COMPREHENSIVE INDUSTRIAL DOCUMENTS FOR PRODUCER GAS PLANTS AND BIOMASS GASIFIERSCentral Pollution Control Board (Ministry of Environment & Forests, Govt. of India) Parivesh Bhawan, East Arjun Nagar,Delhi-110032 e-mail:
[email protected] Website: www.cpcb.nic.in (Placed on Website on 29.08.08 & it is in the process of Printing) Table of contents Chapter 1 Introduction Producer gas................................................................................................... 1 Uses of producer gas ...................................................................................... 1 Thermal.................................................................................................. 1 Power Generation .................................................................................. 3 Introduction to Producer gas technology ......................................................... 4 Historical development........................................................................... 4 Producer gas technology in India ........................................................... 4 Introduction to the Study ................................................................................. 5 Scope of work ................................................................................................. 5 Literature survey and information collection ........................................... 5 In-depth study ........................................................................................ 5 Evaluation of emission norms for producer gas and biomass gasifier based thermal appliances................................................................................. 6 Chapter 2 Producer gas technology and its environmental aspects The need for conversion of solid fuel into gaseous.......................................... 7 Gasification principle ....................................................................................... 7 Biomass gasification .............................................................................. 8 Coal gasification..................................................................................... 9 Gasification process............................................................................... 9 Gasification rate ................................................................................... 13 Type of producer gas units................................................................... 14 Gasification, gasifier operation and gas utilization problems / challenges /Design ........................................................................................... …………17 Environmental aspects of producer gas plants .............................................. 18 Dust ................................................................................................. 19 Wastewater and condensables ............................................................ 21 Fly ash and char .................................................................................. 22 Hazards of gasifier operation ........................................................................ 23 Combustible gases and vapours .......................................................... 23 Combustible dusts ............................................................................... 24 Fire risks .............................................................................................. 24 Carbon monoxide poisoning................................................................. 24 Chapter 3 Methodology for the study Study methodology ....................................................................................... 26 Unit selection ....................................................................................... 26 Methodology for environment monitoring ............................................. 27 Liquid effluent monitoring ..................................................................... 28 Chapter 4 Results and analysis Stack monitoring results................................................................................ 29 Ambient air monitoring .................................................................................. 30 Work area monitoring.................................................................................... 30 Liquid effluent monitoring .............................................................................. 31 Tar and other wastes .................................................................................... 33 Energy balance ............................................................................................. 36 Chapter 5 Environmental Standards for Producer gas units Gaseous & Particular emission……………………………………………………38 Point Sources- stack & vents from gas utilization end…………………38 Fuel pre-treatment, gasification and fugitive emissions……………….40 Liquid effluents…………………………………………………………………… 42 Other Wastes……………………………………………………………………… 42 Chapter 6 Conclusions Technology ................................................................................................... 44 Environmental and safety.............................................................................. 45 Operation and maintenance .......................................................................... 46 Health and safety .......................................................................................... 48 Brief description of Units selected for monitoring Refractories, Belpahar- Unit 1 ....................................................................... 49 Coal Complex, West Bengal-Unit-2............................................................... 50 Steel re-rolloing mill, Raipur-Unit-3................................................................ 50 Steel Industries, Raipur-Unit-4 ...................................................................... 51 Rice Mill, Burdwan-Unit-5.............................................................................. 51 Technology Provider & Research & Development organization, Vadodara-Unit 6............................................................................................ 52 Industrial gases, GIDC Por, Vadodara, Unit-7 ............................................... 52 Ceramics, Morbi, Unit 8................................................................................. 53 Calcium carbonates Industries, Ponta Sahib-Unit 9....................................... 53 Calcium carbonates Industries, Ponta Sahib-Unit 10..................................... 54 Technology Providers of biomass Gasifiers Ankur Scientific Energy Technologies Private Limited.................................. 54 DESI Power/ NETPRO.................................................................................. 55 Indian Institute of Science ............................................................................. 56 Radhe Renewable Energy Development Pvt. Ltd.......................................... 57 The Energy & Resources Institute (TERI) ..................................................... 57 Glossary 59 Annexes 4.3 - 4.5.................................................................................... 60-69 List of tables Table 2.0 The content of CO in the equilibrium mixture of CO and CO2 at one atmosphere pressure............................................................................. 8 Table 2.1 Typical composition of wood based producer gas........................ 8 Table 2.2 Typical composition of coal based producer gas with different gasifying agents........................................................................................... 9 Table 2.3 Gasifier characteristics - up & down draft................................... 16 Table 2.4 Environmental aspects of gasification ........................................ 20 Table 4.1 Mean concentration of pollutants in the stack emissions ............ 29 Table 4.2 Ambient air quality near producer gas units ............................... 30 Table 4.3 Average dust and CO levels in different working environment ... 31 Table 4.4 Details of effluents from producer gas units, treatment and disposal methods....................................................................................... 32 Table 4.5 Details of solid waste generation and the mode of disposal ....... 33 Table 4.6 Tar generation and disposal practices....................................... 34 Table 5.1 Emission Standards for different industries…………………………39 Table 5.2 CO Emission regulations for new engines operating on producer gas in different countries ……………………………………… …....40 Table 5.3 Sources & characteristics and control choices- Emission from fuel pre-treatment gasification………………………………………….40-41 Table 5.4 Effluent standards for different industries…………………….…….42 List of figures Figure 1.1 Schematic of producer gas unit with gas cleaning system for power generation ..................................................................................... 3 Figure 2.1 Reactions of gasification ............................................................. 7 Figure 2.2 Reaction zones in an updraft producer gas unit......................... 10 Figure 2.3 Solid fuel feeding....................................................................... 11 Figure 2.4 Solid fuel feed into the reactor................................................... 11 Figure 2.5 Ash withdrawal .......................................................................... 11 Figure 2.6 Gasification ............................................................................... 11 Figure 2.7 Wet and dry - Gas cleansing train for producer gas power generation units........................................................................................... 12 Figure 2.8 Sources of dust - Solid fuel storage yard, fuel feed, fuel preparation and fly ash ................................................................................ 19 Figure 2.9 Sources of liquid effluent - Reactor bottom water seal, condensate, gas cleaning equipment........................................................ 20-21 Figure 2.10 Fly ash and char................................................................. 21-22 Figure 4.1 CO level variation with time - Unit 6 .................................... ……30 Figure 4.2 Energy balance for coal based single stage fixed bed gasifier ... 35 Figure 4.3 Energy balance for coal based double stage fixed bed gasifier.. 36 Chapter 1. Introduction Producer gas Producer gas is a derived gaseous fuel, which is obtained by gasification of various primary fuels like coal, lignite, charcoal, and biomass. Biomass fuels conducive to gasification are wood, rice husk and coconut shell. Conversion of primary fuels into producer gas by gasification broadens the range of applications of these fuels. The primary advantage of gasification technology is that it enables the substitution of expensive fuels with cheap solid fuels. Gasifier is a potentially viable system for significant fuel savings. The adoption of gasifier technology in many of the processes lead to improved productivity and the quality of the end product, because of better process control, which was not possible with direct combustion. This further improves the economic viability of the system. The heating value of this gas varies between 4.0–6.0 MJ/Nm3, which is about 10-15% of heating value of natural gas. Producer gas from different fuels and different gasifier types may considerably vary in composition, but it consists of mixture of the combustible gases hydrogen, carbon monoxide, and methane and the incombustible gases carbon dioxide and nitrogen. The composition and other characteristics of producer gas are shown in chapter 2, Table 2.1 and 2.2. Uses of producer gas The producer gas obtained by the process of gasification could be used for thermal application or for mechanical/electrical power generation. Like any other gaseous fuel, producer gas has the distinct advantage in power generation when compared to that of solid fuel. This also paves way for more efficient and cleaner operation. Producer gas can be used for decentralised power generation, water pumping and for a variety of other thermal applications. In locations where biomass is already available at reasonably low prices (e.g. rice mills, corn processing units, sugar mills, etc.) or in applications utilising fuel wood (e.g. institutional cooking, silk reeling units, etc), biomass gasifier based systems offer definite economic advantages. The producer gas can be conveniently used in number of applications as mentioned in subsequent paragraphs. Thermal Thermal energy of the order of 4–6 MJ is released on combustion of 1 m3 of producer gas in the burner. Flame temperatures as high as 13000C is obtained by optimal pre-mixing of air with gas. For applications, which 1 require thermal energy, gasifier is a good option and it is used in the following cases, a) Dryers: Drying is the most essential process in beverage and spices industry like tea and cardamom. This calls for hot gases in the temperature range of 120–1300C, in the existing designs. Typically the heat energy required is equivalent to 1 kg of wood for 1 kg made tea. Gasifier is an ideal solution for the above situation, where hot gas after combustion can be mixed with the right quantity of secondary air, so as to lower its temperature to the desired level for use in the existing dryers. b) Kilns: Firing of tiles, potteries, limestones and refractories require hot environment in the temperature range of 800–9500C. Gasifiers are used for such applications, which provide a better option of regulating the thermal environment. There will also be an added advantage of smokeless and soot less operation, thereby enhancing the product value. This is presently being done by combusting large quantities of wood in an inefficient manner. Limekilns in Poanta Saheab, Himachal Pradesh is using charcoal based producer gas for their heating requirements. c) Furnaces: In steel re-rolling mills, non-ferrous metallurgical and foundry industries high temperatures (650 -1000o C) are required for melting metals and alloys. This is commonly done using expensive fuel oils or electrical heaters. Gasifiers are well suited for such applications and one such application (Baroda, Gujarat) . Steel rerolling mills in Raipur, Chattisgarh are using coal-based producer gas in reheat furnaces. d) Boilers: Process industries that require steam or hot water, heating of process fluids use either biomass or coal as fuel in the boilers. In Indian context, biomass is used inefficiently with higher pollutants like particulate matter, NO x and with little control on combustion and heat transfer. Therefore these devices are retrofitted with gasifier for efficient energy usage. e) Retort heating Producer gas is used for heating retorts; retorts in turn carbonise of non-caking coals. Dankuni Coal Complex (DCC), Dankuni, West Bengal, uses producer gas for heating continuous vertical retorts. 