threshold concentrations. with around 40 percent from natural sources. Over 550 trace gases have been identified to date. 1993) Percent (volume basis) 45 – 65 40 – 60 2–5 –1 0–1 –1 0 – 0. and trace amounts of other compounds. Warith B. hydrogen. and carbon monoxide. and doubtless more will yet be discovered. The trace components have chemical or physical properties that differ significantly from the bulk gases. Methane comprises about 50. Some 60 percent of methane emissions come from anthropogenic sources. Table 3 shows the composition of major and minor compounds in landfill gases.2 0 – 0. Methane is the most reduced organic molecule. The composition of landfill gas depends on the activity of the bacteria involved. the available substrate and other factors. Elagroudy and Mostafa A. Table 3. Typical Composition of Landfill Gas Component Methane Carbon dioxide Nitrogen Oxygen Sulfides Ammonia Hydrogen Carbon monoxide Trace constituents (Source: Tchobanouglous et al.14 Sherien A. than carbon dioxide. 1977). It is produced as an end product of anaerobic metabolism. carbon dioxide. cause physiological effects and thus have potential health impacts. Also. Landfill gases can be classified into three groups: (1) major components which consist of methane and carbon dioxide. while 40-45% of LFG is carbon dioxide. nitrogen. Just sixty two landfill gas trace substances were then more recently identified within the landfill gas source-term as those from the list of 500. being likely to be present at a significant concentration and to be worthy of further consideration. The microorganisms turn complex organic compounds in garbage into methane. it is known that some of these trace components. and (3) trace compounds known as ‘trace gases’. In other words. The stoichiometric method is based on several assumptions. (1997) found that the methane yield increased as cellulose and hemicelluose content increased. ppbV (Part per billion per volume) Median Mean Maximum Acetone 0 6..1-Dichloroethene 0 130 4000 Diethylene chloride 0 2835 20000 trans-1. The following equation is commonly used to estimate the theoretical landfill gas yield: . The methane yield was reviewed by El-Fadel et al. the balance of substrates and nutrients is available at all times in all places in the landfill. Landfill Gas Yield Methane yield is defined as the total amount of methane generated per unit weight (dry or wet) of MSW (El-Fadel et al. and no portion of the degraded matter is utilized into cell growth (Ham 1979). b c 3d e ⎞ ⎛ ⎛ a b c 3d e ⎞ + ⎟ H 2O ⇒ ⎜ + − − − ⎟ CH 4 + C a H b Oc N d S e + ⎜ a − − + 4 2 4 2⎠ ⎝ ⎝2 8 4 8 4⎠ [1] ⎛ a b c 3d e ⎞ + ⎟ CO2 + d NH 3 + e H 2 S ⎜ − + + ⎝ 2 8 4 8 4⎠ Table 4. such as whether or not complete degradation of waste has occurred. 2.Biogas Recovery from Landfills 15 C. (1996a). There are two approaches for estimating this yield: theoretical and experimental The Theoretical approach uses the stoichiometric and biodegradability methods to estimate the gas yield.2-Dichloroethane 0 36 850 Ethylene dichloride 0 59 2100 Ethyl benzene 0 7334 87500 Methyl ethyl ketone 0 3092 130000 1. 1. 2-Tetrachloroethane 0 246 16000 Tetrachloroethylene 260 5244 180000 Vinyl chloride 1150 3508 32000 Styrenes 0 1517 87000 Vinyl acetate 0 5663 240000 Xylenes 0 2651 38000 (Source: Tchobanouglous et al.1-Dichloroethane 0 2801 36000 Dichloromethane 1150 25694 620000 1. the degradation product only includes CH4 and CO2. 1996a). Eleazer et al. 1993) Compound . 1-Trichloroethane 0 615 14500 Trichloroethylene 0 2079 32000 Toluene 8125 34907 280000 1. The methane yield is a function of waste composition. 1. Typical Concentrations of VOCs Compounds in Landfills Gases Concentration.838 240000 Benzene 932 2057 39000 Chlorobenzene 0 82 1640 Chloroform 0 245 12000 1. El-Fadel et al. Five main stages of degradation of biodegradable wastes have been identified (Kjeldsen et al 2002. 1995. The amount of biogas produced by biodegradation of MSW can be measured in the laboratory. Table 5 summarizes the estimated methane yield based on this method. based on the stoichiometric method that the estimated methane yield is in the range of 220270 L/kg dry waste after complete decomposition. biological decomposition. LFG generation mechanisms The three primary causes of LFG generation are volatilization. nutrients. LFG Generation 1. LFG Emission LFG emissions are governed by gas-generation mechanisms and gas-transport mechanisms. Warith Table 5. the estimated yield of the landfill gas is 440 L/kg wet waste with a composition of 53% methane and 46% CO2 (Ham 1979). temperature. Organic compounds in the landfill volatilize until the equilibrium vapor concentration is reached. etc. D. The rate at which compounds volatilize depends on their physical and chemical properties. The biodegradation of MSW can be controlled and enhanced by manipulating environmental factors such as pH. Volatilization Volatilization is due to the change of chemical phase equilibrium that exists within the landfill. the landfill gas yield can be obtained from laboratory scale studies. Methane Yield Based on the Stoichiometric Method Sources Barlaz et al. Waste Management Paper 26B. In the experimental approach. and chemical reactions.16 Sherien A. (1996) Peer et al. 1997) Using this method. The following paragraphs describe these mechanisms and the major factors influencing gas generation and transport. 1. (1989) El-Fadel et al. The range of methane yield from lab scale studies varies from no generation to 107 L CH4/kg dry waste. Biological decomposition The rate and composition of landfill gas vary according to the stabilization stages of MSW. Elagroudy and Mostafa A. Figure 4 . (1989) Ham et al. McBean et al 1995). (1993) Methane (L/kg dry waste) 373 carbohydrate 274 protein 270 220-270 230-270 (Source: El-Fadel et al.1. moisture. (1997) reported. This process is accelerated when biological activity increases the temperature of the waste mass. and Figure 5 shows the process in more detail (Waste Management Paper 26B. Throughout the process of degradation. Figure 4. all the different stages may be progressing simultaneously until all the waste has reached stage five and stabilization of the landfill has been reached. 1995.Biogas Recovery from Landfills 17 shows the decomposition pathways of the major organic and inorganic components of biodegradable wastes. Source: Waste Management Paper 26B. because of the heterogeneous nature of waste. 1995). . Major stages of waste degradation in landfills. 1995. Source: Waste Management Paper 26B. Elagroudy and Mostafa A. Details of the stages of waste degradation in landfills. Warith Figure 5.18 Sherien A. . and their formation depends on the composition of the initial waste material. 1995. Hydrolysis/aerobic degradation The hydrolysis/aerobic degradation stage occurs under aerobic (in the presence of oxygen) conditions.Biogas Recovery from Landfills 19 Stage I. carbon dioxide. Stage III. Proteins decompose via deaminisation to form ammonia and also carboxylic acids and carbon dioxide. which can tolerate reduced oxygen conditions. butyric. 1995). that is. The derived leachate contains ammoniacal nitrogen in high concentration. the degree of waste compaction and how quickly the waste is covered. which gives acidity to the leachate. Hydrogen sulphide may also be produced throughout the anaerobic stages as the sulphate compounds in the waste are reduced to hydrogen sulphide by sulphate-reducing micro-organisms (Christensen et al 1996). The micro-organisms are of the aerobic type. Hydrogen and carbon dioxide levels begin to decrease throughout Stage III. This occurs during the emplacement of the waste and for a period thereafter which depends on the availability of oxygen in the trapped air within the waste. and the facultative anaerobes. the methanogens. The heat generated from the exothermic degradation reaction can raise the temperature of the waste to up to 70–90 °C (McBean et al. However. readily form complexes with metal ions. Different micro-organisms. Water and carbon dioxide are the main products. The ammonia is derived largely from the deaminisation of proteins. The organic acids are mainly acetic acid. The temperatures in the landfill drop to between 30 and 50 °C during this stage. proteins and lipids are hydrolysed to sugars which are then further decomposed to carbon dioxide. Acetogenesis The organic acids formed in Stage II are converted by acetogen micro-organisms to acetic acid. chloride ions. The acidic conditions of the acetogenic stage increase the solubility of metal ions and thus increase their concentration in the leachate. organic acids. 1986. Gas concentrations in the waste undergoing stage II decomposition may rise to levels of up to 80% carbon dioxide and 20% hydrogen (Waste Management Paper 26. ammonium ions and phosphate ions. acetic acid derivatives. The aerobic stage lasts for only a matter of days or weeks depending on the availability of oxygen for the process. become dominant. they require oxygen and they metabolise the available oxygen and a proportion of the organic fraction of the waste to produce simpler hydrocarbons. causing further increases in solubiliation of metal ions. but also propionic. ammonia and organic acids. lactic and formic acids and acid derivative products. Carbohydrates. carbon dioxide and hydrogen under anaerobic conditions. water and heat. which in turn depends on the amount of air trapped in the waste. compacted waste achieves lower temperatures due to the lower availability of oxygen. Stage II. Other organisms convert carbohydrates directly to acetic acid in the presence of carbon dioxide and hydrogen. Hydrolysis and fermentation Stage I processes result in a depletion of oxygen in the mass of waste and a change to anaerobic conditions. hydrogen. In addition. Waste Management Paper 26B 1995). Low hydrogen levels promote the methane-generating micro-organisms. all in high concentration in the leachate. with carbon dioxide released as gas or absorbed into water to form carbonic acid. Waste Management Paper 26B. Metal sulphides may be a . which also form carboxylic acids and carbon dioxide. which generate methane and carbon dioxide from the organic acids and their derivatives generated in the earlier stages. as the acids are used up in the production of the landfill gas methane and carbon dioxide. Methanogenesis The methanogenesis stage is the main landfill gas generation stage.20 Sherien A.8 to 7. There are two classes of microorganisms which are active in the methanogenic stage. The reactions are relatively slow and take many years for completion. with the gas composition of typical landfill gas generated at approximately 60% methane and 40% carbon dioxide.5. the pH rises to about pH 7–8 during the methanogenesis stage. the methanogens. However. Where temperatures in the mass of waste drop significantly. but may not commence until 6 months to several years after the waste is placed in the landfill. The conditions maintain the anaerobic. landfill gas can be generated during the methanogenic stage over a temperature range of 30–65 °C. low levels of landfill gas may be generated up to 100 years after waste emplacement. the mesophilic bacteria which are active in the temperature range 30–35 °C and the thermophilic bacteria active in the range 45–65 °C. the methanogenesis stage. most landfill sites fall within this temperature range with an average range for UK landfill sites of between 30 and 35 °C. depending on the level of water content and water circulation. depending on the development of the anaerobic micro-organisms and waste degradation products. generated in the earlier stages. and as the acid concentration becomes depleted. Oxidation The final stage of waste degradation results from the end of the degradation reactions. depending on waste and site characteristics (Landfill Gas Development Guidelines 1996). The presence of the organic acids generates a very acidic solution which can have a pH level of 4 or even less (Moss 1997). hydrolysis and fermentation and acetogenesis stages is followed by the main landfill gas generation stage. which generate carbon dioxide and methane from the organic acids. Low levels of hydrogen are required to promote organisms. Figure 6 shows the changes in composition of landfill gas and leachate as the five stages of waste degradation progress with time. New aerobic micro-organisms slowly replace the anaerobic forms and re-establish aerobic conditions. Landfill gas will continue to be generated for periods of between 15 years and 30 years after final deposition of the waste. In fact. Initial formation of hydrogen and carbon dioxide in the hydrolysis/aerobic degradation. Hydrogen concentrations produced during Stages II and III therefore fall to low levels during this fourth stage. The characteristic landfill gas composition is methane and carbon dioxide with other minor . Stage IV. The organic acids formed during Stages II and III are degraded by the methanogenic microorganisms. to below 15 °C in cold weather in shallow sites. Therefore. Stage V. and their derivatives such as acetates and formates. Stage IV is the longest stage of waste degradation. Elagroudy and Mostafa A. Aerobic micro-organisms which convert residual methane to carbon dioxide and water may become established. but there is some activity between pH 5 and pH 9. then the rate of biological degradation falls off. Warith reaction product of the hydrogen sulphide and metal ions in solution. Methane may also form from the direct microorganism conversion of hydrogen and carbon dioxide to form methane and water. for example. oxygen-depleted environment of Stages II and III. with an optimum temperature range of gas generation between 30 and 45 °C. Ideal conditions for the methanogenic micro-organisms are a pH range from 6. Significant concentrations of methane are generated after between 3 and 12 months. . In addition. Changes in composition of LFG and leachate during stages of waste decomposition (modified from Pohland and Harper. food and garden waste. Microbiological investigations into site characteristics have shown that there are considerable differences between different SWDSs and even different regions within the same SWDS. rapid covering of the waste will reduce the aerobic phase. if the site is well capped. Figure 6. rapid covering of the waste will reduce the chance of rainfall increasing the moisture content of the waste. the bacteria that break down the waste require small amounts of certain minerals such as calcium. Nevertheless. 2. the paper and board. Factors affecting LFG generation Solid waste disposal sites are by nature heterogeneous. Hydrogen sulphide gas may also form. The final stages mark the end of the reaction and a return to aerobic conditions. anaerobic conditions will be created.Biogas Recovery from Landfills 21 components and water vapor. Shallower sites allow air interchange and lower anaerobic activity. and since this is the increasing temperature phase. Waste characteristics The major components of municipal solid waste include the biodegradable fraction. derived from sulphate-reducing micro-organisms. 1.2. This fraction has been shown to vary depending on a number of factors. glass and textiles. for example. a better understanding of the factors thought to most significantly influence the generation of CH4 from land disposal of solid waste can reduce the uncertainty associated with emissions estimates. in wastes with a high concentration of sulphate. The amount of gas produced will vary depending on the proportion of biodegradable components in the waste. and more industrially developed countries produce more paper. this will tend to keep waste temperatures down. Similarly. This makes it very difficult to extrapolate from observations on single SWDSs to predictions of global CH4 emissions. Site characteristics Landfill sites with waste depths exceeding 5m tend to develop anaerobic conditions and greater quantities of landfill gas. that is. However. 1986) 1. plastics. and consequently lower landfill gas production. which in turn reduces the initial rate of biodegradation. Also. and non-biodegradable components. higher concentrations of garden waste are produced in spring and autumn. Age of the waste Landfill gas production begins as soon as waste has been deposited. has been many years. however. that is. If they are lacking or if substances that inhibit bacterial growth are present.22 Sherien A. the period of significant gas production will vary. but every site is different. Similarly. In addition. the composition of the organic components. Peak landfill gas production generally occurs about a year after deposit and thereafter gradually declines. 3. gas production will proceed more slowly and in extreme circumstances may stall completely. Variations in Rate of Landfill Gas Production with Time Source: UK Department of Energy (1992) . The density or degree of compaction of the waste in the landfill will increase the amount of biodegradable material available for degradation and therefore increase the production of landfill gas per unit volume of void space in the landfill. Where gas production is slow. older landfill sites have been shown to contain lower proportions of biodegradable waste than modern sites due to the changing nature of waste over the last few decades. Significant gas production is generally completed within about 20 years of deposition. may limit the percolation of water through the site. Figure 7. the proportion of cellulose. Too high a degree of compaction. Shredding or pulverisation of the waste prior to landfilling results in increased available surface area and consequent increased homogeneity and increased rates of biological degradation. particularly where the period over which waste has been deposited. although actual durations will vary greatly site by site. but anaerobic methane production only occurs when all of the available oxygen has been absorbed. The pattern of gas production for an entire site is the sum of the performance of all of the individual components of waste. and for an entire site most often extends over several decades. proteins and lipids. The rate at which gas is produced depends on the proportions of each type present in the waste. the period of significant gas production may extend for 40 or 50 years. Elagroudy and Mostafa A. Also. Warith potassium and magnesium and other micronutrients. If these are present the bacteria thrive and gas is produced rapidly. others will be slower. Some will be rapidly enter the gas generation stage. Figure 7 below shows an idealised and fairly typical sequence of LFG production. will similarly influence the degradation pathway. which is necessary for the free flow of nutrients for the micro-organisms. Many researches have shown that the methane production rate increases by increasing the moisture content of the MSW. waterlogged landfills may not attain optimum temperatures because the bacteria do not generate sufficient heat to raise the temperature of the excess water. 5. Compaction of the waste and the presence of layers of poorly permeable material such as clay used for covering . 1989. nutrients and microorganisms. Methane production increases with an increase in temperature. (1982) concluded that moisture movement through the MSW increased the methane production rate from 25% to 50%. 1996). Hartz et al. and 40˚C are much higher than rates at 20 and 25˚C. 35. Pressure Atmospheric pressure can have a minor affect on the rate at which landfill gas is released to the atmosphere. (1996) have monitored the temperature changes with depth throughout a 20 m deep municipal solid waste landfill in Italy. 6. Furthermore. The moisture content therefore is one of the most critical factors controlling the biodegradation of MSW. the biodegradation rate of microorganisms involved in the MSW decomposition is highly affected by temperature. This is because the pressure within the landfill changes at a slower rate than the atmosphere and a pressure gradient temporarily develops between the inside and outside of the landfill until these pressures equalize. They showed that the first 1–2m were in the temperature range of 10–15 °C. the exchange of substrate. and the dilution of inhibitors and improved distribution of enzymes and microorganisms within the landfill (Klink et al. Barlaz et al. The increase in moisture content affects the limitation of oxygen diffusion from the atmosphere into the landfill. Chaiampo et al. Likewise. Baldwin et al. Moisture content and movement Moisture is essential for the activity of all microorganisms in the landfill. but the temperature increased to 35–40 °C at the 3–5m depth and to 45–65 °C in the 5–20 m depth region. Temperature Similar to other microbial processes. the rate of gas production and the percentage of methane in the gas are increased. whereas 60 is the optimum temperature for thermophilic waste decomposition (Ham et al. 1990). A decrease in barometric pressure results in a temporary increase in LFG flow and an increase in barometric pressure will cause LFG flow to temporarily decrease. The optimum temperature for methane production in mesophilic waste decomposition is in the range of 30 to 40ºC.Biogas Recovery from Landfills 23 4. (1998) studied the moisture content in three landfills over 1-6 years and found that wastes with high moisture content are more quickly decomposed. Anaerobic bacteria produce only small amounts of heat and may not be able to maintain the temperature of a shallow landfill when external temperatures fall so landfill gas generation may show pronounced diurnal or seasonal variations. Klink et al. They equated the temperature regions with the mesophilic bacteria in the 1–5m range and thermophilic bacteria in the deeper layers. Ham and Barlaz (1989) concluded that gas production rates at 30. 1982. Christensen et al. Rees (1980) found from existing literature that by increasing the water content from 25% to 60% (wt). It can also influence the operation of gas extraction systems. compared to no movement of moisture at the same moisture content levels. Higher temperatures promote volatilisation and chemical reactions within the waste so the trace gas component of landfill gas tends to increase with higher landfill temperatures. (1982) recommended that the optimum temperature for methane generation is in the range of 36 to 41˚C. in a typical engineered landfill where waste is quickly compacted and covered. Atmospheric conditions Atmospheric conditions affect the temperature. and buffering the effects of temperature changes. aerobic biodegradation will proceed rapidly and the resulting gas will comprise mostly carbon dioxide. Landfill covers and liners help to isolate waste from atmospheric conditions by limiting oxygen intrusion. A few modern engineered landfills are designed to function aerobically. If oxygen is present. 1989). Leachate recirculation back into the waste tends to increase the rate of gas production. An increase in the partial pressure of hydrogen causes the generation of propionic and butyric acids with no further conversion. 11. High rates of precipitation may also flood sections of the landfill. limiting infiltration of precipitation. Elagroudy and Mostafa A. 10. Hydrogen concentration The fermentative and acidogenic bacteria produce hydrogen during the biodegradation of MSW. the absence of free oxygen concentration in the landfill is required in order to grow and degrade the MSW into methane and CO2. containing roughly equal amounts of methane and carbon dioxide. In reality. (1989) reported that MSW density values range from 474 to 711 Kg/m3. which will obstruct gas flow. Density of the waste The density of waste fills is highly variable. Where oxygen is not available. In uncontrolled “dumps”. aerobic degradation only occurs until the entrained oxygen is used up in newly deposited waste. the waste is broken down by anaerobic bacteria that produce a “classic” landfill gas. An estimate of waste density is often required for estimating landfill gas generation rates. Low partial pressure of hydrogen is required for the acidogenic processes (hydrogen producing bacteria) and methanogenesis processes. 8. 9. pressure. Oxygen concentration The activity of anaerobic microorganisms is affected by the presence of oxygen.24 Sherien A. Warith will tend to reduce gas production because they obstruct the passage of moisture. The amount of precipitation that reaches the waste is highly dependent on the type of landfill cover system. Stecker. . and in such cases no methane will be produced. where waste is left loose and uncovered. However. breakdown of the waste may be almost entirely aerobic. The conversion of propionic acid requires a hydrogen pressure lower than 9x10-5 atmospheres (Christensen et al. and moisture content within a landfill. the oxygen that diffuses from the atmosphere into the landfill is consumed by aerobic bacteria in the top layers of the landfill (aerobic zone) (Warith 2003). Thus. while the methanogenic bacteria use the hydrogen as a substrate to produce methane. Several researchers reported density values. Precipitation Precipitation dramatically affects the gas generation process by supplying water to the process and by carrying dissolved O2 into the waste with the water. 7. resulting in an accumulation of volatile organic acids which reduce the pH and inhibit the methanogenic bacteria. if the methanogenic activity is inhibited by other factors [O2. . and ammonium. (1996) found from existing literature that all the necessary nutrients and traces of heavy metals are available in most landfills. H2. sulphate.08 for organic matter expressed as chemical oxygen demand (COD). 1996). These inhibitors are carbon dioxide. calcium. magnesium. which is toxic. 1996). The CO2 acts as an inhibitor by raising the redox potential which has an effect on the acetic acid conversion to methane (Christensen et al. and competition for common substrate between methanogenic and sulphate reducing bacteria. potassium. H2. such as nitrogen and phosphorous. calcium. To the author’s knowledge. 12. but heterogeneous insufficient mixing of the wastes may result in nutrient limited environments. Any drop in the pH value below 6. The fermentative and acetogenic microorganisms have a wider range of pH compared to methanogenic bacteria.Biogas Recovery from Landfills 25 Emcon Associates (1980) stated that MSW density is about 650 Kg/m3. pH (acidity) and high concentrations of heavy metals. These cations in low concentrations are required for biodegradation. etc. as well as traces of heavy metals like zinc. The optimal ratios needed in order to enhance the biodegradation are 100:0. the conversion of acetic acid to methane and CO2 decreases and leads to an accumulation of the acids.].0 (Warith 2003). 14. The ideal methanogenic bacteria activity occurs in environmental conditions within a pH range of 6. but in high concentrations they inhibit the methanogenic bacteria. Nutrients and trace metals Microorganisms in the landfill require various nutrients for their activity. The pH of leachate produced from a landfill can have a significant effect on the stabilization of methane production. The pH of a typical landfill site would initially be neutral. where organic acids are produced from waste degradation by the acetogenic micro-organisms. followed by acidic phases. nitrogen and phosphorous (McCarty 1964). Acidity The acidity of the landfill site influences the activity of the various microorganisms and therefore determines the rate of biodegradation.8 will slow down the activity and growth of methanogenic microorganisms. cobalt and molybdenite. In a well-established methanogenic media. The resultant organic acids provide the nutrients for the methanogenic bacteria and as the acids are consumed. Stages II and III. the pH rises. a wider MSW density range of 387 to 1662 Kg/m3 was suggested by Landva et al. and high concentrations of cations such as sodium. Inhibitors There are a number of elements or compounds that can inhibit the biodegradation of MSW (methane production) besides O2. iron. 13. there have been no studies to evaluate the impact of Chloride on the degradation of MSW. potassium.44:0. (1990).8 to 8. and the pH falls to as low as 4. Rees (1980) and Christensen et al.to S2-. Rees (1980) reported that high sulphate concentrations inhibit the methanogenic bacteria for two reasons: reduction of SO42. copper. thereby decreasing the pH which in turn may stop the generation of methane (Christensen et al. LFG Transport 2. Specific compounds exhibit different diffusion coefficients. Transport conditions both within the landfill and for the subsurface surrounding the landfill must be considered.1. Permeability of refuse is often reported in Darcys. compaction. The permeability of waste has a large influence on gas flow rates and gas recovery rates. Diffusion Molecular diffusion occurs in a system when a concentration difference exists between two different locations. so the constituent will tend to migrate to the atmosphere. Diffusion coefficients are the rate constants for this mode of transport and quantify how fast a particular compound will diffuse. 2. The concentration of a volatile constituent in the LFG will almost always be higher than that of the surrounding atmosphere. In landfills. advective forces result from the production of vapors from biodegradation processes. or an active LFG extraction system. Coarse-grain wastes exhibit large values of gas permeability and more uniform gas flow patterns. Published diffusion coefficients have been calculated using open paths between one vapor region (concentration) and another. Variations in water table elevations can create small pressure gradients that either push gases out (rising tide) or draw gases in (falling tide). fine-grained and heterogeneous wastes are characterized by small values of gas permeability and gas flow patterns that are not uniform throughout the waste mass.26 Sherien A. One Darcy = 9. Geomembranes in landfill covers will significantly reduce diffusion because the geomembrane prevents gases from diffusing to the atmosphere. By contrast. Advective flow occurs where a pressure gradient exists. Reported values for the apparent permeability of municipal solid waste are in the range of 13 to 20 Darcys. Diffusive flow of gas is in the direction in which its concentration decreases. Water competes with air to occupy pore space within the solid matrix and ultimately reduces the effective porosity and ability of vapors to migrate through . Warith 2. Factors affecting LFG transport mechanisms LFG transport is affected by the following factors: Permeability. Changes in barometric pressure at the surface can also have an impact on the advective flow of gas. This type of test is not very representative of the conditions found in a landfill. LFG transport mechanisms Transport of landfill gas occurs by the two principal mechanisms of diffusion and advection.85×10–9 cm2. Elagroudy and Mostafa A. In a landfill. Advection. gases must travel a tortuous path around all the solids and liquids in its path. chemical reactions. The rate of gas movement is generally orders of magnitude faster for advection than for diffusion. These transport mechanisms are discussed in the following paragraphs. Gas will flow from higher pressure to lower pressure regions. the published diffusion coefficients must be used with care. Wind often serves to keep the surface concentration at or near zero.2. thus. which renews the concentration gradient between the surface and the interior of the landfill and thus promotes the migration of vapors to the surface. Man-Made Features.e. Landfill Cover and Liner Systems.. gravels. Man-made features also provide a potential pathway for the off-site migration of landfill gas. it is generally used to help estimate the thickness of the zone through which gas can travel. Gas generation within a landfill will result in a positive pressure gradient from the inside to the outside of the landfill. the effective radius of influence of each well is increased. In some instances. Depth to Ground Water. The amount of air . Geologic Conditions. Liner systems prevent the migration of LFG to the surrounding areas. geosynthetic clay liner (GCL). A geomembrane in the cover system will prevent the intrusion of air into the waste. Landfill liner systems consist of various combinations of low permeability layers and leachate collection layers. For a passive LFG collection system. As a result. a drainage layer. the upward rise of the water table toward a vacuum well screened in the unsaturated zone). and a low permeability layer composed of one or more of the following: geomembrane. airflow may be concentrated along these features rather than within the landfill. The low permeability layers are created using natural low permeability geologic formations. Liner systems also prevent gases in the surrounding geologic formations from being pulled into the LFG collection system. The amount of gas escaping from a landfill’s surface changes as barometric pressure changes. increases in atmospheric pressure will cause a decrease in gas flow from a landfill because the pressure differential between the inside and the outside has decreased. and geosynthetic clay liners. This reduction will also reduce the rate of gas flow and decrease gas recovery rates. For an active gas collection system. Permeable strata such as sands. a higher operating vacuum can be applied to the gas collection system without the danger of overdrawing. underground utilities such as storm and sanitary sewers or the backfill that surrounds these features may produce short-circuiting of airflow associated with an active landfill gas collection system. Geologic investigations must be performed to determine the potential for off-site migration.Biogas Recovery from Landfills 27 the landfill due to a reduction in available air pathways. Geologic conditions must be determined to estimate the potential for off-site migration of gas. Barometric Pressure. compacted clay. there is a higher probability of atmospheric air intrusion through the landfill cover during periods when the barometric pressure is rising. Additional attention must be given to areas where houses and other structures are present to ensure off-site migration will not impact these structures. The components of many hazardous and solid waste landfill cover systems consist of a vegetated surface component. The water table surface acts as a no-flow boundary for gas. and weathered bedrock provide a potential pathway for off-site migration. Overdrawing occurs when oxygen from the atmosphere is pulled into the landfills interior during the anaerobic phase. especially if these layers are overlain by a layer of low permeability soil. geomembranes. or compacted clay. Therefore. A consistently high ground water table will significantly reduce the potential for offsite migration of gas. As a result. The depth to groundwater (as well as seasonal variations) also needs to be evaluated during the design process to evaluate well construction requirements and the potential for water table upwelling (i. Thus. the purpose is to control and manipulate the influencing factors in a positive manner in order to accelerate the biodegradation of MSW and increase the amount of LFG produced. Leachate recirculation Leachate recirculation is the process by which the leachate collected at the base of the landfill is recycled or reintroduced in the landfill in order to control the moisture content. Warith et al. sludge addition. daily cover and waste compaction. and reviewed by Barlaz et al. (1998). (1996. (1998. (1998) studied the effect of moisture content on the biodegradation of MSW and concluded that moisture content has a positive effect on gas production. Warith (2003). Pacey (1989). and the potential transformation of waste into energy. E. Leachate recirculation provides optimum conditions for enhancing biodegradation by increasing the moisture content and movement. Klink et al. A landfill with a low permeability (geomembrane) cover will be more resistant to air intrusion than a landfill with a soil cover. (1982). Ham et al. There are many advantages to enhancing the biodegradation of MSW. temperature control. Also.. 2002). (2001). 2002). Christensen et al. (2001). Both moisture content and moisture movement are necessary settings for bacteria growth and the establishment of methanogenic conditions. (1998). The advantages and impacts of leachate recirculation on the degradation of MSW were covered by Barlaz et al. (1998). They also provide better contact between insoluble substrates. Elagroudy and Mostafa A. and by distributing the nutrients throughout the landfill. and pre-treatment of MSW. Warith intrusion will be greatly affected by the type of cover on the landfill. including more rapid waste stabilization and increased gas production. as it increases the rate of methane production. (2002). 1. Chiemchaisri et al.28 Sherien A. (1990). They will all be discussed in the following sections. The technologies used to enhance the biodegradation of MSW are studied by San et al. improved cell design. Stegmann (1983). Stegmann et al. Bae et al. pH buffering. 2002. Baldwin et al. as is the case in conventional landfills (Reinhart et al. (1999a). Komilis et al. Reinhart et al.. and Sponza et al. Warith et al. . soluble nutrients and microorganisms (Klink et al. (1996). LFG Production Enhancement Methods The biodegradation of MSW and LFG production in bioreactor landfills can be enhanced through different methods. 2004). (2002). lower leachate treatment costs through recirculation to the landfill. Laquidara et al. Ham et al. (1986). reduced length and cost of post closure activities. (1996). 2003). The advantages of leachate recirculation lay both in the rapid reduction of the organic content present in the leachate itself which reduces the cost of treatment. 1989). reduced waste particle size. Chan et al. In all cases. leachate recirculation treats the leachate through the landfill (in situ treatment) because the organic compounds in the leachate are reduced with the recirculation due to the biological activity within the landfill (Sponza et al. (2004).. These technologies are leachate recycle. and greater landfill airspace availability due to increased settlement during the operation rather than the post closure stage. (1992). (1982) and Baldwin et al. San et al. 1982). (1982. (2001) found that the highest degree of stabilization occurred in a reactor with a four-time per week recirculation and pH control by addition of buffer. to maintain the pH at a neutral level. 1992). the reactor with buffered and nutrients amended recycled leachate resulted in the greatest reduction of COD concentration over time. Leachate recirculation with a buffering system to control the pH causes a shorter acidogenic stage compared to leachate recirculation without a buffering system (Komilis et al.Biogas Recovery from Landfills 29 Klink et al. It appears that the addition of anaerobic digested sludge with buffering enhanced the biodegradation and increased methane generation. In a study conducted by Warith (2002). 2. (1982) found that the reactor with leachate recycle had 25-50% higher methane production as compared to reactors having the same moisture content but without leachate recirculation. 1990). Buffering controls the pH of the landfill around neutral.. The negative effect of sludge addition to fresh waste is attributed to the acid accumulation that is associated with it which decreases the pH and inhibits the methanogenic bacteria (Barlaz et al. Lab scale experiment results recommend the addition of buffer to leachate recycle. thereby enhancing the methane formation stage. (1999a) concluded that adding anaerobic digested sludge to MSW produces three times more methane than adding primary sludge. . The positive effect of sludge addition occurs if the methanogenic bacteria are already established or the landfill environment is optimum (pH neutral) for methanogenic bacteria (Christensen et al. (2005) studied the effect of alkalinity addition to leachate recycle on the degradation of MSW in an anaerobic bioreactor. Komilis et al. especially in the acid generation phase. The addition of old waste or ashes to new waste could improve biodegradation by diluting the acids produced during the acidogenic stage. Also. This positive effect can be attributed to the following factors: 1) sludge can be a source of nutrients and active methanogenic bacteria. 3.. Ağdağ et al. Sludge addition The effect of sludge addition on the MSW degradation is covered by Pacey (1989). 2) sludge increases the moisture content. Leuschner (1982) and Warith (2002). They concluded that the addition of sewage sludge has both a positive and a negative effect on the MSW biodegradation and methane generation. The percentage of ash should not exceed 10% in weight (Komilis et al. 1999a). VFA concentrations and BOD5/COD ratios were obtained in the bioreactors with alkalinity addition in comparison to the bioreactor (control) without alkalinity addition.. pH buffering The methanogenic bacteria are sensitive to pH and could be inhibited by acidic conditions. a study by San et al. This understanding has led to adding buffer to the leachate prior to recycling it back to the bioreactor landfill. whereas the septic tank sludge is a poor one. Rees (1980) and Leuschner (1982) found that the anaerobic digested sewage sludge is an excellent source of microbial inoculum. and. 1999a). It was observed that lower COD. This helps to establish a methanogenic condition. Also.. allowing the methanogenic bacteria in the anaerobic sludge to acclimatize to the landfill environment faster than without buffer addition. 2004.. Warith 4. since the hydrolysis is the rate-limiting step (Yildiz et al. Elagroudy and Mostafa A. Pareek et al. they found that the reactor with waste shredding had the lowest COD and VFA concentrations and the highest methane percentage. The Florida landfill (30˚C) had a more rapid decomposition compared to the Wisconsin landfill (22˚C). 5. daily cover and compaction of waste.. 1999. Based on that.8 times increase when the temperature rose from 18. This is due to the fact that the smaller particle size increases the rate of hydrolysis and acid formation which in turn decreases the pH and postpones the production of methane. The methanogenic rate is inhibited when the temperature is increased to 55˚C. Sponza et al. (1998) investigated the effect of temperature on a large scale using two different landfills.7 to 40˚C. Kasali et al.5 cm particle sizes in a period of 90 days. Cell design. They compared three types of reactors. 1992). if the negative effect of smaller particle sizes in the initial stage of biodegradation can be controlled (by adding buffer or pre-composting).. The cell thickness has an adverse effect on the biodegradation of waste. the optimum temperature for enhancing the MSW biodegradation is in the range of 30-40˚C. Temperature control The direct effect of temperature on bacteria activity could be manipulated to optimize the decomposition of MSW in the bioreactor landfill. The first reactor was loaded with raw waste. (1989) found that by increasing the temperature of MSW with a 60% w/w moisture content from 18. Naranjo et al. Baldwin et al. Reduced waste particle size Shredding or reducing the particle size of MSW has several advantages. one located in Florida and the other in Wisconsin. shredding may enhance the biodegradation process. Ham et al. it is necessary to realize the temperature constraints on individual microorganisms in order to control the activity of bacteria and enhance waste stabilization. 6. the concentration of leachate and the stabilization time are doubled as well.. The arguments for shredding are: 1) it increases homogeneity and distribution of waste within the landfill. and the third with compacted waste. 2) it improves the contact surface area of the waste.2m deep lift. the second with shredded waste.. Thus. 1996b.2 to 2. . Ham et al. El-Fadel et al. while a 7.6 times increase in the methanogenic rate. (2005) reported that the shredding of MSW has a positive effect on the rate of biological degradation in anaerobic bioreactors with leachate recycle. Based on the experimental work. daily cover and compaction of waste The enhancement of waste biodegradation in the landfill is also affected by the cell thickness. 2004). 3) it promotes better contact between the organic matter and microorganisms (Christensen et al. (1982) found that the shredding of waste increases the rate of decomposition and methane production. (1982) found that the cell with a 2m deep lift produced higher leachate concentrations and took a longer time to stabilize than the cell with a 1.30 Sherien A. Some authors (Buivid et al. By doubling the cell depth from 1..5 cm particle sizes produced 32% more methane than refuse with 1 to 1.5 to 3. At the end of the experiments (57 days later).4 m.7 to 30˚C caused a 2. 1981) concluded that refuse with 2. such as providing more landfill space and greater MSW stabilization. The landfill should utilize thin lifts and the daily cover should not be used immediately. 7. Pre-treatment The objective of the pre-treatment of MSW is to enhance the acidogenic stage and decrease the accumulation of organic acids.2 to 0. This is due to the fact that the composted layer acts as an anaerobic filter which has the ability to treat leachate as it passes through. Beker (1987). (1982). This method was studied by Ham et al. Use of alternative covers that do not create such barriers can reduce these effects. The cell with soil cover has a higher leachate concentration than the cell without it. (1980) found that cells with low-density waste have shorter periods of high leachate concentration. Rees et al. The author suggested that efforts should be made to reduce the time required for aerobic decomposition of the first layer by injecting air through perforated pipes. 1983). This method is based on the stabilization of part of the waste through aerobic processes which will dilute the organic acids and cause a balance between the acidic phase and the methanogenic bacteria. After one year of the placement. there was a decrease in gas production due to acid accumulation. which is examined in this thesis. contain lime) (Christensen et al. Waste compaction causes sudden decrease in the void space of the waste which in turn decreases the moisture content dramatically. the effect of load caused from subsequent waste layers.. the cell without cover produced a high leachate concentration. waste compaction has an adverse effect on the biodegradation of waste in the landfill. (1999b). Initially. The leachate concentration and the temperature of the waste can be used as indicators for the progress of the aerobic process. On the other hand. The composted bottom layer can be prepared by the following procedure: a layer (1. 1982). . the daily cover has a negative effect on the biodegradation of waste because it decreases the O2 diffusion into the waste which in turn diminishes the composting rate. Ham et al.g. which in turn decreased the pH and inhibited the methanogenic bacteria. If a low permeability soil is used as a daily cover. the waste layer is compacted and an additional layer of fresh waste can be added on top (Stegmann. so that the easy degradable material can be decomposed aerobically with leachate recycle. A soil cover more permeable than the waste can direct leachate to the sides.47 t/m3. it could create a barrier and may impact leachate distribution and landfill gas flow into the collection system. This means that there is an enhancement in the acidogenic stage.. positive effects of daily cover soil may be expected if the soil supplies buffer to the landfill (e.Biogas Recovery from Landfills 31 Similarly. On the other side.5m-2m) of waste is placed without compaction. causes a gradual decrease in waste voids in a way that does not affect waste biodegradation. Likewise. (1982) concluded that by increasing the waste density from 0. Beker (1987) and Stegmann (1983) found that by placing fresh waste on top of the composted waste layer caused a shorter acidogenic stage and enhanced the methanogenic stage. but it was followed by a rapid decrease (Ham et al. Ehring et al. The short acidogenic period leads to the rapid establishment of the methanogenic stage. (1982). It appears that the lack of daily cover enhances the aerobic activity and prevents a long acidogenic stage. 1992). and Stegmann (1983) and was reviewed by Komilis et al. Additionally. and some alteration of trace landfill gases occurs due to adsorption onto soil particles. In addition. where containment was not practised. Lateral movement of the gases is caused by overlying low permeability layers such as the daily cover and surface and sub-surface accumulations of water. cracks in the overlying capping layer and through man-made shafts. Movement of gas within the mass of waste is governed by the permeability of the waste. have low gas emission levels (Mosher et al 1999). between bales of waste if a baling system is used to compact and bale the waste. both to the site workers and to the surrounding neighbourhood. . such as mine shafts and service ducts. Elagroudy and Mostafa A. The contribution of a range of chemicals identified in landfill gas has been shown to be significant contributors to the toxic air pollutants in local neighborhoods adjacent to landfill sites (Scheff et al 2001). reduction in methane concentration occurs due to oxidation. through caves. LANDFILL GAS BEHAVIOUR A. it is unlikely that long exposure to such levels would be experienced by landfill site workers and even less likely for members of the public (Allen et al 1997). condensation and dissolution. 1994). oxidation. the gas is collected in gas wells. Gas may migrate considerable distances from the boundaries of the site through these possible pathways. Certain chemicals. including chlorinated hydrocarbons. Sub-surface gas migration out of the mass of waste into the surrounding environment may occur from older sites. leachate movement out of such sites may cause later degradation to landfill gas. That is. It has been reported that changes in the major and trace components of landfill gas occur during subsurface migration (Ward et al 1996). other work has shown that chlorinated hydrocarbons are found in landfill gas at concentrations which exceed occupational exposure levels (Allen et al 1997). where landfilling is still in operation and where the waste is only partially covered by an impermeable layer. and the degree of compaction of the waste. there are higher emissions of landfill gas. Vertical movement of gas may occur through natural settlement of the waste. degradation. where significant leakage has occurred. cavities. the landfill is capped with an impermeable synthetic and natural containment system to prevent migration of landfill gas out of the site and which have gas recovery systems in place. Waste landfills are a source of volatile organic hydrocarbons. Where landfill gas extraction is practised to recover the gas for energy use. Fully contained landfill sites where. overlying daily or intermittent cover. LFG Movement and Migration Gases generated in the landfill will move throughout the mass of waste in addition to movement or migration out of the site. The mechanism of gas movement is via gaseous diffusion and advection or pressure gradient. have been identified as being derived from landfill as the major source. etc. Migration of gas outside the site requires migration pathways such as high-permeability geological strata. after completion. For landfill sites. and piped to the surface (Waste Management Paper 27. or through layers of low permeability inert wastes such as construction waste rubble. the gas moves from high to low gas concentration regions or from high to low gas pressure regions (Kjeldsen et al 2002). or through containment sites. However. For example. Warith V.32 Sherien A. The capping liner system is also designed to prevent ingress of precipitation. More frequent monitoring may be required where migration of gas is suspected. will be dependent on the age of the site. which would normally be housed in a portable laboratory or at the analytical laboratory. Probes or tubes may be permanently installed. Gas monitoring well and boreholes consist of a porous plastic casing in direct contact with the waste or geological strata. The following conditions must be met for landfill gas to pose an explosion hazard: . subject to error. depending on site-specific characteristics. such as ‘Teflon’ bags or glass sample tubes and the sample is then transferred to the instrument for analysis. The most accurate and reliable technique for gas analysis is gas chromatography. Sub-surface monitoring using gas probes is used to monitor gas production and migration at depths of between 1 and 10m in the mass of waste and in the surrounding environment. Monitoring of LFG The monitoring program for landfill gas at waste landfill sites is recommended to determine whether landfill gas is causing a hazard to human health or the environment. sub-surface probes. Portable analyzers may be simple devices. Surface monitoring with portable instruments is mainly used to detect the presence of gas leaks throughout the site. Gas sample analysis may take the form of portable instruments for gas analysis or laboratory-based analysis. such as infra-red gas analyzers and flame ionization detectors.5% by volume of carbon dioxide. LFG Hazards 1. Frequency between measurements will vary from weekly. They are installed within the mass of waste and in the surrounding environment. such as gas indicator tubes. the type of waste and the gas collection and control measures installed. typically below 1. until emission levels of methane and carbon dioxide are at environmentally insignificant levels. surface monitoring.0% by volume of methane and 1. Monitoring takes place throughout the operation of the plant and for many years during the post-closure period. monthly or even quarterly. The method is.Biogas Recovery from Landfills 33 B. and boreholes. The probes may be left for long periods of time to monitor and map the production of gas from the site throughout site operation and post-closure. A sample of the gas is taken in a suitable container to the laboratory for analysis. The gas is drawn through the tube on-site and an immediate indication of gas concentration is obtained. More sophisticated instruments are available. where the gas sample is taken for analysis. even at trace concentrations. The gas sample is piped directly to the analyzer or else a sample of the gas is taken in suitable sealable containers. which produce a color change to indicate a concentration of a particular gas in a sample. however. LFG explosion hazard Landfill gas may form an explosive mixture when it combines with air in certain proportions. The probes are constructed of steel and plastic pipe. The gas chromatograph can separate out individual gas components and provide an accurate analysis. for example. consisting of a porous lower section and a gas transfer pipe which transfers the gas to the surface. gas monitoring wells. C. Monitoring takes place within the landfill and outside the site boundary. including the frequency of monitoring. Monitoring techniques for landfill gas include. The monitoring program. For example. However. Carbon dioxide is not flammable or explosive. however. Gas collection in a confined space. Underground pipes or natural subsurface geology may provide migration pathways for landfill gas. a utility room in a home. methane is unlikely to explode within the landfill boundaries. in most landfills.2% and its UEL is 7.34 Sherien A. The LEL and UEL are measures of the percent of a gas in the air by volume. Elagroudy and Mostafa A. The gas must collect in a confined space to a concentration at which it could potentially explode. the methane gas mixture may be at explosive levels. Potential Explosion Hazards from Common Landfill Gas Components Component Methane Carbon dioxide Nitrogen dioxide Oxygen Ammonia NMOC Hydrogen sulfide Potential to pose an explosion hazard Methane is highly explosive when mixed with air at a volume between its LEL of 5% and its UEL of 15%. Because methane concentrations within the landfill are typically 50% (much higher than its UEL). Gas collection and treatment systems reduce the amount of gas that is able to escape from the landfill. Source: Cheremisinoff 2003 Also. Methane is the constituent of landfill gas that is likely to pose the greatest explosion hazard. or oxygen-depleted. The concentration level at which gas has the potential to explode is called the explosive limit. Hydrogen sulfide is flammable. Its LEL is 15% and its UEL is 28%. but the methane gas usually . or a basement. environment. However. the LEL of benzene is 1. a subsurface space. but is necessary to support explosions. At the surface of the landfill. hydrogen sulfide is unlikely to collect at a concentration high Enough to pose an explosion hazard. benzene and other NMOC alone are unlikely to collect at concentrations high enough to pose explosion hazards. oxygen is a key component for creating an explosion. At some landfills. However. Ammonia is flammable. Its LEL is 4% and its UEL is 44%. However. Gas migration. Methane is explosive between its LEL of 5% by volume and its UEL of 15% by volume. The concentration at which a gas has the potential to explode is defined in terms of its lower and upper explosive limits (LEL and UEL). As methane migrates and is diluted. A confined space might be a manhole. ammonia is unlikely to collect at a concentration high enough to pose an explosion hazard. A landfill must be producing gas. but the biological processes that produce methane require an anaerobic. enough oxygen is present to support an explosion. Potential explosion hazards vary by chemical. Table 6. methane can be produced at sufficient quantities to collect in the landfill or nearby structures at explosive levels. an explosion hazard may exist if a gas is present in the air between the LEL and UEL and an ignition source is present. At concentrations below 5% and above 15%. At concentrations below its LEL and above its UEL. Nitrogen dioxide is not flammable or explosive. methane is not explosive. and this gas must contain chemicals that are present at explosive levels. a gas is not explosive. Warith • • • Gas production. The gas must be able to migrate from the landfill.8%. Oxygen is not flammable. and death in minutes Source: Cheremisinoff 2003 Carbon dioxide. However. the flammable NMOC do contribute to total explosive hazard when combined with methane in a confined space.Biogas Recovery from Landfills 35 diffuses into the ambient air to concentrations below the 5% LEL. such as a basement or an underground utility corridor. very poor muscular coordination. If benzene were detected in landfill gas at a concentration of 2 ppb (or 0. either individually or in combination. Table 6 provides a summary of the potential explosion hazards posed by the important constituents of landfill gas. create an asphyxiation hazard if they are present at levels sufficient to create an oxygen-deficient environment. and NMOC) are flammable. convulsive movements. However. benzene concentrations in landfill gas are very unlikely to reach these levels. accelerated heartbeat.. a basement or utility corridor) at concentrations high enough to displace existing air and create an oxygen-deficient environment. hydrogen sulfide. vomiting. 2. Health effects associated with oxygen deficient environments are described in Table 7. Other landfill gas constituents (e.. LFG asphyxiation hazard Landfill gas poses an asphyxiation hazard only if it collects in an enclosed space (e.g. they rarely pose explosion hazards as individual gases. and intermittent respiration Nausea.g. inability to perform. Other flammable landfill gas constituents are unlikely to be present at concentrations high enough to pose an explosion hazard. Health Effects from Oxygen-Deficient Environments Oxygen Concentration 21% 17% 14 to 16% 6 to 10% Less than 6% Health Effects Normal ambient air oxygen concentration Deteriorated night vision (not noticeable until a normal oxygen concentration is restored). However. Any of the gases that make up landfill gas can. Table 7. because they are unlikely to be present at concentrations above their LELs.0000002% of the air by volume).8%. In order to pose an explosion hazard. ammonia. Because it is denser than air. may pose specific asphyxiation hazard concerns.2% and UEL of 7. and accelerated heartbeat Increased breathing volume. may remain in the area for hours or days after the area has been opened to the air . benzene (an NMOC that may be found in landfill gas) is explosive between its LEL of 1. The Occupational Safety and Health Administration (OSHA) defines an oxygen-deficient environment as one that has less than 19. For example. then benzene would have to collect in a closed space at a concentration 6 million times greater than the concentration found in the landfill gas to cause an explosion hazard. Ambient air contains approximately 21% oxygen by volume. rapid fatigue.5% oxygen by volume. methane must migrate from the landfill and be present between its LEL and UEL. Methane is the most likely landfill gas constituent to pose an explosion hazard. which comprises 40% to 60% of landfill gas. carbon dioxide that has escaped from a landfill and collected in a confined space. increased breathing volume. and unconsciousness Spasmatic breathing. but also pose a special asphyxiation problem for utility workers who fail to follow confined space entry procedures prescribed by OSHA.33 ppb. Humans are extremely sensitive to hydrogen sulfide odors and can smell such odors at concentrations as low as 0. and shaking. and certain NMOC. rapid breathing. Potential sources of landfill odors include sulfides. shortness of breath. The response to carbon dioxide inhalation varies greatly even in healthy normal individuals. hydrogen sulfide is emitted from landfills at the highest rates and concentrations.g. People in communities near landfills are often concerned about odors emitted from landfills. People may also have concerns about health effects associated with these odors and other emissions coming from the landfill. sweating. Carbon dioxide concentrations of 10% or more can cause unconsciousness or death. Landfill odors may also be produced by the disposal of certain types of wastes. dimethyl sulfide. The following are major landfill gases generated: Sulfides.11 to 0. environmental health professionals should investigate the presence of buried utility lines and storm sewers on or adjacent to the landfill. People are exposed daily to low levels of ammonia in the environment from the natural breakdown of manure and dead plants and animals. people can find the odor offensive. Carbon dioxide is colorless and odorless and therefore not readily detectable. According to information collected by the Connecticut Department of Health. These odors can migrate to the surrounding community.. Hydrogen sulfide. Ammonia is common in the environment and an important compound for maintaining plant and animal life. Humans are much less sensitive to the odor of ammonia . On-site or adjacent residences and commercial buildings with basements or insulated (or sealed) crawl spaces should also be investigated for potential asphyxiation hazards. such as headaches and nausea. Landfill odors Landfill odors often prompt complaints from community members. mental depression. such as manures and fermented grains. visual disturbances. These gases produce a very strong rotten-egg smell— even at very low concentrations. These structures not only provide a pathway for migrating gases. if present at concentrations that are high enough. these effects fade when the odor can no longer be detected. They say that these odors are a source of undesirable health effects or symptoms. Ammonia is another odorous landfill gas that is produced by the decomposition of organic matter in the landfill. Landfill gas odors are produced by bacterial or chemical processes and can emanate from both active and closed landfills. Ammonia. ammonia. Elagroudy and Mostafa A. 3. and mercaptans are the three most common sulfides responsible for landfill odors. most people are familiar with its distinct smell.5 to 1 part per billion (ppb). Warith (e. The seriousness of these symptoms depends on the concentration and duration of exposure. Average concentrations in ambient air range from 0. and increased heartbeat. dizziness. At levels approaching 50 ppb. Because ammonia is commonly used as a household cleaner. after a manhole cover has been removed or a basement door opened). In assessing the public health issues of migrating landfill gas. the concentration of hydrogen sulfide in ambient air around a landfill is usually close to 15 ppb.36 Sherien A. At low-level concentrations—typically associated with landfill gas— it is unclear whether it is the constituent itself or its odors that trigger a response. Lower concentrations may cause headache. Of these three sulfides. Typically. The odor threshold for ammonia is between 28. Odor control technologies prevent odor-causing gases from leaving the landfill. Regardless of what model is used. Covering a landfill daily with soil can help reduce odors from newly deposited wastes.000. may also cause odors. Annual rates of gas production have been estimated for a typical municipal solid waste landfill at between 6 and 8m3/tonne/year but much higher rates of over 25m3/tonne/year have been recorded (Characterization of 100 UK landfill sites 1995). Landfill gas has been reported to contain between 1. The LandGEM model is one of these models and was developed by the US Environmental Protection Agency to estimate landfill gas emissions and to determine regulatory applicability to CAA requirements.1% to 1% ammonia by volume. As long as oxygen is present. The Intergovernmental Panel on Climate Change (IPCC) methodology for estimation of CH4 emissions from the landfills is based on First-Order decay (FOD) method. These models vary widely. knowing that undiluted landfill gas can have a calorific value of between 15 and 21 MJ/m3.Biogas Recovery from Landfills 37 than they are to sulfide odors. The .000. This allows the potential amount of energy which could be generated from the site. 1994). Some NMOC. however. bacteria will decompose landfill gas under aerobic conditions. NMOC. Venting landfill gas through a filter is another technology used to reduce odors. VI. For the estimation of landfill gas throughout the lifetime of a site for the assessment of energy recovery from landfill gas utilization. producing carbon dioxide and water.000 ppb of ammonia. There are other LFG emission models in use by industry that also work very well. General Several models are available for estimating the LFG generation rate using site-specific input parameters. not only in the assumptions that they make. NMOC are emitted at very low (trace) concentrations and are unlikely to pose a severe odor problem. such as vinyl chloride and hydrocarbons. compared to the calorific value of natural gas at about 37 MJ/m3 (Waste Management Paper 27. In general. and in the amount of data they require. Landfill gas is collected and vented through a filter of bacterial slime. Estimates of the amount of landfill gas generated throughout the lifetime of the landfill site are highly variable with estimates of between 39 to 500 m3/tonne (McBean et al 1995). Vegetative growth on the landfill cover also reduces odors. or 0.000 and 50. the accuracy of the inputs drives the results and given the level of uncertainty. Flaring is another technique that can eliminate landfill gas odors by thermally destroying the odor-causing gases. Installing a landfill cover will prevent odors from newly deposited waste or from gases produced during bacterial decomposition. MODELING OF METHANE GAS GENERATION AND EMISSION FROM LANDFILLS A.000 ppb.000 and 10. values of between 150 and 250m3/tonne are typically used (Loening 2003). but also in their complexity. More extensive covers are installed at landfill closure to prevent moisture from infiltrating the refuse and encouraging bacterial growth and decomposition. Concentrations in ambient air at or near the landfill site are expected to be much lower. it makes estimating landfill emissions very difficult. Elagroudy and Mostafa A. a narrower range of flame stability and thus lower combustion efficiency (Qin et al 2001).E.1 (1) Where. QCH 4 = Annual Methane generation in the year of the calculation (m3/year) Mi = Mass of waste accepted in the year I (Mg) L0 k j i n = Potential methane generation capacity of the waste (m3/Mg) = Methane generation rate (per year) = Waste type category (index) = = 1Year (year of the calculation). Model . Input Parameters Main Input parameters required for LandGEM are as follows: • • • Annual Waste acceptance rate during the operation of the landfill (tons/year) Start year and end year of the landfill operations Assumed values of methane generation rate ( k ) and methane generation potential ( L0 ) • NMOC concentration and methane content in landfill gas . 3. The presence of carbon dioxide results in reduced flame temperatures and burning rates.(initial year of waste acceptance) Age of the jth section of waste mass M i accepted in the ith year (decimal tij = years.. Model description The landfill gas emission model (LandGEM) developed by US EPA provides an automated estimation tool for estimation of landfill gas emissions from municipal solid waste MSW landfills (http://www.1. The model is based on a first order decomposition rate equation to estimate annual emissions over a specified time period.htmlsoftware). and non-combustible gases such as carbon dioxide. Warith calorific value of the gas depends on the percentage composition of combustible gases such as methane. in that it does not combust and therefore does not contribute to the energy content of the landfill gas. B.Landgem 1. The carbon dioxide is also regarded as ‘inert’. e.S.epa.gov/ttn/catc/products.g. described as follows: 1 n ⎛ M ⎞ − kt QCH 4 = ∑ ∑ kLo ⎜ i ⎟e ij ⎝ 10 ⎠ i =1 j = 0.P. U.2 years) 1.A.38 Sherien A. half life is the time taken by the degradable organic carbon in the waste to decay to half of its initial mass. There are two options to use the value of k for estimation of gas potential: Bulk waste option in which single value of k is chosen for the entire waste and Waste composition option in which k value for each component of waste stream is considered for calculations. This method assumes that the degradable organic carbon (DOC) in the waste decays slowly throughout a few decades. characteristics of the disposal site.02) are associated with dry site conditions and slowly degradable waste such as wood or paper. Model description The Intergovernmental Panel on Climate Change (IPCC) methodology for estimation of CH4 emissions from the landfills is based on FOD method. As per IPCC (1996). the CH4 emissions from the waste deposited in a landfill are highest in the first few years after closure and then gradually start reducing. Therefore. It depends upon the composition of the waste. during which CH4 and CO2 are formed. The most rapid rates (k = 0. the values of Lo may range from less than 100 to over 200m3/Mg. IPCC-First Order Decay (FOD) Model 1.2) are associated with high moisture conditions and rapidly degradable material such as food waste.Biogas Recovery from Landfills 39 LandGEM is considered a screening tool – the better the input data. Methane generation rate (k) The k value is indicative of the fraction of the waste which undergoes decomposition in the given year to produce methane. If conditions are constant. Values of Lo can vary widely and are difficult to estimate for a particular landfill. IPCC (2006) has provided default k values as dry and wet values for various types of waste depending upon the climatic conditions. The FOD model developed by IPCC (2006) has been widely adapted for calculation of methane emissions from the landfills. C. the better the estimates. the rate of CH4 formation depends solely on the amount of carbon remaining in the waste. The slower decay rates (k = 0. climatic conditions at the site. Same model has been used by United Nations Framework Convention on Climate Change (UNFCCC) in its “Tool to determine methane . waste disposal practices etc. The k value for the given mass is actually related to its half life time period of decay: k = ln 2 t1/ 2 (2) Where. This value is affected by a number of factors including the waste composition. The Input parameters in the model are described below in more details: Methane generation potential (L0) The methane generation potential is the total amount of methane that a unit mass of refuse will produce given enough time. LandGEM has bulk waste option for k. (t CO2e) is calculated for each year y.x = DOC j = kj = Decay rate for the waste type j j = x = y = Waste type category (index) Year during the crediting period: x runs from the first year of the first crediting period (x = 1) to the year y for which avoided emissions are calculated (x = y) Year for which methane emissions are calculated = 1.e . using the following equation: BECH 4. y ).kj ) ×e 16 ×F ×DOC f 12 (3) .SWDS . valid for the relevant commitment period Oxidation factor (reflecting the amount of methane from SWDS that is oxidised in the soil or other material covering the waste Fraction of methane in the SWDS gas (volume fraction) Fraction of degradable organic carbon (DOC) that can decompose Methane correction factor Amount of organic waste type j prevented from disposal in the SWDS in the year x (tons) Fraction of degradable organic carbon (by weight) in the waste type j MCF W j .f ) ×GWPCH 4 ×(1 .1.k j ×( y .OX ) y MCF ×å å W j. . combusted or used in another manner Global Warming Potential (GWP) of methane. x ×DOC j ×(1 . SWDS . Input Parameters The input parameters used in the FOD model are more or less similar to the LandGEM model except that IPCC has attempted to make the projections for methane emissions more realistic by incorporating various correction factors to the equation.SWDS . Warith emissions avoided from dumping waste at a solid waste disposal site” to award Clean Development Mechanism (CDM) benefits to a particular landfill closure project. Elagroudy and Mostafa A. y = φ Methane emissions avoided during the year y from preventing waste disposal at the solid waste disposal site (SWDS) during the period from the start of the project activity to the end of the year y (tCO2e) = Model correction factor to account for model uncertainties f = GWPCH 4 = OX = F DOC f = = Fraction of methane captured at the SWDS and flared. the amount of methane that is generated each year ( BECH 4. As per the tool. y = j ×(1 .x ) x =1 j Where: BECH 4.40 Sherien A. wood. MSW contains different types of waste namely food waste.200 0 . However. is: L0 = DDOC m ∗ F ∗ 16 12 (5) Where. 2006 DOCj 0. decomposable degradable organic carbon by mass ( DDOCm ) is: DDOCm = W ∗ DOC ∗ DOC f ∗ MCF (4) Where.Biogas Recovery from Landfills 41 The values for correction factors used in the model are mostly default values suggested by IPCC. IPCC Default DOC Value (In Fraction) For Different Waste Type Type of Waste Wood and wood products. garden waste. F Source: IPCC. metal other inert. B Food.150 0. as described in IPCC (2006). C Textiles. A Pulp. only fraction of the DOC is decomposable in nature ( DOC f ). Hence. textiles. IPCC has mentioned two alternatives to use the value of k for estimation of gas potential. Table 8. Decay rate/methane generation rate ( k j ) As already mentioned in the previous section. the waste composition option is used where degradation of different types of waste is assumed to be independent of each other. beverages and tobacco. The relationship between Methane generation potential ( L0 ) used in LandGEM and DDOCm . plastics etc. E Glass. as mentioned below: Degradable Organic Carbon ( DOC j ) Degradable organic carbon is the fraction of the organic carbon present in the waste that will degrade under anaerobic conditions. In this model. yard and park waste. paper and cardboard. D Garden. paper. IPCC 2006 has recommended default k values for different waste categories dependent upon the location of the landfill site and its climatic conditions as shown in Table 9. plastic. Different waste types contain different amount of degradable organic carbon (DOC).430 0. food waste.400 0. As per IPCC FOD model.240 0. waste composition of MSW is classified into six categories as shown in Table 8. W is the mass of the waste deposited in the landfill in the given year and MCF is the methane correction factor for aerobic decomposition of waste. F = CH4 concentration in LFG and 16/12 is the ratio of molecular weight of CH4 and Carbon. 5). yard and park waste. nitrogen and sulfur (represented by CaHbOcNdSe). Twenty-one US landfills with gas recovery systems were included in the study. Elagroudy and Mostafa A.07 0. average temperature. Part of this program was a field study to gather information that was used to develop an empirical model of methane emissions. landfill size. Site-specific information included average methane recovery rate. C Textiles. IPCC Default of K Used in IPCC in IPCC FOD Modeling Type of Waste Wood and wood products.Theoretical Models The theoretical CH4 generation capacity ( L0 ) can be determined by a stoichiometric method that is based on a gross empirical formula representing the chemical composition of the waste. If a waste contains carbon. Regression Models The EPA Air and Energy Engineering Research Laboratory (AEERL) began a research program in 1990 with the goal of improving global landfill methane emission estimates. Refuse mass was nearly as good (R2 = 0. and climate. hydrogen. metal other inert. refuse mass.035 0.40 0. None of the climate variables (precipitation. Much of the variability in methane recovery remains unexplained. D Garden. dew point) correlated well with the methane recovery rate. A simple model correlating refuse mass to methane recovery with a zero intercept was developed: Qmethane = 4. refuse mass. A Pulp. Regression analysis of the methane recovery rate on depth. oxygen. 3 Qmethane = Methane flow rate (m /min) w = mass of refuse (Mg) E. 2006 D. average age of the refuse. E Glass. volume. operation. but depth was the best predictive variable (R2 = 0. paper and cardboard. and well depth. and volume was significant. F K 0. B Food.52 w (6) Where. Warith Table 9.17 0 Source: IPCC. A correlation analysis showed that refuse mass was positively linearly correlated with landfill depth. plastic. and refuse composition. and is likely due to between-site differences in landfill construction. its decomposition to gas is shown as: Ca H b Oc N d Se ® vCH 4 + wCO2 + xN 2 + yNH 3 + zH 2 S + humus (7) . area.07 0. A model for global landfill emissions estimation was proposed based on this data. beverages and tobacco.42 Sherien A. food waste.53). These processes were hydrolysis. this type of model is of limited use because it provides an estimate of the total amount of gas generated and does not provide information on the rate of generation. A multiplicative model was applied to estimate the growth rate of the sulfidogenic bacteria. and the initial concentrations of acetic acid and methanogenic biomass had a more important impact on gas generation than aqueous and acidogenic biomass. The model was calibrated with experiments done by Pohland et al. The model consisted of four phases. (1996b) developed a mathematical model to simulate the biodegradation of solid waste and biogas generation in a sanitary landfill. In El-Fadel et al. methanogenesis and sulfidogenesis. Monod kinetics were used to simulate the growth rate of acidogenic and methanogenic biomass. The third step was to simulate the anaerobic process involved in landfill stabilization. It also requires knowledge of the chemical composition of the waste. the kinetics constant of acidogenic and methanogenic biomass (µ. (1998) developed a numerical (PITTLEACH) model to predict the leachate quality and quantity and biogas generation from municipal solid waste. including hydrolysis. leachate generation and transport rates were estimated by using the theory of moisture flow through unsaturated porous media. The model results were close to the experimental results for both scenarios (single pass and leachate recirculation). acidogenesis.Biogas Recovery from Landfills 43 However. acetic acid. The biodegradation process occurred in three stages: hydrolysis. Pareek et al. In the first phase. Hydrolysis was assumed to be the rate limiting step in the process and followed first order reaction. (1996c) the model was used to simulate data from the Mountain View controlled landfill. aqueous. In the fourth phase. Other Models El-Fadel et al. The effect of pH inhibition on the methanogenic growth rate was also included. time dependent transport and generation of gas and heat. They assumed hydrolysis to be the rate limiting step in the biodegradation process and was represented by first order kinetics. The model was based on bio-kinetic equations describing the microbial processes. the water budget method was used to estimate the net percolation rate of water flow into the waste layer. kd. acidogenic and methanogenic). The model was based on biochemical processes responsible for the degradation of solid waste in landfills. The results of the model showed good agreement with the field data. ks) and initial carbon concentrations (solid. (1997) several runs were performed to assess the model sensitivity to the hydrolysis rate constant. the effect of acids on the pH was modeled. The values of kinetics required were taken from the literature. In El-Fadel et al. acidogenesis and methanogenesis. . F. (1999) developed a mathematical model to predict the methane and carbon dioxide production from landfill reactors operated under sulfate reducing and methane producing conditions. whereas the Monod kinetics were applied for the growth of acidogenic and methanogenic bacteria. Gas generation showed greater sensitivity to the methanogenic kinetics than to the acidogenic kinetics. acid formation and methane fermentation. In the second phase. The model was calibrated with four experiments run for 700 days. They concluded that the hydrolysis rate is the most important parameter in gas generation in landfills. for both single pass and leachate recirculation. Al-Yousfi et al. (1992) and Yari (1986). They concluded that the model could be used to predict the rate and total production of biogases in landfills. biogas generation and heat release. but the carbon dioxide production was not so accurate in the sulfate reducing reactors for the first 100 days. thermodynamic and microbial processes occurring in landfills. The results of the model matched the experimental data. μ max ⋅ f 1 (s ) ⋅ f 2 ( s ) ⋅ f 3 (T ) ⋅ f 4 ( pH ) (8) Where.44 Sherien A. The model showed results similar to the experiments. microbial growth and death. Naranjo et al. The effect of pH on the biodegradation rate is also taken into account by including an inhibition term in the maximum growth rate and expressed as non competitive inhibition. The model was calibrated with experiments. The kinetics required for the model were obtained from the literature. The model included gas and water flows. temperature. . interphase mass transfer of solids and water phase solutes. chemical. The model was based on physical. Haarstick et al. (2000) proposed a numerical model to predict the change in leachate concentration and gas production by microbial activity in landfills. Suk et al. and pH. (2001) developed a mathematical model to simulate the biodegradation of organic wastes (easily and slowly degraded). The model was applied to measure gas composition and leachate qualities of the experiments done by Lee (1997). Elagroudy and Mostafa A. and in the acidogenic and methanogenic bacteria kinetics. They concluded that the moisture factor and initial concentration of biomass and acetate were important factors in controlling the microbial growth rates and methane production. The specific growth rate was considered to be effected by inhibition terms included substrate limiting. They used the model to simulate the effect of temperature and water content on acetate and methane production. inhibitory substrate. They concluded that temperature had an impact on the growth and activity of bacteria and that an increase in water content enhanced methane production. (2004) modified the model of Haarstrick et al. and aerobic and anaerobic biodegradation. acidogenesis and methanogenesis in which Monod kinetics were used for all of them. si : Inhibition term for substrate limiting K si + si K Ii : Inhibition term for inhibitory substrate f 2 ( s) = K si + si f 3 (T ) = exp− (k (T − Topt )) : Inhibition term for influence of temperature f1 ( s ) = f 4 ( pH ) = K pH K pH + I pH : Inhibition term for influence of pH The temperature effect is taken into account in the hydrolysis rate constant. The model was not calibrated with real data. (2001) by assuming the hydrolysis followed first order kinetics. The biodegradation of organic waste was assumed to follow three biochemical reactions: hydrolysis. Warith The simulated methane production was in good agreement with the measured values in all reactors. (1996a) and occurred in three stages: hydrolysis. 