Accepted ManuscriptAnalysis of the parameters affecting energy consumption of a rotary kiln in cement industry Adem Atmaca, Recep Yumrutaş PII: DOI: Reference: To appear in: S1359-4311(14)00130-6 10.1016/j.applthermaleng.2014.02.038 ATE 5412 Applied Thermal Engineering Received Date: 22 August 2013 Revised Date: 19 January 2014 Accepted Date: 15 February 2014 Please cite this article as: A. Atmaca, R. Yumrutaş, Analysis of the parameters affecting energy consumption of a rotary kiln in cement industry, Applied Thermal Engineering (2014), doi: 10.1016/ j.applthermaleng.2014.02.038. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT Analysis of the parameters affecting energy consumption of a rotary kiln in cement industry Adem Atmaca*, Recep Yumrutaş *University of Gaziantep, Department of Mechanical Engineering, 27310 Gaziantep, Turkey e-mail:
[email protected],
[email protected] Phone: +90 342 317 1734, Fax: +90 342 360 1170 Keywords: cement; rotary kiln; specific energy consumption; energy; exergy. 1. Introduction Cement industry is one of the most energy intensive industries in the world. It is essential to investigate the feasibility of reducing coal consumption and greenhouse gas emissions of the rotary kilns in the industry. In comparison to the other industrial sectors, cement industry has been consuming the highest proportion of energy. A typical well-equipped plant consumes about 4 GJ energy to produce one ton of cement. At the same time, this sector is one of the worst pollutant sector [1], which emits an increasing amount of greenhouse gases such as carbon dioxide, nitrogen oxide, chlorofluorocarbons and methane. For each ton of clinker produced, an equivalent amount of green house gases are emitted [2, 3]. Cement production in the world is about 3.6 billion ton per year [4]. About 2 % of the electricity produced in the whole world is used during the grinding process of raw materials [5]. Total electrical energy consumption for cement production is about 110 kWh/t of cement, roughly two thirds of this energy is used for particle size reduction [6]. Because of high energy consumption rates and high environmental impact of the process, the manufacturing process has been considered by the investigators for many years. Schuer et al. [7] studied energy consumption data and focused on the energy saving methods for German cement industry considering electrical and thermal energy saving methods. Saxena et al. [8] investigated energy efficiency of a cement plant in India. Worell et al. [9] dealt with energy analysis in the U.S. cement industry for the years 1970 and 1997. Engin and Ari [10] analyzed a dry type rotary kiln system with a kiln capacity of 600 t clinker per day. They found that about 40 % of the total input energy was lost through hot flue gas, cooler stack and kiln shell. The study indicates that for a dry type cement production process, the carbon dioxide emission intensity for kiln feed preparation process is about 5.4 kg CO2 per ton cement produced. Camdali et al. [11] have calculated the enthalpies going into and leaving the rotary kiln in cement industry and the heat losses from the system by conduction, convection and radiation according to the first law of thermodynamics. Furthermore, exergy analysis of the system is made based on the second law of thermodynamics. Kabir et al. [12] analyzed a pyroprocessing unit of a typical dry process cement plant. In order to enhance the energy performance of the unit, they considered conservation of heat losses from the system. Application of waste heat recovery steam generator and secondary kiln shell were suggested. They showed that power and thermal energy savings of 42.88 MWh/y and 5.30 MW can AC C EP TE D M AN U 1 SC Abstract In this study, the effects of refractory bricks and formation of anzast layer on the specific energy consumption of a rotary kiln are investigated. Thermodynamic analysis of the kiln is performed to achieve effective and efficient energy management scheme. Actual data, which are taken from a cement plant located in Gaziantep, Turkey, are used in numerical calculations to obtain energy balance for the system. It is calculated that 12.5 MW of energy is lost from the surface of the kiln which accounts for the 11.3 % of the total energy input to the unit. The specific energy consumption for clinker production is determined to be 3735.45 kJ/kg clinker. The formation of anzast layer and the use of high quality magnesia spinel and high alumina refractory bricks provide 7.27 % reduction in energy consumption corresponding to a saving of 271.78 MJ per ton of clinker production. It is recognized that the anzast layer has an important role for durability of the refractory bricks and heat transfer out of the kiln. The applications prevent the emission of 1614.48 tons of CO2 per year to the atmosphere. RI PT The cement plant operates on a dry cement process line. the semi product of cement is produced. In the present study. Fast cooling of the clinker enables heat recovery from clinker. and improves the product quality [9]. and this paper can contribute to a better understanding of rotary kiln operation and parameters affecting its performance. Pulverized coal is burnt in the rotary kiln to reach the required reaction temperature.7 MW to 17. Four stage cyclone type pre-heater is used to pre-calcinate the raw