2 Power Generation Using Producer gas, it is possible to operate a diesel engine on dual fuel mode. Diesel substitution of the order of 80 to 85% can be obtained at nominal loads. The mechanical energy thus derived can be used either for energising a water pump set for irrigation purpose or for coupling with an alternator for electrical power generation, either for local consumption or for grid synchronisation. Figure 1.1 shows schematic of producer gas unit with gas cleaning system for power generation. Now the trend is towards 100% gasifier based power generation systems. Figure 1.1 Schematic of producer gas unit with gas cleaning system for power generation Source: Ankur Scientific, 2004 3 Introduction to Producer gas technology Historical development The technology of producer gas has been developed after the oil crisis. The use of gasifiers during World War II occurred because the industrial nations of Europe found themselves virtually cut off from oil supplies. At the same time they possessed capital and technical resources and the full infrastructure necessary to run a road transport system. Gasification offered a means of helping to maintain a basic transport service, although at considerable cost in finance, convenience, and vehicle wear. Though gasification has been practiced for over 100 years, but there is little commercial impact due to competition from other fuel sources and other energy forms. Since 1975, there has been a renewed interest world wide with many instances of substantial demonstration and commercial scale plants. In particular, the last few years have seen a major resurgence of interest in biomass gasification processes mostly due to environmental and political pressures required of CO2 mitigation measures. Producer gas technology in India Coal is the major primary fuel and is also processed and converted into other forms. Because of low initial investment cost, easy operation and availability of oil at low cost, the refractory manufacturers were allured to use oil for kilns till 1974. But due to the ever-rising cost of petroleum products since 1974, refractory manufacturers in India are finding difficulty to maintain their profitability by running the kilns with oil firing. The producer gas derived from gasification of coal continues to be the main fuel for the refractory industries particularly in the eastern part of India. Coal is available in the eastern parts of the country at a cheaper cost and refractory industry in these areas took advantage of it. Similarly in the Western India, due to availability of charcoal, refractory industries are using charcoalderived producer gas for kiln and furnace heating. In a single location, Morbi (Rajkot district, Gujarat) approximately 80 charcoal based producer gas units are in operation. In Himachal Pradesh, Limekilns are operated using charcoal based producer gas to manufacture lime for pharmaceutical industry. A few rolling mills are being operated with coal-based producer gas in Raipur (Chhatisgarh). Producer gas finds application in glass industry, retort heating and boiler heating. The development and dissemination of biomass gasifiers began in the early 1980s. Since then, a number of research institutions in the country have worked on different aspects of biomass gasifier use as well as on development of indigenous gasifiers and gasifier based energy systems. Much of the initial work was focused on small wood-based gasifiers for applications such as powering irrigation pump sets. Realising the relevance of gasification process, Government of India has taken various initiatives to promote the technology in this country. Biomass gasifiers have now found utility in range of industries and power applications across the country through numerous demonstration projects and commercialisation activities. Over 1200 gasifiers have been reportedly installed under the Ministry of Non Conventional Energy Sources (MNES), Government of India, subsidy programs, and an estimated number of 400 additional gasifiers have been installed outside the subsidy regime. Few small-scale entrepreneurs are also trying to manufacture and install gasifiers on a commercial basis. In view of a large potential of producer gas based applications in the country, there is a need to examine the performance of gasifier-based applications in terms of efficiency and environmental performance. Introduction to the Study Producer gas plants generate various types of pollutants. During gas manufacturing, tar is generated and discharged into the environment, which is non-aqueous in nature. Coal tar is always commingled with other light oils, which are also waste products from producer gas plant. There are also gaseous emissions containing certain volatile organic compounds along with other gaseous pollutants such as CO, NOx and SO2. At present there are no pollution control norms in place for producer gas plants. Though producer gas plants and biomass gasifiers are energy efficient and environment friendly, the local environmental benefits, such as reduction in emission of particulate, CO, SO2 and NOx are not studied in detail. There is a need to contemplate the characteristics of emission from producer gas plants and biomass gasifiers. It is also necessary to take up environmental performance evaluation of producer gas and biomass gasifier plants. With this background, Central Pollution Control Board (CPCB) in association with TERI undertook a project to study the emissions and effluents from producer gas plants & biomass gasifiers and recommend emission standards and stack height and to recommend pollution control measures based on the principle ‘best available technology not entailing excessive cost (BATNEEC)’. Scope of work Literature survey and information collection § § Literature survey/ review of state-of-the art technologies Information collection from the Ministry of Non Conventional Energy Sources, State Pollution Control Boards (SPCBs) and Pollution Control Committees (PCCs), technology providers and users. In–depth study Performance evaluation of gasifier based thermal appliances 5 A total of ten gasifier based thermal appliances (5 producer gas plants and 5 biomass gasifier based) developed by different technology providers and installed in different region of the country has been selected and studied in detail for § § § § § § Identification of source of air and water pollution Monitoring of stack emissions to study the environmental performance Ambient air quality monitoring around gasifier units Monitoring of workplace environment for fugitive emission Monitoring of wastewater. Energy performance of gasifier based thermal appliances The following parameters would be taken into account for the evaluation of environmental and energy performance of gasifier units. § § § § § § § System design Operating practices Fuel characteristics End use application Thermal output Ambient (e.g. temperature, humidity, etc.) and local conditions (e.g. ground thermal properties) Product quality 6 Chapter 2: Producer gas technology and its environmental aspects The need for conversion of solid fuel into gaseous Historically, the justification for gasification was to extend the range of uses for coal. In a gasified form, coal could be more easily transported around an industrial plant; it could be used for illumination and for a wide range of direct heat application requiring a clean and easily controlled flame; and it could be used for internal combustion engines. Indeed much of the early development of internal combustion engines took place in the period before oil was widely available, and the pioneering engines of Otto and others were designed to use coal gas. Coal gasification was subsequently displaced in most applications by the advent of cheap oil, and later by natural gas. Under present conditions, economic factors provide the strongest argument for considering gasification. In many situations, particularly where the local price of petroleum fuels is high, or where supplies are unreliable, a strong economic case is made for using gasifiers - provided a suitable feedstock is available. For individual users, the economic advantages of switching to producer gas must be weighed against the practical disadvantages. Apart from economics, environmental performance, especially gasifiers using biomass as feedstock, is one of the factors influencing gasification. Gasification principle Thermochemical gasification is the conversion by partial oxidation at elevated temperature of a carbonaceous feedstock such as biomass or coal into a gaseous energy carrier. This gas consists of carbon monoxide, carbon dioxide, hydrogen, methane, trace amounts of higher hydrocarbons such as ethane and ethene, water, nitrogen (if air is used as the oxidising agent) and various contaminants such as small char particles, ash, tars and oils. The partial oxidation can be carried out using air, oxygen, steam or a mixture of these. For most gasification processes, oxygen and steam are the agent of choice though some will also accept air or CO2. The chemical reactions of gasification are rather complex, but in summary they are endothermic. The typical Sequence of reactions in a gasifier is shown below The reactions given in figure 2.1 explain the process of gasification fairly well. C + O2 C + H2O(g) C + CO2 CO2 CO + H2 2CO +393 800 kJ/ kg mole (combustion) -131 400 kJ/ kg mole (water gas) 2.1 2.2 -172 600 kJ/ kg mole (Boudouard reaction & Neumann reversal reaction) 2.3 +41 200 kJ/ kg mole (water shift reaction) + 75 000 kJ/ kg mole (Methane reaction) 2.4 2.5 CO +H2O (g) C + 2H2 CO2 + H2 CH4 Figure 2.1 Reactions of gasification 7 As long as oxygen is in excess, carbon dioxide is formed by the reaction [2.1], which then undergoes reduction into carbon monoxide by reaction [2.3]. The latter is known as the Boundouard reaction and is actually the single most important reaction controlling the gasification process. The Boudouard reaction is an endothermic reaction. Its equilibrium constant greatly increases with the rise in temperature. The content of carbon monoxide in the equilibrium mixture of carbon monoxide and carbon dioxide at one atmosphere pressure sharply increases beyond 500o C as shown in the table below (table 2.0). Table 2.0 The content of CO in the equilibrium mixture of CO and CO2 at one atmosphere pressure Temperatur 400 e (0C) 0.9 Carbon Monoxide (CO) - % Source: Sarkar S, 1999 500 6.5 600 26.4 700 63.0 800 89.5 900 97.5 1000 99.6 The Boudouard reaction is a heterogeneous reaction. The kinetics is such that the equilibrium is reached at 13000C in a few seconds and at 1,1000C in about a minute. The above discussion shows that producer gas process is favoured by high temperature of the fuel bed. Biomass Gasification The biomass gasification process converts the solid biomass fuels into producer gas, a gaseous fuel that can be burnt relatively easily and in an efficient manner. In this process, the biomass materials are combusted in a reactor with limited amount of oxygen or air, which leads to thermal cracking of biomass materials to yield producer gas. Producer gas from different biomass fuels and different gasifier types may considerably vary in composition, but it consists of mixture of Carbon Monoxide (CO), Methane (CH4) and Hydrogen (H2) along with non-combustible gases (mainly Nitrogen and small amounts of Carbon Dioxide (CO2)). The heating value of this gas varies between 4.0 and 5.0MJ/Nm3, which is about 10-15% of heating value of natural gas. The composition (range) of wood based producer gas is shown in Table 2.1. Table 2.1 Typical composition of wood based producer gas Composition Carbon Monoxide (CO) Hydrogen (H2) Methane(CH4) Carbon Dioxide (CO2) Nitrogen (N2) Value (% on volumetric basis) 19-21 19-21 2-4 8-12 Balance 8 Coal Gasification Bituminous coal, anthracite and coke are used as the raw material in coal based gas producers. The exact composition of producer gas depends on the type of fuel, the composition of the blast and other operation variables. The data on some typical coal based producer gases are given in Table 2.2 Table 2.2 Typical composition of coal based producer gas with different gasifying agents Composition, percent by volume Air blast Mixed blast with with Coal Coke coke 1.0 33.5 1.5 64 100 1060 0.98 4.0 0.4 29.0 12.0 2.6 52.0 100 1550 0.87 1.28 5.0 29.0 11.0 0.5 54.5 100 1260 0.90 1.00 Anthra cite 6.0 26.0 17.0 1.2 49.8 100 1420 0.85 - CO2 CnHm (unsaturated hydrocarbon) CO H2 CH4 N2 Total Gross CV, kcal/Nm3, dry Specific gravity (air=1) Theoretical air (for combustion), Nm3/Nm3 Source: Sarkar S, 1990 Gasification process The complete gasification process consists of: § § § § § Feeding Gasification Ash removal Heat recovery Gas clean up 9 A number of feed fuel properties are considered in designing feeding systems, which is primarily related to the size of feed fuel. Feeding is done either manually or automatically. Manual feeding is simple and almost any type of fuel can be fed. Because of labour costs and possible health risks, the trend is towards automated feeding. In most of the feeding system for gasifiers fuel is conveyed from storage area on a belt conveyor or bucket elevator to an intermediate storage, from which the fuel is fed via a lock hopper or a rotary valve into the gasifier reactor. Feeding systems normally have gas tight seals. The process of gasification is an important step, which is described in detail. The different steps are shown in figures 2.2 – 2.6. Gasification – Reactions & Reaction Zones Gasifiers have distinct zones characterized by different processes. These are drying, pyrolysis, combustion and reduction zones. The fuel bed in a normal producer gas unit rests on a metallic gate. Fuel bed may be divided into a number of reaction zones, namely, ash zone, oxidation zone, primary reduction zone, secondary reduction zone, and drying-cum-carbonisation zone, depending upon the sequences of reactions that take place as shown in, Fig. 2.2. The air-steam blast is pre-heated by the ash zone, which also serves to do the uniform blast distribution and protects the grate from intense heat. The oxygen is consumed within 75 to 100 mm of the bed, which constitutes the oxidation zone. Once the reactions start, the composition of the gaseous stream goes on changing from point to point along the bed depth. Carbon dioxide forms at the expense of oxygen. Its concentration reaches a maximum at the top of the oxidation zone when carbon monoxide begins to appear. The monoxide continues to form by the reactions [2.2] and [2.3] initially and then by reaction [2.2] alone and approaches an equilibrium with the dioxide at the top of the bed. Soon after the appearance of carbon monoxide, the steam decomposition begins and then vigorously continues for about 25 mm of the bed depth, which is called the primary reduction zone. About 40 mm layer of the bed above the zone constitutes the secondary reduction zone where the steam is decomposed by carbon monoxide. The uppermost layer of the bed is the escaping gas. Therefore, fuels with significant yields of volatile matter results in the production of enriched gases. The topmost zone also serves as the preheating zone for the incoming fuel. The gas composition is slightly changed in the gas space above the fuel bed. Both Neumann's reversal reaction and water gas shift reaction are responsible for a reduction in the calorific value of the final product.Fig.2.2 is schematic representation of the zones. In practice there is no well-defined boundary between two neighbouring zones. Moreover, the gas flow is not uniform across 10 the bed cross-section. It is maximum at the periphery and minimum at the centre. Therefore, temperature profiles are concave-shaped, a horizontal section of the bed having the temperature falling from the periphery to the centre. The reaction zones are similarly concave-shaped and not horizontal. Ash removal The quantity of ash requiring removal and disposal from a gasifier depends mainly on the type of fuel gasified. For example in the case of biomass gasifier, quantity of ash is relatively small at typically 1-2% of the dry feed weight. Removal from the gasifier will vary according to the type of system. Fixed beds will usually have a rotating grate with screw or mechanical discharge from the base of the reactor. Fluid beds may have an overflow arrangement or extraction from the bed, while circulating fluid beds will take a side-stream off from an appropriate place in the circuit. Each process will have its own proprietary system for ash removal depending on the type of fuel used, Biomass Gas Drying Pyrolysis Reduction Oxidation Ash Air Figure 2.2 Reaction zones in an updraft producer gas unit 11 gasifier type and size, operation & maintenance practises. Secondary and tertiary ash removal will arise from producer gas cleaning and cooling systems such as cyclones, hot gas filters and water washing systems. Fig 2.3 Solid fuel feeding Fig 2.4 Solid fuel feed into the reactor Fig 2.5 Ash withdrawal Fig 2.6 Gasification Gas cleaning The usual impurities in the producer gas are steam, tar, dust, hydrogen sulphide and ammonia – depending on the type of fuel & gasifier. Most of the steam and tar is condensed on cooling. Ammonia may be removed and recovered as ammonium sulphate. But recovery is not economical. No special treatment is normally given for the removal of hydrogen sulphide and other impurities. Since these are corrosive and harmful their content is kept low by using low sulphur coals in gas producers. Dust is partly removed with the condensates and is completely removed with cyclones or other types of dust catchers depending on the requirements for end use of producer gas. 12 When raw gas is directly fired in a furnace, the tar contributes to the calorific value of the gas and raises the temperature and emmissivity of the flame. The dust particles also increase the flame emmissivity. But dust is a major cause of fouling of gas mains carrying hot raw producer gas. Therefore, some form of dust catcher is installed even in gasifiers supplying hot raw gas to furnaces. In case of power generation application gas cleaning becomes an important component of the system. The main attempts to eliminate tar concentrate on three approaches: scrubbing, catalytic reforming followed by scrubbing and hot gas clean up. Both dry and wet cleansing methods are adopted as shown in the figures below. Dry cleaning methods include cyclones, different types of dry filters containing - wood wool, coconut fibre, sisal fibre, wool, wood chips soaked in oil, and other types of fibrous or granular material. Counter current washing of producer gas with water is the primary wet cleansing method adopted. It also Fig 2.7 Wet and dry - Gas cleansing train for producer gas power generation units serves the purpose of increasing the density of the gas and avoids condensation of moisture if it is mixed with air is engine application. Most of the dry media used in filters are regenerated or reused by backwashing or washing with water and drying. Water used for cleaning is recirculated, but the blow down from the wet cleansing system is primary effluent generated from producer gas systems. Gasification rate The cross-sectional area at the nozzle location for downdraft designs and at the grate for updraft designs is a measure of the throughput of the gasifier and hence is an indication of the capacity. One of the most important design parameters for gasifiers is the Specific Gasification Rate (SGR), also called grate loading for updraft gasifiers, expressed as kilogram of fuel gasified per hour per square metre of the bed cross-sectional area. It is desirable to achieve a high gasification rate with a good gas quality. This is limited by the following factors: § Fuel properties such as size and size distribution § The form in which ash is discharged, § Use of air / other gasifying agents, § Height of the fuel bed, § Rate of reduction of carbon dioxide and steam. 