2004) developed a mathematical model to simulate solid waste biodegradation and gas generation in landfills. The moisture content and effect of pH inhibition on the biomass growth rates were included in the model.Biogas Recovery from Landfills 45 Zacharof et al. The waste biodegradation was assumed to follow three steps: hydrolysis. The growth rate of acidogenic and methanogenic microorganisms were described by the Monod model. and their inhibition by acetic acid. gases and microorganisms. (2004) proposed a mathematical model to simulate the landfill leachate behavior. and change in pH over time. they considered each layer as a completely mixed reactor having uniformly distributed solid wastes. and methane production. They assumed that landfills consisted of cells and that each cell consisted of several layers. They concluded that the model had the potential to be used during the design of the landfills to estimate the quality and quantity of leachate and methane production for different operation conditions. The model was based on the governing equations that describe leachate production. (2003. the growth of acidogenic and methanogenic microorganisms. distribution of moisture through the landfill. They found the model was sensitive to depth of waste. White et al. waste heterogeneity and biodegradation rate constants. and it included an inhibition terms for acetic acid and pH. The biodegradation part was based on the model proposed by Young (1989) and El-Fadel et al. In the end. These values were then compared with the literature. The model was used to simulate case studies. They used a statistical velocity model to represent the water flow through the waste. they concluded that the model could be used as a tool for modeling landfill processes and that further improvements were required to assess the model’s performance. acidogenesis and methanogenesis. The solubilization of inorganic solid waste was assumed to have followed zero order kinetics. acidogenesis and methanogenesis. The model was solved by the fourth order RungeKulta method and calibrated with real landfill data from the Keele Valley landfill. Yildiz et al. They concluded that it could be used for laboratory and field tests to investigate the geotechnical and hydrogeological properties of biodegrading solid waste. The model was used to simulate case studies but was not calibrated with real data. moisture. Sensitive analysis showed uncertain results. The Monod kinetics were used to simulate the growth rate of biomass in all stages. Also. and transport of leachate and gas. The values of the kinetics required for the model were determined by using a trial and error procedure with the data obtained from the landfill. There was good agreement between the predicted and observed results from the Keele Valley landfill. solubilization of inorganic and organic matter. whereas the solubilization of organic solid waste was assumed to be a function of the concentration difference in leachate and microbial activity. The model included biochemical degradation of solid waste. degradation of soluble organic matter. . and employed a simplified methodology for the rate of biodegradation to reduce the parameter required. infiltration rate. The required kinetics for the model were obtained from the literature. (2004) developed a mathematical model to simulate the hydrological and biochemical processes taking place in solid waste landfills. g. usually through the landfill surface. Gases tend to expand and fill the available space. Some gases. such as methane. LANDFILL GAS ENERGY SYSTEMS With the recognition of the formation of landfill gas and its associated hazards. The natural tendency of landfill gases that are lighter than air. Schematic diagram of a landfill gas energy recovery scheme. LFG Collection System Once gases are produced under the landfill surface. In addition. The energy recovery technology is based around the gas collection system and the pre-treatment and power generation technology. where it can resume its upward path. and the potential to utilize the energy content of the gas. such as utility corridors. the modern landfill site is designed to trap the gases for flaring or use in energy recovery systems. or "migrate. When upward movement is inhibited. The priority for control of the gases is to protect the environment and prevent unacceptable risk to human health. the gas tends to migrate horizontally to other areas within the landfill or to areas outside the landfill. and a landfill gas control system is therefore required. Elagroudy and Mostafa A. by daily soil cover and caps). Basically. so that they move. the gases follow the path of least resistance. Each of those three systems is explained separately in details. Source: Brown and Maunder 1994. particularly for the landfilling of biodegradable municipal solid waste in non-hazardous waste landfills. control mechanisms are required to minimize the risk of migration of the gases out of the site. Figure 8 shows a schematic diagram of a landfill gas energy recovery project. such as carbon dioxide. they generally move away from the landfill. is to move upward.. Three main factors influence . A.46 Sherien A." through the limited pore spaces within the refuse and soils covering the landfill. Upward movement of landfill gas can be inhibited by densely compacted waste or landfill cover material (e. Figure 8. Warith VII. are denser than air and will collect in subsurface areas. wells end at the groundwater table. or perforated pipes are used to vent the migrating gas to the surface (Waste Management Paper 26B. 1995. The gas migrates to gas pits or wells. Waste Management Paper 26B. Efficiencies of barriers are improved if they are combined with a means of removing the gas by either passive venting or pumped extraction. Leachate vapor may also be pumped out with the gas. For these reasons gas control is needed. which are excavated into or at the boundary of the waste. the pipe venting directly to the atmosphere. or where inert wastes are landfilled and similarly low or negligible rates of gas generation are found. for example. The trench is lined at the outer edge with a low-permeability barrier and the trench is filled with highpermeability gravel. flexible polymeric geomembranes. The gases pass through the high-permeability vent to a plain imperforated pipe which draws the gases through to the pump. Figure 9 shows a typical pumping extraction well. physical barriers. pumping extraction systems. 1995. Pescod 1991–93. Other designs of passive gas venting systems include trenches. within the waste. Typically the vents are placed at intervals of between 20 and 50 m and to depths ranging from 50% to 90% of the waste thickness. The passive venting pit consists of a highly permeable vent of gravel material encased in a geotextile fabric to prevent ingress of fine material and reduction of permeability. and permeability. McBean et al 1995. 1994). Physical barriers Physical barriers use low-permeability barriers of. to contain and restrict the gas migration. which has high moisture content. posing indoor air quality threats such as odors or exposures to inhalation hazards. which consist of highly permeable gravel. bentonite cement or clay. Waste Management Paper 27. Waste Management Paper 27. The gas pumped to the surface is either flared by self-sustaining combustion or the use of a support . Passive venting Passive systems use existing variations in landfill pressure and gas concentrations to vent landfill gas into the atmosphere or a control system. pressure. and therefore a leachate condensation trap is required. they are less effective in containing gas. Gases can travel off-site and into neighboring buildings. The vent may also be constructed of granular material but with a central perforated plastic pipe.Biogas Recovery from Landfills 47 the migration of landfill gases: diffusion (concentration). Whilst these barriers might form part of a leachate containment system. Coefficients of permeability for gas containment are required to be lower than 10−9 m/s. Pumping extraction systems Pumping extraction systems pump the gas out of the landfill. and vent passively into the atmosphere through a permeable capping layer of sand and granular soil or crushed stone. or even fire and explosion. 1994): passive venting. stones or rubble with a central perforated plastic pipe. The gases flow up the highly permeable layer. There are three types of systems used to control landfill gas migration (Tchobanoglous and O’Leary 1994. Construction of the passive venting system may be as emplacement of the waste proceeds or afterwards by drilling or excavation into the mass of waste. If groundwater is encountered within the waste. Passive venting systems are only recommended for old sites in the late stages of gas generation where gas generation rates are low. . Elagroudy and Mostafa A. discharged to the atmosphere. Typical combined leachate and landfill gas collection well. Warith fuel. Source: Waste Management Paper 26B. or if the gas concentrations are sufficiently low. utilized in an energy recovery system.48 Sherien A. 1995. Figure 9. the simplest flaring technology. Open flame flares Open flame flares (e. Combustion technologies (Flaring Practices) LFG flaring Combustion is the most common technique for controlling and treating landfill gas.1. Therefore. incinerators. the landfill gas will readily form a combustible mixture with ambient air. resulting in a large greenhouse gas impact reduction. 1. since the gas is at temperatures above ambient and is saturated with water vapour and organic vapours. The simplicity of the design and operation of an open flame flare is an advantage of this technology. natural gas) is required to operate flares. At this methane concentration. A large proportion of the landfill gas consists of carbon dioxide which is non-combustible and therefore reduces the overall calorific value of the gas. Stegmann 1996). Methane is converted to carbon dioxide. greatly increasing operating costs. two different types of flares can be chosen: open or enclosed flares. When combustion is used. . A filter would also be included to remove fine particulate material from the gas flow. As the gas cools the water vapour condenses to form water in the pipe. and internal combustion engines thermally destroy the compounds in landfill gas. aesthetic complaints. Combustion technologies such as flares. which reduces the efficiency of gas collection and transport.g. then clean-up systems to remove carbon dioxide may be required. for example. LFG Utilization System 1. supplemental fuel (e. Condensate systems both below and above ground may be required to de-water the gas. absorption and adsorption systems to scrub the gases. gas chilling to condense certain constituents. The condensate system used to remove the water vapour consists of baffled or expansion chambers which cool and condense the water. Sometimes. Such possible pre-treatments may include further filtration. for utilization systems requiring a high specification gas or a high calorific value. open flame flares are partially covered to hide the flame from view and improve monitoring accuracy. candle or pipe flares). The gas is then compressed and possibly passed to a pre-treatment section if a greater degree of clean-up is required. Over 98% destruction of organic compounds is typically achieved. a pilot light to spark the gas. At landfills with less than 20% methane by volume. and monitoring difficulties.Biogas Recovery from Landfills 49 B. C. boilers.. so that only an ignition source is needed for operation. Such systems include water scrubbing. Combustion or flaring is most efficient when the landfill gas contains at least 20% methane by volume. Disadvantages include inefficient combustion..g. and a means to regulate the gas flow. gas turbines. to remove corrosive trace gases and vapor from the gas stream. LFG Pretreatment System A condensate removal system is required. consist of a pipe through which the gas is pumped. and other gas clean-up systems such as membranes and molecular sieves to remove trace contaminants. absorption on zeolites and membrane separation and are expensive to install and maintain (Brown and Maunder 1994. Most shrouded landfill gas flares have exit temperatures of around 7600C. Other enclosed combustion technologies Other enclosed combustion technologies such as boilers. and internal combustion engines can be used not only to efficiently destroy organic compounds in landfill gas. Flaring of landfill gas is done either in a candle flare or a shrouded flare. resulting in increased dioxin emissions. Warith 1. According to very limited data in a USEPA 1995 report. this is a loose-loose situation. While dioxins can be tested for in such flares. The generation of dioxins has also been questioned. gas turbines. carbon monoxide and NOx emissions are highest from internal combustion engines and lowest from boilers. it is possible that enclosing the flare will keep the post combustion temperature in dioxinformation range.internal combustion engines are much more variable). In such cases. but also to generate useful energy or electricity. 1. Flares and gas turbines are somewhere in the middle. process heaters. Combustion can create acid gases such as SO2 and NOx. as described later in this chapter. Dioxin emissions data are also very sparse. Enclosed flame flares consist of multiple burners enclosed within fire. there is no reliable means to monitor for dioxins or other toxic emissions. making combustion more reliable and more efficient.50 Sherien A. Burning landfill gas is dirtier than burning natural gas. In addition to flaring.resistant walls that extend above the flame. EPA investigated the issue of dioxin formation and . most flares designed today are enclosed. well above the dioxin formation range (which end around 4000C).2. Nevertheless. because this design eliminates some of the disadvantages associated with open flame flares. A candle flare is an open air flame. the amount of gas and air entering an enclosed flame flare can be controlled. There is high variability in dioxin emissions from landfill gas burners (based on composition of waste dumped and also on the combustion technology . Essentially. burning landfill gas to produce energy emits more pollution per kilowatt hour than natural gas does. Some public concerns have been raised about whether the combustion of landfill gas may create toxic chemicals. Elagroudy and Mostafa A. turbines and internal combustion engines). Whether using an internal combustion engine or a gas turbine. Shrouded flares involve enclosing the flame in an insulated cylindrical shroud which can be anywhere from 5 to 18 m tall. dioxins will be formed in midair as the exhaust hits the cooler background air after leaving the stack. Flares are known to generate more dioxin than internal combustion engines or boiler mufflers. With such. the other options for dealing with landfill gas (once collected) are as follows: • • • • • boilers for making thermal energy Internal combustion engine for generating electricity Gas turbine for generating electricity Fuel cell for generating electricity Conversion of the methane to methyl alcohol There are limited data comparing emissions from landfill gas flares to energy producing combustion devices (which includes boilers. Enclosed flame flares Enclosed flame flares are more complex and expensive than open flame flares. Unlike open flame flares.3. the landfill gas must first undergo . landfill gas destruction in a properly designed and operated control device. and they are still largely experimental. Among the concerns with this option are the integrity of the pipeline. including nitrogen oxides. Landfill gas use in boilers brings in the issue of piping the gas to local industries. They emit the most carbon monoxide and NOx and they may be the largest dioxin source of the available technologies.H2S) can damage the pipelines. since corrosive compounds in the gas (particularly the acids and hydrogen sulfide -. • Conversion of Methane to Methyl Alchol One option is to convert the methane recovered from landfills into methyl alcohol or methanol. which produces compounds that contribute to smog. 2. the pipelines do require some cleanup. Boilers are generally less sensitive to landfill gas contaminants and therefore require fewer cleanups than other alternatives. is preferable to uncontrolled release of landfill gas." In order not to poison the fuel cells. and the economic support of neighboring polluting industries which might use the gas. halogenated contaminants must first be removed and destroyed. such as a flare or energy recovery unit. and particulate matter. • Internal Combustion Engines Internal combustion engines are the dirtiest technology for burning landfill gas. Scientists continue to review new information on byproduct emissions from landfill gas control devices as it becomes available. While boilers themselves may not require much cleanup of the gas. Boilers have the lowest NOx and carbon monoxide emissions of the combustion technologies. Because of the potential imminent health threat from other components of landfill gas. for example by pyrolysis. carbon monoxide. liability issues. Regardless of which non combustion technology is used. EPA describes fuel cells as "potentially one of the cleanest energy conversion technologies available. Other novel ideas include converting the carbon dioxide in landfill gas to dry ice for sale to industry. There isn't enough data on dioxin emissions from landfill gas turbines to provide an extensive comparison. They produce thermal energy or heat. sulfur oxides. • Boilers Boilers are among the cheapest options. Non-combustion technologies Non-combustion technologies were developed in the 1990s as an alternative to combustion. Non combustion technologies fall into two groups: energy recovery technologies and gas-to-product conversion technologies.Biogas Recovery from Landfills 51 concluded that the existing data from several landfills did not provide evidence showing significant dioxin formation during landfill gas combustion. • Gas Turbines Gas turbines are somewhere in the middle in terms of carbon monoxide and NOx emissions. • Fuel Cells Fuel cells are the most expensive technology. not electricity. NMOC. This technology has been demonstrated and in the future may become more economically competitive with other options. Currently. Numerous pretreatment methods are available to address the impurities of concern for a specific landfill. such as compressed natural gas. the phosphoric acid fuel cell (PAFC) is the only commercially available non-combustion energy recovery technology. Non-combustion energy recovery systems are not used as widely as combustion based systems.52 Sherien A. 2. electricity. producing a high British thermal unit (Btu) gas that can be sold as pipeline quality natural gas. and carbon dioxide. After pretreatment. Although the high-Btu gas is eventually combusted. the purified landfill gas is treated by non combustion technology options. it . The PAFC system consists of landfill gas collection and pretreatment. Warith pretreatment to remove impurities such as water. Gas to product conversion technologies Gas-to-product conversion technologies focus on converting landfill gas into commercial products. The processes used to produce each of these products vary. Figure 10. Several chemical reactions occur within this system to create water. pretreatment and chemical reactions and/ or purification techniques. a fuel cell processing system. One option that does not involve combustion of landfill gas at or near the landfill is purifying the landfill gas to remove constituents other than methane. solid oxide. purified carbon dioxide and methane. Energy recovery technologies Energy recovery technologies use landfill gas to produce energy directly.2. and waste gases. Some of the processes use flares to destroy gaseous wastes. The waste gases are destroyed in a flare. Fuel cells are a promising new technology for producing energy from landfill gas that does not involve combustion. Schematic diagram of the Calgary Biocell 2. Elagroudy and Mostafa A. or liquefied natural gas. and a power conditioning system.1. and solid polymer) are still under development. but each includes landfill gas collection. Other types of fuel cells (molten carbonate. heat. fuel cell stacks. methanol. extensive treatment is necessary to remove carbon dioxide. material and space). targeting groundwater contamination by landfill leachate and waste related aesthetic issues. Landfills are considered a liability requiring solutions for individual landfill problems. (2) a gas processing. Processing requirements vary. This situation arose because modem landfills have evolved from open dumping of solid waste. Gas is collected from the landfill by the use of active vents.e. The pessimistic view of waste is “waste is a liability and requires high level of resources to manage” but the optimistic view of waste is “waste is a resource in the wrong place and wrong time”. attempts have been made to address the landfill gas issues. treatment. depending on the gas composition and the intended use. 1998). whereas. Waste entombment in a conventional landfill slows down the process of biodegradation by minimizing moisture entry. More recently. The reactive approach followed by landfill engineers has created collateral problems. the current traditional approach of waste landfilling. Introduction Although landfill disposal is an integral part of waste management. minimal treatment is required. most people identify sanitary landfills as a key factor in the mis-management of finite resources and as a source of greenhouse gas emissions. Both combustion and non-combustion energy recovery systems have three basic components: (1) a gas collection system. the gas is filtered to remove any particles and water that may be suspended in the gas stream. bioreactors speed up the biodegradation process by controlled input of moisture (i.Biogas Recovery from Landfills 53 would not contribute to any emissions near the landfill. the general approach towards solving the solid waste problem has been mostly piece meal and reactive. and conversion system. material and space).g. It is then transported to a central point for processing. This reactive approach has ignored the positive aspects of solid waste including the inherent resource value of the waste. by leachate recirculation) and increased cycling of nutrients and bacterial populations (Reinhart and Townsend. For example. solves the problem of groundwater contamination but is counterproductive because of the slow production and atmospheric release of methane (CH4). Since 1960s. Recent advances in sanitary landfill technology research have indicated that the operation of landfills as bioreactors (Reinhart and Townsend. So far. For landfill gas injection into a natural gas pipeline. but typically include a series of chemical reactions or filters to remove impurities. At a minimum. CASE STUDY: CALGARY BIOCELL PROJECT A. VIII.g. including the contribution of landfills towards the global carbon budget and potentially global warming. The operation of traditional “entombed” landfills for the sole purpose of controlling groundwater contamination is not sustainable. Another option is using compressed landfill gas as a vehicle fuel. and loss of resources (e.. namely the dry-tomb landfilling approach. and (3) a means to transport the gas or final product to the user. 1998) could be viable. . For direct use of landfill gas in boilers. and could be counterproductive because of the slow production and atmospheric release of CH4 and loss of resources (e. engineers and scientists have attempted to rectify the problems with “open dumps”. Instead of operating the “entombed” waste cell as a “long-term storage facility”. that can be used as low-quality compost or refuse derived fuel (RDF). This approach has the potential to revolutionize management of waste in Canada. aerobic. with the resulting feedstock placed in three lifts of 5-6 m each. The shape of the biocell is a pyramidal square frustum increasing sectional area with side slope of 3H : 1V up to ground level. There are three different types of bioreactor landfills corresponding to the operational processes involved. a key objective is to enhance the generation of landfill gas. aerobic bioreactor and mining are sequentially applied in one cell. and hybrid (aerobic-anaerobic) as discussed in Section 2. The bottom liner/leachate collection systems are used to minimize groundwater contamination and maximize recovery of leachate. The schematic diagram of the biocell is presented in Figure 10. under anaerobic conditions. landfill gas emission control. and in other countries. in anaerobic bioreactors. the objective is to maintain aerobic conditions by introducing oxygen into the waste mass. containing methane and carbon dioxide. anaerobic bioreactor. the biocell is operated in the aerobic mode to produce stable organic material. B. The biocell received 43. both developed and developing. thus making the landfill operation sustainable. the underlying principle has been to prevent saturation of the waste in order to reduce the potential for leachate generation and leaking into the sub-surface and groundwater aquifers. with energy recovery. The input of air and operation of the cell as an aerobic bioreactor (Stessel and Murphy. Data compiled by Rees and Grainger (1982) from lysimeter studies suggest the rate of gas production increases exponentially as the water content of the waste is increased. The primary difference between the aerobic and anaerobic is that. and resource/space recovery as direct benefits. which covers an area of 100 m x 100 m with a waste footprint of 85 m x 85 m and a maximum height of 18 m. in aerobic bioreactors. In a second stage. 1992) enhances waste decomposition to a level where it could be mined in a third stage for compost/RDF and space recovery. whereas. anaerobic. and it extends 10 m below the ground surface. The base of the biocell is 50m x 50m. In a bioreactor landfill. groundwater contamination control. A pipe system was added to re-circulate the collected leachate.54 Sherien A. thus accelerating the establishment of microbial community. temperature and .000 tonnes of residential (high in organics) and selected commercial wastes. The biocell is a novel and holistic approach. Collected leachate is re-circulated after ensuring the quality is acceptable. The biocell is instrumented to gather moisture. The Calgary Biocell: Background and Construction Phase In dry-tomb type sanitary landfills. The Calgary biocell is a unique facility where the three processes. the biocell converts the cell into a waste processing facility. Re-circulation of leachate adds the much needed moisture and transfer bacteria from well-inoculated waste to freshly deposited waste. Elagroudy and Mostafa A.000 tonnes of waste was found to increase the rate of gas production by 8 m3/tonne/yr than that of a control cell (Knox and Gronow. by minimizing oxygen infiltration. leachate is re-circulated to maintain high waste moisture content. addition of water to test cells containing 15. 1995). At the Brogborough landfill in the United Kingdom. Warith The biocell concept involves the operation of a landfill cell as an anaerobic bioreactor with leachate recirculation to recover the full energy potential of biomass waste. the preferred landfilling option in the United States. The Calgary biocell is a full-scale facility. The thickness of both intermediate covers ranged from 30 to 40 cm. with a depth of 5 m. a 2nd intermediate cover of tree branch mulch was placed in December 2005 over the 2nd lift which was also 5 m in depth. This gas collection system will also be used to pump air into the waste matrix during the second stage aerobic operation to accelerate biological degradation. a granular medium to support methanotrophic bacteria that oxidize methane to carbon dioxoide without producing harmful by-products. The placement of the third and final lift of waste commenced during the third week of January 2006. and to recover. Construction of the biocell started in the summer of 2004. A low permeable final biocover was installed to prevent gas escape from the top surface prior to extraction of biogas. Schematic diagram of the Calgary Biocell The biocell is located at the Shepard landfill owned and operated by the City of Calgary. Gas/energy recovery has commenced after filling and construction of the final cover. The biocell started receiving domestic municipal solid waste in April 2005.Biogas Recovery from Landfills 55 settlement data. A mixture of stabilized compost and tree mulch (9:1 wet weight) was placed in an area of 10m x 10m in the northwest quadrant. The construction was completed in summer 2006 and operation started in September 2006 with gas recovery. The materials for the landfill final cover and leachate collection system were selected to facilitate convenient excavation.5 m biocover. The Calgary biocell pilot project used real-time instrumentation to measure settlement during the . The collected bio-gas is used to produce electrical energy. The produced biogas is collected using this gas collection system comprised of a combination of vertical wells and horizontal trenches. A gas collection system is installed for landfill gas collection and emission control. The 1st intermediate cover consisted of a mixture of partly stabilized leaf compost and soil (6:4 wet weight) and was placed in July 2005 over the 1st lift. Similarly. The biocell reached its final design elevations by April 2006 and was capped initially with a 0. Canada. and to reuse all components of the biocell. CO2 emissions CH4 & CO2 emissions Commercial recovery Oxidation in landfill bio-cover (Methanotrophs) Final bio-cover CH4 & CO2 Solid waste-3rd lift (8 m) generation GL GL 2nd Intermediate thin biocover (30 cm) Solid waste-2nd lift (5 m) CH4 & CO2 generation 1st Intermediate thin biocover (30 cm) Solid waste-1st lift (5m) CH4 & CO2 generation Figure 10. The leachate composition is analyzed on a regular basis. C. it may take as long as 50 to 100 years to degrade the majority of biodegradable organics (Crawford and Smith. higher will be the gas production. Operational Plan of the Calgary Biocell 1. The operation of each stage is described below. Stage of Landfill Stage I: Anaerobic Bio-Reactor Stage II: Enhanced Aerobic Reactor Stage III: Mining. Four million gallons of treated and untreated leachate were injected to waste via . such degradation will occur within a ten year time period. Elagroudy and Mostafa A. (2007) back calculated the average unit weight of waste and also the compression index.1 acres). nutrient and organic content in the waste. Hunte et al. Recycling. According to Hunte et al.000 tonnes of waste annually in an area of 5.56 Sherien A. Operation of the Calgary Biocell The biocell operational plan is illustrated in Figure 11. The field data during construction stage was presented in Hunte et al. Although the concept of bioreactor landfilling is relatively new. Crow Wing County Landfill (CWC) located in north central Minnesota was started in 1998 and accepted 50. a number of demonstration anaerobic bioreactors are underway in Northern America and Europe (Hettiaratchi. the biodegradation rate and landfill gas production depends on temperature. based on the load cell data. Warith construction phase of the biocell. and Recovery Total Expected Life Span of the Biocell Timeline 5 to 7 years 1 to 2 years ½ to 1 year 6 to 12 years Figure 11. two useful parameters of settlement models and found to be consistent with values reported in literature. Biocell stage 1: Anaerobic decomposition with gas extraction In a waste cell. In addition. (2007) the settlement trend follows the waste filling operation. 1985). In the biocell. The higher the organic content.7 hectares (14. 2006). In a conventional dry-tomb sanitary landfill. moisture content. 2007. The Calgary Biocell received 43. The gas production rate from October 2006 to September 2008 is shown on Figure 12. Burlington County bioreactor in northwest New Jersey had full scale leachate and liquid recirculation from 2002 to 2005 in a 4 hectare (10 acre) area accepting about one million tonnes of MSW. the gas production rate increased four-fold to 254 m3/h (150 cfm). Indicators of waste stabilization in these bioreactor landfills include settlement and gas production. Burlington County landfill bioreactor measures quarterly settlement surveys with settlement plates and annual air photography surveys for topographic comparisons. The depth of settlement was the greatest at the injection well and declined with radial distance from the well up to 15 m (50 ft) away and then leveled off. In addition.000 tonnes of waste over a period of about one year.and post-recirculation AUF was 595 kg/m3 (1004 lb/yd3) and 795 kg/m3 (1. indicating the microorganism acclimation stage. At the Calgary biocell. The airspace at CWC landfill had been monitored using airspace factor (AUF) calculations. the pre.341 lb/yd3) respectively.5 m (5 ft) per year. 2007). Salem County bioreactor in southwest New Jersey is another anaerobic bioreactor with about 2 hectare (5-acre) area. Landfill gas was passively vented at Crow Wing County Landfill and concentrations of methane had been as high as 60%. The rate of moisture addition is about 0. Data indicates that about 20% settlement has occurred within 5 years (USEPA. The New River Regional bioreactor was a “research” bioreactor in Union County. 2007). Thereafter. is 120 m3/tonne of solid waste. which was greater than the rate observed before leachate re-circulation commenced (USEPA 2007). working face spray. north central Florida. The Salem County bioreactor showed a settlement rate of about 1. in October 2006 the theoretical gas generation rate at the Biocell should be approximately 282 m3/h (166cfm) which is very close to the field measured value of 254 m3/h (150cfm) reported in Figure 12. Volume of leachate re-circulated was about 24. 2007). and spray on yard waste composting over intermediate cover (USEPA. Leachate was re-circulated into an existing interim capped landfill with an exposed membrane cover. After leachate recirculation was initiated. The cell was constructed in 1991 and recirculation began in 1998. The data also showed a distinct linear relationship between total settlement and the amount of moisture added (USEPA 2007).600 m3 (6.Biogas Recovery from Landfills 57 horizontal laterals. Accordingly.07 hectare (10-acre) area.200 lb/yd3) (USEPA. 2007). The initial gas production rate was low. the gas production rate decreased gradually and reached a steady state flow rate of 170 m3/h (100 cfm) throughout the winter months. Leachate re-circulated from storage tank and force main to subsurface horizontal injection trenches has been performed since 2000. The methane generation potential. Hence.167 m3/tonne (44 gallons/tonne) waste (USEPA.5 million gallons) to date (USEPA. It had about one million tonnes of waste in-place in an existing 5. Substantial settlement over the last 4 years of operation was observed increasing the effective density from 500 kg/ m3 (840 lb/yd3) to over 720 kg/ m3 (1. calculated from waste composition data. . the end of stage 1 will be determined using a combination of settlement and gas generation readings. The New River Regional Landfill measured the settlement with GPS coordinates on the landfill surface with settlement of each nested vertical injection well. 2007). CWC installed four settlement plates in 2000 and 2001 at the waste level of two of the horizontal laterals. 000 700. Williamson County bioreactor in central Tennessee is one of the existing aerobic . 2. 1992. To convert from anaerobic to aerobic conditions.000 0 Oct-06 Jan-07 Apr-07 Aug-07 Monthly methane Generation Nov-07 Feb-08 Cumulative methane Jun-08 Sep-08 Scholl Canyon Figure 12. Hettiaratchi.000 500. Warith 900. periodic testing of waste from boreholes and the analysis of the leachate would ensure complete biodegradation. this stage may take only a year or two to complete. Evidently. Towards the end of aerobic decomposition.000 300. The gas extraction system used during the anaerobic stage will be used to pump air into the landfill to create aerobic conditions. The Calgary biocell is not the first to propose the use of aerobic treatment of waste in a waste cell. Comparison of Gas Production Data at the Biocell and a Conventional Landfill For comparison purposes. 2006). which accelerates and completes biological degradation or organic waste. Biocell stage 2: Aerobic decomposition Once methane production decreases to a critical level. the gas production at the biocell is more than 400% higher than that of a dry tomb type sanitary landfill of similar size and configuration located in Calgary.000 400. that is to use aerobic degradation to rapidly decompose the remaining organic waste. air has to be introduced to the biocell and maintained to enhance the rate of waste decomposition (Stessel and Murphy.7 m3/tonne. Since aerobic degradation occurs at a high rate. k = 0.58 Sherien A.023 yr-1 and Lo = 116.000 200. The recirculation of appropriately adjusted leachate for aerobic degradation is also required for the same reason stated in the first stage of operation.000 tonnes of waste and operated as a dry-tomb sanitary landfill. The parameter values are those proposed by Environment Canada for a typical sanitary landfill in the province of Alberta.000 600. Elagroudy and Mostafa A. The Scholl Canyon model was used to generate this curve using the parameter values. the Figure 12 includes the cumulative methane generation curve for a landfill cell containing 43. the next stage of biocell will initiate.000 Methane generated (m3/month) 800. Alberta.000 100. The aerobic bioreactor concept was first proposed by Merz and Stone (1962) and there are more than 20 operating aerobic bioreactors in North America. the recyclables can be crushed.785 m3 (one million gallons) of leachate has been re-circulated (USEPA 2007). For each aerobic landfill system. It was observed in some areas that the decay process would revert back to anaerobic once temperatures decreased and that the air would make its way to other nearby areas. The operation started in June 2000 and approximately 3. Leachate. vibrating.5% and the greatest settlement was 9% at Columbia County Landfill and 10% at Atlanta Landfill.Biogas Recovery from Landfills 59 bioreactors.000 tonnes of waste in a cell of area 2. the excavated waste is stockpiled and fed to a shaker with sieves to separate the leftover organic waste.7% decrease in waste height over a 59-month period of operation (USEPA 2007). and processing of recyclables. 1999). The air injection rates were 56 m3/min and 100 m3/min for the Columbia County Landfill and Atlanta Landfill. Zee et al. Therefore. respectively (Hudgings and Harper. Separation of waste based on size can be performed through the use of various types of screens (trammel. sorting. several months prior to the start-up of the landfill bioreactor as a baseline. An initial survey of the landfill bioreactor surface was conducted in January 2000. 1993. It was observed that the average settlement was 4. thereby repeating the process. 2003).53-meter to 1. it was also observed that air could provide a cooling effect on the waste mass temperatures above 600C or increase temperatures that were below 200C. The collected non- . In several cases. Conversely. provided sufficient moisture was applied (Hudgins. storm water. The comparisons of the April 2005 elevations with the original survey in January 2000 show a 5. and disc). and air were injected into vertical risers with force main and header from storage tank that were retro-fitted for the closed landfill. before moving to the mining step. The methane generation was reduced to 50% for the Columbia County Landfill and 50 to 90% for the Atlanta Landfill after aeration started. Usually. The operation of each system was also a dynamic process. there would be an insufficient amount of oxygen for the bacteria and reverted the decay process back to anaerobic. This bioreactor landfill contains about 70. 3. the air injection comprises of air compressor and piping connected to vertical air injection wells. Also. bailed or shredded for the convenience of transportation. Two other aerobic landfills are in operation in Georgia (the Columbia County landfill) and in Atlanta (a privately operated bioreactor). Hudgins and Harper.85 hectares (7 acres). 1998. Once recovered. rotating. The organics that passes through 1 cm – 5 cm sieve size can be used as compost in agricultural applications or as refuse derived fuel (RDF). separating. The study conducted in Georgia is interesting since it was conducted after landfills went through anaerobic process first. Results of settlement as of April 2005 show a 0. Monthly topographic surveys of Williamson County Landfill bioreactor surface were performed to detect settlement across the site. Leachate collected in holding tanks at each site was pumped back into each aerobic system through a leachate recirculation system installed on top of the intermediate cap. it is essential to ensure that most of the organic waste is decomposed before mining commences. waste mass temperatures would tend to rise into the thermophillic range (40 to 700C). if too much leachate was applied in the aerobic areas.1% to 10.2meter drop in the surface elevations since the landfill bioreactor operations began. if too little leachate was applied. Recycling a biocell involves a series of activities that includes excavation of cell. Partially degraded waste has produced difficulties in post mining attempts. 1999).. Biocell stage 3: Mining for recovery of useful/recyclable products Mining will ensure recovery of space and various products (Murphy. The practice of this approach will no longer require the need to allocate valuable land for new landfills on an on-going basis and hence will revolutionize the management of municipal solid waste. and HDPE. R. 59(6). textiles. there will be some residual waste which are non-recoverable. Other than these versatile uses. N. The resources that can be recovered include compost-like material and recyclables such as plastics. 2005). Over the last three decades. . Elagroudy and Mostafa A. soften when heated and can be recycled and remolded. Sci. in-situ composting within the cell footprint during aerobic degradation in the second stage and landfill mining for resources and space recovery in a third stage. T. The mixed plastic waste could be shredded into small pieces for further processing. the industrial term for the furnace-ready scrap glass. & Sponza. However. Chris. O. (1997). 1054-1061.K. recyclables can be used as feedstock for a number of products. and a number of other organic waste types. waste wood. emission of landfill gases. Braithwaite. The biocell approach involves sequential operation of a landfill cell to produce methane gas during the first stage of anaerobic degradation. Alan. Matthew. Even with enhanced biodegradation and recycling processes described above. the first three problems. 871-879. (2005). Also. C. ground/surface water contamination with leachate. The majority of the compost-like product resulting from biodegradation is expected to be used as soil conditioner with various agricultural applications. Warith biodegradable fraction will be sent to an automatic sorting unit through a feeding belt with a magnetic drum installed on the belt to remove the ferrous metals. These wastes may include plastics. such as plastic lumber park benches or decks made from plastic milk jugs or soda bottles. Recycled paper has many applications in newspaper industry and packaging. These can be used to produce refuse derived fuel (RDF) and co-incinerated in cement kilns. and extensive space requirements. the design and operation of sanitary landfills have managed to solve. Effect of alkalinity on the performance of a simulated landfill bioreactor digesting organic solid wastes. Thermoplastics. REFERENCES Ağdağ. PVC.. Summary and Conclusions There are four main problems with landfill operation. metal. such as PETE. & Hills. Non-recovered waste but with high energy content can be used as refuse derived fuel. The automatic sorting unit will sort through air flotation the light materials such as plastic. waste disposal sites Environ.. namely aesthetic issues.60 Sherien A. to a large extent. is one of the most important ingredients of the glass manufacturing process. Chemosphere. and non-degraded packaging wastes from heavier materials such as glass and aluminum based on weight difference. 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Journal of Chemical Technology and Biotechnology.. (2003). (2004). & Butler. Compensation. 78-92.66 Sherien A. Young. valid for the relevant (HDPE): (H2S): commitment period High Density Polyethylene Hydrogen Sulfide F: (FOD): (GHG): (GWP): . University of Groningen. R. Warith Yildiz. 24(5). B. K. 46(3). model formulation and uncertainty analysis. (1989). 22(2). combusted or used in (BOD): (CAA): (CDM): (CERCLA): (CH4): (CO2): (COD): (CWA): (CWC): (DOC): GWPCH 4 : another manner Fraction of methane in the SWDS gas (volume fraction) First Order Decay GreenHouse Gases Global Warming Potential Global Warming Potential (GWP) of methane. and Liability Act Methane Carbon dioxide Chemical Oxygen Demand Clean Water Act Crow Wing County Landfill Degradable Organic Carbon Fraction of degradable organic carbon (DOC) that can decompose (EPA): (EU): f: Environmental Protection Agency European Union Fraction of methane captured and flared. M. Modelling leachate quality and quantity in municipal solid waste landfills. C. (2004). Zee. A. 453-462. Waste Management.SWDS . Stochastic modelling of landfill leachate and biogas production incorporating waste heterogeneity. J. Organizations and Management) NOTATIONS The following symbols are used in this chapter: (AEERL): BECH 4. Unlu. 189-208. Research Institute SOM (Systems. Achterkamp. D. Zacharof. & de Visser. A. J. Waste Management & Research. K. Mathematical-modeling of landfill degradation. Research Report 03B39. Elagroudy and Mostafa A. van der. D. A. & Rowe. E. I. Assessing the opportunities of landfill mining. y : Air and Energy Engineering Research Laboratory Methane emissions avoided during the year y from preventing waste DOC f : disposal at the solid waste disposal site during the period from the start of the project activity to the end of the year y (tCO2e) Biochemical Oxygen Demand Clean Air Act Clean Development Mechanism Comprehensive Environmental Response. P. (initial year of waste acceptance) Not in My Back Yard Non-Methane Organic Compounds Non-Methane Volatile Organic Compounds. New Source Performance Standards Occupational Safety and Health Administration Oxidation factor (reflecting the amount of methane that is oxidized in the soil or other material covering the waste Phosphoric Acid Fuel Cell Publicly Owned Treatment Works Annual Methane generation in the year of the calculation (m3/year) Qmethane : Methane flow rate (m3/min) (RCRA): (RDF): (SWANA): (SWDSs): tij : Resource Conservation and Recovery Act Refuse Derived Fuel Solid Waste Association of North America Solid Waste Disposal Sites Age of the jth section of waste mass M i accepted in the ith year (TOC): (TSS): (UNFCC): (VOC): w: W: (WAC): x: y: Total Organic Carbon Total Suspended Solids United Nations Framework Convention on Climate Change Volatile Organic Compounds Mass of refuse (Mg) Mass of the waste deposited in the landfill Waste Acceptance Criteria Year during the crediting period: x runs from the first year of the first crediting period (x = 1) to the year y for which avoided emissions are calculated (x = y) Year for which methane emissions are calculated φ: Model correction factor to account for model uncertainties .Biogas Recovery from Landfills i: 67 (IPCC): k: 1Year Intergovernmental Panel on Climate Change Methane generation rate (per year) kj: Decay rate for the waste type j j: Waste type category (index) L0 : Potential methane generation capacity of the waste (m3/Mg) (LFG): Mi : Landfill Gas Mass of waste accepted in the year I (Mg) MCF: (MSW): n: (NIMBY): (NMOC): (NMVOC): (NSPS): (OSHA): OX: (PAFC): (POTW): QCH 4 : Methane correction factor for aerobic decomposition of waste Municipal Solid Waste (year of the calculation). . but the energy recovery system definition and sizing. Inc. +39 055 4796349. in order to investigate the management possibilities to enhance energy recovery.it . the municipal solid waste component characterisation and biodegradability. The landfill gas energy recovery by means of reciprocating engines is a quite widespread practice in modern landfills. the behaviour of a landfill where leachate is recirculated was observed. The selected model is based on firstorder decay equation and considers as basic inputs the years of landfill operation. 3. have been considered dividing the material categories into rapidly. The model has been used to predict the landfill gas production of a case-study landfill in order to properly size the energy recovery system. implemented and compared among themselves and with data collected from existing landfills. reciprocating engines were considered for energy recovery purposes. also in reference to its economic convenience. collected and combusted landfill gas and recovered electric energy avoided emissions. Further. Fax +39 055 4796342. Italy ABSTRACT In this chapter different landfill gas production mathematical models have been analysed.lombardi@pin. Chapter 2 LANDFILL GAS: GENERATION MODELS AND ENERGY RECOVERY Lidia Lombardi∗ Dipartimento di Energetica “Sergio Stecco” Università degli Studi di Firenze Via Santa Marta. Three different behaviours. moderately and slowly biodegradable. In particular. These models will be presented in the chapter.In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers. lidia. the amount of municipal solid waste landfilled per year. 50139 Firenze. One of these models has been selected for application to some study cases. recording a more concentrated landfill gas production in a shorter time than in ∗ Tel. For this reason. in reference to biodegradation rate. estimating the overall contribution to Greenhouse Effect from escaped landfill gas.unifi. the selection of an appropriate combination of engines has been carried out with the aim of obtaining the maximum profits from selling the produced electric energy. The obtained configuration for energy recovery was evaluated also from an energetic and environmental point of view. is a crucial and tricky issue. biodegradable organic matter contained in Municipal Solid Wastes (MSW) is degraded by anaerobic biological processes in landfills giving place to a LFG. considering the avoided emissions from conventional sources of energy. The proper design of LFG collection and energy recovery system needs to be based on an adequate LFG production estimation during the landfill operation and post-closure phases. energy conversion and environmental impact.and reproduced by means of adapting the landfill gas production model. 1. during which the oxidation/reduction potential decreases. Hence the LFG has two main features: it is composed of two of the main Greenhouse gases and it has a not negligible heating value (approximately 16. which is approximately composed of 50% methane and 50% carbon dioxide. When LFG is combusted with energy recovery.000 kJ/Nm3).000-17. At the beginning. Trace constituents mainly belong to the VOCs family. LANDFILL GAS CHARACTERISTICS AND GENERATION MECHANISMS LFG is composed of a number of gases that are present in large amounts (the principal gases) and a number of gases that are present in very small amounts (the trace gases). 2. Moreover. The economic analysis showed that the specific disposal cost is lower for the landfill with leachate recirculation with respect to the conventional landfill. carbon monoxide (CO). the landfill with leachate recirculation shows better indicator values both for the overall energy conversion efficiency and for Greenhouse Effect specific emission. arising from landfills containing biodegradable wastes (Lombardi et al. hydrogen (H2) and oxygen (O2) can be present.70 Lidia Lombardi conventional landfills . because certain amount of air is trapped within the waste (phase I). since Global Warming Potential (GWP) of methane is twenty-one times larger (on mass basis) than GWP of carbon dioxide. anaerobic conditions begin to develop and after a transition phase (phase II). Simple flare combustion of LFG allows reducing landfill GHE contribution converting methane to carbon dioxide. the acid phase (phase III) starts. in place of which LFG is exploited. 2006). The landfill gas production and energy recovery for the conventional landfill and the landfill with leachate recirculation were compared from different points of view: economic evaluation.. but also ammonia (NH3). consisting in . both thermal and electric energy can be delivered and landfill GHE is further reduced. When oxygen is depleted. INTRODUCTION Energy recovery from landfill gas (LFG) is strongly recommended as a means to reduce the environmental impact. it undergoes microbial decomposition in aerobic conditions. The principal gases are produced from the decomposition of the organic fraction of municipal solid waste (OFMSW) and they include mainly carbon dioxide (CO2) and methane (CH4). As a matter of fact. The typical percentage composition of LFG is reported in Table 1. this can be done through LFG production modelling. as OFMSW is placed in the landfill. The generation of LFG takes place in different steps. in terms of Greenhouse Effect (GHE). as typified mainly by acetic acid (CH3COOH). the moisture content of waste.1-1.0 0-0.1-1. Ammonia Hydrogen Trace constituents Percent (dry volume basis) 0-1. which convert the acetic acid and the hydrogen to methane and carbon dioxide. The rate of LFG generation decreases significantly because most of the available nutrients have been previously removed and the remaining substrates are slowly biodegradable.0 0-0. disulfides. although the rate of acid formation is considerably reduced. Finally the last phase – the maturation phase (phase V) occurs when almost all the readily available biodegradable organic material has been converted. Table 1. mercaptans. In this phase both methane and acid formation proceed simultaneously. Generalised phases in the generation of LFG (Tchobanoglous et al..2 Component Sulfides. the availability of nutrients.2 0. consist of facultative and obligate anaerobic bacteria. Small amounts of hydrogen gas will also be produced. described collectively as nonmethanogenic. etc. . In the following phase – the methane fermentation phase (phase IV) a second group of microorganisms. The duration of the individual phases in the production of LFG will vary depending on the distribution of the organic components in the landfill.6 The microorganisms involved in this conversion. Carbon dioxide is the principal gas generated in this phase. Figure 1. 1993). Typical composition of LFG (Tchobanoglous et al.Landfill Gas: Generation Models and Energy Recovery 71 hydrolysis of higher molecular mass compounds into compounds suitable for use by microorganisms as a source of energy and cell carbon. The microorganisms responsible for this phase are strict anaerobes and are called methanogenic. followed by the acidogenesis of the previous formed compounds to produce lower-molecular mass intermediate compounds. 1993) Component Methane Carbon dioxide Nitrogen Oxygen Carbon monoxide Percent (dry volume basis) 45-60 40-60 2-5 0.0 0.01-0. moisture routing through the landfill and the degree of initial compaction. becomes more predominant.. considering more or less substrates and including or not the parameters influencing the degradation (temperature. 1995) (Young.. 2001). Stoichiometric models differ in the selected stoichiometric reaction. biochemical models and ecological models. the LandGEM model (EPA. 2005) and a modified version of first order decay model (Van Zanten and Scheepers 1995). related to typology of landfilled waste. quite often the proposed models are a mixing of different elements. 1976) (Ham.. and a biochemical-kinetic sub-model which supplies the evolution during the time of LFG from biodegradable compounds. 1993. 1979) (Halvadakis. 1980) (Boyle. Biochemical models are based on biodegradable substrate removal equations. The Triangular Model In the triangular model. In technical literature several models have been proposed (EMCON. etc). These kind of models are very site and data specific.. 1993). Stoichiometric models are based on a global stoichiometric reaction.S. 1995) (Bonori et al. mainly using a stoichiometric sub-model which uses waste composition as input. stoichiometric models. as shown in . Ecological models describes the dynamic coexistence of the different bacterial populations which compete in the waste degradation. supplying the amount of biodegradable compounds as output. in reference to collected data from existing landfills and experimental data. correlating input. using more or less complex kinetics. 1995). etc. moisture. MATHEMATICAL MODELS FOR LANDFILL GAS PRODUCTION PREDICTION Mathematical models for LFG production prediction are tools used to estimate. 2001) in order to both estimate the potential amount of LFG that can be produced from a given amount of waste and forecasting the temporal evolution of LFG production. in which the reactant is waste.. on the basis of some parameters as temperature. 1988) (Christensen et al. 1983) (Findikakis. gas or methane production from a given amount of waste starting from some input data supplied by the model user. Actually these are the only models which are able to highlight nutrients imbalances and substrate characteristics. However. but their application is quite complex due to the non homogeneous characteristics of landfills and moreover it is too onerous in the frame of LFG collection and recovery. The models proposed in literature can be classified into: empirical models. compaction. 1996) (Swarbrick and Lethlean.. in waste components considered and whether they include or not cellular growth. Obtainable results are generally overestimated. a linear growth of the LFG production rate is assumed until it reaches a peak after which a linear decrement starts (Tchobanoglous et al. since actual biodegradation efficiency is not taken into account.72 Lidia Lombardi 3. Bonori et al. and output related to LFG production. and the products include methane and carbon dioxide. In this chapter the attention is focused on four previously proposed models which are: the Triangular model (Tchobanoglous et al. Empirical models are based on black box approach.. the Scholl Canyon equation model (Department of the Army U. represented by an empirical chemical formula. along the time. moisture. which require up to fifty years for degradation. 1993). Triangular distribution of LFG production rate. distinguishing waste components in rapidly biodegradable. In the original version. The total rate of LFG production from a landfill operated for a given time is obtained graphically – as shown in Figure 3 .Landfill Gas: Generation Models and Energy Recovery 73 Figure 2. LFG production is assumed to start at the end of the first year of full landfill operation and to finish after a finite time tend. in the original version (Tchobanoglous et al. therefore. distinguishing waste components in rapidly. the total amount of LFG produced from an amount Ri of waste placed in landfill at year i is equal to: Ri L0 = 1 (tend . which are degraded within five years or less. and slowly biodegradable. the Triangular model has been applied considering three different behaviours in biodegradation rate. The area under the triangle is equal to one half the base (which represents the time during which LFG production lasts) times the altitude (which represents the peak rate of LFG production).by summing the LFG produced from the rapidly and slowly biodegradable portions of waste deposited each year. as it will be described later.i 2 (1) LFG production rate [m3 /year] where: L0 = waste potential gas production [m3/t] tend. characterised by a different peak rate time. In the present chapter.max = maximum gas production rate [m3/(t · year)] Ri = amount of waste placed in landfill at year i [t] Q LFG smax year t end . The triangular model.t 0 Figure 2. For each of the two categories a triangular LFG production distribution is assumed. moderately and slowly biodegradable.max.i − t0.i = time during which gas production takes place [year] t0. . considers two different behaviours in biodegradation rate.i ) ⋅ QLFG .i = time at which LFG production starts for waste placed at year i [year] QLFG.i. Equation 1 and Equation 2 can be solved for all values of Ri and the results summed: QLFG . Graphical representation of LFG production over a five-year period from the rapidly and slowly decomposable organic materials in landfill (Tchobanoglous et al.t.i (2) QLFG .. t max.i − t 0..i = QLFG .i ≤ t i ≤ t end .i = 0.i .t = t ∑Q LFG .i ≤ t i ≤ t max.i = time at which LFG production reaches the peak for waste placed at year i [year] In order to estimate the current emissions from waste placed in all years.t .i .i t max.i decreasing phase : QLFG .max. t i ≤ t 0.t .i = 0.t .i − t i t end . t 0.74 Lidia Lombardi Figure 3.i where: QLFG.i t i − t 0 .i = LFG production rate at year t for waste placed at year i [m3/(t · year)] tmax. Analytically. t i ≥ t end .t .i i =initial year (3) . 1993).i t max.max.i = QLFG . the LFG production rate in the Triangular model can be described as a function of time as it follows: QLFG .t .i − t max.i growing phase : QLFG . Landfill Gas: Generation Models and Energy Recovery 75 First Order Decay Model: The Scholl Canyon Equation The Scholl Canyon Model is a model which assumes that LFG generation is a function of first-order kinetics. The model equation takes the form: (4) QLFG = Ravg ⋅ L0 ⋅ (e − kc − e − kT ) where: QLFG= LFG generation rate at time T [m3/year] L0= waste potential LFG generation capacity [m3/t] Ravg = average annual acceptance rate of waste [t/year] k = LFG generation rate constant [1/year] c = time since landfill closure [year] (c = 0 for active landfills) T = time since initial waste placement [year] To allow for variances in annual acceptance rates. 1995).t .S. 1995): . 1996). the derivative of Equation 4 with respect to the time can be used to estimate LFG generation from waste landfilled in a single year (Ri) (IPCC.during which anaerobic conditions are established and decreases exponentially (first-order decay) as the organic content of the waste is consumed (Department of the Army U. The lag time before which anaerobic conditions are established may range from two-hundred days to several years (Department of the Army U. The LFG production rate is assumed to be at its peak upon initial placement after a negligible lag time – in the original version .i = t ∑R ⋅L i i = initial year 0 ⋅ k ⋅ e − k (t −i ) (6) Lag time due to the establishment of anaerobic conditions could also be incorporated into the model by replacing “t” by “t + lag time”. which represents the number of years the waste has been in the landfill.i = L0 ⋅ k ⋅ Ri ⋅ e− k ( t − i ) QLFG. and the time measurements are in years. This model ignores the first two stages of bacterial activity and is simply based on the observed characteristics of substrate-limited bacterial growth.t.. the variable T is replaced with t-i. In this equation.i = the amount of LFG generated in the current year (t) by the waste Ri [m3/year] Ri = amount of waste disposed in year i [t/year] i = the year of waste placement [year] t = current year [year] In order to estimate the current emissions from waste placed in all years. The resulting equation thus becomes: (5) QLFG .S.t . Equation 5 can be solved for all values of Ri and the results summed: QLFG . Average annual placement rates are used.t = t ∑ i = initial year QLFG .. EPA developed LandGEM (Landfill Gas Emissions Model).76 Lidia Lombardi QLFG . 1992). Hence on . the number of years of waste acceptance.t . The required inputs for estimating the amount of generated LFG are: design capacity of the landfill. The equation of this model is represented by Equation 8 (Van Zanten and Scheepers. The potential for LFG generation capacity. THE ESTIMATION OF K AND L0 IN THE MODELS The tricky parameters for the first order models are the gas generation rate constant (k) and the waste potential LFG generation capacity (L0). usually expressed as the volume of gas per mass of waste. so biochemical methane potential values are available for various waste fractions. 1995): QLFG . based on the application of Scholl Canyon model in the form of equation (6) (EPA. can be estimated based on theoretical prediction. there is no method for determining gas potential that is without fault (Reinhart and Faour. Graphs and reports of estimated gas emissions can be produced. Modified First Order Model A modified version of the first order decay model assumes that LFG generation is initially low and then rises to a maximum before declining exponentially. Default values for k and L0 can be used or site-specific values can be introduced. the LFG generation rate constant k and LFG generation potential L0. amount of waste in place or the annual acceptance rate. i = Ri ⋅ L0 ⋅ k ⋅ e − k ( t − i − lag ) (7) lag = time to reach anaerobic conditions [year] Software Application of First Order Decay Model: Landgem U. The software can be operated under the Windows environment. Such a procedure has been modified for solid waste (Owens and Chynoweth. 2005). 2005). which is a software for quantifying LFG emissions. which determines the methane yield of an organic material during its anaerobic decomposition by a mixed microbial flora in a defined medium.i = Ri ⋅ Lo k+s (1 − e −s ( t −i−lag ) )k ⋅ e −k ( t −i−lag ) s (8) where s = rise phase LFG generation rate constant [1/year] 4.ASTM Method E1196-92). laboratory experiments or actual gas production data. At present.S. Experimental procedure to evaluate the gas potential has been developed (biochemical methane potential . t . not gas generated. Theoretical predictions are based on the chemical composition of the waste and would give absolute maximum gas potential. biodegradability of the waste. and full-scale landfills. by the generic formula CaHbOcNdSe.e. theoretical gas potential must be adjusted by a biodegradability factor. controls the rate of decline of the first-order model and. The biodegradation process of the organic biodegradable fraction to form the LFG can be described by the global stoichiometric reaction (Tchobanoglous. consequently. In the present chapter both L0 and k have been estimated on theoretical basis. such as waste mass and actual dates of placement.28 (9) where Temp is the landfill body temperature expressed in °C. Assuming a landfill body temperature of 35°C the biodegradable fraction availability results 0. For each material component the chemical composition. 2005). Consequently. the drawback of utilizing these data is that they reflect gas recovered. Actual gas production data have been collected from lysimeters. etc.). also based on various assumptions (Reinhart and Faour. 1982): Biodegradable fraction availability = 0. the period of LFG generation predicted by the model..Landfill Gas: Generation Models and Energy Recovery 77 the basis of waste component characterization. 2005). Further. The first-order rate constant. On the basis of component characterisation of waste. It would be expected that as conditions within a landfill are optimized with respect to waste degradation (i. these studies rarely last sufficiently long to actually reach the point of total gas production. Gas recovery efficiency is believed to be far less than 100% and depends on many factors such as the presence and integrity of a cover and the type and quality of the gas collection system. the duration of LFG production declines. for determining methane potential may not be available (Reinhart and Faour. with reference to the unit mass of waste. k would increase. k. moisture content. using a stoichiometric based approach. However.77. The presence of cracks and fissures will reduce collection efficiency.1993): C a H b Oc N d S e + w ⋅ H 2 O → x ⋅ CH 4 + y ⋅ CO2 + z ⋅ NH 3 + k ⋅ H 2 S (10) . temperature.1993). pilot-scale cells. gas generation would never reach this potential due to the inaccessibility of some waste. the moisture and the biodegradability coefficients reported in Table 2 have been assumed (Tchobanoglous. and the likely production of other non-methane carbon compounds other than carbon dioxide. In calculating the biodegradable fraction. the inability to biodegrade all organic wastes.014 Temp + 0. chemical composition of each component and biodegradability of each component it is possible to describe the biodegradable fraction. specific for the analysed site and reported in Table 2. L0 can be calculated as weighted average of biochemical methane potential values. in reference to a component characterization of the waste. In addition. 2005). As the value of k increases. it was also considered that not all the biodegradable fraction is available for being converted to LFG according to an efficiency depending on the landfill body temperature as it follows (Tabasaran. assuming that L0 remains the same (Reinhart and Faour. In reality. other data necessary. 50% 8. Values assumed for gas generation rate constant. moisture and biodegradability Organic fraction Paper and cardboard Plastics Textile Pruning scrap Wood Glass and inert Metals Sewage sludge Component characterization % 17.70% 6.00% 70% Biodegradability % 82% 50% 0% 54% 60% 72% 0% 0% 57.50% 11.00% 0.10% 4.00% 3.155 2 0.40% 4.44 Calculated as weighted 29.60% 1.50% 6.36 0.54 average* 0.90% 0.24% Inert %SS 36.90% 94.83% 6.60% 0.07 L0 [Nm3/t] 13.10% 0.80% 0.70% 44.20% 16.70% 1.97% S %SS 0.00% 2.00% 60.74% O %SS 29.53% 32.20% 0.43% N %SS 1.30% 20.10% 0.346 5 0.00% 0.50% 2.90% 5.50% 9. potential gas generation capacity and lag time of materials with different biodegradation velocity k [1/year] k [1/year] Rapidly biodegradable fractions Moderately biodegradable fractions Organic fraction Pruning scrap Paper and cardboard Textile Slowly biodegradable fractions Wood Sewage sludge * input to LandGEM 0.50% 0.40% 70.50% 0.31% 10.231 .00% 10.60% 6.00% C %SS 28.Table 2.5% Table 3.20% 40. rise phase gas generation rate constant (for modified first order model).30% 23.50% 39.10% 0.30% 25.10% 0.20% 2.3 1.30% 26.90% 11.86% 4.00% 5.50% 47.00% 2.60% 45.46% 6.139 29.70% 0.90% 22.40% 11.15 0.00% 20.30% 0.20% 0.69 L0 [Nm3/t] Calculated as weighted average* 24.50% 98.90% 4.10% 42. Waste component characterisation for the study case site and assumed values for chemical composition.70% 0.59 Lag Time [year] s [1/year] 0.07% H %SS 3.54% Moisture % 70.10% 5.90% 0.50% 49.61% 3. b..dry = x + y + z + k = 4a + b − 2c − 3d − 2e 4a − b + 2c + 3d + 2e + + d + e = a + d + e [kmol 8 8 (12) In order to consider the presence of water vapour in the LFG it has been assumed that the gas is saturated with water vapour. according to (EMCON. 2001) (US-EPA. LandGEM and modified first order model the input data consisted in: amount of waste landfilled yearly. y. also.23%. possible to calculate LFG composition. After a literature review (Nutting. 1998) (Lifshits and Galueva.. The composition is assumed not to change during the time. The different behaviours have been considered distinguishing the materials in rapidly. H2S 0. In reference to Scholl Canyon model. 2005) (Christensen et al. 1982) (Warith and Sharma. 1995) (IGES. total number of dry kilomoles of LFG will be: LFG kmol . From the total number of kilomoles it is then possible to calculate the potential gas generation capacity (L0): L0 [ Nm 3 3 ] = LFGmol [kmol ] ⋅ 22. moderately and slowly biodegradable.39%. in this case. 2000) (Metcalf and Eddy (1991) (Baldwin et al. Also the potential LFG generation capacities (L0) for each class of material with different biodegradation velocity were calculated separately (calculated values are reported in Table 3) in order to apply the models – when this is allowed by the model itself – in order to proceed with separate calculations and adding up the three contributions of LFG production. different values for LFG generation rate constant have been assumed for each class of materials with different biodegradation velocity. 1998) (Hartz et al. z and k as a function of a. potential LFG .42 %..Landfill Gas: Generation Models and Energy Recovery 79 Applying the stoichiometric balance to the reaction above it is possible to obtain the stoichiometric coefficients w. APPLICATION OF THE MODELS TO A STUDY CASE The above described models – with the exception of LandGEM – have been implemented using a calculation worksheet. which. 1996). x. CO2 47. From Equation 11 it is. e: ⎛ 4a − b − 2c + 3d + 2e ⎞ C a H bOc N d S e + ⎜ ⎟ ⋅ H 2O → 4 ⎝ ⎠ ⎛ 4a + b − 2c − 3d − 2e ⎞ ⎛ 4a − b + 2c + 3d + 2e ⎞ →⎜ ⎟ ⋅ CH 4 + ⎜ ⎟ ⋅ CO2 + dNH 3 + eH 2 S 8 8 ⎝ ⎠ ⎝ ⎠ (11) Hence. 5.414[ Nm ] t t kmol (13) Actually. results: CH4 48. 1997) (McBean et al. the different components of waste undergo biodegradation according to different degradation rates. as reported in Table 3.. c. d. NH3 3. 1980).95%. max) was obtained from the total amount of produced LFG i.. peak rate time.214 246.000 The triangular model requires as inputs: amount of waste landfilled yearly.000 240. Table 4. The analysed site is a landfill for non-hazardous waste with an overall capacity of about 3.606 260.000 240. hence single average values were introduced for potential gas generation capacity and gas generation rate constant.700.929 263. maximum gas production rate (QLFG. potential gas generation capacity (L0) used for the other models. Assumed values for start time. 5. are summarised in Table 5. as reported in Table 3.80 Lidia Lombardi generation capacity. . using values for potential LFG generation capacity and LFG generation rate constant reported in Table 3. Values until seventh year are real data collected on-site.634 240. time at which gas production starts (t0). 6 and 7. as reported in Table 3. The results obtained applying the different models. Figure 8 shows the comparison of results obtained from the different applied models. from equation (1) according to: QLFG .896 7 8 9 10 11 278. The LandGEM model does not offer the possibility of considering different velocities of biodegradation for different materials. Amount of waste landfilled yearly in the analysed site Year Waste [t] Year Waste [t] 1 2 3 4 5 6 171. end time and maximum LFG production rate for each group of waste components with different biodegradation velocity.max). time at which the peak rate of gas production occurs (tmax). Concerning the modified first order model. assumed values for the rise phase gas generation rate constant (s) are reported in Table 3 (Youcai et al.000 m3 located in central Italy.e. LFG generation rate constant. It is not possible to introduce lag time in the software. a lag time was considered. The maximum gas production rate (QLFG. The amount of waste landfilled yearly is reported in Table 4.453 315. are shown in Figures 4.max = 2 L0 t end − t 0 (14) Also in this model calculations have been performed separately for group of waste components with different biodegradation velocity. adding up the results to obtain overall LFG production. for these two models.159 259. while values between after eighth year are assumed according to the hypothesis of filling up the site authorised capacity within the ninth year (last year of operation). time at which gas production finishes (tend). In the case of Scholl Canyon model and modified first order model. 2002). calculation have been performed separately for group of waste components with different biodegradation velocity. according to the assumed inputs.000 240. Also. 78 t0 [year] tmax [year] tend [year] QLFG.862 Nm3 in the sixth year.51 1. as shown in Table 6. The specific carbon dioxide emission resulting from those previous measurements is 350 g/(m2 · day).max [Nm3/t] Moderately biodegradable fractions 0 4.713. Assuming a composition of LFG of 50% CH4 and 50% CO2 and an overall landfill surface of about 90. the estimation escaped LFG from the landfill surface.. estimated escaped LFG at the studied landfill site and estimated collection efficiency Year 5 6 7 Collected LFG [Nm3] 7. for each group of waste components with different biodegradation velocity. Table 6.000 7.000 m2 (at sixth year).92 9.Landfill Gas: Generation Models and Energy Recovery 81 Table 5.0E+06 4.62 23. For the analysed landfill site.707. obtained by the application of Scholl Canyon model. This allows the estimation of the LFG collection efficiency.. Results of LFG production.862 - Estimated collection efficiency [%] 40 - .0E+07 Nm3 8.19 1.55 Slowly biodegradable fractions 0 9. 2003) (Börjesson et al. 2005) during the sixth year of operation.0E+00 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 Year Rapidly biodegradable fractions Slowly biodegradable fractions Moderately biodegradable fractions Figure 4.500. 2000) (Raco et al.818 11. is available from a measuring campaign previously carried out.63 2. Assumed input parameters for Triangular model Rapidly biodegradable fractions 0 1..10 2. the amount escaped LFG is about 11.0E+06 2.500.2E+07 1.0E+06 6. Collected LFG data. Results obtained from the different models have been compared with the data of collected LFG at the landfill site during three years of operation. which are reported in Table 6. by means of the accumulation chamber method (Cardellini et al.90 49.000 Escaped LFG [Nm3] 11.0E+06 0.713. Results of LFG production.0E+06 4.00E+06 6. 1.0E+06 2.00E+07 Nm3 8. for each group of waste components with different biodegradation velocity. 81 .0E+06 0.0E+06 6.0E+00 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 Year Slowly biodegradable fractions Rapidly biodegradable fractions Moderately biodegradable fractions Figure 5.2E+07 1.0E+07 Nm3 8. obtained by the application of LandGEM model. Results of overall LFG production.20E+07 1.00E+00 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 Year Figure 6. obtained by the application of modified first order model.82 Lidia Lombardi 1.00E+06 4.00E+06 2.00E+06 0. 00E+06 2. sixth and seventh year. Results of LFG production. for each group of waste components with different biodegradation velocity. Applying the estimated collection efficiency to the model results. .50E+07 2.00E+06 4.00E+07 Nm3 8.00E+06 0.00E+06 6. at least in the years for which data are available.50E+07 1.20E+07 1. 2. For these reasons the selected model is the Scholl Canyon one.00E+06 0.00E+00 1 6 11 16 21 26 31 36 41 Year 46 Rapidly biodegradable fractions Slowly biodegradable fractions 51 56 61 66 71 76 81 Moderately biodegradable fractions Figure 7.00E+07 5. it is evident that the model which fits better the measured data. it is possible to estimate the collected LFG from the model results and compare it with the collected LFG measured data available for the fifth.00E+07 Nm3 1.00E+00 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 Year Scholl Canyon Modified first order Triangular LandGEM Figure 8. is the Scholl Canyon one. obtained by the application of Triangular model.Landfill Gas: Generation Models and Energy Recovery 83 1. From a first look at Figure 9. as shown in Figure 9. Comparison of results obtained from the different applied models. then the assumed collection efficiency coefficient is equal to 40% for the sixth and seventh years. kWe 1048. The LFG energy recovery by means of reciprocating engines is a quite wide spread practice in modern landfills. In particular.00E+00 5 6 7 Year Measured collected landfill gas Triangular . Several sizes of engine have been considered with reference to existing Jenbacher engines (kWe 143.collected LandGEM . is a crucial and tricky issue. also in reference to its economic convenience.00E+07 5.84 Lidia Lombardi 2. and 60% for the following years (on the basis of the designed improved collection network in the specific plant). kWe 1413. kWe 330. kWe 625.50E+07 1. kWe 511. kWe 1698). Comparison of results obtained from the different applied models with the data of collected LFG. ENERGY RECOVERY The selected Scholl Canyon model has been used to predict the LFG production for the case-study landfill in order to properly size the energy recovery system along the time. For this reason. reciprocating engines were considered for energy recovery purpose.collected Scholl Canyon . The amount of potential electric energy has been calculated according to: EE = η el ⋅ LHV LFG ⋅ VLFG where: EE = electric energy [kW] ηel = engine electric energy conversion efficiency VLFG = LFG flow rate [Nm3/h] LHVLFG = LFG low heating value [kWh/Nm3] (12) .00E+07 Nm3 1. kWe 836.00E+06 0. the selection of the engine configuration along the time has been carried out with the aim of obtaining the maximum profits from selling the produced electric energy.collected Figure 9. It has been assumed that no LFG collection takes place until the fifth year included.50E+07 2. 