material before it enters the kiln.2 m and 59 m length. Turkey. They determined that 1056. clinker. thermal performance of the rotary kiln presented in a cement plant is investigated using energy analysis based the first and second laws of thermodynamics. calcination process. accounting for about 90% of total thermal energy use [8].1. (c) increasing the temperature of farine (pre-calcination) in preheating tower with flue gases from the kiln.3 MW by the application of insulation to the system. The process includes five main stages: (a) mining and grinding of raw materials into fine powder. TE D M AN U 2 SC RI PT be achieved respectively. type and composition of refractory bricks on the performance parameters of the kiln are examined. The raw material passes through the rotary kiln towards the flame. The rotary burner is a refractory lined tube type kiln with a diameter of 4.AC C EP 2. The average clinker production capacity of the rotary kiln is 65 t/h. In a typical dry rotary kiln system.14. It is inclined at an angle of 3. The clinker is ground together with gypsum and other pozzolans materials and finally cement is produced. The temperature of the pre-heated material is about 1000 ºC. (d) burning the prepared mixture of farine in a rotary kiln (calcination) after the preheating tower and (e) grinding the clinker in a cement mill.5 million tons. In the calcination zone. and approximately one third of the raw material would be pre-calcined at the end of pre-heating.15] have employed energy and exergy analysis on a pyroprocessing unit in Turkey. After the combustion and the reactions inside the kiln. ACCEPTED MANUSCRIPT . combination of alumina. (b) blending the farine in homogenization silos prior to preheating in four staged cyclone preheaters.5º. The flow diagram of the rotary kiln is shown in Fig. Annual cement production capacity of the plant is 1. and its rotational speed is 1–2 rpm. In this study. The literature survey indicates that studies on rotary kiln is limited in number and scope. and annual emission rates have been reduced by 8. Atmaca et.2 %. the rate of heat loss is reduced from 22. System description Cement production is a long process which consumes large amounts of fossil fuels and electricity. The effects of the anzast layer and thickness. al [13. Clinker production in rotary kiln system is the most energy intensive stage in cement production. The data collected from a cement plant located in Gaziantep. pre-calcination gets started in the pre-heaters. are used in numerical calculations to obtain realistic performance parameters. silica and ferric oxide with lime take place at about 1500 ºC.7 kW of electricity can be generated by using the waste heat. Gaziantep cement plant located in the South-east of Turkey is considered as a case study for the thermal energy analysis. Clinker is rapidly cooled in cooling unit after the rotary kiln. Rotary kiln flow diagram. Many measurements have been taken for about 3 years and average values are used. W & is the rate of work. we waited for the appropriate time. pressure values and constant specific heat of the input and output materials are determined for the operating rotary kiln. Energy and exergy analyses for the kiln unit of the cement factory are performed by using the first and second laws of thermodynamics.in net. In order to enter into the rotary kiln and measure the thickness of the anzast layer. the following balance equations are applied. Cement production is a continuous process. Stopping the production process in order to change the refractories is a long. (5) the ambient and kiln average surface temperatures are constant throughout the period of the study. steady flow process. input and output mass of each item. costly and undesirable process. Thermodynamic analysis of the kiln system is performed in this section to achieve effective and energy efficient management scheme. and the rate of irreversibility in a steady state flow process. and h is enthalpy. energy and exergy efficiencies. which is: & E η I = ∑ &out (4) E ∑ in The general exergy balance is expressed as: & − ∑ Ex & & ∑ Ex in out = ∑ Exdest 3 EP ∑ TE D in in M AN U SC RI PT (5) . the following assumptions are made: (1) the system is assumed to be steady state. Specific heat capacity. temperature. (2) kinetic and potential energy chances of input and output materials are negligible. The mass balance for an open system operating under steady state conditions is expressed as: & in = ∑ m & out (1) ∑m & is the mass flow rate of the kiln.out ∑ out out & is the rate of heat transfer. In order to find heat and work interactions. 1. subscripts “in” and “out” in all expressions stand for where m input and output values of each parameter. The refractory bricks of the rotary kiln are changed when they lose their thermal properties. Thermodynamic analysis of the rotary kiln The rotary kiln is heart and the most energy consuming part of a conventional cement plant. (4) electrical energy produces the shaft work in the system. where Q The first law (energy or energetic) efficiency is defined as the ratio of energy output to the amount of energy input. The general energy balance can be expressed as: & = ∑E & (2) ∑E in out & & & h − m & h −W = m Q (3) AC C net. During the analysis. 