13 In normal producers gas units, the ash is removed in the solid form. The ash fusion point seriously limits the bed temperature and hence the gasification rate. The presence of large amounts of nitrogen in the blast leads to high wastage of heat in the form of sensible heat of the gases leaving the reaction zone, and hence automatically limits the bed temperature. The use of oxygen or oxygen enriched air helps to maintain high bed temperatures and hence, high gasification rates. The gas quality is also improved. The operations without inert nitrogen have an unfavourable factor of the increased partial pressure of the carbon dioxide gas entering the reduction zone, which displaces the equilibrium of reaction [2.2] towards carbon dioxide. The effect, however, is more than compensated by the other merits of a high oxygen blast. Conventional producer gas reactor needs a certain minimum bed height of 0.6 to 3 m for achieving the desired reduction of carbon dioxide and steam. Deep beds, however, offer resistance to the blast and hence limit the gasification rate. A preheated blast increases the gasification rate. Temperature control is the problem in preheated blast gasification. Besides the reactivity, two other properties of the fuel greatly affect the gasification rate. These are size and size distribution, and hardness. Uniform size, say 20 to 40 mm, promotes uniform gas flow across the bed crosssectional area. The presence of excessive amounts of fines leads to high carryover losses and prevents the use of a high blast rate. If the fuel is soft, it is degraded during handling and operation and thus produces non-uniform fuel with excessive fines. The clean gas yield in a large conventional producer ranges between 4 to 4.5 Nm3/kg of dry coal and one kg of biomass produces about 2.5-3.0 Nm3 of gas (Ghosh et al, 2003 and Sarkar S, 1990). Types of producer gas units The design of a gasifier varies with respect of the following features: § Direction of travel of producer gas and fuel, § Effective pressure in the reactor, § Method of ash removal, § Method of introduction gasifying agent, § Fuel feeding system, § Bed stirring devices and § Shell construction. Several types of gasifiers exist: fluidized bed gasifiers, entrained bed gasifiers, circulating fluidized bed (CFB) gasifiers, and moving bed gasifiers. The first three types are generally used for large-scale industrial applications and for pulverized coal or similarly-sized biomass (e.g., rice husk). Moving bed gasifiers are widely used. Moving bed gasifiers further classified as: downdraft (or co-current; fuel flow and gas flow in the same direction), updraft (or counter current; fuel flow and gas flow in opposite directions), cross 14 draft (gas flow perpendicular to fuel flow) and natural draft (gas flow induced by natural draft, hence no need for a blower). Updraft gasifiers In up-draft producers, the blast travels upwards and the fuel downward. Ash is removed from the bottom of the bed and the gas from the top. This is the most conventional type of gas producers. The earlier discussion on the reaction zones pertains to this. Downdraft gasifiers Both the fuel and the blast travel downwards in the downdraft producers. Hence, the volatile matter of the fuel undergoes decomposition during its travel through the bed. This is preferred in power generation systems. Other types Another rare type is the double-draft gasifier with the air/blast entering both from the top and the bottom.A cross draft gasifier, the fuel travels downwards but the blast is introduced on one side of the bed and allowed to travel practically horizontally before the gas is taken out from the other side. This type of gasifier is used in gas-fired vehicles. A summary of relative advantages and disadvantages of updraft and downdraft units is given in the Table 2.3. Depending upon the pressure conditions, there may be atmospheric (balanceddraft), suction or pressure gasifiers. The atmospheric type is by far the most common owing to the elements of safety and control. The suction types are of limited capacity and find use in the manufacture of power gas and in heating built-in type gas retorts. Pressure gasifiers are used to supply methane-rich gas to furnaces. The gas pressure at the top of an atmospheric producer bed is usually slightly positive, 25 to 125 mm water column. Table 2.3 Gasifier characteristics – up & down draft Gasifier Advantages Simple, reliable and proven for certain fuels Relatively simple construction Close specification on feedstock characteristics, Uniform sized feedstock required Possible ash fusion and clinker formation on grate Disadvantages High residence time of solids Needs low moisture fuels High carbon conversion Low ash carry over Fairly clean gas is produced Low specific capacity 15 Product gas is laden with high levels of tar & dust Very simple and robust construction Good scale up potential Suitable for direct firing High residence time of solids Relatively simple construction Low exit gas temperature High thermal efficiency High carbon conversion Low ash carry over In conventional gasifiers, ash is removed in the solid state by some form of mechanical ash removing system. The gasifier shell is placed on a water pan (seal) and either the shell or the pan is rotated. The ash falls on the pan and is continuously removed by placing an obstruction in the path of the relative movement of the ash. When both shell and pan are rotated, the ash is ploughed from the pan intermittently. Older types of gasifiers had stationary grates where ash was manually removed at definite intervals. In slagging gasifiers, ash is allowed to melt and then removed by tapping at set intervals as in a cupola or blast furnace. Some high-speed gasifiers allow the ash to be carried away with the gas and collected in dust pockets in the gas line. The most common position of feeding of the blast in updraft gasifiers is below the grate. The old gasifiers had a flat, inclined or stepped bar grate. The newer units have a conical shaped or mushroom-like grate. The blast inlet is just below the hollow centre of such a grate and enters into the fuel bed through holes or slots in the grate. The slagging gasifiers receive a high velocity blast through cooled tuyeres in the sides of the gasifier. There is no distribution problem in the downward blast. The gasifiers usually receive intermittent fuel feeds through hoppers. A more complicated arrangement such as a worm feed may be necessary for special fuels. There are variations in the method of uniform distribution of fuel and the levelling of the bed. The gasifier bed needs occasional stirring to maintain its uniform porosity. The rotation of the shell or water pan provides agitation. Coking coals need extra stirring from the top by rotary or oscillating, water-cooled mechanical poking rods. Gasifiers are usually built of cylindrical steel shells. The shell may be lined with firebrick and / or may have a water jacket to protect it from intense 16 heat. Low pressure and sometimes high-pressure steam is raised in the water jacket. Larger capacity gasifiers have water-jacketed shells. The walls of the brick-lined gasifiers should be kept relatively cool to avoid the formation of wall clinker by the slagging of the bricks with the coal ash. Gasification, gasifier operation and gas utilization problems/ Challenges Design A number of designs have been utilized in various demonstration or commercial projects around the world. While there is consensus on some design elements of gasifiers for specific feedstock and/or applications, there has been no systematic effort at validating the performance claims of the various designs and carrying out a comparative assessment of various gasifier and energy systems’ designs to reach consensus on technical choices which would help in streamline the future design process. Operation and maintenance A typical starting problem of the gasifier is that after the ignition of the fuel bed, continuous and stable gas production does not occur, even after prolonged torching of the fuel bed. This almost always happens if the fuel is very wet. Sometimes, even though the gasifier can be started without any problem, gas production will either cease or gas quality will deteriorate (lean gas, smoky, and unable to sustain combustion). The two main reasons for this are bridging and clinker formation. Bridging is caused if all the fuel in the vicinity of air entry is burnt out and no fresh fuel drops into the empty space thus created. There could be several reasons for this but unless the bridge is broken by poking the fuel bed or shaking the grate or the gasifier itself, gas production will not resume. The operator usually resorts to opening the top of the gasifier and poking the fuel bed with a long rod. Some gasifier manufacturers provide openings or ports on the sides of the gasifier so that one does not have to use a long rod. Some designs try to overcome this problem by insisting on a certain size of the fuel but it is not very practical to obtain consistent size always unless good care is taken for fuel preparation. Clinker formation occurs if the ashes contained in the biomass melt easily. Clinker usually develops over time, almost always near the nozzles or grate where combustion occurs. Many times this occurs when the gasifier is restarted after allowing it to cool overnight. Clinker formation is particularly difficult to handle because it cannot be observed visually, and if it is suspected after the bed is completely charged, it is an arduous task to remove the fuel and then try to break the clinker into pieces so that the pieces can be pushed through the grate. Coconut shells with fiber, firewood with bark, cashew shells, and briquettes are usually susceptible for clinker formation. Another problem which occurs is the build-up of ash on the grate, especially for high ash fuels like rice husk. A very effective continuous ash removal system has to be designed to tackle this problem. 17 In all the above cases, fresh fuel does not fall into the combustion zone, and the circular chain ‘fuel-air-temperature’ breaks, and gas production ceases. Another frequent problem interrupting stable and continuous gas production is related to deposition of impurities anywhere in the gas cleaning and cooling train. Such depositions lead to an increase in pressure drop and reduce the gas flow rate and ultimately prevent operation of the gasifier. Attempts to continue operation by keeping the blower on and tinkering with the system without making an educated guess or without a measured parameter that indicates the location and nature of the problem often result in accumulation of gases in the reactor leading to and explosion. Most gasifiers experience explosions (or back-fire) at some point during their operating lifetime. Fortunately, the explosions are not very strong but can unnerve a new or untrained operator or user. As gasifiers are high temperature reactors and the resulting gases are corrosive in nature, it is quite logical that many kinds of material problems occur and questions about the lifetime of the various components keep arising. Some attempts have been made to analyse these problems but there are no standard material selection procedures or codes to be followed. Tar removal The efficient removal of tar still remains the main technical barrier for the successful commercialisation of biomass gasification applications for power. A number of different sampling and analysis methods have been developed by manufacturers and various institutes working in this field to determine the level of particulates and tar in the gas exiting the gas cleaning system of a gasification installation. This diversity of methods makes the comparison of operating data from different sources very difficult and represents a significant barrier to the further development and commercialisation of the technology. Work for running engines with producer gas has been continuing for decades now but with few breakthroughs if any. The main problem relates to efficient removal of tar, however, the engine manufacturers have not been able to design and construct more robust engines, which can tolerate some tar in the gas. Environmental Aspects of Producer gas Plants The operation of a gasification plant can result in environmental pollution, occupational health and safety hazards unless adequate and effective preventive measures are taken and continuously enforced. A gasification system consists of: § § § Fuel storage, handling and feeding system; The gasifier, gas cooling and cleaning equipment; Utilization of the gas. Each part of the plant creates specific occupational, health and safety hazards. 