6. but the energy recovery system definition and sizing.collected Modified first order . a combination of engines which maximises the profit was found. based on the use of one 143 kWe engine. was carried out with the aim of maximising the profits coming from the balance of energy system investment and maintenance costs and electric energy selling earnings. with the indication of the time during which engines have been used. the maintenance costs (assumed 0.50E+07 1. distributed as shown in Figure 10. the earnings for electric energy (EE) selling assuming a selling price equal to 0. overall costs and earnings are reported in Table 8.e. Results of produced LFG. Energy conversion efficiency was considered dependant on the engine load (i. decreasing when load decreases) according to the indications on Jenbacher engine technical forms.e.03 €/kWh for programmed maintenance plus 3% for non programmed maintenance). maximum LFG flow rate) for each engine and 90.13 €/kWh (considering an engine availability of 88%). obtained from the Scholl Canyon model. different combinations of engine sizes and numbers can be adopted to exploit the LFG: the selection of the final combination. The economic evaluation was carried out considering the depreciation annual cost for the engine investment (considering 6. considering as constraints the maximum load (i.00E+07 625 kWe 625 kWe 625 kWe 1413 kWe 1413 kWe 2.00E+07 1. Results in terms of produced EE. it is possible to estimate the appropriate size and number of reciprocating engines required every year for the LFG exploitation. Table 7 reports the engine costs. during the energy recovery time.00E+06 0.000 hours as maximum amount of operating hours for each engine (about ten years).5% interest rate and 10 years investment time).50E+07 143 kWe 143 kWe 2.00E+00 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 Year Recovered EE [kWh] Produced LFG [Nm3] Collected LFG [Nm3] Figure 10.Landfill Gas: Generation Models and Energy Recovery 85 The values of engine maximum LFG flow rate and energy conversion efficiency were retrieved from Jenbacher engine technical forms. Assuming the energy recovery to start at the sixth year of landfill operation and to finish in year thirty-eight. three 625 kWe engines and two 1413 kWe engines.00E+07 5. 3. As a matter of fact. On the basis of the LFG collected yearly. . collected LFG and recovered electric energy. Table 9 summarises the above mentioned contributions. From an energetic point of view. dividing the amount of generated electric energy (Table 8) by the energy content of the LFG (considering the . Being the specific emission of about 0.844 2.182 Table 8.803 751.646 5.800 Depreciation [€/year] 74.678. estimating the overall GHE produced.035 tCO2eq and the reduction by means of collection and combustion is about 34%).154. is no more produced by conventional energy system. Investment costs and depreciation cost for the selected engines Engine size kWe 143 kWe 625 kWe 1413 Engine cost [€] 252. Costs and earnings for the LFG energy recovery system Produced EE [kWh] Total produced EE [kWh] EE selling earnings [€] Engine costs + maintenance costs [€] Net profit [€] Total net profit [€] kWe143 6. When EE is produced the contribution of avoided GHE allows a further decrease of about 7%.052 The simple collection and combustion of LFG (for example by means of flaring) offers the possibility of reducing GHE with respect to uncontrolled emission of all LFG to atmosphere (in that case the GHE production would be 2.051 2. considering the contribution due to the presence of both carbon dioxide and methane in the escaped LFG and considering the contribution due to carbon dioxide (originally present in LFG and obtained from methane combustion) in collected and combusted LFG. it is possible to consider that the amount of electric energy produced by the engines fed with LFG.740 135.175 234.351 2.997.249 95.014 .500 282.791 kWe625 42.700 18. 1999)) the overall avoided effect can be calculated. Contributions to GHE during the landfill life time GHE from escaped LFG [tCO2eq] GHE from collected LFG [tCO2eq] Total produced GHE [tCO2eq] Avoided GHE form EE production [tCO2eq] Net produced GHE [tCO2eq] 1.500 659. this term can be considered as an avoided effect of GHE emissions and then subtracted from the overall balance.513. Moreover.962 1.573.300 Additional cost [€] 282.551 kg of equivalent CO2/kWh for electric energy production (with reference to the Italian situation (ENEL.538 Table 9.501. Table 7.178 846. it is possible to calculate an overall energy conversion efficiency.868 188.000 377.456.927.199.500 282.553 17.351 91.000 689.306 15.103.839 1.500 971.86 Lidia Lombardi The obtained configuration for energy recovery was evaluated also from an environmental point of view.774 kWe1413 139.652.315.500 Total investment cost [€] 534.826.352.221.328. 00% 0% - 0. and in particular to saved conventional fossil fuels. by means of adapting the Scholl Canyon equation based model previously described. In order to define the different parameters to be used to describe a conventional landfill and a landfill where leachate is recirculated.90% 5.00% 42.10% 0.90% 0. pilot cells and real landfills highlighting its beneficial effects on the waste biodegradation process (Reinhart and Townsend.10% 0.reported in Table 10 and Table 11. In the present chapter.00% 0% 54% Slow 45.20% 1.60% 0.30% 0.10% 1.90% 5.Landfill Gas: Generation Models and Energy Recovery 87 calculated content of methane) generated in the landfill life time (both collected and non).20% 23.50% 6.60% 11. the aim is to highlight the behaviour differences between a landfill where leachate recirculation takes place and a conventional landfill.10% 29.90% 0.30% 0.90% 2. Table 10. measured data from a landfill where leachate recirculation takes place were considered and the Scholl Canyon equation based model was built around data and inputs –referred to the analysed landfill . the above described model has been applied to simulate the behaviour of an existing reference landfill.80% 0.50% 0. In order to highlight the contribution to natural resources conservation.60% 36.50% 20. MANAGEMENT OPTION TO IMPROVE ENERGY RECOVERY The Scholl Canyon equation based model has been applied to a second study case in order to evaluate the possibility of improving energy recovery from LFG by means of leachate recirculation (Corti et al.00% 98. the EE production from this renewable source allows to save about 40.10% 1.70% 60.30% 25. biodegradability and biodegradation rate category Material Organic matter Paper and cardboard Plastics Textiles Pruning scrap Wood Glass and inert Metals C H O N S Inert Humidity Biode Grada bility Biode Gradation rate 28.10% 0.40% 0. 1998).00% 60% Rapid 49.00% 94.50% 8.00% 10.70% 4. The practice of leachate recirculation has been studied in several laboratory cells. In order to do this.40% 4. where MSW are deposited. in the two periods in which it was operated without leachate recirculation and with leachate recirculation.70% 20.50% 0.50% 50% Moderate 70.00% 72% Slow 0.599 TEP (ton of equivalent petrol) (assuming an average energy conversion efficiency of 37% for conventional plants).50% 6. 7.30% 9.70% 0.60% 4.50% 70.90% 22.50% 11.30% 2..00% 0% - .50% 39.90% 0.40% 40.10% 0. The value of the overall energy conversion efficiency results about 15%. 2005).50% 3.20% 0. Chemical composition of waste component fractions and their humidity.70% 3.00% 82% Rapid 44. 69 0.97 20.413 The application of the previously described Scholl Canyon equation based model.020 28.05 0.311 49. but it fails after leachate recirculation starts.308 80. kCV = LFG generation rate constant for the conventional landfill [1/year] kLR = LFG generation rate constant for the landfill with leachate recirculation [1/year] Figure 11.69 Lag time [year] 0.14 0.883 94. defined as reported in Equation 13. So. it is necessary to introduce a proportional coefficient β between reaction rate for a conventional landfill and a landfill with leachate recirculation. k CV = k LR β where. Comparison of model results and collected data for the existing reference landfill.600 47. in order to fit the real data after the third year.05 4.53 2.47 19. Waste component characterisation.3 5 - K[1/year] 0.75.544 25.05 - Year 1 2 3 4 5 6 7 8 MWS [t] 9. As a matter of fact the model fits the real data properly in the period before starting the leachate recirculation (the third year). which are compared with the real data collected at the existing reference landfill. input parameters for Scholl Canyon model and amount of MSW landfilled yearly in the analysed site Material Organic matter Paper and cardboard Plastics Textiles Pruning scrap Wood Glass and inert Metals Mass composition [%] 15.54 23.88 Lidia Lombardi Table 11. It has been assumed that the LFG generation potential remains the same in the case of presence or absence of leachate recirculation. supplied the results shown in Figure 11.3 1 5 0.37 4.69 0. applying a LFG collection efficiency of 0.38 9.598 36. (13) . 538 101. it is possible to obtain quite good accordance between real data. It is quite important to note that in the case of landfill with leachate recirculation the 95% of LFG is produced ten years before than in the conventional landfill case. Waste component characterisation and yearly landfilled amount for the hypothetical study case Material Organic matter Paper and cardboard Plastics Textiles Pruning scrap Wood Glass and inert Metals Mass composition [%] 36.0 6. the modified model has been applied to a hypothetical study case .characterised by the waste component characterisation and amount of MSW yearly landfilled reported in Table 12 . This feature allows the concentration of energy recovery during a smaller period of time.3 21.655 104. Further.775 99.163 107.9 3.865 The model results.in order to understand the behaviour differences between a conventional landfill and a landfill with leachate recirculation.873 111.5 11. Model results applying different β coefficients. in terms of produced LFG.4 12. after the recirculation beginning. Table 12.0 5. Figure 12.4 Year 1 2 3 4 5 6 7 MSW [t] 113. as shown in Figure 12. and model results.Landfill Gas: Generation Models and Energy Recovery 89 With a value of β in the range of 2-2.5 3. are plotted in Figure 13. .521 98.5. 00E+07 8.00E+06 6. Assuming that waste density passes from 0. From an economic point of view. collection system. environmental and energetic point of view. capping and flaring it is necessary to consider . but while in the conventional landfill the recovered volume can host about 55. In order to properly calculate the annual instalment connected to the investments relative to bottom impermebilisation.000 t. Comparison of model results – LFG production . the two hypothetical plants have been compared from an economic. in the landfill with leachate recirculation about 80.00E+00 1 6 11 16 21 26 31 36 41 46 51 56 Year Figure 13. and combining this effect with the material loss in LFG.20E+07 Landfill with leachate recirculation Nm3 1.40E+07 Conventional landfill 1. In order to evaluate the overall waste volume reduction it is necessary to account for both the increasing density of the waste.90 Lidia Lombardi 1.000 t of waste can still be placed.00E+06 0. the considered investment costs included: bottom impermeabilisation cost. and the accelerated biodegradation. due to the weight of the upper layers. The accelerated biological degradation also strongly contributes to the volume reduction of the landfilled waste. it is possible to estimate the overall volume reduction in the two cases. LFG and leachate collection system costs and capping (Table 13).for landfill with leachate recirculation and conventional landfill. It was calculated that at the end of the seventh year (last year of operation) in both plants the volume reduction allows further landfilling. while for the conventional landfill a vertical LFG collection system (with a LFG collection efficiency of about 60%) and a separate conventional leachate draining system were considered.6 to 1 t/m3 in thirty years and then it keeps constant.00E+06 4. This possibility of higher recovered volumes and higher capacity has been accounted in the following considering as input to the landfill with leachate recirculation the higher amount of waste. In order to understand the benefits that can derive from leachate recirculation. both in a conventional landfill and landfill with leachate recirculation. In the case of landfill with leachate recirculation a horizontal piping system for both LFG collection and leachate recirculation has been assumed (with a LFG collection efficiency of about 70%).00E+06 2. assuming to apply LFG collection and energy recovery until about 95% of total LFG is produced.13 €/kWh. . Table 15 summarises the engine number used for each of the considered case. using relative large size engine in the high LFG production period and small size engines in the final LFG production.7.000 1. The estimation of electricity production also took into account the energy conversion efficiency lowering when energy input is less than nominal size. 625 kW – 38. The engine selection has been based on existing models (Jenbacher).803 460.Landfill Gas: Generation Models and Energy Recovery 91 the effective utilisation time of the equipment. Considering a reciprocating engine average life of ten years.957.8) it is possible to evaluate the electricity production and assuming an electric energy selling price of about 0.5%. 836 kW – 38. On the basis of the LFG collected yearly in the two considered cases.809 Table 14.803 750. Table 13.957. Assumed construction phases and the depreciation times Equipment Construction phases Depreciation time [years] Bottom impermeabilisation All placed at the beginning 8 Capping All placed at the closing time 1 Flare Life time of 1 flare 10 Landfill with leachate recirculation Collection system Collection/recirculation system is placed at three different moments At the beginning 8 After 2 year 6 After 5 years 3 At the beginning 8 After 2 year 6 After 5 years 3 Conventional landfill with vertical collection system Collection system Collection system is placed at Landfill operation time = 8 the beginning years From the electric energy conversion efficiency of the considered engines (143 kW – 34.816. it is possible to estimate the gain from electricity sell. it is possible to calculate the overall number and combination of engines required. Investment and operation costs for the different considered plants Equipment Landfill with leachate recirculation Bottom impermeabilisation [€] Collection system (leachate and LFG) [€] Capping [€] 4.816.3%.000 1. The interest rate used is 6. it is possible to estimate the appropriate size and number of reciprocating engines required every year to use the LFG energy content. Table 14 summarises the construction phases and the depreciation times assumed.809 Conventional landfill with vertical collection system 4. it is possible to calculate the specific GHE production for the different considered cases.740 131 Conventional landfill with vertical collection system 3 x 625 kW engines + 3 x 143 kW engines 2. Summary of the operation costs Operation costs Personnel. it appears that applying the leachate recirculation.720 105 Table 16 summarises operation costs. even if a slightly higher investment cost for the collection/recirculation system is required. From an environmental point of view. electricity. Table 17 shows the results in terms of specific disposal cost for disposing one ton of MSW. The lower cost is mainly due to the shorter time during which the LFG production exhausts with a . These contributions have been calculated for the two cases (landfill with leachate recirculation and conventional landfill). Number. general maintenance. 1999) the overall avoided effect can be calculated. dividing the amount of generated electric energy (Table 15) by the energy content of the LFG generated in the landfill life time (assuming an average low heating value of 16. Operation cost have been assumed equal for the two different plants considered. it is possible to calculate an overall energy conversion efficiency. this term can be considered as an avoided effect of GHE emissions and then subtracted from the overall balance. a lower specific disposal cost can be reached in comparison to a conventional landfill.000 From an energy point of view. size and overall investment cost of the reciprocating engines and energy production for each considered case in the operating and post-closure phases Considered configurations Investment cost [€] Produced electric energy [GWh] Landfill with leachate recirculation 4 x 625 kW engines + 1 x 143 kW engines 2. assurance Vigilance [year] 8 9 [€/year] 380.000 630.92 Lidia Lombardi Table 15. Table 16.000 10 275.246.000 58 25.000 kJ/Nm3).551 kg of equivalent CO2/kWh for electric energy production (with reference to the Italian situation (ENEL.000 49 460. in the two cases of landfill with leachate recirculation and conventional landfill. while after the end of the post-closure phase the residual LFG is all emitted to the atmosphere contributing as well to GHE. Being the specific emission of about 0. fuels and lubricating oil. environmental and topographic analysis.469. From the economical point of view. etc Mechanical machines. is no more produced by conventional energy system. grouping together the costs that last for the same number of years. Contributions to GHE during operation and post-closure phases come from collected LFG combustion and from uncollected LFG directly emitted to the atmosphere. covering soils Leachate disposal. water. machine maintenance Leachate disposal. considering that the amount of electric energy produced by the engines fed with LFG. Further. The use of landfill gas production models is definitely useful in order to properly design landfill gas collection and energy recovery systems since it supplies an estimation of landfill gas amount during the landfill operation and post-closure phases.390 32. When considering avoided effects.512 40. collected and combusted landfill gas and recovered electric energy avoided emissions. a further decrease in CO2 equivalent specific emission is registered. implemented and compared among themselves and with data collected from existing landfills. but also to the possibility of higher landfill volume recovery due to the accelerated biodegradation process with a consequent higher amount of disposed waste that corresponds to a higher amount of LFG production. Energy recovery offers the possibility of decreasing the contribution to Greenhouse Effect. selecting one of them for application to some study cases.28 20 644 571 From the results concerned with overall energy conversion efficiency. Table 17. with respect to . The selected model has been used to predict the landfill gas production of a case-study landfill in order to properly size the energy recovery system.679.518 37. The obtained configuration for energy recovery was evaluated also from an energetic and environmental point of view. Concerning GHE production the landfill with leachate recirculation allows the reduction of specific CO2 equivalent emitted per each ton of landfilled waste. The accuracy of the landfill gas production estimation depends in part on the complexity of the model and mainly on the accuracy and specificity of the input data. CONCLUSION Different landfill gas production mathematical models have been analysed. Specific disposal cost for MSW. since in the landfill with leachate recirculation case a higher energy recovery is possible.Landfill Gas: Generation Models and Energy Recovery 93 more concentrated energy recovery using a lower number of engines (lower investment). estimating the overall contribution to Greenhouse Effect from escaped landfill gas. thanks to the less LFG emitted directly to the atmosphere after the post-closure phase (without any collection and combustion). overall energy conversion efficiency and specific CO2 emission Landfill with leachate recirculation 817.35 Disposed MSW [t] Total cost [€] Specific disposal cost [€/tMSW] Overall energy efficiency and environmental impact Overall energy conversion efficiency [%] 25 GHE [kgCO2/tMSW] without avoided effects 528 GHE [kgCO2/tMSW] with avoided effects 439 Conventional landfill with vertical collection system 792. with the aim of obtaining the maximum profits from selling the produced electric energy.980. a higher value was obtained for the landfill with leachate recirculation with respect to the conventional landfill.930 46. then.. (2005). The same selected model was. January 2003.. 6. Stanford University . H. Granieri D. 124(12): 1193-1202. EMCON Associates (1980). Bonori B. Landfill Gas Emissions Model (LandGEM) Version 3. consisting in leachate recirculation. vol.. REFERENCES Baldwin T. Corti A. Italy. “Accumulation chamber measurements of methane fluxes: application to volcanicgeothermal areas and landfills”.D. Ann Arbour. Bergonzoni M. 34. CISA Environmental Sanitary Engineering Centre. Cardellini C. Eds. Schlegel H. Puglierin L. Danielsson A. “Landfill gas production and energy recovery in bioreactor landfill”. EPA/600/R-05/047. "Methane Fluxes from a Swedish Landfill Determined by Geostatistical Treatment of Static Chamber Measurements". PhD Thesys.. Chiodini G.. 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Ann Arbor. 67-89.96 Lidia Lombardi Van Zanten. Hua Renhua. Xu Dimin and Gu Guowei. New Orleans. +433168761327. the only C-rich material source available on the Earth. a LCA of a biorefinery system based on a lignocellulosic feedstock (e. Elisabethstraße 5. This chapter describes the emerging biorefinery concept and provides an overview of the most important biomass sources. wood industrial residues) and producing bioethanol and methyltetrahydrofuran (MTHF) as transportation biofuels. System performances are also ∗ Corresponding author. the environmental concerns and the fact that they are not a renewable resource. the uncertain availability. conversion technologies and platforms (or intermediates). In biorefinery. biomethane. electricity and heat as further energy carriers. tel. sun. The biorefinery system is compared with a reference system based on fossil sources. Institute of Energy Research.g. Results focus on greenhouse gas (GHG) and energy balances and estimate the possible GHG and fossil energy savings. fax: +433168761330. Austria ABSTRACT A great fraction of worldwide energy carriers and material products come from fossil fuel refinery. almost all the types of biomass feedstock can be converted to different classes of biofuels and chemicals through jointly applied conversion technologies. Electricity and heat can be provided by a variety of renewable alternatives (wind. Because of the on-going price increase of fossil resources. a relatively young concept in the scientific literature. biomass). alternative solutions able to reduce the consumption of fossil fuels should be promoted. Chapter 3 ENERGY AND MATERIAL RECOVERY FROM BIOMASS: THE BIOREFINERY APPROACH. is reported. The replacement of oil with biomass as raw material for fuel and chemical production leads to the development of “biorefinery”. CONCEPT OVERVIEW AND ENVIRONMENTAL EVALUATION Francesco Cherubini∗ and Gerfried Jungmeier Joanneum Research. Therefore. while the fossil resource alternative for production of fuels and chemicals can be just biomass. water. The advantages of biorefinery systems over conventional fossil systems are outlined by means of Life Cycle Assessment (LCA): in the second half of this chapter. e-mail: [email protected] . furan resins. the feasibility of their exploitation is predicted to decrease in the near future. 8010 Graz. besides fossils.In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers. fumaric acid and oxygen as chemicals and hydrogen. Inc. A biorefinery is a facility that integrates biomass conversion processes and equipment to produce transportation biofuels. energy. The replacement of oil with biomass as raw material will require some changes from the today’s production of goods and service: biological and chemical sciences will play a leading role in the generation of future industries and new synergies of biological.98 Francesco Cherubini and Gerfried Jungmeier investigated with calculations of product yields and mass. their potential availability is limited by soil fertility and per hectare yields and the effective savings of CO2 emissions and fossil energy consumption are limited by the high energy input required for crop cultivation and conversion (Lange. 1. Biomaterials Biomass Pretreatment Biomass components Conversion technologies Bioenergy Biochemicals Figure 1. 2006a). chemical and technical sciences must be elaborated (Kamm et al. and energy. while the fossil resource alternative for production of transportation fuels and chemicals is biomass. A first generation of transportation biofuels and chemicals is today produced from sugars. The evaluation of the environmental performances reveals that relevant environmental benefits can be gained with a shift from oil refinery to biorefinery: almost 89% of GHG emissions and 96% of fossil energy demand can be saved. grasses. the only C-rich material source available on the Earth. physical. Electricity and heat can be provided by a variety of renewable alternatives (wind. . besides fossils. combined with diminishing petroleum resources. INTRODUCTION Our strong dependence on fossil fuels results on the intensive use and consumption of petroleum derivatives which. Different allocation procedures (substitution method. causes environmental and political concerns. new renewable sources of energy and chemicals are object of research and development activities. biofuels and chemicals (see Figure 1). exergy and C conversion efficiencies. corn…) into their building blocks (carbohydrates. Simplified scheme of biorefinery: conversion of biomass into bioproducts.. water. 2007). The biorefinery concept is analogous to today's petroleum refinery. power. an allocation issue must be addressed. exergy. Since the biorefinery system co-produces many high value products. giving rise to several issues: these raw materials compete with food for their feedstock and fertile land. economic allocation) are therefore used and final results compared. and chemicals from biomass. As a consequence. which produces multiple fuels and products from petroleum. sun. starches and vegetable oils. fats…) which can be converted to value added products. proteins. The term “biorefinery” is raising importance in the scientific community and the concept embraces a wide range of technologies able to separate biomass resources (wood. biomass and so on). g. Afterwards. furfural derivates. 2006). biomethane.. 2. The importance of recovering transportation biofuels and chemicals from lignocellulosic biomass feedstocks is evident: they are the most abundant biomass source in the Earth. heat.1. Katzen and Schell. The transportation sector is growing steadily and in the same way grows the demand for renewable (bio-)fuels. Several allocation methods are used to share the environmental burdens of the biorefinery among the co-products and the final results are compared. exergy and carbon conversion efficiencies are also reported. a Life Cycle Assessment (LCA) of a biorefinery system based on wood residues is reported. a case study is evaluated by means of Life Cycle Assessment (LCA). electricity. . The biorefinery is compared with a reference system producing the same products from fossil sources.. Information concerning product yields and mass. straw and corn stover) or in non-agricultural lands and they have high potential for converting their main components (cellulose. hydrogen and oxygen from wood industrial residues. hemicellulose and lignin) into a wide spectrum of biofuels and chemical products (Kamm et al. they can be recovered from residue streams in different sectors. industry and dedicated crops (Cherubini et al. This work addresses this aspect: after a definition of the biorefinery concept. which can only be provided from biomass. Since this is a relatively new concept in the scientific literature. related to the biorefinery concept. The chapter starts with a formal definition of biorefinery and a list of criteria that a bioenergy/biomass system has to meet to be a real “biorefinery”. 2006b. In order to investigate all the environmental aspects of biorefinery systems. Numerous countries have targets for improving the shares of biofuels in the national transport sector. the most important biomass feedstocks. processes and platforms.Biorefinery Concept: Energy and Material Recovery from Biomass… 99 These limitations can be partly overcome by the utilization of lignocellulosic materials. forestry. the most exhaustive was recently performed by the IEA Bioenergy Task 42 on biorefineries (IEA 2008) (Figure 2): “Biorefining: the sustainable processing of biomass into a spectrum of marketable products and energy”. Background and Current Status Among the several definition of biorefinery. are depicted and a comparison between biomass and oil as raw materials is presented. such as residues from agriculture. One of the main driving factors for the future development of biorefinery can be seen in the efficient production of transportation liquid biofuels. energy. 2009). APPROACHING BIOREFINERY: DEFINITION. they can be grown in combination with food (e. The biorefinery system produces bioethanol. few published papers on environmental performances of biorefinery systems are currently available. CRITERIA AND CHARACTERISTICS 2. 5 Mtoe (GBEP 2007). made by combining vegetable oil (from rapeseed. biodiesel and biogas (or biomethane). packaging materials. and in the last few years it has been strong implemented in countries with high feed in tariffs for electricity generation from biogas (especially European countries). However. lignocellulosic feedstocks can be supplied either from dedicated crops or as residues from agricultural. polymers. with a total fleet of approximately 4500 vehicles with 45 % of its fuel supplied by biomethane (Jönsson and Persson. For instance. is mainly produced in European countries and its total production in 2005 was about 2. canola and others) or animal fat with an alcohol and a catalyst through a reaction known as transesterification.75% in 2010 and 10% in 2020 of biofuels. Moreover.100 Francesco Cherubini and Gerfried Jungmeier Figure 2. hemicellulose and lignin) which can be refined into different final products using a set of jointly applied technological processes. Their exploitation is thereby limited. solvents. Europe aims at a share of 5. and have raw materials in competition with the food and feed industry. while IEA and IPCC expect a significant contribution of biofuels on transportation market in 2030 (10 – 20%) (EBS 2007). For instance. and sorbents. The production of biogas is diffused in all the countries. most of these biofuels and biochemicals are produced in single production chains and not with a biorefinery approach. biogas is also used as transportation biofuel. 2003). plastic fillers. paints and coatings. lubricants. This feedstock is made of 3 main components (cellulose. in comparison with conventional starch and oilseed crops that can contribute only with a small fraction (grains and seeds) of the above standing biomass to bioenergy and biochemical . soybean. whereas for the coproduced biomaterials and biochemicals additional economic and environmental benefits might be gained. The main challenge for biorefinery development is therefore the efficient and cost effective production of transportation biofuels. paper and box board. Biorefinery recovers energy and materials from biomass sources. according to the draft directive for renewable energy. The most common biofuels produced today in the world are bioethanol. dyes. detergents. An alternative can be represented by lignocellulosic materials. sunflowers. hydraulic fluids. In some countries (such as Germany and Sweden). inks. Already commercially available biobased products include adhesives. In fact. Bioethanol production from sugar or corn starch was more than 17 Mtoe in 2005. Sweden currently leads the world in automotive biogas production. dielectric fluids. Biodiesel. United States (from corn starch) and Brazil (from sugar cane) are the largest producers (GBEP 2007). after upgrading to biomethane. There is not anymore a competition with the food and feed industry since lignocellulosic biomass can be grown on land which is not suitable for agricultural crops. forestry and wood industry. cleaning compounds. Biorefinery Concept: Energy and Material Recovery from Biomass… 101 production, biorefineries based on lignocellulosic feedstocks can rely on bigger biomass per hectare yields, since the whole crop is available as feedstock. Therefore, lignocellulosic raw materials are the most suitable biomass source for providing a large and constant feedstock supply to biorefineries, on condition that sustainable practices and managements are followed. Over the next 10 to 15 years, it is expected that lower cost residue and waste sources of lignocellulosic biomass will provide the first influx of next-generation feedstocks, with cellulosic energy crops expected to begin supplying feedstocks for bioenergy production towards the end of this time frame, then expanding substantially in the years beyond (Worldwatch Institute, 2006). 2.2. Criteria for Biorefinery System In addition to the definition, biorefinery systems should also follow some requisites which act as guidelines for the future deployment of biorefinery concepts. The criteria which a biomass or bioenergy system has to follow to be named biorefinery are the following: 1. Biomass Refining: a biorefinery, similarly to the upgrading of crude oil that occurs in oil refinery, is based on feedstock upgrading processes, where raw materials are continuously upgraded and refined. This means that a biorefinery should separate all the biomass feedstock components in order to be individually exploited, leading through a chain of several processes to a high concentration of pure chemical molecules (e.g. ethanol) or a high concentration of molecules having similar functions (e.g. the mixture of C alkanes in FT-fuels). 2. Combustion of residues: a feedstock can not be directly combusted without any previous treatment, since the aim of a biorefinery is to increase the value of the different biomass components as material and energy source. Therefore, the most desirable option is to send combustion for heat and electricity production only the residues and leftovers of the several technological treatments and conversion processes. 3. Value chemicals/materials: a biorefinery should produce at least one value chemical/material product, besides the low-grade and high-volume animal feed and fertilizers, according to the specifications of the first criterion. 4. Fuel-Energy products: as a direct consequence of the second criteria, a biorefinery should produce at least one energy product besides heat and electricity. Therefore, the production of at least one biofuel (liquid, solid or gaseous) is required. 5. Fossil fuel replacement: the products of a biorefinery must be able to replace fossil fuel based products coming from oil refinery, both chemicals and energy carriers. Concerning the chemicals, this objective can be met by producing the same chemical molecule from biomass instead of from fossils (e.g. phenols), or producing a molecule having a different structure but an equivalent function (e.g. succinic acid from biomass vs. maleic anhydride from fossils) or new biobased products able to replace petroleum based products (e.g. synthetic biodegradable plastics from starch). Concerning the fuels, a biorefinery must replace conventional fossil fuels (mainly gasoline, diesel, heavy oil, coal and natural gas) with the production of biofuels coming from biomass upgrading, both liquid (e.g. bioethanol, biodiesel, FT-fuels), gaseous (e.g. synthetic natural gas, hydrogen) and solid (e.g. lignin, charcoal, residues). 102 Francesco Cherubini and Gerfried Jungmeier 6. Energy self-sufficiency: a biorefinery plant should have the aim to run in a sustainable way: all the energy requirements of the several biomass conversion processes should be internally supplied by the production of heat and electricity from combustion of residues. For instance, in a lignocellulosic ethanol plant, lignin, after separation from cellulose and hemicellulose, can be burnt to provide the heat and electricity required by the plant. However, direct external fossil energy inputs are allowed if they ensure economic benefits to the system and do not unduly burden the overall GHG and energy balances. 7. Waste minimization: solid, liquid and gaseous wastes released by a biorefinery should be minimized. This target can be achieved in two ways: using the different biomass components for producing a wide spectrum of multiple products, or setting up “bioclusters”, where material flow exchanges among different plants are promoted in order to transform a downstream residue of a plant into an upstream raw material for another plant. 2.3. Fossils vs. Biomass as Raw Materials The structure of biorefinery raw materials is totally different from that on which the current oil refinery is based. Crude oil is a mixture of many different organic hydrocarbon compounds (based on C and H) while biomass is made of different compounds (with a large abundance of O and ashes). The first step of oil refinery is to remove water and impurities, then distill the crude oil into its various fractions as gasoline, diesel fuel, kerosene, lubricating oils and asphalts. Then, these fractions can be chemically changed further into various industrial chemicals and final products. Unlike petroleum, biomass composition is not homogeneous, because the biomass feedstocks might be made of grains, wood, grasses, biological wastes and so on, and the elemental composition is a mixture of C, H and O (plus other minor components such as N, S and other mineral compounds). This biomass compositional variety is both an advantage and a disadvantage. An advantage is that biorefineries can make more classes of products that can petroleum refineries and can rely on a wider range of raw materials. A disadvantage is that a relatively larger range of processing technologies is needed, and most of these technologies are still at a pre-commercial stage (Dale and Kim, 2006). In order to be used for production of biofuels and chemicals, biomass needs to be depolymerized and deoxygenated. Deoxygenation is required because the presence of O in biofuels reduces the heat content of molecules and usually gives them high polarity, which hinders blending with existing fossil fuels (Lange, 2007). Chemical applications may require much less deoxygenation, since the presence of O often provides valuable physical and chemical properties to the product. The main benefits which can be related to an extensive deployment of biorefinery in replace of oil refinery are based on the supply of renewable biomass. In fact, if this is managed with sustainable practices, biomass has a closed carbon cycle: its use release to the atmosphere almost the same amount of CO2 that was captured during the photosynthetic process. Furthermore, unlike fossil resources, biomass resources are locally available for many countries and their provision, together with an implementation and development of biorefinery industries, will create a large number of jobs, especially in rural areas. Therefore, biorefinery technologies should be compact and suitable for local installations. Biorefinery Concept: Energy and Material Recovery from Biomass… 103 Another important point concerning biorefinery processing is the fact that environmental impacts and consumption of non renewable resources should be minimized, while complete and efficient biomass use maximized. This ecological perspective requires: analyses of three important agricultural and forestry cycles as carbon (respiration, photosynthesis, and organic matter decomposition), water (precipitation, evaporation, infiltration, and runoff) and nitrogen (N fixation, mineralization, denitrification) and their interdependencies (Gravitis and Suzuki, 1999); system performance evaluations and environmental impact estimations carried out by means of Life Cycle Assessment (Cherubini et al., 2007). Especially soil degradation minimization and biodiversity conservation seems to be two dominating factors to consider in the assessment of biorefinery systems. With all this, biorefinery represents a change from the traditional refinery based on large exploitation of natural resources and large waste production towards integrated systems in which all resources are used. An example of how the biorefinery of the future will evolve can be found in the history of the existing corn wet-milling industry (Lasure and Min, 2004). Initially the corn wet milling industry produced starch as the major product. As technology developed and the need for higher value products drove the growth of the industry, the product portfolio expanded from various starch derivatives such as glucose and maltose syrups to high fructose corn syrup. Later, fermentation products derived from the starch and glucose such as citric acid, gluconic acid, lactic acid, lysine, threonine and ethanol were added. Many other by-products, such as corn gluten, corn oil, corn fiber and animal feed are now being produced. The final vision is then the development of the technical, commercial and political infrastructure for a biomass refinery (biorefinery), which will be similar to the current oil refinery concept. 3. OVERVIEW OF BIOREFINERY FEEDSTOCKS, PROCESSES AND PLATFORMS 3.1. Biorefinery Feedstocks The term of feedstock refers to raw materials used in biorefinery, from which biofuels and biochemicals are produced and recovered by means of a set of jointly applied technological processes. The biomass of the world is synthesized via the photosynthetic process that converts atmospheric carbon dioxide to sugar. Plants use the sugar to synthesize the complex materials that are biomass. Renewable carbon-based raw materials are produced in agriculture, silviculture and microbial systems. Although a tremendous variety of biomass resources is available, only four basic chemical structures are of significance for production of biofuels and biochemicals: carbohydrates (sugar, starch, cellulose, hemicellulose), lignin (polyphenols), triglycerides (lipids, vegetable oils and animal fats) and proteins (vegetable and animal polymers made up of amino-acids). The average composition of synthesized biomass in the world is 75% carbohydrates, 20% lignin and 5% other compounds (oils, proteins and so on) (Lichtenthaler, 2006). As a consequence, the main attention of research and development activities should first be focused on efficient access to carbohydrates, and their subsequent conversion to chemical intermediates and corresponding final products. 104 Francesco Cherubini and Gerfried Jungmeier All the existing types of biomass feedstocks can be divided in five groups: sugar crops, starch crops, oil based materials, grasses, lignocellulosic materials and organic residues and others. In the next sections, each of this group is depicted. 3.1.1. Sugar crops Concerning sugar crops, they provide sugars in a simple form, i.e. mono- or disaccharides, which can be readily used in conversion processes. Six-carbon, singlemolecule “monosaccharide” sugars (C6H12O6) include glucose, galactose and mannose, while the most common 5-carbon sugars (C5H10O5) are xylose and arabinose. The two most important sugar crops are sugar cane and sugar beet which, together with corn (a starch crop), supply almost all the bioethanol that is produced today (Rajagopal and Zilberman, 2007). The drawback of this type of feedstock is that requires dedicated hectares for the production and can compete with the food industry. Chemical structures of glucose and xylose are reported in Figure 3. Figure 3. Chemical structures of glucose and xylose. 3.1.2. Starch crops Starch crops provide grains containing starch. Starch (C6H10O5)n is a very large polymer molecule composed of many hundreds or thousands of glucose molecules (polysaccharides), which must be broken down into one or two molecule pieces prior to be fermented to bioethanol or biochemicals. The most widespread starch crops are wheat and corn (Tuck et al., 2006; Wright, 2006). The major drawback of the use of these crops in biorefinery is that they are also used in the food and feed industry and their provision as biorefinery feedstock can have adverse impacts on food supply, soil carbon content (if straws and corn stovers are removed) and land pressure. The chemical structure of starch is illustrated in Figure 4. Biorefinery Concept: Energy and Material Recovery from Biomass… 105 Figure 4. Chemical structure of starch (segment). 3.1.3. Oil based materials Oil based materials are made of triglycerides which typically consist of glycerin and saturated and unsaturated fatty acids (the chain length ranges between C8 and C20). The sources of oils and fats are a variety of vegetable and animal raw materials. Soybean, palm, rapeseed and sunflower oil are the most important in the terms of world wide production (Demibras, 2003; Hill, 2006; Sheehan et al., 2000). Vegetable oils are nowadays used for production of biodiesel by reacting with an alcohol, usually methanol. However, they can also be used as a substrate for chemical reactions thanks to two chemically reactive sites: the double bond in the unsaturated fatty acid chain and the acid group of the fatty acid chain (Biermann et al., 2001). Like sugar and starch crops, oilseed crops are characterized by low yield, high use of agrochemical inputs and competition with food market. In the future, nonedible crops like Jatropha curcas and Pongamia pinnata, which require lower inputs and are suited to marginal lands, may become the most widespread oil crops, especially in dry and semiarid regions (Achten et al., 2007; Rajagopal and Zimermann, 2007). Other sources of oil provision are the food industry, where waste edible oil is mainly generated from commercial services and food processing plants such as restaurants, fast food chains and households (Tsai et al., 2007), and the micro-algae, microscopic single cell aquatic plants with the potential to produce large quantities of lipids. The latter seems to have promising advantages over conventional oil crops because of the possibility to be grown in arid and semi-arid regions with poor soil quality, with a per hectare yield estimated to be many times greater than that of even tropical oilseeds. Moreover, algae can also grow in saline or polluted water, which has few competing uses in agriculture, forestry and industry (Chisti, 2007; Sheehan et al., 1998). A chemical structure of a saturated triglyceride is illustrated in Figure 5. 106 Francesco Cherubini and Gerfried Jungmeier Figure 5. Chemical structure of triglycerides. 3.1.4. Grasses Grasses are the raw materials for the so-called green biorefinery. This group includes the large family of green plant materials (green grass from meadows, willow and other natural resources), alfalfa, clover grass, grass silage, immature cereals and plant shoots (Kromus et al., 2006). The main components of green plant materials are carbohydrates, proteins, fibers, fats, amino acids and others. This composition allows to the green biorefinery to produce biogas, lactic acid, amino acids and fibers. An important green raw material source is the green harvesting residue material from agricultural cultivated crops, mainly the green foliage from sugar beet leaves, hemp scrape and leaves. 3.1.5. Lignocellulosic materials Lignocellulosic materials include dedicated energy crops (such as switchgrass and miscanthus), agricultural residues, forestry wastes, agroindustrial wastes, and other industrial wastes. The importance of lignocellulosic biomass as feedstock for biorefinery is evident: their use allows either the production of valuable biofuels and chemicals able to replace fossil derived products, and the utilization of a wide range of residues of domestic, agricultural and industrial activities. Among the potential large scale industrial biorefineries, the biorefinery systems based on lignocellulosic feedstocks will most probably achieve the greatest success in terms of market penetrations and product volumes. On the one side the raw material situation is optimum (widespread and easily available), on the other side conversion product have a good position on both the traditional petrochemical and future biobased product market. All kinds of lignocellulosic biomass are made of three main components: cellulose, hemicellulose and lignin. Cellulose (see Figure 6) has a strong molecular structure made by long chains of glucose molecules (C6 sugars) and is one of the most important raw materials for a variety of industries. Currently, major uses of cellulose are in pulp and paper industry, in medicine and in pharmacy (Kamm et al., 2006b). Biorefinery Concept: Energy and Material Recovery from Biomass… 107 Figure 6. Cellulose structure. In the biorefinery concept, the first treatment which cellulose undergoes is usually acid or enzymatic hydrolysis to glucose, if the feedstock is not pyrolysed or gasified. This sugar monomer is a key chemical that can mainly follow two routes: fermentation or chemical synthesis (Schiweck et al., 1991). The second main component of lignocellulosic biomass is hemicellulose (see Figure 7), which is relatively easier to breakdown to sugar monomers with chemicals and/or heat than cellulose. It contains a mix of C6 sugars (galactose and mannose) and C5 sugars (xylose and arabinose), which represent a great potential for the production of biofuels or chemicals. Xylose, the most representative sugar in hemicellulose, can mainly undergo three different pathways: hydrogenation to xylitol, acid treatment to furfural and fermentation to bioethanol together with C6 sugars (Kamm et al., 2006b). Figure 7. Hemicellulose structure. 108 Francesco Cherubini and Gerfried Jungmeier Figure 8. Fragment of lignin structure. The third component of lignocellulosic feedstock is lignin, made of phenolic polymers (see Figure 8). Even if lignin cannot be hydrolyzed to sugars and then fermented, it is useful for other purposes. For instance, it can be used in its polymeric forms as adhesives for wood materials, cement additive and so on, or can be fractionated into low molecular mass compounds (e.g. phenols), completely degraded to gas or liquid bio-oil through gasification or pyrolysis, or burnt as a solid fuel to generate heat and electricity. Table 1 reports the composition of some lignocellulosic biomass which can constitute the raw materials for biorefinery systems. The abundance of the three main components can vary significantly among the feedstocks. For instance, lignin ranges from 17% in wheat straw up to 28% in softwood. 3.1.6. Organic residues and others This group refers to the other biomass raw material sources that do not fall into the other categories, i.e. the organic fraction of Municipal Solid Waste (MSW), manure, wild fruits and crops and residues from the food production chain (such as fresh fruit and vegetable). The physical and chemical characteristics of this wide spectrum of biomass resources vary largely. Certain streams such as sewage sludge, manure from dairy and swine farms and residues from food processing are very wet, with moisture contents over 70%. Therefore, these feedstocks are more suited for an anaerobic digestion process to generate biogas, rather than other biofuels or chemicals (Berglund and Börjesson, 2006). Other streams, such as organic MSW, may be more or less contaminated with heavy metals or other elements (Faaij et al., 1997). Clearly, the different properties and characteristic of the biomass wastes require the application of different conversion technologies. Biorefinery Concept: Energy and Material Recovery from Biomass… 109 Table 1. Composition of some lignocellulosic feedstocks. Parameter Water LHV Cellulose Glucan (C6) Hemicellulose Xylan (C5) Arabinan (C5) Galactan (C6) Mannan (C6) Lignin Acids Extractives Ash C H O N S Unit (dry) % MJ/kg % % % % % % % % % % % % % % % % Softwood Switchgrass Corn stover Wheat straw 15 19.6 44.55 44.55 21.9 6.3 1.6 2.56 11.43 27.67 2.67 2.88 0.32 50.26 5.98 42.14 0.03 0.01 15 18.6 35.39 35.39 26.52 22.44 2.73 0.96 0.39 18.17 2.15 11.46 4.28 46.9 5.54 41.96 0.62 0.7 15 18.51 38.12 38.12 25.29 20.25 2.03 0.74 0.41 20.24 4.84 4.78 8.59 46.75 5.49 38.4 0.67 0.1 15 17.56 32.64 32.64 22.63 19.22 2.35 0.75 0.31 16.85 2.24 12.95 10.22 43.88 5.26 38.75 0.63 0.16 Sources: softwood Hammelinck et al., 2005; swithgrass EERE 2008 (biomass sample type: Switchgrass Alamo Whole Plant #94); corn stover EERE 2008 (biomass sample type: Corn Stover Zea Mays Stalks and Leaves w/o cobs #55); wheat straw EERE 2008 (biomass sample type: Wheat Straw (Triticum Aestivum) Thunderbird Whole Plant #154). 3.2. Technological Processes Biomass must be chemically converted for production of biofuels and biochemicals. Obviously, changes are necessary to convert biomass from a solid to a liquid state. As discussed in the previous section, fundamental is the biomass feedstock composition: it generally has too little hydrogen (which must be added), too much oxygen (which must be rejected), and other undesirable elements (such as nitrogen and sulphur) which also must be rejected (Cherubini and Jungmeier, 2008). The aim of each technological process which acts on raw biomass can be summarized in depolymerising and deoxygenating the biomass components. Especially for producing fuels, deoxygenation is particularly important as the presence of oxygen reduces the heat content of the molecules, while some chemical products may require much less deoxygenation, because the presence of oxygen often provides valuable physical and chemical properties to the compound (Lange, 2007). In order to convert biomass feedstock into valuable products within a biorefinery approach, several technological processes must be jointly applied in multiple steps. These 110 Francesco Cherubini and Gerfried Jungmeier technologies can be grouped in 4 main categories: thermochemical, biochemical, mechanical / physical and chemical processes. 3.2.1. Thermochemical processes There are two main thermochemical processes for converting biomass into energy and chemical products. The first is gasification, which consists in keeping biomass at high temperature (> 700°C) with low oxygen levels to produce syngas, a mixture of H2, CO, CO2 and CH4 (Paisley et al., 1998; Spath and Dayton, 2003). Syngas can be used directly as a fuel or can be a chemical intermediate (platform) for production of fuels (FT-fuels, Dimethyl ether, ethanol, isobutene…) or chemicals (alcohols, organic acids, ammonia, methanol and so on). The second most common thermochemical pathway is pyrolysis, which uses high temperatures (300 – 600°C) in absence of oxygen to convert the feedstock into a liquid pyrolytic oil (or bio-oil), solid charcoal and light gases similar to syngas (Bridgwater and Peacocke, 2000; Guo et al., 2001). Their yields vary with process conditions and for biorefinery purposes the treatment which maximizes the production of liquid bio-oil is the most desirable (flash pyrolysis). The application of bio-oil as a transportation fuel is problematic (see following section) and its use as a chemical source of phenols or levoglucosan is still under development (Helle et al., 2007; Meister, 2002; Zhuang et al., 2001). Together with charcoal, it is generally best suited as a fuel for stationary electric power or thermal energy plants. In addition to gasification and pyrolysis, direct combustion is also included among the thermochemical processes (Gani and Naruse, 2007; Senneca, 2007). This is the most common and oldest form of biomass conversion that involves burning biomass in an oxygen-rich environment mainly for the production of heat. Another less widespread thermochemical process is the biomass hydrothermal upgrading (HTU), which can be conducted at different conditions of temperature and pressure and with or without a catalytic mean (Karagöz et al., 2005; Zhang et al., 2002). The purpose of the HTU process is to convert biomass into the so-called “biocrude”, a liquid fuel with an energy density approaching that of fossil fuels which requires additional treatment before to be used as a transportation biofuel. This technology is still at a research and development stage. 3.2.2. Biochemical processes Unlike thermochemical processes, biochemical processes occur at lower temperatures and have lower reaction rates. The most common types of biochemical processes are fermentation and anaerobic digestion. The fermentation uses microorganisms and/or enzymes to convert a fermentable substrate into ethanol, the most common fermentation product, but the production of many other chemical compounds (e.g. hydrogen, methanol, succinic acid, among others) is nowadays object of many activities of research and development. Hexoses, mainly glucose, are the most frequent fermentation substrates, while pentoses (sugars from hemicellulose), glycerol and other hydrocarbons have required the development of customized fermentation organisms to enable their conversion to ethanol (Hamelinck et al., 2005; Lynd, 1996). Anaerobic digestion involves bacterial breakdown of biodegradable organic material in the absence of oxygen over a temperature range of about 30 – 65 °C. The main end product of this process is biogas (a gas mixture made of methane, CO2 and other impurities), which can be upgraded up to > 97% methane and used as a surrogate of natural gas (Berglund and Börjesson, 2006; Romano and Zhang, 2008). Biorefinery Concept: Energy and Material Recovery from Biomass… 111 3.2.3. Mechanical/physical processes Mechanical/physical processes are processes which do not change the state or the composition of biomass, but only perform a size reduction or a separation of feedstock components. In a biorefinery pathway, they are usually applied first, because the following biomass utilization requires reduction of the material size within specific ranges, depending on feedstock specie, handling and further conversion processes. Biomass size reduction is a mechanical treatment process that significantly refers to either cutting or commuting processes that significantly change the particles size, shape and bulk density of biomass. Separation processes involve the separation of the substrate into its components, while with extraction methods valuable compounds are extracted and concentrated from a bulk and inhomogeneous substrates (Huang et al., 2008). Lignocellulosic pre-treatment methods, (e.g. the split of lignocellusic biomass into cellulose, hemicellulose and lignin) fall within this category, even if some hemicelluse is also hydrolized to single sugars (Cadoche and Lopez, 1989; Lasser et al., 2002, Sung and Cheng, 2002). 3.2.4. Chemical processes Chemical processes are those processes which carry a change in the chemical structure of the molecule by reacting with other substances. The most common chemical processes in biomass conversion are hydrolysis and transesterification, but this group also includes the wide class of chemical reactions where a change in the molecular formula occurs. Hydrolysis uses acids, alkalis or enzymes to depolymerise polysaccharides and proteins into their component sugars (e.g. glucose from cellulose) or derivate chemicals (e.g. levulinic acid from glucose) (Lynd, 1996; Sung and Cheng, 2002). Transesterification is the most common method to produce biodiesel today and is a chemical process by which vegetable oils can be converted to methyl or ethyl esters of fatty acids, also called biodiesel. This process implicates the coproduction of glycerine, a chemical compound with diverse commercial uses (Crabbe et al., 2001; Demirabas, 2003; Marchetti et al., 2007). Other important chemical reactions in biorefining are Fisher-Tropsch synthesis, methanisation, steam reforming, catalytic synthesis or reactions, hydrogenation, oxygenation and so on. 3.3. Platforms In biorefinery, the platforms are the intermediates which constitute the link between feedstock and final products. This concept is similar to the petrochemical industry, where the refinery starts with a massive distillation to separate the crude oil into a large number of intermediates that are further manipulated into the desired products. Among the several possible alternatives, the chemicals (or mix of chemicals) which are individuated as the most important biorefinery platforms are the following: biogas, syngas, hydrogen, C6 sugars, C5 sugars, levulinic acid, furfural, pyrolytic oil, oil and organic juice. 3.3.1. Biogas Biogas is a biomass derived gas made of mainly CH4 and CO2. It can be produced either by anaerobic digestion of biological materials or by methanisation of the syngas coming out from gasification. Biogas can be used as such for electricity and heat generation or can be Hamelinck et al. Mozaffarian et al. leading to ethanol. . As in the previous case. FT-fuels. 2006b). leading to 5Hydroxymethylfurfural. acetic acid.. NH3. Hydrogen Hydrogen can be produced by syngas after a water shift reaction process (CO + H2O → H2 + CO2).2-propylene glycol. H2S. producing bioethanol and other chemicals (Kamm et al. The main products that can be obtained from syngas are: ethanol.. 2006b). are arabinose and galactose. formaldehyde and others (Dybkjaer and Christensen. 2004b).3. C6 sugars C6 sugars are the most abundant renewable resource available. 2001. other alcohols and organic acids (such as lactic acid. but it may also contain different contaminants such as nitrogen. Stojic et al. by alkaline water electrolysis (H2O → H2 + ½ O2) or by fermentation of suitable substrates and microorganisms (Spath and Mann.112 Francesco Cherubini and Gerfried Jungmeier upgraded to biomethane by removing CO2 and other undesired elements.3. CH4 and CO2. there are three main chemical conversion pathways for producing fuels or chemicals from xylose: (a) hydrogenation. They can be found in the hemicellulose fraction of lignocellulosic raw materials or as free monomers. by methane after a steam reforming process (CH4 + H2O → 3 H2 + CO). citric acid and others) (Kamm et al. 3. water gas shift reaction (adjusts the H2/CO ratio by converting CO with steam to H2 and CO2) and CO2 removal (with an amine). starch or as a free monomer.. 3. Biomethane can be used as a transportation biofuel.. 3.2. 2003). present in hemicellulose.4. b) acid treatment. 2004a. C5 sugars The most common C5 sugars in biomass feedstocks are xylose and mannose (with xylose having a dominant position). 2004. the syngas undergo a cleaning process in which the contaminats are removed and its main components can be tailored to the needs of the following conversion processes. c) fermentation. hydrogen. producing xylitol. alkali compounds.3. levulinic acid and their derivates. Glucose is the most important C6 sugar and. is present in cellulose. ammonia. (b) acid treatment producing furfural and its derivates. 3. Spath and Dayton. 2003). Other C6 sugars.. as a stationary biofuel for electricity and heat generation or can be transported through the existing gas infrastructure and substituting natural gas in all its existing applications. in Nature.3. by means of methane reforming (which converts CH4 with steam to CO and H2). Spath and Mann. H2. Since these contaminants can lower activity in the FT or other chemical synthesis due to catalyst poisoning. Glucose may be used as substrate for producing energy and material product through mainly 3 pathways: a) hydrogenation. condensable tars. methanol. acetic acid. particulates. It is mainly made of CO.. HCN and COS. (c) fermentation. like H2S (Mozaffarian et al. HCl. leading to sorbitol and 1.3. 2004. Syngas Syngas is the product of the gasification process. Hydrogen can be used either as a fuel or as a chemical reducing agent. 2001.5. A possible reaction mechanism for the production of levulinic acid from C6 sugars is illustrated in Figure 9. Firstly.. cellulose is hydrolyzed to C6 sugars and then levulinic acid is obtained through hydroxymethylfuran (HMF) with an efficiency of 50% (Hayes et al.Biorefinery Concept: Energy and Material Recovery from Biomass… 113 3... Figure 9.. 2000. a polymer constituent coming out from the reaction of levulinic acid with phenols). a fuel produced by the reaction with ethanol) and others (Bozell et al.6. a herbicide which can be produced after a chemical synthesis process). 1999). Hayes et al. Timokhin et al. Its main derivates are: methyltetrahydrofuran (MTHF. ethyl levulinate (EL. δ-aminolevulinic acid (DALA. 2006. diphenolic acids (DA. 2006). thanks to its high reactivity: since it has both a ketone carbonyl group and an acidic carboxyl group.. 2006). Levulinic acid Levulinic acid (C5H8O3) is formed by acid hydrolysis of C6 sugars and can be easily converted to chemical derivates. it can react as a ketone and as a fatty acid. a fuel which can be obtained by dehydratation and hydrogentation).3. . A possible reaction mechanism of levulinic acid from C6 sugars via HMF (Hayes et al. furans..7% (dry weight) of pyrolytic oil.6 (a polyamide).114 Francesco Cherubini and Gerfried Jungmeier 3. Pyrolytic liquid (or biooils) is a multi-component mixture of different size molecules derived from depolymerization and fragmentation of the feedstock. Many of these substances can be extracted. esters. but a wide range of products can also be produced through different chemical reactions. oil and diesel fuel. volatile organic acids. Furfural (C5H4O2). a commodity chemical) and Nylon 6. 1998). to date. The 99. guaiacols. but the utilization of pyrolytic oil as a fuel for stationary generation of steam and power remains. among others (Hill. phenols. a pharmaceutical compound). it is highly corrosive and with a lower heating value of 20 MJ/kg (Bridgwater and Peacocke. the most suitable alternative (Zhang et al. Production of xylose from dehydratation of xylose. is an important chemical because is a selective solvent for separating compounds in petroleum refining.3. bio-plastics). polyamides and polyurethanes (i.3 H2O Furfural Xylose Figure 10. gas. such as phenols.. maleic acid (MA. 2006b.7.e.. and they cannot be mixed. the yield of pyrolytic oil is about 75%. alcohols. a basic component for furan resins. 2000. is composed of acids. 2007). Pyrolytic liquid has a water content of 20-30%.3. Furfural Since there is no synthetic route available for furfural production. a wide range of products can be produced. the elemental composition of bio-oil and petroleum derived fuel is different. syringols. such as: biodiesel (giving glycerin as a co-product). and an oxygen content of 35-40% (but if only lignin is pyrolysed this value can decrease to 20%). Vegetable oil Vegetable oil can be extracted from nearly any oilseed crop for potential use as biofuels or as a chemical substrate. 3. methyltetrahydrofuran (MTHF. levoglucosan and others. this chemical compound is exclusively produced from lignocellulosic biomass by dehydrating C5 sugars (mainly xylose) which are present in the hemicellulose fraction (see Figure 10). dicarboxylic acid (by bio-oxydation). lignin derived phenols and extractible terpene with multi-functional groups.3. 2007). sugars. Therefore.8. . They are made of triglycerides which typically consist of glycerin and saturated and unsaturated fatty acids. Pyrolytic liquid Pyrolytic liquid is the product of the pyrolysis process applied to biomass feedstocks. Vazquez et al. Triglycerides have two chemically reactive sites and thanks to this reactivity. . a fuel additive). among others (Kamm et al. in the case of flash pyrolysis. together with its derivates. aldehydes. such as methylfuran (MF. 2006).. 3. ketones. The main furfural derivate is furfuryl alcohol. Spilae et al.9. Biorefinery Concept: Energy and Material Recovery from Biomass… 115 3. bioenergy and material products. 3. hydrogen.10. 1995). 4.1. or service by identifying energy and materials used and emissions released to the environment. A Life Cycle Assessment study is a tool for evaluating environmental impacts associated with a product.3. fumaric acid (FUMA) and oxygen. Goal and scope definition (ISO 14041). mainly organic acids of different size and proteins. with compilation of data both about energy and material flows and on emissions to the environment. The products of the biorefinery are the following: 1. A typical LCA study consists of the following stages: 1. The investigated biorefinery is a system where several conversion technologies are jointly applied to produce transportation biofuels. . Life cycle inventory (LCI) analysis. 2.. process. The aim of this work is to analyze a biorefinery system by means of LCA. 3. Lindfors et al. 4.. an evaluation by means of Life Cycle Assessment (LCA) of the full production chain. moreover it also allows an identification of opportunities for environmental improvements (Consoli et al. the functional unit and the system boundary of the assessment are described.2. is required. the scope. Assessment of the potential impacts (Life Cycle Impact Assessment. Goal and Scope Definition The goal and scope definition is the first part of an LCA. LIFE CYCLE ASSESSMENT OF BIOREFINERY SYSTEMS: A CASE STUDY 4. LCIA) associated with the identified forms of resource use and environmental emissions (ISO 14042). Interpretation of the results from the previous phases of the study in relation to the objectives of the study (ISO 14043). Transportation biofuels: bioethanol and methyltetrahydrofuran (MTHF). electricity and heat. where the purpose. from supply of raw materials to final use of products. which can be extracted and concentrated in order to become value added products. throughout the life cycle of the case study (ISO 14041). fruits and others. Organic juice Organic juice refers to the liquid phase which can be obtained after pressing of fresh biomass feedstock such as grasses. This organic fraction is extremely reach of chemical compounds dispersed in an aqueous solution. Introduction to LCA In order to investigate all the environmental aspects of biorefinery systems. 1993. Biomaterials: furan resins. vegetables. 2. 4. Bioenergy carriers: biomethane. This biorefinery produces bioethanol from fermentation of C6 sugars. because reduction of GHG emissions and decrease of fossil fuel consumption are two driving forces of biomass utilization strategies. 4. The feedstock is assumed to be collected from industries. ./MJpellets.1. and transported to the biorefinery plant (100 km). processing and delivery of raw materials to biorefinery gates are equal to 1. a biorefinery is characterized by multiple useful outputs (both energy and material products). Process scheme of the investigated biorefinery.47 kJ/MJpellets (Gemis. Environmental concerns are focused on energy and greenhouse gas (GHG) balances of biorefinery and fossil reference systems.2. which was addressed using different allocation methods. furfural from hydrolysis of C5 sugars (which is then chemically converted to fuel additive and other chemicals). where it is dried and pelletized. The software tool Gemis is used to model LCA calculations and as database source (Gemis. As a direct consequence of the definition. transported to a pellet facility (20 km). biorefinery system performances are investigated by means of several indices and indicators such as conversion yields and mass. The results of the biorefinery systems are shown in comparison with a fossil reference system providing the same amount of energy and chemical products from fossil sources.94 g CO2-eq. hydrogen and oxygen through alkaline water electrolysis and biomethane and fertilizer via anaerobic digestion of wastewaters (Figure 11). Biorefinery: scope and system boundaries Wood industrial residues are the raw materials for this biorefinery system. electricity and heat from combustion of lignin and residues. 2008). MTHF H2 C5 sugars Pretreatment Feedstock C6 sugars Acid treatment Furfural Chemical reactions Furan resins O2 FUMA Hydrolysis Fermentation CO2 Distillation Bioethanol Fertilizer Wastewater Legend Feedstock Intermediate Energy Product Anaerobic digestion Biogas Process Output not exploited Lignin & residues Combustion Material Product Electricity Heat Upgrading Alkaline water electrolysis Biomethane Hydrogen Oxygen Figure 11. This fact gives rise to an allocation issue. while the primary fossil energy consumption is 8. The GHG emissions estimated for collecting. exergy and C efficiencies.116 Francesco Cherubini and Gerfried Jungmeier Wood industrial residues are used as raw materials and are delivered to the plant in the form of pellets (chemical and elemental composition in Table 1). Finally. 2008). energy. 2nd reaction: C5H6O + 2H2 → C5H10O.... Conversion of furfural to MTHF via methylfuran. 2006b. Conversion of furfural to FUMA via oxidation. 2000). overall yield 76%). molar efficiency 80%. . 15% to furan resins. Furfural is then converted to the following products (Kamm et al. molar efficiency 95%. as illustrated in Figure 12 (1st reaction: C5H4O2 + 2H2 → C5H6O + H2O.Biorefinery Concept: Energy and Material Recovery from Biomass… 117 The lignocellulosic feedstock (530 ktonnes/a) is pretreated through an acid catalyzed hydrolysis step which splits the raw material in 2 flows: a solid flow containing cellulose and lignin and a liquid flow containing the hydrolyzed C5 sugars. furfuryl alcohol or other compounds containing a furan ring. 2002). obtained with an efficiency of 90% by the following reaction: C5H10O5 → C5H4O2 + 3H2O (Kaylen et al. The liquid flow is made of C5 sugars (xylose and arabinose monomers coming from hemicellulose hydrolysis with an efficiency of 95%) which are treated with a dilute sulfuric acid solution at low temperature for a short period of time. both reactions needs a Ni catalyst. The product output is furfural. Figure 13. made by polymerization of furfural. • • • 70% to the fuel additive methyltetrahydrofuran (MTHF) by reduction with H2 via the intermediate methyl furan. Vazquez et al. 2007): Figure 12. The pretreatment occurs at temperatures higher than 160°C and with a reaction time of 2-10 minutes (Sun and Cheng. 15% to fumaric acid (FUMA) by oxidation (followed by opening of the furan ring) in presence of a V2O5 catalyst (C5H4O2 + 2O2 → C4H4O4 + CO2) (Figure 13). Undesired methane emissions to the atmosphere during digestion and biogas treatments are estimated to be 3.47 mg/MJ and the upgrading of biogas to biomethane (CH4 content greater than 97%). while the quantities come from (Kaylen et al. Other releases of GHG emissions are the following (Gemis. urea. 2008). Lignin (lower heating value 22...9 MJ/kg) and the unconverted cellulose and hemicelluse (lower heating value15. 2008). 2000). lime. 2006).4 ktdry and generate biogas at a rate of 6 GJ/tdry (Berglund and Börjesson. 2006). Emissions from combustion of biomethane in its final use (0. assumed to be 3 g CO2eq. These wastewaters have a total dry matter content of 54.63 MJ/kg) are combusted to produce electricity and heat with an efficiency of 26% and 44%. 2008): • • • Emissions from lignin (and biomass residue) combustion in turbine. 2000). phosphporic acid and sodium sulfite) are calculated using the software tool Gemis./km (with a specific consumption of 2. Fossil energy consumption and GHG emissions related to the supply of auxiliary materials (such as sulphuric acid.118 Francesco Cherubini and Gerfried Jungmeier The reactants H2 and O2 are internally produced in the biorefinery system by alkaline water electrolysis./MJ of heat set free from combustion. which generates H2 with an energy efficiency of 77% and O2 at a rate of 7. while 9% is set aside for bacteria cultivation. from mannan to mannose 89%. by removing impurities and CO2. all the C6 sugar monomers are then fermented to bioethanol with the following efficiencies (Hamelinck et al. Emissions from combustion of bioethanol in a passenger car. 89% and 22% of the generated H2 and O2 are required in the production of MTHF and FUMA. Ashes are delivered to landfill. estimated to be 1. Wastewaters coming from xylose conversion to furfural and C6 sugar fermentation are anaerobically digested to produce biogas. needs 5% of the energy content of the biogas (Gemis. 2005): • • glucose to ethanol 93%.. The conversion efficiencies are the following (Hamelinck et al. galactose and mannose to ethanol 90%. About 2% of cellulose is lost during acid recycle activities. Since H2 and O2 are required for the chemical conversion of furfural to its derivates. 20% of the total electricity output is destined to water electrolysis. The solid fraction coming out from pretreatment step is subjected to a further hydrolysis to hydrolyze the remaining cellulose and other C6 polymers and separate lignin.67 g CO2-eq.59 g CO2-eq. sodium hydroxide.92 g/gH2 (Gemis. .45 MJ/km). from galactan to galactose 82%./MJ). Bioethanol is finally recovered via distillation. potassium chloride. The produced biogas has a heating value of 24 MJ/m3 and methane content of 60% (Alzate and Toro. 2005): • • • from cellulose to glucose 90%. respectively (De Feber and Gielen. in chemical industry and in the manufacture of polyester resins and polyhydric alcohols. 15% in unsaturated polyester resins. it is not accounted for as a GHG and the above emission factors are mainly due to N2O and CH4. while 7. 22% as food acidulant. 2007). The market share of products produced from biomass is expected to rise from the current level of 5% to 20% in the short run (Sauer et al.65 GJ of electricity and 0.1 GJ of heat per tonne of dry matter in wastewaters (Berglund and Börjesson. Functional groups that must be introduced by costly oxidative process steps into oil are already available in plant materials. heat or transportation service. 5% as plasticizers and 17% miscellaneous (including lubricating oils and oil field fluids. O2 and fertilizers. 2007). esters. It is mainly used in medicine.g. This biorefinery plant requires 0. Fumaric acid (HO2CCH=CHCO2H) is a carboxylic acid currently produced from the oxygenation of the fossil derived product benzene. lignin and biomass residues. In fact. The major uses of furan resins are as foundry binders and their production in biorefinery is assumed to play a major role in chemical conversions of furfural. biomethane and MTHF) releases CO2 which has a biological origin. no benefits from this material output are considered in LCA calculation. .60 MWh of heat per ton of feedstock for producing bioethanol and furfural (Kaylen et al. The uses are the following: 35% as paper size resins. Another chemical product is oxygen in its diatomic form (O2). which can be used in a lot of chemical applications like oxidizing agent.. Since the combustion of these biofuels (e. furfuryl alcohol or other compounds containing a furan ring. lacquers.Biorefinery Concept: Energy and Material Recovery from Biomass… 119 Because of a lack in available data. 2008). but an economical production process will create new markets by providing new opportunities for the chemical industry. material products are not used for an energy generation purpose but for their chemical or physical properties. Energy products are those products which are used for their energy content. due to a lack of data on its use and fossil fertilizers replacement rate. Fumaric acid has an annual production of 12 ktonnes but a projected market volume of more than 200 ktonnes (Sauer et al. succinic acid and formic acid could replace the petroleum-derived commodity chemical maleic anhydride.. whereas the current market for the organic acids mentioned is small. carboxylating agent for styrenebutadiene rubber) (CMR. 6% in alkyd resins.. Biorefinery material products All the products produced by biorefinery systems can be grouped in two broad categories: material products and energy products. The chemical structure of energy and material products of the investigated biorefinery system are reported in Figure 14. 4. The anaerobic digestion step and following biogas upgrading requires 0. For example. 2000). inks. or by reaction of these furan compounds with other molecules (not over 50%). Fertilizers are the residues of the anaerobic digestion step which can partly replace the use of synthetic fertilizers. 2006). bioethanol. providing electricity. these products are favourable from a chemical point of view. The material products of the analyzed biorefinery system are fumaric acid. the GHG emissions from MTHF combustion and its specific consumption in cars are assumed to be equal to bioethanol. The market for maleic anhydride is huge. However. 2008).16 MWh of electricity and 0. It is noteworthy that for many biomass derived chemicals the actual market is small. Furan resins are made by polymerization or polycondensation of furfural. in food industry as a food acidulent.2. On the other hand.5 kJ of heat per g water are needed to distil the water required by the electrolysis process (Gemis. furan resins.2. 2. MTHF. The production of large quantities of biofuels or fuel additives via renewable feedstocks offers perhaps the greatest potential for mass-market penetration of biorefineries. Biorefinery energy products The energy products of the biorefinery are bioethanol. thereby reducing fuel evaporation and improving air quality. Hydrogen is produced via alkaline water electrolysis and is used as a reducing agent for conversion of furfural to MTHF at the biorefinery plant site. The remaining H2 fraction is delivered to the market.120 Francesco Cherubini and Gerfried Jungmeier Figure 14. MTHF. Bioethanol is one of the most common transportation biofuels currently produced in the world and can replace gasoline in vehicles. Chemical structures of the bioproducts from the biorefinery: bioethanol. MTHF also boasts a high octane rating (87) and a low vapour pressure. biomethane. Biomethane is obtained from upgrading of biogas by removing CO2 and other undesired elements. MTHF is a very important compound because it can be added to gasoline (to be blended at the refinery rather than later in the distribution process) or bioethanol up to 30% by volume without effects on performances and engine modification.3. . Biomethane can be used as a transportation biofuel or can be transported through the existing gas infrastructure and substituting natural gas in all its existing applications. like H2S. hydrogen. electricity and heat. Using MTHF as a fuel additive increases the oxygenate level in gasoline without adversely affecting engine performance. Properties of MTHF as fuel are reported in Table 2. furfural and fumaric acid 4. Methyltetrahydrofuran (MTHF) is produced from furfural by reduction to methyl furan. biomethane. This can be seen as an innovative way to safely store H2 in a transportation biofuel. which is then reduced to MTHF (both reductions occur with H2). it has a higher specific gravity and hence mileage is competitive. Although it has a lower LHV than gasoline. H2. Fossil reference system LCA environmental performances of the analyzed biorefinery system are compared with those of a fossil reference system based on oil refinery.2. heat. . Property Boiling point (102 mmHg) Boiling point (Atm. Selected properties of MTHF as a transportation biofuel. Part of this electricity and heat production is used to meet the plant energy demand and the rest is delivered to the public grid. Comparison between production chains: biorefinery system vs. 4.) Flash point Reid vapour pressure Lower heating value Specific gravity Octane rating Unit °C °C °C psig MJ/kg MTHF 20 80 11 5. methane) Figure 15. fossil reference system. producing the same amount of energy and chemical products.4.7 32 0. electricity. ReferenceSystem Biorefinery Collection Wood residues Transport Natural decomposition Natural gas Oil Extraction & Conveyance Extraction & Conveyance Transport Transport Power plant Refinery Processing Air Steam reforming Biorefinery plant Processing Distribution Electric net Distribution Distribution Heavy oil Gasoline Distribution Heating plant Distribution Heating network Gasoline vehicles Distribution O 2 H2 Biofuel vehicles Heating Chemicals Electric net network andH2 Chemicals Productsandservices (transportation.813 80 Electricity and heat are produced by combustion of lignin and process residues. A comparison between the two systems is illustrated in Figure 15. chemicals.Biorefinery Concept: Energy and Material Recovery from Biomass… 121 Table 2. If compared in this manner. the differences between the two systems producing the same product/service can be presented. reported in the right part of the table. considering all the material and energy inputs and emissions associated with its life cycle stages: production of the raw fossil fuel. b ./MJ). The fossil reference system is dealt with in a similar way. 2008). Table 3.29 1. efficiency 85%.13 0. 1997). have been calculated by means of the LCA software tool Gemis (Gemis. Particular importance should be given to the numerous co-products which a biorefinery may produce. c Heavy oil boiler for industrial process heat.36 Mainly fossil energy (> 98%) Large scale gas-fired combined-cycle (CC) power plant with efficiency of 57% and low NOx burner./unita 2. because they can have relevant implications in the assessment of the overall system./unit Gasoline km 189 b Electricity from natural gas MJ 120 c Heat from oil MJ 106 Conventional methaned MJ 76 Gasoline km 189 H2 Furan resins Fumaric acid H2 from natural gas Epoxy resins Conventional fumaric acid MJ g g 72 6. all the energy and material inputs and emissions occurring for planting and harvesting the crop (or collect the raw materials). transporting and storing of the feedstock.05 O2 Fertilizer Conventional O2 (from air) No benefits g 0. In the right part of the table the environmental impacts.. distribution and combustion. or. Along the whole process chain. in terms of GHG emissions and total energy demand. refining. Table reporting the conventional alternatives of the different products of the biorefinery and their specific factors for GHG emissions and fossil energy consumptions. processing the feedstock into fuels and products. At the end of the biorefinery chain a certain amount of useful energy and products are supplied.36 1. efficiency 85%.32 1.96 1. storage.24 0.07 0. it is assumed that 1/3 of the electric capacity comes from the steam turbine. biomass C taken as biomass waste from the forest sector. a Biorefinery Bioproducts Bioethanol Electricity Heat Biomethane MTHF Fossil reference system Conventional alternative Unit g CO2-eq.122 Francesco Cherubini and Gerfried Jungmeier The biorefinery chain starts at the top with carbon fixation from the atmosphere via photosynthesis.15 g CO2-eq.001 MJtot. Table 3 reports the bioproducts produced by the investigated biorefinery and the fossil conventional counterparts that they replace. of the fossil derived products are listed: these are the GHG emissions and energy consumption saved by the biofuels and biochemicals of the biorefinery. These values. as it occurs in this case study.07 1. d Including emissions from combustion in natural gas boiler (66. distributing and final use of the products must be accounted for in a life cycle perspective (Schlamadinger et al.31 2. electricity produced from natural gas turbine and heat generated from a heavy oil boiler.Biorefinery Concept: Energy and Material Recovery from Biomass… 123 The transportation biofuels bioethanol and MTHF replace conventional gasoline as a liquid transportation fuel in passenger cars. It is assumed that furan resins replace epoxy resins. is an organic compound with two phenol functional groups and constitutes a building block of several important polymers and polymer additives. Reaction between BPA and epichlorohydrin and formation of epoxy resins. are illustrated. Epoxy resins are polymers originated from polymerization of epoxy monomers. and are produced by reaction of epichlorohydrin and bisphenol-A. Epoxy resins are used as adhesives (they are one of the few adhesives that can be used on metals). Epichlorohydrin is a highly reactive epoxide and polymerizes upon treatment with acid or strong base. commonly abbreviated as BPA. biomethane (fed to the national grid) replaces conventional natural gas in its applications as a stationary fuel while bio-H2 replaces conventional hydrogen production from steam reforming of natural gas. as materials in electronic circuit boards and for patching holes in concrete pavement. Figure 16. epichlorohydrin and the reaction mechanism leading to epoxy resins. the chemical structures of BPA. respectively. . In Figure 16. Regarding the two remaining biofuels. their GHG emissions and fossil energy requirements were been estimated considering their production chains in the current oil refinery. Concerning the chemicals. as protective coatings. It is assumed that the electricity and heat produced by the biorefinery substitute. bisphenol A. in this study. Therefore. 2004). it undergoes additions across the double bond. This weak acid forms a diester. where multiple energy and material products are produced. which are subtracted to the total GHG emissions and the remaining emissions are completely assigned to the main product. the identification of one of the output as main product is an arbitrary choice and can be a difficult decision in biorefinery systems. where multiple useful and valuable outputs are produced. 2005). 4. However. 4. Ekval and Finnveden. Scientific LCA publications show benefits and disadvantages of several allocation methods (Curran 2007.2. Furthermore.6 Allocation Allocation in LCA is carried out to attribute shares of the total environmental impact to the different products of a system. all the input flows reported in the following inventory list and the final results of GHG emissions and cumulated primary energy demand are referred to this amount of biomass input. 2001. this method relies on identification of a main product and the environmental benefits of coproducts are assumed as credits. they cannot be expressed per hectare basis or per unit of output. About 100 million tonnes of O2 are extracted from air for industrial uses annually. The most common method to recover O2 is to fractionally-distill liquefied air into its various components. Frischknecht 2000. 2001). and it is an excellent dienophile. For instance. Wang et al. In fact. the results of a bioenergy system from dedicated biomass crops should be expressed on a per hectare basis. The question of the most suitable allocation procedure is still an open issue.124 Francesco Cherubini and Gerfried Jungmeier Conventional fumaric acid is currently produced from oxygenation of benzene (C6H6 + 4O2 → C4H4O4 + 2 CO2H2). is the amount of biomass treated per year by the biorefinery: 530 ktonnes/a. The most suitable functional unit is then the unit of biomass input which. One of the main purposes of the functional unit is to provide a reference to which the input and output data are normalized and the basis by which the final results are shown. This procedure (also called substitution method) has the advantage to avoid allocation issues while has the disadvantage to make the system too complex. biorefinery results have the need to be independent from the kind of biomass feedstock (dedicated crops or residues) and from the conversion processes which act on the biomass raw materials. when possible. This concept is extremely important for biorefinery systems. below zero) of the . As a consequence. This method relies on the expansion of the product system to include the additional functions related to the co-products.e.5. The chemical properties of fumaric acid can be anticipated from its component functional groups.. The O2 produced by the biorefinery plant (via alkaline water electrolysis) replaces the molecular oxygen (O2) that is currently produced from processing of air. this situation can even lead to a negative value (i. Functional unit The functional unit is the foundation of biorefinery systems LCA: it sets the scale for comparison of different technological routes which a biomass feedstock can undergo in order to be converted to biofuels and chemicals. system expansion is not recommended when an elevated number of high quality outputs is produced.2. in order to be comparable. from which O2 is separated. Therefore. especially if multiple co-products are present (like in biorefineries). The ISO standards suggest to avoid allocation by expanding system boundaries. since the available area for the production of biomass raw materials is the biggest bottleneck for the production of biofuels (Schlamadinger et al. with nitrogen N2 distilling as a vapor while oxygen O2 is left as a liquid (Emsley.. market values of products can fluctuate consistently according to the reference year. Allocation based on economic values focuses on external characteristics of the products and has the disadvantages that do not take into account the environmental perspective and the physical properties of the products. Pierru 2007). 1996). biomethane 34. because is based on their “value” in human societies. the main product is assumed to be bioethanol and the environmental benefits of co-products are assumed as credits. they shall reflect the way in which the inputs and outputs are changed by quantitative changes in the products or functions delivered by the system (Curran 2007). Oxygen does not have a heating value.08 MJ/kg).3. the GHG and fossil energy saved by the co-products) are then subtracted to the total GHG emissions and energy consumption of the whole system. input and output data might be allocated between co-products in proportion to thermodynamics parameters (such as energy or exergy content of outputs) or to the economic value of products.. MTHF 32 MJ/kg.Biorefinery Concept: Energy and Material Recovery from Biomass… 125 burdens allocated to the main product. hydrogen 114 MJ/kg. Allocation methods based on thermodynamics parameters (energy and exergy content) and economic values of the products share the environmental burdens among the different outputs. lacking of a correct logical relation) and results in misleading conclusions if there are some products which are not used as energy carriers (e. If system expansion cannot be applied. the resulting environmental burdens are completely assigned to the main product. Allocation based on exergy overcomes this inconsistency but can be problematic to be applied because of the difficulties for estimating the exergy content of substances (especially new bio-based products). without identifying a main product.e. in addition. Allocation based on energy content of products can be easily carried out but its application is inconsistent (i. The energy content of the material products has been estimated by means of the Dulong’s formula (furan resins 21. These credits (i. Concerning allocation based on energy content. production chain and geographical location (Ekvall. 4.22 MJ/kg. calculated thanks to the fossil reference systems. i. . In order to do not disregard these issues and provide a sensitivity analysis on how the different allocation procedures affect the final results.e. Where physical relationship alone cannot be established or used as the basis for allocation. Where system expansion cannot be applied and the allocation cannot be avoided. 2001. Exergy content of products are collected from a specific database (Ayres et al. Concerning system expansion. FUMA 9.e. all the above mentioned allocation methods are applied to the biorefinery system assessed in this chapter. for biofuels the following heating values are considered: bioethanol 27 MJ/kg.g. The results focus on two types of impact categories: greenhouse gas (GHG) emissions and cumulative primary energy demand.75 MJ/kg. ISO norms suggest that the inputs and outputs of the system should be partitioned between its different products or functions in a way which reflects the underlying physical relationships between them (physical allocation). the inputs should be allocated between the products and functions in a way which reflects other relationships between them. chemicals). Life Cycle Impact Assessment Life Cycle Impact Assessment (LCIA) stage deals with the evaluation of environmental impacts of the biorefinery system and fossil reference system over their whole life cycle. conversion processes. which is a measure of how much a given mass of GHG contributes to global warming relative to a reference gas (usually CO2) for which GWP is set to 1. energy. 1. while the exergy contents of the molecules are derived from (Ayres et al. with equivalency factors. Product Unit Transportation (bioethanol) Price $/kg 1. Their effect on global warming can be assessed by an index called Global Warming Potential (GWP). 1996).126 Francesco Cherubini and Gerfried Jungmeier Table 5 reports the prices of the products for the allocation based on economic values. 2008). the mass. Using this index. Estimate on the basis of the price of epoxy resins c The price is referred to low grade fumaric acid d Average electricity price for households in the US e Price based on energy content of replaced natural gas f Average price natural gas for households in the US g Average estimated price of H2 in future markets (Ducharme et al. . GWPs of CO2. 2005) f Average O2 price for laboratories The first impact category refers to all the GHG emissions released for feedstock production. 2007). one can calculate the equivalent CO2 emission by multiplying the emission of a GHG by its GWP.09 f $/kg 8. the cumulative primary energy demand accounts for all the life cycle stages. from feedstock provision to final use of products. In order to gain information concerning performances and conversion efficiencies of the biorefinery system. For a 100-year time horizon. exergy and carbon efficiencies are carried out through the whole biorefinery conversion chain. price in market not available.29 FUMA c d Electricity e Heat f Biomethane $/GJ 9. The C content of the different feedstock components and final products are estimated and the C balance of the system calculated according to the methodology depicted in (Cherubini and Jungmeier. transport./gemission (IPCC. respectively. renewable and other energy demand.78 $/GJ 9. Similarly. These emissions are accounted for and converted to g CO2-eq. The same impact categories are evaluated for the fossil reference system as well.29 g $/GJ 35. with the intent to make comparisons and quantify savings..06 $/L) b New chemical commodity.93 H2 a a O2 Calculated on the basis of gasoline price in the US (1. The primary energy demand is divided into fossil.31 Furan resinsb $/ton 3555 $/ton 1278 $/GJ 27.. CH4 and N2O. List of prices of biorefinery products to be used in the allocation procedure based on economic values. provision of auxiliary materials and final use of the products. CH4 and N2O are. Table 5.34 Transportation (MTHF)a $/kg 1. 25 and 298 g CO2-eq. The analysis considers three long lived GHGs released by human activities: CO2. 07 kt kt TJ TJ TJ TJ kt Environmental impacts (including heat): Total GHG emissions 336 CO2 322 N 2O 7. Birefinery System Product/service: Transportation (bioethanol) 1. where the results of the biorefinery and fossil reference systems are also shown.Biorefinery Concept: Energy and Material Recovery from Biomass… 127 4.34 333 224 261 13. GHG emissions and primary energy demand of biorefinery system and fossil reference system. Biorefinery shows a relevant decrease of total GHG. providing the same quantities of products and services.61 Fossil energy saved 4./a t CO2-eq.7 7. of which 208 TJ/a fossil energy. of which 4736 TJ/a fossil energy./a kt CO2-eq.527 10. biofuels) combustion steps.231 9. the fossil reference system releases 336 kt CO2-eq.9 Environmental impacts: Total GHG emissions 36.22 CH4 0.91 3.858 Fossil 208 Renewable (biomass) 10.8 CO2 27.772 4. ./a CO2-eq.34 Electricity 333 Heat 224 Biomethane 261 H2 13./a kt CO2-eq./a kt CO 2-eq.204 Mio km Epoxy resins (from fossil) FUMA (from fossil) Electricity (from natural gas) Heat (from oil) Natural gas H 2 (from natural gas) O2 (conventional./a CO 2-eq. Quantities of final products.05 Excluding heat credits GHG emissions saved 276 0. Table 6.474 4./a kt CO2-eq.07 Fertilizer (no benefit) 36.082 Transportation (MTHF) 122 Furan resins 2. The biorefinery releases about 36./a and requires 4772 TJ/a. because of the biomass (lignin.1.27 CH4 7./a 4.6% of fossil energy in respect with its fossil reference system.8 kt CO2-eq./tdrywo od TJ/a GJ/tdrywood Primary energy demand Fossil Renewable Others TJ/a TJ/a TJ/a TJ/a kt kt kt kt CO 2-eq.39 Mio km Mio km kt kt TJ TJ TJ TJ kt ktd ry Fossil Reference System Product/service: Transportation (gasoline) 1.15 kt CO2-eq.495 Others 16 GHG and energy savings With heat credits GHG emissions saved 300 0.0 N2O 9. residues. On the other hand./a kt CO 2-eq.736 7 25 4. In Figure 17.69 kt CO2-eq./a and requires 10858 TJ/a of primary energy. Results and interpretation The final quantities of products produced are reported in Table 6 (upper part).440 6 24 This means that the biorefinery system is able to save 89% of GHG emission and 95.3.7 O2 7. from air) 2./a t CO2-eq. CO2 and CH4 emissions. the GHG emissions of the biorefinery and fossil reference system are compared. while it has a slight increase in N2O emissions./a kt CO 2-eq.61 Primary energy demand 10.91 FUMA 3./a TJ/a TJ/a TJ/a TJ/a Primary energy demand Fossil Renewable Others TJ/a TJ/a TJ/a TJ/a kt CO 2-eq./tdrywo od TJ/a GJ/tdrywood Environmental impacts (excluding heat): Total GHG emissions 313 CO 2 299 N 2O 6./a CO 2-eq.76 CH 4 7./a kt CO2-eq.66 Fossil energy saved 4. Comparison between GHGs of biorefinery and fossil reference system. pelleting and transport).5% H2 (from natural gas) 987 0. with the following shares: • • • 61% of these emissions comes from feedstock provision (e. sodium hydroxide (5%) and others.61 Biorefinery 7 8 Fossil reference system Figure 17.3% O2 (conventional) 509 0.8 kt CO2-eq. 16% from lignin and process residue combustion for CHP production (i. Going into details. distribution and final use of products are responsible for an emission of 3.7%). emissions of CH4 and N2O)./a are released by feedstock production and biorefinery plant activities.1% Natural gas 21. sulfuric acid. about 33 kt CO2-eq. Fossil reference system Product/service kt CO2-eq.8% Heat (from oil) 23.2% Electricity (from natural gas) 39.00% Total GHG emissions . GHG emissions of the fossil reference system./a 250 Total GHG 200 CO2 N2O 150 CH4 100 50 37 27 9 - 0. collection of wood residue. Table 7.8 7./a % Transportation (gasoline) 227 67.128 Francesco Cherubini and Gerfried Jungmeier 336 350 322 300 kt CO2-eq.6% FUMA (from fossil) 4.9 6.8 11.e.2% 336 100.3% Epoxy resins (from fossil) 17./a (coming from combustion of transportation biofuels in passenger cars (95%) andfrom combustion of biomethane in its final application (5%)).g.31 1.7 5. In addition to these emissions. phosphoric acid (5. 23% from manufacturing of auxiliary materials such as urea (9%). followed by electricity (12%) and then other products. More than half of the GHG emissions are due to feedstock provision. Detailed information concerning the contributors to the total GHG emissions of the fossil reference system are reported in Table 7. collection. The differences between biorefinery systems with and without process heat utilization are reported in the . Results highlight both the importance of generating high quantities of electricity and the benefits deriving from an utilization of the process heat produced for achieving high GHG emission and fossil energy savings. In the fossil reference system. It is assumed that the fossil reference system produces electricity from natural gas but the savings would be larger if. “Other” includes wastewater treatment. processing and delivery of wood residue pellets. fundamental is the possibility to use it in an application located in the surrounded of the biorefinery. a fundamental role is played by the fossil reference system considered. the total GHG emissions are mainly due to gasoline (68%). waste disposal (mainly ashes) and uncontrolled CH4 emissions from anaerobic digestion. for instance. Concerning the fossil reference system. the higher the savings. In the determination of the magnitude of these savings.5% in cars 10% 129 Other 0. Concerning electricity. The primary energy demand of biorefinery system and fossil reference system has similar contributions than those of GHG emissions.Biorefinery Concept: Energy and Material Recovery from Biomass… Biomethane combustion Biofuel combustion 0. Contributions from all the stages to the total GHG emissions of the biorefinery system are illustrated in Figure 18. Regarding the heat. heat is assumed to be produced from oil and even in this case. i. Contributions to the total GHG emissions of the biorefinery system. environmental savings would be larger if coal-derived heat is replaced.e. the lower the share of electricity sent to alkaline water electrolysis. maximizing the environmental benefits which can be gained. electricity from coal or oil is displaced.5% Manufacture of auxiliary materials 20% Feedstock provision 55% Residue combustion 14% Figure 18. energy.49 C conversion efficiency from wood to EtOH 22./a (0. Table 8. furan resins. Comparison of the biorefinery with its fossil reference system shows that the biorefinery can reduce GHG emissions of about 299. this energy efficiency decreases to 35%.45% C conversion efficiency from cellulose to EtOH 56.05 GJ/tdry wood).66 t CO2-eq.22 and 0. FUMA and O2) constitute 2. electricity and heat) store about 37% of the raw material energy content. Conversion yields and mass.96% of the total mass of the dry feedstock. As a consequence. while the aforementioned . The reason is that a biorefinery system is made of several conversion steps and biomass undergo chemical reactions and changes of state.6 kt CO2-eq./tdry wood) and save 4527 TJ/a of fossil energy (10.15% Exergy conversion efficiency: with heat 44.38% without heat 42. energy and exergy efficiencies of the biorefinery system. the energy content of biomass feedstock.e. only final energy outputs included) t/tdry t/tcell t/tdry t/txylan Biorefinery system performances in terms of product yields and mass.86% a Material products per t of feedstock (tprod/tdry wood) 2. The material products of the biorefinery (i.28% without heat 35.04 t per tonne of dry feedstock.12% C conversion efficiency (from feedstock to products) 29.95% a Only material products included (e. H2.04 Furfural yield per ton of xylan 0. and the savings of fossil energy are relevant (almost 96%). In fact.e.38%. furan resins. it is mainly constituted (97%) by renewable energy. FUMA.98% Furfural yield per t of feedstock (dry) 0. carbon. while final net energy products (bioethanol. Without heat.35% C conversion efficiency from hemicellulose to furfural 74.130 Francesco Cherubini and Gerfried Jungmeier lower part of Table 6: GHG and fossil energy savings are about 8% lower if heat is not used to substitute oil-derived heat. the provision of biomass with sustainable practices is a crucial point to ensure a renewable energy supply to biorefineries. which have energy efficiencies higher than biorefinery. Even if the biorefinery system requires more than twice the primary energy demand of the fossil reference system. exergy and C conversion efficiencies are reported in Table 8. but the yields increase up to 0.g. The overall C conversion efficiency of the plant from feedstock to products is 29. Ethanol yield per t of feedstock (dry) 0.68 C conversion efficiency from wood to furfural 5.15% and the exergy conversion efficiency is 44. i. MTHF. biomethane. and O2) b Energy feedbacks to the plant subtracted (i. production of heat from wood combustion can reach efficiencies higher than 85%.96% Energy products (net) per GJ of feedstock (GJprod/GJwood)b: with heat 37.22 Ethanol yield per ton of cellulose 0. Bioethanol and furfural yields are respectively 0.78 t of furfural per tonne of xylan.49 t of bioethanol per tonne of cellulose and 0.e. A comparison can be done with other biomass conversion systems. while in CHP application the overall energy efficiency is around 80%. 18 2.99 0.6 credits kt CO2-eq.07% 2./a 25.26% 4./a kt CO2-eq. For instance.69% 0.78% 0. Allocation based on energy and exergy content of products show similar results also for the other energy products and chemicals.8 0.68% 2./a 0. FUMA and mainly oxygen.8% 25.30% 0.86% 8.11% 1.6 produc t kt CO2-eq. During fermentation almost half of the C in C6 sugars is converted to the useless product CO2./a 2.41% 25.Biorefinery Concept: Energy and Material Recovery from Biomass… 131 conventional biomass system mainly involve one step (biomass combustion).6 39. where the GHG emissions of the biorefinery system are allocated.01 1.83% 6. while decreasing the environmental burdens assigned to electricity. Results of these biomass derived products and services can be compared with those derived from oil refinery (reported in Table 3).59 0. The allocation criteria are based on energy content.05 3.98 8.22 0. such as furan resins. The specific GHG emission factors for each product according to the allocation procedure are listed in Table 10. Table 9. In particular./a kt CO2-eq.47 0.02% 2.8 23.29 3.83 1.31 17. Allocation results The allocation procedures previously described are applied in order to share the environmental burdens of the biorefinery among the different products.14 2.62 0.60% 0. Results are reported in Table 9. exergy content and economic value of products.13 - 1.38% 4.64% 5./a kt CO2-eq./a kt CO2-eq./a kt CO2-eq.1 68.8 21. heat and biomethane. without microorganisms) is about 75%.36 6.e.25% 9. An attempt to avoid allocation through system expansion was also done.3.80 0. Allocation of the GHG emissions to the biorefinery products using different allocation methods. i. while allocation based on economic values increases the shares of chemical products. these factors can be applied in a LCA if these products are used as auxiliary materials in a future biobased society.60 1. are reported.36% 0. GHG emissions per unit of product. In this table. energy and C conversion efficiencies of the biorefinery are lowered by the fermentation step. Allocation method Unit Transportation (bioethanol) Transportation (MTHF) Furan resins FUMA Electricity Heat Biomethane H2 O2 Energy Exergy Economic value System expansion main -97.51 credits credits credits credits credits credits credits In Figure 19.29% 0. GJ for electricity and heat. g for chemicals and gaseous biofuels.09% 2.2. For . all the allocation criteria lead to similar results. the influence of the allocation methods on GHG emissions allocated to biorefinery products is shown.3% 25.7 69. It can be noticed that.90% 1. where C6 sugars are converted to bioethanol: C efficiency from cellulose to bioethanol is about 57% while from hemicellulose to furfural (a chemical pathway.75% 0.9% kt CO2-eq.00% 0.41 0.09 3. especially concerning transportation biofuels (bioethanol and MTHF). besides system expansion which uses a different approach.02 0.79% 8.33 2. km driven for biofuels.11 0. allocation can be performed considering the same shares of the total GHG emissions of Table 9. Concerning the cumulated primary energy demand.49 0.82 7.45 5.4 68. thus lowering the overall efficiency of the process.90% 7.48% 2./a kt CO2-eq. 4. e q .21 0.00 credits Biomethane g CO2-eq.09 0.09 0.25 5.38 210./km).20 System expansion main product Transportation (MTHF) g CO2-eq.49 0.74 23.47 19./g - 0. emissions .78 8. driving a car fuelled with bioethanol produced from biorefinery (23./km.56 4./km 23./km 23.69 1.60 credits Heat kg CO2-eq. energy allocation) instead of gasoline from oil refinery (189 g CO2-eq./a 20 15 10 5 O2 H2 B io m e th a n e H eat E le c tr ic ity FU M A F u r a n r e s in s T r a n sp o r ta tio n (M T H F) T r a n sp o r ta tio n ( b io e th a n o l) - Energy allocation Exergy allocation Economic allocation Figure 19. mparison among the different allocation methods (data from Table 9).42 119.48 credits FUMA g CO2-eq./GJ 9.23 credits O2 g CO2-eq. 25 k t C O 2 .23 24.132 Francesco Cherubini and Gerfried Jungmeier instance.43 0. saves approximately 88% of CO2-eq. Unit Energy Exergy Economic Transportation (bioethanol) g CO2-eq.91 credits H2 g CO2-eq.69 1./g 1.23 23.81 106.10 0.43 -90.82 5. Table 10./GJ 9.23 credits Furan resins g CO2-eq./g 0.29 credits Electricity kg CO2-eq.06 2.56 7./g 0. Specific factors of GHG emissions of biorefinery products according to the different allocation methods used.07 credits .92 0./g 0.33 0.001 0.23 g CO2eq.18 0. A lot of biorefinery pathways. Biomass energy and material recovery is maximized if a biorefinery approach is considered. Energy and C efficiencies result affected by the fermentation step.8 kt CO2-eq. conventional FUMA and epoxy resins from oil refinery. lignocellulosic materials have great potentials for production of bioenergy and biochemicals in biorefinery. can then be established./a and requires 4772 TJ/a. chemicals (furan resins.Biorefinery Concept: Energy and Material Recovery from Biomass… 133 5. The investigated biorefinery produces transportation biofuels (bioethanol. Furthermore. while the fossil reference system releases 336 kt CO2-eq. Therefore. exergy and C conversion efficiencies. CONCLUSION The use of biomass as raw materials for bioenergy and biochemical production is encouraged by the need for a secure energy supply. electricity from natural gas and heat from heavy oil. conversion technologies and products. which produces multiple fuels and products from petroleum.e. Even if the biorefinery has higher primary energy demand than the fossil reference system. Biorefinery concept is analogous to today's petroleum refinery. gaseous biofuels (biomethane and H2). several allocation procedures were applied. exergy content and economic value of outputs have been carried out. Results also show biorefinery system performances in terms of product yields and mass. . the energy content of the processed feedstock): the provision of biomass with sustainable practices is then a crucial point to ensure a renewable energy supply to biorefineries. energy./a and requires 10858 TJ/a of primary energy. Among the different biomass resources. processing and delivery). more than half of the total GHG emissions of the biorefinery are originated from feedstock provision (collection. The biorefinery releases 36. where almost half of the C of the feedstock is loss in the formation of the useless product CO2. replacing fossil derived products and services. a reduction of fossil CO2 emissions and a revitalization of rural areas. while the fossil reference system produces gasoline as transportation fuel. In order to share the environmental impacts of the biorefinery among the different coproducts. All the findings are finally compared and the specific GHG emission factors (g CO2-eq. natural gas. it is mainly based on renewable energy (i. An attempt to avoid allocation through system expansion was developed and then allocations based on energy content./unit) of each product are reported. followed by manufacture of auxiliary materials and biomass combustion. H2 from natural gas. MTHF). The LCA depicted in this chapter shows that significant GHG and fossil energy savings are achievable if a biorefinery system is compared with a fossil reference system. where many technological processes are jointly applied to different kinds of biomass feedstock for producing a wide range of bioproducts. 89% of GHG emissions and 96% of fossil energy can be saved. from feedstock to products. of which 208 TJ/a fossil energy. according to the different types of feedstock. of which 4736 TJ/a fossil energy. when biorefinery products will be widely used by customers and as auxiliary materials in production processes. These factors can be applied in LCA studies of a future biobased society. electricity and heat from softwood forest residues. FUMA and O2). conventional O2 from air processing. S.) (1993). & Vigon. Aerts. Jungmeier. Exergy and life cycle. ranges and recommendations. F. F.com/chemprofile. C. V. Elliot. Neuenschwander. 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Levoglucosan kinase involved in citric acid fermentation by Aspergillus niger CBX -209 using levoglucosan as sole carbon and energy source, Biomass and Bioenergy 21: 53-60. In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers, Inc. Chapter 4 PINCH TECHNOLOGY FOR WASTE HEAT RECOVERY APPLICATIONS IN OIL INDUSTRY * Mahmoud Bahy Noureldin Consulting Services Department, Saudi Aramco, Dhahran, Saudi Arabia. Part I: Pinch Technology for Energy Utilities Targeting and HEN Design Constructing the Composite Curves for Energy Utilties Targeting Targeting using Algebraic and Mathematical Programming Methods Constructing the Grand Composite Curve (GCC) Utility Selection Using Grand Composite Curve (GCC) Understanding and Applying Grand Composite Curve Heat Exchanger Network Synthesis using Pinch Design Method Part II: Heat Integration Applications in Oil Industry Oil and Gas Separation Process Crude Atmospheric Distillation Unit INTRODUCTION In process industries the main source of waste heat is associated with hot utilities; that include furnaces, steam boilers, gas turbines and diesel engines. Energy efficiency optimization not only keeps operating cost under control and conserve depleted resources but also reduces GHG emissions. Oil and gas industry consists of very energy intensive processes. Oil and gas separation; crude atmospheric and vacuum distillation; Naphtha and Diesel hydro-treating and gas oil and Naphtha reforming, are only some examples. In the oil and gas business, energy cost is a major element in any facility operating cost. It usually comes before maintenance cost and sometimes even labor cost. Implementation of a * [email protected] Tel: 9663-873-6045, Fax 9663-873-0766 142 Mahmoud Bahy Noureldin decent level of energy integration in any industrial facility, most of the time, needs capital investment. This chapter addresses the problem of waste heat recovery via presenting an introduction to the pinch technology and two industrial applications of heat integration for waste heat recovery in oil and gas business. Pinch technology, after almost three decades of its emanation in the late seventies for a reason or another, is still the most widely used method for energy integration in oil industry. The chapter comes into two parts; the first part introduces some aspects of Pinch technology in brief. Pinch technology is now well documented in several literatures and the references 1 to 4 at the end of this chapter are only few main examples. In this part, I will show how we can use pinch technology for energy utility targeting, selection of utility mix and heat exchanger network synthesis using pinch design method [1, 2, 3 and 4]. The second part introduces two important applications for heat integration in oil industry [5]. The first application is showing the effect of heat integration on both energy consumption and GHG emission reduction in an oil-gas separation facility, and in the second application an evolutionary approach to crude distillation pre-heat train design is introduced. TARGETING USING GRAPHICAL METHOD Any heat exchanger can be represented as a hot stream that is cooled by a cold stream and/or cold utility and a cold stream that is heated by a hot stream and/or hot utility with a specified minimum temperature approach between the hot and the cold called ∆Tmin. The process exhibited below in the graph shows the situation when the two streams do not have a chance of overlap that produce heat integration between the hot and the cold. Figure 1. Two Non-Overlapping Streams Pinch Technology for Waste Heat Recovery Applications in Oil Industry Feed 120 H C PROCESS 143 Product HOT UTILITY T 100 HEAT RECOVERY 80 Pinch 60 (MAT) 40 20 0 COLD UTILITY 0 10 20 30 40 50 60 H Figure 2. Heat Integration between Hot and Cold Moving the cold stream to the left on the enthalpy axis without changing its supply and target temperatures until we have a desired small vertical distance between the hot stream and the cold stream we obtain some overlap between the two streams that result in heat integration between the hot and the cold and less hot and cold utilities. As seen depicted in the graph below with shrinkage in the red and blue lines span. Now we want to represent all the hot streams in the process by one long hot stream and we will call this line the hot composite curve. We will also do the same thing with all the cold streams in the process. The next step will be drawing the two composite curves/lines on the same page in a Temperature (T)-Enthalpy diagram with two conditions: 1. The cold composite curve should be completely below the hot composite curve, and 2. The vertical distance between the two lines/curves in terms of temperature should be greater than or equal to a selected minimum approach temperature called global ∆Tmin The resulting graph is depicted below and known as thermal pinch diagram. Net Heat Sink Above the Pinch Opportunity for heat recovery Net Heat Source Below the Pinch Figure 3. Composite Curves 144 Mahmoud Bahy Noureldin Constructing the Composite Curves 1. Draw the hot composite curve and the cold composite curve via developing the following tables. 2. These tables list all the hot and cold streams temperatures in an ascending order with the cumulative enthalpy corresponding to the lowest hot temperature and lowest cold temperature respectively equal to zero. 3. In every temperature interval the cumulative hot load is calculated using the following formula H= FCp * (Tsupply – Ttarget) 4. In every temperature interval the cumulative cold load is calculated using the following formula H= FCp * (Ttarget – Tsupply) Hot streams temperature list T0=30 T1=70 T2=120 T3=170 Cumulative Enthalpy (H) H0=0.0 H1=800 H2=2300 H3=2800 Cold streams temperature list T0=20 T1=50 T2=90 T3=110 Cumulative Enthalpy (H) H0=0.0 H1=450 H2=2650 H3=3450 As we mentioned before the cold composite curve shall lie completely below the hot composite curve and this can be done via dragging the cold composite curve to the right on the enthalpy axis (H). This process shall stop at a vertical distance between the cold and the hot composite curve for a temperature equal to the minimum temperature approach selected earlier. Table 1. Data for Constructing Composite Curves Supply Temp (º C) 170 120 50 20 Target Temp. (º C) 70 30 90 110 FCp (kW/ ºC) 10 20 40 15 Temperature (T) Enthalpy (H) Diagram 1 Temperature (T) .Enthalpy (H) Diagram T Hot composite curve Cold composite curve 30 20 Cold composite curve is not completely below the hot composite curve H Figure 4.Enthalpy (H) Diagram Minimum Heating Utility T Qh=300 kW Hot composite curve Cold composite curve Minimum Temperature Approach 30 20 Qc=150 kW Minimum Cooling Utility H Figure 5. Temperature (T) Enthalpy (H) Diagram 2 145 .Pinch Technology for Waste Heat Recovery Applications in Oil Industry Temperature (T). Draw horizontal lines again at the start and the end of any arrow representing the hot streams in the hot section of the table Repeat step 1. It is also feasible to transfer heat from a hot stream in an interval “x” to any cold stream which lies in an interval below.4.6 for any arrow representing cold stream in the cold section (at the start and the end of any arrow) Count the number of segments generated and number them starting at the highest temperature (they are called temperature intervals) Make sure that each temperature interval has now temperature value on both the hot temperature scale and cold temperature scale.3 for all cold streams in the cold section of the table Start at the highest temperature of any hot stream in the hot section and draw a horizontal line that spans across the two sections of the table. the hot and the cold. 1. 1. To calculate T* we take the average interval inlet temperature of the hot and cold temperature scale.7. 1.6. Data for Algebraic Method Supply Temp Target Temp. 1. Constructing Temperature Iinterval Diagram 1. (º C) (º C) 520 330 380 300 300 550 320 380 1. 10 ºC) Draw all the hot streams (in the table hot section) to be cooled according to the hot steam scale as arrows that start at the supply temperatures and end at the target temperatures Repeat step 1.2.5.9. Note: The temperature symbol T* ‘(Figure 6) is the interval inlet temperature used later on constructing what is know as grand composite curve for selecting the suitable energy utility mix. .1.8. 1.146 Mahmoud Bahy Noureldin TARGETING USING ALGEBRAIC METHOD Information needed Given a unit with a list of hot streams to be cooled and cold streams to be heated FCp (kW/ ºC) 10 5 10 5 Table 2. 1. 1. The difference is the desired minimum temperature approach (for instance the 10 ºC used in this example) These procedures are depicted in the figure below Note: This structure means that within any temperature interval it is thermodynamically feasible to transfer heat from the hot streams to cold streams. 1.3. Draw two temperature scales one for the hot streams and another for the cold streams Select a reasonable minimum temperature approach between the hot streams and the cold stream. (for instance. F2Cp2= 5 kW/K Figure 6.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 147 ∆ T minimum = 10 K T* 555 515 Interval 1 Hot Streams 560 H1 T t Cold Streams 550 520 510 390 380 2 385 3 H2 380 370 4 330 320 305 5 310 300 295 6 300 290 375 310 Hot Streams:H1. Constructing Tables of Exchangeable Heat Loads and Cooling Capacities 2. Determining individual heating loads and cooling capacities of all process streams for all temperature intervals using this formula: Qnm = F1Cp1* (Ts-Te) in energy units (kW) Ts is the interval start temperature and Te is the interval end temperature “n” is stream number and “m” is the interval number Example 1: Interval # 1 in the hot section: The interval start temperature is 560 K The interval end temperature is 520 K Q11 (Q for stream #1 in interval #1)= F1Cp1*(560-520) Since there is no H1 stream in this interval.0 Q stream # 1(exchangeable load) in this interval = 0. F2Cp2= 5 kW/K C2 C1 Cold Streams:C1. The Temperature Interval Diagram 2.1. F1Cp1= 10 kW/K C2. hence.0*(560-520) = zero Example 2: Interval # 2 in the hot section: The interval start temperature is 520 K The interval end temperature is 390 K The flow specific heat F1Cp1= 10 kW/K Then. F1Cp1= 10 kW/K H2. F1Cp1=0. Q stream #1(exchangeable load) in interval #1= 10*(520-390) = 1300 kW . 0= 0 .0*(300-290)= 0.0 5*(380-370)= 50 0.0*(560-520)= 0.148 Mahmoud Bahy Noureldin Example 3: Interval # 1 in the cold section: The interval start temperature is 550 K The interval end temperature is 520 K The flow specific heat of this cold stream is F1Cp1= 10 kW/K Then.0 1300+0= 1300 3 10*(380-370)= 100 100+50= 150 4 10*(370-320)=500 5*(370-320)= 250 500+250= 750 5 10*(320-300)= 200 0. Q stream #1(cooling capacity) in interval #1= 10*(560-520) = 400 kW Upon the completion of this step.0*(300-290)= 0.0*(320-300)= 0.0 5*(310-300)= 50 0. 2. kW Load of H2.0= 1300 3 10*(390-380)= 100 0. kW 0.0= 0.0 0.0+0.0 100+0.0*(510-380)= 0.0= 400 2 10*(510-380)= 1300 0.0 2 10*(520-390)= 1300 0.Cooling Capacities for Process Cold Stream Intervals Interval 1 Capacity of C1.0*(310-300)= 0.0*(550-510)= 0.0= 200 6 0.0 0.0 200+ 0.0 5*(330-310)= 100 0.2 We can now obtain the collective loads (capacities) of the hot (cold) process streams.0 Total Load. kW 400+0.0+50= 50 Table 4.0*(390-380)= 0.0*(330-310)= 0.0 Total Load. These collective loads (capacities) are calculated by summing up the individual loads of the hot process streams that pass through that interval and the collective cooling capacity of the cold streams within the same interval These calculations for the above problem is shown in the following tables Table 3. kW 0.0= 100 4 10*(380-350)= 500 5*(380-330)= 250 500+250= 750 5 0.0 1300+0.0+ 100= 100 6 0. Exchangeable Loads for Process Hot Streams Intervals Interval 1 Load of H1. kW 10*(550-510)= 400 0.0*(520-390)= 0.0*(560-520)= 0. kW Capacity of C2.0+0. First Interval Heat Balance Numerical Example of First Interval Heat Balance Hot Load From Utility Source “Top Input ”= 0. Numerical Example of First Interval Heat Balance = .0 kW Cooling Capacity From Process Source Hot Load From Process Source “Left Input ”= 0.Right Output = Bottom Output Figure 7.Right Output = Bottom Output 0.400 = .400 kW Figure 8.0 kW 1 “ Right Output ”=400 kW Residual Hot to Subsequent Interval “Bottom Output ” from first interval Heat Balance Top Input+ Left Input .400 kW 149 .0 + 0.Pinch Technology for Waste Heat Recovery Applications in Oil Industry Hot Load From Utility Source “Top Input” Hot Load From Process Source “Left Input” Cooling Capacity From Process Source 1 “ Right Output” Residual Hot to Subsequent Interval “Bottom Output” from first interval Heat Balance Top Input+ Left Input.0 . 150 Mahmoud Bahy Noureldin Subsequent Intervals Heat Balance Hot Load From Above Interval “Top Input” Hot Load From Process Source “Left Input” Cooling Capacity From Process Source N “ Right Output” Residual Hot to Subsequent Interval “Bottom Output” Heat Balance Top Input+ Left Input.Right Output = Bottom Output Figure 9.400 Hot Load From Process Source “Left Input”= 100 Cooling Capacity From Process Source “ Right Output”= 150 3 Residual Hot to Subsequent Interval “Bottom Output” = .400 + 100 -150 = . Subsequent Intervals Heat Balance Numerical Example for Subsequent Intervals Heat Balance For instance.Right Output = Bottom Output . Interval # 3 Hot Load From Above Interval “Top Input” = .450 Heat Balance Top Input+ Left Input.450 Figure 10. Numerical Example for Subsequent Heat Balance . The output from the right is the total cooling capacity of this interval ( for instance. Thermal Cascade Diagram (Un-Balanced) Note: During this step the input from Hot Utility to the first interval is equal to zero 0.500 Figure 11.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 3.N intervals.[1. 1300 kW in case of interval # 2) The inlet from above is the utility input load.400 3 1300 150 .-400 energy unit.550 0 6 .450 750 4 -450 100 50 200 5 .3] The temperature intervals are drawn as “rectangular” with two inlets and two outlets. or the input from interval above in case of second. The inlet from the left is the total hot load available in this interval (for instance. Upon the completion of the heat balance around each interval the following energy deficiency diagram will be produced.……. in case of the first interval.0 1300 100 750 400 1 -400 2 . third. 151 Constructing Thermal Cascade Diagrams This diagram is constructed using the total hot loads and cooling capacities obtained in the previous step for each temperature intervals. Thermal Cascade Diagram (Un-Balanced) . 1300 kW in case of interval #2). The output from the bottom is the difference between the total inputs and the cooling capacity of the interval The heat balance around each interval will be conducted as above. The reader is encouraged to do the calaculation for interval number 2 and see that in interval number 2 the hot side input is equal to the cold side output and hence the final output of the interval will be the same as interval number one .0 0.2. Mathematical programming at a Glance: Let us consider the following constrained problem.0 is the set of (m) equations in variables x g(x) ≤ 0. Thermal Cascade Diagram (Balanced) With the completion of this step. h(x) =0.0 is the set of r inequality constraints. This deficiency in heat will be supplied via an outside hot utility. Min f(x) s.0 n xє R Where: f(x) is the objective function h(x) = 0.t. A very famous approach is the “transshipment model formulation as we mentioned in the first module. Balanced Thermal Cascade Diagram Minimum Heating Utility = 550 units 0.0 1300 400 1 150 2 1300 150 100 750 150 3 100 750 4 100 100 Pinch Point 50 200 5 0. .0 g(x) ≤ 0. This value will be the input (from the top of the first interval) and the same heat balance calculation conducted above will be repeated to produce the energy balanced thermal cascade diagram below.0 0 6 Minimum Cooling Utility = 50 units Figure 12. the minimum heating utility and minimum cooling utility required are 550 kW and 50 kW respectively. TARGETING USING MATHEMATICAL PROGRAMMING METHOD The algebraic method mentioned above can be generalized using optimization techniques.152 Mahmoud Bahy Noureldin The maximum difference between the available hot loads and cooling capacities from the heat balances of these intervals is – 550 kW. let us go back to our small problem solved algebraically before using pinch technology and use FCP for cold streams of 19 and 2 kW/ºC resepctively. tables of exchangeable loads and un-balanced thermal cascade diagram.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 153 In general the number of variables. n.0 1 760 r1 1300 2 2470 r2 100 3 210 r3 750 4 1050 r4 100 5 380 r5 50 6 0. and then solving the optimization problem using any commercial software. will be greater than the number of equations. The model formulation is a heat balance around each temperature interval in the graph below as follows: min Q heating 0. Now for the heating and cooling utilities minimization problem. • Objective function Minimize (5* 10 −6 min −6 min Qheating + 9* 10 Qcooling )*3600*8000 • Define the loads of heating and cooling utilities in each temperature interval and the surplus from each interval as we did before in the algebraic method through the development of temperature interval diagram. Thermal Cascade diagram for LP model min Qheating + 0. m. Any optimization problem can be represented in the above form. We write our objective function not only including heating and cooling utiltities loads but also including heating and colling utilitie costs in dollar value. If we want to maximize a function this is equivalent to minimizing the negative of that function.0 min Q cooling Figure 13. The new problem can be easily solved using mathematical programming model. formulate our model/constraints using the cascade approach.0-760 = r1 r1+1300-2470 = r2 . and the difference between (n-m) is commonly denoted as the number of degrees of freedom of the optimization problem. min Qcooling -r5= 50.0. r2≥0.0 = Qcooling Now using any optimization software: Model: Min = (3* 10 −6 min −6 min Qheating + 5* 10 Qcooling )*3600*8760.0.0. To get a better idea in terms of utility types needed.0. We can then utilize these findings to compare the current .0.0.154 Mahmoud Bahy Noureldin r2+100-210 = r3 r3+750-1050 = r4 r4+100-380 = r5 min r5+50-0. r5≥0. give an idea about the potential utility needs of any industrial facility.0. min r1. r1≥0. r3-r2= -110. r3≥0. r4≥0.Qheating = -760. we need to construct a diagram known as the grand composite curve (GCC) and use it for defining the kind of utilities we need and how much we need. r5-r4= -280. The targets obtained graphically or algebraically or using mathematical programming. min Qheating ≥ 0. r2-r1= -1170. min Qcooling ≥0. r4-r3= -300. C. CONSTRUCTING THE GRAND COMPOSITE CURVE (G. as shown below.0 kW Thermal Pinch 6 295 50 kW Enthalpy ( kW) Figure 14.C) This curve will be drawn between T* calculated before during the temperature interval diagram construction which is the average temperature of hot and cold side each interval boundary and the corresponding surplus heat/enthalpy from each interval.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 155 facility needs with the minimum utility needs calculated before to define the gap needed to be tackled.C T* (K) Enthalpy ( kW) 2620 kW 555 T* (K) 515 1 1860 kW 2 690 kW 385 3 580 kW 375 4 280 kW 310 305 5 0. These data are shown below for a generic balanced cascade diagram that can be developed for any application as shown before: Data Required To Construct The G. . This step will help us evaluate potential savings upon the heat integration for certain process area.C.C.) Drawing these data as T* versus Enthalpy results in the following diagram that can be used to define different levels of utilities mix that can be used to satisfy the process heating utility requirement for instance.C. Data required to drawing Grand Composite Curve (G. It is usually available at several levels. the actual hot utility . This method means that an allowance of ∆Tmin is already built into the graph between the hot and the cold for both process and utility streams. those heating duties and cooling duties not serviced by heat recovery must be provided by external utilities. cooling water. In other words.C.156 Mahmoud Bahy Noureldin Grande Composite Curve (G. It shows the heat flow through the process against temperature. High temperature heating duties require furnace flue gas or a hot oil circuit. they are not a suitable tool for the selection of utilities. The grand composite curve drawn above is a more appropriate tool for understanding the interface between the process and the utility system. air cooling. Although the composite curves can be used to set energy targets. Grand Composite Curve Multiple Utility Targeting/Selection using Grand Composite Curve (GCC) Upon maximizing heat recovery in the heat exchanger network. The GCC is obtained via drawing the problem table cascade as we shown earlier. The most common utility is steam. Hot streams are represented by ∆Tmin/2 colder and the cold streams ∆Tmin/2 hotter than they are in the streams problem definition. boiler feed water preheating. The graph shown above is a typical GCC. or even steam generation at higher temperatures. furnace air preheating.C) Should Be Drawn To Scale Total hot utility required is equal to 2620 kW T* (K) 600 Hu3 Hu2 500 Hu1 400 300 200 Enthalpy ( kW) 700 1400 2100 2800 Figure 15. It should be noted that the temperature plotted here is the shifted temperature T* and not the actual temperature. Cold utilities might be refrigeration. The graphs below further illustrate such capability for both heating and cooling utilities. Grand Composite Curve for Utility Selection-1 The above figure 16(a) shows a situation where HP steam is used for heating and refrigeration is used for cooling the process. intermediate utilities MP steam and cooling water (CW) can be introduced. Considering that furnace .Pinch Technology for Waste Heat Recovery Applications in Oil Industry 157 temperature will be {T*(obtained from graph)+(∆Tmin/2)} and the actual cold utility temperature will be {T*(obtained from graph)-(∆Tmin/2)} The point of “zero” heat flow in the GCC is the pinch point. In order to reduce utilities cost. The points where the MP steam and CW levels touch the GCC are called utility pinches since these are caused by utility levels. This maximizes the MP steam consumption prior to the remaining heating duty be fulfilled by the HP steam and therefore minimizes the total utilities cost. The remaining heat duty required is then satisfied by the HP steam. The grand composite curve (GCC) provides a convenient tool for setting the targets for the multiple utility levels of heating utilities as illustrated above. The graph. The open “jaws” at the top and the bottom represent QHmin and QCmin respectively. The second graph (b) shows the targets for all the utilities. 17(C) below. shows a different possibility of utility levels where furnace heating is used instead of HP steam. Similar logic is followed below the pinch to maximize the use of the cooling water prior the use of the refrigeration. The target for the MP steam is set via simply drawing a horizontal line at the MP steam temperature level starting from the vertical axis until it touches the GCC. Figure 16. Grand Composite Curve for Utility Selection-2 . If the process pinch temperature is above the flue gas corrosion temperature. In the temperature range above the MP steam level. This will reduce the MP steam consumption. And for the cold utilities it is recommended to use it at the highest possible temperature. These recommendations are best explained using the grand composite curve. Using the entropy balance equation for an open system we can conclude and generally recommend to use hot utilities at the lowest possible temperature while we generate it at the highest possible temperature to generate work. we have a choice of many hot and cold utilities. the heating duty has to be supplied by the furnace flue gas. The targeting involves setting appropriate loads for the various utility levels by maximizing cheaper utility loads and minimizing the loads on expensive utilities. (C) T-tft T* MP CW Refrigeration H Figure 17. the heat available from the flue gas between the MP steam and pinch temperature can be used for process heating. Normally. the use of the MP steam is first maximized. The flue gas flowrate is set as shown in the graph via drawing a sloping line starting from the MP steam to theoretical flame temperature Ttft.158 Mahmoud Bahy Noureldin heating is more expensive than MP steam. In summary the GCC is one of the basic tools used in pinch technology for the selection of appropriate utility levels and for targeting for a given set of multiple utility levels. For instance. These right noses/pockets represent another possibility of heat integration among hot and cold process streams at a minimum approach temperature ∆T higher than that of the ∆Tmin. In such cases an ooprtunity for lost work recovery can exist on the expense of process to process heat integration. Understanding the Grand Composite Curve Before closing this part of GCC and its use in selecting process requirements of utilities mix. the steam system shown below in figure 19 needs to be integrated with the process demands to minimize low pressure steam flaring and high or medium pressures steam let downs. sometimes known as “pockets”. GCC can also helps in selecting steam header pressure levels and loads. Each time a utility is used a “utility pinch” is created.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 159 Understanding and Applying the Grand Composite Curve The graph below shows that utility pinches are formed according to the number of utilities used. It also shows that the GCC right noses. In addition. This rule says that: “do not use cold utility above the pinch” to avoid buying extra heating and cooling utiltities. Figure 18. are areas of heat integration/energy recovery and hence does not need any external utilities. I need to mention one important fact here about a rule in pinch technology that is generally accepted by many people in the industrial community. This rule is absolutely true when we talk only about cost of heating . The GCC curve can be used by engineers to select the best match between the utility profile and process combined heat and power requirements profile. 160 Mahmoud Bahy Noureldin utilities. minimization of utility waste via heat integration. #4 MP Process Condensate Proc. then using steam turbines exhaust for process heating than literally doing process to process integration using minimum approach temperature ∆T among hot and cold process streams much higher than the originally selected minimum approach temperature ∆T_min. #1 HP Process Condensate Proc. in some situation we can have a trade off between heating utilities cost and benefits obtained from reducing power import or exporting power to the grid. Combined Heat and Power System Example In summary.3]. the Grand Composite Curve can be utilized to help optimize combined heat and power systems (CHP) shown in figure 19. With the aid of GCC we might find situations in which it is better from work generation point of view to use cold water above the pinch to produce steam and generate electricity. selectivity. #3 LP Process Condensate Figure 19. process modifications for the sake of more heat integration has been explored and the plant utility system is configured. #2 chemicals MP Boiler MP Vent Proc. the optimization of major design variables such as reactor conversion. select the load and return temperature of hot oil circuits. the material and energy balance can now be more or less fixed and hence the hot and cold streams which contribute to the heat exchanger network can be . HEAT EXCHANGERS NETWORK (HEN) SYNTHESIS Upon deciding on process reaction-separation system design. #1 Vent Deaerator BFW Raw water Make-up Treatment Plant LP Effluent Proc. etc. However. HP Boiler HP Proc. minimization of process waste.. recycle inert concentration. best integration between process and furnaces exhaust and process refrigeration levels as well as the synthesis of the multiple-cycle refrigeration systems [1. #1 Process Condensate Proc. but the required capital cost will be less.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 161 identified. In a little elaboration define the HEN streams matching. duty of each heat exchanger. The lower the DTmin chosen. In the section below we will be defining the topology. A large DTmin on the other hand will mean increased energy costs due to less overall heat recovery. duty and temperatures information of the HEN. Designers may find that a very large DTmin might lead to high levels of heat duties available to be handled by process to process heat exchangers and process to utiltities ones resulting in high surface area needs and consequently both capital cost and energy cost will be increased. The task is then becomes to design the heat exchanger network. The Pinch Design Method The best design for an energy efficient heat exchange network will often result in a tradeoff between the equipment and operating cost. . However. Any way early in this chapter we introduced how to set energy and area targets for the process before considering the HEN design because in the early days of pinch technology this technique was important to help make the trade-off between the HEN capital cost and operating cost quickly and without any heavy calculations. This is dependent on the choice of the DTmin for the process. Having calculated an estimate to HEN minimum number of units we can then use the composite curves again used before to determine the energy targets for a given value of DTmin to determine another estimate to the minimum heat transfer area required to achieve the desired energy targets ahead of HEN design. This is true most of the time but not all of the time. inlet and outlet temperatures of each heat exchanger and with given overall heat transfer coeffiecients calculate the surface area of each heat exchanger. as lower temperature driving forces in the network will result in the need for greater area. nowadays lot of software is available to make a preliminary synthesis of any large size HEN and estimate its capital cost directly and then automatically make the trade-off between the operating cost and the capital cost for the HEN in order to determine the optimal Dtmin for the HEN to be designed. but conversely the higher the heat exchanger capital costs. S = number of streams (hot and cold) including utilities It is important to keep in mind that using the above formula for HEN minimum number of units calculation will only be giving an estimate and in some cases designers can come up with designs which exhibit less number of units due to some perfect matches in temperature range and load among hot and cold process streams. the lower the energy costs. Now let us first estimate the minimum number of units in a HEN (Nunits ) using the following formula:[1] Nunits = S – 1 Where. Grid Diagram for HEN Design H2=5 QC_min = 50 kW . Now we will start the design of the HEN using the well known pinch design method. HEN DESIGN METHOD Four Streams Problem Example The graph below shows the stream data of a very simple HEN problem drawn on a grid diagram [1. To comply with these two guidelines the design problem needs to be divided at the pinch and using the grid diagram as shown in figure 20.T. Nowadays due to widespread use of computer programs for HEN automated design such area targeting calculation is not very beneficial any more in industry. These rules are important for the HEN design to achieve the energy target. where the pinch temperature is shown on both the hot and the cold sides using a minimum approach temperature.2. Then the balanced composite curves are divided into vertical enthalpy intervals to calculate the total minimum area targets assuming constant overall heat transfer coefficient and pure vertical counter current heat transfer using the famous formual in heat transfer Q=U*A*T_L.M.D [4]. A good initialization of this design is to assume that no individual heat exchanger will have a temperature difference smaller than ∆Tmin calculated from the targeting phase and there must be no heat transfer across the pinch by process to process heat transfer or/and inappropriate use of utilities. ∆T_min=10 ºC The Grid Diagram for the Step -By-Step HEN Design Pinch CP (kW/ ºC) 310 ºC QH_min = 2870 kW 520 ºC 330 ºC H1=10 380 ºC 550 ºC 380 ºC 300 ºC 300 ºC C1=20 320 ºC C2=2 300 ºC Figure 20.162 Mahmoud Bahy Noureldin To calculate the HEN estimated surface area from the composite curves. given that no individual exchanger should have a temperature difference smaller than ∆Tmin.3]. The resulting balanced composite curves should have no residual demand for utilities. utility streams must be included with the process streams in the composite curves to obtain the balanced composite curves. If the number of hot stream above the pinch at the pinch is less than the number of cold streams in such situation we can consider splitting cold streams to enable us keep the following two rules intact above the pinch at the pinch. We need to start at the pinch. Number of hot streams above the pinch at the pinch shall be less than or equal to number of cold streams. If such matches are not made. Upon matching hot and cold streams. cold stream CP(FCp) should be less than or equal to the hot stream matched with it (lighter in load) to avoid infeasiibilty in . With efficienct we mean that a hot stream shall be matched above the pinch at the pinch in a way that he/she reaches its target temperature at the pinch. Otherwise we will be needing to buy cold utility above the pinch!! Resulting in more heating and cooling utilities than the ones originally calculated during the energy targeting step. As a result. and 4. the number of feasible matches in this region is severely restricted. Otherwise we end up using cold utility above the pinch. and 2. ∆Tmin exists between all the hot and cold streams. Number of cold streams at the pinch shall be less than or equal to number of hot streams. Upon matching hot and cold streams. we reach the target heating utility calculated beforehand. But for now we need to keep in mind the following two rules for streams matching above the pinch at the pinch: 1. Before going through the design of the network for this simple example in a step-by-step manner. At the pinch. during matching above the pinch we have to have enough number of cold streams above the pinch at the pinch to enable each hot stream above the pinch at the pinch reaches its pinch temperature via matching with a cold process stream. These rules of the inch design method will be further elaborated in this section. We will be elaborating more about feasibility later in this section. the result will be either using a temperature differences smaller than ∆Tmin or we have to buy more utilities due to heat transfer across the pinch. Quite often there are essential matches to be made. Start at the Pinch The pinch is the most constrained region of the problem. In order to be able to achive this requirement. Hence.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 163 The example given in this chapter for the illustration of the pinch design method for heat exchangers network design is very simple. hot stream CP(FCp) should be less than or equal to the cold stream matched with it (lighter in load) to avoid infeasiibilty in matching at some point and again to avoid using cold utility above the pinch at the pinch that results in consuming more than originally calculated energy target For streams matching below the pinch at the pinch the reverse is true: 3. With feasible we mean that the hot stream shall always have a ∆T_min over the matched cold stream. some important rules in pinch design method need to be mentioned to enable the reader solve more complicated problems. Since the pinch point divides the problem into two subproblems we are going to solve first the above pinch subproblem. There are some rules for matches to be both feasible and efficienct for the designated ∆T_min. Thus starting with ∆Tmin at the pinch. The relative slopes (1/FCp) of the temperature-enthalpy profiles of the two streams mean that the temperature differences become smaller while we are moving away from the pinch. for temperature difference to increase while moving away from the pinch. Thus starting with ∆Tmin at the pinch. CPH(FCpH) is less than or equal to CPC(FCpC) (Above the pinch for streams at the pinch) So a very simple explaination for you to remember: Above the pinch at the pinch the CP (FCp) of the hot stream shall be less than (lighter in load) or equal the cold stream matched with to enable it reach its pinch target tempetraturte without aid of cold utility above the pinch. then the temperature differences away from the pinch will become smaller which is infeasible. moving away from the pinch. the temperature difference must increase. the matching will be infeasible and to avoid infeasibility we have to use hot utility below the pinch to enable the cold stream reach its pinch target temperature that results in both heating and cooling utilities increase than originally obtained in the energy targeting step. On the other hand if we match this hot stream with another cold stream having a greater CP(FCp). If the same cold stream is matched with a hot stream with a larger CP(FCp) different situation will arise. which is infeasible. the matching will be infeasible and to avoid such infeasibility we have to use cold utility above the pinch to enable the hot stream reach its pinch target temperature. Otherwise. which is feasible. If a cold stream is matched with a hot that has a smaller CP(FCp). Otherwise. in such case the relative slopes (1/FCp) of the temperature-enthalpy profiles now cause the temperature differences to become larger moving away from the pinch. A less steep slope(1/FCp) will be obtained resulting in temperature differences that become larger away of the pinch which is feasible. if a hot steam with CP(FCp) greater than a CP(FCp) of a cold stream.164 Mahmoud Bahy Noureldin matching at some point and again to avoid using hot utility below the pinch at the pinch that results in consuming more than originally needed energy target The CP(FCp) inequality for individual matches In summary for hot and cold streams matching above the pinch at the pinch. in such case steeper slope(1/FCp) will result. At the pinch the match starts with a temperature difference equal to selected ∆Tmin. below the pinch at the pinch the CP (FCp) of the cold stream shall be less than (lighter in load) or equal to the hot stream matched with to enable it reach its pinch target tempetraturte without aid of hot utility below the pinch. for temperature difference to increase while we are moving away from the pinch we have to have the following inequality achieved CPH(FCpH) is greater than or equal to CPC(FCpC) ( below the pinch for streams at the pinch) Again a very simple words for you to remember. Below the pinch at the pinch the rules are the opposite. we have to have this inequality achieved. Hence we should not consider such match. . space.2. Therefore if there are cold streams below the pinch where the duties are not specified by pinch matches. both heating and cooling. the CP(FCp) values of the hot and the cold streams at the pinch are listed in descending order. This problem can only be resolved by splitting a cold stream into two . instrumentation. the design should be continued in such a way to keep capital cost to a minimum. In conclusion there are some essential matches at the pinch or the region of minimum choice (ROMC) that need to be made around the pinch or the ROMC. In a CP(FCp) table as is shown in the graphs below. even if it leads to more number of units in the network than the estimated minimum. Away from the pinch. additional process-to-process matches for more heat recovery shall be identified. It is important to note here that the CP(FCp) inequality constraint applies only when a match is made between two streams that are both at the pinch. It means that all hot streams must be cooled to pinch temperature by heat recovery. If we have a number of hot streams greater than the number of cold streams (Three hot streams and two cold streams for instance) a problem will then arise. In other words we need to decide the matched heat loads which minimize the HEN number of units. temperature differences increase and it is no longer essential to obey the CP(FCp) inequalities. individual units are made as large as possible. Cooling water must not be used above the pinch to avoid unwarranted excessive use of utilities. additional process-to-process matches for more heat recovery shall be explored. therefore if there are hot streams above the pinch where the duties are not specified by pinch matches.2.3]. One important criterion in the capital cost is the number of units since more heat exchangers mean more skids. Same logic is correct for heating utilities application below the pinch. Since regardless of the CP(FCp) values of the streams. Cooling utilities should not be used above the pinch.3]. In other words the smaller of the two heat duties on the streams being matched shall be taken completely.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 165 The CP(FCp) table Identification of the essential matches in the pinch region can be clarified using what we call CP(FCp) table [1. The next task is to design a network that exhibit minimum number of units. To tick off a stream. control. there will be one of the hot streams that will not be cooled to pinch temperature without some violation of the ∆Tmin constraint. Hot utilitites must not be used below the pinch to avoid unwarranted excessive use of utilities. Keeping the number of units at a minimum can be achieved using the “tick-off” heuristic [1. even if it leads to more number of units in the network than the estimated minimum. Streams Splitting Stream splitting is sometimes necessary to overcome the CP(FCp) constraints mentioned above and/or to avoid using cold utility above the pinch or hot utility below the pinch. The “tick-off” heuristic Once the matches around the pinch have been chosen to satisfy the criteria for minimum energy. concrete and so on. That’ means that all cold streams must be heated to pinch temperature by heat recovery. for instance) regardless of the CP(FCp) values. Here hot utility must not be used below the pinch. one of the cold streams can not be heated to pinch temperature without some violation of the ∆Tmin constraint. At the same time. It is important to emphasize here the need to satisfy both criteria. since hot utility can be used above the pinch. this would not have created a problem. since cold utility can be used below the pinch. Thus there is also a stream number criterion below the pinch such that Sh is greater than or equal to Sc (below pinch) If we have more hot streams than cold streams below the pinch. there is a stream number criterion above the pinch such that Sh is less than or equal to Sc (above the pinch) Where: Sh = number of hot streams at the pinch Sc = number of cold streams at the pinch If there had been more cold streams than hot streams in the design above the pinch. If this is not the case the cold stream needs to be split into two. if we have the number of cold streams greater than the number of hot streams (3 cold streams and two hot streams. each cold stream at the pinch will have a partner with which to match and be capable of heating it to pinch temperature. In such a case. for below the pinch. . the stream population and the CP(FCp) inequality. It is instructive to mention here that it is not only the stream number that creates the need to split streams at the pinch but also the streams CP(FCp) inequality. Sometimes the CP(FCp) inequality criteria for the streams above the pinch “at the pinch” and below the pinch “at the pinch” can not be met at the pinch without a stream split. The problem can be solved by splitting a hot stream into two parallel branches. the CP(FCp) of the hot stream above the pinch at the pinch shall be less than or equal to the CP(FCp) of the cold stream above the pinch at the pinch in order to be able to match them in a heat exchanger. this would not be a problem.166 Mahmoud Bahy Noureldin parallel branches. Let us now consider the sub-problem below the pinch. Thus in addition to the CP(FCp) criterion. The number of hot streams above the pinch at the pinch needs to be less than or equal to the number of cold streams above the pinch at the pinch. If this is not the case then we need to split a cold stream to achieve this guideline. Again. and the minimum heating and cooling utiltities are 2876 kW and 50 kW. one sub-problem below the 310 ºC-300 ºC pinch point and a third sub-problem in between the two pinch points. In such situations two pinch points will be arised and three sub-problems will be produced. If this is not the case the cold stream needs to be split into two lighter loads cold streams. the CP(FCp) of the hot stream below the pinch at the pinch shall be greater than or equal to the CP(FCp) of the cold stream below the pinch at the pinch in order to be able to match them in a heat exchanger. minimum utiltities consumtion and minimum number of units. One sub-problem above the 330 ºC-320 ºC near pinch point. the design procedure known as the pinch design method can be lumped as follows: • • • • • Divide the problem at the pinch into two separate sub-problems The design for the separate sub-problems is started at the region of minimum choice known as the pinch point and then moving away Temperature feasibility requires constraints on the CP(FCp) values to be satisfied for matches between streams “at the pinch” for the two problems above the pinch and below the pinch The loads on individual heat exchangers are determined using the tick-off heuristic to minimize the number of units Away from the pinch there is usually more freedom in the choice of matches. The pinch point has divided the problem into two sub-problems one above the pinch and another below the pinch. . The division lies at 310 ºC on the hot streams side and 300 ºC on the cold streams side. Briefly. Before closing the pinch design method (PDM) general description with its rules and heuristics let us summarize the methodology in a step-by-step fasion. Using the minimum number of units formula mentioned before we can estimate that the network minum number of units shall be 5 units. respectively. The problem minimum approach temperature used is ∆T_min=10 ºC. The impact of such situation in the systematic design of the HEN is generating a HEN design that exhbits more number of units than the estimated minimum number of units HEN originally calculated without considering the near pinch point. At the same time. Now we will synthesize a feasible HEN that realizes these two design objectives. the number of cold streams below the pinch at the pinch needs to be smaller than or equal to the number of hot streams below the pinch at the pinch. If this is not the case then we need to split a hot stream to achieve this guideline.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 167 On the other hand. In this case the designer can choose on the basis of his/her process knowledge Having described the pinch design methodology. Handling situations like that is not difficult but less systematic than one pinch point situation [1]. let us solve the numerical example mentioned above. This load (Q) in this example is equal to 350 kW. Grid Diagram with near pinch representation We will start now the design above the pinch at the pinch. The Grid Diagram for the Step -By-Step HEN Design Near Pinch Pinch CP (kW/ ºC) 310 ºC QH_min = 2870 kW 520 ºC 330 ºC H1=10 380 ºC 550 ºC 380 ºC 300 ºC 300ºC H2=5 C1=20 320 ºC C2=2 300 ºC QC_min = 50 kW Figure 21. The heat exchganger heat duty/load can now be calculated by simply using Q= FCp (Ts-Tt) formula. It is clear in figure 22 above that the hot stream H1 and the cold stream C2 can also have a good match since hot stream H1 can be ticked-off completely. we will check the CP(FCp) matching rule. and is equal to 12. . The designer can use his/her common sense to complete the design to reach feasible network rendering the exact minimum utilities requirements with minimum number of units. figure 21. hence we let the stream with lower heat load ticked-off. The minimum approach temperature between the two streams is still not violated. Since we have only one possibility for hot stream matching with cold stream at the pinch. In this example it is the hot stream H2.168 Mahmoud Bahy Noureldin It is instructive to mention here that the hot stream H1 and the cold stream C2 can be called “near” pinch streams and in some commercial software another near pinch vertical line will be drawn at 330 ºC-320 ºC as shown in figure 21 below. Since stream H2 has CP(FCp) equal to 5 while the cold stream C1 has a CP(FCp) equal to 20. we do not need to make any split and we can match the hot stream H2 and the cold stream C1 as shown in the graph below. the CP(FCp) matching rule here rule is satisfied. The hot stream H2 has now been cooled down to its pinch target temperature of 310 ºC and the cold stream C1 has been heated up from its pinch temperature at 300 ºC to 317.5 ºC as shown in figure 22. away from the pinch there is no systematic technique to complete the HEN. It is also important to note here that in the pinch design method.5 ºC. Upon matching H2-C1 in a heat exchanger uint we need to tick-off one of the streams to minimize the number of heat exchangers. upon such matching with C2 resulting in a HEN with the desired estimated minimum number of units calculated earlier for the this example (5 units). greater than or equal to the specified ∆T_min=10 ºC. 5 ºC 330 ºC H1=10 Q= 350 kW 317. The Grid Diagram for the Step -By-Step HEN Design Pinch CP (kW/ ºC) 310 ºC QH_min = 2870 kW 520 ºC Q= 1900 kW 380 ºC 550 ºC 380 ºC 412. Grid Diagram for H1-C1 matching away from the pinch .5 ºC 380 ºC 300 ºC C1=20 320 ºC C2=2 300 ºC QC_min = 50 kW Figure 22.5 ºC 300 ºC 300 ºC H2=5 C1=20 320 ºC C2=2 300 ºC QC_min = 50 kW Figure 23. Grid Diagram for H2-C1 matching above the pinch at the pinch The hot stream H1 has a heat load of 1900 kW and hence the process to process heat exchange between H1-C1 match shall be 1900 kW which is now the duty of this heat exchanger as shown in figure 23 below.169 Pinch Technology for Waste Heat Recovery Applications in Oil Industry The Grid Diagram for the Step -By-Step HEN Design Pinch CP (kW/ ºC) 310 ºC QH_min = 2870 kW 330 ºC 520 ºC H1=10 Q= 350 kW 380 ºC 550 ºC H2=5 300 ºC 317. 