18 Table 2.4 describes the main environmental concerns and major hazards associated with the operation of gasification system. Table 2.4 Fuel prepara Environmental aspects of tion gasification and associated hazardsProcess activity Environmental Concerns Dust Noise Odour Wastewater Tar Fly ash Exhaust gases Hazards Fire Dust explosion Mechanical hazard Gas poisoning Skin burns Gas explosion Gas leaks Fuel Feeding system Gasifie r Gas Cleaning system Gas utilization * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Dust Dust is generated during feedstock preparation, storage and handling, feeding, and fly ash removal by particulate collection equipment. The handling of solid materials is a notorious source of airborne particles, especially when the solids are dry and friable. Some of the sources are shown in the figure 2.8. Dust generation creates several problems including: § § § § § Airborne or entrained dust may form explosive mixtures with air in which a primary explosion can render the dust airborne causing secondary explosions and these can be devastating; Inhalation of dust is a potential source of lung damage; Eye and skin irritation may occur; Layers of combustible dust may cause smells, or smoulder and ignite; Dust settlement on all exposed horizontal surfaces lead to safety problems for personnel in routine operations, as well as increased maintenance and aesthetic detraction; 19 § Increased friction and wear of mechanical equipment caused by dust deposition increases costs and reduces reliability, both increasing the potential for accidents; Dust generation due to fuel feeding Solid fuel storage and preparation Bottom ash from the reactor Fig 2.8 Sources of dust - Solid fuel storage yard, fuel feed, fuel preparation and fly ash Solid particles also arise in the product gas from gasification such as cinders, fly ash, filter dust, charcoal, fluid bed inert material and catalyst fines. Since such sources are localised they are, in principle, easier to control. In the discharge of fine material such as fly ash, they may need to be wetted to prevent re-entrainment during handling and disposal. Carbon formed by secondary cracking or incomplete gasification can also form explosive mixtures with air but it is usually contained in appropriate vessels. Charcoal from 20 biomass can be pyrophoric and needs to be adequately cooled prior to discharge and storage if arising in significant amounts. Some types of gasifiers may produce hot particles as a consequence of malfunction or equipment faults. These may ignite flammable materials and cause a fire. From an occupational health viewpoint, dust particles of the intermediate size range 0.2 – 5 µ is the most dangerous; Shape and composition of some materials are known to cause lung damage, for example silica (fibrilosis) may arise from fluid bed materials. Dust particles may also adsorb non-polar organic compounds up to 40 % of their weight, which may be higher for soot and carbon black with their very high specific surface areas. The dispersion of gasifier dust leads to air pollution. Wastewater and condensables Wastewater and condensates may be produced during gas cooling and wet gas-cleaning (1). The condensate is known to contain, for example, acetic acid, phenols and many other organic compounds. There is a risk of water pollution and adverse health effects from the tars and soluble organics. The condensate and wastewater consists mainly of water and can be divided into an aqueous i.e. water soluble, and a non-water soluble fraction consisting of tars and oils. The insoluble fraction consists mainly of tars, fly ash, phenolic compounds and light oils. The tars in particular, as well as the condensates, are toxic and require careful evaluation of their occupational and safety aspects. Typical sources of wastewater are shown in figure 2.9. Reactor bottom water seal Condensate 21 Reactor bottom water seal cleaning Effluents from Gas Figure 2.9 Sources of liquid effluent – Reactor bottom water seal, condensate, gas cleaning equipment Fly ash and char Fly ash and char present similar problems to those caused by dust as described above. There is an additional risk of fire that dictates that fly ash and char should be stored moist. Disposal of this wetted mixture presents its own environmental problems. The solids need to be separated from the water in a wastewater treatment facility. Extracted water will be contaminated and may require further treatment before discharge using orthodox wastewater treatment technology. Ash disposed nearby field stored within in plant premises Ash from charcoal based unit 22 Fig 2.10 Fly ash and char Hazards of Gasifier operation Combustible gases and vapours A flammable gas is combustible only within a certain range of concentrations, bounded by the LEL (Lower Explosion Limit) and the UEL (Upper Explosion Limit). Below the LEL, the mixture is too lean to sustain combustion. Above the UEL the reaction stops because of a deficiency in oxygen. In both cases the generation of heat becomes too slow to give rise to the characteristic acceleration in reaction rates, which marks the start of an explosion. The range between the LEL and UEL values depends on the reactivity of the flammable compound or mixture. It widens when the flammable gas or the combustion air is preheated or under pressure. Explosive mixtures could arise when: § Air leaks into the gasifier plant as a consequence of a reduction in operating pressure. Reduced pressure may arise due to rapid cooling, condensation of vapour such as water, chimney effects, and the suction of an induced draft fan or of an engine. Fuel gas leaks out of the gasifier plant into a confined space thus building up a substantial concentration in an enclosed space. When a flammable mixture of gas and air is formed, an explosion may occur when the mixture is ignited. Ignition may occur from static electricity, sparking equipment, or contact with a hot surface. In view of the wide explosion limits of the main components of producer gas - hydrogen and carbon monoxide - the accidental formation of explosive gas mixtures should be prevented. Mixtures of producer gas with oxygen enriched air or pure oxygen have a higher UEL compared to mixtures with air. The LEL does not change significantly. This means that oxygen gasifiers present an even higher explosion risk, e.g. when oxygen breaks through the fuel layer or there is a perturbation in the fuel supply. § 23 Combustible dusts Combustible solids such as wood, flour and coal dust when as very small particles can also form explosive mixtures with air within certain concentration limits. These boundaries usually range from a LEL of 20 to 50g/m3 and a UEL of 2 to 6 g/m3. Numerous carbohydrate materials, including starch, sugar and wood flour, have given rise to extremely destructive explosions. Fire risks The main fire risks in gasifier systems are associated with: § Fuel storage; § Combustible dusts formed in fuel comminution; § Fuel drying (in forced draft conditions a fire is likely to expand quickly); § Ignition procedure (especially for moving bed gasifiers); § The product gas. Carbon monoxide poisoning In many cases normal producer gas installations work under suction, so that even if a minor leak in the installation occurs, no dangerous gases will escape from the equipment during actual operation. The situation is different however during starting-up and closing down of the unit during which substantial quantity of gas is vented into the surroundings. During starting-up the gas is generally vented, and it is necessary to ensure that the gases produced cannot be trapped in an enclosed room. During closing-down of the installation a pressure buildup in the gasifier will occur, caused by the hot and pyrolysing fuel. As a result gases containing carbon monoxide will be released from the installation during a relatively short period. Carbon monoxide is a major constituent of producer gas and is by far the most common cause of gas poisoning. It is particularly noxious due to the absence of colour or smell. CO diffuses rapidly across alveolar, capillary and placental membranes. Approximately 80-90% of the absorbed CO binds with haemoglobin to form carboxyhaemoglobin (COHb), which is a specific biomarker of exposure in blood. The affinity of haemoglobin for CO is 200-250 times that for oxygen. During exposure to a fixed concentration of CO, the COHb concentration increases rapidly at the onset of exposure, starts to level off after 3 hours, and reaches a steady state after 6-8 hours of exposure (WHO, 1999). The binding of CO with haemoglobin to form COHb reduces the oxygencarrying capacity of the blood and impairs the release of oxygen from haemoglobin. These are the main causes of tissue hypoxia produced by CO at low exposure levels. At higher concentrations, the rest of the absorbed CO binds with other heme proteins such as myoglobin and with cytochrome oxidase and cytochrome P-450. The toxic effects of CO first become evident in organs and tissues with high oxygen consumption, such as the brain, heart, exercising skeletal muscle and the developing fetus. Severe hypoxia due to acute CO poisoning may cause both reversible, short-lasting, neurological 24 deficits and severe, often delayed, neurological damage. The neurobehavioral effects include impaired coordination, tracking, driving ability, vigilance and cognitive performance at COHb levels as low as 5.1-8.2%. In apparently healthy subjects, the maximal exercise performance decreases at COHb levels as low as 5%. The regression between the percentage decrease in maximal oxygen consumption and the percentage increase in COHb concentration appears to be linear, with a fall in oxygen consumption of approximately 1% for each 1% rise in COHb level above 4% (WHO, 1999). Epidemiological and clinical data indicate that CO from smoking and environmental or occupational exposures may contribute to cardiovascular mortality and to the early course of myocardial infarction. 25 Chapter 3: Methodology for the study Study Methodology The various steps in the methodology followed in the project were: § Project inception and planning; § Interaction with technology providers, users and State Pollution Control Boards/ Pollution Control Committees § Questionnaire survey § Literature survey; and § Field studies, data analysis - Source characterisation; - Work environment monitoring; - Ambient air monitoring; - Collection of information on control technologies adopted and their performance; - Arriving at standards and good operational practises for improved environmental performance - Energy related performance of producer gas units Unit selection The selection of producer gas units is based on the following criteria: § Gasifier type and Production capacity § Fuel type § End use § Geographical location Based on the response of the questionnaire sent through CPCB to different State Pollution Control Boards (SPCBs) (Annexure 3.1), interaction with the technology providers (details are provided3.2) and users and on aforesaid four criteria, 8 units were selected. In all the cases the gasifiers were fixed bed near atmospheric pressure type. But there is variation in terms direction flow of fuel – gasifying agent. Both updraft and downdraft gasifiers were selected for monitoring. In terms of fuel type, there were three variations – Coal, Charcoal and Biomass, all three type were included. There is significant variability exists in terms of end use. Broadly they fall under two major categories, thermal and power. Two power generation units were selected of which one was 100% gas based and the other was in dual fuel mode. The remaining six had different thermal applications such as kiln heating, retort heating and boiler heating. There is widespread installation of producer gas units in India, especially in the case of biomass gasifiers, with no geographical concentration. But most of the coal-based gasifiers are located in eastern part of the country. Units were selected for monitoring include from eastern, western and northern parts of the country. Description of these units is given in the annexure 3.2 26 Methodology for Environment monitoring In order to study the environmental performance of the Producer gas units, detailed environmental monitoring of eight units was carried out. The environmental monitoring includes stack emission monitoring, ambient air quality monitoring and fugitive dust measurement in the work place, and trade effluents monitoring. CPCB officials participated in the monitoring. Stack emissions Stack gas emissions were monitored for particulate matter, SO2 and NOx. Stack emission monitoring was carried out as per the standard procedures and CPCB procedures. Stack sampler (APM 615 of Envirotech make) was used to sample the flue gas for particulate and gaseous pollutant. Flue gas temperature was measured by thermocouples and velocity was measured using differential density velocity monitor. Iso-kinetic sampling procedure was followed for particulate sampling. Pre conditioned and weighed thimbles (GFA, whatman make) were used for sampling. Flow rate for gas analysis was maintained at 2 lpm (litre per minute) and the analysis was done by chemical method. Carbon monoxide (CO) levels were also checked using flue gas analyser and Orsat apparatus. Flue gas samples from some of the units were also analysed for Total hydrocarbons by the gas chromatographic method (GC). Ambient air quality monitoring Ambient air quality was monitored in 3 locations at each unit. The ambient air monitoring locations were selected at a distance of 50 – 100 meters from producer gas units. Suspended particulate matter (SPM), Sulphur dioxide (SO2) and Nitrogen dioxide (NO2) were monitored in the ambient air. High volume air sampler (Envirotech assembly) was used for sampling SPM at the flow rate of 1m3/min. Gaseous sampling kit attached to the high volume sampler was used for gaseous sampling and the flow rate was maintained at 1 litre/min. The samplers were kept at a height of 3 to 10 meters from the ground level. Personal exposure monitoring Ambient air quality monitoring (using Envirotech HVS) For SPM sampling, pre conditioned and weighed GFA filters were used. For SO2 and NO2 the gas was bubbled through suitable absorbing media. SO2 was analysed by West and Gake method. For NOx measurement modified Jacob Hoischier method was followed. Ambient air quality samplings were done for duration of 8hours. Ambient meteorological conditions were also recorded. Workplace environment monitoring Concentration of dust or particulate (SPM) and carbon monoxide (CO) in the work environment such as loading and unloading platform, producer gas units, 27 and near gas utilisation area were monitored. Particles were collected on a pre conditioned and pre weighed membrane filters (Millipore, Ireland make) and analysed by gravimetric technique. Personal dust sampler (SKC, USA make), was used for sampling the air. The flow of the personal air sampler was calibrated by the soap bubble technique. During the monitoring the flow was maintained at 2 litre/min. The monitoring was done for a period of 8 hours. CO levels in the working area were recorded by the personal CO monitors (National Dragger, USA make). Trade Effluent Quantification, Monitoring and Analysis Liquid samples were collected from water seals (bottom pan seal, leg seals and safety seals), condensates, effluents from cooling and cleansing system, floor washing and were analysed for the following components § PH § Temperature § TS, SS and TDS § Oil & grease § COD § BOD § Phenols § Total cyanide Flow quantification was carried out with Velocity-Area method. 28 Chapter 4: Results and analysis Ten units were selected for monitoring of which four units were using coal gasifiers; three were using biomass gasifiers and remaining three was using charcoal gasifiers. Producer gas units and gas utilization appliances were monitored for the following: § § § § § § Stack emissions Ambient air quality Work station air quality Trade effluents Solid waste Energy performance Units 1- 8 were monitored for all the above-mentioned parameters. Unit 9 was monitored for ambient air and workplace environment and trade effluents. Unit 10 was monitored for trade effluents. The details of the results and the analysis are presented in the following sections. Stack monitoring results The stacks/ vents attached to kilns, reheat furnace, waste heat recovery & reheat boilers and engines were monitored for PM, SO2, NO x, efflux and combustion parameters. In some cases, the units were running on dual fuel mode (producer gas + diesel/FO/waste oil). The plant operations were not altered and samples were collected during steady state conditions. The results of the stack emission monitoring are summarized in table 4.1. Table 4.1 Mean concentration of pollutants in the stack emissions Param Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit eter 6 Emissi ons Particul 98-40 24-21 78 60 58-53 51 ate (mg/N m3) SO2 140189109 150 62-30 45 (mg/N 380 192 m3) CO 1088-28 124 90 24835974 (ppm) 335 6445 Figures in brackets indicate the ranges; NA – Not available Unit 7 Unit 8 39 63-33 32 40 114 5-8 29 Ambient air monitoring In addition to the emissions from producer gas units other parameters such as process emissions, meteorological condition, topography and other activities in the near by vicinity affect the ambient air quality. Some of the monitored units such as Unit 3, 4 and 7 are located in Industrial areas; emissions from other industrial sources may also contribute to ambient air levels. Unit 7 is located close to Highway. In most the producer gas plant solid fuel preparation (loading, unloading, size separation & sizing) is also carried out in the vicinity of producer gas units, which may also contribute to ambient air levels. Apart from these, since producer gas units are an integral part of an industrial complex, emissions associated with other industrial processes may contribute to ambient air pollution. The summary of the ambient monitoring results is shown in the table 4.2. The detailed results are given in the Annex 4.3. Table 4.2 Ambient air quality near producer gas units Parameter SPM (µg/m3) RSPM (µg/m3) 150 131 358-366 214 264 NA NA NA NA 582 NA SO2 (µg/m3) 150 3-7 3 7-18 6-7 12-19 33-45 32-44 40-88 25-3 3 NO2 (µg/m3) Ambient air quality 500 standards* Unit 1 203 Unit 2 407-491 Unit 3 389 Unit 4 422 Unit 5 128-395 Unit 6 51-67 Unit 7 39-59 Unit 8 33-63 Unit 9 439-763 Unit 10 390-462 120 9-26 26-50 24-51 13-15 21-47 31 53 42-44 24-40 23-81 Note: * = 24 hour standard for Industrial area Following inferences are drawn from the ambient air quality results: § Concentrations of all gaseous pollutants were below the prescribed ambient air standards for Industrial area. § Particulate levels in ambient air were comparatively higher for Unit 9 and Unit 10, which may be attributed to particulate emission from lime production process. Work area monitoring The dust emissions and carbon monoxide levels at various working environment is shown in annexure 4.4. The summary data is shown in the table 4.3. The microenvironments