550 ºC. the network streams matching to realize the minimum heating utility target will not be adequate. Grid Diagram for C1 matching with hot utility away from the pinch Figure 24 above shows that. The Grid Diagram for the Step -By-Step HEN Design Pinch CP (kW/ ºC) 310 ºC QH_min = 2870 kW 520 ºC Q= 1900 kW 380 ºC Q= 2750 kW 550 ºC 412. we see that the estimated minimum number of units.5 ºC. and minimum heating utiltity requirements are both satisfied. Otherwise. above the pinch. synthesize and generate more than one HEN structure to study other process objectives satisfaction .5 ºC 380 ºC 330 ºC H1=10 Q= 350 kW 317.5 ºC 300 ºC H2=5 300 ºC C1=20 320 ºC C2=2 300 ºC QC_min = 50 kW Figure 24. it is instructive to note that same result obtained in figure 25 above for the estimated minimum number of units and minimum heating utility equal to 2870 kW. Before we move to the network design below the pinch. Upon the completion of defining the matches for the two hot streams H1 and H2 at the pinch cold stream C1. Bear in mind that in order to reach the minimum heating utiltity target the cold stream C2 should not require more than 2870-2750 kW of heating utility. 1900 kW. Counting the number of units and adding the duties of the two utilities units. may be obtained again using different HEN structure and process engineers are always encouraged to explore. Adding this raise in temperature to the the cold stream C1 inlet temperature to H1-C1 heat exchanger renders the cold stream C1 outlet temperature equal to 412. on cold steam C1 CP(FCp) to get the raise in temperature of this stream upon matching it with the hot stream H1. we need now to decide the amount of hot utility needed to allow the cold stream C1 reaches its target temperature. the hot utility unit has a heating load/duty of 2750 kW.170 Mahmoud Bahy Noureldin Now to calculate the cold stream C1 outlet temperature from H1-C1 heat exchanger we divide the load/duty of this hea exchanger. To enable the cold stream C2 reaches its target temperature we need a hot utility heater with duty equal to 120 kW as shown in figure 25 below. which is exactly the cooling utility target obtained earlier during the utilities targeting step. In this simple example we have only one hot steam H2 below the pinch. Therfore the amount of cooling utility required using cooler will be 50 kW.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 171 The Grid Diagram for the Step -By-Step HEN Design Pinch CP (kW/ ºC) 310 ºC QH_min = 2870 kW 520 ºC Q= 1900 kW 330 ºC Q= 350 kW 380 ºC Q= 2750 kW 550 ºC 412. Grid Diagram for H2 matching with cold utility below the pinch Now after we completed the network above the pinch we go below the pinch.5 ºC Q= 120 kW 300 ºC H2=5 300 ºC C1=20 320 ºC C2=2 QC_min = 50 kW 300 ºC Figure 25. The hot stream H2 needs to be cooled down from 310 ºC to 300 ºC. Grid Diagram for C2 matching with hot utility away from the pinch The Grid Diagram for the Step -By-Step HEN Design Pinch CP (kW/ ºC) 310 ºC QH_min = 2870 kW 520 ºC Q= 1900 kW 380 ºC Q= 2750 kW 550 ºC 412.5 ºC 300 ºC 300 ºC H2=5 C1=20 320 ºC C2=2 300 ºC QC_min = 50 kW Figure 26.5 ºC 380 ºC H1=10 317.5 ºC 380 ºC Q= 120 kW 330 ºC H1=10 Q= 50 kW Q= 350 kW 317. The amount of load needed to be removed from this stream is equal to 50 kW. . Combining the design above the pinch and below the pinch gives us the complete design of the heat exchanger network that satisfy our two objectives of minmum number of units and minimum utitilties consumption at ∆T_min equal to 10 ºC. remain to be the main source used for energy generation in our societies. acid rain. then any excessive use of the hot utility will automatically produce excessive utility waste and consequently excessive generation of atmospheric emissions. In these two application pinch technology has been used for targeting and utility selection.172 Mahmoud Bahy Noureldin Figure 26 above is showing such complete heat exchanger network that achieves the desired heat recovery level exhibited in minimum heating utility equal to 2870 kW and minimum cooling utility equal to 50 kW. A major concept in the energy efficiency optimization techniques is the concept of “Heat Integration” applied in Pinch Technology and others to enhance waste energy recovery in industrial processes. Such combustion processes. and its main constituents are carbon dioxide and methane. They are urban smog. protect energy-based natural resources and last but not least to minimize energybased emissions and reduce the impact on the environment. PART II. Having introduced the fundamentals of energy integration using pinch techniques. If the process industries require a furnace or a boiler to provide hot utility. the second part will discuss two industrial applications. In process industries. energy efficiency optimization techniques have become a major tool in NOx. to date. Nowadays. HEAT INTEGRATION APPLICATIONS IN OIL INDUSTRY Environmentally. It also consists of the estimated minimum number of units that equal to 5 units. Until late last century the preferred method of dealing with the atmospheric emissions were known to be taking the end-of-pipe approach. ozone layer destruction and the greenhouse effect or global warming. two process to process heat exchangers and three utiltity service units (two heaters and one cooler). Atmospheric emissions are mainly formed as by-products of combustion processes. the essential sources of energy waste are associated with hot utilities. This view does not tackle the problem at the source where solving could and indeed has proved in many cases to be easier and more cost effective. but also protecting the environment via minimizing energy-based GHG emissions. The greenhouse gas effect or global warming phenomenon problem arises mainly from the burning of fossil fuels. leading to melting of the polar ice caps and thus rising sea levels. One way of using this concept is to look first in our plants to satisfy some of their thermal energy needs through letting the hot streams (sources) that are to be . CO and CO2 emissions minimization from combustion-based processes. SOx. The result is that global temperatures increase. Therefore. However. there are essentially four phenomena associated with atmospheric emissions. This approach is myopic view and usually an expensive one. Systematic methods and tools have been developed and are currently utilized to conserve energy. of which methane has more than ten times the effect of carbon dioxide. increased weather disruptions and changes to ocean currents. because of capital cost and end user preference its strict application has been sacrificed for the sake of easy to operate networks and less capital investment. energy conservation is one important way of not only saving money and natural resources. Heat input to the stabilizer bottom is provided through reboilers utilizing a heating oil media in a closed loop circulation system. This tight split ensures maximization of stabilized crude and minimization of crude oil quality loss (API Gravity). . These light ends are combined with overheads from the column to the compression system. This methodology in turn attacks. not shown in this graphs but by arrows only. are also directed to the gas compression section. flare pilot and purge gas process blanketing. Major streams in the process have been listed below with its supply temperatures. The stabilizer is fed after removing some light ends.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 173 cooled help the cold streams (sinks) that are to be heated to enable both hot and cold process streams reach their heating and cooling targets. Light ends from the stabilizer overhead system is used as fuel for the heating oil furnace. The stabilized crude flowing from the bottom of the stabilizer column is cooled before going to its final destination partially by heat exchange with the stabilizer bottoms and completely in a final cooling stage using air coolers. In this chapter Pinch technology has been used for targeting purposes and HEN synthesis. the main contributor to the atmospheric emissions problem by reducing the heating utility requirement. The approach give the process owner the facility to select scheme based upon not only capital but also energy resources sustainability and environmental impact on the world. In this paper a step-by-step modifications are applied to an actual oil and gas separation plant to minimize its environment-footprint via GHG emissions reduction using heat integration. However the problem solved in this chapter is considering HEN sophistication as the primary dominant objective and energy cost and/or GHG emissions reduction as the secondary one. Heat Integration Application in Oil and Gas Separation Facility Pinch Analysis techniques have been applied taking into consideration legitimate process constraints such as safety and operability to evaluate the possibility of improving heat recovery in the process and consequently reducing energy-based GHG emissions. Oil and Gas Separation Plant Process Description The un-stabilized crude oil is pumped to the stabilizer unit through a pipeline. Net light gases are then compressed. The fractionation capability provides a well defined split between the light ends and the crude oil. This approach of “Integration” of heat sources and sinks in industrial facilities reduces the need for external hot thermal energy utility that mostly come from fossil materials combustion processes. condensed and pumped to the natural gas liquid pipeline. at the source. Light end gases from other stabilizers and low pressure and high pressure production traps. A furnace is used to heat up the return cold heating oil. Table 1. expressed in terms of number of heat exchangers and its surface area. Typical Oil and Gas Separation Process Flow Diagram The design shown above is used as a base case to make comparisons among other design options regarding energy consumption.2 191. Heat integration role is not only to save energy consumption and its environmental impact but also it can save some capital investment.174 Mahmoud Bahy Noureldin Figure 1. and the GHG emissions reductions.0 109.9 . capital investment.0 210.5 165.8 157.3 265.0 195. Stream 1 2 3 4 5 6 7 8 Name De-gassing Tank Feed Desalter Feed Stabilizer Feed Stabilizer Btms to Reb Stb Btm Product Atm Comp 1st stg HP Comp 1st stg HP Comp 2nd stg TS [F] 90. According to pinch technology heuristics for defining the minimum number of units.8 MM Btu/h savings in heating oil duty and about 180 T/d reductions in GHG emissions and of-course savings air cooling duties savings too.In early design stages it might be much better to consider cogeneration application. people were triggered with its capability in such direction. Figure 2 below shows that for hot and cold streams minimum approach temperature of 17 ºF. This number can increase and form a very complex network in order to satisfy the desired energy targets for the oil and gas separation system while the base case design network is using only seven heat exchangers. In many other cases realizing all possible potential in energy consumption collided with excessive needs for capital investment. Considering a CHP combined heat and power system in oil and gas separation processes can produce the desired electricity for the plant and the low pressure steam produced as a by-product of the cogeneration system in process heating purposes. hence many plants have been reporting successful applications. This furnace will produce about 300 kg of CO2 per hour for each megawatt of heat delivered to the heating oil media used in the process [1]. we have 8 streams above the pinch and 3 streams below the pinch. Realizing such results needs significant capital investment and the decision makers are always looking for scenarios to select among it. In case of the oil and gas separation presented in this paper. the one used in the base case design. The capital investment is exhibited in the extra heat exchangers surface area increase shown in graph below. where they get highest possible impact on energy consumption and GHG emissions reduction with minimum capital investment. Heating oil media is used to render the desired heating and air is used for the desired cooling. In addition to the relocation of the stabilizer bottoms feed heat exchanger to make the matching happens before the desalter instead of having it after the desalter. eleven heat exchangers will be required. In figure 4 below only one heat exchanger has been added to the base case design to integrate the discharge of the first stage compressor with a branch from the crude stream before the desalter. as per the shown grand composite curve in Figure 3. .Pinch Technology for Waste Heat Recovery Applications in Oil Industry 175 In the early days of its application in process plants. minimum heating and minimum cooling utilities consumption due to heat integration are 615 and 24 MM Btu/h respectively. Enabling the process owners to exercise their best budget allocation in reducing energy consumption and GHG emissions by a little defined increase in the capital investment is shown in the graphs below. A furnace with about 90 percent efficiency is used to heat up the return hot oil and electricity is taken from the grid to supply for air coolers and others. This change requires an increase in the reboiler duty from the base case design of 197 MM Btu/h to 272 MM Btu/h Such modifications in the base case design due to better integration results in about 85. In this chapter the HEN design is only considered and not the whole utilities system. It is important to note here that even though the hot oil system used in the process can better match the process requirements for heating purposes compared with steam due to the slope of the heat deficit curve. Oil and Gas Separation Utilities Targeting Figure 3.176 Mahmoud Bahy Noureldin Figure 2. Oil and Gas Separation GCC . Pinch Technology for Waste Heat Recovery Applications in Oil Industry 177 Figure 4. Oil and Gas Separation Design Option # 1 Pushing the envelope for more reduction in both energy consumption and GHG emissions lead us to design option # 2 shown in figure 5 below.4 MM Btu/h and 142. three heat exchangers have been added to the base case design but with different surface area requirements as shown in the three figures below. Further push towards more reduction in heating oil duty and GHG emissions through design modification produces design options three. four and five shown in Figures 6. The reduction in heating oil duties are 128. In these three new design options. It is instructive to note here that the reduction in both heating oil duties and GHG emissions with the increase in number of heat exchanger and associated surface area is happening with steeper change. In this design option more waste heat has been recovered and consequently more GHG emissions have been reduced as follows. 292 t/d and 300 t/d.6 MM Btu/h.9 MM Btu/h. respectively and the reduction in GHG emissions due to such reduction in heating oil duties are 270 t/d. In this design option two heat exchangers have been added to the base case design to integrate the discharge of the first and third stage compressors with a branch from the crude stream before the desalter. 139. respectively too. 7 and 8. about 124 MM Btu/h savings in heating oil duty and about 260 T/d reductions in GHG emissions and of-course again more savings in air cooling duties. Again the relocation of the stabilizer bottoms feed heat exchanger has been also implemented and extra duty for the reboiler has been added. . About 60 % of the reduction in GHG emissions can be attained with 50 % of extra heat exchangers surface area. Oil and Gas Separation Design Option # 3 .178 Mahmoud Bahy Noureldin Figure 5. Oil and Gas Separation Design Option # 2 Figure 6. Pinch Technology for Waste Heat Recovery Applications in Oil Industry Figure 7. Oil and Gas Separation Design Option # 5 179 . Oil and Gas Separation Design Option # 4 Figure 8. Petroleum Gas & Light Naphtha Distillation tower ~40°C ~25-175°C ~150-260°C Fired heater ~235-360°C ~350370°C Heavy Naphtha Crude oil feed Kerosene Light Gas Oil (LGO) ~330-380°C Heavy Gas Oil (HGO) Atmospheric residue Preheated Crude oil ~250-280°C Figure 9. Crude feed get heated up from the ambient temperature to the desalting temperature. normally between 126 and 140 ºC.180 Mahmoud Bahy Noureldin Heat Integration in Crude Atmospheric Distillation Unit In crude atmospheric distillation units. Crude Atmospheric Distillation Unit As shown in the generic crude atmospheric distillation. feed get separated to different cuts according to difference in boiling points. using its simulation cooling curves. After desalting operation that reduces the crude temperature between 3 to 6 ºC. The incoming crude then is fed to the heater to raise its temperature to the desired flash zone temperature in the atmospheric distillation column. The same is also practiced for some hot streams as shown in the table. Table 2 below. crude is fed to the pre-flash drum or sometimes even tower to remove some of the light hydrocarbons before the crude goes to the crude furnace. Figure 9 above the products from the crude tower and circulating pump-around that are used as tower inter-coolers are used to aid the products in heating the incoming crude. The cold stream is segmented into several streams using its simulation heating curve to avoid in-accuracy for assuming constant specific heat along long temperature range. a real industrial application is introduced and discussed. shows data extracted from plant process flow diagrams for the crude as a cold stream and other hot streams. . It is always of high importance in the design of this unit to integrate the cold stream represented by the crude feed stream and products as well as pump-arounds to reduce the heat load the crude heater as much as possible. In this chapter. 27 1.23 CP [MM kCal/C] 0.12 0.1 265 160.55E-02 2. In most cases in oil refining heating utility is more expensive than cooling water. As you notice both heating and cooling utilities are considered being of the same important. to reach desired level of waste heat recovery and to minimize the heating load of the crude heater results in the network below in Figure 11.115876 3.378721 0.52 16.27 13.1 265 378 75 105 61 40 103.570974 0.38E-02 9.42 126.9 188 225.192042 0.8257 16.16 90. the second after the desalter and before the flash drum and the third after the flash drum up to the crude heater.3 60 138 198. This need pushes the plant designers to the extreme in considering the easiness of operation to the extent that they design networks that do not give enough attention to decent level of waste heat recovery and GHG emissions reduction compared with their emphasis on capital investment.7 158.02 2. The network exhibits three splits in the cold crude stream.399614 0.50E-02 0.7 169.52 13.1 105 61 241. Stream Name PreDesalter PreFlash AfterFlash TPA Kero LDO Prod IPA HDO Prod BPA RCO TS TT [C] 37.5 13.41689 0.100976 0. These targets are shown in Figure 10. The heating utility which is our main focus in this application is about 48 MM Kcal/h Using pinch design method (PDM) to synthesis the crude pre-heat train. Therefore. maintenance and operation of the network.16 90.216 14.74 3.96E-02 8.43 4.64 64.9 80 DH [MM kCal/hr] 16.42 125 158.187369 2.36262 0.9 318.5 346.68 13.83E-02 2. less sophisticated configuration and the easiness of heat exchanger network operation and maintenance.9 [C] 84. First split happens before the crude desalter.417043 0. many designer put more emphasis on saving in heating utility since it also reduce emissions than saving on the cold side.35 16.02 2.06 3.89 10.397738 0.147164 The first step in applying pinch technology is to find for a reasonable minimum approach temperature the minimum heating utility and minimum cooling utilities required for this crude unit.81E-02 0.7 169.5 185.172829 0.4 327.2 103.74 13.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 181 Table 2.4 60 225 259.9 193 225.4833 14.3 253.46 84.343041 0.65 15.39E-02 2. Another very important objective in designing new pre-heat train in crude distillation unit is the number of units of the heat exchangers.4 259. .2 198. 182 Mahmoud Bahy Noureldin Figure 10. The schematic network shown is only used for topology comparision. This design means that the approach advocating the easiness of operation and minimum number of units results in more energy consumption in the crude heater and consequently more GHG emissions. no split at all. It is important to note here that maintenance and easiness of operation of heat exchanger networks in crude oil refining facilities are very legitimate issues. it needs to be handled with care and at the end a balanced picture and right trade-off based upon economic should prevail over the argument of we did not do designs like this before. but much less crude temperature . The design exhibits less number of units. . Crude Atmospheric Distillation Unit Utilities Targeting This approach is demonstrated here in the schematic pre-heat train design shown below in Figure 12 for the same industrial application in hand. or our operators are not trained to operate such sophisticated network or even we do prefer this one since it has no splits and less potential for fouling and cleaning. However.265 ºC before the crude heater. 7 C 205. Crude Atmospheric Distillation Unit HEN (I) TPA 141.2C 259.5C 138.6C 318.9 C 0.4 C 0. 60 C 150.9C 265.3 133.8 C 0.5C 90.0C E-3 V04-V6 \Desalter E-4 241.2 308. 75 C HDO 217 C HDO Prod.32 322.4 C 0.38 207 C 0.5 C RCO Prod.5 C IPA 157.5 37.1 C HDO 217.7 C TPA 160.4 C IPA 253. .9C E-1 E-2 185.9 C Desalter 136.2 C Flash 0.5C E-9 HDO-2 225.5C E-7 127.9C 159C 198.24 0. E-5 37.2 C 205.3 204.5C 84.9 C Figure 11.5 C 134. 60 C LOD Prod.2 C RCO 346.8 C 0.1C KERO 327.46 133.2 C IPA 217.4C 196C 206C BPA RCO .183 Pinch Technology for Waste Heat Recovery Applications in Oil Industry RCO 150.8 C 292.2C E-8 IPA-b 346.8C 137.5 C HDO 318.4C LDO IPA Figure 12.9C 199. 241.08 378 C 292.2 C 238.2C Toairandwatercoolers 160.5 C 0.32 HDO 327.9 To Tower LDO 150.8 C 0. Crude Atmospheric Distillation Unit HEN (II) 378C .8C E-6 253. 80 C LDO Prod.8 C 133.4 199.1C 169.4C 225.7C 253.9 C To Colm. The pre-heat train in Figure 13 kept the simple design before the desalter almost as it is and focused only on the heating utility minimization.7C RCO 225. Simulating these possibilities only and then ranking them based upon the impact on the heating utilities requirement but with only one split in the crude stream after the preflash drum to avoid increasing fouling.9C E-7 193.6C FlashDrum E-8 200C E-6 327.8C Furnace 220C RCO Figure 13. will conclude this step and move the approach to the second step. The point that we are trying to make here in this crude unit pre-heat train design approach is that instead of designing the heat exchanger network using pinch design method to get the best possible waste heat recovery scheme and try an ad hoc approach to simplify the network.8C E-5 137. some sense of systematic technique has been also used here. .9C 193.5C 37. The second step is to reconcile the selection of the new matches after the preflash drum with that before it. and all hot streams available at temperatures higher than its supply temperature.2C 185. It tried to push the temperature before the crude heater from 265 ºC in the simple design to about 276 ºC in the new design via better heat recovery in the area after the pre-flash drum only.2C 80C 378C 276.45C 127C 90. It is designed differently than the first network since it does not use the pinch design method. easy to operate and more importantly less area and capital cost.7C 186.4C 275.184 Mahmoud Bahy Noureldin LDO Kero TPA 160. A systematic technique can be used for that purpose via enumerating all matches possibilities between the crude stream.1C 134.5C 318. This network design evolves from the simplest design desired by most of the process owners and plant operators.3C 105C 137.2C 60C Desalter 61C 40C FlashVap IPA-b 253. less possibility of fouling and frequent cleaning needs. However. after the pre-flash drum.9C 84.8C E-3 E-4 103.1C 145C BPA 199. no splits.2C 183.3C 60C E-9 346. Crude Atmospheric Distillation Unit HEN (III) The third network shown in figure 13 set the right compromise to some facilities.1C IPA-a 253. It has less number of units.4C 275.5C 241. The possibilities that can arise can also be ranked based upon the level of simplicity in it.8C E-1 E-2 75C 75C 138.4C HDO 141. GHG and other energy-based undesired by-products atmospheric emissions. B. B. M. IChemE. A. Aseeri. April 23-27. Trans. it is important to consider it in a step-by-step approach especially for the heat exchangers network grassroots design modifications and existing plants retrofit to enable the decision makers selects the right scenario that best fit his/her capital investment budget. B. M. K. Egypt. EL-Halwagi. REFERENCES Douglas. Inc. & Al Qahtani. Noureldin. clean to maintain and capital cost objectives satisfied. 374-381. & Hasan.Smith. Improved heat recovery systems designs while can be attained systematically using Pinch Technology. AIChE Spring Meeting Orlando. 503-522 Noureldin. Systematic waste heat recovery in oil and gas industry is very beneficial to plant operating cost reduction. B. (1996). H. (1996). January.. It has been successfully used to systematically address the problems of energy efficiency optimization and the reduction of energy-based un-desired emissions. M. Chemical Process Design . McGraw-Hill. Aggressive waste heat recovery is an essential approach for inprocess GHG emissions avoidance. (1993). Noureldin. (2006). The details of this new approach and its step-by-step implementation will be published latter elsewhere. Report.Pinch Technology for Waste Heat Recovery Applications in Oil Industry 185 we can start from the simplest possible straight line network shown in this chapter and evolve from it systematically to reach to better networks from waste heat recovery point of view and of-course GHG emissions reduction while keeping the easy to operate. Hamilton. Global energy targets and optimal operating conditions for waste energy recovery in Bisphenol-A plant. 71(A5). Pinch Analysis-a state-of-the-art. A. (1985). Department of Materials and Process Engineering. TEM_icons™ 1. (2003). B. Every megawatt of heating utilities obtained from process boilers and/or furnaces that can be saved through efficient waste heat recovery system design and operation means less greenhouse gas and other harmful NOx and Sox emissions. Linnhoff. R. M. McGraw-Hill. Cairo University Conference on Mechanical Design and Production. J. Systematic in-Process Modification Approach for Enhanced Waste Energy Recovery in Gas Plants. S. Florida. Computer-Aided design software for energy optimization through interval constraint logic propagation. Proceeding of MDP-8. (2006). . University of Waikato. produced during oil and gas separation processes and crude oil distillation can be reduced significantly through proper application of heat integration concepts. Academic Press.2 User’s manual. Inc. Cairo. Pollution Prevention Process Integration. New Zealand. CONCLUSION Pinch technology as a new systematic method for advanced waste heat recovery and heat integration in industrial facilities emanated in the early seventies during the first oil crisis is still nowadays the most widely used technique for energy integration in oil industry. Noureldin. E. Applied Thermal Engineering 26. (2004). J. M. A. & Swan. Conceptual Design of Chemical Processes. . In this chapter. INTRODUCTION Primary and secondary sludges are produced as a result of primary and secondary wastewater treatment in municipal or industrial wastewater plants. we have overviewed a variety of secondary sludge post treatment methods for energy recovery. 1. Unlike the primary sludge. 2007). Sludge disposal has become a worldwide problem for many reasons including rapidly shrinking landfill space. Thunder Bay. increased environmental awareness. Secondary sludge waste management issues are a continuing challenge. The advantages and drawbacks of each treatment option are also highlighted in this chapter. Inc. For instance. 955 Oliver Road. about 40-50 kg of sludge (dry)is generated in the production of 1 tonne of paper at a paper mill in North America (Joyce et al..In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers.g. Chapter 5 TREATMENT OF SECONDARY SLUDGE FOR ENERGY RECOVERY Chunbao (Charles) Xu* and Jody Lancaster Department of Chemical Engineering. including incineration. gasification.. direct liquefaction. The primary sludge * E-mail: cxu@lakeheadu. e.ca . and dewatering challenges. A critical comparison between these methods is presented with respect to their net energy efficiencies. Canada P7B 5E1 ABSTRACT Primary and secondary sludges are produced as a result of primary and secondary wastewater treatment in municipal wastewater plant or pulp and paper mills. pulp and paper mills. pyrolysis. Lakehead University. This together with record high oil prices have contributed to a need to examine methods of converting secondary sludge waste into energy.. more stringent environmental standards governing the disposal of sludge. supercritical water oxidation (SCWO) and anaerobic digestion. the secondary sludge as byproduct of the biological treatment is far more difficult to dewater and to be disposed. Ont. and of that approximately 70%is primary sludge and 30% secondary sludge (Elliot and Mahmood. 1979). Figure 1.5 to 2% solids (Winkler. Normally. Disposal methods for the pulp and paper residues in Europe (adapted from Monte et al.. This together with record high oil prices have contributed to a need to examine methods of converting secondary sludge waste into energy. 1993). agriculture as soil improvers. sludges are disposed by landfilling and incineration (Reid. 1994). 2008 and CEPI.188 Chunbao (Charles) Xu and Jody Lancaster can be relatively easily dewatered for disposal. For example.. In recent years. in road construction. and about half of the incoming organic pollution load is converted into secondary sludge. The secondary sludge consists predominantly of excess biomass produced during the biological process (Ramalho.. due to rapidly shrinking landfill space and the secondary pollution issues associated with the conventional sludge disposal approaches as well as the increasingly stringent environmental regulations. and (2) the significant energy loss in evaporating the sludgecontaining water in incineration or combustion of the sludges in a recovery boiler. 1983). Compared with the primary sludge. the secondary sludge is far more difficult to dewater. 1998). the percentage of pulp/paper sludges disposed by landfills has constantly decreased in Europe in recent years. land reconstruction) and for energy recovery has steadily increased. however. In the meantime. 2006). dropping 40% in 1990 to 20% in 2002. Canadian municipalities spend $12–15 billion annually for sewage sludge treatment (Buberoglu and Duguay. 2004). For instance. The management of municipal and industrial wastewater sludges has been a long-standing challenge for many utilities. the percentage of pulp/paper sludge used as a raw material in other industries and other applications (e. containing 0. 1. as shown in Fig. 2004) . suffered from their inherent drawback of poor economics due to many reasons including (1) the high cost associated with dewatering the sludge to 20-40% solids or higher so as to meet the requirements of landfilling or incineration. which have. the disposal of sludges continues to be one of the major challenges for the municipal wastewater plants and most pulp and paper mills (Mahmood and Elliott. The sludge disposal/management costs can be as high as 60% of the total wastewater treatment plant operating costs (Canales et al.g. g. supercritical water oxidation (SCWO) and aerobic/anaerobic digestion.6 22-25 To evaluate different post-treatment options and in order to provide a means of comparison.) may be neglected.) have been recently reviewed by Mahmood & Elliot (2006). 2005. it is advantageous to compare the energy efficiency for each option if possible.33-2.5-8.8 0. 2008).3-7. . incineration.2 59-68 2. feedstock preparation and feeding. etc. and to heat the dewatered sludge from room temperature (Trm) to the specified reaction temperature (T).Treatment of Secondary Sludge for Energy Recovery 189 Comparing with other typical industrial sludges containing 16-35% of total dry solids (Oral et al. Rato Nunes. 2008).g. Comparison of municipal and pulp and paper activated sludge (modified from Elliott and Mahmood.. products separation and recovery. 2007) Total dry solids (TS) (%) Volatile solids (%TS) N (%TS) P (%TS) Fe (g/kg_TS) PH Heating value (MJ/kg_TS) Municipal 0. For simplification of the discussion.2 6. et al. the energy input may be approximated by the energy required to dewater/thicken the sludge from its original TS content (e. secondary sludge post-treatment technologies and in particular those aimed at energy recovery are the focus of this chapter.. etc.5-2. carbonization gasification. From the above assumptions.0 19-23 Pulp/Paper 1.7 0 6. A comparison of municipal and pulp and paper secondary sludge characteristics is presented in Table 1.4-5.0-2.0 65-97 3. A definition of net energy efficiency may be outlined as follows (Xu and Lancaster. for many hydrothermal treatment processes for the treatment of sludge. The net energy efficiency or “Energy Output/Input Ratio” can be defined as the ratio of energy content of the objective products to the energy input to produce it.8-1. several assumptions may be adopted: (1) Since the feedstock used is waste biomass or waste sludge. Similarities exist between municipal and pulp and paper waste activated sludge. pyrolysis. Table 1. and return activated sludge treatment) or through post-treatment (e. (1)..5-0.7 0.g 25% TS or above).0-7.0 0. General processes and technologies of sludge reduction technologies through process changes (e. the original secondary sludges from municipal wastewater treatment plant or a pulp and paper mill usually contains a much higher ratio of water (98-99%). 1-2% for secondary pulp/paper sludge) to a suitable TS content for the process use (e. (2) the heat loss of the reactor or process is negligibly small assuming well insulation and (3) the energy consumption by other auxiliary operations (e.. as show in Eq.g. operational control. it can be considered as the feed of “ZERO” energy value. While changing/optimizing the sludge producing process would certainly reduce the amount of secondary sludge generation and thus alleviate the issues of sludge waste management. which would suggest that technologies used in the municipal wastewater sector could be transferred into the pulp and paper industry.g. 2000). Outline of treatment options of secondary sludge for energy production 2. chemical oxidation and sludge digestion whose processes have been overviewed recently by Mahmood & Elliot (2006). the energy input calculation may differ method to method and may be difficult to determine due to shortage of experimental data reported. while depending on different requirements and characteristics of each process. pyrolysis. for energy recovery. It shows that the sludge is fed into the boiler. SECONDARY SLUDGE TREATMENT METHODS Secondary sludge can be treated by employing a variety of post-treatment technologies such as heat treatment. super critical water oxidation and anaerobic digestion follows. fixed bed furnace or. An outline of the many post-treatment options and their primary energy products can be summarized in Figure 2. gasification. Emphasis is put on the discussion on the energy efficiency for each process.e. 2. direct liquefaction. which could be rotary kiln. waste activated sludge (WAS). Incineration Incineration technology is the controlled combustion of waste with the recovery of heat to produce steam that in turn produces power through steam turbines (Kumar.190 Chunbao (Charles) Xu and Jody Lancaster Energy Output/Input Ratio = ∑ (HHV of the product) × (mass of the product) (Energy Input) (1) The approximate energy efficiency of each process can be estimated by the equation above. The objective of this chapter is to provide an overview of different types of posttreatment methods of secondary sludge. i. A description of each treatment method including incineration. Figure 2..1. A general flow diagram of the incineration process is depicted in Figure 3. common in the . while advantages and disadvantages of each process are also highlighted. Figure 3. For power generation the steam is directed through steam turbines.. 2008). 2006).. (2005a/b) described a three-stage retrofit of an incinerator in the Czech Republic and concluded that the thermal treatment through incineration of sludge for energy recovery is favorable both economically and environmentally. While depending on specific waste regulations in Europe 850oC must be achieved for at least 2 seconds. specifically designed fluidized-bed combustors produce fewer pollutants through the flue gas (Kumar. Oral et al. which work to produce power through the electric generator.. the temperature is raised to 1100oC for 2 seconds in order to reduce the formation of the toxic compounds such as polychlorinated dibenzodioxins (PCDDs) (Monte et al.... 2000).. The incinerator yields products of steam and byproducts of ash and flue gas.. Typical fluidized bed operating temperature is between 700-900oC (Latva-Somppi et al. 2008). The flue gas requires treatment through air pollution control before discharge through the stack. combined with power and steam generation. (2008) cited eleven European pulp mills which burn some portion of pulp sludge in combination with other biomass. 2000) . Alternatively steam can be used locally for process steam reducing the mill’s dependence on costly fossil fuels for steam production (Monte et al.. Ash can be disposed directly into the nearest landfill or it can be used as the raw materials of light-weight aggregate and constructional brick in the building industry (Liaw et al. General flow diagram of incineration (modified from Kumar. 2008). Incineration of residues (both rejects and sludge). 1997).Treatment of Secondary Sludge for Energy Recovery 191 paper industry. and if hazardous waste with a content of more than 1% of halogenated organic substances. Sludge incineration is widely practiced on a full-scale basis in many highly populated urban areas such as in Japan and Germany (Stark et al. 2008). 1997). Efficient heat and mass transfer in the fluidized bed enables the endothermic fuel drying and devolatilization to occur simultaneously with exothermic combustion of char and volatiles (Latva-Somppi et al. However. is one of the most commonly applied disposal methods in Europe (Monte et al. 1998. a fluidized-bed incinerator (Latva-Somppi et al. 1997). Monte et al. A recent review by Monte et al. (2008) illustrated that self-supporting incineration (combustion) can be attained for feedstock containing approximately > 25% combustible/organic content and an ash content of 0-60%.sludge × ΔT (2) Where Mws is unit mass of wet sludge using a basis of 1kg.95 kJ/kg/oC) and ΔT is temperature difference between initial temperature of 25oC and the temperature of drying of 105oC. The chemistry of pyrolysis mainly associates with degradation of carbohydrate polymers (cellulose and hemi-cellulose) and conversion of carbohydrate components.water × ΔT) + ΔHvap] + [Mws × (1-W)] × Cp.. Energy output of the incinerator may be estimated given the steam generation data for the incinerator.) shall be added (Monte et al. W is the water fraction in sludge. An estimated energy consumption of the evaporation energy input plus the energy required for heating the feedstock to the reactor temperature is thus approximately 5000 kJ/kg.water is heat capacity of water (4. CH4. 1991). and non-condensable gases (H2. When heated at a temperature higher than 300°C. wood waste and oil. which may be illustrated in Figure 4. including methanol and acetic acid). CO. accompanied by slow dehydration and subsequent reactions to form unsaturated polymer intermediates that may be eventually condensed to form char (Lomax et al. 2. water in the sludge is completely evaporated and the organic matter in the sludge is effectively oxidized at high temperatures to CO2 and H2O. ΔHvap is latent heat for vaporization of water (2090 kJ/kg).192 Chunbao (Charles) Xu and Jody Lancaster In a sludge incineration process. as shown in the following two reactions: Evaporation: Oxidation and combustion: H2O (l) → H2O (g) sludge solids/organics + O2 → CO2 + H2O + ash + heat Since the water evaporation reaction is highly endothermic. therefore 70% is combusted. where additional fuels are not necessary. Cp. the de-polymerization reactions will liberate volatile products as oil or tar. Pyrolysis Pyrolysis is a thermal decomposition process in the absent of oxygen to convert biomass or waste materials into solid charcoal. Further energy input is required to raise the temperature of the sludge from drying temperature of 105oC to an average reactor temperature of 800oC. Cp. The further energy input can be estimated at 2753 kJ per kg of the sludge with 10% total solids (TS). Approximately 30% of the solids remain in the ash (Fytili and Zabaniotou. water. the carbohydrate polymers depolymerize into short chains of sugars. etc. in order to sustain the combustion for sludge with a low TS content. Cleavage of C-C . water-insoluble organics grouped under the term of “tar” or “bio-oil”. water-soluble organics (pyroligneous acids.186 kJ/kg/oC). This results in an approximate energy input for drying of 2198 kJ/kg. Evaporation. CO2).sludge is heat capacity of solids in sludge (1. When heated at a higher heating rate to a higher temperature. The energy required for evaporation can be estimated using an equation from Kim and Parker (2008): Qdrying = Mws ×W × [(Cp. dewatering of the original sludge must be conducted or additional fuels (bark. oxidation and combustion occur simultaneously.2. 2008).. 2008). Monte et al. High yield of bio-oil up to about 70-75% (Agblevor et al. process efficiency is affected by sludge moisture content. which can be used as a valuable fuel for generating heat and electricity. pyrolysis oil contains a high concentration of water (15-30%). a low temperature and low heating rate would be preferred. H2 and CH4). 2004). 1995) can be produced in fast pyrolysis processes (with very short residence time and elevated reactor temperature of ~500°C or higher). 1975). Figure 4. pyrolysis process can be tuned to produce char. Water reduction is accomplished by dewatering to about 25% DS followed by thermal drying to 95% DS. 1999). The char produced typically has a higher heating value of ~ 30 MJ/kg. but these do not compensate for the losses of carbon monoxide and thermal efficiency (Carre. oil and/or gas by properly selection of the operating conditions of temperature. such that co-pyrolysis with other wastes has been recommended in order to increase the dry-solids content of the sludge (Olexseyr. 2006). However.Treatment of Secondary Sludge for Energy Recovery 193 bond will occur at a high temperature. and vacuum reactors (Mohan et al. or can be turned into activated carbon by activation.. entrained flow. hemi-cellulose and lignin components of the biomass (Mohan et al. or it can also be applied to produce chemicals directly. Tsai et al. ablative. The process normally needs additional treatment to remove excess water. The physical properties of wood fast-pyrolysis oil are compared with those of a petroleum-based heavy fuel oil in Table 2 (Czernik and Bridgewater.. while for high char production. Accordingly. . et al. and is highly acidic (corrosive) and unstable liquid with a lower caloric value of 16-19 MJ/kg compared with 40 MJ/kg for the petroleum-based heavy oil.. 2006. circulating fluidized bed. rotating cone reactors. 1975). 2007). A significant amount of char and equal amounts of oil and gas products can be obtained in slow pyrolysis processes (operating at a low temperature for a long residence time). Pyrolysis oils are normally composed of a variety of organic oxygenates and polymeric carbohydrate and lignin fragments derived from the thermal cracking of cellulose. energy recovery. Pyrolysis oil is a potential liquid fuel for turbines and boilers.. heating rate and reaction time. As shown in this Table. CO2. Chemistry of biomass pyrolysis (Lange. If the purpose is to maximize the oil yield then a high heating rate and short gas residence time would be required. and the control of heavy-metal emissions (Lewis. leading to formation of gas products (mainly CO. 2007) Pyrolysis has long been recognised more advantageous over conventional incineration processes for the treatment of sewage-sludge with respect to fuel economy... or be upgraded to high-quality fuels by hydro-cracking or catalytic cracking (Vitolo et al. 1989). The commonly used reactors for fast pyrolysis include bubbling fluidized bed. Higher water content feedstocks cause increases in the production of hydrogen and methane. which can be used as a fuel (Bridle and Hertle. Cadmium has a lower evaporation temperature than most other metals and is dispersed into the gas phase at about 60°C.5 - Specific gravity 1.5-7. heavy metals in the sludge (except mercury and cadmium) could be safely retained within the solid chars (Kistler and Widmedz. and heating of the sludge feedstock to necessitate the pyrolysis process.194 Chunbao (Charles) Xu and Jody Lancaster Table 2.2 0.0 N 0-0. the energy input for pyrolysis. 95-98% of the energy in the dried sludge is recovered in the various products.0 11 O 35-40 1.. including energy consumption for thickening. This is a significant portion of the energy consumption for pyrolysis. As an extension of standard pyrolysis.2 0. and the net energy efficiency could be greater.94 C 54-58 85 H 5. Karayildirim et al. For a pyrolysis temperature maintained between 500 and 600°C. the energy consumption required to dry thickened waste activated sludge (TWAS) containing about 10% TS to a dry sludge at 105°C is about 2220 kJ/kg-ws. but can be condensed in gas-cleaning and scrubbing equipment with relative ease.1 pH 2. cP) 40-100 180 Elemental composition (wt %) Low temperature pyrolysis with reactor temperature <500oC has also been widely adopted for the treatment of sewage sludge in order to promote the oil yields and to minimize heavy metal evaporation.1 HHV (MJ/kg) 16-19 40 Viscosity (at 50 oC. In the OFS process.3 ash 0-0. The process can produce 200-300 litres of oil per tonne of dried sludge. according to Kim and Parker (2008). Physical property Bio-oil Heavy fuel oil Moisture content (wt %) 15-30 0. The vapours are then contacted with residual tar to catalyze the formation of high caloric value hydrocarbons. Typical properties of pyrolysis bio-oil and of a petroleum-based heavy fuel oil (Czernik and Bridgewater.2 0. However. While the data of energy consumption for thickening of the sludge is unavailable. 2006). an oil-from-sludge (OFS) process has been developed with the system arranged to maximise the production of high quality oil. 1998). while mercury can be completely evaporated at temperatures above 350°C and is difficult to eliminate from the gas stream (Furness et al. 2004). until about 50% of the sludge is evaporated. drying. In comparison with incineration and anaerobic digestion. Kim and Parker (2008) also found the energy consumption for increase of . 2000). is still fairly high.. 1987. pre-dried sludge (25% DS) is heated to 450°C for a heating period of about 30 minutes under anoxic conditions and at a pressure just above atmospheric. suggesting that pyrolysis is still an energy inefficient process. the total energy consumption for pyrolysis at 500oC is 3290 kJ/kg. for hydrogen and substitute natural gas production. 2000). Biomass gasification technology has received increased interest in the last decade since it offers several advantages over direct combustion. Average calorific values in kJ/kg of oil. It has been shown that biomass gasification plants can be as economical as conventional coal-fired power plants (Badin and Kirschner. Gasification Gasification is a thermo-chemical process during which carbonaceous content of coal. calculated using Eq. 2008). and 3 vol% N2. the major technical challenge for biomass (as well as for sludge) gasification is associated with ash slagging and the formation and removal of tar (high . accurate combustion control. 1998). 2005). in particular larger scale circulating fluidized bed (CFB) concepts. The total energy output is thus estimated to be 1649 kJ/kg.1 is determined to be about 0. and 50 vol% N2. As revealed in the Table. Thus.Treatment of Secondary Sludge for Energy Recovery 195 temperature of the dry sludge from 105oC to reach target reactor temperature of 500oC to be about 770 kJ per kg. Gasification technology if integrated with combined cycle gas turbine system has an overall thermal efficiency of 70-80% and an electrical efficiency as high as 50%. based on TWAS). Typical producer gas from an air-blown gasification process has the following compositions: 9 vol% H2.4 MJ/Nm3 (Furness et al.. based on dry sludge (or 2. 2000). offering better perspectives for power generation from biomass (IEA Bioenergy Executive Committee. of a magnitude of 100 kJ per kg of dry sludge. O2 or steam (Fytili and Zabaniotou. 14 vol% CO. the average yields of oil. As a comparison. 2 vol% CH4. also offers excellent possibilities for co-firing schemes. The gas product of gasification. 15 vol% CO2. for fuel cell feed. Gasification technology has been widely used around the world for the production of a fuel gas (or producer gas) from coal biomass. 20 vol% CO2.5. with a calorific value of 5.4 MJ/Nm3 (Furness et al. 10% and 65%..3. an O2-blown gasification process produces a gas of the following compositions: 32 vol% H2. CO. respectively. 1999). The net energy efficiency.5%.500. gas and char were used and are 22. 2007). and for the synthesis of liquid fuels such as methanol and F-T liquid through various gas-to-liquid catalytic conversion processes (Dry. gas and char. also known as producer gas or syngas. CO4. while the energy consumed during pyrolysis they assumed to be 300 kJ/kg. 7 vol% CH4. 2. respectively. Gasification of biomass has been achieved with various types of gasifiers. which shows that pyrolysis is a rather endothermic process.g.500 respectively. whose advantages and disadvantages are as summarized by Rampling and Gill (1993) in Table 3. ranging from fixed-bed to fluidized-bed and entrained bed gasifiers. 48 vol% CO. This conclusion may be supported by the work of Fytili and Zabaniotou (2008). which is not easy to estimate. H2. with an increased calorific value of 10. and CH4) in the presence of air.5% yield of oil. gas and char were used as 25%. and 16. and high thermal efficiency (Rezaiyan and Cheremisinoff. such as reduced CO2 emission. 1% and 6. 1400. biomass or lignocellulosic wastes is converted to a combustible gas at a high temperature (as high as 900-1400°C) into combustible gases (e. gas and char products. Gasification. can be mainly used for steam or heat generation as the fuel gas. compact equipment with small footprint. Using data from Kim and Parker (2008). Energy outputs for pyrolysis include the amounts and heating values of the oil. and it has great application potential for a wide range of hazardous waste treatment. supercritical water gasification can utilize the wet biomass and wastes directly. 2002). More importantly. carbon monoxide. As a primary method. Addition of catalysts. hydro-reforming/hydro-cracking. 2005). The presence of tar in the producer gas is undesirable not only because it is an indicator of low gasification efficiency. The most common catalysts for the decomposition of tar and NH3 are dolomite (a calcium magnesium ore.e. Hot gas cleanup. SCW has strong solubility for organic compounds. Nunes et al. Compared to conventional gasification processes. Ni and Fe). Xu et al. proved to be an effective means to reduce tar formation by converting tar into combustible gases through steam reforming. thermal cracking. Tar removal can be achieved either by primary method taking place insider the gasifier or by secondary treatments outside the gasifier (e. with the assistance of a plasma torch heating the biomass feedstock to a temperature of 3000°C or higher (Rezaiyan and Cheremisinoff. In addition. but also due to the fact that it increases the difficulty of syngas cleanup by fouling and plugging the pipes and tubes of some equipment (Rezaiyan and Cheremisinoff..g. K. (2005) summarized . Na. 1998).g. A wide range of biomass including some model compounds and lignocellulosic wastes have been successfully gasified in supercritical water (Xu and Antal. It is thus necessary to develop technical approaches to eliminate tar. As the secondary method for tar removal. accompanied with its high reactivity (Akiya and Savage.g. such as plasma gasification and supercritical water gasification. Williams and Onwudili. 2002). 2005). Mo-. as well as inexpensive Fe catalysts (such as chars from low rank coals with inherent Fe and Ca cations and limonite iron ore) (Ohtsuka et al. supercritical water (SCW). or Ru-based catalysts (Dayton. Recent developments in biomass gasification including some non-conventional gasification processes are under investigation. 1998).. 2006). hydrogen yield and less tar formation (Xu and Antal. 2005).and capital-intensive drying process. CaMg(CO3)2) and Ni-.. Brandt and Larsen (2000) produced a significantly low tar formation by employing a novel two-stage gasifier composed of a pyrolysis unit and a gasification unit with a charcoal bed. 1998. i.. 2005. 2004. choosing the proper configuration of a gasifier can reduce tar formation. hot gas cleanup). and water-gas reactions (Kimura et al. toluene and xylene). has been chosen as an ideal gasification medium for biomass or lignocellulosic waste conversion primarily because of its special properties such as liquid-like density and gas-like diffusivity. Thus. hot gas cleanup has attracted increasing attention in recent years due to the development of integrated gasification combined cycle (IGCC) and integrated gasification fuel cell (IGFC) technologies. supercritical water gasification (SCWG) has higher gasification efficiency. and carbon dioxide in an oxygenstarved environment. Recently. such as char. A recent study by Izumizaki et al.. (2007) also observed a reduction in tar formation when the producer gas went through a second-stage bed packed with char in a downdraft fixed-bed gasifier.. Plasma gasification is a gasification process that decomposes biomass into basic components. This plasma technique has high destruction and reduction efficiencies. and Ca) and transitional metal-based catalyst (e. highly compressed water at above its critical temperature of 374°C and critical pressure of 22 MPa. CO2 reforming. 2006). eliminating the energy. alkali/alkaline earth metal-based catalysts (e. Hao et al. catalytic destruction of tarry products and NH3 (a contaminant species in the producer gas) at a high temperature is needed to further increase the overall power generation efficiency of IGCC and IGFC.196 Chunbao (Charles) Xu and Jody Lancaster molecular-weight hydrocarbons rich in benzene. SCWG is particularly suitable for gasifying biomass with high moisture content and some waste streams such as sewage sludge (Xu and Antal. Yoshida et al. including both organic and inorganic compounds. 2004. such as hydrogen. Comparison of different types of gasifiers (Rampling and Gill. 1993). The reaction conditions were 100 mg paper sludge. and hence the optimal reaction conditions are difficult to achieve. methane and carbon dioxide in molar ratios of 27%. 27% and 45%. To the best of the authors’ knowledge.Treatment of Secondary Sludge for Energy Recovery 197 experiments where hydrogen was produced from paper sludge in supercritical water in the presence of ruthenium (IV) dioxide. including the location of energy inputs and outputs. temperature of 450oC for 2 hours. In order to improve the gasification efficiency. (2007). to date there is no other investigation worldwide that is focused on the use of pulp/paper secondary sludge as feedstock for hydrogen generation. Energy requirement in different stages of a typical gasification process is outlined in Figure 5. RuO2. The major components of gases produced were hydrogen. According to Ptasinkski et al. gasification of raw sludge is not very energy efficient because the raw sludge contains a substantial amount of water (at as high as 98-99 wt%). Table 3. 20 mg catalyst. respectively. One of the author’s research group has recently started an extensive study on catalytic gasification of pulp/paper secondary sludge in SCW for hydrogen production. the moisture content of the sludge must be greatly reduced or dried . 2000). as described .4. 2000) 2. For instance.g. the gasification technology has shown to be an energy efficient process..7 m3 of fuel gas per kg of dry sludge (DS). Baumgartel. the gasification of pulp/paper secondary sludge is a relatively new method and hence not very well documented so far. With dry sludge used. except for several reports on gasification of a mix of municipal sewage sludge and coal and other domestic waste (Dinkel et al.. Energy requirement in different stages of a typical gasification process (modified from Furness et al. bio-oils and bio-crude) from biomass through liquefaction... and the calorific value of the gas was as high as 22. It may be possible to use the enthalpy of the producer gas for drying the sludge and biomass feedstock for the gasification. According to Kim and Parker (2008).. the total process can thus be energetically self-sustaining (Furness et al. Figure 5. the energy consumption required to dry thickened waste activated sludge (TWAS) containing about 10% TS to a dry sludge at 105°C is about 2220 kJ/kg-ws.7 MJ/m3. 1993).198 Chunbao (Charles) Xu and Jody Lancaster prior to being fed to a gasifier. i. Direct Liquefaction Due to the skyrocketed oil price and the increased concerns over greenhouse gas emissions. However.e. Fast pyrolysis. there is a worldwide resurgence of interest in the production of liquid oil products (e. Hamilton (1998) reported that gasification of dried sewage sludge thermally with the Lurgi-Rhurgas process based on a circulating fluidized bed produced 0. For dry sludge. a total energy output of about 16 MJ//kg-DS. 1991. residence time. Extensive research work has been conducted on direct liquefaction of biomass in sub. In a typical direct liquefaction process.. A pioneer work was reported by Appell et al. 2005) and alcohols (Miller at al. The main purpose of liquefaction is to produce oil products of increased H/C ratios and decreased O/C ratios. usually with a high hydrogen partial pressure and a catalyst to enhance the rate of reaction (Furness et al. is so far the only industrially realized technology for bio-oil production (with a liquid yield of 50-70%) (Onay and Kockar. (1998a. H2).and near-critical water.Treatment of Secondary Sludge for Energy Recovery 199 in the preceding section. 1985. 1999. Many successful studies on direct liquefaction of biomass in organic solvents such as anthracene oil (Appel et al. 1992). However. Direct liquefaction of biomass feedstocks into liquid oils has attracted more intensive interest. the pyrolysis oil is not regarded as an ideal liquid fuel for heat and power generation. initial biomass concentration. It has also been demonstrated by Suzuki et al. However. and the oil is highly corrosive due to its low pH value.. dehydration and hydrogenolysis/hydrogenation (when hydrogen is present in liquefaction). 1985). However. the oil product in fast pyrolysis (i. Qu et al. decarboxylation. sewage sludges were converted to oils in a reaction medium of water or oil at 295-450°C with the presence of a reducing gas (hydrogen) and catalysts of Na2CO3. conducted by Kranich (1984). high-pressure conversion in the liquid phase.e. N2 or reducing. 1999). the feedstocks tested so far were mainly wood and municipal sewage sludge... catalysts and liquefaction atmosphere (inert.. Yields of the products depend on temperature. b) obtained heavy oil (HO) (with calorific values of around 30MJ/kg) at a yield of 21-36 wt% from a variety of biomass feedstocks in water at 300oC and around 10 MPa with Na2CO3 as catalyst. Beckman and Elliot. and hence a low heating value (<20 MJ/kg. and to the best of . bio-oil) consists of a high content of water (20-25%) and oxygen. 1984. where a variety of lignocellulosic materials were efficiently converted to oily products in water at around 350oC in the presence of Co and Na2CO3 as the catalysts. about only half of that of crude oil). 2000). (1986) that the treatment of sewage sludge by direct liquefaction in water at around 300oC could be a profitable alternative means for sludge disposal. For indirect liquefaction. Crofcheck et al. the oil yields were found very low with the water medium (usually less than 20%). (2003) obtained liquid organic products at a total yield of 30-35% by direct liquefaction of Cunninghamia lanceolata in water at 280-360oC for 10-30 min. Maschio et al. due to its simpler technical route and better conversion economy and efficiency relative to the indirect liquefaction processes. depolymerization. biomass is converted to liquid products directly but through a complex sequence of processes involving solvolysis. 2006. (1971). The effects on the liquefaction product yields were investigated. Minowa et al. 1996. NiCO3 and Na2MnO4. 2007) have been reported. in an early study on liquefaction of sewage sludge. Direct liquefaction is a low-temperature. Liquefaction can be accomplished indirectly or directly. Boocock and Sherman. The organic conversion rates varied from 45% to 99% and the oil yields were from 35% to 63% in the reaction medium of oil. Hot compressed water and sub-/supercritical water (at temperatures of 200-400°C) are however more advantageous for being used as the solvent in biomass direct liquefaction in that water is likely the most “green” and environmentally benign solvent. biomass is converted into liquid products through first gasification to syngas followed by catalytic conversion (Dry. Research on direct liquefaction has been widely performed in the 1980’s for the purpose of alternative energy production (Kranich. Without further upgrading. and hence a high caloric value relative to those present in the feedstock. as given in Table 2. For instance.. Xu and Etcheverry. Treatments of secondary pulp/paper sludge in water at 250-380°C for 15-120 min in the presence of N2 atmosphere resulted in yields of water soluble oils (WSOs) at 20 wt% . Figure 6.45 wt% and yields of heavy oils (HOs) at 15 wt% – 25 wt%. Filtration is performed on the liquid product mixture in order to separate the liquid oil products from the solid residue. while as temperature increased further to above 350oC. respectively. residence time. An outline of a direct liquefaction process for the treatment of sludge is pictured in Figure 6. 2008) The effects of liquefaction temperature. initial biomass concentration. For temperatures lower than 350oC. Outline of the direct liquefaction process (adapted from Xu and Lancaster. accompanied by an increase in the yield of WSO. catalysts and liquefaction atmosphere (inert. H2) on the liquefaction product yields were investigated. An increased residence time produced a greater yield of HO (reaching as high as 25wt% for 120min) but a lower yield of water-soluble and a reduced yield of total oil. A higher initial biomass . as temperature increased the yield of heavy oil (HO) increased at the expense of the watersoluble oil (WSO) formation. the yield of HO decreased. where sludge is fed into a pressure reactor where liquid products are primarily produced and gas products are collected. with HHVs of 10-15 MJ/kg and >35 MJ/kg. As a result. other than the published work by Xu and Lancaster (2008). N2 or reducing. no work has been reported on treatment of pulp/paper secondary sludge in hot-compressed water or sub-/supercritical water.200 Chunbao (Charles) Xu and Jody Lancaster the authors’ knowledge. Xu and Lancaster (2008) experimentally treated secondary pulp/paper sludge in hotcompressed or sub-/supercritical water at a temperature of 250-380oC in order to produce liquid oils for energy recovery from the secondary pulp/paper sludge. Liquid products are a mixture of water-soluble oil (WSO) and heavy oils (HO) and solid residue or char. liquefaction as a treatment method is still in the research stages but could potentially be an effective approach to recover energy from the secondary sludge waste for production of liquid oil products. char. 0 None Liquefaction in N2 0 21.5 51.9 20. i. (1).0 34. irrespective as to whether a catalyst was present or not.0 Ca(OH)2 Liquefaction in H2 4.3 None 20 280oC. the energy efficiency can be improved by employing a flow-type reactor and installing a heat exchanger to pre-heat the reactor feed stream using the hot product stream as well as by combusting the resulting chars/gases to provide a portion of the heat for the process. did not alter biomass conversion significantly. .7 80 100 Yield (wt%.e.4 13. were all <1.6 35.2 22. and it produced total oily products (HO+WSO) at a yield as high as 60 wt%.76. in a batch reactor.3 36. the energy output/input ratios.e. 2008). but catalyzed the formation of WSO and produced much higher yields of total oil products.1 wt% biomass Initial gas pressure: 2 MPa 40 60 5. resulted in significantly improved net energy efficiencies. H2) in the liquefaction process promoted the HO formation while suppressing the WSO formation.6 wt%). the operation in H2 with the presence of Ca(OH)2 catalyst dramatically enhanced the efficiency to as high as 0.201 Treatment of Secondary Sludge for Energy Recovery concentration produced a greater yield of HO but a reduced yield of WSO. The use of the two alkaline earth metals catalysts.6 Ca(OH)2 7.3 20..2 26.. liquefaction of the sludge powder in water at 280oC for 60 min produced a high yield of HO (26 wt%). Ca(OH)2 and Ba(OH)2. while resulting in negligible change in the formation of total oil products. daf) HO WSO Char Gas Figure 7. it was demonstrated that the reducing atmosphere (i.6 21. 60 min 9. The presence of 0.1M Ca(OH)2 and 2MPa H2. was energy inefficient. calculated based on Eq. However. In Xu and Lancaster’s (2008) work. almost two times as high as that in N2 (13. With the presence of 0.0. However.1M K2CO3 dramatically enhanced organic conversion leading to a low yield of char. The liquefaction atmosphere (inert or reducing) was found to be another important factor influencing the liquefaction process. Liquefaction of sludge in H2. while the use of the K2CO3 suppressed the formation of both types of oils. As shown in Figure 7. suggesting that the liquefaction operation tested.8 21. 6. Variation in the product yields with different liquefaction atmospheres (N2 and H2) (adapted from Xu and Lancaster. (2004). about half of the heating value of the sludge can be recovered in the studied process. .5MPa) and pressurized oxygen are fed into the preheater reactor at 25 degrees Celsius. 2006). After reaction. at temperatures and pressures above the critical point of water. respectively (Bermejo et al.. 2000. Water at its supercritical state can dissolve organics and hydrolyze even polymers and hence prevent the formation of char (Perry and Green 1999. also referred to as hydrothermal oxidation.5. 374oC and 22MPa. Sludge can be processed at 10% solids by weight or even less (Mahmood and Elliott. a low viscosity. the low temperature of the SCWO process in comparison to conventional combustion can lead to a greatly reduced NOx and SO2 formation. 2006). The SCWO process has been under development since the early 1980’s when the well known process of wet oxidation was developed at MIT (Modell.e. water is not only the reaction medium but it participates directly in the reaction through the formation of free radicals (Griffith and Raymond. 2006). Schematic of a SCWO system (modified from Mahmood and Elliott. 2006). The solid and liquid products are separated and the wet inorganic solids can be sent to a landfill or spread on dedicated land while the water can be redirected to the wastewater treatment plant. Moreover. 2002). SCW is a superior reaction medium with a high diffusivity. Pressurized sludge (25.202 Chunbao (Charles) Xu and Jody Lancaster 2. Since water is utilized in the reaction there is no requirement to dewater the sludge before processing.. Mahmood and Elliot. 2006). In the preheater the mixture of sludge and oxygen are heated up to approximately 300 to 400oC. and relatively high-density therefore rapid oxidation reactions are expected. In addition. SCWO. Figure 8 outlines a schematic of a SCWO process. to achieve the supercritical state of water. 1982). the effluent is cooled and energy is recovered. Figure 8. The reaction mixture enters the main reactor where the remaining portion of the organics is oxidized in short hydraulic residence time of 510 min at the maximum process temperature of around 600oC (Mahmood and Elliott. Fang and Koziński. is a process that oxidizes organic solutes in an aqueous medium using oxygen/air or hydrogen peroxide as oxidants. i. Supercritical Water Oxidation (SCWO) Supercritical Water Oxidation. According to Svanstrom et al. a variety of biomass slurries including pulp mill sludge (Modell. In the first hydrolysis step.. Anaerobic digestion processes are widely recognized as particularly suitable for highly polluted wastewater treatment and for the stabilization of primary and secondary sludges.. 2003). and sewage sludge (General Atomics.. Secondary sludge is fed into the hydrolysis tank. 2004). many are not completely removed during sewage treatment processes and are merely transferred to wastewater sludge (Farrah and Bitton. The digested and separated solids can undergo further processing and potentially be used as a fertilizer or soil conditioner for land application (Kumar. Two-stage systems have been proposed to enhance this process (Ponsá et al. Texas to process up to 9. .. Anaerobic digestion of municipal or pulp/paper bio-solids could reduce solid wastes by 30-70% with the benefit of energy recovery through methane production. Anaerobic digestion occurs in the absence of oxygen while in the presence of bacterial activity. Anaerobic Digestion Since a large number of the enteric bacteria and viral pathogens presented in untreated sewage are associated with wastewater solids. methane and water.8 dry tonnes per day of municipal sludge (Griffith and Raymond. For mesophilic processes.6. 2007). 2003). 2004). 2. 1983). in particular SCWO. 2000).. hydrolysis is regarded as the rate-limiting step in the degradation of complex organic compounds. 2002). four major steps can be distinguished. A supercritical water oxidation sludge processing plant has been installed at Harlingen. and the second stage separates the undigested solids from the liquid to form carbon dioxide. The first stage digests the solids. 1997). is currently being considered by various research and waste management organizations as an alternative treatment option (Stark et al. while 55oC is desirable for thermophilic processes (Song et al. 1989). The microbiology of anaerobic digestion is complicated and involves several bacterial groups forming a complex interdependent food web. 1990). Acidogensis and acetogenesis follow in the second and third step while in the fourth and final step methane is produced by menthanogenic archaea (Gavala et al. Figure 9 outlines a flow diagram of anaerobic digestion of secondary sewage sludge for energy production. The methane gas produced can be used to generate power by fueling a biogas engine connected to an electric generator.. 2008). Generally about half of the organic matter in sludge is susceptible to anaerobic biodegradation into the formation of biogas (Elliot and Mahmood. including hazardous wastes such as hexachlorobenzene.Treatment of Secondary Sludge for Energy Recovery 203 The effectiveness of SCWO has been demonstrated at the laboratory and pilot scale with a wide broad range of feedsctocks. There are two typical operating temperatures for anaerobic digesters determined by the desired species of methanogens.. However. such as sewage sludge. It has been demonstrated that complete oxidation of virtually any organic material. the optimum operating temperature is 37oC. 2000. Hydrothermal oxidation. could be achieved by SCWO. In conventional single-stage anaerobic digestion processes. while the treated water may be used for irrigation (Kumar. 2006). producing bio-gas (mainly methane). An environmental assessment was conducted on the Harlingen plant and found large environmental gains from recovery of heat thereby reducing natural gas consumption for heat generation (Svanström et al. both solubilization of insoluble particulate matter and biological decomposition of organic polymers to monomer or dimmers take place. such as pig manure (Rulkenes et al. Gavala et al. In these tests. H.N. thus substantially reducing the quantity of the secondary sludge from the aerobic treatment operation. With sludge containing 38% lignin. with no noticeable scum or foaming problems..204 Chunbao (Charles) Xu and Jody Lancaster Thermophilic anaerobic digestion is generally more efficient in terms of organic matter removal and methane production than the mesophilic process (Gavala. 1992). having a concentration of volatile suspended solids (VSS) of 24-29 gL-1. 2003). The COD reduction in these experiments reached 29. 40% reduction of the sludge and a biogas production of 0.. (1989) reported that the anaerobic digestion process for the treatment of Kraft mill primary sludge could be significantly more economical than the conventional landfilling. Fein et al. Stahl et al.5 m3-biogas/kg sludge removed were achieved. 2000) Telles et al. Figure 9 . Anaerobic digestion of Kraft waste activated sludge (or secondary sludge) was tested with a pilot-scale digester for sludge reduction and biogas production (Puhakka et al. 21 and 45% in the sludge. 13 g NaOH/kg sludge was added to maintain the optimum pH in the system for the maximum sludge reduction efficiency. (2002) evaluated the performance of a slow rate anaerobic digester in treating secondary sewage sludge. Flow diagram of anaerobic digestion for power generation (modified from Kumar. (2004) also reported a pilot trial using anaerobic digestion to pre-treat wastewater and to digest untreated paper mill effluent. which resulted in a much lower amount of organics entering the activated sludge system. The operation of anaerobic digestion at room temperature was stable. et al. The digester was fed by secondary sewage sludge without any previous thickening. Anaerobic digestion has been widely adopted for the treatment of municipal sewage sludge before final disposal . 2008). Methane The greatest sludge volume reduction (over 90%) can be achieved with the hightemperature methods including incineration. pressure. while these methods differ in the objective products. Incineration. ~150oC) Yes No No No Operating Temp (oC) 850-950 400-800 800-1400 250-400 400600 37 (Mesophilic) 55 (Thermophilic) Operating Pressure Ambient Ambient or slightly above Ambient 4-20 MPa 22 MPa Ambient Operating atmosphere Air Oxygen depleted Air or oxygen H2 – reducing N2 . and gasification favors production of gas. etc. The major disadvantage for these high-temperature processes is their lower net energy efficiency for the treatment of secondary sludge containing very high content of water (98-99%). which is advantageous as it effectively reduces the physical amount of sludge for disposal. atmosphere and products. Gas and Char Syngas Oil.) vary among the methods discussed in the preceding sections.205 Treatment of Secondary Sludge for Energy Recovery and it is employed worldwide as the oldest and most important process for sewage sludge stabilization and treatment (Ponsá et al. Summary of Comparison of Secondary Sludge Treatment Methods Comparison Parameter Preheating/ Drying required Incinerat ion Pyrolysis Gasification Direct Liquefaction SCWO Anaerobic Digestion No Yes (25% solids. . incineration. gasification and SCWO methods utilize air or oxygen while the remaining methods are conducted under oxygen depleted or anaerobic conditions.. For example. DISCUSSION AND COMPARISON OF TREATMENT METHODS The operating conditions (temperature. pyrolysis targets a high yield of oil. resulting from the need of the energy intensive operations of dewatering/thickening and complete evaporation of the water in the sludge. There is currently no full-scale anaerobic digestion facility in the pulp and paper sector for the digestion of solid residues. pyrolysis and gasification operate at high temperatures.inert Air or oxygen Anaerobic Primary Energy Products Steam Oil. there is recent technological advancement that potentially can make anaerobic digestion of pulp/paper sludge more feasible by the development and establishment of pretreatment of sludge prior to anaerobic digestion to accelerate the hydrolysis of sludge. Incineration aims to produce heat and steam/electricity. Table 4. Gas and Char Gas Biogas. Nevertheless. it has not gained popularity in the pulp and paper industry mainly because of its long sludge residence time requirement of 20-30 days (Elliot and Mahmood. pyrolysis and gasification. 2007). 3. as summarized in Table 4. While anaerobic digestion is commonly practiced in the municipal sector. Some direct liquefaction processes employ hydrogen gas to obtain better product yields and results. High organic carbon destruction efficiencies .Reduced environmental emissions . the water in the sludge is the reaction medium and participates directly in the reaction through the formation of free radicals (Griffith and Raymond.Corrosion and salt deposition in the equipment which accelerates the deterioration of the reactor Anaerobic Digestion . . therefore..Reaction occurs in aqueous phase. 2008) Treatment Method Advantages Disadvantages Incineration .Air pollution problems (NOx and SO2 emissions) ..Dewatering and drying of sludge is needed .Not commercially developed for pulp and paper sludge treatment .Less technical maturity for its application to paper/pulp sludges Gasification . Mahmood and Elliot. so no dewatering/drying required . Advantages and disadvantages of sludge treatment methods (Kumar. i.. 2000.Production of an inert solid waste .Easily controlled by operator . need for extensive air pollution equipment and. 2006. 2002)..Dewatering/thickening of the sludge is required. Karayildirim et al.High energy recovery efficiency .Low operating temperature . 2000.Possible utilization for the ashes obtained . direct liquefaction. Accordingly.Production of a mixture of gaseous and liquid fuels and a solid inert residue .Production of a mixture of high calorific value liquid fuels .Dewatering/thickening of the sludge is required . Table 5.Complexity of technology Direct Liquefaction . A comparison of advantages and disadvantages of different treatment methods are presented in Table 5.High reduction of sludge volume by about 90% .Volume reduction by as much as 90% and production of a sterile carbon char .Ability to handle most inorganic compounds found in sludge .Nearly complete elimination of the organic materials . the other three treatment methods.Incineration process can be energy deficient . so that no dewatering.No dewatering/drying required . As a matter of fact. thickening and drying of the feedstock is required . high capital costs (Monte et al.206 Chunbao (Charles) Xu and Jody Lancaster Other main problems concerning these high-temperature thermal processes include excessive energy to reach high temperatures. these methods are more promising for the treatment of secondary sludge from the standpoint of energy recovery. SCWO and anaerobic digestion. 2006.e.Conversion of all sludge biomass fraction into useful energy .Not commercially developed Supercritical Water Oxidation .Conversion of all sludge biomass fraction into useful energy . 2008).Emission of chlorinated compounds . long residence times . Bermejo et al.2006.Non-burning process .Monte et al.Reaction medium is water. In contrast.Cannot accept shock loading and excessive foaming is often a problem . operate at a relatively lower temperature and more importantly without the need of dewatering /thickening and complete evaporation of the water in the sludge.Slow process.. Furness et al..Higher efficiency of energy recovery . for SCWO and direct liquefaction methods.High cost due to the increasing demand on the flue gas cleaning Pyrolysis . gasification. F. 25 Baumgartel. (1971). G.. (1995). Pyrolysis 27. operate at a relatively lower temperature and more importantly without the need of dewatering /thickening and complete evaporation of the water in the sludge. & Savage. Rev. & App. Incineration. 120. pyrolysis and gasification. E. & Wender. H. I. A.. secondary sludge as a byproduct of biological treatment is far more difficult to dewater and to be disposed.. pressure. The major disadvantage for these high-temperature processes is their lower net energy efficiency for the treatment of secondary sludge containing very high content of water (98-99%). direct liquefaction. ACKNOWLEDGMENTS Part of this work was financially supported by the Natural Science and Engineering Research Council of Canada (NSERC) through the Discovery Grant awarded to Dr. Charles XU. i. The Siemens thermal waste recycling process – a modern technology for converting waste into useable products. which is advantageous as it effectively reduces the physical amount of sludge for disposal. 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Subcritical and supercritical water gasification of cellulose. G. 17. 2008. T. J. besides the combustible fraction stream. Through this process a biogas with elevated content of methane can be produced and supplied to engines for energy recovery. The combustion can be applied directly to Municipal Solid Waste or can be applied to a stream of selected waste obtained by means of mechanical sorting of Municipal Solid Waste. to push energy recovery also from this stream. The combination of schemes will be analysed in this chapter in reference to a study case characterised by an average waste material composition. ABSTRACT Energy recovery from waste can follow several routes. but another option. When Municipal Solid Waste mechanical sorting is applied. alternative possibilities for thermal treatment are gasification and pyrolysis. Via Santa Marta. Chapter 6 ENERGY RECOVERY FROM WASTE: COMPARISON OF DIFFERENT TECHNOLOGY COMBINATIONS 1 Lidia Lombardi and 2Andrea Corti 1 2 Università degli Studi di Firenze. At present the fate for this stream is biological aerobic stabilisation. which can be applied through different technologies (wet and dry digestion). Via Roma Siena – Italy. the most common of which is mobile grate combustor. available for energy recovery. The above-mentioned technologies can be combined in several schemes to optimise the overall energy recovery. 3. Università degli Studi di Siena. The comparison will be carried out using some indicators of the overall energy recovery for each scheme. Dipartimento di Ingegneria dell’Informazione. The most common one is waste direct combustion associated with conventional energy recovery in a steam turbine cycle. Inc. . is biological anaerobic digestion.In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers. Besides the direct combustion of waste. characterised by a high presence of organic biodegradable fraction. a humid fraction is also obtained. 50139 Firenze – Italy. These processes require being fed by a homogeneous combustible fraction obtained by mechanical sorting and supply as output one or more combustible streams. using several technologies for the combustion. this is called the pyrolysis (Bridgewater et al.214 Lidia Lombardi and Andrea Corti INTRODUCTION The thermal treatment of solid residues was introduced as the most suitable way to reduce the mass (up to 70–80% reduction) and the volume (up to 90% reduction) of waste and to clear up their potential for putrefaction. while combustion can be applied to MSW directly. the bonds of long chain molecules of solid materials are broken to obtain smaller molecules in gaseous form. keeping a high level of plant reliability. calorific value and composition. 1981). to the simple disposal. in the case of waste. The combustion is an exothermic process. the energy recovery process. the solid waste thermal treatment collected attention also in reference to the possibility of associating. In this chapter the application of the above-mentioned thermo-chemical processes to Municipal Solid Waste (MSW). from the compounds present in the solid mass. At increasing temperature. which still has an energy content. In order to obtain an adequate stream from MSW to be fed to gasification and pyrolysis. is applied with the aim of . 1993). in terms of size. 1999). the process outputs are a gaseous stream (called the syngas). the waste thermal treatment represents an inescapable part of the integrated waste management and treatment system and the challenge for the future lays in the improvement of energy recovery. When the solid material undergoes a process that takes place at a relatively high temperature and in complete absence of oxygen. is considered from a process analysis point of view. The most common thermo-chemical process applicable to solid materials—and hence waste—is combustion (Tchobanoglous et al.. a pre-treatment. releasing thermal energy and heating up the system. Hence. Nowadays. a liquid stream (called the tar) and a solid stream (called the char). Further. Whether the oxygen is present or not it is possible to obtain different thermo-chemical processes. When oxygen is added in sub stoichiometric ratio to solid materials. Such a process requires a heat supply from the external environment and its outputs are in general—with different yields depending mainly on the temperature—a gaseous stream (called the syngas). with the connected sanitary risks (Tchobanoglous et al. gasification and pyrolysis require a more homogeneous entering material. The term “thermal treatment” means a process which takes place at relatively high temperatures involving several different chemical reactions evolving. Such a process is called gasification (Reed. coupled with appropriate energy recovery systems.1993). and solid residues which may contain unreacted compounds. since the aim is the complete oxidation of organic material made of mainly carbon and hydrogen.. with the aim of comparing the energy recovery potential in the different cases. according with the growing awareness of conventional fuels availability reduction and along with the increasing costs of traditional energy sources. based on mechanical sorting of MSW. partial oxidation reactions of the organic material take place.. carried by partially oxidised compounds and small hydrocarbons. with all three having combustible characteristics. It takes place in a large excess of oxygen with respect to the stoichiometric ratio. Of course. and since its outputs are combustion gases and bottom ashes—both of which are completely oxidised materials—there is no energy content left. a reference study case was assumed. but another option to push energy recovery also for this stream is biological anaerobic digestion. It is worth noticing that the anaerobic digestion is not an alternative to the aerobic biostabilisation. as it will be illustrated in the next paragraph. Figure 1. With respect to this MSW composition a simplified mechanical sorting process was considered. MSW Characteristics and Pre-treatment In order to perform a comparison among the different possibilities for energy recovery from MSW. The process outputs are mainly a combustible fraction—adequate for feeding a thermal treatment—and a humid fraction. characterised by a high presence of organic biodegradable fraction. Through this process a biogas with elevated content of methane can be produced and supplied to engines for energy recovery. mass flow rate and LHV of the output stream are reported in table 1. the energy recovery potentials from MSW were evaluated including not only the thermo-chemical processes but also their integration with anaerobic digestion. The analysis is reported in reference to a study case in terms of MSW flow rate and composition. since an aerobic post-treatment for the anaerobic digestate is always required. wood and paper—in a stream which is commonly called combustible fraction (CF) or in some cases—if some law requirements are complied with—can be addressed as Refuse Derived Fuel (RDF). All the considered processes were analysed by means of thermodynamic and chemical simulation using specific tools. based on grinding.Energy Recovery from Waste: Comparison of different Technology … 215 removing humid and inert fractions and concentrating high energy content materials—as plastic. considering for each process the appropriate entering stream. According to the considerations above. besides the combustible fraction stream. which can be applied through different technologies (wet and dry digestion). . Schematic of simplified mechanical sorting line. also a humid fraction (HF) is obtained. mass flow rate and low heating value (LHV). illustrated in the following. characterised by the features reported in table 1 in terms of MSW material composition. characterised by a large presence of organic fraction— appropriate to feed a biological process. The material composition. When MSW mechanical sorting is applied. metals removal by magnetic separator and sieving (figure 1). in order to reach high levels of stabilisation and sanitary risk avoidance. At present the most common fate for this stream is biological aerobic stabilisation. Assumed elemental composition and moisture content for each material fraction Paper and cardboard Organic fraction Pruning scrap Plastics Metals Wood Glass Textiles Carbon 33.02% 1.80% 0.57% 54.30% 16.74% 3.20% 96.39% 22.85% 13.53% 30..00% Combustion with Energy Recovery The most common route followed to realise energy recovery from waste is their direct combustion associated with conventional energy recovery in a steam cycle.10% 5.95% 15. The WtE can be applied directly to MSW or can be applied to the combustible fraction obtained by means of mechanical sorting.59% 19.49% 35.93% 0.77% Nitrogen 0.99% 5.30% 2.536 12.75% 13.23% 0. 1993).46% 8.61% 9.74% 8.22% 5.43% 1.53% 4.09% 0.99% 0.68% 13.24% 4.44% 16.00% 0. whose results are coherent with literature values (Tchobanoglous et al.08% 0.00% 45. combustible fraction and humid fraction. were determined and results are reported in table 3.649 3.98% 0. humid fraction). Table 2.00% 65.86% 0.84% 7. The elemental composition for each waste stream is required in the chemical and thermodynamic models used for the mathematical simulation of the analysed processes.16% 0.81% 4.14% 0.36% 2.60% 0.64% Hydrogen 3.07% 4.91% 0.14% 8.63% 7.78% 34.00% 2.56% 23. This is conventionally addressed as a Waste-to-Energy (WtE) process.11% 0.00% 5.06% 10.79% 10.16% 0.80% 25.66% 83.16% 11.03% 11.04% 4.01% 2.16% 1.10% 5. the overall elemental composition and moisture content of each waste stream (MWS. .85% Oxygen 30. Material composition and mass flow rate for MSW.04% Sulphur 0.99% Combustible fraction Humid fraction 21.216 Lidia Lombardi and Andrea Corti Table 1.03% 66.647 14.07% Moisture 25.00% 20.92% 20.344 10.86% 0.00% 10.00% 0.201 2.43% 7.127 On the basis of the assumed elemental composition and moisture content for each single material fraction (table 2).44% 39.63% Inert 7. combustible fraction.17% 5.00% 12.08% 0. Paper and cardboard Organic fraction Pruning scrap Plastics Metals Wood Glass Textiles Mass flow rate [kg/h] LHV [kJ/kg] MSW 15. the steam cycle maximum pressure. previously reported in table 1.45% Oxygen 0. and the remaining non differentiated residual MSW are characterised by relatively high low heating values (since the humid fraction and inert fractions are preliminarily eliminated). The code requires as input the mass flow rate of waste.91% 44.91% 24.74% 17. considering as input the mass flow rates.23% Moisture 49.14% 2.10% 30.32% 1. . Figure 2 shows the simplified schematic of the considered WtE process. previously reported in table 3. the combustion temperature is imposed. and evaluates the steam production in the HRSG. the net power production and the net efficiency. estimates the thermal energy losses. with respect to the previous technology which was based on adiabatic (unless the unavoidable thermal losses) combustion.00% 0.58% 0.81% Sulphur 0.57% Nitrogen 1. The main output results from the WtE simulations. the temperature levels in the heat recovery steam generator (HRSG) and the estimation of the internal consumption in term of percentage of the produced gross power. the combustion temperature. The simulation of the WtE process was carried out using an in-house developed mathematical code.00% 11. The code calculates the energy and mass balance in the combustion chamber and the volumetric percentage of oxygen in the combustion gases. with reference to the two different feedings of MWS and combustible fraction. the steam turbine power output.24% MSW direct combustion could be of particular interest when a well developed separate collection system is applied.81% 47. its elemental composition. The main operating parameters assumed for the simulations are reported in table 4. are reported in table 5. This integrated boiler in the combustion zone represents the most recent technology for WtE and it is able to improve the energy recovery in this kind of plant.76% 2. Calculated elemental composition and moisture content of the considered waste streams MSW Combustible fraction Humid fraction 16.56% Carbon 26. using the Engineering Equation Solver software (F-Chart Software).Energy Recovery from Waste: Comparison of different Technology … 217 Table 3.13% Inert 20. From a modelling point of view. maximum temperature and condenser pressure. while the amount of heat recovered in the integrated boiler is subtracted – from energy balance in the combustion chamber – to such an extent that the excess combustion air is enough to assure a minimum level of about six percent of oxygen volume in the exhausts. This means that the waste fractions that can be recovered are separated up-stream of the waste collection. the bottom and fly ash production. The recovery of the heat released in the combustion is assumed to start within the combustion chamber itself.34% 0. and elemental compositions. placing evaporator pipes in the wall of the combustion and post-combustion zone.84% Hydrogen 1. The WtE process was simulated for both MSW and combustible fraction.27% 0. The simplified schematic of the proposed gasification process with energy recovery is shown in figure 3.).201 32.8 12 22.322 8. Main operating parameters assumed for the waste combustion with energy recovery Combustion temperature [°C] Steam maximum temperature [°C] Steam maximum pressure [bar] Steam cycle condenser pressure [bar] Exhausts HRSG entering temperature [°C] Exhausts HRSG exiting temperature [°C] Internal consumption [%] 1. in reference to the elemental composition and mass flow rate reported in table 3.376 68. Main results form the WtE simulations.127 40.841 Combustible fraction 9.356 7.1 12 22.344 10.05 13.350 10.582 25.109 8.896 90. Simplified schematic of the considered WtE process. . Waste mass flow rate [kg/h] LHV [kJ/kg] Entering thermal power [kW] Gross power output [kW] Net Power output [kW] Exhaust mass flow rate [kg/h] Gross efficiency [%] Internal consumption [%] Net efficiency [%] CO2 mass flow rate output [kg/h] MSW 14.82 10.218 Lidia Lombardi and Andrea Corti Table 4.25 620 150 12 Figure 2.643 Gasification with Energy Recovery The simulation of the gasification process with energy recovery was carried out using the commercial software Aspen Plus® (Aspen Technology Inc.750 25. Table 5.537 12. considering as input only the combustible fraction.100 400 40 0. together with the amount of steam produced in the first syngas cooler. Gasification temperature [°C] Gasification pressure [bar] Steam supplied to process gasification [kgH2O/kgC] Unreacted carbon [%] Syngas temperature at the exit of first cooler [°C] Syngas temperature at the exit of scrubbing [°C] Syngas combustion temperature [°C] Steam maximum temperature [°C] Steam maximum pressure [bar] Steam cycle condenser pressure [bar] Temperature of exhausts after last cooling [°C] 875 1 0. Once imposed the gasification temperature. This steam.Energy Recovery from Waste: Comparison of different Technology … 219 Figure 3. supplied to push the hydrogen production. Table 7 shows the simulation main results and the details of calculated syngas characteristics. . The gasification solid residues leave the reactor from the bottom.25 150 The main operating parameters assumed for the simulations are reported in table 6. while the syngas exits from the top. Table 8 reports the gasification and energy recovery cycle synthetic results. The exhausts exiting from the boiler are further cooled down in order to produce the amount of process steam required by the gasification reactor. producing power output. Actually the removal process is simulated only from a thermodynamic point of view. Table 6. Simplified schematic of the proposed gasification process with energy recovery. The waste enters the gasification reactor together with the gasification air and a stream of steam. Syngas is cooled down to an assumed temperature – recovering the heat to produce superheated steam . expands in a steam turbine. Main operating parameters assumed for the waste gasification with energy recovery.60 150 80 850 400 40 0.11 4. Then the syngas is fed to a boiler together with combustion air. The energy released in the combustion is in large part recovered in the boiler to produce superheated steam. which is evaluated on the basis of the assumed combustion temperature.before entering a wet scrubbing for the removal of undesirable compounds. considering the syngas further cooling and its moisture content saturation. at the temperature assumed at the exit. The overall process efficiency is calculated as the ratio between the power output an the energy entering with the waste. the amount of required gasification air is evaluated. down to the condenser pressure. 322 Net Power output [kW] 5.096 18. Part of the syngas is burnt to supply the heat required by the pyrolysis reactor.345 H2 0. The possibility of using relatively high efficiency .01 Pump consumptions [kW] 72 Other trace compounds 0. The simplified schematic of the proposed pyrolysis process with energy recovery is shown in figure 4.124 5.273 Net efficiency [%] 16. since the assumed operating temperature is relatively high. The remaining syngas is burnt with air combustion in a reciprocating engine to produce electric energy.072 CO2 0. In this study the attention was focussed on syngas production. which can be accepted by the reciprocating engine.).537 LHV [kJ/kg] 12.176 Exhausts boiler exiting temperature [°C] Turbine power output [kW] 200 H2O 0. Gasification and energy recovery cycle synthetic results Combustible fraction Waste mass flow rate [kg/h] 9.112 1.31 CO2 mass flow rate output [kg/h] 10.59 Steam produced in the first syngas cooler [kg/h] Steam produced in the boiler [kg/h] 9.280 Pyrolysis with Energy Recovery The simulation of the pyrolysis process with energy recovery was carried out using the commercial software Aspen Plus ® (Aspen Technology Inc. Main simulation results and details of calculated syngas characteristics Cycle main results Gasification air mass flow rate [kg/h] Evaporated water in the scrubbing process [kg/h] Syngas mass flow rate after scrubbing process [kg/h] Combustion air mass flow rate [kg/h] Exhausts mass flow rate [kg/h] 23.004 Table 8.220 Lidia Lombardi and Andrea Corti Table 7.277 LHV [kJ/kg] 2. considering as input only the combustible fraction. This layout solution was proposed on the basis of the very good LHV obtained for the pyrolysis syngas.210 34. The waste enters the pyrolysis reactor were the temperature is kept at the assumed value.870 CO 0.700 66. rather than on liquid and solid outputs. A syngas is produced and the solid products/residues are discharged from the bottom.197 32.080 Syngas characteristics at gasification reactor exit Temperature [°C] 875 Mass flow rate [kg/h] 31.201 Entering thermal power [kW] 32. in reference to the elemental composition and mass flow rate reported in table 3.977 Compounds N2 Mass fraction 0. with respect to steam cycles proposed previously for the WtE and gasification cases.1 - NO3 0.5 Temperature [°C] 750 2. Table 10 shows the simulation main results and the details of calculated syngas characteristics.850 35 Compounds Mass fraction 65 N2 0.893 LHV [kJ/kg] 19.028 H2O 0. The overall process efficiency is calculated as the ratio between the power output an the energy entering with the waste. Main simulation results and details of calculated syngas characteristics.778 CO2 0.447 CO 0. Main operating parameters assumed for the waste pyrolysis with energy recovery.009 H2 0. Pyrolysis temperature [°C] Pyrolysis pressure [bar] Unreacted carbon [%] Reciprocating engine efficiency [%] 750 1 4. Table 9.003 .018 9. The main operating parameters assumed for the simulations are reported in table 9.057 CH4 0. Figure 4 – Simplified schematic of the proposed pyrolysis process with energy recovery. Cycle main results Heat required by the pyrolysis reactor [MW] Syngas mass flow rate for heating the reactor [kg/h] Syngas mass flow rate to engine [kg/h] Syngas mass flow rate for heating the reactor [%] Syngas mass flow rate to engine [%] Reciprocating engine power output [kW] Syngas characteristics at pyrolysis reactor exit 14.640 Mass flow rate [kg/h] 7.60 35 Table 10.Energy Recovery from Waste: Comparison of different Technology … 221 equipment for energy conversion of this syngas open the potential to high energy recovery.533 4.007 Other trace compounds 0. the Volatile Solids (VS) content was estimated. Then the general anaerobic stoichiometric reaction (1) was considered: . 2002). assuming a biodegradability coefficient (BC). Then. Pyrolysis and energy recovery cycle synthetic results Combustible fraction Waste mass flow rate [kg/h] 9. which contains a large amount of biodegradable fraction.201 Entering thermal power [kW] 32. that can be supplied to a reciprocating engine to produce electricity. For this reason a simplified approach was followed in this application. is a good candidate to be processed in such a way. Figure 5. 2002).222 Lidia Lombardi and Andrea Corti Table 11. that can be obtained in the anaerobic digestion (Mata-Alvarez .22 CO2 mass flow rate output [kg/h] 10.322 Net Power output [kW] 9. recalculated on dry basis (table 12). 2002). and a VS removal efficiency (RE). but this can be particularly onerous especially if we are dealing with solid waste. aimed to evaluate biogas production from anaerobic degradation of humid fraction. Thus the humid fraction mechanically sorted from MSW (table 1). Starting from the material composition of the humid fraction and the moisture content assumed in table 2..447 Net efficiency [%] 29. This amount of biodegraded material was characterised – for each material fraction – in term of brutal chemical formula of the type CaHbOcSdNe. coherent with literature data (Tchobanoglous et al.280 Anaerobic Digestion Anaerobic digestion is a sequence of biological processes in which different types of bacteria break down biodegradable material in the absence of oxygen (Mata-Alvarez . as illustrated in Figure 5.1993). for each material fraction. the amount of the biodegraded material was evaluated. which is based on some simplified assumptions. The main product of anaerobic digestion is a biogas with good LHV. From TS. on the basis of elemental composition (table 2). The anaerobic biological process could be simulated in a complete way reproducing the microbial reaction kinetics by mathematical models (Mata-Alvarez .537 LHV [kJ/kg] 12. Simplified schematic of the anaerobic digestion process with energy recovery. assuming the inert content of table 2. the amount of Total Solids (TS) was evaluated. 06 99.00 23.01 2. Anaerobic digestion with energy recovery cycle synthetic results Waste mass flow rate [kg/h] Waste LHV [kJ/kg] Entering thermal power [kW] Net Power output [kW] Net efficiency [%] CO2 mass flow rate output [kg/h] Humid fraction 4.85 13.36 2.82 The overall biogas production resulted to be about 530 Nm3/h.99 99.420 kJ/Nm3 (on the basis of the CH4 volumetric fraction) and assuming an electric conversion efficiency of 0.00 72.43 7.00 95.00 60.00 60.05 0.95 99.24 0. the power output was calculated and reported in table 14. Humid fraction TS Paper and cardboard Organic fraction Pruning scrap Plastics Metals Wood Glass Textiles Inert VS BC RE Wet % [kg/h] % [kg/h] % TS % TS [kg/h] % VS % 2.14 294.00 55. with the overall efficiency of the process (the ratio between the net power output and the entering power with the humid fraction).43 9.002 21.00 60. Being the biogas LHV of about 19.50 1.57 54.00 88. Produced [kg/h] Produced [kmol/h] Produced [Nm3/h] Volume composition [%] CH4 210.15 3.30 99.34 55.00 98.00 60.82 13.76 99. Table 12. Table 12 summarises the calculation procedure steps and table 13 reports the calculation results.00 82.34 9.647 4.27 438 .81 90 893 333 63 287 110 700 118 120 2550 605 66 326 137 714 131 75. which resulted coherent with literature data (Mata-Alvarez .70 4.00 60.06 H2S 5.36 Nm3 per kg of VS.650 3. 2002).63 1.11 Nm3 of biogas per kg of humid fraction or 0.02 1.00 90.90 99.00 80.00 60. Table 14.00 54.00 60. Summary of calculation procedure for biogas production estimation.11 42.00 VSREMOVED Brutal chemical [kg/h] formula 24 CHO 417 C18H28O10 91 C5H10O2 47 C 2H 3O 30 CH2O Table 13.50 98. which correspond to about 0.35 for the reciprocating engine.00 60.00 60.95 15.711 1.63 NH3 7.96 223.95 99.00 9. Results of the biogas production modelling.78 81 848 254 60 16 108 8 91 50. the biogas production. hence.90 94.00 35.90 5.Energy Recovery from Waste: Comparison of different Technology … 223 CaHbOcSdNe + rH2O Î mCH4 + sCO2 + dH2S + eNH3 (1) in order to evaluate the amount of the reaction products which build up the biogas and.49 CO2 438.90 22.36 0.01 99. 224 Lidia Lombardi and Andrea Corti Comparison of Thermal Processes The resulted obtained above are compared in this section in term of several performance indicators for the different thermo-chemical treatments with energy recovery applied to the considered waste. 2006). Waste mass flow rate [kg waste/h] LHV [kJ/kg waste] Entering power [kW] Net power output [kW] Efficiency [%] Energy source saving [TOE/year] Specific energy production [kWh/kg waste] Gross CO2 emission [tCO2/year] Avoided CO2 emission [tCO2/year] Net CO2 emission [tCO2/year] Gross specific CO2 emission [kg CO2/kWh] Net specific CO2 emission [kg CO2/kWh] Gross specific CO2 production [tCO2/t waste] Net specific CO2 production [tCO2/t waste] MSW-WtE 14.417 73. assuming a continuous operation of processes for 325 days per year.075 0.62 107.528 0.322 9. specific energy production per unit mass of processed waste. energy source savings. due to the pre-treatment of the MSW to obtain the combustible fraction. gross CO2 emission/production – overall amount and specific values – due to the waste/syngas combustion.501 54.99 80.73 0.08 1.633 1.551 43. avoided CO2 emissions. net CO2 emission/production as the difference between the gross and the avoided CO2 emission/production.06 0.80 0.201 32. due to the avoided use of conventional energy replaced by the amount produced in the energy recovery process. are to be considered in the processes which accept the combustible fraction as input.95 1.96 1.071 0.56 1. the additional energy consumptions. Table 15 reports the comparison.184 -36.447 29 17. in order to have a complete view of the energy recovery potential.273 16 9.322 7. Table 15.08 0. considering a specific emission for conventional processes of about 0.77 83.184 -20.201 32. expressed in Ton of Oil Equivalent (TOE) per year.311 0.016 -28.344 10.896 22 16. Comparison of studied processes according to some energy and environmental performance indicators.960 -34.543 CF-WtE 9.496 kgCO2/kWh (ENEL.66 0.201 32.44 1. an average value in the .12 1.515 CF-GAS 9.45 0.322 5. In order to consider this contribute.127 40.55 80.376 23 13.400 59.59 0.09 1. The compared systems are: - MSW WtE (MSW-WtE) combustible fraction WtE (CF-WtE) combustible fraction gasification with energy recovery (CF-GAS) combustible fraction pyrolysis with energy recovery (CF-PYR).784 CF-PYR 9.95 1.537 12. The calculated performance indicators consist of energy conversion efficiency.537 12.537 12.350 8.59 With respect to the results in table 15. 201 12. Energy performance indicators. MSW is mechanically sorted: the combustible fraction (CF) is sent to pyrolysis with syngas energy recovery in engine.Energy Recovery from Waste: Comparison of different Technology … 225 range from 29 kWh/tMSW (Lombardi et al. MSW is mechanically sorted: the combustible fraction (CF) is sent to WtE. the combustible fraction pyrolysis.815 4. Gasification of combustible fraction with energy recovery of syngas in steam cycle offers a lower efficiency and lower amount of recovered energy with respect to WtE in general. 2007) and 48 kWh/tMSW (Lombardi et al. while the humid fraction (HF) is sent to anaerobic digestion with biogas energy recovery in engine.896 6. from a theoretical point of view.5 38.537 9.201 12.273 9.344 9. while the humid fraction (HF) is sent to anaerobic digestion with biogas energy recovery in engine.447 Specific pre-treatment consumptions [kWh/tMSW] - 38.350 32..367 5.721 8. Consequently the performance indicators related to energy are modified as reported in table 16. Comparison of Integrated Energy Recovery Systems The possibility of combining the thermo-chemical treatments for the combustible fraction and the biological treatment for the humid fraction gave the possibility of composing four integrated scenarios for the processing of MSW.5 kWh/tMSW was assumed. but the amount of recovered energy is higher in MWS WtE.5 38. MSW-WtE CF-WtE CF-GAS CF-PYR Waste mass flow rate [kg waste/h] 14. On the contrary.322 32. MSW is mechanically sorted: the combustible fraction (CF) is sent to gasification with syngas energy recovery in a steam cycle.322 Net power output [kW] 8.5 Pre-treatment consumption [kW] - 552 552 552 Net power output considering pretreatment consumption [kW] 8.895 Efficiency [%] 22 21 15 28 Results in table 15 and 16 show that the efficiency of WtE applied to MSW or combustible fraction is quite similar. In scenario II..896 7. 2006) – dependant on the type pre-treatment – of about 38. Scenario I is the direct MSW combustion in WtE. Table 16. as shown in figure 6. considering the pre-treatment consumptions. . In scenario IV.537 9. leads to a higher efficiency with respect to the other considered systems. In scenario III.537 LHV [kJ/kg waste] 10.322 32.127 12.201 Entering power [kW] 40. with syngas energy recovery in engine. while the humid fraction (HF) is sent to anaerobic digestion with biogas energy recovery in engine. Results for the compared scenarios are reported in table 17. the market of energy recovery from waste offers today a wide number of proven technical systems only in reference to processes based on waste direct combustion. since a more complete use of the carbon content is performed with respect to the combination of combustion with anaerobic digestion. their reliability. is lower with respect to WtE. the gasification process coupled with syngas energy recovery in a steam cycle does not offer a potential in the direction of the efficiency improvement in energy recovery from waste. with respect to the traditional WtE. while the one based on pyrolysis has the best energy and environmental results. Schematic of the compared integrated waste treatment scenarios. From the results reported in this chapter. in reference to the continuous operation. It is a mature technology which has reached a high reliability.226 Lidia Lombardi and Andrea Corti Figure 6. . They present a significant complication both at plant level and at operating level.e. Up to now. with relatively small plant sizes. WtE. Table 17 shows that the energy and environmental performances for scenario I and scenario II are quite similar. Again the scenario based on gasification reports lower performances. WtE is the most widespread thermal treatment for waste at the international level. CONCLUSION From a technological point of view. Gasification and pyrolysis processes are far less common and especially applied to particular typologies of wastes. even if the CO2 emissions are higher in the case of MSW WtE. i. 56 1. while energy from WtE is not. The possibility of coupling the thermal treatment. Comparison of proposed scenarios according to some energy and environmental performance indicators.53 107.882 0.350 8. for the humid fraction.344 14.275 16 10.77 0. .437 61.Energy Recovery from Waste: Comparison of different Technology … 227 Table 17. since its application to the biomass sector (small sizes) in still in development.3037 1. at least in some countries (as in Italy for example).05 1.72 0.26 0. allows keeping efficiency and energy recovery levels similar to the MSW WtE case.350 10.127 40.78 0. for the combustible fraction. The first one is related to the lower CO2 production. since this is acknowledged as a renewable source.56 0.576 45. However.075 15.400 73.450 26 16.852 -34.75 1.960 84. with the anaerobic digestion.06 0.338 18.276 -40.417 -32.425 1.344 10.47 0. The second one is related to the possibility of obtaining incentive pay for the energy produced from anaerobic digestion.344 14.344 14. today the pyrolysis technology is not yet competitive in reference to commercial industrial scale installations for waste treatment. coupled with syngas energy recovery in a reciprocating engine.369 21 10.66 0. with two additional benefits.815 85.350 6.41 MSW WtE Waste mass flow rate [kg waste/h] LHV [kJ/kg waste] Entering power [kW] Net power output [kW] Efficiency [%] Energy source saving [TOE/year] Specific energy production [kWh/kg waste] Gross CO2 emission [tCO2/year] Avoided CO2 emission [tCO2/year] Net CO2 emission [tCO2/year] Gross specific CO2 emission [kg CO2/kWh] Net specific CO2 emission [kg CO2/kWh] Gross specific CO2 production [tCO2/t waste] Net specific CO2 production [tCO2/t waste] On the contrary the pyrolysis process.896 22 10.852 85.543 52. Scenario 1 Scenario II CF WtE + HF AD Scenario III CF GAS + HF AD Scenario IV CF PYR + HF AD 14.62 0. due to lower carbon transformation in the biological process.56 0.127 40.62 0.127 40.377 -24. can reach quite high performances in terms of efficiency and energy recovery.127 40.122 11.80 1.78 0.350 8.96 0. pp. Integrated solid waste management – Engineering principles and management istsues. Biomethanization of the organic fraction of municipal solid wastes. . VIII SIBESA Simposio Italo-Brasiliano di Ingegneria Sanitaria Ambientale. A.228 Lidia Lombardi and Andrea Corti REFERENCES Aspen Technology Inc. ISWA/NRVD World Congress 2007.. & Iossifidis E. The Netherlands. (1999).. Reed. (2002).. R. Meier. Corti. G. V. No. Corti. “An overview of fast pyrolysis of biomass”. “Analisi di ciclo di vita per la valutazione di scenari di trattamento di rifiuti urbani”. & Radlein. L. www.enel. Energy Technology Review. A.. F-Chart Software. 2007. IWA Publishing. J. A. ISBN 0-8155-0852-2. 24-27 September. 17-22 Settembre 2006. 1479–1493. info@fchart. H. Organic Geochemistry. N..it Engineering Equation Solver. & Sirini. B. Biomass Gasification: Principles and Technology.. ENEL. Amsterdam. 1981.com Lombardi.aspentech.J. T. D. S.. Tchobanoglous. Noyes Data Corporation. 67. P. D. Meoni. Inc. Theisen. 30. McGraw-Hill. Rapporto Ambientale 2006. “Comparing different Municipal Solid Waste management scenarios by means of Life Cycle Assessment”.com Bridgewater. (1993). Mata-Alvarez. Fortaleza Brasil. Park Ridge. ISBN: 85-7022-148-7 Lombardi. Aspen Plus ®. L. & Vigil. www. Conflicts between the internal market in the European Union and waste management goals are shown. The design of two policy instruments will be described as examples of the conflicting goals in the two systems. Some models for assessing waste incineration/management are therefore described together with strengths and weaknesses when dealing with the dual function of waste incineration. Waste incineration thereby links the systems of waste management and energy. but this chapter will address only waste incineration.liu. together with trading in waste and electricity and how this impacts waste incineration in Sweden.se Digestion also has this function. various models are often used as decision support tools. Since policy instruments in Sweden are dependent on the common legislation of the European Union this will be addressed. where the residual products are a fertilizer and a gas which can be used for electricity and heat production or for transportation after cleaning.: +46 13 286687. E-mail address: kriho@ikp. Chapter 7 ENERGY RECOVERY FROM WASTE INCINERATION: LINKING THE SYSTEMS OF ENERGY AND WASTE MANAGEMENT Kristina Holmgren∗ Linköping Institute of Technology.g.In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers. Inc. . This chapter addresses the importance of taking this into consideration when e. A conflict is also that increased waste incineration can decrease production of combined heat and power in the district heating systems. INTRODUCTION Energy recovery through waste incineration1 connects two vital systems in modern society: the waste management system and the energy system. making investment decisions or designing policy instruments. since it is a treatment method for easily biodegradable waste. Linköping. In Sweden. Sweden ABSTRACT Energy recovery from waste incineration has a double function as a waste treatment method and a supplier of electricity and/or heat. fax: +46 13 281788. with an extensive ∗ 1 Corresponding author: Tel. When making investment decisions. and of special importance for waste incineration in Sweden is naturally the trade in waste. This information has been collected from a report from the Swedish Association of Waste Management (2005a) and from Hrelja (2006). Two policy instruments that impact both technical systems will be described and the difficulties in handling the double function of waste incineration will be the central issue. DEVELOPMENT OF WASTE INCINERATION IN SWEDEN This section will include a description of the historical development of waste incineration in Sweden.g. it has been done in the open at landfills or in simple furnaces in order to reduce waste volumes and decrease problems with vermin. Historical Development Burning waste has been carried on for a long time. Therefore. 2004).230 Kristina Holmgren district heating (DH) system that supplies just over 40% of the total heating demand of buildings and premises. important in this case are the common electricity market and trading in waste. The European Union has common legislation which impacts both systems in the member countries. changes are being made in both systems. This brought inconveniences. The consequences of this will be discussed. When designing and using these models. The methodology applied to address these issues consists of a literature review and knowledge gained in earlier studies. it was . This chapter will emphasise the importance of taking this into consideration with regard to. the second issue in focus in this chapter is the connection via common legislation between countries in the EU. both these systems are the focus of attention due to environmental concerns. Furthermore. when municipalities make investment decisions. but also in electricity. Furthermore. decision making and when designing policy instruments. together with its impact on district heating. and in 1903 Sweden’s first waste incineration plant began operations in Stockholm. heat supply from waste incineration has a substantial share of the total DH supply of about 12% (Swedish Energy Agency. Policy instruments in Sweden are highly dependant on legislation in the European Union. The first is the dual purpose of waste incineration as a waste treatment method and as a supplier of electricity and/or heat. The current situation with regard to waste incineration in Sweden will also be described. the policy instruments that will be described in this chapter are no exception. with a special emphasis on its impact on waste incineration in Sweden. However. and for this reason. e. The aim of this chapter is to highlight two issues. the countries in the EU are connected via trade. such as hazardous emissions to the atmosphere. e. Apart from the legislation. the countries of the European Union are connected through trade. These policy instruments are a recently proposed tax on incinerated waste in Sweden and green electricity certificates. Various models are often used as decision support tools in decision making processes. combined heat and power production and also the material recovery market. the dilemma of the two functions needs to be faced and the ways in which some models handle this will be described.g. 2 During the 1980s. over the years up until 1985.800. Waste Incineration in Sweden Today Today. Cleaner fractions of waste can also be incinerated at other facilities and is not included in the figures presented here. Waste incineration was found to be an important cause of this diffusion of hazardous substances in the environment. The oil crises of the 1970s led to a growth in interest in waste incineration as an indigenous fuel. Skövde went ahead and built the plant. in 1975 a proposition from the government stated that recovery had to increase in the future.Energy Recovery from Waste Incineration: Linking the Systems … 231 not until the 1960s that waste incineration really began to show some development. The Environmental Agency and the Energy Agency were commissioned to analyse the risks associated with waste incineration and concluded that it was possible to reduce the emissions to acceptable levels through a number of measures. until the issues of emissions and technology had been solved.000 tons annually to 1. and the safe disposal of residual products. which was inaugurated in 2005. . when municipalities’ interest in district heating was aroused. and treatment capacity from 100. The prerequisites for this were the district heating networks that began to appear after the Second World War. This expansion created opportunities for waste incineration plants. Later. of which waste incineration is one. both hot water boilers (14) and combined heat and power plants (15) producing about 8. more sorting of waste). In 1948. including “cleaner” waste (i. the ban on investment was lifted. Of the existing plants. Spontaneous fires at landfills are also a source of dioxins. 20 went through with modernisations while 7 were shut down. a number of plants with central sorting and composting were built.e. There are a number of sources.74 TWh electricity (Swedish Association of Waste Management.3 In 1985. waste began to be seen as a resource rather than a problem. The proposition did not state which technology was to be preferred. mainly from the manufacturing industry. where the contribution of emissions is hard to estimate. These facilities treat about 1. more efficient combustion. Hrelja (2006) shows that in the 1980s the municipality of Skövde chose not to build a waste incineration plant due to lack of confidence in the treatment method. there are 29 waste incineration facilities in Sweden. researchers began to report widespread diffusion of heavy metals and dioxins in the environment and the effects on humans and animals. However. but incineration was regarded as preferable in bigger cities. This served to increase interest in waste incineration. This venture failed since the plants did not work satisfactorily and there was no outlet for the residual product. The number of plants increased from 2 in 1960 to 27 in 1985.95 million tons of municipal waste and 1. 2005b). giving the waste a value. Figure 1 shows the waste treatment methods 2 3 This was only one of a number of measures to decrease oil dependency. since it provided an outlet for the heat produced. Sweden’s first district heating network was operational in the city of Karlstad and other cities soon followed. in order to decrease oil dependency. however. In the 1970s. Limits were set for emissions. especially during the 1970s. Waste incineration expanded significantly. As a result of the new view of waste as a resource. advanced flue gas cleaning equipment.6 TWh heat and 0. Industrial processes can also give raise to dioxins as can power plants using other fuels. the debate on dioxins in the municipalities did not end there. On the basis of these results.2 million tons of other waste.000 tons. a ban on investment in waste incineration was issued by the Swedish Environmental Agency. 8 Mton in 2002 to 4.g.9 Mton in 2008. 2004). legislation. total amount 4. if all planned projects are carried out (Swedish Association of Waste Management.3 €4/ton (Ministry of Finance. 2005b). and policy instruments in the energy system. . Therefore. As can be seen. 2005a) and a ban on landfill of combustible waste from 2002 and from 2005 also of organic waste (Ministry of the Environment. Capacity for waste incineration is currently increasing and is forecast to increase from 2. at present 46. Energy taxation in Sweden has had a significant effect on what fuels are used in the DH systems. in (Holmgren.1 €/ton. Waste incineration and district heating The role of waste as a fuel makes it part of the energy system. energy recovery is the treatment method for almost half of the municipal waste today. the use of waste as a fuel is dependent on such factors as the prices of other fuels used. This can be seen in Figure 2.g. fossil fuels or biofuel increase. additional waste treatment capacity will also be needed after 2008. The value of using the waste is higher when the prices of e. Despite these investments there will still be a lack of treatment capacity. 4 5 An exchange rate is 1 € = 9. 2001). resulting in a total of 40 waste incineration plants. The carbon dioxide tax is at present 0. 2006). A historical survey of the development of the DH sector can be found in Sjödin (2002). More details of the energy taxation can be found e. Treatment methods of municipal waste in 2004. between 1985 and the present by some 2-3% per year.232 Kristina Holmgren for municipal waste in Sweden. This development is mainly a result of recent regulations in the waste management system aimed at decreasing landfill. the introduction of a tax on landfill in 2000. The fact is that quantities of waste are also increasing.2 million tons (Swedish Association of Waste Management. If this trend is not broken. 9% 1% 33% 47% 10% Material recovery Biological treatment Energy recovery Landfill Hazardous waste Figure 1. since heat from fossil fuels has been heavily taxed.40 SEK is used throughout this chapter (January 2006).5 There has been a major shift from an almost total dependency on oil up until 1980 to a diversified supply where renewables represent a substantial proportion. in Trygg and Karlsson (2005). which is an overview of the consequences of using waste as fuel in Swedish DH systems. also shows that waste incineration enables DH networks to expand due to the low cost of the heat. as stated e.5% at capacity 150 MWe and biomass fuelled power plants 34% at capacity 80 MWe (Elforsk. A study by Sahlin et al (2004). 2005). a natural gas fired CHP plant has an electrical efficiency of 46-49.7 However. Combined heat and power (CHP) production is an efficient way to use resources and is recognized by the European Union as one of the measures needed to meet the demands in the Kyoto protocol (European Union. Waste incineration and combined heat and power production One disadvantage of waste incineration is the low electrical efficiency in the plants. 2003).7 TWh between 2002 and 2010. Many utilities have chosen not to invest in electricity production in their waste incineration plants due to difficulties in producing electricity in combination with historically low electricity prices in Sweden. Development of heat supply to the district heating networks between 1970 and 2003 (Swedish Energy Agency. (Swedish District Heating Association.Energy Recovery from Waste Incineration: Linking the Systems … 233 60 50 40 30 20 10 Waste heat Heat pumps Electric boilers Biofuel & peat Refuse Coal Natural gas Oil 19 70 19 73 19 76 19 79 19 82 19 85 19 88 19 91 19 94 19 97 20 00 20 03 0 Figure 2. 6 The electrical efficiency of waste incineration plants is around 23% at capacity 30 MWe (Elforsk. By way of comparison.7 to 1. . In the city of Linköping. from 0.g. 7 A more detailed explanation of this can be found e. electricity production at waste incineration plants is forecast to increase. 2003). the temperature of the steam in the boiler can not exceed 400ºC without entailing high maintenance costs due to corrosion.g. Palm (2004) shows that also institutional factors can connect the waste management system and the DH system. by Korobitsyn et al (1999).6 This is due to the many impurities in the fuel. 2004). 2004a). one reason for the introduction of waste incineration was that the same municipal utility operated both the waste management system and the DH system and saw that with waste incineration they could solve two problems at the same time: both an acceptable waste treatment method and heat production for the DH system. different metal fractions such as copper and steel have had a functioning market for recycling for a long time – half of the raw material used to produce steel comes from collected scrap. levels of material recycling are stated. 2004). the plant is the base supplier of heat to the DH network. Waste and Connection to the Material Market Waste management is connected to the material markets through the material recovery systems. but it is reasonable to believe that it is a result of the higher electricity prices anticipated when Swedish electricity prices are harmonized with those in continental Europe. Ministry of the Environment. This is different to newspapers. 2003. The incentive to material recovery of municipal waste comes mainly from the Ordinance on Producer Responsibility. If waste incineration is chosen as the treatment method. e. This can of course vary between systems as shown by Holmgren (2006).g. This heat can occupy much of the heat sink leading to lower electricity production in the DH system. is probably also a factor. Packaging producers have set up companies to handle the collection of packaging. compared to if a plant with higher electrical efficiency were chosen instead of a waste incineration plant. the new CHP plant mostly replaces heat boilers in the system. How to use the heat sink can in this perspective be seen as a conflict between waste management and the energy system. waste heat from industries.8 The prices of materials naturally influence the attractiveness of material recovery. for example. which the producers pay. and electric and electronic devices (e. which do not show this deficit in collection. There is room in the system for all types of waste heat. such as the introduction of the concept of Producer Responsibility. this is further explained in the section on Impact on Waste Incineration of Trade in Electricity. 1997). it is vital to recover as much as possible of the energy content of the waste.g. 2004) and an overall study of the DH systems in Sweden (Sahlin et al. 1994. Also. the development of the material recovery system is highly dependent on political decision. due to the negative operational cost of receiving the waste. where there is heat from waste incineration. For the included fractions. car tyres. for a municipal system (Holmgren and Bartlett. .234 Kristina Holmgren Existing waste-fired CHP plants will increase their electricity production and the total number of waste-fired CHP plants will double over the same period. The reason for the increase in electricity production at waste fired CHP plants is not clarified. cars. and also investment in a natural gas fired CHP plant. 8 Personal communication with Åsa Ekdahl. This can remove the heat sink for more efficient plants and shorten their annual operational times. which includes packaging. newspapers. However. in industry. The companies have a deficit in financing this system. European Confederation of Iron and Steel Industries. The proposed tax on incinerated waste. Earlier studies have shown that this can be the case. a functioning market existed even before the legislation was introduced. which is designed to promote CHP production. This study deals with the ”competition” in the DH system in the city of Göteborg. In the municipalities that have a waste incineration plant. people. which is a shortcoming. This weak point has been observed by the European Commission. Differences and similarities in waste management and district heating will also be outlined. through combined heat and power. It says “the heat generated during the incineration and coincineration process is recovered as far as practicable e. The Directive on the incineration of waste sets permitted maximum levels for emissions to the atmosphere and directions for monitoring the emissions. Environmental concerns may be in conflict with free trade. The use of . The performance of waste incineration plants differs widely. This is stated in the Framework Directive (European Union. both in terms of differing cost for waste treatment options due to varying standards and subsidies to the material recovery market.Energy Recovery from Waste Incineration: Linking the Systems … 235 CONNECTION BETWEEN COUNTRIES IN THE EUROPEAN UNION VIA LEGISLATION AND TRADE AND THE IMPACT ON THE SWEDISH WASTE INCINCERATION This section will describe the connections between EU countries in terms of common legislation and trade in waste and electricity. meaning that waste should be treated in the proximity of its origin and that member states should be self-reliant as regards treatment capacity. European Legislation Affecting Energy and Waste The common legislation in the European Union connects the countries to each other. it is vague on how to classify efficient energy recovery of waste. there are directions as to how the combustion process should be controlled. The Directive on landfill (European Union. and capital. In the Shipment of Waste Ordinance (European Council. examples are the principles of proximity and self-sufficiency. and is detailed further in the section on European differences in waste management and use of district heating. in order to satisfy both the internal market and the proximity and self-sufficiency goals. A definition of what an efficient energy recovery of waste is should be introduced. the generating of process steam or district heating”. The core of the European Union is the internal market which means free mobility of goods. It concerns both waste incineration plants and plants that burn both waste and other fuels. which suggests that the energy efficiency of the plant should decide whether to classify it as a disposal plant or a recovery plant. 1975) which also defines waste as “any substance or object which the holder disposes of or is required to dispose of” and establishes the fundamental concept of the Polluter Pays Principle. 1999) and the Directive on the incineration of waste (European Union. 2000) have this purpose. This section will describe policies and directives that influence waste incineration. as can be seen from Figure 3. One problem with the Framework Directive is that it does not clearly state when waste ceases to be waste and becomes a secondary material.where trading in the former is forbidden.for disposal and for recovery . Whereas the directive is specific about emission levels. and how to take care of the residual products. and has meant investment costs for the plants in Sweden in order to fulfil these demands. It is important to harmonise standards for waste treatment options in order not to “draw” waste to less controlled plants. The European Union’s member states are obliged to implement the directives in their national legislation. services. waste is divided into two categories . 1993).g. This can be in conflict with waste management goals. Emissions to water are also regulated. European Differences in Waste Management and Use of District Heating This section presents some figures with regard to the amount of district heating in different European countries and waste management methods. There is a directive promoting CHP (European Union. 2003c). Also this is seen as a measure to meet the demands in the Kyoto protocol and strengthening the domestic supply of energy. 2004b). There is a directive promoting electricity produced from renewable energy sources (European Union. This will further be described in the section on Impact on Waste Incineration of Trade in Electricity. 2003b). When digested. The aim is to 9 Biological treatment includes digestion and composting. 2005). since Sweden will be harmonized with continental Europe which currently has a higher electricity price (e. Directives that impact the energy sector include the directive on the common electricity markets (European Union. but are affected by the fact that the costs for fossil fuels increase as do electricity prices due to marginal pricing. stating that CHP is an effective way to use resources and one measure to meet the demands in the Kyoto protocol. is to be preferred. and a residual product which can be used as fertilizer. . Another directive regulates the emission allowance trading (European Union. raises issues. however. 2001). This does not go undisputed. Swedish waste policy is based upon this hierarchy. including biological treatment9 is preferred to energy recovery) and finally disposal.g. Recently. Apart from this. which will be explained in the section on Green electricity certificates and waste incineration. Trygg and Karlsson. biodegradable waste is degraded with access to oxygen. The EU’s waste policy is founded on the waste hierarchy. which states that Europe should have free trade in electricity in member states. It also dictates lower quantities of biodegradable waste in landfill and the collection of methane emissions. Waste incineration plants are not included in the trading sector. 2005). This has probably had an impact on the design of the proposed tax on incinerated waste. and the residual product can be used as a soil amender. The Landfill Directive specifies operational and technical requirements for landfills. This has in Sweden led to the implementation of a system of green electricity certificates. further explained by Trygg and Karlsson (2005). It sets the demands that the pricing for receiving waste should include after-care for at least 30 years. biodegradable waste is degraded without access to oxygen. This will mean higher electricity prices than historically in Sweden. 2004a). where the marginal power producer is coal condensing power in the European system. material and energy recovery where material recovery. including biological treatment. there is a directive on producer responsibility for packaging waste (European Union. resulting in biogas which can be used as fuel for vehicles or for electricity and heat production. where landfill and waste incineration without energy recovery are included. Figures for electricity and heat output from waste incineration in different European countries are given. the European Union managed to agree on minimum energy tax levels (European Union. described in the Sixth Environmental Action Programme from the European Commission (2001) and states that first comes waste prevention. which will be explained in the section on Introduction of a tax on incinerated waste in Sweden. 2003a). When composted.236 Kristina Holmgren resources in other plants that the waste incineration plant could replace should also be taken into consideration (European Commission. then recovery (reuse. in particular the question of whether energy recovery or material recovery. stipulating levels of material and/or energy recovery for different packaging materials. Energy Recovery from Waste Incineration: Linking the Systems … 237 investigate if any unambiguous trends can be seen in this material. As regards the proportion of DH produced in CHP plants. that if the data in the diagram were recalculated into oil equivalences. and the two fuels account for about 85% of the total supply. It should be noted. Figure 3 shows the amount of fuel used for DH production by some European countries. It can be seen that the supply differs between countries. The CEE countries show a less diversified supply than the old EU member states and a large untapped potential exists for using more heat from waste incineration. countries would show more similar figures. Figure 4 shows the total DH production in several European countries together with its share of the heat market. Sweden has the highest energy recovery of the countries surveyed. 2002) and (Trygg and Karlsson. mainly due to the country’s extensive DH network. 2005). . 10 One reason for this is the historically low electricity prices in Sweden (Sjödin. Coal is the major fuel used in the Central and Eastern European (CEE) countries and natural gas is also widely used. and industrial surplus heat. Figure 5 shows the extent to which the useful energy content of the incinerated waste is taken care of in a number of countries. is there a correlation between high DH production and/or high market share and high proportion of energy recovery as a waste treatment method? In Sweden this is the case. along with some CEE countries. Profu (2004) identifies a number of “key-factors” when assessing environmental impact of waste incineration. The efficiency of using waste as a fuel varies between the countries surveyed. Fuels used for DH in the countries surveyed in a report by Euroheat and Power (2003). the proportion is lower (35-72%). however. It can be seen that Poland and Germany are the largest producers. where one is energy recovery per ton waste. renewables. this is high in the old member States (64-94%) with the exception of Sweden. but what about other European countries? 100% 80% 60% 40% 20% Au st Bu ria lg ar Cr ia oa ti Cz a e De ch nm a Es rk to n Fi i a nl an Fr d a G nce er m a Hu ny ng ar y Ita Ic ly el an d La Li tvi t a Ne hua th nia er la n No d s rw a Po y l Ro and m a Sl nia ov a Sw kia Sw ed itz en er la nd 0% Coal Oil Natural gas Renewables Waste Others Figure 3. The highest market shares exist in some Nordic countries.10 In the CEE countries. to see whether anything has been omitted. destruction 134 Landfill Total 594 4761 3 2097 2845 : 11673 0 : : 875 : 111 : 0 : : : : : : 36 : 0 65 0 : 7 : : 0 3 215 11266 419 4233 14723 12991 1967 18500 450 657 1000 : 3907 188 810 1500 10142 3388 699 1192 1512 825 27545 3188 6695 24573 245 482 80 3587 52532 553 4640 : 33024 2724 29929 500 866 1000 : 4646 187 9900 4634 10509 4618 956 1524 2372 4172 33535 3945 8365 33324 293 3061 4900 : The data in the Recycling. and Landfill columns are taken from “Treatment of municipal waste”. Incineration destruction. The data differs somewhat in some cases. These were obtained from the Eurostat website. This is done in order to compare data. The data in the Total column is taken from “Generation of municipal waste”.238 Kristina Holmgren Table 1. . Energy recovery. Treatment methods for municipal waste in European countries 2002 in 000s of tons (Eurostat. 2005)11 Belgium Czech Republic Denmark Germany Estonia Greece Spain France Ireland Italy Cyprus Latvia Lithuania Luxembourg Hungary Malta Netherlands Austria Poland Portugal Slovenia Slovakia Finland Sweden UK Bulgaria Romania Turkey Iceland Norway Switzerland 11 Recycling Composting 1442 1088 Energy recovery 1493 175 122 398 796 17250 13 375 3811 4715 463 3897 : 35 : : 67 : 2133 : 116 252 87 37 659 1295 3733 : 170 : 19 507 : 555 7844 2 32 3914 4208 34 7335 : 24 : : 47 : 2365 : 215 135 11 39 : 354 1423 : : 383 3 225 : 2008 153 0 : 1567 10235 : 2587 : 55 : : 288 : 3125 490 : 944 5 91 201 1675 2674 : : 9 7 492 : Incineration. Composting. 5 Ita Ne ly th er la nd s Sp G re ai n at Br it a P o in rtu g Hu a l ng ar y Sw ed en Au Sw stri it z a er la nd No rw De a y nm ar k Fr an ce G er m an y 0 Figure 5. The statistics are not exhaustive because not all data is available. 3. DH production (TWh) and DH market share (%) in the countries surveyed by the report in Euroheat and Power (2003). Regarding the correlation between high amount of DH and energy recovery.239 Energy Recovery from Waste Incineration: Linking the Systems … 100 90 80 70 60 50 40 30 20 10 0 120 100 80 60 40 20 DH production UK S lo v a k ia S weden S w it z e rla n d P o la n d R o m a n ia L it h u a n ia N e t h e rla n d s N o rw a y I t a ly L a t v ia H u n g a ry I c e la n d F in la n d F ra n c e G e rm a n y D e n m a rk E s t o n ia B u lg a ria C ro a t ia Czech A u s t ria 0 DH market share Figure 4. 2002.5 1 0.5 3 2. Energy recovery by waste incineration (International Solid Waste Association. 2000) Table 1 shows different waste treatment methods in the European countries.5 2 1. some comments can be made. this can . Nonetheless. Swedish Association of Waste Management. rubber and plastics. mainly intended for use in waste incineration plants with energy recovery. The information on what type of waste the categories include is taken from Ericsson and Nilsson (2004). and this increases the value of heat. mixed fractions of used wood. The Swedish Environment Protection Agency must approve imports of yellow and red fractions. Green waste includes e. the data is contradictory. it would appear that incineration is used mainly as a destruction method but as Figure 3 shows. Norway. yellow and red. paper and rubber.1 €/kg. In general for Table 1. Norway and Denmark both have taxes on waste incineration. Examples of yellow waste are chemically treated used woods. The following factors may be significant.000 tons in 2002 (Olofsson et al 2005). Some countries have a large proportion of heat from waste incineration in the DH systems.000 tons. The countries in CEE with a high amount of DH and/or large market share (the Baltic countries. and Holland. Olofsson et al analyse which factors lie behind Swedish yellow waste imports. wood chips. Norway. tall oil and sorted fractions of plastics.240 Kristina Holmgren mainly be seen in Sweden and Denmark. Five countries account for almost all imports to Sweden: Denmark. . since the fuels are similar in composition.g. Imports of yellow waste increased from 200. Italy and Switzerland. thus raising energy recovery significantly Energy taxation on fossil fuels is high12 in Sweden. but the total amount of DH and/or market share is low. Taxes on waste and a ban on landfill are also driving factors. The carbon dioxide tax is at present 0. Red waste is e.000 tons in 1999 to 430. pellet. imports of waste in this category do not have to be registered. and Romania) have not evolved their waste management sector and landfill is still the dominating treatment method. with DH systems that can utilise the heat. This means that clean fractions of waste are suitable to combust in existing plants. some of the heat comes from waste. it can be said that waste treatment differs widely between countries and many still rely heavily on landfill. Different types of bio fuel are the most common alternative for the base supply of heat. logging residues. Germany. – – – – – 12 The infrastructure in Sweden. 1993) and waste is divided into different categories: green. such as France. Poland. Finland. about 40% in Denmark compared to around 8% in Sweden. Both factors in the waste management system and the energy system are analysed. The authors estimated imports of green waste in 2000 at 760. and municipal solid waste. Impact on Waste Incineration in Sweden of Waste Trade with Some European Countries Trading in waste in the European Union is regulated (European Council. One thing that separates Denmark from Sweden is the high proportion of total electricity production that comes from CHP plants. the Czech Republic. but this is starting to level out due to stricter sorting requirements in Sweden.g. The quality of the imported waste has been higher than waste from Sweden. Slovakia. What can be said is that Germany has put a lot of effort into developing their material recycling. In Table 1. paper. waste containing or contaminated with polychlorinated biphenyl (PCB) or polychlorinated dibenzo-dioxin. For Germany. Energy Recovery from Waste Incineration: Linking the Systems … 241 All the above factors lead to a difference in gate fees. the predominant factor to decrease the driving factors for import to Sweden would be the introduction of a waste incineration tax. 2003a) on a common internal electricity market is to open up the electricity market by subjecting it to competition. Gate fees for municipal waste. the value of heat would be lowered. This may be in conflict with the EU’s rules with regard to state aid. If the differentiation were changed and the same rules were valid for the whole of the business sector. in the DH network of Göteborg (Holmgren. The European Commission publishes a yearly report about the implementation of the internal market (European Commission. Industrial consumers can choose their supplier from July 1st 2004 and all consumers from July 1st 2007. market structures and the need for additional investments in infrastructure. co-owned by several neighbouring municipalities owned the waste incineration plant and sold the heat to the utility operating the DH network. However. 2006). The reason for this is to increase efficiency in the energy sector. 2004) and that report states that the result of the implementation so far is unsatisfactory. It also effects the cost of heat in the DH networks. e. which are higher than in Sweden. In Sweden. since the high taxes on fossil fuels would be lowered. The impact of this directive in Sweden is that electricity prices will increase due to harmonisation with the electricity prices in continental Europe. 2003). This is further described in Trygg and Karlsson (2005). Instead. the report states that these problems must be solved. Waste incineration plants are base suppliers of heat due to their negative operational costs and the need to treat the waste. The authors assume that in the future. . Table 2 shows the gate fees in Sweden for different treatment options for municipal waste. However. 13 In this case. A higher electricity price reduces the cost of heat from CHP plants and their possibility to compete with other plants also improves. there is great variation between plants. it is suggested that there would be taxation on heat for consumers (Ministry of Finance. 2005b) Treatment method Cost (€/ton) Landfill 74-128 Incineration 32-64 Biological treatment 43-106 Impact on Waste Incineration of Trade in Electricity The objective of the directive (European Union. another company. but Sweden has been granted temporary exemption. including VAT and taxes (Swedish Association of Waste Management. As can be seen. the municipal utility had a better negotiation position towards those companies when they invested in a natural gas fired CHP plant assuming electricity prices harmonized with those on the continent. and naturally also interest in electricity production in waste incineration plants. Table 2.g. where the municipal energy utility buys heat from a waste incineration plant13 and also waste heat from industries. business is divided into different sectors. One reason is barriers to cross-border trade. with differentiated energy tax levels. Higher electricity prices increases interest in producing electricity in the DH systems. A change in energy taxation in order to better fit in to the European Union legislation could also have a significant impact. 2005b). The aim here is to show how policy instruments in one system affect the other. at the time of writing. 2005b) Energy tax (€/ton waste) Carbon dioxide tax (€/ton waste) Fossil content 100% Hot water boiler 16 355 Condensing power plant 0 0 51-62 CHP plant14 Fossil content: 14% of total weight (assumed value for municipal waste) Hot water boiler 2 45 Condensing power plant 0 0 CHP plant 0 6.g. see e. The proposal is that waste should be incorporated in the existing energy taxation system by taxing the fossil content of the waste. However. since electricity is taxed for the consumer (industrial consumers are exempt). heat from hot water boilers is taxed in full. plastic packaging.5-8 Total (€/ton waste) 371 0 51-62 47 0 6. and the difficulties in handling the double function of waste incineration as a supplier of heat and/or electricity and as a waste treatment method. Table 3 shows the level of the tax on incinerated waste and how it applies to different energy conversion units. However. How the tax steers according to the waste hierarchy and to make material recovery including biological treatment more . It can also be noted that the DH networks are part of the emission allowance trading systems. Waste incineration tax as proposed (Ministry of Finance. 2005c). with a carbon dioxide tax and an energy tax. this is not included here. since waste incineration plants are not included in the trading system. the tax has been postponed due to difficulties in measuring the fossil content in municipal waste. which is not applied to electricity production. For a more detailed description of energy taxation. Holmgren (2006). meaning e. Introduction of a Tax on Incinerated Waste in Sweden A government investigation on a tax on incinerated waste was presented recently (Ministry of Finance.g. The description of the assignment to carry out the governmental investigation of this tax includes several goals that should be taken into consideration. and heat from CHP plants is taxed at deducted levels as is heat to industrial consumers.5-8 The design of the tax is in accordance with how existing energy taxation is applied to the DH sector. and the plants included will therefore probable be granted additional deductions of carbon dioxide taxes. Table 3.242 Kristina Holmgren DISCUSSION OF TWO POLICY INSTRUMENTS Two policy instruments will be discussed in this section: the introduction of a tax on incinerated waste and the green electricity certificate system. and a proposal of the tax was incorporated in the government budget proposition (Ministry of Finance. all have electricity production16 (Swedish District Heating Association. is contradicted by the lack of waste treatment capacity (Swedish Association of Waste Management. The results indicate. Most existing plants without electricity production can not easily convert to CHP production since they consist of hot water boilers. Plants with electricity production could maintain lower gate fees than other plants. Swedish Association of Waste Management. This is corrected if the tax on incinerated waste is designed in this way. 16 Personal contact with Anders Hedenstedt. 2005). Tax levels of 11 and 42. and it also provides the incentive for CHP production in waste incineration plants which has hitherto been lacking. an earlier study has shown large energy savings when recycled plastic material is used instead of virgin material (Holmgren and Henning. 2004). The EU directive on promotion of CHP (European Union. This fraction is appropriate for material recycling in an energy efficiency perspective. Swedish Association of Waste Management. 17 Again. The prerequisite for the results is naturally that the utility can not raise the gate fee for receiving the waste. 2002).Energy Recovery from Waste Incineration: Linking the Systems … 243 economically competitive is important. since those were the levels proposed in an earlier government investigation (Ministry of Finance.5 €/ton were analysed. The investigation states that the fossil content of waste is subsidized in comparison to fossil fuels and that the value of the subsidization of biomass fuels is lessened if there is no tax on incinerated waste. the investment was not profitable. however. except for fractions of plastic waste. Another study has analysed the consequences for a municipal energy utility of investing in waste incineration if a tax on incinerated waste were introduced. Other questions which are raised concern the impact on gate fees of waste incineration plants. 2004a) has influence over this. Note that in Table 3 these levels are in the proximity of the levels proposed for plants with CHP production and hot water boilers respectively. The only fraction which will have an increased incentive to material recover is various plastics. since this opportunity to increase incentive was not taken. it can be said that the energy perspective has been given first priority and the waste management priority second. however. In the waste incineration tax proposal. waste is seen primarily as a fuel. One question in a waste management perspective is what will happen in terms of encouraging material recovery and biological treatment. the energy system perspective is the predominant. other treatment options begin to be of interest. Would that mean transportation of waste to those plants? This. resulting from the government investigation. Personal contact with Anders Hedenstedt. due to waste management regulations. When summarizing the proposal. 2004). but also impacts on the DH networks and the incentive for CHP production from waste incineration. but at the 42.15 and conversion would virtually mean building a new plant. The conclusion was that at the tax level of 11 €/ton. that at these tax levels. Of the planned waste incineration plans. the investment was still profitable for the utility. 15 .5 €/ton level. Another issue is to what extent the energy utilities will raise their gate fees to let consumers shoulder the increasing costs. in accordance with the waste hierarchy. The problem is that the goals that are enumerated conflict. and therefore the main objective is that waste taxation be harmonized with energy taxes on other fuels.17 14 Electrical efficiency in the interval 15-28%. 2004). (Holmgren and Gebremedhin. and in order to be so. tidal power. 2001). e. The Renewable Energy 18 The Swedish goals for biodegradable waste state that at least 35% should be biologically treated by 2010 (Swedish Environmental Protection Agency. The producers of electricity receive a certificate when they produce electricity in approved conversion units. even if municipal waste is estimated to be of about 80% biological origin. creating a demand for certificates and thus giving them an economic value. and electricity produced from biogas. 2005b).5 MW). 2005). When the electricity certificate system is analysed. as regards which sources should be included in a certificate system. 2005c). . peat. The issue of whether municipal waste should receive electricity certificates has been debated since the electricity certificate system was originally designed and in the government investigation on a tax on incinerated waste (Ministry of Finance. 2001) provides scope for interpretation by member states. sorted wood waste from demolition waste. it would further increase the incentives for CHP in waste incineration plants since it pays off for every produced MWh of electricity.244 Kristina Holmgren Green Electricity Certificates and Waste Incineration The green electricity certificate system is designed to increase electricity produced by renewables (Ministry of the Environment. Electricity produced from municipal waste does not receive certificates in the Swedish certificate system. it is deemed important to remove the subsidies that the fossil part of municipal waste has enjoyed in comparison to fossil fuels. it could steer waste of biological origin towards incineration and that would not comply with Swedish waste management goals. solar power. 2004a). From an energy system viewpoint. the quota between electricity and heat needs to be at least 20% (Ministry of Finance. These are wind power. 2005d) the question is analysed once again.18 Again. The certificate system is influenced by the directive on increased electricity from renewables (European Union. It is also proposed that animal fat. The conclusion is that the new tax on incinerated waste is enough to steer towards increased CHP in waste incineration plants and if electricity certificates were given for municipal waste. it is not important to insert the biological part in the system which benefits biomass fuels. hydropower in new or small plants (installed after the end of 2002. the main issue is to be classified as a CHP plant. 2005). When the tax on incinerated waste is introduced. 2003a. it is logical to implement electricity certificates for municipal waste.g. The aim is to increase annual electricity production from renewable energy sources by 10 TWh between 2003 and 2010. If municipal waste were to be included. should receive certificates (Ministry of Finance. It would increase electricity production in waste incineration which is in line with the European directive on promotion of cogeneration (European Union. the government investigation states that the waste management goals are more important than the goals of the energy system. In the proposed tax on incinerated waste. the conflict between the goals in waste management and in the energy system can be seen. When it comes to green electricity certificates. b). The directive on electricity from renewables (European Union. Consumers will need a quota of certificates in relation to their total electricity consumption. biomass. and also increased power in old plants renovated after April 2003 and hydropower in plants with a maximum capacity of 1. but a proposal to extend it to 2030 is in place (Ministry of Sustainable Development. The system ends in 2010. A voluntary certificate system exists in Europe. meaning residual products from the food industry. geothermal power. g. but it can also be used to optimize the operation of existing plants. The effects of various policy instruments are also an appropriate issue to assess. MODELS AS DECISION SUPPORT Various models are often used as decision support tools. using the MODEST model (Henning 1998. which analyses the impact on Swedish district heating systems as a whole. it is vital to be aware that also considerations. which fractions of the waste are suitable to energy recover and which to material recover? Another example of a study with the energy system in focus is Sahlin et al (2004). as shown e. e. using a questionnaire and a simulating energy model named HEATSPOT.Energy Recovery from Waste Incineration: Linking the Systems … 245 Certificate System19 (RECS) which in contrast to the Swedish system does include municipal waste. such as waste treatment capacity and energy utility plants. Holmgren. This shows that opinions as to how to classify waste in terms of whether it is a renewable or not differ throughout Europe. Other methods have the waste management system in focus.g. System analysis can be a mean to assess complex systems in order to e. and how to handle this. by Sundberg et al (1994). and the amount of electricity produced in the DH networks. should be included. when municipalities make infrastructural decisions. understanding and knowledge of the system and the correlation between components in the system is gained.g. The paper describes the model MIMES/WASTE. The main purpose of the model is to find suitable investments. By building a model. A study has also been made that has broadened the scope by comparing waste treatment options from an energy efficiency viewpoint (Holmgren and Henning. The models have been used to assess waste management systems and waste incineration and the common theme is the dilemma of the two purposes waste treatment and production of heat and sometimes electricity. Models and How to Handle the Double Function of Waste Incineration The method used in earlier studies carried out by the author (Holmgren and Bartlett. more related to the waste management sector. Limits on amount of available waste is also set. 2004). A model can be built that should include the essential features of the system. 2004. which seeks the most cost19 More information can be found at www. When analyzing the results.org (November 2005). the impact on other fuels used. MODEST is a linear programming model which minimizes the cost of supplying heat and/or power demand during the analysed period.g. This section describes some models based on system analysis. 2006) is energy system modelling. 2004. . The influence of the waste management system in the model is mainly via economic signals as regards the cost of waste as a fuel. determine how available resources should be used to satisfy the aim of the system or to evaluate environmental impacts of various measures. 1999).recs. Holmgren and Gebremedhin. Assuming that there is a district heating system that can utilize the heat. e. the cost of supplying heat with different amounts of waste used as fuel. The results from these studies are mainly how waste functions as a fuel in the district heating system. To assess the robustness of the results. subject to certain restrictions on land availability. Cyprus and Malta are not included. and compared it with the EU’s targets for increasing the proportion of the total primary energy supply produced with biomass. though it will probably not be met due to slow implementation of the renewable energy policy. Their assessment shows that. One model for assessing waste management options based on LCA methodology is ORWARE.6 EJ/year in the EU15 by 2010. Life cycle assessment (LCA) is a widely used method for evaluating the environmental impact of products and services (Rydh et al. acidification. Another study has linked MIMES/WASTE with an energy system model. The resource studies showed large variations in the amount of biomass fuels. such as food production. MARTES.246 Kristina Holmgren efficient way to treat waste. for waste incineration. eutrophication. 