included in the monitoring are, 30 § § For CO the area in and around producer gas unit and its application end. Dust levels were monitored in fuel preparation area, fuel-loading area and near producer gas unit. Carbon Monoxide (ppm) Dust level (µg/m3) 1-468 986-5164 1-10 222-335 16 187-830 1 780 5-15 97-127 25 NA 3 NA 2 NA 7-38 586-1056 3-16 344-844 Table 4.3 Average Dust and CO levels in different working environment Unit Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Unit 8 Unit 9 Unit 10 The CO levels were very high in Unit 1, i.e at top floor of gasifier. This was due to some operational problems, due to which the reactor inlet was kept open for long period. The continuous CO level measurements are shown in figures of annexure 4.4. In some cases values peak at regular intervals, which can be attributed to opening and closing of the reactor for solid fuel loading. Such typical plot is shown in figure 4.1 160 140 120 100 80 60 40 20 0 12:39:16 12:26:16 13:18:16 13:44:16 14:28:16 12:52:16 13:05:16 13:31:16 12:13:16 14:01:16 14:46:16 CO(ppm) time Figure 4.1 CO level variation with time - Unit 6 Liquid effluent monitoring The sources and type of effluents from producer gas units and treatment & disposal practised is presented in the table 4.4. In most of the units wastewater is generated in batches and are recirculated /reused after gravity settling. The quantity of wastewater generated is dependent on size of the unit, type of fuel and also on the gas cleaning and conveying methods adopted. It is difficult to quantify the wastewater generation rate as in most of the cases either water is topped up in the recirculation system or seals, to make up the loss or wastewater is discharged in batches once in fortnight or month. Field observations, estimation based on the number of cycles of cyclic operations 31 and measurement by area-velocity methods were used to quantify effluents generation rates. The estimated quantity of effluent generated is given in the annexure 4.5.Grab samples were collected from the following three main sources: § § § Ash pan/ Reactor bottom water seal Gas cleaning/ cooling Condensable vapours, tar separated effluents Detailed analysis of the effluents was carried out which is shown in the annexure 4.5. Table 4.4 Details of effluents from producer gas units and treatment & disposal methods Source Gas Conde Ash cleaning nsable pan/ vapours Reactor / bottom cooling water seal/ √ √ √ Unit Treatment Disposal Unit 1 Unit 2 √ √ √ × × √ √ √ √ Unit 3 Unit 4 Unit 5 √ √ √ Unit 6 √ × × Complete recirculation in the case of gas cleansing, ash pan water & condensable vapours are separated for Tar by gravity settling tanks No major source except ash pan water which is routed to plant’s ETP No major source except ash pan water. Significant quantity of condensable vapours/ tarry effluent is generated as gas is conveyed over long distance. Tar is separated in the in the cyclone Gas is cleaned & cooled with counter current flow of water; the water is recirculated/reused after gravity settling. This water is discharged in batches if it is laden with too much dust/tar, which makes it unsuitable for gas cleaning. No further treatment. Water is utilized for reactor cooling & ash/char collection Tar and oil bearing liquid effluent is stored in catch pit/pond. No further treatment/disposal is adopted Land/ pond Land Tar is sold to vendors. Untreated liquid effluent is disposed on land The wastewater is sprinkled on char that is separated from ash and excess is disposed on land. Diluted with other stream of effluents and disposed on 32 Unit 7 Unit 8 √ √ × √ × √ Unit 9 √ × √ which is recirculated after gravity settling No major source and also the quantity is less Gas is cleaned & cooled with counter current flow of water; the water is recirculated/reused after gravity settling. This water is discharged in batches if it is laden with too much dust/tar, which makes it unsuitable for gas cleaning. No further treatment. No major source except ash pan effluent. Land Land Unit 10 √ × √ No major source except ash pan effluent. Mixed with streams of effluents of industry Mixed with streams of effluents of industry other trade the other trade the Tar and other wastes Apart from trade effluents and gaseous emissions, the other wastes generated are ash (solid waste) and tar. In most of the cases the ash generated were dumped in the low-lying areas within the premises of the industry. In some cases unburnt carbon in the form of char, cinder, or coke is also present in the reactor bottom ash, which is hand picked by the local residents and utilized as domestic fuel. The details of solid waste generation and the mode of disposal are shown in table 4.5. Solid waste is also generated in the form solid fuel reject, which may be fine or coarse. Table 4.5 Details of solid waste generation and the mode of disposal Unit Unit 1 Quantity of ash generated (tpd) 12 Quantity of fuel (tpd) 50 Type of fuel Coal Recovery, method of disposal Unburnt coal is recovered (2TPD), waste is stored in dump yard Stored in dump yard Stored in the plant premises & off site brick manufacturing Stored in the plant premises Stored in the plant premises Stored in the plant premises Unit 2 Unit 3 30-40 0.5-1 260 5.2 Coal Coal Unit 4 Unit 5 Unit 6 2.5-3 Information not available Information not available 15 - Coal BiomassRice husk Biomass 33 Unit 7 Unit 8 Unit 9 0.02 0.2-0.5 0.6 3 6.4 15 Biomass Charcoal Charcoal Unit 10 Information not available - Charcoal Stored in the plant premises Used in bricks (offsite) Disposed offsite – road filling, construction & in villages Disposed offsite – road filling, construction & in villages Tar generation is dependent on type of fuel, reactor, size of the plant and end use. It is also dependent on gas cleaning methods adopted or degree of gas purity required. There is only one unit (Unit 2), which further processed tar in tar distillation column. The tar distillation unit is part of complex and is not attached exclusively for producer gas unit. The complex generates tar from other unit (retort) in significant quantity, which is subjected to distillation to recover phenols, tar acids, neutral oil and high boiling tar acid. These products have very high commercial value. But, tar distillation involves high initial investment and operational cost. In case of biomass gasifiers, generation of tarry waste is very less or almost nil. Summary on tar generation and disposal is presented in the table 4.6. Table 4.6 Tar generation and disposal practices Unit Fuel React or Updraft single stage Gas cleaning Water spraying system (spray header) Top gasESP Bottom gas – tar knock pot & cyclone Applicatio n Kiln heating Tar generati on 1.6 TPD Disposal / Processing Sold to authorised vendors Unit 1 Coal Unit 2 Coal Updraft double stage Retort heating & retort flue is used waste heat recovery boiler 6-10 TPD Unit 3 Coal Updraft Cyclone separator Reheat Tar generation Tar is distilled in tar distillation column to recover valuable products. This distillation unit is common for both retort tar & gas producer tar. Producer gas tar is 5-3% of the total tar distilled. None 34 Unit Fuel React or Gas cleaning Applicatio n furnace Tar generati on is almost nil as ultra clean gas is not needed NA Tarry water is generated in closed circuit, exact quantity is not known, quantity is less Nil Disposal / Processing Unit 4 Unit 5 Coal Biom assRice husk Updraft Updraft Wet cleaning Counter current wash with water, followed by dry & chemical filters Reheat furnace Power generation Sold to outside parties Thick liquor is concentrated by drying & used as domestic fuel with char Unit 6 Biom ass Downd raft Unit 7 Biom ass Updraft Venturi scrubber with water recirculatio n followed by dry filters Venturi scrubber Power generation Not applicable Reheat boiler Nil Not applicable Unit 8 Charc oal Updraft Cyclone, wet cleaning & dry filters Kiln heating Unit 9 Unit 10 Charc oal Charc oal Updraft Updraft Cyclone Cyclone Kiln heating Kiln heating Tarry water is generated in closed circuit, exact quantity is not known, quantity is less Nil Nil None Not applicable Not applicable 35 Energy balance The energy balance, and thus the thermal efficiency, of low-or mediumcapacity gasifier, depends entirely on the state (temperature, tar and oil components, etc) of the product gas. To a large extent, the end use of the gas and the characteristics of the feed will determine this state. If the hot raw product gas from a gasifier can be burned directly, the overall gasifier thermal efficiency will be high because, not only the heating value of the gas is included, but also the sensible heat contained in the hot gas. If this is the case, any tar and oils produced will be combusted along with the gas that is not cooled to allow condensation. In some cases, it is necessary to cool the gas and remove any tars and oils. However, cooling and by-product removal will lower the thermal efficiency of the process. The major energy input to a gasifier is contained in the feed material. Because invariably in the fixed bed gasifiers, there is no energy input associated with the heat content of the gasifying agent (in case of steam – it is the waste heat recovered from the reactor is used for steam generation). Electrical inputs required by the gasifier itself (for air blowing, feedwater pumps, etc) are essentially zero compared to the feed input, and constitute only a half percent or less, of the total energy input. Typical energy balances of coal based single and double stage fixed bed gasifiers are shown in Figures 4.2 and 4.3. HOT RAW GAS HOT RAW GAS COAL 100 GASIFIER 93 COOL CLEAN COLD FUEL GAS 71-75 TAR / OIL ~10 Figure 4.2 Energy balance for coal based single stage fixed bed gasifier 36 HOT RAW GAS COAL 100 GASIFIER 85-93 TAR CYCLONE OR PERCIPITATOR HOT DETARRED GAS COAL CLEAN 77-87 COLD FUEL GAS 6976 TAR ~8 OILS ~8 Figure 4.3 Energy balance for coal based double stage fixed bed gasifier 37 Chapter 5 Environmental standards for producer gas units The air emissions and liquid & solid waste discharges from producer gas units and from application ends, control measures and proposed standards, control options/ choices are discussed in the following sections. Gaseous and Particulate emissions Point sources Stack & vents from gas utilization end The stack emissions from producer gas utilization is influenced by the following factors § § § Secondary/ auxiliary fuel use Process for which gas is utilised (kiln, boiler, engine etc) Combustion device and efficiency of combustion The SPM concentrations measured in all the selected units were less than 100 mg/ Nm3. The SO2 levels form coal based producer gas utilization was significantly higher than biomass based producer gas utilization units. In all the monitored units there was no end on/ tail pipe emission control device. As producer gas is only a fuel, and there would be a significant contribution from to the emissions from the processes (kiln, furnace), especially SPM. Nevertheless, producer gas being a gaseous fuel, the contribution of SPM from producer gas combustion to the overall emission, when compared to other fuels such solid coal and biomass use is very less. The results of measurements presented in table 4.1 support this fact. The maximum SPM concentration is 98 mg/Nm3. Since industry/ process specific standard already exists (for SPM, SO2 & stack height – Table 5.1), no separate standard for units utilizing producer gas is proposed. But, in the case of SPM, industries using producer gas, more stringent standard of less than 100 mg/Nm3 is recommended. Apart from SPM and SO 2, Carbon monoxide (CO) levels were also measured. CO levels were high in some of the units and are higher in producer gas based engine emissions. The high CO emissions may be due to the high content of CO in the fuel and can– in origin – be compared with the emission of unburned hydrocarbons (UHC) from natural gas engines, thus CO emissions from producer gas engines are a measure of fuel passing unburned through the combustion. 38 Table 5.1 Emission standards for different industries Inde x Unit 18 19 24 Calcination Smelting Calcium Carbide Kiln Arc furnace Iron & SteelRolling mill (Integrated) Coke oven Refractory material plant Sensitive areas Aluminium PM CO Others Stack height mg/Nm3 mg/Nm3 255 1% 150 250 150 150 50 150 150 3 kg/ ton of coke 31 Re-heating furnaces Small boilers (12% CO2) 34 49 Lime kiln Other areas 450 Less than 2 T/hr 1600 Less than 2 T/hr 1200 2-10 T/hr 800 10-15 T/hr 600 More than 15 T/hr 150 5-40 TPD capacity 500 More than 40 TPD150 capacity Step grate 250 500 Horse shoe/pulsating grate Spreader stroker 800 Tunnel kiln 150 30(kiln+stac k) S-rate 59 Baggasse-fired boilers (12% CO2) 61 (12% CO2) Ceramic industry 64 Beehive coke oven hardNew units 150 Hydrocarbons 25 ppm Based on coal consumption & SO2 emission 20 m Research on development of gasifier-based engine is new. Currently the existing natural gas or diesel engine is modified to run on producer gas by introducing a spark plug. These initiatives have been taken recently. It is nascent field. Two out of ten units selected were using producer gas for power generation; one is 100% gas based and the other is dual fuel mode (diesel being the supplementary fuel). To promote decentralized power generation system in rural and remote areas, there is a growing interest to develop suitable engines for producer gas operation. Many issues related to low thermal efficiency, high CO emission could be resolved by efforts focused on development of new engine designs for producer gas operation. Further studies are necessary once the appropriate engine is developed. 39 Table 5.2 shows CO emission regulations for new engines operating on producer gas in different countries. Table 5.2 CO emission regulations for new engines operating on producer gas in different countries Country CO [mg/m3n] 500 300 250 650 800 650 1000 625 300 Denmark Germany Holland Switzerland1 Italy1 Italy1 Portugal Greece2 France3 Spain Belgium4 1 2 Capacity Ref. [MWth] [Vol.%O 2] 0.12-5 5 All 5 1.5-5 11 5 0-3 5 >3 5 All 5 National levels, levels can be lowered regionally. Limited emission concentration in the atmosphere at a specific location, regardless the source. For CO, this limit is 10 mg/m3 in 8-hour basis. 3 The regulations for natural gas combustion is 650 mg/m3 n @5%O2. 4 The regulation used in Belgium for emissions is the German TA Luft [5,6]. Fuel pre-treatment, emissions gasification and fugitive Three major sources were identified in monitored units, which are either from the gasifier or from fuel handling. It is not possible to quantify or to characterise these emissions and in most of the cases it can be minimised with better operation and maintenance practises. Based on field observations and ambient air & workplace environment monitoring, the sources & characteristics and control choices are given in Table 5.3. There may be instances such as start-up or shutdown of gasifier, gas utilization breakdown or stoppage; under these conditions producer gas is not utilised/ combusted. The producer gas should not be let out without flaring. Table 5.3 Sources & characteristics and control choices - Emissions from fuel pre-treatment, gasification Drying, partial Operation/Emission Gasification oxidation, and Solid fuel Source/Stream Pretreatment briquetting - Vent gases These emissions comprise OfIn addition particulateControl Characterization Summary Of to Emission dust and combustion gases control Emission Choices devices, afterburners along with a variety of may be needed to destroy organic organic compounds species. Water sprays can be used to Emissions from solid devolatilized from the control dust emissions from storage, handling, and coal/ biomass. mainly storage piles. Water sprays and crushing/sizing consist of coal/ sawdust. enclosed equipment are vented to These emissions vary from a dust capture device such as site to site depending on, baghouse to reduce or capture plant size, wind particulates from solid fuel 40 velocities, solid fuel and handling. Emissions from pile size, and water crushing/sizing are also usually content. vented to a baghouse or other particulate control device. Storage, handling, and crushing/sizing - Dust emissions Feeding - Vent gases These gases contain all the This stream could represent a significant environmental species found in the raw problem. Control could include product gas exiting the scrubbing or incineration (to gasifier including H2S, capture or destroy the most SO2, CO, NH3, tars and hazardous species), or venting oils, particulates, and to the raw product gas or trace organics and gasifier inlet air. The desired inorganics. The size and composition of this stream control depends on the type and size of gasification facility. depend on the type of gasifier, e.g., fluidized Screw fed conveyors can be used instead of lock hoppers. The bed gasifiers emit reactor can be isolated during substantially fewer tars feeding. and oils than fixed bed gasifiers. A flare can incinerate the Startup and shutdown This vent gas initially combustible constituents in the - Vent gases resembles a solid fuel startup gas, but heavy tars and combustion gas in coal particulates will affect composition. As the the performance of the flare. operating temperature of the gas increases, the Potential problems with tars and startup gas begins to particulates can be avoided by resemble the raw product using charcoal or coke as the gas. startup fuel. If the quantum of shutdown vent gas is more it has to flared. Fugitives Control methods mainly involve These emissions have not good maintenance and operating been characterized, but practices. they comprise hazardous species found in the raw product gas. Workplace standards for Carbon Monoxide: The carbon monoxide levels (8 hour average) measured in different working environment near producer gas units were between 38 - 0.4 ppm, except in one unit where the average level was 498 ppm, which had temporary operational problem. The CO levels in ambient air can be minimised with sound operational and maintenance. Exposure to CO has health effects as described in Chapter 2 of this report, work place standards for CO may be considered. Carboxyhaemoglobin (COHb) is a specific biomarker of CO exposure in blood. Endogenous production of CO results in COHb levels of 0.4-0.7% in healthy subjects. The COHb levels in non-smoking general populations are usually 0.51.5% due to endogenous production and environmental exposures. Nonsmoking people in certain occupations (car drivers, policemen, traffic wardens, garage and tunnel workers, firemen etc.) can have long-term COHb levels up to 5%, and heavy cigarette smokers have COHb levels up 41 to 10% (WHO 1999). Well-trained subjects engaging in heavy exercise in polluted indoor environments can increase their COHb levels quickly up to 10-20%. The WHO guideline values (ppm values rounded), and periods of time-weighted average exposures, have been determined in such a way that the COHb level of 2.5% is not exceeded, even when a normal subject engages in light or moderate exercise. The guideline values for CO are 100 mg/m3 (90 ppm) for 15 minutes, 60 mg/m3 (50 ppm) for 30 minutes, 30 mg/m3 (25 ppm) for 1 hour, and 10 mg/m3 (10 ppm) for 8 hours. Liquid effluents All the ten units generated wastewater, but the volume of generation differed significantly, which is dependent on § Size and type of the gasifier § Fuel Coal & biomass § Gas cleaning methods Units 1, 4, 5, 6 & 7 generated considerable volume of effluent, as it is mentioned in chapter 5, quantification of exact volume of generation is not possible, estimates were made based on the field observation and information provided by the unit operators. Only Unit 1 discharged effluents continuously; rest of the units discharged in batches and in most the cases the batch time varies between days to few weeks. In all sampled effluents the COD levels were greater than 240 mg/L and also COD level as high as 30,000 mg/L was also observed. Some effluents also contained phenols. The effluent standards for different comparable industries/ processes are shown in the table 5.2. At present none of the monitored unit has advanced treatment facilities and are disposed off with simple physical separation/ treatment. Therefore a minimum national standard for pH, oil and grease, COD, BOD and phenols is proposed. Table 5.4 Effluent standards for different industries Ind ex Unit 3 Oil refinery 4 Sugar 5 Thermal power 30 aCoke oven COD Phenol (mg/l) BOD (mg/l) (mg/l) 15 1 100/30 250 30 1 pH 6-8.5 6.5-8.5 6.0-8.0 Oil & grease (mg/l) 10 20 10 CN 0.2 42 Other wastes The tar generated if not further processed or utilized within the plant, the tarry waste is categorized as hazardous under Hazardous Wastes (Management and Handling) Rules, 1989. It comes under process type Petrochemical processes and pyrolytic operations, Hazardous waste category - 1.2 Tarry residues. This waste has to be handled and managed as per the Hazardous Wastes (Management and Handling) Rules, 1989. The options for further processing are distillation (if the volume of tar is high) and separation methods to recover fine chemicals, which are of high commercial value. 43 Chapter 6: Conclusions The response of the technology providers and the end users for the questionnaire indicated that fixed bed – near atmospheric pressure gasifiers are widely used, other types such moving bed, fluidised bed or entrained bed are absent or in the development stage. Even in the case of fixed bed only two variations exit – updraft & downdraft, in most of the cases it is single stage gasification process. Coal gasifiers installations are less and are concentrated in eastern part of India. But, biomass gasification technology and utilisation has made rapid progress in research, design and development of gasifier systems and gasifier based application packages. Keeping in view the promise of biomass for supplementing the energy needs, particularly in rural areas, the Ministry of Non-conventional Energy Sources (MNES) has formulated a broadbased program in the area of Biomass Gasification Technology and Utilisation. Biomass fuels differ greatly in their chemical, physical and morphological properties; they make different demands on the method of gasification and consequently require different reactor designs or even gasification technologies. It is for this reason that, a large number of different gasifiers has been developed and marketed, all types geared towards handling the specific properties of a typical fuel or range of fuels. Also, the requirements of different consumers are often different, the design, size and characteristics of the gasifier may vary from customer to customer, even if the same gasifier is used. Therefore, even though the gasifier is a relatively simple ‘core technology,’ the effectiveness of its utility for any particular application and context depends on the design of the gasifier being tailored to the available solid fuel – charcoal or biomass resource and on the customization of the overall energy system. Thus there exists significant diversification. The MNES has come up with a document that spells out the minimum requirements for the manufacturers to follow and the codes and standards, system specifications, operating and maintenance procedures, performance guarantees, list of items supplied and user site layout requirements for safety for the system. This document also details the qualifying and acceptable performance levels, testing and performance evaluation procedures for biomass gasifiers and gasifier-thermal systems. The manufacturers and the users should adhere to the minimum requirements and standards as detailed in the document titled “Qualifying, Testing and Performance Evaluation of Biomass Gasifiers and Gasifier-Thermal Systems” End use There are two major end use of producer gas i.e. power generation and thermal application. Producer gas is used to fuel external burners to produce heat for boilers, dryers, ovens, or kilns. Thermal application is well established, but producer gas based engines for power generation is in the primitive stage. Currently the existing natural gas or diesel engine is modified to run on producer gas by introducing spark-ignition. Spark-ignition engines can be 44 operated on producer gas only. Diesel engines, however, must be operated on mixtures of diesel fuel and producer gas (dual-fuel). The temperature of the gas influences the power output of a producer-gas engine. Highest power output is realized at lowest gas temperature. Thus, in power applications, gas is cooled before application. Cooling, however, allows vaporized tars in the gas to condense on engine parts such as inlet manifolds and valve stems. Also, soot and ash particles in the gas may form deposits in the engine. These phenomena will result in excessive engine wear and tear, so in power applications, it is absolutely necessary to filter and clean the gas of soot, ash, and tar. To design a proper engine for dual-fuel and producer gas mode operations, one will have to optimize the air fuel ratio, compression ratio and ignition timings. This is a subject that needs to be studied by the concerned agencies. In addition other problems like de-rating (loss of power), low conversion efficiency, speed control, knocking and engine life are to be addressed. These problems could be solved if efforts are made for the development of reliable and efficient engines for producer gas. Environmental and safety Gasification systems produce solid, liquid, and gaseous wastes, depending on type of gasifier and solid fuel used for gasification. Environmental issues pertain to emission levels of exhaust gases and wastewater treatment and tar handling. Gasifiers are closed systems; gaseous emissions from gasifiers are not a significant factor except possibly in the immediate vicinity of the plant, where there is possibility of CO leakages. Water is used for scrubbing the gas and cooling, water seal and if the tar levels in the gas are very high (especially for updraft gasifiers), highly polluted wastewaters are produced. Chemical oxygen demand (COD) levels of up to 30,000 mg/lit have been observed in wastewaters from gasifiers and these waste streams are generally not treated at present. Apart from the above specific issues, following general features may also be considered for technology. § Solid wastes are primarily residue ash. The amount produced may vary between 1 and 40 percent, depending on the solid fuel. In most cases, disposal of this ash is not a problem, and in some cases, such as rice husks, the ash may have value for use by other industries. The quantity of trade effluents produced, depends on the type of gasifier and end use of producer gas. The situation exacerbated if wet-gas cleaning systems are used, which can increase the volumes of contaminated trade effluent. In all cases, the effluent COD is high, which has to be treated before disposal. The problem is not acute in the case of gasifiers used for thermal applications, because such systems usually § 45 combust the producer gas completely that is, inclusive of the tarry components, which are gaseous at higher temperatures. Some important industrial safety issues pertain to exposure to high temperature surfaces, exposure to CO emissions, and prevention (and control) of explosions and backfires. The first item requires good design of the insulating system and the last two items require good instrumentation and control. Especially if the gas is burning inside a vessel (such as a furnace or a drier), there is a strong possibility that the flame might extinguish during the operation and with the blower on; combustible gases will accumulate in the closed space. So when the burner is restarted, explosion may take place. A control mechanism that stops the blower if the flame extinguishes or a pilot injection, which will always allow the gas to burn, is thus highly desirable. Similarly when people are working in restricted spaces and if leakage of gases occurs, they will be exposed to dangerous emissions. It is required that CO alarms be installed in such situations. Operation and maintenance Technological aspects of producer gas generation are simple but the control aspects are very critical and negligence in any area of control, like selection of the appropriate feedstock with acceptable analysis and ash fusion point, maintaining the optimum blast saturation on temperature, feed control, air blast control, ash discharge optimisation, maintaining the required fuel bed temperature, tar and dust separation system may invite immense problem. Good operation and maintenance practices are summarised below: Use of appropriate feedstock The technology providers indicate that in many cases the end users are not following the given fuel specifications. The end user should adhere to feedstock size and moisture content specifications as these two parameters are ignored frequently. If necessary appropriate feed-sizing equipment should be used so that feedstock meets the specified size. Depending on the fuel type and variation in fuel quality, routine analysis of fuel for physical and chemical properties, should be an integral part of gasifier operation. Operation of gasifiers There are several problems associated with gasifier operations such as starting problem, bridging and clinker formation, build-up of ash on the grate (especially for high ash fuels like rice husk), interruption in stable and continuous gas production of gas. Therefore proper design and good operation and maintenance practices play critical role. As gasifiers are high temperature reactors and the resulting gases are corrosive in nature, it is quite logical that many kinds of material problems occur and questions about the lifetime of the various components keep arising. Some attempts have been made to analyze these problems but there are no standard material selection procedures or codes to be followed. Any future attempts of 46 technology or component standardization should include a thorough study of the suitability of different materials for different parts of the gasifier system. Typically, the operating personnel would monitor and control the following variables: • • • Fuel feed - optimum feed rate should be maintained. Gasifying agent – air and or steam optimum feed rate should be maintained Ash bed depth – In fixed bed units, the depth of the ash bed serves two purposes: o Distributing and heating the gasifying agents, and o Protecting the grate on which the bed sits from the heat generated in the combustion zone. o This depth should be controlled by the rate of ash removal and ensuring proper working of ash withdrawal system. Some gasifiers resort to poking to ensure smooth flow of solid fuel. Poking the fuel bed in the gasifier is a very important operation. Do not allow fuel bed to move up. If the fire moves up, it requires a long time to normalise the producer. Proper sealing of the poke holes is must as the operators are exposed to high CO levels due to leaks. The emissions from the poke holes should be vented out using blowers or exhaust fans. Ensure the functioning of all trips & alarm along with all other instruments & control systems. Check the gas composition & Calorific value of the gas regularly. Install automatic Calorific value and gas analyser for the purpose. Wide variation in the Calorific value of gas will upset the temperature conditions at the user's end. High CO2 content in producer gas indicates abnormality in the gasifier and therefore corrective steps should be taken to ensure normal operation. The solid fuel/char loss in bottom ash/cinder should be checked regularly. Efforts should be made to maintain it at minimum level. Never vent producer gas without flaring/burning. All safety norms that are applicable, whether these are for the plant or for the persons, should strictly followed. Operators would be required to monitor key parameters continuously. • • • • • Training of operating personnel The labor necessary for operating a gasification plant is considerably different from other systems. This difference is both quantitative and qualitative. During operation, the gasifier operator must frequently check a number of temperature and pressure meters and, based on this information, make decisions on actions such as adding new fuel, shaking the grate, deblocking filters, and adjusting valves. At the end of daily operation the operator must normally clean reactor and filters from ash and dust. Finally, the operator may be also in charge of fuel 47 preparation and fuel quality control. Thus, unlike diesel engine operations in which the engine driver may also be given other, unrelated tasks, the running of a small-scale gasification system is basically a full-time job. Health and Safety Operation of gasifiers may result in exposure to toxic gaseous emissions (i.e., carbon monoxide); fire and explosion hazards; and liquid effluents. § Avoiding poisoning by toxic gases is mainly a matter of following sound workplace procedures, such as avoiding inhalation of the exhaust gas during start-up and ensuring good ventilation of gas-filled vessels before personnel enter them for service and maintenance. In addition, such an atmosphere is also likely to present a lethal toxicity hazard from carbon monoxide so suitable detectors should be fitted. Avoiding fires and explosions is also primarily a matter of following sound procedures. A source of ignition is necessary for an explosion, so explosion proof or flame proof or spark proof motors would be specified in any such areas. Smoking should be strictly prohibited in the vicinity of Producer Gas Plant. Avoiding contact with condensates, which requires the use of protective gloves, clothing, or both. § § § From the above, it may be concluded that with proper operator training, equipment and procedures, health and safety hazards can be minimized or even eliminated. 