2002). (2003) are reviewing 17 studies on the contribution of biomass in future global energy supply. the potential is up to 11. Ericsson and Nilsson (2006) have assessed the potential in the 15 old EU countries (EU15).6 EJ. a sensitivity analysis of these compensatory systems is recommended. 24 The meaning of resource-driven studies is the possibility to produce biomass for energy purposes in competition with other land uses. e. These figures can be compared with the fact that total energy supply in the EU15 in 2001 was 62. where data is compiled 3. e. Finnveden and Ekvall (1998) compare LCA studies of recycling versus incineration of paper. Both demand-driven studies23 and resource studies24 were reviewed. al.g. The methodology in short has four steps: 1. The article 20 Such as greenhouse gases. 8 newcomers21 and 2 candidate countries22 (ACC10) and also Belarus and Ukraine. also means district heating and/or electricity. The studies with the highest assumptions assumed vast areas of Africa to be given over to energy crop production with exports to the rest of the world. 4. 22 Bulgaria and Romania. should it be regarded as a scarce resource? A number of studies have attempted to estimate the potential biomass supply.7 EJ/year in the EU15 and 5.g. Eriksson et al (2002). Interpretation of results. see e. where the data is analysed as to the extent to which they contribute to different impacts. what is made of the saved biomass when recycling paper? This question indicates a need to define how biomass should be regarded. Goal and scope definition 2. Life cycle assessment involving classification of data to different environmental impacts. and valuing or weighting. This model handles the double functions of waste incineration by compensatory systems. Inventory analysis.g. 2001). There are no resource limitations in meeting the EU target of 5. if district heating is produced by biomass fuel or oil. 21 . How to perform an LCA is laid down in ISO standards. 23 The meaning of demand-driven studies is the potential of energy from biomass in competition with other energy carriers. The step of valuing is however in question since it is considered to be subjective.5 EJ/year in the ACC10. by using both models in two case studies (Olofsson. A compensatory system. Berndes et. and show the importance of assumptions made with regard to compensatory systems and also take up the question of biomass. in line with LCA methodology.20 characterization. apart from the function of waste treatment. One drawback of using MODEST when analyzing waste incineration is that few environmental effects have been taken into account. In earlier studies (Holmgren and Bartlett. A positive impact in one of the systems may be negative in the other. The main findings in this chapter are as follows. 2004. This has been solved by prohibiting exports of waste for disposal but not for recovery. However. These studies give an indication that biomass utilization could increase substantially. for example. A Information about the ExternE project can be found at http://www. There is a correlation between extensive DH networks and substantial incineration as waste treatment method in Sweden.externe. since that is essentially also to put a value on environmental effects. hence indicating lower environmental concerns. both as a waste treatment method and a supplier of electricity and/or heat is discussed in this chapter. and social factors are also overlooked. 2004. This can be compared to the step of valuing or weighing in the LCA methodology. making a study where biomass fuel replaces fossil fuel as a compensatory system for district heating production.Energy Recovery from Waste Incineration: Linking the Systems … 247 criticizes the studies for not including other environmental effects of such expansion. for example that waste should be treated close to its origin. Holmgren. acidification and health impacts. and include these costs in the optimization calculations of the D networks. however. This correlation can not be unambiguously shown to exist in any other EU country. Waste incineration can decrease possibilities for producing CHP in DH networks and this can be seen as a conflict between the need to treat waste in an acceptable way and the goal of more CHP production in the energy system. One solution could be to use external costs of environmental effects. This is a significant issue. this step is not really accepted in LCA methodology since it is considered to be subjective and the recommendation is to use it with care. for example on local employment. Holmgren and Gebrenedhin. In that study. can also occur. – – – 25 26 Sweden has extensive DH networks and therefore better possibilities to efficiently recover the energy content in the waste than countries with a less developed infrastructure. . 2006). since relatively little DH is produced in CHP plants.25 The basic idea behind the concept of external cost is that electricity and heat production give rise to several negative external effects. otherwise a suboptimal consumption of energy occurs from a socio-economic perspective.info/ Positive external effects.26 such as climate change. There is a conflict in the European Union between the internal market and waste management policy. and strategies and goals in the two sectors can conflict. lead to environmental and social problems which are not taken into account when. such as biodiversity. In this context. only carbon dioxide emissions from the analysed DH networks have been calculated. and the connection is both historical and organisational. since it has been shown that these assumptions are often crucial for the results in LCA studies. The cost of these effects should be internalized in the price of the energy supply. external cost data was obtained from the European Union’s ExternE-project. Sweden differs from other Western European countries. This has been done by Carlsson (2002). this could. CONCLUSION The double function of waste incineration. . the Swedish Energy Agency and Swedish Industry. Carlsson. which is financed by the Swedish Foundation for Strategic Research. J. (Electricity from new plants – 2003. (2004). When actual decisions are to be made. & van den Broek. Stockholm. The double function is also addressed when different models for assessing waste incineration are reviewed. The contribution of biomass in the future global energy supply: a review of 17 studies. Hoogwijk. for example more biological treatment. Dissertation No 766. In the design of the electricity certificate system. R. 03:14. & Nilsson. Sweden. Linköping Institute of Technology. Jämförelse mellan olika tekniker för elgenerering med avseende på kostnader och utvecklingstendenser. 26:205-220. L. Mats Bladh and Björn Karlsson for valuable comments on the chapter. The author is grateful to Maria Saxe. there are other aspects that can be of importance that has not been included in the model. Elforsk. in Swedish) Elforsk report no. Tekniska Verken i Linköping AB is acknowledged for their financial support. Comparison between different technologies for electricity generation with regards to costs and development trends. except in the case of plastic waste. 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Industrial DSM in a deregulated European electricity market – a case study of 11 plants in Sweden. Stockholm. (Strategy for sustainable waste management. & Karlsson. (2004). (2005). Trygg. Keywords: energy recovery.85. The configuration chosen (crossed flow) is the most adequate from an operational point of view. consisting of a ceramic semi-indirect evaporative cooler and a heat pipe device to recover energy at low temperature in air conditioning systems. Inc. Tel. It is a new alternative device for use as a recovery system. Chapter 8 EXPERIMENTAL ANALYSIS OF A COMBINED RECOVERY SYSTEM R. +34-96832. heat pipes. For characterization purposes. The superiority of the evaporative cooling device under the operating conditions was clearly shown. a design of experiment (DOE) and an analysis of variance (ANOVA) were applied with the aim of better understanding the energy behaviour of the combined device. improving the operation in air-conditioning systems.59. Experimental research has been carried out whose aim is the characterization of combined recovery equipment. evaporative cooling. The characterization of the system was carried out by employing experimental design methodology.59. An estimation of the energy saved by the combined system was carried out. Murcia (España). E-mail: ruth. Fax +34-968-32. The contributions of the single factors and their interactions were presented by carrying out a variance analysis. showing the possibilities of implementing this solution to save energy and also to improve the indoor air quality by means of increasing the ventilation rates. * Corresponding author: C/ Dr. ABSTRACT The present work is found in the field of energy recovery in air conditioning systems to promote energy saving and improve environmental quality.es . 30202 Cartagena . s/n (Campus Muralla).In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers. A factorial design was performed by analysing how the factors used affect the characteristics analyzed. The combined system built allows a feasible energy exchange between the supply airstream and the return one. [email protected]. Herrero Martín* Departamento de Ingeniería Térmica y de Fluidos Universidad Politécnica de Cartagena. in which experimental research has been carried out whose aim is the energy study of combined recovery equipment. an experimental design technique was employed by calculating all the characteristics which are involved in the energy analysis developed. interest has grown in reducing energy demand at all levels. The quantity of heat exchanged from the air is equal to the quantity of heat absorbed by the evaporation of water. thus enhancing the performance of the air conditioning installations in which they are used [1]. that which is provided by the air-conditioned premises. there was a change in approach on a world scale. the air supplies heat in order to evaporate the water. In Direct Systems. The circumstances currently favouring the use of conventional energy sources not only involve facing up to increased costs as well as the foreseeable exhaustion of sources. The systems used can be considered as heat recoverers when they use. together with a search for more efficient energy equipment. both in political circles as well as among the population who realised their dependency on oil producing countries. but also include the costs involved in environmental protection and the harmful effects on the planet arising from their use (increase in the greenhouse effect due to greater CO2 emissions into the atmosphere or the destruction of the ozone layer due to emissions from coolants used in mechanical compression processes for cooling). on the other side of the exchanger. Indirect Systems or a multi-step combination of both systems (Mixed Systems). Traditionally. or just a mixture of this and outdoor air. the primary airstream is cooled (involving just sensible heat so humidity is not added).254 R. This is the reason why this process is called indirect and is especially used in those applications where humidity addition is not allowed in . As a result of these events. Herrero Martín INTRODUCTION After the 1973 oil crisis and subsequent rise in fuel prices. the water evaporates directly into the supplied air. The heat transfer surface is cooled by contact with this secondary airflow and simultaneously. consisting of an evaporative cooler and a heat pipe device to recover energy at low temperature in air conditioning systems. its temperature is almost the wet bulb temperature of the air used in the process. In the Indirect evaporative coolers. three different types of evaporative cooling systems were available: Direct Systems. cooling and increasing the amount of water in this air in an adiabatic heating process. To characterize the device empirically. Nowadays. energy saving is not an option but rather a priority concern. EVAPORATIVE COOLING SYSTEMS Evaporative cooling offers an alternative for reducing water or air temperature in the systems that operate using this principle. so the dry bulb temperature decreases and the humidity increases. as secondary air. This is the target of this work. a solution in terms of improving energy efficiency is the use of air conditioner recoverers. water evaporation takes place in a secondary airstream which only allows sensible heat exchange with the primary airflow using an interchanger. If the water is recycled inside the device. In HVAC installations. in many cases. the most effective and economic alternative for achieving environmental protection. Using energy efficiently is. Indirect Evaporative System with a Returning Air Recovery Configuration: this is an Indirect Evaporative Cooler where the air that comes from the installation is used as a secondary airstream. As aforementioned.Experimental Analysis of a Combined Recovery System 255 the renewed air and the contamination risks are avoided (“useful” airflow does not come into contact with the water that has been cooled evaporatively). which allows an increase in the cooling effect (Figure 1). Figure 2. Indirect Regenerative Evaporative System. Other possibilities are heating exchange batteries and classical cooling systems. as secondary air. This is the configuration which we have used (Figure 2). The mixed systems are a combination of direct and indirect systems. . Figure 1. the air provided by the conditioned premises. or just a mixture of this air and outdoor air. These configurations are called regenerative or recoverable based on the following explanations: Indirect Regenerative Evaporative System: this is an Indirect Evaporative Cooler where a percentage of the primary airstream is used as a secondary airstream. Indirect Evaporative System with a Returning Air Recovery Configuration. using sequential modules in order to improve the performance and increase their utility in wet climates. the evaporative systems can be considered as heat recoverers when they use. the spread of many liquid phase-born bacterial diseases. The semi-indirect evaporative cooler works with the following mechanisms: • • • Heat and mass transfer in the return air flow. thus combining heat and mass transfer. in all cases. Spread of mass due to porosity and heat transport through the solid wall. there is greater or lesser liquid diffusion (water) with evaporation towards the air flow supply from the external pores.256 R. The cooling effect of the impulsed air would thus be the addition of two processes: the heat exchange between the two air flows (supply and return) plus the heat exchange process. Depending on the permeability of the wall of the solid porous cooler which separates the two air flows. Herrero Martín As Johnson [2] et al. . Figure 3. All of these features are presented together. most notably Legionnaire’s disease. which is why it has been called semiindirect. There exists an environment of almost stagnant water in direct contact with the outside air. increasing the cooling effect of the air to be conditioned and achieving optimisation of the thermal process [4] (See Figure 3). most conventional direct evaporative cooling methods involve collection and recirculation of water to keep the wetting media or misting region saturated. An evolution from indirect evaporative cooling systems is the semi-indirect evaporative cooling system with porous media. via evaporation. Evaporative Cooler: heat and mass transfer mechanisms. indirect evaporative cooling application has been commonly used. The absolute humidity of the air supply is the controlling factor in this mass transport process. despite the fact that indirect systems have lower efficiency in comparison with direct systems [3]. Due to this fact. if not properly maintained at significant costs. mentioned. between the air supply and the external wall. Evaporation or condensation as well as heat and mass exchange in the air flow supply. which aids. but the ceramic material used has a pore diameter that prevents the exchange of harmful agents through the porous structure.2*10-3m Pipe Lengt h 0. The coolant material chosen yields low thermal resistance. Evaporative Cooler geometric configuration Table 2. [7] . high resistance to corrosion and is also economical and offers high porosity. The geometric dimension and configuration of the ceramic exchanger are shown in Table 1: Table 1.-Geometric configuration of the evaporative cooler Arrangement Staggered Number of columns 7 Number of rows Number of pipes 7 49 Material Ceramic It is important to point out that this system allows water evaporation in the air supply.3 m2 Figure 4.257 Experimental Analysis of a Combined Recovery System Several prototypes for cooling building using porous ceramic materials as wetting media in indirect evaporative cooling applications as this paper proposes.6 m Area (Ao) 2. thus avoiding impulsed air contamination from the pollutants carried by the return air. Geometric dimensions of the evaporative cooler Internal diameter (di) 15*10-3m External diameter (de) 25*103 m Thicknes s (δ) 5*10-3m Section T (ST) Section L (SL) Section D (SD) 30*10-3m 25*10-3m 29. have been built in recent years such as those by Ibrahim et al [5] or Riffat and Zhu [6] who also combined an indirect evaporative cooler using porous ceramic as the cooling source and a heat pipe as the heat transfer device. constructed and tested an air-to-air heat exchanger using thermosyphon heat pipes using water as the working fluid for heat recovery in industry. oil-refining. NoieBaghban and Majideian [11] designed and constructed a heat pipe heat exchanger for heat recovery in hospital and laboratories. Figure 5. The optimum . the characteristic design and heat transfer limitations of single heat pipes for three types of wick and three working fluids were investigated using computer simulation. The heat transfer and enthalpy ratio between heat recovery and conventional air mixing are also targeted. power. Lukitobudi et al. [10] designed. The experimental results presented agreed with the data obtained through computer simulation. There are many articles carried out in the field of work of heating recovery using heat pipes such as the one by Shao et al [9] who presented a low pressure-loss heat recovery device based on heat pipes which was suitable for application in passive stack ventilation where a low pressure loss is essential. the heat pipe or two-phase thermosyphon device is an important concept in heat exchangers. such as bakeries.258 R. etc. The Evaporative Cooler device. In their research. glass. Abd El-Baky and Mohamed [12] investigated the thermal performance and effectiveness of heat pipe heat exchanger for heat recovery in air conditioning applications by measuring the temperature difference of fresh warm and return cold air through the evaporator and condenser side. which can be used in different branches of industry such as metallurgy. HEAT PIPE SYSTEMS As Vasiliev [8] mentioned. Herrero Martín The following photograph (Figure 5) shows the semi-indirect evaporative cooler and its arrangement above the tank that contains the water used in evaporative cooling. each of which is sealed at both ends. Heat applied to one end evaporates the working fluid from the wick. thus completing the cycle. The following photograph (Figure 6) shows the heat pipe system and its set-up. Numerous investigations have been made to obtain the thermal performance. The heat pipe recuperator is a super-conducting device comprising of an array of tubes. . type and filling ratio of the working fluid. and pipe material. Each heat pipe consists of an envelope (the tube).Experimental Analysis of a Combined Recovery System 259 effectiveness of heat pipe heat exchanger is calculated and compared with the experimental results. a wick. Lin et al [19] also carried out a thermal model for simulating the performance of a heat pipe system for recovering waste heat in the drying cycle in a domestic appliance. the vapour flows to the cold end of the tube where it is condensed and returned by the wick to the hot end for reevaporation. The HP device. The heat pipe exchanger built only recovers sensible heat from the airstreams expelled outdoors. Several experiments were carried out under different operating conditions by varying the parameters in order to determine and investigate their effect on the thermal performance of the thermosyphon heat exchanger. Figure 6. ensure efficient and reliable operation of heat pipe heat exchangers [13–17]. Soleymez [18] presented a thermoeconomic optimization analysis is presented yielding a simple algebraic formula for estimating the optimum HPHE effectiveness for energy recovery applications. The heat pipe device is arranged over a metal bank bench. Many factors affect the thermal performance of thermosyphon heat exchangers including velocity and temperature of input air. and a working fluid. Noie [20] presented experimental and theoretical research carried out to investigate the thermal performance of an air-to-air thermosyphon heat exchanger. These tubes are the actual heat pipes. H. Spain.260 R.5 m. fins perpendicular to the heat pipes are located parallel to the air flow. (E. The configuration chosen is done taking into account boundary layer limitations.1 × 10−3 Wick porosity (m2) 5. and three rows. A porous evaporative cooler with energy recovery. In order to decrease the convection heat transfer resistance between the air and the heat pipes. The tube bundle consists of 4 pipes per row.) A heat pipe device with energy recovery. (H. smooth Wick material: Stainless steel Working fluid water EXPERIMENTAL INSTALLATION Experiments were developed in the Air Conditioning Laboratory at the University of Valladolid. Table 3.H. Air distributing System: all the measuring instruments are inserted here.U. The systems used to carry out the trials are the following: (Figure 7 -8) • • • • • • • • Supply system: this has a fan with a potentiometer to keep the air flows under control.6 × 10−3 Pipe length (m) 0. and built of layers of an aluminium-manganese alloy within which the heat pipes are inserted.): this equipment allows us to simulate the conditions of the air supplied (temperature and humidity). Water distribution System: there is a water pump to which a rotameter is joined. Design characteristics of the heat pipe device Maximum heat output (W) 85 Pipe wall thickness (m) 2.3 × 10−11 Inner radius (m2) 10. the air goes inside the EC. From the A. . Air Handling Unit (A.) The conditioned room: the dimensions are 2x2x2.U. As mentioned.P. both in the impulse air area as well as the return air area. which contains an air to air reversible heat pump inside to guarantee when needed necessary that the space is properly conditioned. This main airstream is called the primary airstream and when this airstream is conditioned in the SIEC it goes to the HP and after passing through this device it enters the room.C.62 Wick type 350. Herrero Martín Table 3 presents the main design characteristics of the heat pipe recoverer that has been built. the system is located in a recovery configuration to condition a room. As was mentioned the system is located in a recovery configuration. The recovery system plus the conditioned room takes up approximately 20 square metres. Monitoring and Data-Acquisition system: a computer monitors and stores all the results from the measuring instruments. The system also has a pressure spray system with downward directed nozzles and a water droplet remover to avoid water loss. Experimental Analysis of a Combined Recovery System 261 Figure 7. Experimental Facility. when it is impulsed into the heat pipe in a cross-flow in relation to the primary airstream. until it leaves in the upper part. Thus. thus obtaining a three-recovering configuration. which might carry aerosols. Figure 8. . the air expelled from the room goes through the EC in a cross-flow. Experimental Installation Schema. After passing through the HP. ensuring non-dispersion of Legionella in the expelled air. it is impulsed to the exterior heat pump unit. the following characteristics: sensible heat. (Accuracy: ±2 % RH (0-100% RH)) Figure 9. (Accuracy: 0. 10ºC (T2) and 5ºC (T1). 40ºC (T8). From the experimental results. • Temperature The temperature levels correspond to summer and winter conditions in Valladolid (Spain) in order to analyze the behaviour of the device in both working modes. A complete factorial design was developed. EXPERIMENTAL MEASUREMENTS The characterization of the recovery system was carried out following the experimental design method. to analyse the total heat recovered by the system in heating mode and in cooling mode. latent heat and total heat are evaluated separately to better explain the combined system behaviour. 400m3/h and 500m3/h. 30ºC (T6) and 25ºC (T5) and the winter levels are: 20ºC (T4).1 C) HR: relative humidity measuring sensor. The summers levels are: 45ºC (T9). 35ºC (T7). Measurement Sensors.262 R. (See Figure 10) There were two factors analyzed: • Air Flow The airflow levels correspond to three levels: 300m3/h. Herrero Martín The measurement sensors are shown in Figure 9: • • T: temperature measuring sensor. . 15ºC (T3). 2 7.6 5.2 7. latent and total heat (GUM procedures with k=2) [21] Sensible Heat UV3 UV1 UV2 (%) (%) (%) 4.8 Latent Heat UV1 UV2 UV3 (%) (%) (%) 4.1 8.4 5.5 6.3 5.6 5. The conclusions derived by single factors and interaction values inspection will not be accepted if the ANOVA analysis do not corroborate them.2 5.5 5. final conclusions are supported by the variance analysis.5 5.8 8. latent and sensible heat were considered in order to obtain the total heat recovered. Experimental Design Schema.3 7. The uncertainty values for the characteristics analyzed are shown in Table 4.3 30 4.7 4. average values of the single factors and their interactions are given and afterwards.1 5.0 4.2 6. Firstly.3 5.2 6. Table 4.8 8. For the evaporative cooler.8 5. where UVi. The heat pipe exchanger built only recovers sensible heat from the airstreams expelled outdoors.6 6.7 5. .1 5.6 45 4.7 6.5 4.2 5.5 5.4 8.5 40 4.9 Total Heat UV3 UV1 UV2 (%) (%) (%) 6. Uncertainty values for the characteristics analyzed: sensible.263 Experimental Analysis of a Combined Recovery System Figure 10.8 Temperature (ºC) 25 The characteristics analysis was carried in two stages.6 7.6 6.1 7.5 5.3 8.4 4.0 35 4.1 6.4 6. represent the uncertainty values for each volumetric flow described.4 5. 62 -1984. Average values of sensible heat recovered are plotted against single factors levels. in Figure 12 the mean values of the characteristic are plotted against factor interaction (VxT).89 -1220. T9 .93 -203.264 R. Herrero Martín The results will be presented in the following order: - - Sensible heat combined system analysis evaporative cooler analysis o heat pipes battery analysis Latent heat o evaporative cooler analysis Total heat o evaporative cooler analysis SENSIBLE HEAT RECOVERED Combined System In Figure 11 the average values of sensible heat recovered are plotted against single factors levels (temperature (T) and airflow (V)). In table 6 the ANOVA is presented.62 -2591.22 -1439. Column 3 shows the sum of squares (SS) of the factors column 4 gives the associated variance values (V) and in column 5 the contributory percentage is given (%). In the ANOVA table column 1 shows the factors analyzed.77 -1691.29 977.37 2000 S e n sib le H e a t R e co ve re d ( W ) ( A ve ra g e V a lu e s) Factors 1000 0 -1000 -2000 -3000 -4000 -5000 V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 Single Factors Figure 11. V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Mean Values -1124. remarkable conclusions in terms of the most contributory factor are fully addressed. temperature and the interaction between the aforementioned factors (VxT).74 -4042. Furthermore. The corresponding values are also given.19 577.78 -785.93 -3491. which are: volumetric flow rate (Vi). Column 2 represents the degree of freedom (Dof) of the factors analyzed. 84 V1T8 -2988.10 554.1 73561119.50 -2548.68 -2059.9 96. VxT interaction mean values Sensible Heat (W) Factors Mean Values V1T1 1137.265 Experimental Analysis of a Combined Recovery System Table 5.21 S e n sib le H e a t R e co ve re d (W ) (A ve ra g e va lu e s) 2000 1000 0 V1 -1000 V2 -2000 V3 -3000 -4000 -5000 T1 T2 T3 T4 T5 T6 T7 T8 T9 Temperature Factor Figure 12.38 -1552.0 2926158.84 -3923.6 0.89 V1T4 -784.0 1065784.21 -4635.19 V1T5 -972.37 571.33 V1T6 -1751.21 V1T9 -3161. Average values of sensible heat recovered are plotted against temperature factor.0 % 1.74 -306.80 -4330.36 Factors V2T1 V2T2 V2T3 V2T4 V2T5 V2T6 V2T7 V2T8 V2T9 Mean Values 1039.9 66611.62 -705.26 V1T7 -2125.84 -2143. (VxT interaction ) Table 6-. ANOVA results Factors V T VxT Error Total DoF 2 8 16 0 26 SS 1453205.7 1.0 .10 V1T2 608.0 100.00 V1T3 -79.5 0.0 V 726602.4 0.11 -3563.53 Factors V3T1 V3T2 V3T3 V3T4 V3T5 V3T6 V3T7 V3T8 V3T9 Mean Values 755.10 -1136.5 9195139.11 -3101.05 -224.0 76080109.84 -868. 0 .0 100. fact which represents a different behaviour of the device from heating mode to cooling mode falling from positive values to negative ones.29 V3 -1640.37 T9 -3886.6 1.62 T5 -1189. (See Figure 11) In Table 7 the average values of sensible heat recovered for the combined system and the single systems are given and in Table 8 the corresponding ANOVA are shown.0 186950.16 Table 8.1 1.0 96.6 1.45 V2 -1439. the sensible heat recovered is higher.9 67024437.0 0.0 Evaporative Cooler SS % 1296814.12 T1 977.79 48.9 1. since the heat transfer rate is related to the temperature difference.6 0. As in common heat exchangers. next to temperature level 3 (T3) a change can be clearly observed.77 -37.1 2.0 96.19 T1 878.5 26 100.22 V1 -1104.14 -20.0 0.66 V3 -1691.12 T9 -4042.9 181267.0 Total 76080109.1 97.59 -88.77 V2 -1402. (See Figure 11). Furthermore.0 Heat Pipe System SS % 1727. when the temperature difference between the outdoor and the return airstreams rises.0 0.58 T8 -3491.266 R.62 -156. In Figure 13 the single devices contribution in comparison with combined system contribution is given.58 T5 -1220.49 59.7 1065784. Table 7.62 T6 -1920.03 T7 -2591.07 -64.70 T2 577.54 T6 -1984.4 0. ANOVA (combined system and single systems separately) Sensible Heat Factors DoF V 2 T 8 VxT 16 Error 0 Combined System SS % 1453205.93 T2 562.74 T8 -3366.0 100. Herrero Martín Analysis of Results Temperature This is the most contributory factor with a percentage close to 97% (See Table 6).5 1102928.1 0.35 98.2 0. Single factors mean values for the combined system and the single systems separately Sensible Heat Recovered (W) Combined System Evaporative Cooling System Mean Factors Factors Mean values Values V1 -1124.10 -36.78 T3 -251.30 -31.0 3956.9 73561119.21 Heat Pipes System Factors V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Mean Values -19.89 T4 -765.0 69424180.35 -125.93 T7 -2503.59 T3 -203.93 T4 -785. Evaporative Cooler and Heat Pipes contribution in global recovery. the dominant recovery system is the evaporative cooler. the corresponding results for both working modes are shown ( See Figure 14 and 17 and Tables 9-10). . This factor can be easily explained taking into account its location within the test ring where the heat pipes battery works with lower temperature differences during its operation cycles. Sensible Heat Recovered (W) (Average values) 2000 1000 0 -1000 -2000 -3000 -4000 -5000 V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Factors Levels Figure 14. one conclusion is inferred. these results are studied separately for heating mode (See Figure 15 and 18 and Tables 11 and 13 ) and cooling mode (See Figure16 and 19 and Tables 12 and 13). Sensible Heat Recovered (W) (Average Values) 2000 1000 0 -1000 -2000 -3000 -4000 -5000 V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Single Factors Combined System Heat Pipes Evaporative Cooler Figure 13.267 Experimental Analysis of a Combined Recovery System When analyzing Figure 13. Average values of sensible heat recovered are plotted against single factors levels. and secondly. Evaporative cooling system In this subsection a detailed analysis for the evaporative cooling system was carried out. Firstly. 58   800 600 400 200 0 -200 -400 -600 -800 -1000 V1 V2 V3 T1 T2 T3 T4 Factors Levels Figure 15. Heating Mode: Average values of sensible heat recovered are plotted against single factors levels.93 T4 -765. Herrero Martín Table 9.12 T1 878.67 V2 -2627.70 T2 562.70 T2 562.58 V2 128.45 T1 878.58 -1189.45 V2 -1402.12 T9   -3886. Cooling Mode: Average values of sensible heat recovered are plotted against single factors levels.58 -3366.21 1000 S e n sib le H e a t R e co ve re d (W ) (A ve ra g e va lu e s) Sensible Heat (W) Factors Mean Values V1 174.59 T3 -251. 0 S e n sib le H e a t R e co ve re d (W ) (A ve ra g e va lu e s) Calor Sensible (W) Factores Promedio V1 -2127.03 -2503.80 V3 14.93 Factors T4 T5 T6 T7 T8 T9 Mean Values -765.03 T7 -2503.54 -1920. .58 T8 -3366.83 V3 -2963.54 T6 -1920.59 T3 -251.66 V3 -1640.79 T5 -1189.268 R.21 -500 -1000 -1500 -2000 -2500 -3000 -3500 -4000 -4500 V1 V2 V3 T5 T6 Factors Levels T7 T8 T9   Figure 16. Single factors mean values Sensible Heat (W) Factors Mean Values V1 -1104.12 -3886. 96 Sensible Heat Recovered (W) (Average values) 1500 1000 500 V1 V2 V3 0 -500 -1000 T1 T2 T3 T4 Temperature factor ( Heating Mode) Figure 18.28 -4168.56 -2992.33 -1113.28 V2T1 V2T2 V2T3 V2T4 V2T5 V2T6 V2T7 V2T8 V2T9 950.11 -2054.36 548. Average values of sensible heat recovered are plotted against temperature factor.02 517.95 -3009.26 -2443.35 -840.17 -3790. VxT interaction mean values Sensible Heat (W) Factors Mean value Factors Mean Value Factors V1T1 V1T2 V1T3 V1T4 V1T5 V1T6 V1T7 V1T8 V1T9 1043.44 -954.27 -2074.02 -686.98 -1501.42 -769.20 -1712. (VxT interaction in Heating Mode) .269 Experimental Analysis of a Combined Recovery System Sensible Heat Recovered (W) (Average values) 2000 1000 0 V1 -1000 V2 -2000 V3 -3000 -4000 -5000 T1 T2 T3 T4 T5 T6 T7 T8 T9 Temperature factor Figure 17.31 -1993. Average values of sensible heat recovered are plotted against temperature factor.13 -4480.52 -266.72 621.92 -3420.65 -2887.41 -365. (VxT interaction) Table 10.83 -124.39 V3T1 V3T2 V3T3 V3T4 V3T5 V3T6 V3T7 V3T8 V3T9 Mean Value 642. 17 -3790.00 100. Average values of sensible heat recovered are plotted against temperature factor.39 Factors V3T5 V3T6 V3T7 V3T8 V3T9 Mean value -1501.33  V3T4 ‐840.78 0.02  V3T3 ‐365.82 86.42  V2T3 ‐266.56 -2992.72  V1T2 548.21 0.92 V2T8 -3420.65 -2887. Herrero Martín Table 11.00 16360984.00 474071.52  V3T2 621.02 0. ANOVA (heating and cooling mode) Factors V T VxT Error Total DoFheat 2 3 6 0 11 DoFcool 2 4 8 0 14 Heating Mode SS 54418.28 Sensible Heat (W) Factors Mean value V2T5 -1113.00 V 885094.16 3.37 5079918. (VxT interaction in Heating Mode) Table 12.60 14096108.19 1693306.80 3524027.02  V3T1 642.40 80448.13 0.41 1.83  V2T2 517.11 -2054.00 1168641.04 97.44  V2T4 ‐686.60 V 27209.00 100.98  Sensible Heat Recovered (W) (Average values) 0 -500 -1000 -1500 -2000 V1 -2500 V2 -3000 V3 -3500 -4000 -4500 -5000 T5 T6 T7 T8 T9 Temperature factor ( Cooling Mode) Figure 19.41  V1T3 ‐124.13 13408.28 V2T9 -4168.96 Table 13.00 Cooling Mode SS 1770189.00 5214785.13 -4480. VxT interaction mean values Sensible Heat (W) Factors Mean Value Factors Mean Value Factors Mean Value V1T1 1043.54 0.35  V1T4 ‐769.80 0. VxT interaction mean values Factors V1T5 V1T6 V1T7 V1T8 V1T9 Mean value -954.20 -1712.31 V2T6 -1993.42 % 1.36  V2T1 950.00 .26 V2T7 -2443.00 494686.00 61835.71 % 10.95 -3009.270 R.27 -2074. the cooling mode potential in terms of energy recovery in comparison with heating mode is clearly shown.16 . Heating and cooling mode analysis Temperature Factor: • Heating Mode: This is the most contributory factor.49 T7 59.62 -156. the transition between heating and cooling mode can be clearly appreciated next to temperature level 3. Single factors mean values Factors V1 V2 V3 T1 T2 T3 Sensible Heat (W) Mean Values Factors -19. and secondly. due to the fact that more negative values results in a gain in terms of energy recovered in cooling mode. Table 14-. • Cooling Mode: this is the most contributory factor.79 T8 48. are essentially linked to the evaporative cooler behaviour.Experimental Analysis of a Combined Recovery System 271 Analysis of Results All the considerations mentioned for the combined system. Due to the aforementioned fact.14 T9 Mean Values -20. the behaviour of the analyzed device can be considered as irreversible and thus it should be operated under cooling conditions.07 -64. This fact can be easily explained in terms of thermal differences between primary and secondary airstream when temperature factor is increased from T5 to T9.59 -88. a conclusion can be inferred.35 T6 98. Its shows a lineal decreasing trend. where primary air and secondary air temperatures are very similar.77 T4 -37. Its shows a lineal decreasing trend. although this trend could be considered as increasing trend. Furthermore.35 -125.30 -31. Firstly. the corresponding results for both working modes are shown ( See Figure 20 and 23 and Tables 14-15 and 18). these results are studied separately for heating mode (See Figure 21 and 24 and Tables 16 and 19) and cooling mode (See Figure22 and 25 and Tables 17 and 20).10 T5 -36. Heat Pipes System In this subsection a detailed analysis for the heat pipes system was carried out. 16 Sensible Heat Recovered (W) (Average values)   -20 -40 -60 -80 -100 -120 -140 -160 -180 V1 V2 V3 T5 T6 Factors Levels T7 T8 T9   Figure 22.30   100 80 60 40 20 0 -20 -40 V1 V2 V3 T1 T2 T3 T4 Factors Levels   Figure 21. Average values of sensible heat recovered are plotted against single factors levels. Cooling Mode: Average values of sensible heat recovered are plotted against single factors levels.272 R.07 T6 -64. 120 Sensible Heat Recovered (W) (Average values) Sensible Heat (W) Factor Mean s Values V1 45. Heating Mode: Average values of sensible heat recovered are plotted against single factors levels.89 V3 -107. .54 T1 98.35 T8 -125. Herrero Martín Sensible Heat Recovered (W) (Average values) 150 100 50 0 -50 -100 -150 -200 V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Factors Levels Figure 20.38 V3 52.14 T4 -20.67 V2 41.62 T9  -156.49 T2 59.46 T5 -31. 0 Sensible Heat (W) Mean Factors Values V1 -72.59 T7 -88.13 V2 -99.79 T3 48. Average values of sensible heat recovered are plotted against temperature factor.24 V2T7 -104.08 Sensible Heat (W) Factors Mean Values V2T1 89.77 V2T5 -23.99 -51.18 -100.35 V2T2 53.40 V2T4 -18.19 V2T8 -143.38 66.52 V2T9 -162.55 -109. VxT interaction mean values Factors V1T1 V1T2 V1T3 V1T4 V1T5 V1T6 V1T7 V1T8 V1T9 Mean Values 93.50 -27.25 Sensible Heat Recovered (W) (Average values) 150 100 50 V1 0 V2 -50 V3 -100 -150 -200 T1 T2 T3 T4 T5 T6 T7 T8 T9 Temperature factor Figure 23.14 Factors V3T1 V3T2 V3T3 V3T4 V3T5 V3T6 V3T7 V3T8 V3T9 Mean Values 112.39 -51.53 V2T3 41.17 44.67 -133. (VxT interaction in Heating Mode) . (VxT interaction) Sensible Heat Recovered (W) (Average values) 120 100 80 60 V1 40 V2 20 V3 0 -20 -40 T1 T2 T3 T4 Temperature factor ( Heating Mode) Figure 24. Average values of sensible heat recovered are plotted against temperature factor.67 58.74 59.26 -152.73 -88.08 -154.75 -18.273 Experimental Analysis of a Combined Recovery System Table 15.53 -14.13 -38.36 V2T6 -66. 52 V2T9 -162.67 58.77 Factors V3T1 V3T2 V3T3 V3T4 Mean Values 112.26  2.36 V2T6 -66.73 -88.96  VxT  16  3956.40  100.00  Mean Values -51.39 Sensible Heat Recovered (W) (Average values) 0 -20 -40 -60 V1 -80 V2 -100 V3 -120 -140 -160 -180 T5 T6 T7 T8 T9 Temperature factor ( Cooling Mode) Figure 25.274 R.12  22658.50 -27. Herrero Martín Table 16.40 V2T4 -18.13 -38.23  SS  863.00  Total  26  186950.62  V  %  0.67 -133.99 -51.08 -154.38 66.25 .12  Error  0  0.75 Sensible Heat (W) Factors Mean Values V2T1 89.39  96.24 V2T7 -104.08 Sensible Heat (W) Mean Factors Values V2T5 -23.35 V2T2 53.92  T  8  181267. ANOVA Factors  DoF  V  2  1727.14  247.14 Factors V3T5 V3T6 V3T7 V3T8 V3T9 Table 18.0  0.17 44.26 -152. VxT interaction mean values Factors V1T1 V1T2 V1T3 V1T4 Mean Values 93.74 59.19 V2T8 -143.18 -100.53 V2T3 41.53 -14. VxT interaction mean values Factors V1T5 V1T6 V1T7 V1T8 V1T9 Mean Values -18. (VxT interaction in Cooling Mode) Table 17.0  0. Average values of sensible heat recovered are plotted against temperature factor.55 -109.49  7190. When the temperature difference between the outdoor and the return airstreams rises. the sensible heat recovered is higher. these results are studied separately for heating mode (See Figure 27 and 30 and Tables 23 and 26) and cooling mode (See Figure 28 and 31 and Tables 24 and 26 ).59 0. LATENT HEAT RECOVERED Latent heat is only recovered by the evaporative cooler device. and secondly.00 100.00 100.87 2060.31 1730. when the temperature difference between the outdoor and the return airstreams rises.72 7344.00 0.16 1587.52 63.12 85. with a percentage next to 97%. In this subsection a detailed analysis for the evaporative cooling system was carried out.00 Analysis of Results Temperature • • Heating Mode: This is the most contributory factor.91 198. the sensible heat recovered is higher. the corresponding results for both working modes are shown ( See Figure 26 and 29 and Tables 21-22 and 25). since the heat transfer rate is related to the temperature difference.91 381.24 4.00 0. (See figure 7) Cooling Mode: This is again the most contributory factor.82 22034. ANOVA (cooling mode) Factors V T VxT Error Total DoFheat 2 4 8 0 14 Cooling Mode SS V 3460.68 0.20 1.63 % 10.00 34196. .64 0.66 7287. Firstly.64 126.12 97.Experimental Analysis of a Combined Recovery System 275 Table 19. The transition between cooling and heating modes occurs next to temperature level 4.00 Table 20.49 0.90 % 1.00 22669. ANOVA (heating mode) Factors V T VxT Error Total DoFheat 2 3 6 0 11 Heating Mode SS V 253.88 2442.16 29148. 36 T8 247.37 V2 385.60 T9 Factors V1 V2 V3 T1 T2 T3 Mean Values 516. Herrero Martín Table 21.65 T1 326. Heating Mode: Average values of sensible heat recovered are plotted against single factors levels.276 R.   .64 704.22 997.53 811. Single factors mean values Latent Heat (W) Mean Values Factors 671.25 Sensible Heat Recovered (W) (Average values)   500 400 300 200 100 0 V1 V2 V3 T1 T2 T3 T4 Factors Levels Figure 27. Average values of sensible heat recovered are plotted against single factors levels.90 Latent Heat Recovered (W) (Average values) 1200 1000 800 600 400 200 0 V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Factors Levels Figure 26.31 T5 473.25 699.36 T3 247.95 T6 326.80 827.66 V3 291.29 T4 672.60 T4   516.35 T2 321.35 T7 321. 600 Latent Heat (W) Mean Factors Value V1 381. 22 T8 997.86 V2T7 942.31 914.41 827.63 544.09 V2T6 1021.78 171.23 V2 901.76 1267.35 Sensible Heat Recovered (W) (Average values) 1400 1200 1000 V1 800 V2 600 V3 400 200 0 T1 T2 T3 T4 T5 T6 T7 T8 T9 Temperature factor Figure 29.24 Mean Value 424.06 V2T5 670.75 V2T3 351.48 V2T9 976. Average values of sensible heat recovered are plotted against temperature factor.68 541.48 846.17 471. VxT interaction mean values Factors V1T1 V1T2 V1T3 V1T4 V1T5 V1T6 V1T7 V1T8 V1T9 Latent Heat (W) Factors Mean Value V2T1 188.53 T7 811.82 614.80 T5 699.80 T6 827.59 V2T4 569. Table 22.90 1000 800 600 400 200 0 V1 V2 V3 T5 T6 T7 T8 T9 Factors Levels Figure 28.05 508. Cooling Mode: Average values of sensible heat recovered are plotted against single factors levels.11 Factors V3T1 V3T2 V3T3 V3T4 V3T5 V3T6 V3T7 V3T8 V3T9 Mean Value 366.77 597.63 V3 619.39 514.50 V2T8 897. (VxT interaction) .277 Experimental Analysis of a Combined Recovery System 1200 Sensible Heat Recovered (W) (Average values)   Sensible Heat (W) Mean Factors Value V1 903.07 234.25 157.23 V2T2 433.11 946.04 359.64 T9   704. (VxT interaction in Cooling mode) .53 41.40 -18. Herrero Martín Sensible Heat Recovered (W) (Average values) 600 500 400 V1 300 V2 V3 200 100 0 T1 T2 T3 T4 Temperature factor ( Heating Mode) Figure 30. Average values of sensible heat recovered are plotted against temperature factor.67 58. VxT interaction mean values Sensible Heat (W) Mean Value 93.278 R.74 59.53 -14.17 44.39 Sensible Heat Recovered (W) (Average values) 1400 1200 1000 V1 800 V2 600 V3 400 200 0 T5 T6 T7 T8 T9 Temperature factor ( Cooling Mode) Figure 31.75 Factors V1T1 V1T2 V1T3 V1T4 Factors Mean Value Factors Mean Value V2T1 V2T2 V2T3 V2T4 89.77 V3T1 V3T2 V3T3 V3T4 112.35 53.50 -27.38 66. (VxT interaction in Heating mode) Table 23. Average values of sensible heat recovered are plotted against temperature factor. 73 -88.00 Table 26.52 -162.00 Cooling Mode DoF % 2 39.68 209581.0 87029.67 -133. thus it cannot be considered the controlling resistance. this means that this airflow value can be considered as a maximum. the humidity addition lowers (in absolute terms).58 6 32.19 -143.36 -66.57 0. nevertheless.55 -109.9 117434.00 14 100.65 0 0.25 Table 25.0 2262779. ANOVA (heating and cooling mode) Factors V T VxT Error Total Heating Mode DoF % 2 10.18 -100.38 74.08 -154. due to the increase in the mass heat coefficient.00 Analysis of Results All the factors and interaction with a percentage of contribution in the ANOVA higher than 15% are considered. VxT interaction mean values Sensible Heat (W) Factors Mean Value Factors Mean Value Factors V1T5 V1T6 V1T7 V1T8 V1T9 -18.Experimental Analysis of a Combined Recovery System 279 Table 24.26 -152.66 4 26. It was observed that when increasing the airflow above 400 m3/h. reaching this value the system behaves as a current .24 -104.11 0 0.99 -51. Air Flow • Cooling Mode: This factor presents the highest contributory percentage (39%).00 11 100.10 15.99 10.00 351256.36 1676654.23 8 34.00 100.52 0. ANOVA Factors DoF V T VxT Error Total 2 8 16 0 26 SS V % 234869. it is thought that when the airflow rises the latent heat recovered also does.13 -38.54 0.08 V2T5 V2T6 V2T7 V2T8 V2T9 -23.75 21953. A priori.14 V3T5 V3T6 V3T7 V3T8 V3T9 Mean Value -51.77 3 56. the convective mass diffusion does not limit mass transport. 0037 0.0032 0.6 21.0036 0.2 x1-x2 (gwater / kg dry air ) 0.6 3.2 1.5 0.0087 0.0081 0.3 9.9 0.9 10.1 23.0109 T1-T2 (C) -2.5 18.0041 0.6 1.9 20.5 .0096 0.3 1.0091 0.4 20.1 14.6 25.0035 0.7 0.9 10.8 39.9 33.95 6.0037 0.1 9.0034 0.0090 0.7 1.7 Table 28. Table 27.94 3.5 0.9 21.3 19.0084 0.0 24.4 2.7 13.2 39.0 x1 (gwater / kg dry air ) 0.61 2.2 0.9 19. T1 (C) 4.4 0.4 0.0088 0.3 0.0032 0.4 30.9 0.4 30.5 23.4 0.0091 0.3 0.0095 0.7 x2 (gwater / kg dry air ) 0. Results for 400 m3/h. Herrero Martín indirect evaporative cooler system.1 44.0039 0.7 1.5 0. diminishing the latent heat recovered.1 34.1 0.6 0.0033 0.3 1.1 28.8 10.3 28.3 29.0 13.5 39. Results for 500 m3/h.0093 0.6 5. in the last column the specific humidity values are provided.5 x1 (gwater / kg dry air ) 0.3 0.0 26.0105 0.0090 0.9 11.0094 0.2 10.3 44.7 25.8 13.0099 x2 (gwater / kg dry air ) 0.0102 0. a series of charts are provided ( See Tables 27-29). To observe the aforementioned fact (“so called” by-pass effect).20 7.4 13.0036 0.0102 0.0092 0.13 8.0088 0.8 1.0078 0.3 5.0083 0.1 0.0094 0.0085 0.0037 0.0035 0.7 33.4 5.1 0.9 x1 (gwater / kg dry air ) 0.0 22.0076 0.280 R.0090 0.0 Table 29.28 0.6 2.9 x1-x2 (gwater / kg dry air ) 0.0087 T2 (C) 5.0035 0.0080 0.3 32.1 29.79 x1-x2 (gwater / kg dry air ) 0.6 -1. T1 (C) 4.0108 0.8 T2 (C) 7.0109 T1-T2 (C) -3.0036 0.4 34.5 0.7 14.2 31.0082 0.4 -1.6 7.0 35.0092 T1-T2 (C) -1.0100 0.0086 0. In this tables.9 7.6 0.5 26.0081 0.0087 0.3 12.0040 0.5 18.0035 0.3 T2 (C) 8.76 1.6 33.21 -1.4 44. Results for 300 m3/h.0040 0.4 0.0101 x2 (gwater / kg dry air ) 0.4 11. T1 (C) 5. firstly. the heat exchanged is mainly sensible heat. As previously discussed. There are two different trends. within this situation the saturation vapour pressure enables water evaporation. under these conditions. cooling one from level 4. these results are studied separately for heating mode (See Figure 34 and Table 34 ) and cooling mode (See Figure 35 and Table 34). the corresponding results for both working modes are shown ( See Figure 33 and 36 and Tables 31-33). TOTAL HEAT RECOVERED Due to the fact that the combined system mostly reproduces the evaporative cooler device behaviour (see Figure 32). Evaporative Cooler In this subsection a detailed analysis for the evaporative cooling system was carried out. (See Table 30). condensation conditions could occur. Firstly. where latent heat increases. the latent heat recovered rises. (although temperature rises the corresponding relative humidity is lower). Level 4 presents a different behaviour similar to the one observed in cooling mode. • Heating Mode: evaporation is governed by the water vapour partial pressure between the tubes surface and the primary airstream.Experimental Analysis of a Combined Recovery System 281 Temperature • Both Modes analysis: this is the dominant factor. Level 4 presents a different trend in comparison with levels 1 to 3). • Cooling Mode: The dates present low relative humidity values and high temperatures. • Cooling Mode: in this case an interaction occurs. Even next to saturation. and secondly. The specific humidity levels of the dates (See Tables 6-9) are closed. When increasing airflow and temperatures together with lower relative humidity levels. diminishing the latent heat exchanged. fact which motivates the intersection. lower than expected. this behaviour is limited by the maximum airflow (V2). heating one. . VxT interaction • Heating Mode: When analyzing the data in detail. form levels 1 to 3. The results offered corresponds to the evaporative cooler device. which corresponds to large evaporative capacity. The ANOVA also corroborates this fact. whilst for lower temperature levels (heating mode) the relative humidity levels associated are higher. which corresponds to low evaporation capacity. where latent heat decreases and secondly. it is observed that T1 for V2 presents an anomalous value. 6 50688523 1274684.0 186950.41 93.00 100.00 100.33 -489.50 -1692.12 0.16 T4 -730.74 -1092. Table 30.8 56340888 1275887.12 3956.00 Evaporative Cooler Heat Pipes SS 2446733.35 T5 -1166.23 181267.96 2.2 0.49 % 4.48 2.94 T8 -4.31 % 0. Single factors mean values Factors V1 V2 V3 T1 T2 T3 Total Heat (W) Mean Values Factors -433.00 Table 31.36 -2368.4 0.48 -3181.14 0.282 R. Herrero Martín Total Heat Rec ov ered (W) (Av erage Values ) 2000 1000 0 -1000 -2000 -3000 -4000 V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Single Factors Combined System Heat Pipes Evaporative Cooler Figure 32 Evaporative Cooler and Heat Pipes contribution to total heat recovered.0 60273695 DoF 2 8 16 0 26 % 4.16 2.12 0.33 T9 Mean Values -249.00 100.0 54409941 SS 1727.05 T7 883.92 96. ANOVA (combined system and single systems separately) Total Heat Total Factors V T VxT Error Total SS 2656919.50 93.34 0.00 .17 T6 1205. 283 Experimental Analysis of a Combined Recovery System 1500 Total Heat Recovered (W) (Average values) 1000 500 0 -500 -1000 -1500 -2000 -2500 -3000 -3500 V1 V2 V3 T1 T2 T3 T4 T5 T6 T7 T8 T9 Factors Levels Figure 33.10 T1 1205.05 T2 883.20 V3 -2343. Cooling Mode: Average values of sensible heat recovered are plotted against single factors levels. Heating Mode: Average values of sensible heat recovered are plotted against single factors levels. 1400   1200 Total Heat Recovered (W) (Average values) Total Heat (W) Mean Factors value V1 555.48 T9  -3181.50 T7 -1692.33 1000 800 600 400 200 0 -200 -400 V1 V2 V3 T1 T2 T3 T4 Factors Levels   Figure 34.74 T6 -1092.95 V2 514. .36 T8 -2368.94 T3 -4.46 V3 306. Average values of sensible heat recovered are plotted against single factors levels.31 Total Heat Recovered (W) (Average values)   -500 -1000 -1500 -2000 -2500 -3000 -3500 V1 V2 V3 T5 T6 Factors Levels T7 T8 T9   Figure 35. 0 Total HeatW) Mean Factors Value V1 -1224.99 T5 -489.33 T4  -249.44 V2 -1726. 80 V2T9 -3192.0 54409941 V 1223366. ANOVA Factors V T VxT Error Total DoF 2 8 16 0 26 SS 2446733.57 V2T4 -117.90 109.63 -261.00 .17 Total Heat(W) Mean Factors value V2T1 1138. Herrero Martín Table 32.40 907.89 -1620.72 -866.284 R.93 -2447.66 -208.34 0.18 -369.40 V2T7 -1501.43 V2T8 -2522.35 -3883.6 50688523 1274684. (VxT interaction) Table 33.50 792.28 -2468.16 2.8 0.15 Factors Mean Value V3T1 V3T2 V3T3 V3T4 V3T5 V3T6 V3T7 V3T8 V3T9 1009.16 -1127. Average values of sensible heat recovered are plotted against temperature factor.4 79667.13 -39.50 93.4 0.75 -2962.26 V2T5 -443.62 To ta l H e a t R e co ve re d (W ) (A ve ra g e va lu e s) 2000 1000 0 V1 -1000 V2 -2000 V3 -3000 -4000 -5000 T1 T2 T3 T4 T5 T6 T7 T8 T9 Temperature factor Figure 36. VxT interaction mean values Factors Mean Value V1T1 V1T2 V1T3 V1T4 V1T5 V1T6 V1T7 V1T8 V1T9 1467.0 2092690 % 4.25 V2T2 951.00 100.27 V2T3 85.8 6336065.22 V2T6 -971.29 -1439.60 -986. with a very high percentage of approximately 95%. due to the increment of the film coefficients: both the thermal coefficient. Temperature • • Heating Mode: this is the most contributory factor. It is shown that. the effects produced by the temperature increments are cancelled out by the sensible and latent heat recovered.00 4580358. . which characterises the sensible exchange. The behaviour of the system is clearly shown.60 % 18. as well as the mass coefficient linked to the latent exchange. ANOVA (heating and cooling mode) Factors V T VxT Error Total DoFheat 2 3 6 0 11 DoFcool 2 4 8 0 14 SS 143416. the total heat recovered rises.13 95.00 Analysis of Results Airflow Analysis • Cooling Mode: its contribution is higher.65 79.20 1.00 Cooling Mode V 1572340. and the ones in dark grey are the most contributory squares.00 SS 3144680. The rising trend to negative values. The light-grey coloured squares represent a medium contributory percentage. which goes from the positive values that characterize the heating mode to the negative ones which represent the cooling mode.20 Heating Mode V 71708.66 0.23 12703. In this factor.40 13361816.12 0.00 100. when the airflow is increased.00 1204542.55 4360719.97 0.70 76221.28 1453573.00 44637. Cooling mode: this is the most contributory factor whose values are approximately 80%.00 357099.66 0.42 0. The transition between these behaviours occurs near the temperature level 3 which corresponds to 15ºC. as well as the white squares.00 16863596. This value is increased for the highest temperature differences between both airstreams (supply and return).39 0.00 416396.Experimental Analysis of a Combined Recovery System 285 Table 34. around 18%.23 2.00 100.20 3340454. SUMMARY In Table 35 the main conclusions from the analysis performed are summarized.20 % 3. The legend to understand the following table is: “x” means no contribution (negligible contribution in terms of variance analysis). the continuity and the linearity that presents the evaporative cooler in this working mode are clearly shown. their effects were previously explained. Sensible Heat • Temperature is the most contributory factor in terms of sensible heat. . Summary of Results (combined system and single systems separately) Factors V T VxT Factors V T VxT Factors V T VxT • • Sensible Heat Evaporative Cooler TOTAL Heating Cooling Mode Mode Decreasing x x (-) Decreasing Decreasing Decreasing (+/-) (+/-) (-) x x x LATENT HEAT Evaporative Cooler Heating Mode Decreasing (+) Decreasing (+) Corroborates individual factors Total Heat RESI TOTAL Heating Cooling Mode Mode Decreasing x x (-) Decreasing Decreasing Decreasing (+/-) (+/-) (-) x x x Heat Pipes Heating Cooling Mode Mode Decreasing x (-) Decreasing Decreasing (+/-) (-) x x Cooling Mode By. Cooling mode: an important by-pass effect was found.P Heating Mode x Decreasing (+/-) x Cooling Mode Decreasing (-) Decreasing (-) x It should be mentioned as a general conclusion that level 4 is a discordant point of the Heating mode behaviour. Latent Heat • • Heating mode: temperature was the most contributory factor. The dominant recovery system is the evaporative cooler in terms of total heat recovered. Herrero Martín Table 35.pass efect Increasing (+) Interaction H. A decreasing trend is clearly observed from positive values (heating mode) to negative ones (cooling mode).286 R. F. showing the possibilities of implementing this solution to save energy and also to improve the indoor air quality by means of increasing the ventilation rates. Pages 159-171. B. New York. An estimation of the energy saved by the combined system was carried out. ISBN 0-387-94550-4. Performance of porous ceramic evaporators for building cooling application. (2003). Comparative Study Of Two Different Evaporative Systems: An Indirect Evaporative Cooler And A Semi-Indirect Ceramic Evaporative Cooler. W. & Pruis.Experimental Analysis of a Combined Recovery System 287 Total Heat • Temperature is the most contributory factor. J..D. J. S. R. Herrero Martín.. Rey Martínez. . The characterization of the system was carried out by employing experimental design methodology. Energy and Buildings. Journal of Membrane Science. scholarship with the reference number: AP20033730 IME in order to carry out the Ph. Chapman & Hall. J. Energy and Buildings. work entitled: “Waste Energy Recovery using a combined system: SIECHP”. It is a new alternative device for use as a recovery system. F.. The configuration chosen (crossed flow) is the most adequate from an operational point of view. Ibrahim. M. C. Shao. 15 December.D. Principles of Heat Transfer in Porous Media. The contributions of the single factors and their interactions were presented by carrying out a variance analysis. R. The superiority of the evaporative cooling device under the operating conditions was clearly shown. CONCLUSIONS The combined system built allows a feasible energy exchange between the supply airstream and the return one. L. improving the operation in air-conditioning systems. This value is increased for the highest temperature differences between both airstreams (supply and return). 227. A factorial design was performed by analysing how the factors used affect the characteristics analyzed. 35. & Riffat. Johnson. (1999). J. E. 941-949. Evaporative Air Conditioning Handbook. Issues 1-2. New York. Kaviany.. ACKNOWLEDGMENTS This work was developed thanks to the support of the Spanish Ministry of Education and Science of Spain which awarded a Ph. Analysis of heat and mass transfer phenomena in hollow fiber membranes used for evaporative cooling. Velasco Gómez. Martínez Gutiérrez. E. Springer-Verlag. REFERENCES Watt. & Varela Diez. (2003). vol.. D. (1986). (2003). Yavuzturk. “Investigation of thermal performance of an air-to-air thermosyphon heat exchanger using ε-NTU method”. Energy Conversion and Management. G. Applied Thermal Engineering. W. B. vol. P.. J. B. The application of heat pipe heat exchanger in exhaust gas heat recovery system and its thermodynamic analysis. S. A. M. Vasiliev. (September 2003). Mech. vol. (1991). construction and testing of a thermosyphon heat exchanger for medium temperature heat recovery in bakeries” Heat Recovery Systems and CHP. ASHRAE Trans. (January 2005). H. vol. Nilsson. O. in: 8th International Heat Pipe Conference. C. Issue 4. “Numerical study of heat pipe application in heat recovery systems”Applied Thermal Engineering. vol. S. S. Pages 559-567 International Organization for Standardization. (1995). Söylemez. ISO Geneva. October 1998. (2005). Beijing. 28. J. & McGlen. (2003). (April 2006). in: 5th International Heat Pipe Symposium. Sauciuc. Larson. Applied Thermal Engineering 25. Herrero Martín Riffat. Y. R. 25. Abd El-Baky 1 & Mousa M. March. 111 (6) (1989) 72-75. Pages 1271-1282 Mostafa. 376-379. I. Guide to the expression of uncertainty in measurement:101. & Hendy. Pages 127-133 Noie. Issue 5. 1-19. E. (1996). Water Technol Mag. et al. (2004). (July 1995). A. Noie-Baghban. & Akbarzadeh. Riffat. L. 363-377. J. 11 (4). L. & Zhu. Issue 14. Minimizing Legionella concentration in cooling water systems. 20. Robert. Issues 5-6. R. L. Shao. V. Eng. S. et al. (1990) Predicting the performance of a heat pipe heat exchanger using the NTU method. P. Energy and Buildings. 582–585. S. . Heat pipe for hands. Issue 2. Australia. A. A.. Design construction and testing of a thermosyphon heat exchanger for medium temperature heat recovery. Broadbent. S. G.. Faghri. Mohamed. 15.. “On the thermoeconomical optimization of heat pipe heat exchanger HPHE for waste heat recovery”. Issue 15. R. Pages 457-470. Johnson. 795-801.Pages 481-491. Int. Dube.. China. (1 October 2000). vol. Pages 179-184 Lukitobudi. & Liu. L. Liu. 26. J. vol. Mathematical model of indirect evaporative cooler using porous ceramic and heat pipe Applied Thermal Engineering. “Waste heat recovery using heat pipe heat exchanger (HPHE) for surgery rooms in hospitals” Applied Thermal Engineering. Tan. G. & Gan. Melbourne. “Design. 27. J. L. “Heat pipe heat exchanger for heat recovery in air conditioning”. (2007). Applied Thermal Engineering. 97 (part 2).. H. “Heat pipes in modern heat exchangers”. 44. Issue 1. vol. & Majideian. D. Akbarzadeh. (1992). A. “Heat recovery with low pressure loss for natural ventilation”.288 R. Electricity use and efficiency in pumping and air handling system. Heat Fluid Fl. Pages 2509-2517 Lin. 24. All three technologies can be fed with basically every type of waste.it .In: Energy Recovery Editors: Edgard DuBois and Arthur Mercier ISBN: 978-1-60741-065-2 © 2009 Nova Science Publishers. the latter two produce syngas that can be burned after depuration to produce energy. A cost-benefit analysis is then carried out to plan how the whole industrial park can use the industrial waste to produce the energy it needs. We present the results of a research study that we are conducting on an Italian firm that produces polyethylene terephthalate (PET) supports for waterproof membranes from plastic bottles. Sara Bellini and Giovanna Matarrese Università della Basilicata. Too often in the past people have failed to take into account that the environment is not an inexhaustible resource and that its indiscriminate use ∗ silvana. and can produce electric and/or thermal energy. with economic and environmental benefits for all. Italy ABSTRACT In this chapter. Francesca Intini.kuhtz@unibas. Chapter 9 ENERGY RECOVERY SYSTEMS FROM INDUSTRIAL PLANT WASTE: PLANNING OF AN INDUSTRIAL PARK LOCATED IN THE SOUTH OF ITALY Silvana Kühtz∗. the waste represents only an undesired cost rather than a potential energy source. we compare environmental and technological aspects of some innovative energy recovery systems from industrial waste. Facoltà di Ingegneria DIFA – via Lazzazzera. We first compared a traditional thermal waste treatment with a molecular dissociator and then with a specific gasifier. In particular. Inc. 75100 Matera. For this firm (and all of the firms in the same industrial park). INTRODUCTION The gradual depletion of environmental resources is one of the most complex and pressing problems facing the world today. A STRATEGY FOR SUSTAINABLE MANAGEMENT OF INDUSTRIAL PARKS The environmental management of industrial parks was a new topic until some time ago. have been carried out through the creation of eco-industrial parks. is part of the methodological apparatus developed for an objective environmental assessment aimed at comparing alternative scenarios. The situation has evolved rapidly.1. In this chapter. combined with cost-benefit analysis.S. Eco-industrial parks (EIP). aiming to achieve shared goals of environmental and economic performance. Life cycle assessment. Francesca Intini. together with Asia and Europe. we are going to analyze various waste disposal methods by identifying their specific skills in the ecological exploitation of waste products and the respective plant/environment interactions. and which regards (like all of the firms in the same industrial park) industrial waste only as an undesired cost. The plans to set up a dense network of relations within an industrial park. Environmental Qualification of Industrial Parks The issue of the environmental qualification of industrial sites is relatively new. and it can be used as a decision support tool for the framing of industrial and environmental policies. by collaborating in dealing with environmental issues and resource use (including energy.290 Silvana Kühtz. In order to make our analysis more realistic. whereas it could represent an energy source. 1. These notions.. our comparative assessment of technological and management aspects of the various systems present in the waste to energy sector has referred to the results of a research study we have conducted on an Italian firm that produces polyethylene terephthalate (PETP) support membranes from plastic bottles. water and . has witnessed the spread of voluntary experimentations aimed at creating industrial areas equipped with tools for minimizing the impact on the environment [1]. are networks of manufacturing companies and service firms which are linked by a joint management and commit themselves to improving their own environmental. Sara Bellini and Giovanna Matarrese would have led sooner or later to a highly critical situation. even on an international level: it is only since the early 1990s that the U. and it has increasingly drawn the attention of public and private institutions which are becoming increasingly aware of the need to promote sustainable development. economic and social performances. as theorized by Lowe [2]. which take into account the complex relationships between the environmental variables. thanks to the introduction of regulations and directives concerning this sector. especially in terms of energy saving and of improving life and work conditions. are today topics of wide interest. that only a few years ago were considered too innovative and as potential obstacles to industrial development. Waste management in industrial parks is a particularly relevant issue for the purpose of minimizing the global impact on the environment and introducing an advanced model of industrial ecology. it is necessary to introduce innovative methods and tools of analysis. design and planning. To this purpose. 1. Figure 1. and economic performance in a region (see Figure 1). Some of the shared services may be: environmental management systems of a single production cycle. companies in industrial parks. energy. although there are various ways projects can overlap.Energy Recovery Systems from Industrial Plant Waste: Planning … 291 minerals). the strategic objectives of environmental performance pursued by the EIPs are: • • • efficient resource use environmental impact reduction management of interactions between the environment and surrounding communities. and social benefits as well as business excellence. when feasible. energy efficiency and business cooperation. recruitment of other businesses. 3. or water among companies. Eco-industrial network. and materials) rather than disposing of them as waste. The strategies to achieve such a goal require a new design or a revitalisation of infrastructures and of industrial park planning. By-product exchange (BPX) – a set of companies seeking to utilize each other’s byproducts (energy. One form of collaboration is to exchange by-product materials. logistics. Eco-industrial network (EIN) – a set of companies collaborating to improve their environmental. management of green areas. water. EIPs and EINs may include by-product exchange programs. cleaner production. EIN members collaborate to enhance their performance and to create shared services and facilities. 2. One or more EIPs may participate in either a BPX or an EIN [3]. protection from pollution. external promotion. This integrated approach pursues collective benefits that are greater than the sum of individual benefits that each company would obtain individually from the optimization of its own performances. etc. social. We distinguish three basic categories of eco-industrial projects: 1. Eco-industrial park or estate (EIP) – an industrial park developed and managed as a real estate development enterprise and seeking high environmental. An eco-industrial network may include stand-alone companies. by-products exchange. We believe these distinctions are important to maintain. . Hence. economic. and the park management organizations. 292 Silvana Kühtz. because at least the final products have to be released outside the system. This model brings about also the mutual dependence between the various parts of the system.2. characterised by symbiotic relationships and by the absence of the idea of waste: each waste product is put back into the system. In a dynamic balance. while all by-products should be constantly reused or recycled. Traditional industry. Figure 3. with the aim to reduce significantly resource use and pollution. An ecological system. Figure 2. in order to start a process essential to maintain a global balance. by contrast. Francesca Intini. a total cycle closure cannot be achieved at the level of eco-districts. which is the study of material and energy flows. Principles of Industrial Ecology Eco-Industrial Parks take up the principles developed by industrial ecology. energy and waste are constantly recycled and reused by other organisms and processes within the system. to produce energy or as a raw material. traditional industry follows a linear process: the consumption of energy and materials to produce goods and services generates a significant amount of waste (Figure 2). Sara Bellini and Giovanna Matarrese 1. Figure 4. . According to Allenby’s scheme [4]. Ecological system. Indeed it proposes to apply to industrial systems and to their transformationproduction cycles the same rules and principles governing the functioning of non-human biological systems that are the ecosystems. In a perfect closed-loop system. Such a system could operate in a sustainable manner only if the resources fed and the space to dispose of the waste are unlimited. Figure 3. Nevertheless. along with problems and advantages connected to it. Eco-industrial parks. only solar energy (or other renewable energy sources) should come from the outside. is characterised by the right combination between dynamic balance and closed loop. encounters a lot of difficulties in implementing preventive measures. Consequently. Industrial parks are important tools of economic and social qualification of an area but. along with its waste. and it requires business cooperation. emissions. also by means of associations. the main requirements for service sharing and for a successful industrial symbiosis are the following: • • • • complementary needs as far as material/energy are concerned. both vertical and horizontal. organised into chains and districts. water. There are therefore two possible approaches: 1. the Italian business sector. 1. importance of personal relationships between the various enterprises. Ecologically Equipped Industrial Areas The notion of industrial park as an eco-friendly place (as well as an area of economic and urban development) has evolved in time and has led Italy to the construction of the so-called Ecologically Equipped Industrial Areas (in the year 1998). 2. whose aims of efficiency and effectiveness in the use of materials and energy are the basis of business cooperation. they are potential sources of pressure on the environment and on surrounding communities. physical proximity in order to implement cascade systems of energy and water supply and to cut transport costs. the creation of symbiotic production processes with regard to material flow (energy. Joint environmental management. as it also takes into account the whole process.3. The Italian production system. presence of a homogeneous service demand in order to obtain economies of scale. at the same time. people. the planning of services and infrastructures within the industrial parks applying the principles of environmental sustainability and closed-loop natural cycles. heat. goods…). But as regards the environmental field. Figure 4. a collaboration between the various components of the industrial ecosystem through the exchange of energy and materials. above all. whose main feature is a high concentration of small and medium-sized enterprises. a limited amount of waste discharged from the system and. This model goes beyond the principle of “product stewardship”. due to a lack of culture in such issues. dialogue with local authorities and business participation in the process are key elements in the enhancement of a new territorial governance framing and supporting a sustainable environmental policy on industrial areas. is characterised by a great flexibility and by the tendency to networking.Energy Recovery Systems from Industrial Plant Waste: Planning … 293 Therefore the goal to be pursued is a limited use of inputs (virgin resources and materials). development and activities . waste. The Ecologically equipped industrial area may be regarded as a forum for environmental dialogue where all the stakeholders involved in its constitution. from an economic and technical point of view. each enterprise in the area achieve their environmental goals. Generation of Industrial Waste in Europe Manufacturing industry waste comprises many different waste streams arising from a wide range of industrial processes. it is possible to create economies of scale allowing the environmental issues to be settled with a reduction in cost. public authorities and local populations. In particular. The introduction of Ecologically Equipped Industrial Areas should not be viewed by stakeholders (enterprises.4. Waste from the manufacturing sector continues to rise. Sara Bellini and Giovanna Matarrese share their experiences. manufacturing products in such a way that they last longer and may be recycled or reused at the end-of-life stage. social and environmental point of view. 1. It has been estimated that over 33 million tonnes of industrial waste were generated in Europe in 1998. closely meeting businesses and citizens’ needs and becoming one of the most effective strategies toward growing territorial competitiveness from an economic. Some of the largest waste generating industrial sectors in Western and Central Europe include the production of basic metals. their resources and their goals and perform partnership actions aimed at complying with regulations but. Francesca Intini. local authorities) as an external constraint hindering economic development but rather as a tool for revitalizing the area and increasing the enterprises production system’s competitiveness. The aim of joint environmental management is to provide mutual benefits to industries. be they prescriptive or voluntary. Industrial parks as well may take part in this change process.294 Silvana Kühtz. food. The enterprise system is evolving and territories are being provided with policies and tools aimed at their strengthening. in broader terms. Manufacturers can achieve innovative solutions: • • • • considering the impacts of their products throughout its life at the design stage of the product (LCA). The manufacturing industry has a central role to play in the prevention and reduction of waste as the products that they manufacture today become the wastes of tomorrow. it is not meant just to supply industries with specific environmental equipment. provided with technical and organisational tools aiming to minimize and manage jointly the pressures on the environment. despite national and international declarations to reduce waste from manufacturing industry. responds to the need to replace the so-called end of pipe approach (combating pollution as a last stage of the process) with the precautionary principle preventing pollution. Through a joint management of shared infrastructures and services. but to organize the industrial site so as to help. eliminating or reducing where possible the use of substances or materials hazardous to health or the environment. beverage and tobacco products. using manufacturing processes that minimise material and energy usage. planned in concert with the resident group of enterprises. as it has been so far. at meeting the environmental needs and expectations of the resident industries and the local communities. The introduction of this new concept of industrial area. to introduce cleaner technologies and other waste minimisation initiatives and to work towards manufacturing practices that are sustainable in the long term. wood and wood products and paper and paper products [5]. . The objective is to decrease the amount of waste generated and to achieve a relative decoupling between economic growth and generation of waste. the use of resources. Therefore natural resources and wastes is one of four key environmental priorities described in the 6th European Action Programme. Manufacturing waste generation in Western Europe and Central Eastern Europe in Mtonnes.Energy Recovery Systems from Industrial Plant Waste: Planning … 295 EU and government policy across Europe is increasingly driven by the need to influence manufacturing practices in an effort to decrease the environmental impact of products during their manufacture. Figure 5 shows the amounts of manufacturing waste generated in nine Western European (WE) countries and seven Central and Eastern European (CEE) countries [6]. use and end-of-life. and the generation of waste. The gross value added by the manufacturing sector is steadily rising in the period (6%). The three countries are responsible for about half of the manufacturing waste generation in WE. Figure 5. Figure 6 depicts generation of manufacturing waste held against the gross value added in the manufacturing sector in the years 1996 to 2002 in the 13 European countries for which data are available. The EU Strategy for Sustainable development emphasises the strategic target to break the link between economic growth. but not as much as the generation of manufacturing waste (24%). Europe aims to reduce the final amount of waste by 20% by the year 2010 and by 50% by the year 2050. . From 1996 to 2002 the generation of waste in the manufacturing sector increased by 15% in WE (from 123 Mtonnes to 141 Mtonnes) and by 42% in CEE (from 60 Mtonnes to 86 Mtonnes). France and Spain are missing in the indicator. The few data available from the countries indicate a slight decrease in waste generation. Due to lack of proper time series data from the large countries UK. The European manufacturing sector is very diverse and the individual countries have had very different trends in the period analysed. . The growth at European level can mainly be explained by the massively rising waste amounts in the three countries Italy. e. Manufacturing waste generation in Europe compared to gross value in the manufacturing sector. 2. Theoretically. while seven countries have increasing amounts of manufacturing waste per capita. and establishing causal relations to driving forces are beyond the scope of the indicator framework. The above figure shows how important it is to also be aware of the trends inside the countries since this varies a lot and perhaps shows how the resource efficiency varies and changes within the countries.296 Silvana Kühtz. Figure 7 does not reveal the reasons for the observed trends and distributions. Figure 7 shows the national differences in manufacturing waste generation per capita as well as the temporal trends for 1996-2002 for a range of European countries. Netherlands and Poland. The manufacturing waste generation per capita is generally higher in the CEE countries (1000 kg per capita) than WE countries (ca. In nine countries a declining or steady trend can be observed. the reliance of a country on the manufacturing sector (measured. This means that overall objective of decoupling waste generation in Europe from economic development has failed as regards manufacturing waste. Francesca Intini.g. 700 kg per capita). Sara Bellini and Giovanna Matarrese Figure 6.. a given level of generation per capita could be explained by two factors: 1. as the share of the sector in the total economy). Finland has a very high manufacturing waste generation per capita. the resource efficiency of the manufacturing sector and the structure of the manufacturing sector. However. while most other countries have stagnating or even falling waste amounts. Thus gross value added is equal to net output. Figure 8 shows the manufacturing waste generated per gross value added1 in the manufacturing sector.org/wiki/Value_added) . Figure 8. (http://en. gross value added is obtained by deducting intermediate consumption from gross output. Trends in manufacturing waste generation per gross value added in the manufacturing sector.wikipedia. Trends in generation of manufacturing waste per capita. 1 In national accounts such as the United Nations System of National Accounts (UNSNA) or the NIPA’s.Energy Recovery Systems from Industrial Plant Waste: Planning … 297 Figure 7. in terms of the prevailing sectors and branches. 