48 Brief description of Units selected for monitoring Ten units were selected based on field observation, fuel use, capacity of units (thermal & power) and end-use. Description of these units is given below. Refractories, Belpahar – Unit 1 Unit1 is located Orissa. Unit 1produces shaped and unshaped refractories using Magnesite, Dolomite, Chromite, High Alumina products and Silica products. These raw materials are crushed and grounded to required sizes, and then the sized fractions are mixed proportionately with additives & binders. After mixing, the mixture is pressed to give shape to refractories. The pressed material is then dried and fired/tempered in kilns as per the requirement to attain the desired properties. Producer gas is used as fuel for firing in tunnel and gas ring kilns. Unit 1 during monitoring period had three producer gas units and the fourth one was under construction. Gasifiers are single stage, extended shaft, double off take with rotary grate. Details of these units are given in the table below Unit Year of commissioning Capacity GP3 April, 2004 1800 nm3/hr GP8 April, 2004 2000 nm3/hr GP9 October, 1999 1800 nm3/hr Grade C coal is used in the gasifier and approximately 60 TPD coal is gasified. Coal is supplied by MCL (Coal India Limited). The size of coal used is between 20mm and 40 mm. Sieves shakers are used to separate the fine and coarse size. Producer gas is passed through water spraying system to separate dust and tar. Cleaned gas is supplied to different kilns through common header as shown in the figure below. G R K 2 GP9 (3000 nm3/hr) G R K 3 200 S (nm3/ D hr) R S T H 1000 3 K (nm / hr) 900 (nm3/ hr) 900 (nm3 / hr) 200 (nm3/ hr) B T M K GP3 (2000 nm3/hr) GP8 (1800 nm3/hr) 1200 (nm3/ hr) F T K 1 1000 (nm3/ hr) F T K 2 800 (nm3/ hr) S K 2 200 (nm3/ hr) D R Y 1 300 (nm3/ hr) D R Y 2 100 (nm3/ hr) D R Y 3 49 Coal Complex, West Bengal – Unit 2 Unit 2 is located in Hoogly district, West Bengal. Unit 2 has double stage producer gas plant (4 nos. working and 1 as stand by) of 3.6m dia (each) used to generate adequate gas at 200 C to heat the Continuous Vertical Retorts (CVR). CVR is used to Carbonise 1500 tonnes of non-caking Coals brought from Raniganj Coalfield. A fraction of the same Coal (-40 +25m) is used in the producer gas plant. The average C.V. of Coal varies from 5400-5600 K.Cal/Kg (gross). Moisture content in the Coal ranges from 5-6%, ash 20-23%, and V.m 29-32%. The quality of the gas is good (CV around 1650 K.Cal/NM3 gross). Table below gives some indication about the inputs and outputs of the Unit 2 producer gas plant. SI 1 2 3 4 5 6 7 8 9 10 11 Parameter Diameter of producer 3.6m (4 working, 1 stand by) gas unit Coal input 260 TPD, (65 TPD per producer gas unit) Air input 2 kg/kg Coal (dry) or 1.56 Nm3/ kg Coal dry Steam with blast 0.35 kg/kg Coal dry or 0.175 kg/kg dry air GCV of Coal 5400-5600 kcal/kg Coal loss in cinder 10% Top gas volume (wet) 1.15 Nm3 /kg of Coal Bottom gas volume 1.60 Nm3 /kg of Coal (wet) GCV of producer gas 1600 kcal/ Nm3 Heat generation in one 9x106 kcal/hr producer Tar 6-10 TPD The gas cleaning plant consists of the following units(a) Cold gas cleaning (i) Tar knock out pot one for each producer. Operating temp. 120-130 C for a gas flow of about 2000-2500 NM3/hr. (ii) Electrostatic Tar precipitator (ETP) - 2 nos. Both working and are common to five producer gas plants. Gas flow total - 10,000 Nm3/hr (in two) gas entering at 80-120 mm W.G. (b) Hot gas cleaning (i) Dust cyclone - one in each producer , Dry gas in 3400-3700 Nm3/hr in each operating temp. 620 - 650 C Hot gas & cold gas mix at one point and then go the retort flues at 200-220 C (5mm W.G. pressure in gas main inlet to CVR). The flue gas from retorts is used in the waste heat boilers to recover the waste heat. 50 Steam required for blast saturation is taken from the water jacket boilers attached to each gas producer via steam drums. Steam is produced at the rate of 0.976/hr/producer at 2.5 Kg/cm2. The requirement of steam by each producer is about 0.77 Kg. There are 3 air fans (2 working & 1 stand by) each having normal discharge capacity of 7000 Nm3/hr at a normal pressure of 400 mm W.G. The four producer gas plants require about 13,800 Nm3 air per hour (each producer requires 3450 Nm3/hr air) to produce about 25,750 Nm3 gas (each producer producing about 5,150 Nm3/ hr gas). Steel re-rolling mill, Raipur – Unit 3 Unit 3 is located in Urla Industrial area of Raipur. It produces re-rolled steel. Raw material is re-rolled in reheat furnace; producer gas along with furnace oil is used in furnace heating. Unit 3 has one single stage; rotary grate updraft producer gas unit with a capacity of 1250 nm3/hr. Grade E coal from Korba mines is used as feedstock for the gasifier. The size suitable for gasification falls in between 25 to 40 mm. Coal consumption in gasifier is in the range of 450-600 Kg/hr. The GCV of producer gas is 1200-1300 Kcal/Nm3. Producer gas is burnt in the reheat furnace to attain temperature close to 11000C, furnace oil is fired as supplementary fuel to reach the desired temperature. Steel Industries, Raipur – Unit 4 Unit 4 is located in Urla Industrial area of Raipur. It produces re-rolled steel. Raw material is re-rolled in reheat furnace; producer gas is used in furnace heating. Unit 4 has one single stage; rotary grate updraft producer gas unit with a capacity of 1600 nm3/hr. Grade E coal from Korba mines is used as feedstock for the gasifier. The size suitable for gasification falls in between 25 to 40 mm. Coal consumption in gasifier is in the range of 600 -700 Kg/hr. The GCV of producer gas is 1200-1300 Kcal/Nm3. Single producer gas unit satisfies the heat requirement of two reheat furnaces. Producer gas is burnt in the reheat furnace to attain temperature close to 11000C, furnace oil is fired as supplementary fuel to reach the desired temperature. Rice mill, Burdwan – Unit 5 A 350 kWe biomass gasifier system with rice husk as fuel, installed by Grain processing industries (I) pvt., ltd Unit 5, Burdwan, 150 km from Kolkata. The gasifier at Unit 5 - Modern Mini Rice Mill is an updraft one. Both steam and air are used as gasification agent. The Feeding material is a mixture of husk and immature paddy. The average diesel replacement is about 75 to 80% at full load condition. In addition to these, a good amount of tar has also been collected as a by-product. The flow diagram of gasification and gas-cleansing system is shown below. 51 Blow down sump Water Water storage (Settling & re-circulation) Water spray tower (Wet cleansing and gas cooling) Rice husk conveyer Chemical conditioningneutralization- (Bubbling with alkaline solution) Dry filtration (Filter material-coke) Condenser (tar removal) Updraft Gasifier Blower Tar Safety water seal and storage tank Ash Air & steam blower Dry filter (Filter materialPVC plastic, rubber pipes/covers Cyclone Dry filter (MaterialCoir) Oil bubbling Emissions Fabric filter (0.9 micron) Water condensation column Engine- Power generation Diesel Technology provider & research & development organisation , Vadodara– Unit 6 Unit 6 has 100% producer gas based engine at its factory in Savali. Biomass gasifier is downdraft and it has extensive gas cooling & cleansing system. Woody biomass is used as feedstock for the gasifier. Approximately 1.4 to 1.6 Kg of woody biomass is required for generation one Kwh electrical energy. Both wet and dry methods (dry predominant) are adopted for gas cleaning. The rated electric output of the producer gas based engine is 100 kW. Industrial gases, GIDC Por, Vadodara – Unit 7 Industrial Gases plant has Carbon-di-oxide generation unit and has installed a biomass gasifier for its thermal application. The producer gas generated is used as a fuel in the reheat boiler. The flue gas coming out of the boiler is the source for CO2. A selective absorption solution Mono-ethanol Amine (MEA) absorbs CO2 through chemical reaction in an absorber column. Since the reaction is reversible, the CO2 can be stripped- off by heating the CO2-rich amine in a separate stripper column. The MEA is recycled through the process. Chemical absorption is the most suitable method for the separation of CO2 from exhaust gases, when carbon dioxide has a low concentration (5-15% by volume) in a gaseous stream at atmospheric pressure. 52 The separation process of carbon dioxide by chemical absorption consists of two steps: 1. The absorption of CO2 by chemical solvents at a low temperature (40-65°C) 2. The recovery of CO2 from chemical solvents by using low-grade heat (a temperature in the range of 100-150°C), Absorption reaction: 2MEA+CO 2 PCO2 = K MEAH+ MEACOO-+MEAH+ MEACOO/ MEA 2 In the MEA process CO2 from the exhaust gas reacts with aqueous solution of MEA in a contacting device, usually an absorption tower at a pressure slightly above the ambient pressure and at a temperature depending on the exhaust gas upstream. First, they are compressed to about 1.3 bars, to overcome pressure drops within the system, and cooled to nearly 50°C. Then, the gases go to the absorption column where the carbon dioxide binds to the solvent chemically. The rich solution (i.e. the solution containing the absorbed CO2) flows to a lean/rich heat exchanger: here the hot lean solution, coming from the stripper column (regenerator), cools itself giving out its heat to the rich solution, which then goes to the regenerator. Here the solvent is regenerated by heat where the chemical bonds are decomposed thermally. The CO2 and water vapour leaving the stripper is next cooled and essentially pure CO2 leaves the separation plant for further treatment (in this case compression and drying). The profile of the CO2 plant and biomass gasifier is shown below. § Gasifier installed in the year 1994 and operational for the past 10 years § Gasifier – Down draft- 120 kg/hr § Fuel consumption 3 TPD woody biomass § Water consumption for cooling and condensing 10 KLPD § Ash generation 16 kg/ day. Ceramics, Morbi – Unit 8 Unit 8 is located in Morbi, near Rajkot. There are many producer gas units in this area, most of which cater the thermal energy requirements of kilns. Unit 8 has installed two producer gas units (Unit8 PG1 & Unit8 PG2); both are updraft, rotary grate with a capacity of 160 kg/hr and 120 kg/hr (charcoal feed rate). Producer gas generated from charcoal based gasifier is used in heating tiles in tunnel kilns. The gas generated from one unit is distributed among two biscuit tunnel kilns and from the other unit; it is supplied to one glazed tile tunnel kiln. The kiln temperature as high as 1100 deg C is achieved with the help of producer gas combustion in kilns. Producer gas is cleaned and cooled with wet and dry cleansing system to eliminate tar and particulate matter. The gasifier is supplied by Radhe Renewable Energy Development Associate (RREDA). Calcium Carbonate Industries, Poanta Sahib – Unit 9 Unit 9 manufactures Calcium Carbonate (CaCO3) from limestone. The CaCO3 production capacity of the industry is around 55 TPD. Unit 9 has installed an updraft charcoal based producer gas unit of capacity 20 TPD. Approximately 53 60% of producer gas is used for heating in limekiln and the remaining 40% for product drying. Charcoal obtained from Trichy (Southern India) has 80-85% Carbon and 4-6% ash. The producer gas technology is German- ModifiedLurgi. Calcium Carbonate Industries, Poanta Sahib – Unit 10 Unit 10 manufactures Calcium Carbonate (CaCO3) and PCC from limestone. Unit 9 has installed an updraft charcoal based producer gas unit of design capacity 8 TPD. Currently it operates in the range of 6-2 TPD depending on heating requirement. Charcoal obtained from Trichy (Southern India) has 8085% Carbon and 4-6% ash. The producer gas technology is provided by Sharanpur engineering Works Pvt. Ltd, Roorkee, UP. Technology Providers of Biomass Gasifier Ankur Scientific Energy Technologies Private Limited Ankur Scientific Energy Technologies (ASCENT) was set up in the year 1986 by Dr. B.C. Jain. Ankur’s involvement in the area of biomass gasification started with its participation in the National Programme for Demonstration of Gasification Technology launched by the Government in 1987. Ankur installed about 185 systems in the first phase of this program, of which about 150 were for irrigation pumping and the rest for power generation (mostly 20 kW and 40 kW). In the second phase of the demonstration program initiated in the first half of 1990 and which lasted for two and a half years, another 165 systems were installed with 133 of them being for pumping applications and the rest for power. After 1990, the company shifted its focus to development of largercapacity gasifiers, i.e., around 100 kW. At present, the company has the capability to build single unit sizes of 500 kW capacities. Ankur has concentrated on the development of downdraft biomass gasification systems. The present aggregate capacity of gasifiers it has installed stands close to 20 MW, which gives it a market share of around 60 to 65 percent. More than 80 percent of Ankur’s gasifiers are installed for power, while the rest are for thermal applications – this includes chemical industries, brick kilns, ceramic tiles, annealing of tubes, biscuit factory, and tea and coffee drying. Thermal applications are mainly in the states of Gujarat, Rajasthan and Maharashtra. Ankur’s technical development efforts have been mainly directed towards improvements in performance and system reliability as well as increasing process automation of gasifier-based systems to ensure their continuous operation. Ankur has also been developing, with internal funding, gasifiers in the capacity range of 4 to 10 kW for power generation based on 100% producer gas, primarily for rural area applications. The gasifiers are capable of handling woody biomass, cotton stalk and corn cobs. System packages have been developed for irrigation pumping (5-10 hp) and thermal applications (cooking, small cottage industries, etc.). It is also involved in the development of 100% producer-gas-based systems in the capacity range of 30 kWe and 54 above. These systems are being developed through a collaborative R&D project jointly funded by MNES and Ankur. The systems are currently based on naturally-aspirated Cummins engine, but work is going on in adapting turbocharged and after-cooled engines to run on producer gas. Yet another area of development in 100 % producer gas based systems is coupling of the gasifiers to high-speed gas turbines. As part of a collaborative research work with a US based partner, a 200 kW gasifier has been shipped to test run high-speed turbines on producer gas. DESI Power/NETPRO Decentralised Energy Systems (India) Pvt. Ltd. (DESI) Power was set up in 1995 with an objective to promote decentralized power stations based on renewable energy. It is a joint venture between Development Alternatives (DA), TARA and DASAG India, not-for-profits working in the field of sustainable technologies. DESI Power is licensed to use the gasifier technology developed at IISc, Bangalore. The licensed manufacturer of IISc technology is NETPRO Renewable Energy (India) Ltd. (NETPRO), which is a sister concern of DESI power. NETPRO was set up in 1994 to design, manufacture and supply biomass gasification plants in association with IISc and DASAG Energy Engineering. DASAG, a Swiss company, was the original licensee of IISc for the 100 kW range and undertook the re-engineering and design improvements of the gasifier based power plants. In addition, DASAG coordinated the development, pilot, and field-testing activities in India and Switzerland and undertook the technical and financial packaging of projects for the commercialisation of the technologies. NETPRO is one of the approved manufacturers listed by MNES. NETPRO also assists in marketing of the technology and provides performance guarantee to the users. DESI Power focuses on local decentralized energy services provision. Its orientation is towards promoting, packaging, building, and ultimately transferring power projects to local ownership, and generally receives external funding support for setting up these projects. DESI Power aims to supply electricity and energy services to two distinct decentralized energy markets – captive power plants for small-scale industries and institutions, which depend on diesel generators; and Independent Rural Power Producers (IRPPs) for villages and semi-urban areas. DESI Power is following the EmPower (Employment and Power) model that intends to provide electricity and energy services to villagers and rural enterprises using a cluster approach. Here the cluster is formed by a number of power plants and linked micro-enterprises in neighboring villages, and the target is to build a capacity of at least a MW in geographical proximity so that that each group generates an adequate financial base to maintain the ‘cluster center.’ Seven DESI power projects based on biomass gasification technology have also been set up under the Actions Implemented Jointly (AIJ) mechanism. The objectives of these AIJ projects are to demonstrate and quantify carbon emission reductions. Almost all of DESI Power/NETPRO’s projects have been 55 on a non-commercial basis and have been supported by external grants from donor agencies and foundations, government subsidies and internal funding. Indian Institute of Science The technology development efforts in the area of biomass gasification at the Indian Institute of Science (IISc) began in 1979. The group’s initial efforts, focusing on low power gasifiers, resulted in the development of an open-top gasifier based on a laboratory model of Reed and Markson. Engineering inputs from design of cleaning/cooling systems of existing closed-top designs were integrated into the new open-top design and the IISc gasifier system with twin stainless steel shell was eventually developed into the “Mark I’ product for operation with diesel engines. Most of the initial experience at IISc was gained in the development of 3.7 kWe systems for electrical generation and mechanical drive. This development program received a boost by the introduction of a National Programme for Biomass Gasification. IISc was also designated as a Gasifier Action Research Centre (GARC) by the MNES and hence undertook a number of research projects under its sponsorship. The gasifier design ultimately developed at IISc is of the ‘open-top reburn throatless downdraft’ design. The open-top design enables adjustment of the reaction zones by air feeding and gas generation with very low tar content. The gasifier is also designed to handle a variety of feedstock – weeds, coconut shells, sawdust briquettes, rice husk briquettes and cane trash briquettes. There are over 30 units of power gasifiers based on IISc Technologies in India and three units outside India (one in Switzerland and two in Chile). The first field demonstration of decentralized power generation using wood gasification technology developed at IISc has been in operation in a village in southern India called Hosahalli in the southern state of Karnataka since 1988. The aim of the project was to demonstrate the techno-economic feasibility of energy forestwood gasifier based system for meeting the lighting and shaft power needs of non-electrified villages. The design was at its developmental stage during the experiment and therefore it served the purpose of monitoring the performance of the gasifier. The second field demonstration of rural electrification was in 1996 in a neighbouring village. The execution of these projects was by ASTRA (Application of Science and Technology to Rural Areas) at IISc. IISc gasifiers have also been utilized in a number of thermal applications. Current ongoing R&D activities at IISc include a focus on utilization of a variety of agro-residues in briquette form for gasification. Work is also underway on the development of 100 % producer gas systems as is an effort on advanced gasification (high pressure gasification at elevated temperature) under an MNES-sponsored project with Bharat Heavy Electricals Limited – this is for a 100 % producer gas system coupled to a gas turbine. 56 Radhe Renewable Energy Development Pvt. Ltd Radhe Renewable Energy Development Pvt. Ltd. is the core company of the Radhe Group of Companies located at Rajkot, Gujarat, India. The group’s main line of activity is, research, development, manufacturing and marketing of nonconventional & renewable energy equipments, i.e. Briquetting plants, biomass gasifiers & fluidized bed furnace/gasifier. The firm has been active in the field for over a decade. It has installed many updraft gasifiers with capacities ranging between 10,00,000 to 60,00,000 K.Cal/Hr. Gasifier Plants are installed in various industries like Ceramics Industries, Rolling Mills, Sodium Silicate, Precipitated Silica and Chemical Industry at Morbi, Himatnagar & at other places. The Energy and Resources Institute (TERI) TERI researchers were first trained on gasifiers at the Jyoti SERI in 1982 – these were the first group of people trained there. The researchers came back and constructed a 5 horsepower gasifier in 1984 at TERI’s Field Research Unit (FRU), then at Pondicherry. This effort was funded by TERI, with the FRU providing the hardware component as well as manpower. In 1985, TERI consolidated its offices and moved them to Delhi. TERI researchers built another gasifier there and also set up an effort focused on characterization of biomass and studies on gasifiability of different fuels. About this time, TERI also undertook a study to develop a renewable energy plan for the Andaman & Nicobar and Lakshadweep islands for the Planning Commission that included a focus on gasifiers. It also undertook a study to evaluate the potential of gasifier systems for the plantation industry. Simultaneously, it carried out a study funded by FAO to evaluate the potential of biomass briquetting. TERI started work on a series of project in the latter part of the 1980s. It began a project with Department of Science and Technology (DST) funding on efficient use of biomass in cardamom curing. It also received a project from MNES to develop a 7kW non-wood gasifier system for mechanical and electrical applications. The field-testing of this system was carried out in the village Dhanvas in Haryana. To overcome difficulties in handling different agroresidues, TERI developed an integrated briquetting-gasifier system. TERI did not put any systems in the field during the MNES irrigation-power gasifier program since they did not feel that the gasifiers were ready yet for implementation, as a number of issues still needed attention, especially tar and materials problem. TERI subsequently engaged on a project to scale their gasifiers up to 40kW, which they felt was the minimum scale for economic viability, following on their Dhanvas experience. A 50 kW gasifier system currently provides electricity to the TERI RETREAT for training. TERI was one of the first institutes to develop and test a small (5 kW) 100%-producer-gasengine system. A second prototype is currently being tested and will be deployed to a remote village in Orissa for a joint field-testing with Gram Vikas, an NGO with substantial experience in the area of village-level development. 57 In 1994, with support from the Swiss Development Cooperation (SDC), TERI launched a program for inducting gasifier systems into the silk industry. Several types of gasifier based silk reeling ovens and silk dyeing units were developed, field-tested, and disseminated. At the same time, a collaborative project with ISPS (Indo-Swiss Project, Sikkim) launched gasifier-based systems for cardamom curing. Initial successes with these thermal applications led to several other applications throughout the country, such as rubber drying, institutional cooking, brick drying, and crematoria. TERI licensed its designs to 6 different manufacturers who have installed a cumulative capacity of about 10 MW(th) so far. 58 Glossary Gasification A process in which biomass, coal (usually dry) is converted into a mixture of gases consisting of combustible gases (mainly hydrogen, carbon monoxide and methane), non-combustible gases (nitrogen, carbon dioxide), and water vapor. Gasifiable Material Sized, relatively dry, Coal, firewood (prosopis juliflo ra, eucalyptus, casurina, acacia, neem wood,mango wood, etc); wood-like materials such as corncobs, lantana (a wildly-growing weed),Ipomea, mulberry sticks; coconut shells, cashew shells, biomass briquettes, and rice husk. Most naturally available biomass materials have similar elemental composition (C,H,O) on an ash-free and moisture-free basis. Hence all these materials can be gasified in suitably designed reactors (gasifiers). Gasifier A reactor in which coal/biomass can be converted through a thermo-chemical reaction under controlled conditions, to yield an uninterrupted flow of producer gas. Air (or oxygen) required for gasification is generally fed into the gasifier either through a blower or by creating suction from the downstream side of gas exit. After ignition, the various zones in the gasifier attain certain equilibrium temperatures, after which both the production rate and quality (composition, etc.) of the producer gas become steady. Several types of gasifiers exist: fluidized bed gasifiers, entrained bed gasifiers, circulating fluidized bed (CFB) gasifiers, and moving bed gasifiers. The first three types are generally used for large-scale industrial applications and for pulverized coal or similarly sized biomass (e.g., rice husk). Producer gas The mixture of gases produced by the gasification of organic material such as biomass at relatively low temperatures (700 to 1000ºC). Producer gas is composed of carbon monoxide (CO) and hydrogen (H2) plus carbon dioxide (CO2) and typically a range of hydrocarbons such as methane (CH4). Producer gas can be burned as a fuel gas such as in a boiler for heat or in an internal combustion gas engine for electricity generation. Pyrolysis This is the process in which heating of the biomass at high temperatures (usually in the range of 350-450 ºC) results in the production of a mixture of gases, volatiles and vapors (termed ‘pyrolysis gases’) 59 Annex 4.3 Ambient air quality monitoring S.no Produc er gas unit Unit 1 Location SPM (µg/m3) NA 203 NA 407 491 478 389 NA 422 NA 395 128 51 67 39 59 63 33 763 NA 439 462 NA 390 RSPM (µg/m3) 131 NA 131 358 366 NA NA 214 NA 264 NA NA NA NA NA NA NA NA NA 582 NA NA 654 NA SO2 (µg/m3) 7 6 3 3 3 3 18 7 6 7 19 12 45 33 32 44 40 88 3 3 25 3 3 3 NO 2 (µg/m3) 9 15 26 50 26 46 51 24 15 13 47 21 31 NA 53 NA 42 44 30 24 40 23 29 81 1 1A 2 1B 3 1C 4 Unit 2 2A 5 2B 6 2C 7 Unit 3 3A 8 3B 9 Unit 4 4A 10 4B 11 Unit 5 5A 12 5B 13 Unit 6 6A 14 6B 15 Unit 7 7A 16 7B 17 Unit 8 8A 18 8B 19 Unit 9 9A 20 9B 21 9C 22 Unit 10 10A 23 10B 24 10C NA – Not Available 60 Annex 4. 4 Workplace monitoring S. No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 SI 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Unit Details of work place Max Unit 1 Gasifier – top floor Gasifier – mid floor Gasifier – First floor Gasifier poking floor Gasifier ash pan floor Near gasifier Near gasifier Near gasifier Near engine Producer gas & engine area Near gasifier Near gasifier Near kiln area Near gasifier Near gasifier Near kiln area Unit Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 Unit 9 Unit 10 2000 1180 49 57 101 21 38 119 43 140 87 5 235 369 596 152 CO (ppm) Min Avg (8 hrs) 0 468 0 13 0 0.4 0 10 0 0.5 3 15.6 0 0.5 0 0 0 25 0 0 0 0 0 0 3.3 2 7 38 16 3 Unit 2 Unit 3 Unit 4 Unit 5 Unit 6 Unit 7 Unit 8 Unit 9 Unit 10 Workplace description Producer gas unit Coal loading area Poking area Retort charging area Near furnace Near producer gas unit Coal preparation area Near gasifier Near engine Near producer gas unit Near lime kiln Near producer gas unit Near lime kiln Dust level (µg/m3) 986 5164 222 335 187 830 780 127 97 1056 586 844 344 61 CO (ppm) CO (ppm) 1000 1500 2000 2500 500 0 10 20 30 40 50 60 0 15:12:23 16:12:23 14:58:04 16:09:04 17:18:23 17:20:04 18:31:04 19:42:04 20:53:04 22:05:04 23:16:04 23:55:04 0:20:04 0:46:04 1:24:04 time 2:09:04 2:46:04 3:46:04 4:23:04 5:16:04 6:20:04 7:31:04 8:42:04 9:53:04 11:04:04 12:21:04 13:38:04 14:51:04 18:23:23 19:27:23 20:27:23 21:27:23 22:27:23 23:27:23 0:27:23 tim e 1:27:23 2:27:23 3:27:23 4:27:23 5:27:23 6:27:23 7:27:23 8:27:23 9:27:23 10:27:23 Workplace CO measurement - unit 1 (Near producer gas unit) Wor kplace CO m eas ure m e nt - unit 1 (Ne ar produce r gas unit) 62 CO (ppm) 10 20 30 40 50 60 0 11:18:36 1000 1200 1400 CO (ppm) 11:40:36 12:02:36 12:24:36 12:46:36 13:08:36 13:30:36 13:52:36 14:14:36 14:36:36 14:58:36 15:20:36 time 15:42:36 16:04:36 16:26:36 16:48:36 17:10:36 17:32:36 17:54:36 18:16:36 18:38:36 19:00:36 19:22:36 19:44:36 20:06:36 200 400 600 800 0 15:11:24 16:15:24 17:19:24 18:23:24 19:27:24 20:31:24 21:35:24 22:39:24 23:43:24 0:47:24 1:51:24 2:55:24 3:59:24 5:03:24 6:07:24 7:11:24 8:16:24 9:20:24 10:24:24 15:05:24 tim e Workplace CO measurement - Unit 2 (Near gasifier unit, poking floor) Workplace CO m e as ure m ent - unit 1 (Near produce r gas unit) 63 CO ppm 100 120 20 40 60 80 CO-ppm 0 11:15:08 11:37:08 11:59:08 12:21:08 12:43:08 13:05:08 13:27:08 13:49:08 14:11:08 14:33:08 14:55:08 15:17:08 time 15:39:08 16:01:08 16:23:08 16:45:08 17:07:08 17:29:08 17:51:08 18:13:08 18:35:08 18:57:08 19:19:08 19:41:08 20:03:08 10 15 20 25 0 5 10:20:05 10:34:35 10:49:05 11:03:35 11:18:05 11:32:35 11:47:05 12:01:35 12:16:05 12:30:35 12:45:05 Workplace CO measurement - Unit 3 (Near producer gas unit ash pan) Workplace CO measurement - Unit 3 (Near producer gas unit) 64 12:59:35 time 13:14:05 13:28:35 13:43:05 13:57:35 14:12:05 14:26:35 14:41:05 14:55:35 15:10:05 15:24:35 15:39:05 15:53:35 16:08:05 CO (ppm) 20 15 10 30 25 40 35 5 0 CO(ppm) 8:05:28 120 140 160 100 20 40 60 80 0 8:23:28 8:41:28 8:59:28 9:17:28 9:35:28 9:53:28 10:11:28 10:29:28 10:47:28 time 11:05:28 11:23:28 11:41:28 11:59:28 12:17:28 12:35:28 12:53:28 13:11:28 13:29:28 13:53:28 Variation in CO con w ith time Workplace CO measurement - Unit 6 (Near gasifier unit) 65 time CO ppm CO ppm 0 10:55:10 10 20 30 40 0 50 1 9:02:29 9:15:29 9:28:29 9:41:29 9:54:29 10:07:29 10:20:29 10:33:29 10:46:29 10:59:29 11:12:29 11:25:29 time 11:38:29 11:51:29 12:04:29 12:17:29 12:30:29 12:43:29 12:56:29 13:09:29 13:22:29 13:35:29 13:48:29 14:01:29 2 3 4 5 6 100 60 70 80 90 11:13:10 11:31:10 11:49:10 12:07:10 12:25:10 12:43:10 13:01:10 13:19:10 13:37:10 13:55:10 14:13:10 time 14:31:10 14:49:10 15:07:10 15:25:10 15:43:10 16:01:10 16:19:10 16:37:10 16:55:10 17:13:10 17:31:10 17:49:10 18:07:10 Workplace CO measurement - Unit 7 (Near gasifier) Workplace CO measurement - Unit 7 (Near producer gas unit) 66 CO (ppm) CO-ppm 100 150 200 250 500 600 700 100 200 300 400 50 0 0 10:42:36 11:50:02 12:10:02 12:30:02 12:50:02 13:10:02 13:30:02 13:50:02 14:10:02 14:30:02 14:50:02 15:10:02 15:30:02 Time 15:50:02 16:10:02 16:30:02 16:50:02 17:10:02 17:30:02 17:50:02 18:10:02 11:02:36 11:21:36 11:41:36 12:00:36 12:20:36 12:39:36 12:59:36 13:18:36 13:38:36 14:01:36 14:27:36 15:19:36 15:39:36 16:00:36 16:37:36 16:57:36 17:17:36 17:37:36 17:57:36 tim e Work Place CO measurement -( Unit 9 Near kiln area) Work Place CO measurement - Unit 10 (Near producer gas unit) 67 18:30:02 18:50:02 19:10:02 19:30:02 CO (ppm) 100 150 200 250 300 50 0 Concentration of CO (ppm) 350 400 100 150 200 50 11:38:42 12:00:42 12:22:42 12:44:42 13:06:42 13:28:42 13:51:42 14:13:42 14:52:42 time 16:26:42 16:48:42 17:10:42 17:32:42 17:54:42 18:16:42 18:38:42 19:00:42 19:22:42 0 10:51:04 11:12:04 11:33:04 11:54:04 12:15:04 12:36:04 12:57:04 13:18:04 tim e 13:39:04 14:00:04 14:21:04 14:42:04 15:03:04 15:24:04 15:45:04 16:09:04 Work Place CO measurement - Unit 9 (Near producer gas unit) Work Place CO m e as ure m e nt - Unit 10 (Ne ar k iln are a) 68 Annex 4.5 Details of Liquid effluent Monitoring Unit Source Estimated Quantity (m3/day) pH COD (mg/l) BOD (mg/l) Oil & Grease (mg/l) Met han ol (g/l) Acetic acid (g/l) P h e n o l ( m g / l ) Unit 1 Unit 2 Inlet – collection pond (includes effluents from gasifier bottom ash pit, supernatant from leg seals, gas cooling & cleansing system) Collection pond Final effluent of the entire plant Condensable vapour & Ash pan Condensable vapour & Ash pan Recirculation chamber/ Blow down sump of gas cleansing system Ash pan Ash pan Condensable vapours + gas cleaning Condensable vapours Ash pan Ash pan 5-7 7.2 1080 302 1 BDL BDL 27 Unit 3 Effluent from PGP plant is 1 0.5 8.1 720 2759 210 2153 0.5 0.5 BDL BDL BDL 0.8 11 6.6 1280 360 BDL BDL BDL 18 Unit 4 1.0-1.5 7.8 400 110 BDL BDL BDL 15 Unit 5 3.0 6.1 30,32 3 13437 BDL 5.5 8.3 - Unit 6 Unit 7 Unit 8 1.0 0.5 0.2 – 1.0 6.5 6.8 8.1 760 240 2300 220 60 875 BDL BDL BDL BDL 0.2 - BDL BDL - 31 20 - Unit 9 0.2 0.1 7.2 6.8 7.8 1124 2831 2244 392 928 750 BDL 0.20 0.20 BDL BDL BDL BDL 12 40 34 Unit 10 BDL - Below detection limit 69 70 71