2. Although different wastes cause different environmental impact potential. The three of them aim to dispose of every kind of waste. Excessive quantities of waste result directly from a large industrial production and inefficient production processes. The complicated fluid-dynamic behaviour of multiphase systems is another factor of influence [7]. Different countries and industrial sectors are differently positioned in the process of optimising resource use. Sara Bellini and Giovanna Matarrese It can be seen that relatively small decoupling is seen in Belgium. like biomass. are gaining importance. Norway and Denmark have the lowest. Waste also represents a loss of resources both in the form of materials and energy. when analysing the thermo treatment processes with energy recovery from solid urban wastes and industrial wastes it is necessary to look for their environmental and energetic performances. The nature of fuels influences choices in the processes and systems. Combustion and gasification technologies of alternative fuels. due to the high variability of physicochemical parameters of the initial fuels. . Manufacturing waste is typically heterogeneous and with differentiated range of potential impact on the environment. Combustion and gasification processes of non-conventional solid fuels increasingly require the integration of different skills. fuels from wastes and from other types of industrial wastes. Francesca Intini. a molecular dissociator and a gasifier licensed in Italy. factory-level waste minimisation and the adoption of certification instruments. There is a falling tendency in five countries while the waste intensity is increasing in five other countries.298 Silvana Kühtz. The energy conversion technologies are increasingly constrained by environmental regulations on regional. quantities of manufacturing waste can be seen as an indicator of the material efficiency of the manufacturing sector. Romania. is an important factor for the amount and the kinds of waste generated. Indirectly it reflects low durability of goods and unsustainable consumption patterns leading to high demand for manufacturing products and thereby potentially high waste quantities. The three technologies analyzed in this chapter are: a waste to energy plant of the latest generation. Waste minimisation in manufacturing production processes is an increasingly important objective of manufacturing environmental strategies also in the framework of environmental certification. So it is necessary to move towards advanced technologies like gasification systems in combined cycles. The industrial structure. there is also a quantitative aspect as more waste means potentially higher pressure on the environment. Poland and Slovakia have the highest waste intensity while Iceland. THE MAIN FINAL THERMAL TREATMENTS OF WASTE The thermal treatment which takes out energy from waste includes also combustion and gasification processes. Indeed. So. Denmark and Germany while the waste intensity in the CEE countries (871 tonnes per million USD) are many times higher than the WE countries (129 tonnes per million USD). national and international level. some sectors being the source of large quantities of hazardous waste with high environmental impacts. at the same time producing electricity and/or thermal energy but in different ways and with different results. treatment of combustion rests: ashes. The incinerators produce two kinds of solid wastes: slags discharged by furnaces. But these smokes embed pollution elements. starting and combustion. . fluid bed and rotary drum. Waste to Energy Plant – System a Although the traditional waste to energy plant uses a more obsolete technology. smokes. It is difficult to manage them because they embed large quantities of toxic compounds. During combustion the smokes come out at a temperature of 1000°C. also called incinerators (waste burning plants) with energy recovery. Waste combustion phase is performed in furnaces and it involves three phases: drying. feeding.The primary purpose of waste to energy plants. slags. studying it helps to understand evolution and innovations in energy efficiency occurred in the last few years [8]. with a great advantage that is the production of electricity and thermal energy. Polluting gas control equipment can be performed by mixing smokes with chemical elements (solids. which toxic characteristics. generates steam which is used for energy production and for the heating [9].1.2. hydrogen to water (H2O) and sulphur to sulphur dioxide (SO2). waste waters. In order to meet various needs. liquids or gas) able to remove one or more polluting components.Energy Recovery Systems from Industrial Plant Waste: Planning … 299 2. It is possible to treat these smokes. hydrochloric acid and hydrofluoric acid. Another problem of wastes incineration is due to solid residual products and to their impact on the environment. is to burn waste (at 900°–1000°C) and make it biologically and chemically inert. such as the creation of nitrogen oxide (NO). 2. producing simple molecules in a gaseous state at standard temperature (gas): organic carbon is oxidized to carbon dioxide (CO2). Molecule Dissociation – System b The molecular dissociation process includes the thermo chemical conversion of a carboncomposite into a burning gas [10]. so it is necessary an intermediate phase of cooling in a combustion section and the extraction of heat from the smokes. The cycle of wastes combustion is divided into the following phases: • • • • • acceptance and storage. and fine particles (flying ash mixed to smoke) seized by smoke treatment. like heavy metals and organ chlorinated compounds easily released in the environment through percolation. by reducing its volume. Municipal waste incineration is a controlled combustion process which oxidizes the organic substances contained in waste. Also unpleasant chemical transformations take place. combustion. cooling of combustion smokes and warmth recovery. like active carbon. generally the inorganic part of the waste is not subject to reactions and becomes a solid waste to be disposed of and/or to be recovered (ash or slag). The heat produced by the combustion. Often the absorption process on solids are used. several kinds of furnaces have been introduced: moving grid. energy generation section: it is the final step where the syngas is used. gasification produces thermo chemical decomposition of waste’s organic matter and change this matter into syngas [11]. that can be listed according to their functions: • • • materials preparation section: this involves the storage building and machinery where wastes are treated and stored (raw materials for the plant) in order to make their size suitable for feeding the reactor where the gasification process takes place. where there are thermodynamic cycles. and it can be disposed of in a dump or used for tiles construction or mixed with asphalt. furthermore..3. Thanks to the technology licensed in Italy. a specific reactor has been designed (with new characteristics). by producing a synthesized gas (syngas) with good combustible characteristics. the process consists in a chemical splitting up of complex organic molecules into simpler ones through thermal gasification at low temperature (T = 400°–500°C) performed in controlled conditions of warmth and oxygen availability (max. gasification section: this is the technological heart of the system. Gasifier Licensed in Italy – System c A gasifier with a new technology was licensed in Italy. Thermal recovery . It is different from the traditional gasifier and the molecular dissociation thanks to the gasification reactor and to different conditions of management and control. Here. Nowadays the groups with endothermic/alternator engine are more used thanks to their high electric (about 38% compared to the fuel input) and global efficiency. After breakdown. like co-generator cycle. 2. These lances produce high turbulences which create an immediate gasification.e. with vertical development. The process is very slow and the whole cycle lasts 24 hours. Thermic lances fed by pure methane and oxygen characterize this process which grant high ecological and energetic results. wih all the wastes categories independently from their calorific value and chemical composition. 3–4% of O2) inside a locked cell. The remaining waste is composed of ash. descending flow and best temperature of process at 1200°C. carbon matrix changes from a solid condition into a gas one. Gasification is a chemical decomposition produced by thermal energy. These treatments are usually meant to transform the waste into waste fuels (dry and crushed municipal solid waste). inert and non toxic. carbon chemical links are broken and simpler molecules take origin. Francesca Intini. The systems can use several thermodynamic cycles. thanks to warmth effect during starting phases of fuel use (i. Without a surplus of air and oxygen. The waste is fed at the top of reactor and by falling down from top to bottom (as a fluid bed) is covered by flames come out from thermic lances which are tangentially in reactor.300 Silvana Kühtz. The system which produces the above-mentioned process involves a lot of sections. Another peculiarity of this reactor is that it can be fed continuously. Sara Bellini and Giovanna Matarrese Briefly. methane gas). the reduced turbulence and the flames absence lessen the powder presence in smokes. The synthetic gas after depuration stage can be burnt in the presence of air (T≈1100°C) in a following stage. consequently they are more flexible in regulation between heat and electricity production. performance. System b has a lower self-consumption (less than 2%) and it can treat any kind of waste without a pre-treatment. so it only triggers the reaction with a moderate electric resistance (200-300kW per 100 t/g of waste). and are completely inert. Its reactor has a variable thermic profile (optimum temperature at 1200°C). The solid wastes of gasification are transformed into glass. in system b is the cell and in system c is mono-tube reactor with vertical development. System c has a different mechanism. thanks to high temperatures. whereas system b (dissociator. The main body of system a is the furnace of combustion. This brings to total efficiency even higher than 80/90%. or 6–8 bar of pressure in case of steam production. described in paragraph 2. Despite the fact that the final product is the same. by using again combustion smokes to produce electric and/or thermal energy. and have a modular process. Furthermore. the working temperature. the procedures and the scheme for syngas production. in presence of oxygen at 4–5%. and it is burnt by flames generated by thermic lances which are fed with methane and oxygen. environmental impact. show how syngas brings higher . but with unavoidable economic consequences (262 m3/h of methane and 560 m3/hof oxygen per 3 t/h of input waste are necessary). system a does not present these advantages.4. Analysis results. The waste falls down in the reactor from top to bottom. Another important aspect is the very high chimney for system a compared to the chimney a few meters high for system b. so the raw material transformation is exothermic. independently from changes of waste calorific value. described in paragraph 2.1 and here called system a) reduces waste in ash. The temperature of the thermal energy recovery is about 80°C in case of water use. listed in Figure 9. This lets the process be controlled. both the gasification technologies dimensions fill a minimum space. the last two produce syngas. This comparison considers the following aspects: • • • structure-process. system a (waste to energy plant described on paragraph 2.3 and here called system c) transform (in different ways) the raw material into a synthetic gas used then as a fuel.Energy Recovery Systems from Industrial Plant Waste: Planning … 301 takes place during the cooling cycle (engine side. 2. System b works at about 400°C. there are a lot of differences between b and c systems: the main body of the system. The energetic results depend on the choice of the system for the production of electric and/or thermic energy. From the structural-processing point of view.2 and here called system b) and system c (gasifier. smoke side and oil engine side) of the machine. Comparison among Systems for Waste Disposal with Energy Recovery It is necessary to point out which is the most efficient technology from an environmental and an energetic point of view. Sara Bellini and Giovanna Matarrese efficiencies. For systems b and c it’s important to emphasize the conversion energetic efficiency. and low percentage of nitrogen and negligible sulphur compounds. Francesca Intini. Experimental data demonstrate that emissions to atmosphere generated by the combustion of the synthetised gas of system b and c are lower than emissions produced by system a. especially when it comes to sulphur. the smokes of system a present organic material deriving from uncompleted combustion or thermic synthesis reaction. system b produces very low percentages of inert ashes. Figure 10. Percentage composition of syngas. and also the percentage composition of syngas. from an environmental point of view. so they do not give rise to hazardous dioxins and furans.98 for the first and 0. about the 3– 4%. Energy efficiencies (expressed in percent) of system a and b. System c offers a cleaner gas compared to system b. Despite the sophisticated instruments for the reduction of smokes. nitrogen and chlorine compounds. Systems b and c generate syngas in good conditions. Moreover. (see Figure 10).302 Silvana Kühtz.68 for the latter. . with high concentrations of hydrogen and carbon monoxide. compared to 30% of toxic wastes produced by system a. Figure 9. that is 0. ozone depletion potential. 3. In other words the energetic resources management needs measures and means related to industrial systems eco-efficiency. It not only evaluates the impact on climate change. but also other impact categories such as acidification potential. transport systems. In order to achieve the established purposes in a transparent and comprehensible way. which emphasise environmental and socio-economic aspects in order to make the best choice. as well as many of the underlying materials.1. LCA calculations remain very complex [13]. on the purpose of decision process. Moreover. the actions to undertake and the analytical and procedural means to use [12]. energy recovery. by taking less natural resources and using them as efficiently as possible. The choice of the most appropriate instrument depends first of all on the object to be studied. the space and time context of the project. The main purpose of a sustainable development consists in granting a high quality level of life to all people. Nevertheless. etc. one can make use of extensive databases containing life cycle profiles of many goods and services. a unique method to establish the most appropriate instrument does not exist. energy. Anyway. Life Cycle Assessment and Cost Benefit Analysis (CBA) are the major instruments. The product system: an ensemble of processes linked by flows of matter. wastes. as those purposes determine the demands which to answer to. the relationship between industry and its local environment misses a main dimension of sustainable development: the environmental protection. materials. For each of these impact categories. water. eutrophication potential. the available information about environment impacts. and ground level ozone creation. that is the connection between products and pollution phenomena linked to them. A large number of instruments have been created as methodological aid for strategies and techniques of environmental management. The decision-taking processes in the environmental field depend on the purposes to be attained. . Life Cycle Assessment Life cycle assessment (LCA) is the broadest indicator and an internationally standardized method (ISO 14040 and ISO 14044). from the extraction of raw material and manufacturing. and on the doubts about costs and benefits. and ultimate waste disposal. The ISO standards provide robust and practice-proven requirements for performing transparent LCA calculations. natural resources). The environmental and economic assessment methods let the industries analyse the environmental matters considering not only the production but also the resources that is possible to re-use and save (energy. the product or system is evaluated over its complete life span. energy resources. therefore often multiple instruments with the same technical aids and the same information are used in an integrated way. ENVIRONMENTAL AND ECONOMIC ASSESSMENT METHODS In the industrial areas analysis. it is necessary to take into consideration and describe the following elements: • • The function unit: measurement of input and output flow of the product system.Energy Recovery Systems from Industrial Plant Waste: Planning … 303 3. to the use of the product by final consumers and end-of-life processes like recycling. medium values or values from literature and data bank. later on. The inventory analyse involves the construction of reality analogical model. which. High quality and reliability of data (data bank. the second step is data collection. temporal. Sara Bellini and Giovanna Matarrese • • The system’s borders: selection of productive processes and environments. Figure 11. regional. Inventory analysis. such as greenhouse gas effect or stratospheric ozone deletion. would be processed in order to take useful assessments for an improvement of processes analyse (see Figure 11). The results are estimated and associated under their effects on the environment. Consequently. such as mass. estimations. . Francesca Intini. The inventory aim is to get objective data. First of all the flow-chart including the product system’s processes is necessary [14]. Environmental effects can be on global. local scale: for example GHG effect has global effects. while a noise has local effects.304 Silvana Kühtz. economic values of the products. volume and energy. geographic and technological coverage). The environmental and energetic allocation could be carried out as: • • physical quantity. that is direct surveys. CBA is divided into three phases: 1. especially when they refer to support measures on territory. acidification. The positive effects could be: employment. wastes production.. human and environment toxicity. in case the proposal is only one. that should be lower than the benefits.e. decibel of produced noise.e. on an international level (i. stratospheric ozone deletion. 2. it verifies the project costs. etc. water availability for civil agricultural or industrial use. assessment of carbon footprint. identification of all positive and negative effects of the project. an improving intervention that moves a problem from the analysed area to another one. the creation of a green area or a system for waste water conditioning. The negative effects involve: water consumption. eutrophication. but it allows people to evaluate a service or a product in a total way.. . etc.). photochemical oxidant formation. In the last phase of LCA. to estimate the pro-capite environmental charge) and to carry out a weighing in order to get a single index of impact. the equivalent CO2 quantity). it chooses the best proposal. which consists in choosing the solutions to be applied to productive system and suitable to maximize the global environmental energetic efficiency. progress of environmental policy strategies. 3. that is the interpretation. it is necessary to make the data normal (i. while the other effects are expressed in their own measure units (jobs number. i. to propose better measures for a reduction of environmental charges.Energy Recovery Systems from Industrial Plant Waste: Planning … 305 Nowadays in life cycle analyses the main impact categories are: • • • • • • greenhouse effect. or.e. in order to improve the general social and economic welfare of the project context [15]. Life cycle assessment is used for more aims: processes’ improvement. the results of inventory analysis are correlated with those ones of impacts analysis. The costs and the benefits of a project are expressed in monetary terms. quantification of effects from the previous phase. The environmental impacts quantification is performed in the phase of distinction thanks to scientific models and correspondence’s factors. LCA application does not always guarantee a reduction of energy consumption or emissions. in order to avoid a wrong interpretation.2. greenhouse effect follows global warming potential. that is. Cost Benefit Analysis CBA CBA is one of the most popular method for investment assessment. products innovation under new standards of production. To synthesize the analysis and compare it with more productive systems. On a planning and organizing level it is very hard to reach a production improvement. It is important to include stakeholders in decisional process as they could be stimulated through offsetting measures. (d) intangible – of intangible quantification. it is important to give population a right information about benefits project. There are direct financial costs and benefits (expenses and revenues of project) and indirect economical ones (damages and benefits caused by project to other activities). and indirect. its maintenance and management. These lasting benefits are direct. and it involves more phases. (b) social – supported by community. but they have no influence on the market. furthermore. and suggest some ways to reduce them (external effects). CBA must pay attention to the beneficiary of project benefits. when they give advantages to receivers. benefits could be: (a) transitory – they can be carried out only during project realization. They are primary if they refer to projects’ costs that the community supports by renouncing other alternative projects. the less the decision-makers have the possibility to discuss faults. (b) lasting – linked to the entire life of the project. This firm is located in the south of Italy within a technological park that is managed by a company that provides services for the firms in the . The more the identification reaches a high and complete level of information. Sara Bellini and Giovanna Matarrese 3. when they are in favour of the community. including identification and assessment which are the most important. identification must show eventual project damages on environment. After realizing the project. 4. Francesca Intini. (c) concrete – they can be quantified. and to the supporters of direct and indirect costs. The identification phase requires a lot of time in order to avoid errors. as they are expensive and resources are very few. or secondary if they refer to external effects on people or things. And costs can be divided into: (a) monetary – supported directly by public administration and related to complete realization of project.306 Silvana Kühtz. When the best project is chosen an ongoing process is established. interpretation in monetary terms of all the effects measured in quantification phase. CASE STUDY The examined case study is an industry leader in the world for production of polyester nonwovens with high toughness by continuing thread and flake. as PET bottle after use. cultural and economic aspect of social groups. and to establish an active cooperation between population and public decision-maker (particularly regarding rural population). To let the changes in life and habits be accepted. social. The firm produces an industrial fabric that is a supporter for bituminous membranes destined to waterproofing of roads and roofs. Identification means to consider demographic. Industrial waste referred to in the considered firm are divided into two categories: • • waste products: these are not dumped. with advantageous conditions for the industries. some oils. but used again in the production cycle or sold for other purposes (polymer badge. felts. To summarize. water and ground) and production of waste. . Thanks to software. it treats the waste of the industrial activities of the industrial area. mechanical binding process (needlepunch technology). The obtained product is called flake. and data refer to their functional unit. In the following inventory analysis. and also sustains the territory industrialization by giving services and utilities similar to the most industrialized areas of the country. measure units are converted. thermo-fixture and longitudinal cut. paper. such as electric and thermal energy. technical gas (i. wastes of various origin (residues of the washing system. After extrusion. glass thread inclusion between the two films and further mechanical binding. melted selvedges. and also waste coming from activities of regional and extra-regional territories with specific authorization codes (EWC European Waste Catalogue). energy consumption. If the analysis is extended to the whole area where the firm is located. the melted polymer gives rise to a film. at the end bottles are centrifugated to set apart the water. all emissions (to air. and considers one year’s time for the system and the process. and consequent selvedge production.) For an economic-environmental assessment. and sent to a washing section. it is necessary to incorporate the system analysis with a cost/benefit analysis by emphasising emissions and energy savings. the analysis of life cycle defines the functional unit as 1 m2 of fixed and reinforced nonwoven. CO2eq. as shown in Figure 12. iron waste. the processes of all the productive activities have to be analysed in order to find the the best area for fuel coproduction. The industrial process of nonwovens production is divided into the following phases: • • • • • • bottle washing and flake production: from plastic bottles PET material is selected and sent to a washing centre and then to the mill to be reduced into little pieces. etc. Before the final discharge. SOX e PM10. it has been possible to assess the impacts on the environment (i. roll line starts). Furthermore. wood waste. water and electric energy. BOD and solids).. polyester drying-up and extrusion by forming threads set in a random way on a sucked carpet: flakes are heated until they become crystals. The firm in this case study is a partner of the manager company and purchases from it steam.e. then they are dried and extrapolated.e. data are collected. thermal consolidation and product incorporation in resins. The diagram in Figure 12 summarizes resources. it sends the wastes to the treatment plant [16][17]. steam overheated) and industrial water. nonmelted selvedges.. COD. CH4.Energy Recovery Systems from Industrial Plant Waste: Planning … 307 industrial area. 308 Silvana Kühtz. to study the draw-plate for waste treatment after production and their technologies. to find out the critical elements of the system. To carry out an energy system from wastes in an industrial park. to assess possible environmental effects in the neighbouring area (air quality. Flow diagram of nonwoven production. on waters. etc. it is necessary: • • • • • • • • to verify the area and examine the physicochemical characteristics of the wastes. . to make a hypothesis about the logistics of the waste collection. impacts on territory. on ground. to give the system dimensions. on noise.) to emphasize relief and reward measures of impacts. both environmental and social. Francesca Intini. to study the economic/financial feasibility and analyse the economic new effects in the industrial area. Sara Bellini and Giovanna Matarrese Figure 12. G. n. Chitone. Indicator fact sheet. E. L. European Topic Centre on Resource and Waste Management/EIONET. eco-tax and local duties must be introduced. Impianti di Termovalorizzazione. In the end.europa. 11/04/2008. E. The traditional industrial system is based on a unique direction: take-transform-dump Materials are taken from the earth’s crust. it is important to integrate the responsibilities of community.Cleaner Prod. A Report to Asian Development Bank. Lowe. R. destined to the disposal or waste to energy plant. in Italian.eionet. Eco-industrial Park Handbook for Asian Developing Countries. The economic and social system must know that the circular course of nature is the most efficient. This consideration involves rejecting the whole notion of waste. Generation of manufacturing waste. Lowe. it is necessary to introduce a Zero Waste strategy. (2001). (2006). To overcome the crisis of waste management. as otherwise transport costs. (1997). Ricerca e Futuro.. production. (2006). and several production systems stil require virgin products rather than recycled ones.. and to use energetic and economic benefits from waste use for energy purposes. and removal of resources are causes of environmental destruction and global heating. EEA European Environment Agency (2006). (2001). used to produce finished goods and waste. and Russo. Furthermore the disposal of wastes at a local level means a reduction of costs. Bologna: Delibera della Giunta Provinciale N. and moves the problem towards the starting point of an industrial eco-system [18]. Industrial waste. 1-2. Oakland. Available from: http://waste. Cammarata. (1992). Linee guida per la realizzazione di Aree Produttive Ecologicamente Attrezzate della Provincia di Bologna. moved to firm. transport.eu/waste. It is necessary to revise the unidirectional industrial system and form a closed circular one by recycling the resources dumped from community to industries. CONCLUSION Because of the continuing increase in population. 407 del 21 novembre 2006. Trattamento termico di rifiuti solidi industriali e civili con recupero di energia.Energy Recovery Systems from Industrial Plant Waste: Planning … 309 The main benefits of this system are to close the waste cycle at local level.CA: Indigo Development. the resources of our natural environment are limited: most of the materials we use to create products come from natural sources. V. Materials Research Bulletin. B. 5. less expensive and more profitable. industry and government in order to make a zero wastes strategy feasible. Environment Department. Allenby. and avoids the environment’s deterioration. Creating by-product resource exchanges: strategies for eco-industrial parks. and Stracchini. J. Dipartimento di Ingegneria Industriale e Meccanica-Sezione di Energetica Industriale ed Ambientale-Univerisità . Extraction. vol. G. in Italian. REFERENCES Corsari. pp 46-51. Number 20. Industrial Ecology: The Materials Scientist in an Environmentally Constrained World. 17 (3). Valutazione del ciclo di vita. (2008). SETAC Society of Environment Toxicology and Chemistry (1990).ecologiainformatica. in Italian. Rifiuti zero? Serve realismo. 48 (1). and Mastellone. principi e quadro di riferimento. and Bonanno. in Italian. L. Centrali di termovalorizzazione di rifiuti solidi urbani. Gestione Rifiuti. Private communication. Arena. BIODEC and EPPM AG (2008). Documento di Valutazione del rischio. Available from http://www. ISO 14040 (2006).310 Silvana Kühtz. Incerti. The Freudenberg Politex Srl (2006). L. Gasification System. Analisi del Ciclo di Vita (LCA): Metodologie di Valutazione Ambientale.com Breedveld. Il resto del carlino. Private communication. M. in Italian. Brisighella. Workshop report from Pensacola FL USA. L. The Freudenberg Politex Group (2007). CEN. U. The Waste Remedy. (2006). Francesca Intini. August 18-23. EN ISO 14040:2006. Tecniche di valutazione: Metodologie di Valutazione Ambientale [DVD]. 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A technical Framework for Life-Cycle Assessment. 26/01/2008. 303 air. 204. 7 amine. 8. 181 acetate. 37. 3. 29. 55. 21. 108. 100. 34. 298. 215 aerobic bacteria. 51. 119. 35. 19. 101. 19. 307. 54. 50. 45. 306 administrative. 207. 65. 43. 41. 49. 271. . 164. 114 alfalfa. 50. 44. 70. 20. 99. 106 aid. 52. 160. 20. 195. 62 agent. 189. 261 affect. 103. 172. 71. 100 agricultural residue. 196. 5. 49. 260. 24. 97. 36. 64 acetic acid. 253. 34. 126. 193 acidification. 112. 193. 7. 122 aluminium. 12. 280. 253. 59. 254. 114. 173. 120.INDEX A absorption. 19. 119. 24. 287. 209 activation. 287. 210 alcohols. 67. 60. 188 agroindustrial. 25. 3. 213. 31. 129. 1. 210. 103. 138 alkali. 136. 14. 192 acid. 61. x. 246 age. 110. 19. 124. 212 ammonium. 27. 209 acute. 30. 29. 37. 156. 60. 308 air emissions. 36. 112. 210. 60. 11. 24. 10. 257. 114. 203. 20. viii. 213. 13. 25 Amsterdam. 71. 122. 31. 13. 191. 103. 112. 242 Africa. 51. 287. 209. 177. 139. 98. 11. 41. 124. vii. 106. 192. 303. 25. 120. 45. 305 agricultural crop. 114. 15. 19. 100. 19. 113. 58. 120. 37. 220. 49 aerobic. 58 alcohol. 70. 110. 105. 119. 201 alkalinity. 112. 299 access. 206. 100. 71 anaerobic. 247. 134. 122. 217. 42. 191. 13. 63. 199 aldehydes. 35. 7. 259. 112. 106 agriculture. 119. 118. 175. 11. 300. 7. 116. 105. 254 administration. 123 adhesives. 202. 93. 25 activated carbon. 43. 193. 33. 199 alternatives. 211. 49 amendments. 61 alkanes. 9. 98. 30. 32. 114. 44. 111. x. 19. 105. xi. 12. 8. 56. 260 ambient air. 123 adiabatic. 43. 54. x. 205. 111. 4 air pollutants. 54. viii. 36. 8. 70. 254. 256. xi. 12. 32 air pollution. 299 acidic. 19. ix. 181. 106. 99. 27. 51. 70. 19. 26. 306 alternative energy. 31. 13. 107. 13. 9 additives. 288. 120. 228 anaerobes. 10. 101 alternative. 112. 50. 19. 46. 258. 8. vii. 60. x. 59. 34. 117. 117. 120. 120 agents. 257 agricultural. 60. 1. 21. 308 Alberta. 29. 31. 3. 25. 113. 215. 4 adsorption. 57. 139. 31. 246. 14. 24 aerosols. 100. 105. 201 alkaline earth metals. 29. 97. 199. 59. 112 amino. 106 algae. 210 alkaline. 112. 133. 106 amino acids. 106 ammonia. 219. 10. 253. 62. 124. 97. 236 accuracy. 4. 118. 123. 290. 22. 240. 11. 5. 103. 41. 115. 122. 35. 3. 32. 31. 217. 196. 255. 47. 305 acidity. 9. 37. 206 air quality. 110. 49. 44. 128. 33. 1. 21. 58. 312 Index 57, 58, 59, 60, 61, 65, 70, 71, 75, 76, 108, 110, 111, 116, 119, 129, 138, 187, 189, 190, 194, 203, 204, 205, 206, 207, 208, 209, 211, 213, 215, 222, 225, 226, 227 anaerobic bacteria, 8, 24, 71 anaerobic digesters, 203 anaerobic sludge, 29 analysis of variance, x, 253 animals, 36, 231 anomalous, 281 ANOVA, x, 253, 263, 264, 265, 266, 270, 274, 275, 279, 281, 282, 284, 285 anoxic, 194 anthracene, 199 anthropogenic, vii, 1, 2, 14 API, 173 application, viii, ix, 62, 69, 72, 76, 81, 82, 83, 88, 93, 94, 108, 110, 125, 128, 129, 130, 136, 142, 155, 165, 172, 175, 182, 185, 196, 203, 206, 208, 210, 214, 222, 227, 256, 258, 287, 288, 305 aqueous solution, 115 aquifers, 54 Arabia, 141 archaea, 203 argument, 183 arid, 105 Army, 72, 75, 94 Army Corps of Engineers, 94 ash, 29, 191, 192, 194, 195, 211, 217, 299, 300, 301 Asia, 290 Asian, 61, 309 Aspergillus niger, 139 asphalt, 300 assessment, 37, 103, 115, 122, 134, 136, 203, 211, 246, 249, 251, 290, 303, 305, 306, 307 assignment, 242 assumptions, 3, 15, 37, 77, 189, 222, 246, 248 ASTM, 61, 63, 76 atmosphere, vii, 1, 14, 23, 24, 26, 27, 47, 48, 86, 92, 93, 102, 118, 122, 199, 200, 205, 207, 230, 235, 254, 302 atmospheric pressure, 12, 27 attacks, 173 attention, 72, 230 attractiveness, 234 Australia, 288 Austria, 97, 134, 135, 238 availability, viii, 2, 19, 28, 71, 77, 85, 97, 98, 135, 137, 214, 246, 300, 305 avoidance, 185, 215 awareness, ix, 187, 214 B bacteria, vii, 1, 8, 14, 20, 21, 23, 24, 25, 28, 29, 30, 31, 37, 43, 44, 54, 55, 59, 71, 118, 203, 222 bacterial, 22, 36, 37, 53, 72, 75, 110, 203, 256 barrier, 31, 47 barriers, 7, 31, 47, 241 base case, 174, 175, 177, 180 batteries, 255 battery, 264, 267 behavior, 45, 63 behaviours, viii, 69, 73, 79, 285 Beijing, 136, 288 Belarus, 246 Belgium, 65, 135, 238, 249, 298 beneficial effect, 87 benefits, ix, xi, 7, 10, 40, 54, 90, 98, 100, 102, 119, 122, 124, 125, 129, 138, 160, 211, 227, 244, 289, 291, 294, 303, 305, 306, 309 benign, 199 benzene, 13, 15, 34, 35, 119, 124, 196 beverages, 41, 42 binding, 307 bioconversion, 137 biodegradability, viii, 15, 69, 77, 78, 87, 222 biodegradable, vii, viii, x, 2, 4, 5, 16, 21, 22, 46, 56, 60, 69, 70, 71, 72, 73, 77, 78, 79, 81, 101, 110, 213, 215, 222, 229, 236, 244 biodegradable wastes, 2, 16, 70 biodegradation, viii, 7, 8, 10, 16, 21, 23, 24, 25, 26, 28, 29, 30, 31, 43, 44, 45, 53, 56, 58, 60, 61, 62, 69, 72, 73, 77, 78, 79, 80, 81, 82, 83, 87, 90, 93, 203 biodiesel, 100, 101, 105, 111, 114, 134, 137, 138, 139 biodiversity, 103, 247 bioethanol, ix, 97, 99, 100, 101, 104, 107, 112, 115, 116, 118, 119, 120, 123, 125, 126, 130, 131, 132, 133 biofuel, 100, 101, 110, 112, 120, 121, 134, 232, 248 biofuels, ix, 97, 98, 99, 100, 101, 102, 103, 106, 107, 108, 109, 114, 115, 119, 120, 122, 123, 124, 125, 127, 128, 131, 133, 138 biogas, x, 8, 16, 43, 44, 55, 61, 66, 95, 100, 106, 108, 110, 111, 118, 119, 120, 134, 203, 204, 213, 215, 222, 223, 225, 236, 244 Biogas, v, 1, 62, 65, 95, 111, 136, 205 biological activity, 16, 28 biological processes, 2, 34, 65, 70, 222 biological systems, 292 biomass, ix, 43, 44, 45, 54, 97, 98, 99, 100, 101, 102, 103, 104, 106, 107, 108, 109, 110, 111, 112, 114, 115, 116, 118, 119, 122, 124, 127, 130, 131, 133, Index 134, 135, 136, 137, 138, 139, 188, 189, 191, 192, 193, 195, 196, 198, 199, 200, 203, 206, 207, 208, 209, 210, 211, 212, 227, 228, 233, 243, 244, 246, 248, 249 biomass growth, 45 biomaterials, 100 bioreactor, 2, 3, 7, 8, 9, 10, 11, 28, 29, 30, 54, 56, 57, 58, 59, 61, 63, 64, 94 Bioreactor, 6, 7, 8, 9, 10, 11, 65 bioreactors, 7, 10, 11, 29, 30, 53, 54, 56, 58, 59, 61, 62, 65, 94 biorefinery, ix, 97, 98, 99, 100, 101, 102, 103, 104, 106, 107, 108, 109, 110, 111, 115, 116, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 136, 137 biotechnology, 137 bisphenol, 123 body temperature, 77 boilers, 49, 50, 51, 53, 141, 185, 193, 231, 234, 242, 243 boiling, 180 bonds, 214 boreholes, 33, 58 bottleneck, 124 Brazil, 2, 95, 100 breakdown, 24, 36, 107, 110, 300 breathing, 35, 36 Brussels, 62, 65, 135, 249 buffer, 29, 30, 31 building blocks, 98 buildings, 36, 47, 230 Bulgaria, 238, 246 burn, 191, 235, 299 burning, 38, 50, 51, 110, 172, 206, 299 butyric, 19, 24 by-products, 55, 103, 172, 185, 291, 292 C cadmium, 194, 209 calcium, 21, 25, 196, 210 Canada, 1, 3, 54, 55, 58, 63, 65, 96, 135, 137, 187, 207 capital cost, 161, 165, 172, 184, 185, 206 caps, 46 carbohydrate, 192 carbohydrates, 19, 98, 103, 106 carbon, vii, 1, 3, 8, 11, 12, 13, 14, 19, 20, 24, 25, 33, 35, 37, 38, 39, 40, 41, 42, 43, 46, 49, 50, 51, 52, 53, 54, 55, 64, 66, 70, 71, 72, 77, 81, 86, 99, 102, 103, 104, 122, 126, 130, 139, 172, 193, 196, 197, 203, 206, 209, 211, 214, 219, 221, 226, 227, 232, 240, 242, 247, 299, 300, 302, 305 313 Carbon, 6, 12, 13, 14, 34, 35, 41, 66, 67, 71, 209, 216, 217, 242, 251 carbon dioxide, vii, 1, 3, 8, 11, 12, 13, 14, 19, 20, 24, 25, 33, 35, 37, 38, 43, 46, 49, 51, 52, 53, 54, 70, 71, 72, 77, 81, 86, 103, 172, 196, 197, 203, 232, 240, 242, 247, 299 carbon fixation, 122 carbon monoxide, 14, 50, 51, 70, 193, 196, 302 carbonization, 189 carboxyl, 113 carboxylic, 19, 119 carboxylic acids, 19 cardboard, 41, 42, 60, 78, 87, 88, 89, 216, 223 case study, 3, 95, 99, 115, 122, 134, 252, 306, 307 catalyst, 100, 112, 117, 196, 197, 199, 201, 210 category d, 240 cavities, 32 C-C, 192 CEE, 237, 240, 295, 296, 298 cell, 3, 15, 28, 30, 31, 45, 50, 52, 54, 56, 57, 58, 59, 60, 63, 71, 105, 135, 195, 300, 301 cell growth, 15 cellulose, 15, 22, 99, 100, 102, 103, 106, 107, 111, 112, 113, 117, 118, 130, 135, 192, 193, 209, 210, 212 Cellulose, 106, 107, 109, 210 cellulosic, 101 cement, 47, 60, 108 Central Europe, 294 ceramic, x, 253, 257, 287, 288 CERCLA, 4, 6, 66 cereals, 106 certificate, 242, 244, 248, 251 certification, 298 CH3COOH, 71 CH4, vii, viii, 1, 2, 3, 8, 13, 15, 16, 21, 37, 39, 41, 42, 53, 66, 70, 79, 81, 110, 111, 112, 118, 119, 126, 127, 128, 129, 192, 193, 195, 221, 223, 307 chain molecules, 214 charcoal, 101, 110, 192, 196 chemical composition, 42, 43, 77, 78, 300 chemical industry, 119 chemical oxidation, 190 chemical properties, 16, 102, 109, 124 chemical reactions, 16, 23, 26, 52, 53, 105, 111, 114, 130, 134, 207, 214 chemical structures, 103, 123 chemicals, ix, 11, 32, 34, 50, 97, 98, 99, 101, 102, 106, 107, 108, 110, 111, 112, 116, 119, 123, 124, 125, 131, 133, 136, 193 China, 136, 288 chloride, 13, 15, 19, 37, 118, 209 Chloride, 25 314 Index chlorinated hydrocarbons, 32 chlorine, 302 CHP, 128, 130, 160, 175, 233, 236, 237, 240, 241, 242, 243, 244, 247, 248, 249, 288 chromatography, 33 chromium, 209 Cincinnati, 209 circulation, 20, 54, 57, 173 citizens, 294 classes, ix, 20, 97, 102 classical, 255 classification, 246 clay, 23, 27, 47 Clean Air Act, 2, 3, 66 Clean Development Mechanism, 40, 66 Clean Water Act, 2, 3, 66 cleaning, 100, 112, 183, 184, 194, 206, 229, 231 cleanup, 51, 196 cleavage, 210 climate change, 247, 303 closed-loop, 292, 293 closure, 3, 4, 11, 13, 28, 33, 37, 39, 40, 70, 75, 92, 93, 292 clusters, 102 Co, 135, 138, 139, 199 CO2, vii, 1, 8, 13, 15, 16, 24, 25, 39, 66, 70, 79, 81, 86, 92, 93, 98, 102, 110, 111, 112, 116, 117, 118, 119, 120, 122, 126, 127, 128, 130, 131, 132, 133, 138, 172, 175, 192, 193, 195, 218, 220, 221, 222, 223, 224, 226, 227, 254, 299, 305 coal, 101, 129, 195, 198, 210, 236 coatings, 100 cobalt, 25 codes, 307 collaboration, 291, 293 collateral, 53 Colorado, 138 Columbia, 59 combustion, vii, x, 38, 47, 49, 50, 51, 52, 53, 70, 86, 92, 93, 101, 102, 110, 116, 118, 119, 121, 122, 127, 128, 130, 133, 135, 138, 172, 173, 188, 190, 192, 195, 202, 213, 214, 216, 217, 218, 219, 220, 224, 225, 226, 231, 235, 298, 299, 301, 302 combustion chamber, 217 combustion characteristics, 135 combustion processes, 172, 173 commodity, 114, 119, 126 common rule, 249 communication, 234, 310 communities, 36, 291, 293, 294 community, 36, 54, 98, 159, 306, 309 community support, 306 compaction, 19, 22, 26, 28, 30, 31, 32, 71, 72 competition, 25, 100, 105, 234, 241, 246 competitiveness, 294 compilation, 115 complex systems, 245 complexity, 3, 37, 93 compliance, 3, 4, 5 components, 12, 14, 17, 21, 22, 27, 32, 33, 51, 53, 55, 62, 65, 71, 72, 73, 79, 80, 81, 82, 83, 99, 100, 101, 102, 106, 108, 109, 111, 112, 124, 126, 192, 193, 196, 197, 245, 293, 299 composition, x, 3, 12, 14, 15, 16, 19, 20, 21, 22, 38, 39, 41, 42, 43, 44, 50, 53, 55, 57, 70, 71, 72, 77, 78, 79, 81, 87, 88, 89, 102, 103, 106, 108, 109, 111, 114, 116, 194, 209, 213, 214, 215, 216, 217, 218, 220, 222, 223, 240, 300, 302 compost, 54, 55, 59, 60 composting, 30, 31, 57, 60, 63, 231, 236 compounds, 13, 14, 16, 19, 25, 26, 49, 51, 64, 71, 72, 77, 100, 102, 103, 108, 110, 111, 112, 114, 115, 117, 119, 191, 196, 206, 212, 214, 219, 220, 221, 299, 302 Comprehensive Environmental Response, Compensation, and Liability Act, 4, 66 concentration, 13, 14, 16, 19, 20, 21, 24, 26, 29, 30, 31, 32, 33, 34, 35, 36, 38, 41, 44, 45, 47, 49, 89, 101, 160, 193, 199, 200, 204, 288, 293 concrete, 123, 165, 306 condensation, 32, 47, 256, 281 conditioning, vii, x, 52, 253, 254, 258, 287, 288, 305 confidence, 231 configuration, viii, xi, 58, 69, 84, 86, 93, 182, 196, 253, 255, 257, 260, 287 conflict, x, 229, 234, 235, 241, 243, 244, 247, 248 Congress, 228 Connecticut, 36 conservation, 87, 103, 172 consolidation, 307 constraints, 30, 85, 152, 153, 165, 167, 174 construction, 10, 27, 32, 42, 55, 60, 65, 91, 155, 188, 248, 288, 293, 300, 304 construction materials, 60 consumers, 241, 242, 243, 303 consumption, viii, ix, 97, 98, 103, 116, 118, 119, 122, 125, 134, 142, 157, 158, 172, 174, 175, 177, 183, 189, 192, 194, 198, 203, 217, 218, 225, 244, 247, 292, 297, 298, 301, 305, 307 consumption patterns, 298 contaminant, 63, 196 contaminants, 49, 51, 112 contamination, 2, 7, 53, 54, 60, 255, 257 context, 247 continuity, 285 315 Index control, vii, 2, 3, 4, 5, 6, 7, 10, 28, 29, 30, 33, 37, 46, 47, 51, 54, 55, 62, 63, 64, 141, 165, 189, 191, 193, 195, 210, 249, 260, 299, 300 convection, 260 convective, 279 conversion, viii, ix, 7, 8, 13, 20, 24, 25, 51, 52, 53, 70, 71, 84, 85, 86, 87, 91, 92, 93, 94, 97, 98, 99, 101, 102, 103, 104, 106, 108, 110, 111, 112, 115, 116, 118, 120, 124, 126, 130, 133, 135, 137, 139, 160, 192, 195, 196, 199, 201, 209, 221, 223, 224, 242, 243, 244, 298, 299, 302 conversion rate, 7, 199 cooling, xi, 59, 147, 148, 151, 152, 153, 156, 157, 159, 163, 164, 165, 167, 172, 173, 175, 177, 181, 182, 219, 249, 253, 254, 255, 256, 257, 258, 262, 266, 267, 270, 271, 275, 279, 281, 285, 286, 287, 288, 299, 301 Copenhagen, 63, 64, 136, 137, 250 copper, 25, 209, 234 corn, 98, 99, 100, 103, 104, 109 correction factors, 40, 41 correlation, 42, 237, 239, 245, 247 correlation analysis, 42 corridors, 46 corrosion, 158, 233, 257 corrosive, 49, 51, 114, 193, 199 cost-benefit analysis, xi, 289, 290 cost-effective, 208 costs, 3, 11, 28, 49, 85, 86, 90, 91, 92, 153, 161, 188, 206, 214, 233, 235, 236, 241, 243, 247, 248, 254, 256, 293, 303, 305, 306, 309 Council of Ministers, 137 coupling, 227 covering, 5, 21, 23, 40, 46, 67, 92 Cp, 192 CPC, 164 cracking, 193, 196 CRC, 134, 211 critical temperature, 196 Croatia, 250 crop production, 246 crops, 99, 100, 101, 104, 105, 106, 108, 124, 139 cross-border, 241 crude oil, 101, 102, 111, 173, 183, 185, 199 crust, 309 crystals, 307 cultivation, 98, 118 culture, 293 customers, 133 cycles, 103, 221, 267, 292, 293, 298, 300 cycling, 53 Cyprus, 238, 246 Czech Republic, 191, 238, 240 D dairy, 108 danger, 27 Darcy, 26 data collection, 304 database, 116, 125 death, 35, 36, 44 decay, viii, 3, 37, 39, 59, 69, 72, 75, 76 decibel, 305 decision makers, 175, 185 decision making, 230 decision support tool, x, 229, 230, 245, 290 decisions, x, 229, 230, 245, 248 decomposition, vii, 1, 2, 3, 7, 10, 11, 12, 13, 14, 16, 17, 19, 21, 23, 30, 31, 36, 37, 38, 39, 41, 42, 54, 56, 58, 61, 67, 70, 76, 103, 192, 196, 203, 209, 210, 212, 300 decoupling, 295, 296, 298 deficiency, 151, 152 deficit, 175, 234 definition, viii, 69, 84, 99, 101, 115, 116, 156, 189, 235, 246 degradation, 8, 10, 11, 15, 16, 17, 18, 19, 20, 22, 24, 25, 28, 29, 30, 32, 41, 43, 45, 55, 56, 58, 60, 61, 63, 64, 65, 66, 72, 73, 77, 79, 90, 95, 96, 103, 192, 203, 222 degradation pathway, 22 degradation rate, 79 degrees of freedom, 153 dehydration, 192, 199 delivery, 8, 116, 129, 133 demand, 230, 244, 245, 246, 249 denitrification, 63, 103 Denmark, 136, 238, 240, 250, 298 density, 8, 11, 12, 22, 24, 31, 57, 90, 111, 196, 202 density values, 24 Department of Energy, 11, 22, 65, 135, 251 depolymerization, 114, 199, 210 deposition, 20, 22, 206 depreciation, 85, 86, 91 depression, 36 derivatives, 19, 20, 98, 103 designers, 161, 182 destruction, 10, 49, 51, 172, 196, 206, 208, 210, 238, 240, 248, 254, 309 detergents, 100 developed countries, 21 developing countries, 2 devolatilization, 191 dew, 42 diesel, 101, 102, 114, 141 diesel engines, 141 316 Index diesel fuel, 102, 114 differentiation, 241 diffusion, 23, 26, 31, 32, 47, 231, 256, 279 diffusivity, 196, 202 digestion, vii, x, 108, 110, 111, 116, 118, 119, 129, 138, 187, 189, 190, 194, 203, 204, 206, 207, 208, 209, 211, 213, 215, 222, 223, 225, 226, 227, 236 dioxin, 50, 51, 240 dioxins, 50, 231, 302 directives, 235, 248, 290 discharges, 4 Discovery, 207 dispersion, 261 dissociation, 299, 300 distillation, ix, 111, 118, 141, 142, 180, 181, 182, 185 distribution, 23, 30, 31, 45, 71, 73, 120, 122, 128, 139, 260 district heating, x, 229, 230, 231, 232, 233, 235, 236, 245, 246, 247, 250, 251 division, 167 dizziness, 36 draft, 100 drainage, 27 dry ice, 51 dry matter, 118, 119 drying, 191, 192, 193, 194, 196, 198, 206, 259, 299, 307 DSM, 252 dumping, 2, 40, 53 durability, 298 duration, 8, 36, 71, 77 duties, 156, 161, 165, 171, 177, 180, 309 dyes, 100 E earnings, 85, 86 ears, 91 earth, 196, 309 Eastern Europe, 237, 295 ecological, 72, 103, 137, 290, 292, 300 Ecological models, 72 ecology, 290, 292 economic development, 294, 296 economic growth, 295 economic performance, 136, 290, 291 economic welfare, 305 economics, 137, 188, 209 economies of scale, 293, 294 ecosystem, 96, 293 ecosystems, 292 Education, 1 EEA, 309 effluent, 6, 202, 204, 212 egg, 36 Egypt, 1, 185 elaboration, 161 electric energy, viii, 69, 70, 84, 85, 86, 91, 92, 93, 220, 307 electric power, 110 electricity, vii, ix, x, 3, 50, 51, 52, 91, 92, 97, 99, 100, 101, 102, 108, 111, 115, 116, 118, 119, 120, 121, 123, 126, 129, 130, 131, 133, 160, 175, 193, 205, 207, 222, 229, 230, 231, 233, 235, 236, 237, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 298, 299, 300 electrolysis, 112, 116, 118, 119, 120, 124, 129, 138 e-mail, 97 emission, viii, ix, 3, 5, 32, 33, 37, 38, 42, 54, 55, 60, 70, 81, 86, 92, 93, 94, 119, 126, 127, 128, 129, 131, 133, 142, 195, 224, 227, 235, 236, 242, 249 employment, 247, 305 endothermic, 191, 192, 195, 300 energy consumption, ix, 98, 116, 118, 122, 125, 142, 174, 175, 177, 183, 189, 192, 194, 198, 224, 305, 307 energy density, 110 energy efficiency, 93, 118, 130, 172, 173, 185, 189, 190, 194, 201, 205, 207, 235, 243, 245, 254, 291, 299 Energy Efficiency and Renewable Energy, 135 energy recovery, vii, viii, ix, x, xi, 1, 3, 11, 37, 46, 48, 51, 52, 53, 54, 55, 69, 70, 84, 85, 86, 87, 89, 91, 93, 94, 95, 159, 173, 185, 187, 188, 189, 190, 191, 193, 200, 203, 206, 207, 210, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 232, 235, 236, 237, 239, 240, 250, 251, 253, 259, 260, 271, 289, 298, 299, 303 energy supply, 130, 133, 246, 247, 248 engines, viii, x, 49, 50, 51, 69, 84, 85, 86, 91, 92, 93, 141, 213, 215 England, 135 enterprise, 291, 294 Enthalpy, 143, 144, 145, 155 entropy, 158 environment, vii, 2, 3, 4, 7, 20, 29, 32, 33, 34, 35, 36, 46, 76, 110, 115, 172, 173, 196, 208, 231, 250, 256, 289, 290, 291, 293, 294, 298, 299, 303, 304, 305, 306, 307, 309 environmental awareness, ix, 187 environmental conditions, 25 environmental effects, 247, 308 environmental factors, 16 317 Index environmental impact, viii, 62, 64, 70, 93, 94, 103, 115, 122, 124, 125, 133, 173, 174, 237, 245, 246, 291, 295, 298, 301, 305 environmental influences, 64 environmental issues, 290, 294 environmental policy, 293, 305 environmental protection, 254, 303 Environmental Protection Agency, 3, 5, 37, 66, 244, 252 environmental regulations, 2, 3, 188, 298 environmental resources, 289 environmental standards, ix, 187 environmental sustainability, 293 enzymatic, 107 enzymes, 23, 110, 111 EPA, 2, 5, 8, 9, 10, 13, 38, 42, 50, 51, 63, 66, 72, 76, 79, 94, 95, 209 epoxy, 123, 126, 133 epoxy resins, 123, 126, 133 equilibrium, 16 equipment, 91, 231 EST, 251 esters, 111, 114, 119 estimating, viii, 2, 3, 15, 24, 37, 69, 76, 86, 93, 125, 259 Estonia, 238 ethane, 13, 14, 23, 34, 203 ethanol, 101, 102, 103, 110, 112, 113, 118, 134, 137, 139, 212 Ethanol, 130, 136, 137 Europe, 2, 56, 100, 139, 188, 191, 234, 236, 241, 244, 249, 290, 294, 295, 296 European Commission, 235, 236, 241, 249 European Community, 249 European Environment Agency, 309 European Parliament, 249 European Union, x, 66, 210, 229, 230, 233, 235, 236, 240, 241, 243, 244, 247, 249 Eurostat, 238, 249 eutrophication, 246, 303, 305 evaporation, 13, 103, 120, 192, 194, 205, 207, 254, 256, 259, 281 evolution, 72, 256, 299 exchange rate, 232 exercise, 175 experimental design, xi, 253, 254, 262, 287 exploitation, viii, 85, 97, 100, 103, 290 explosions, 34 exports, 246, 247 exposure, 12, 32, 36, 64 external costs, 247 external environment, 214 extraction, 2, 23, 26, 32, 47, 55, 56, 58, 111, 208, 299, 303 extrusion, 307 F fabric, 47, 306 factorial, xi, 253, 262, 287 failure, 7 family, 70, 106, 136 FAO, 135 farms, 108 fast food, 105 fat, 100, 244 fatigue, 35 fats, 98, 103, 105, 106, 134 fatty acid, 105, 111, 113, 114 faults, 306 fax, 97, 229 February, 135, 249 fee, 5, 243 feeding, 60, 189, 215, 299, 300 feedstock, ix, 54, 60, 97, 98, 100, 101, 103, 104, 106, 107, 108, 109, 110, 111, 114, 115, 116, 117, 119, 122, 124, 126, 128, 129, 130, 133, 135, 137, 189, 192, 194, 196, 197, 198, 199, 206 fees, 241, 243 feet, 11 fermentation, 19, 20, 43, 64, 71, 103, 107, 110, 112, 116, 118, 131, 133, 139 ferrous metal, 60 ferrous metals, 60 fertility, 98 fertilizer, 116, 203, 229, 236 fertilizers, 101, 119 fiber, 103, 287 fiber membranes, 287 fibers, 106 fillers, 100 film, 285, 307 filters, 53 filtration, 49 financial support, 248 financing, 234 Finland, 238, 240, 296 fire, 3, 47, 50, 195 fires, 231 firms, xi, 289, 290, 306 first generation, 98 fixation, 103, 122 flame, 33, 38, 49, 50, 158 flame ionization detector, 33 flare, 49, 50, 51, 52, 70, 91, 173 105. 25. 105. 221. 87. 290. 41. 198. 226. viii. 37. 298. 142. 183. 65. 205. 108. 246 gasification. 303 governance. 132. 100. 203. 110. 114. 211. 225. 196. 84. 301. 224. 198. 125. 98. 295 free radicals. 21. 135 garbage. 14. 304 flow rate. 50. 45. 147. 14 gas chromatograph. 112. 298 GHG. 59. 42. 261. 236. 244. 112. 126. 123. 295. 64. 102. 39. 240. 116. 204. viii. 120. 300. 108. 240. 258. 122. 118. 236. 47. 245. 40. 207. 193. 191. ix. 12. 240. 240. 296. 57. 50. 243. 43. 100. 184. 133. 67. 49. 220. 292. 300. 260. 97. 119. 172. 223. 299. 206. 127. 141. 243. 241. 116. 246. 138. 115. 95. 191. 135. 232. 119. 133. 298. 58. 209. 106. 84. 238. 107. 42. 27. 199. 236. 119. 20. viii. 232. 101. 110. 26 Georgia. 98. 301 gasifier. 250 gaseous waste. 98. 128. 27. 104. 173. 99. 51. 11. 57. 173. 209. 191. 125. 129. 293 France. 264. 236. 215. 254. 123. 158. 120. 103. 100. 126. 60. 130. 287. 191. 217. 50. 106. 191. 216. 24. 247. 225. 190. 304 glass. 212. 114 glycerine. 298. 66 geothermal. 100. 120. 126. 59. 264 flue gas. 195. 118. 133. 119. 185. 101. 244. 160. 195. 27. ix. 94. 128. 195 fugitive. 256. 46. 119. 180. 172. 157. 159. 87. 224. 307 fuel cell. 189. 97. 38. 60 flow. 187. 300 Geneva. 75. 22. 131. 102 gases. 124. 300 fluidized bed. 79. 112 fossil. 173. 108. 263. 295 GPS. 181. 219. 191. 230. 114 framing. 244. 232. 244 food production. 194. 35. 244. 77. 190. vii. 14. 138. 45. 54. 104. 128. 70. 199. 7. 154. 193. 111. 116. 237. 42. 242. 101. 3. 227. 100. 129. 148. 110. 300. 115 fuel. 127. 198. 76. 24 flora. 290. 208. 196 fractionation. 123. 123. 173 fragmentation. 67. 301. 153. 123. 110. 141. 129. 62. 52. 16. 300. 141. 106 formaldehyde. 119. 242. 122. 98. 244 Germany. 206 free trade. 135. 46. 160. 242. 49. 213. 99. 231. 94.318 Index flexibility. 120. 101. 177. 111 glycerol. 110. 122. 214. 32. 142. 105. 210. 134. 101. 197. 217. 49. 185. 117. 97. vii. 221. 197. 60. 53. 157. 248. 108. 210. 48. 122. 307 global warming. 182. 138. 60. 259. 119. 158. 102. 47. 185 gas turbine. 305 Global Warming. 208. 133 furnaces. 221. 248. 52. 117. 156. 102. 136. 72 forestry. 104. 126 furan. 196. 251. 126. 233. 247. 97. 246 forecasting. 67. vii. 220. 114. 1. ix. 26 . 196. xi. 105. x. 191. 134. 3. 130. 10. 117. 191. 264 fructose. 45. 215. 110 glycol. 195. 201. 134. 218. 172. 195. 293. 70. 111. 293 flood. 115. 23. 110. 130. viii. 122. 121. 42. 101. 218. 39. 51. 21. 23. 125. 112 goals. 195. 2. 212 glycerin. 57. 240. 229. 109 glucose. 294 food industry. 247 fossil fuel. 194 gas separation. 141. 201. 54. 217. 97. 135. 113. 172. 131. 297. 138. 47. 189. 191. 232. 87. 299 G G8. 199. 14. 33. 57 grain. 22. 103. 293 government. 38. viii. 43. 33 gas phase. 309 government budget. 211. 156. 243. 237. 183. 216. 85. 41. 24. 220. 80. 29. 102. 98. 102. ix. 174. 301 gasoline. 63 food. 192. 103 fruits. 192. 223. 258. 175. 137. 26. 294 goods and services. 108. 102. 253. 242 government policy. 173. 124. 212. 138. 203. 202. 176 generation. 123. 70. 295. 246. 99. 227. 36. 238. 172. 59. 67. 198 flushing. 260. 247 fossil fuels. 236 freedom. 111. 175. 97. 139. 160. 214. 110. 235. ix. 2. 222. 172. 126 Glucan. 76 flotation. x. 85. 193. ix. 132. 173. 243. 289. 231 fluid. 303. 37. 52. 218. 78. vii. 195. 225. 240. 244. 288 geology. xi. 21. 11 fumaric. 133 GCC. 116. 97. vii. 203. 241. 243. 53. 244 fouling. 241. 52. 224. 136. 156. 63. 235. 67. 197. 222. 117. 44. 26. 49. 34 Geomembranes. 97. 71. 231. 298. 114. 1. 141. 156. 31. 167. 88. 26. v. 180. 133. 266. 162. 36. 43. 28. 35. ix. 94. 199. 95. 54. 162. 163. 159. 53. 126 hospital. 305 Greenhouse. 45. 135 greenhouse gas. 128. 8. 243 House. 195. 266. 59 hemicellulose. 203. 214. 238 greenhouse. 279. 254. 112. 200. 231 hazardous wastes. 257. 111. 116. 169. 200 height. 133. 25. 12. 95. 123. 298 heuristic. 288 hands. 160 heat loss. 25. 14. 121. 137. 192. 199. x. viii. 195. 202. 1. 206. 97. 134. 281 Hungary. 180. 247. 111. 302 . 125 greenhouse gases. 214. 46. 193. 32. 93. 196. 123. 233. 7. 123. 205. vii. 299 heavy oil. 4 guidelines. 110. 199. 249. 49. 267. 168. 51. 147. 126. 235. 194 Greece. 44. 101. 152. 172. 117. 285. 168. 126 human. 165. 251. 246 groundwater. 44. 196. 258 hospitals. 167 hexachlorobenzene. 212. 33. 164. 250. 300. 97. ix. 249. 193. 131 hemicellulose hydrolysis. 101. 167. 124. 170 H2. 26. 36. 142. 192 heavy metals. 193. 173. 231. 116. 90 hot water. 171. 196. 15. 185. 99. 245. 102. 157. 185. 106. 255. 24. 102. 134 holistic approach. 249 heat transfer. 70. 299. 110. 195. 194. 36 heat capacity. 123. 8. 92. 54. 153. 193. 160. 112. 184. 157. 92 groups. 1. 214 hydrochloric acid. 125. 153. 144. 45. 13. 205. 19. 246. 305 humanity. 173 high temperature. 115 grassroots. 130. 54 grouping. 214 hydrocarbons. 242. 271. 51. 107. 299. 212. 262. 143. 185 gravity. 25. 134. 180. 194. 114. 106 herbicide. 156. 43. vii. 101. 300 heartbeat. 198. 192 Heat Exchangers. 36 heart. 37. 121. 33. 25.Index grains. 115. 70. 258. 13. 301 hips. 136. 163. 156. 207. 214. 158. 249. 54. 275 319 heating. 34. 130. 232. 37. 180 heating rate. 109. 169. 37. 270. 309 heating oil. 177 grass. 231. 254 harvesting. 219. 120. 110. 242. 30 horizon. 34. 17. 125. 113 heterogeneity. 294 health effects. 114. 2. 203 high pressure. 20. 60. 75. vii. 144. 177. 260. 36 health. 141. vii. 295. 296 growth rate. 36. 104. 238 hybrid. 191 handling. 110. 170. 217 heat storage. 106 grasses. 47 HDPE. 110. 281. 27. 304 greenhouse gas (GHG). 262. 221. 134 Holland. 155. 139 household. 161. 69. 231. 196. 36 households. 159. 275. 67 headache. 221 halogenated. 138. 194. 117 hemp. 193. 306 growth. 102. 54 hydraulic fluids. 51. 108. 215. 177. 240 homogeneity. 66 heterogeneous. 286. 72. 185. 202. 299 hydrogen. 14. 192. 147. 51. 138. 171. 35. 111. 70. vii. 254. 35. 10. 236. 201. 49. ix. vii. 194. 122 hazardous substances. 122. 36. 114. 170. 4. 256. 46. 258. 95. 103. 1. 192. 14. 116. 175. 198. 217. 42. 21. 281. 231. 104. 103. 229. 165. 137. 196. 254. 279. 100 hydro. 125. 32. 53. 70. 199. 87. ix. 4. 112. 162 H H1. 246. 118. 98. 120. 106. 46. 132. 247. 131. 22. 246. 84. 119. 134 humidity. 19. 117. 3. 173. 181. 100. 260. 125. 189 heat release. 126. 116. 100. 97. 240 holistic. 172. 299 hydrofluoric acid. 53. 45 guidance. 19. 288 host. 1. 44. 47. 220. 7. 4. 205. 254. 230. 104 graph. 172. 99. 175. 166. 168. 71. 97. 4. 105. 22. 203 hazards. 288 harmful effects. 125. 110. 120. 182. 230. 118. 304. 2. 44 injection. 51 identification. 233 in situ. 115. 102 industrial production. 187. 78. 294. 50 International Organization for Standardization. 116. 3. 142. ix. 277. 217. 234. 298. 309 industrial application. 189. 303. 80. 245 infrastructure. 247. 227. 23. 142. 263. 135. 31. 110. 240. xi. 250. 89. 30. 308. 36. 152. 310 Israel. 306. 243. 90. 53. 246 imports. 290 instruments. 265. 306. 113. 115. 72 implementation. 309 inequality.320 Index hydrogen gas. 47 inhibition. vii. 232. 106. 279. 78. 172. 213. 248 incentives. 306 integrated waste management. 86. 23. 155. 49. 94. 299 input. 291. 136. 290. 191 Jatropha. 41. 207. 193. 100. 53. xi. 222. 116 indigenous. 305 investment. 177. 2. 63. 289. 42. 296. 152. 164. 173. 305 ionization. 298 industrialization. 232. 199 hydrological. 281. 244 incineration. 191. 108. 189 intangible. 134 . 33 ions. 116. 117 hydropower. 155. 71. 202. 263. 185. 196. 242. 237. 39. 246. 112. 111. 159. 303 insulation. 187. 128 hypothesis. 240. 105. 137. 156 Intergovernmental Panel on Climate Change (IPCC). 51. 90. 19. 200. 103. 207. 104. 264. 37. 188. 87. 160. 205. ix. 299 inclusion. 37. 92. 251. 93 inspection. 293. 159. 246. 189. 118. 302. 28 incentive. 242. 29 inorganic. 185. 95. 2. 244 hydrothermal. 75. 205. 136 internal combustion. 146. 88. 240. 298 industrial sectors. 212. 298 integrity. 102. 142. 44. 39. 175. 231. 188. 270. 230. vii. 189. 34. 214 integration. 5. 25. 106. 107. 243 interface. 250. 303. 174. 231 industrial. 141. 234. 61. 95. 143. 234. 118. 52. 162. 100. 51 hydrogenation. 117. 138. 77 interaction. 230. 134. 231. 241. 263 institutions. 274. 72. 111. 120. 91. 205. 234. 250. 102. 1. 241. 45. 44. 19 IPCC. 242. 288. 231. 100. 227. 189. 137. 244 interval. 81. 14. 307. 42. 273. 190. ix. 12. 33. 136. 237. 233. x. 1. 60. x. 229. 182. 51. 293. 122. 192. 210. 99. 209 imbalances. 248. 181. 43. 44 interpretation. 299. 110. 154. 290. 60. 241. 235. v. 47. 40. 8. 185. 227. 165. 235. 205 hydrogen peroxide. 97. 111. 236. 64. 85. 185. 3. 153. 238 iron. 229. 160. x. 124. 33. 306 IEA. 203 ISO. 175. 298. 213 indices. 244. 245. 294. 38. 41. 300. 183 industrial chemicals. 147. 196. 174. 253. 249. 17. 243 intervention. 305. 9. 137. 298 industrial wastes. 103. ix. 59 innovation. 124. 116. 181. 248. 205. 144. 185. 209 hydrolyzed. 191. 240 impurities. 8. 289. 284 interactions. 294. 166 inert. 258. 250. 45 inhibitors. 229. 278. 307 irrigation. 79. 194. 243. 151. 99. 215. 260. 241. 302 influence. 247 inhalation. 269. 243. 231. 307 industry. 298. 20. 71. 244. 206. 203 hydroxide. 202 Hydrothermal. 307 indication. 243. 247 indicators. 210. 6. 25 inhibitory. 183. 292. 235. 126. 142. 239. 112. 291 interest. 102. 306 J Japan. 206. 301. 303. 62. 199. 202 hydrogen sulfide. 80. 211 Italy. 136. 43. 308 I ice. 173. 300. 142. 210. 185. 107. 203. x. 113. 288 interphase. 57. 67. 99. 230. 105. 148. 172. 305 inoculum. 88. 69. 36. 305. 287. 236. 124. 118. 35. 292. 177. 172. 5 Ireland. 7. 32. 45. 210. 245. 45 hydrolysis. 215. 172. 195. 238. 119. 136 IPPC. 106. 85. ix. 66. 14. 288 legislation. 3. 299 Lithuania. 93. 39. 70. 60. 217 lover. 11. 20. 7. 33. 17. 215 maintenance. 8. 60. 305. 54. 136.321 Index jobs. 233. 54. 134. 34. 11. 233. 231. 114 kinase. 30. 2. 199. 34. 27. 206. 222 knowledge. 245 links. 112 land. 228. 258. 135. 63. 305. 92 Madison. 58. 57. 103. 21. 51. 235. 233. viii. 100 lubricating oil. 1. 57. 64. 55. 303 life-cycle. 138. 3 K kerosene. 306 Malta. 65 magnesium. 234. 207. 43. 238 local authorities. 65 lysine. 229. 97. 303. 43. 52 liquid fuels. 198. 43. 5. 100. 139 kinetic equations. 211. 193. 65. 24. 61. 47 low-temperature. 4. . 4 LCA. 48. viii. 215. 49. 126. 245. 119. 77. 4. 135. 2. 31 low-level. 229. 26. 108. 35. 139. 59. 115. 95. 203. 38. 72. 246. 136 kinetics. 7. 245. 69. 193. 136. 18. 50. 141 lack of confidence. 4. 25. 51. 235. 303. 300 lipids. 64 Latvia. 60. 294. 10. 188. 187. 23. 30. 199. 1. 25. 3. 36. 89. 300 machines. 308 London. 195. 135. 115. 94 leachate recirculation. 56. 135. 54. 21 land use. 187. 53. 14. 14. vii. 241 life cycle. 62. 261. 102. 182. vii. 9. 183. 29. 65. 105 liquefaction. 28. 208 long period. 2. 114. 87. 122. 53. 63. 10. 47. 60. 99. 62. 7. 247. 37. 19. 305 jurisdictions. 106. 127. 92. 37 lignin. 104. 208. 19. 65. 206 liquid phase. 212 liquefied natural gas. 61. 134. 72. 228. 134 lifetime. 72. viii. 121. 60. 13. 93. 91. 230. 122. 238. 66. 15. 32. 57. 62. 63. 2. 62. viii. 236. 238 lysimeter. 188. 45. 64. 32. 21. 124. 63. 28. 57. 44. x. 59. 22. 292 linear programming. 45. 256 liquids. 63. 36 low-permeability. 20. 46. 91. 207. 115. 246 maltose. 291. 1. 202. 95. 234. 45. 247 leakage. 229. 54. 62 landfills. 94 landfill management. 5. 211. 92. 208. 53. 9. 248 Kyoto protocol. 62. 69. 103. 23 limitations. 92. 116. 32. 70. 196 magnetic. 42. 22. 205. 103 management. 115. 11. 27. 232. 26. x. 199. 25. 293 logging. 24 linear. 102. 6. 106 low-density. 119. 61. 7. 23. 230. 8. 49. 246 land disposal. 65. 8. 238 law. 307 Life Cycle Assessment. 210 limitation. 8. 48. 22. vii. 203. 89. 65. 188. 246. 37. vii. 54. 69. 111. 53. 86. 128. 121. 118. 61. 75. 64. 88. 32 leaks. 12. 94. 139. 117. 90. 137. 87. viii. 64. 246 landfill gas. 94. 87. 102. 241. 90. 29. 64. 106. 133. 231 lactic acid. 69. 54. 59. 70. 210. 61. 102 ketones. 201. x. 103. 2. 46. 98. 101. 10. 204. 94 lead. 103 M machinery. 43 kinetic model. 62. 64. 11. 44. 75. 250 laws. 119 Luxembourg. 16. 27. 44. 131. 7. 103. 26. 236 L labor. 65. 97. 99. 116. 43. 211 lubricants. 141. 24. 28. 53. 96. 93. 4. 10. 92. 55. 236 large-scale. 9. 52. 100. 31. 260 limiting oxygen. 33 Legionella. 21. 125. 56. 310 leachate. 84. 240 logistics. 61. 31. 99. ix. 38. 3. 189. 200. 85. 190. 36. 10. 93. 47. 60. 207. 5. 230. (LCA)ix. x. 88. 232. 4. 33 losses. 202 mixing. 134 microbes. 215. 256. 14. 45. 30. 110. 76. 69. 66. xi. 24. 63. 57. 288. 51. 214. 305 modern society. 255 moisture. 22 microorganisms. 236. 32. 28. 290. 249. 1. 154 matrix. 119. 62. 37. 30. 217. 70. 4. 71. 26. 43. 208 municipal solid waste. 7. 229 modules. 59. 231. 51. 21. 209 metabolic. 300 myopic. 203 monomers. 117. 245. 14 metal ions. 103 minerals. 104 movement. 33. 106. 30. 84. 215. 19. 303. 196. 13 methylene chloride. 24. 27. 47. 60. 32. 299. 175. 23. 94. 23. 94. 201. 40. 301 methanogenesis. 110. 229. 60. 46. 300 maturation. 123 monosaccharide. 93. 103. 8. 43. 227 municipal sewage. 175. 2. 197 molar ratios. 63 MSW. 106. 308 media. 21. 193. 54 micronutrients. 5. 54. 2. 112. 233. 287 Minnesota. 118. 1. x. 26. 114. 195 methodology. 217. 126. 56. 197. 303. 10. 185 melt. 236 Maryland. 11. 248. 7. 119. 30. 38. 11. 172 . 198. 230. 291 mining. 237. 138. 43. 71. 23. 110. 107. 20. 108 molecular oxygen. 239. 45. 8. 38. 88. 196. 108. 16. 72. 26. 44. 240 market structure. 72. 294 methane. 28. 258. 61. 56 misleading. 226. 59. 64 mass transfer. 254 MIT. 63. 66 Ministry of Education. 60 melting. 222. 45. 20. 46. 38. 58. 197. 197 molecular mass. 44. 133. 34. 43. 290. 290. 50. 9. 213. 34. 247 methylene. 10. 86. 41. 23. 128. 28. 226. 67. 306 market penetration. 289. 33. viii. 300. 69. 172 membranes. 93. 13. 240. 216. 44. 19. 57. 287 mathematical programming. 108. 45. 299 mobility. 199. 72. 7. 67. 293. 309 manufacturing companies. 81. 102. 41. 32. 105. 224. 231. 222 Microbial. 234. 6. 194. 118. 119. 28. 60. 106. 252. 241 market value. 63. 77. 15. 46. 125. 21. 61. 235. 230. 83. 222 molar ratio. 77. 22. 28. 246. 64. 29. 71. 249. 41 molecules. 120 market share. 53. 126. 105. 54. 79. 13 microalgae. 197. 55. 68. 45 methanol. 245. 125 missions. 108. 108. 226. 131 migration. 296. 214. 138. 52. 23. 25. x. 5. 77. 39. 106 molecular weight. 260 man-made. 306 mercaptans. 22. 31. 55. 35. 297. 65 milk. 109. 112. 13. viii. 294. 252. 10. 65. 53. 216. 89. 295. 247. 126. 62. 3. 3. 71 measurement. 234. 11 microbial. 36. 59. 66. 222. 30. 8. 70. 45. 28. 101. 243. 309 manganese. 124 molecular structure. 49. 112. 56. 172 monitoring. 21. 172. 7. 306. 139 models. 16. 119. 203 market. 194. 34. 71. 305. 24. 43. viii. 19 metallurgy. 119 Mediterranean. 57. 54. 257 medicine. 14. 60. 258 metals. 123. 306. 87. 219. 15. 112. 11. 107. 191. 8. 29. 8. 203. 300 money. 51. 298. 303 measures. 37. 14. 46. 209. 47. 246. 192. 71. 36.322 Index 240. 29. 12. 78. 37. 112. 16. 193. 33. 25. 25. 80. 20. 44. 49. 216. 3. 43. 65. 45. (MSW)vii. 240. 215. 247. 138 microbial community. 54. 60. 55. 87. 31. 8 metabolism. 100. 95. 91. 57. 25. 24. 39. 62. 52. 216. 237. 231. 72. 241. vii. 293. 47. 29. 251. 104. 106. 303. 290 manure. 217. 42. 225. 120. 29. 11. 64. 8. 9. 244. 173. 2. 248. 92. x. 218. 235 monomer. 64. 64. 246. 11. 24. 251. 219. 76. 26. 262. 3. 21. 153. 222 moisture content. 291. 245. 210 megawatt. 229. 25. 256. 66. 239. vii. 235 modeling. 71 mercury. 76. 24. 31. 44. 172. 212. 61. 25. 135. 60 mineralization. 70. 61. 32 manufacturing. 204. 300. 56. 2. 54. 61. 193. 63. 23. 70. 23. 230. 125 markets. 247. 23. 228. 3. 75. 194. 193. 119 oxide. 288. 59. 170. 125. 302 organic chemicals. 138. 233. 27. 110. 114. 22. 210 onion. 117. 50. 119. 106. 6. 101. 50. 56 nutrients. 175. 165. 14. 25. 182. ix. 110. 110. 173. 133. 120. 216. 185. 244 negotiation. 103. 297 nitrogen. 303 nausea. 309 natural environment. 234. 74. 71 observations. 114. 183. 80 non-human. 298 NTU. 196. 309 natural gas. 190. 52. 198. 302 nitrogen oxides. 305. 300 organic polymers. 36. 35. 28. 13. 200. 110. 70. 241. 142. 187 Norway. vii. 47 323 OFS. 53. 120 odors. 108. 36. 61. 7. 293 New Jersey. 119. 122. 13. 156. 40. 134. 189. 104. 76. 54. 215. 214 oxidative. 103. 49. 212. 115. 135. 207. 199. 66. 295. 20 output. 185. 230. 60 newspapers. 199. 156. 123. 205. 200. 141. 115. 105. x. 180. 203 organic solvent. 129. 123. 49. 114 oligomers. 52. 1. 5. 120. 61. 10. 304. 172. 195. 234. 237. 8. 50. 231. 87. 293. 105. ix. 290. 7 optimization. 100. ix. 62. 95. 35. 23. 196. 103. 187. 70. 103. 34. 37. 51 oxygen. vii. 214. 62. 63 New Orleans. 139. 138. 101. 67. 188. 185 newspaper industry. 123. 101. 139. 231. 84. 142. 183 oils. 193. 63. 299 organic. 241 Netherlands. 209 nickel. 187. 135. 31. 112. 209. 303. 106. 44. 203 organic matter. 196. 198. 1. 14. 173. 12. 161. 45. 7. 168. 36 needs. 240. 207. 194 oil. 102. 208. 133. 236 oxidants. 66. 173. 236. 96 New York. 58. 37. 203. 206. 54. 288 nutrient. 203. 299. 234. 65. vii. 300. 138 operator. 291 organ. 202. 112. 71. 209. 7. 172. 112. 232. 250. 207. 45. 14. 182. 131. 123. 124. 27. 184. 138. 64. 3. 202. 109. 199 organic solvents. 129. 177. 208. 46. 56. 97. 10. 99. 111. 39. 304. 210. 1. 29. 247. 22. 25. 64. 21 obsolete. 97. 71. 87. 172. 51. 201. 34. 46. 52. 34. 240. vii. 7. 114. 112. 287 New Zealand. 103. 211. 122. 171. 191. 222. 72 O obligate. 209. 8. 138. 3. 154. 119. 167. 133. 36. 28. 258. 102. 128. 207. 259. 288. 241. 32 octane. 203. 305 . 49. 300 non-hazardous. 24. 232. 100. 254. 14. vii. 95 non toxic. 203. 246. 121. 254. 62. 217 oxygenation. 196. 32. 199 oil refining. 2. 135. 60. 16. 72. 36. 37. 237. 125 North America. 19. 13. 32. 23. 117. 25. 103. 59. 214. 42. 173. 10. 11 organic compounds. 53. 8. 13. 119. 57. 32. 160. 126. 1. 128. 129. 203. 108. 49. 160. 192. 124. 228. 217. 19. 185. 41. 172. 109. 192. 24. 303. 238. 126. 241 natural resources. 295. 36. 305 norms.Index N natural. 20. 122. 291 networking. 192. 299 oxides. 195. 203. 153. 111. 70. 296 network. 20. 28. 199. 116. 15. 209. 160. 175. 199. 22. 233. 58. 299 occupational. 25. 212. 103. 124 ozone. 11. 131. 183. vii. 188. 7. 199 organism. 234 Ni. 114. 70. 51 noise. 308 non invasive. 307 oilseed. 210 NIPA. 99. 210. 141. 301 oil production. 202. 37. 42. 19. 17. 30. 204. 205. 136. 192. 77. 238. 24. x. 213. 205. 53. 8. 35. 163. 172. 110. 135. 25. 292 normal. 237. 128. 182. 12. 299. 228. 71. 206 opposition. 202 oxidation. 50. 14. 209. 25. 104. 237. 30. 105. 301 Oxygen. 300. 98. 92. 111. 192. 152. 113. 107. 229. 193. 106. 306. 102. 101. 257 porosity. 123 phenolic. 43. 250 PET. 19 phosphoric acid fuel cell. 249. 114 phenol. 111 petroleum. 27. 192. 104. 119. 29. 223. 195. 32. 32. 103 prediction. 100. 256 permit. 291. 119. 14 pig. 258 power generation. 294 poison. 119. 6. 52. 47. 236. 300 power. 111 polyurethanes. 238 potassium. 203 pilot study. 160. 233. 20. 247. 32. 195. 293. 211 pharmaceutical. x. 125. 242. 240. 26. 108 Philadelphia. 242. 123. 112. 53. 46. 307 polymer molecule. 103 polysaccharides. 6. 22. 25 photochemical. 298. 289. 34. 98. 287. 66. 225. 108. 91. 231. 41. 43. 236. 159. 252. 247. 195. 208. 122. 27. 289. 60. 99. 58 permeability. 24. 123. 60. 298 polar ice. 296. 308 physiological. 309 pore. 203 pathways. 237. 250 politics. 235. 103 physical properties. 119. 231. 52 phosphorous. 306. 234. 224. 199. 16. 64. 103. 251 pipelines. 102 policy instruments. 114. 118 potential energy. 242. 209 Parliament. 24. 51. 31. 307 plastics. 290. 244. 250 PAFC. 305 photosynthesis. 231. 199. 257. 3. 139. 76. 219. 122 photosynthetic. 117. 118. 114. 294 passenger. 105. 224. 42. 196 plastic. 307 petrochemical. 230. 166. 90. 208. 100. 58 Paris. 101. 43. 26. 114 poor. 199. 233 precipitation. 33. 139 pH. 245. 240. 112 Poland. 44. 290. 47. 256. 201. 236. 218. 42. 194 Petroleum. 97. 114 polychlorinated dibenzodioxins (PCDDs). 296. 118. 251. 98. 195. 202. 110. 288 porous media. 111 play. 232. 293 personal relationship. 45. 104 polymerization. 43. 36. 248. 72. 260 porous. 52. 173. 204 power plant. 215. 102. 249 particles. 243. 187. 294. 28. 260. 241. 64. 32. 191. 191. 256. 122. 21. 133 peat. 289. 87. 4. 290 polymer. 250 pollutants. 299 plasma. 212. 28. 245. 248. 134 . 194. 123. 225. 292. 235. 242 power plants. 63. 47. 104. 31. 25. 303 polyamides. 233. 100 Pap. 204. 14. 46. 230. 27. 29. 33. 206. 192. 220. 193 physicochemical.324 Index P packaging. 306. x. 41. 238. 98. 234. 63. 297 percolation. 248. xi. 172 polar ice caps. 105. 50. 103. xi. 243. 233. 257 pollution. 229. 289 powder. 45. 203 polyphenols. 254. 243 platforms. 46. 136. 138 petroleum products. 190. xi. 51 poisoning. 203. 242. 134. 114. 245. 103 Portugal. 25. 172 polarity. 307 polyethylene terephthalate. 244 per capita. 227. 17. 35. 119. 217. 242. 191 polycondensation. xi. 62. 257. 204. 3. 227 periodic. 203 partnership. 60. 248. 237. 211 parameter. 133. 52. ix. 128 passive. 188 population. 22. 138. 243. 51 planning. 192 polymers. 175. 188. 210. 102. 258 pathogens. 299 particulate matter. 185. 221. 222. 123. 175. 240. 92. 100. 232. 195. 67 paints. 111. 63 phosphate. 5 personal relations. 43. 293 perspective. 299 performance indicator. 231. 119 polyester. 188. 256 portfolio. 291. 305 plants. 244. 110. 30. 191. 26. 299. 229. 247. 243. 232. 77. 46 recyclables. 4 relationship. 123 protein. 286. 237. 205. 106. 3. 89. 42. 36. 6. 86 profits. 116. 51. 54 pyrolysis. x. 88. 205. 226. 303 relationships. 52. 306 public health. 161. 241. 91. 130. 260. 111. ix. 206 reaction rate. 98. 36 pulp mill. 207. 300. 196. 198. 194 propionic acid. 29. 75. 307 range. 231. 219. 281. 210. 185. 184 reconstruction. 42. 182. 187. 233. 47. 301 prevention. 202. 108. 95. 27. 294 regulatory framework. 59. 156. 236. 234. 134. 192. 214. vii. 228 Q quality loss. 12. ix. 89. 218. 293. 115. 161. 296. 238. 94. 122. 103. 199. 25. 240. viii. 225. 215. 203. 300 regulations. 175. 77. 112. 13. 292. ix. 253. 105. 254. 128. 133. 69. 90. 194. 190. 288. 173 questionnaire. 304 remediation. 139 refining. 123 reaction medium. 103. 174. 294. 187. 133. 208 programming. 207. 99. 4 renewable energy. 57 radius. 114. 135. 136. 234. 24. 189. 142. 260 rain. 3. 172 pressure. 213. 125. 59. 234. 60. 5. 135. 93. 303. 85. 249. 288 purification. 114 reactivity. 65. 57. 133. 117. 299. 72 reactants. 103. 19 protocol. 32. 212. 160 regression. 32. 287. vii. 4. 139. 225. 220. 138. 262. 188. 30. 1. 133. 213. 290 probability. 87. 13. 116. 112 protection. 196 real estate. 85. 210 pumping. 294 preventive. 126. 244. 237. 54. 246. 70. 101. 86. 133. 46 reconcile. 100. 227. 157. 104. 106. 33. 203. 244 product market. 98. 97. 11. 203. 110. 105. 130. 60 pyramidal. 114. 207. 24 proposition. 113. 298. 243. 221. 239. 67 reactant. 237. 303 raw materials. 230. 4. vii. 226. 152. 3. 258. 196. 121. 1. 173. 70. 110. 249. 234. 72. 221. 85. 118 reaction mechanism. 191. 99. 106. 182. 55. 113. 232. 110 reaction temperature. 236 public administration. 125. 227. 16. 224. 300 RCRA. 191. 3 regular. 242 propylene. 86. 115. 293 prices. 41. 190. 106. x. 5. 166. 184. 251. 138. 27. 209. 5. 101. 125. 122. 3. ix. 217. 114. 105. 3. 93. 26. 46. 108. 300 recovery technology. 106 profit. 114. 159. 293 reliability. 200. 214. 20. 22. 183. 226. 98. 158. 165. 243. 55 regulation. vii. 217. 24. 214. 59. 191. 301. 258. 231. 233. 309 redox. 236. 172 rainfall. 288. 188. 303 protective coating. 242. 98. 189. 112. 133 refineries. 21 325 random. 130. 100. 189 reactive sites. 93 program. 115 Proteins. 100. 2. 102. 254 private. 129. 188. 172. 258 refrigeration. 127. 108. 60 recycling. 188 recovery. 216. 84. 246. 156.Index preference. 208. 69. 191. 126. 122. 60. 219 producers. 110. 102. 248. viii. 235. 240. 19. 135. 232. 122. 236. 138. 254. 124. 181. 159. 24. 32. 50. 99. 250. 23. 16 proteins. 124. 116. 4. 193. 121. 267. 100. 196. 27 process gas. 47. 292. 199. 225. 102. 260. 26. 304 recognition. 194. 292 . 236. 39. 291. 185 property. 52 PVC. 245 propagation. 120. 23. 298 raw material. 38. 245 R radial distance. 291 reality. 2. 249. 95 reference system. 290. 97. 5. 25 reduction. 290. 102. 234. 26. 84. 210. 108. 102. 246 Romania. 206. 210. 131. 35. 190 shortness of breath. 240 rule of law. 307 resistance. 102. 1. 298 Slovenia. 224. 71 rubber. 96. 299 social benefits. 249 scholarship. 237 sharing. 188. 249. 160 self. 202 sea level. 199. 133. 199. 46. 303. 133. 208. 67 resources. 60. 262 separation. 212 shape. 141. 204. 194. 246. 245 simulation. 189. 128. 215. 6. 121. 87. 172 search. 204. 240. 209. 301 SO2. 11. 290 skills. 197. 159 selectivity. 204 routing. 128 . 293. 211. 100 selecting. 299 Slovakia. 219. 240. 251. 255 robustness. 43. 131. 29. 133. 109 sand. 8. 61. 3. 196. 250 restaurants. 97. 287 scientific community. 99. 60 satisfaction.326 Index renewable resource. 50. 103 responsibility. 33. 291 social factors. 174 saline. 301 Resource Conservation and Recovery Act. vii. 214. 97. 192. 108. 231 sediment. 25. 207. 112 replacement rate. 171 saturation. 203. 136. 137 room temperature. 243 Siemens. 54. 217. 93. 127. 303. 54 residues. 98. 119. 127. 98 SCW. 210. 155. 133 rural population. 221 sites. 233. 216. 240. 307. 105 restructuring. 8. 200. 100. 132. 298 Rome. 61 seeds. 173. 106. 97. 133. 8. 306 sewage. 160. 110 residential. 306 rural areas. 117 short run. 129. 108. 236. 172. 146. 185. 247 social group. 307 schema. 119. 190. 8. 188. 298 slag. 219. 298. 243. 119 research and development. 231. 205. 212 rice husk. 133. 33. 290. 206 sample. 290 social problems. 116. 175. 208. 2. 7. 101. 142. 196. 105 semi-arid. 51. 238. 206. 122. vii. 217. 46. 235. 98. 61. 103. 196. 23. 118. 291. 238 sludge. 258 simulations. 193. 193. 108. 29 services. 246. 212 smog. 295. 181. 219. 219. 189. 197 S safety. 7. 97. 191. 281 Saudi Arabia. 198. 188. 211. 4. 214. viii. 306 Russian. 2. 114. 117. 36 Short-term. 102. 172 smoke. 246 sensors. 53. 289. 130. 106. 293. 111 shares. 130. 292. 97. 123. 189 septic tank. 206 short period. 194. 78. 135. ix. 220. 260. 133. 215 risks. 47. ix. 236. 2. 309 respiration. 105. 306 social performance. 6. 103 rural. 294. 61. 139 ruthenium. ix. 103. 114. 119. 210 shoulder. 105. 27 Second World War. 125. 202. 247 sodium. 211. 187. 22. 209. 105 sensitivity. 245. 105 salt. 10. 103. 4 runoff. 173. 115. 205. 28. 21. ix. 99. 124. 208. 64. 177. 61. 102. 307 resins. 37. 64. 203. 254 seasonal variations. 111. 131. 60. 202. 141. 119 shortage. ix. 220. 235 semiarid. 218. 238. 4. 299. 12. 138. 212 risk. 104. 141 savings. 207 signals. 218. 135. vii. 201. 279. 125. 195. 32. 128. 49. 294. 124. 221. viii. 292. 293 shock. 249. 102. 54. 126. 29. 249 rice. 257. 3. 20. 47. 306. 98. 247. 28. 240. 214. 65. 246. 60 surgery. 307 soil. 66. 197. 298. 213. 231. 148. 27 surface water. 27. 253. 38 stabilization. 203. 153. 260. 106 sugar cane. 107. 3. 262 Sun. 5. 246. 294 327 subjective. 196. 104. 292 solar energy. 293 symbols. 136. 251. 7 synthesis. 27. 139. 234. 237. 174. 26. 199. 219 superiority. vii. 47. 105. 244 subsidization. 163. 118. 167. 112. 101. 212. 299 substitution. 290. 64. 108. 117. 263 stakeholders. 107. 98. 100. 293 sustainable development. 155. 232. 287 supervision. 98. 126. 114. 233. 7. 210. 113. 203. 19. 22. 243 substances. 215. 244. 200. 128 sulphate. 208. 124. 116. 67 starch. 237. 247. ix.Index sodium hydroxide. 67. 33. 202. 104. 3. 206. 142. 228. 212 starches. 19. 55. 230. 206 Stochastic. 28. 257. 162. 181. 160. 21. x. 46. 235. 117. 143. 102. vii. 156. 104. 93 spectrum. 184. 120 specific heat. 203 specific gravity. 148. 174. 21. 13. 305 Standards. 16. 72. 135. 248. 299. 106. 137. 242. 293. 105 supercritical. 9. 303 Sweden. 153. 199. 14. 299. 192 sulfate. 104. 236 soil particles. 54. 208. 65. 303. 70. 103. 307 . 294. 187. 235. 180 surface component. 12. 209. 115. 288 surplus. 128 software. 57. 67 sulfur. 241. 293. 4. 303. 189. 113. 43. 109. 240 Southampton. 112. 138. 25. 153. 173. 182. 146. 245. 220. 125. 175. 214. 40. 116. 43. 210. 2. 18. 3. 210 sugar beet. 28. 7. 4. 51 sulfur oxides. 188. 114. 247 subsidies. x. 147. 114. 22. 170. 241 statistics. 240 symbiosis. 43 Sulfide. 76. viii. 236. 124 substrates. 181 specificity. 205 stabilize. 253. 100 sorbitol. 287. 233. 285. 195. 251. 60. 231. 30. 264. 32 soils. 112 sucrose. 122. 237. 212 superheated steam. 137 sugars. 117. 239 steady state. 92. 98 state aid. 112 sorting. 218. 248. 177. 252 Switzerland. 143. 175. 198. 118. 139 sunflower. 200. 246. 111. 30. 196. 57. 105. 309 streams. 131. 161. 300 sustainability. 15. 71. 43. xi. 173. 118. 175. 302 summer. 217. 7. 30. 103. 250. 240. 216. 107. 105. 99. 293 symbiotic. x. 187. ix. 29. 61. 111. 7. x. 104. 305. 165. 60. 134. 229. 11. 217. 122. 64 soybean. 11. 209 solvents. 31. 110. 23. 185. 247. 49 suppliers. 166. 45. 174. 111. 1. 104. 66. 214. 115. 75. 161. 57. 100. 299. 196. 211. 300 stormwater. 100. 76. 19. 292 solid matrix. 21. 147. 209. 292. 32. 26 solid waste. 108 speed. 144. 213. 249. 122. 249 supplemental. 104. 250. 118. 53. 249. 235. 129. 95. 2. ix. 46. 294 surface area. 238. 100 Spain. 230. 80. 112. 240. 17. 103. 20. 137. 256. 37. 161. 210 sorbents. 64. 203. 203. 110. 306 standards. 154. 302 system analysis. 220. 98. 301 solubility. 25 sulphur. 287. 62. 37. 101. 10 strategies. 47. 112. 260 sterile. 38. 7. 31. 160. 238. 162. 4. 53 stability. 211. 106. 55. 63. 111. 69. 174. 45. 213. 6. 59. 210 solar. 7. 95. 51 sulfuric acid. 57 steel. 159. 295 species. 40. 42. 66 storage. 16. 100. 102. 168. 161. 222. 36 syndrome. 19. 142. 66 symptoms. 294. 196 solvent. 241 supply. 238. 236. 191. 168. 62. 55. 116. 184. 291. 99. 94. 10. 164. 46. 108. x. 59. xi. 60. 146. 100. 138 sugar. 173 stages. 262. 232. 231 Teflon. 54 United Nations. 133. 293 territory. 26. ix. 65 . 181 trade. 74. 226. 175. 12. 232. 39 uniform. 243. 100. 3 toxicity. 307 thermal resistance. 157. 101 time series. ix. 241. 292. 37. 296. 134 Thermophilic. 206. 100 toughness. 54. 43. 192. 308 Texas. 122. 230. 230. 191 urea. 111. 300 thermodynamic cycle. 227. 3. 146. x. 51. viii. 299. 72. 249 trans. 233. 234. 256. 136. 294 TOC. 33 TEM. 100 urban areas. 249. 187. 204. 300. 246 total product. vii. 100. 11. 260. 59. 185 temporal. 89. 91. 242 time frame. 115. 59. 181. 213. 39. 75. 214. 235. 93. 121. 205 threat. 295 tobacco. 65 USEPA. x. 219. 299. 243 transshipment. 233. 183 trading. 288. 156. 58 territorial. 51 threats. 128. 162. 60 thermal decomposition. 240. 205. 138 toluene. 229. 307. 66. 250 technological advancement. 26. 62. 13. 263. 298. 110. 305 TPA. 43. 45. 240. 27. 236. 207. 123. 258. 86. 99. 28. 216. 92. 59 tar. 2. 105 triglycerides. 303 transport. 3. 78. 119. 254. 41. 250. 152 traps. 207. 301. 162. 99. 114 Triglycerides. 304 Tennessee. 103. 87. 191. 247. 195 thermal energy. 98. 209 targets. 246 tariffs. 195. 118. 302 toxic gases. 271. 45. 229. 300 Turkey. 128 US Army Corps of Engineers. 193. 215. 41. 33. 103 threshold. 196 topographic. 11. 301 transformations. 183. 196. 205 technology. 234. 161. 92 topology. 72 U Ukraine. 299 transition. xi. 235. 288 UNFCCC. 139. 289. 208. 243. 246. 49. 67 Tokyo. 125. 128. 126. 112. 163. 110. 3. 279. 229. 79. 238 typology. 298 thermodynamic. 195. 257 thermal treatment. 161. 242. 4. 47 treatment methods. 64. 47 threonine. 160. 301 triglyceride. 209. 242. 32. 293. 45 triggers. 6. 242. 161. 173. viii. 305. 65. 297 United States. 76. 275 transformation. 217. 266. 13. 14. 100 taxation. 161. 5. x. 50. 236. 275. 309 transport costs. 303. 70. 251 T Taiwan. 21. 120. 215. 88. 190. 248 trade-off. 26 United Kingdom. 57. 106. 214. 231. 136 trend. 257. 25. 54. 67. 251 taxes. 161. 72. 239 trees. 227. 16. 44. 245. 69. 230. 192 thermal efficiency. 191. 2. 173 travel. 6. 285 transparent. 194. 240. 99. 57. 85. 84. 135. 242. 53. 241. 241. 185. 97. 214 tar removal. 309 transportation. 173. 15 transesterification. 111 transfer. 196. 204 trial and error. 300 thermodynamics. 21. 198. 248. 241. 37 time. 306 toxic. 12. 246 uncertainty. 42. 114 turbulence. 154. 131. 105. 203 textiles. 59. 230. 232 trial. 2. 73. 50. 50. 80.328 Index systems. 232. 139 tanks. 183 total energy. 2. 293. 31 volatilization. 160. 50. 1. 126. 16. 211 wastewaters. 138 World Health Organization. 307 woods. 2. 203. 286. 210 wind. 12. 233. 129. 244. 116. 122. 290. 244 winter. 21. 80. 231. 242 X Xylan. 257. 258. 254. 234. 64. 209 . 49. 108. 240. 33. x. 109. 12. 61. 264. 200. 288 Victoria. 289. 27 water vapor. 240. 35. 200 web. 32. 301. 227. 214. 193 values. 247. 305. 284. 1 vehicles. 283. 98. 95. 80. 243. 263. 272. 277. 294. 210. 35 W waste disposal. 103 voids. 247. 47. 236. 65. 167. 233. 226. x. 125. 217. 274. 9. 130. 199. 25. 243. 253. 47. 43. 129. 240 word of mouth. 8. 281. 61. 188. 10. 49. 137. vii. 58. 115 vegetation. 187. 195. 264. 193. 59 Western Europe. x. 196.329 Index V vacuum. viii. 307 waste treatment. 6 water quality standards. xi. 248. 253. 57. 252. 307. 203 wells. 192. 26. 195. 41. 245. 75. 15. vii. 102. 13. 118. ix. 298 variables. 21. 294. 21. 244. 119 water evaporation. 42. 211 wastewater treatment. 300. 102. 49. 251. 193. 271. 27. 270. 10. 3. 233. 13. 207. 205. 287 variation. 241 vegetable oil. 281 water gas shift reaction. 299. 81. 2. 37 viscosity. 94. 287. 295 wetting. 65. 21 water vapour. 235. 239. 256. 188. 244. 229. 85. 232. 247. 131. 3. 249. 280. 285. 203. 13. 55. 250. 203. 262 Wisconsin. 207 Z zeolites. ix. 240. 40. 65 wood. 1. ix. 215. 109 xylene. 268. 26. 129. 120. 196 Y yield. 267. 281 water-soluble. 76. 38. 141. 242. 308. 273. 32. 16. 165. 308 wastes. x. 60. 26. 241 VAT. 39. 195. 266. vii. 307 wood products. 189. 202. 245. 269. 42. 189. 108. 98. 224. 208. 128. 41. 64 writing. 244. 240 waste incineration. 152. 285. 9. 37. 237. 47. 232. 229. 2. 276. 290. vii. 39. 235. 235. 237. 1. 60. 303 waste disposal sites. 124 variability. 199. 192. 257 wheat. 248. 100. 259 ventilation. viii. 39. 79. 4. 209. 70. 203. 6 water table. 290 variance. 79. 76. 202 vision. 189. 66. 21. 196. 8. 187. 202. 25. 199. 56. 111 vegetables. 246. 298. 97. 129. 78. 112 water quality. 36 World Bank. 137 vinyl chloride. 236 velocity. 294 wood waste. 13 work. 130. 302. 16. 229. 278. 100. 212 zinc. 16 vomiting. 243. 32. 134. 105. 138. 53. 44. 166. 279. 232. 242. 41. 74. 231. 153. 23. 13. 187. 231. xi. 45. 61 waste imports. 295. 24. 98. 83. 230. 204. 78. 70. 193. 239. 62. 12. 304 vapor. 246. 216. 108. 30. 309 waste products. 251. 104. 236. 82. 10. 42. 103. 100. 4. 263. 192. 13. 26. 1. 42. 117. 299 waste management. 230. 247. 79. 97. 192. 248 workers. 246. 99. ix. 309 wastewater. 282. 45. 7. 245. 265. 196. 114. 241.