3. (3) the gases inside the kiln are assumed to be ideal gases.ACCEPTED MANUSCRIPT Fig. m & is mass flow rate. (9) and use exergies of outgoing and input materials to the unit. Conservation of this heat will improve the thermal efficiency of the rotary kiln. Due to negligible pressure change the enthalpy change is equal to the internal energy change. Higher exergy efficiency permits a better matching of energy sources and uses [16]. convection and radiation. 4 AC C EP TE D M AN U (9) ∆h = ∆u + υ ∆P where cavg is average specific heat. we use Eq. their ∆s values are expressed as: T (14) ∆sin = c p . This heat transfer is considered waste heat. the exergy values of input and output materials in the rotary kiln are calculated from the equations. The second-law (exergy or exergetic) efficiency may generally be defined as the rate of exergy output divided by the rate of exergy input: & Ex η II = ∑ & out (7) ∑ Exin In this study. there will be heat transfer from the kiln to atmosphere. The subscript zero indicates properties at the dead state of Po and To. (16) ∆ψ in = ∆hin − T0 ∆sin (17) ∆ψ out = ∆hout − T0 ∆sout 4. Heat loss calculation of the rotary kiln Due to temperature difference between inner surface and ambient air temperature. The heat transfer from the rotary kiln takes place due to conduction. The subscript dest indicates destruction.avg ln 1 T0 T (15) ∆sout = c p . For incompressible substances the entropy change is: T (12) s2 − s1 = cavg ln 2 T0 For ideal gases the entropy change is: T P (13) s2 -s1 = c p.avg ln 2 T0 After obtaining the entropy and enthalpy values of the input and output materials.∆hout = cavg (T2 − T0 ) (11) where T1 and T2 are the input and output temperatures of the materials and To is the ambient air temperature. Maximum improvement in the exergy efficiency for a process is obviously achieved when the exergy loss or irreversibility is minimized. The enthalpy values of the input and output materials can be expressed with reference to ambient conditions: ∆hin = cavg (T1 − T0 ) (10) 1 SC ∆u = ∫ c (T ) dT = cavg (T2 − T1 ) 2 RI PT T0 & −W & & & & (6) 1− Q ∑ net.avg ln 2 -R ln 2 T0 P0 Since the pressures of the input and output materials are equal. Internal energy change and enthalpy change values are: (8) ACCEPTED MANUSCRIPT .out + ∑ minψ in − ∑ moutψ out = ∑ Exdest T p p & where Qp is the heat transfer rate through the boundary at temperature Tp at location p. υ is specific volume and ∆P is pressure change. Substantial quantity of heat is transferred to the atmosphere from the surface. 1 60.48[MgO]+7. the energy consumed during the formation of clinker is calculated.SiO2 K2 O SO3 MgO Na2O - Chemical form C4AF C2 S C3 A C3 S - Percentage (%) 10.SiO2 3CaO.2 = ln 2 2π r4 L1h1 2π L1k1 r4 2π L1k2 r3 r 1 1 1 (21) Rconv . The rate of heat transfer between the control volume and its surroundings is calculated from the following equations: & = Tin − Tout (19) Q total Rtotal where Rtotal is the total thermal resistance of the system and calculated from x Rrad R Rtotal = Rconv . Formation energy (kcal/kg) = 4.To obtain the general energy balance of the system. 1.5 2.2 (20) Rconv . AC C Energy is transferred by mass.2 1. k is the thermal conductivity.3 + conv .2.1 1.Fe2O3 2CaO.59[Fe2O3] (18) Table 1 Clinker composition.3 100 RI PT .1 + Rcond . 26.4 13. The clinker composition which is taken from the facility laboratory is shown in Table 1.76. convection and radiation thermal resistance values are determined from the expressions: r r 1 1 1 Rconv . Al2O3. and σ is Stefan-Boltzman constant as 5.2 2. Al2O3.1 + Rcond . convection and radiation equations in a cylindrical structure for the case of constant conductivity for steady conduction with no heat generation is applied (Fig.2 + Rcond . Al2O3 3CaO.2).3 = ln 1 2π L1k3 r2 2π r1 L1h2 2π r1 L1hrad where h is the convection coefficient.67×10−8 W/m2 K4. respectively.2 = Rrad = Rcond .116[SiO2]–0. SiO2 and Fe2O3 percentages in the manufactured cement has been analyzed to be 3. Formation energy of the clinker is calculated by using the Zur Strassen equation [17]. CaO. surf + Tout ) EP TE D M AN U 5 SC Chemical structure 4CaO. heat and work within the rotary kiln which we choose as the control volume.2 9.646[CaO]–5.2 + Rrad Conduction.5 %. Chemical name Calcium ferrite Di-calcium silicate Calcium aluminate Tri-calcium silicate Potassium oxide Sulfur trioxide Magnesium oxide Sodium oxide Total ACCEPTED MANUSCRIPT where ε is the emissivity of the surface. MgO. 2 2 hrad = εσ (Tout (22) .1 = Rcond . 51. The simplifications of the one dimensional heat conduction.5 and 4.1 = ln 3 Rcond .11[Al2O3]+6. surf + Tout )(Tout . and hrad is the radiation heat transfer coefficient and its value is determined from. 5. thermodynamic analysis was performed to find performance parameters of the kiln such as heat losses. the raw ingredients are prepared and stored without addition of water. AC C EP TE D M AN U 6 SC RI PT . The thermal resistance network for heat transfer through the mantle of the rotary kiln.ACCEPTED MANUSCRIPT Fig.4. r2. Actual data are used in numerical calculations. and the kiln is commonly divided into five zones (Table 2 and Fig.5. For that reason. efficiency and SEC. and the performance parameters are obtained. r1. 2. Results and discussion The effects of the refractory bricks and formation of anzast layer on specific energy consumption (SEC) of the kiln are investigated in this study. The results obtained are presented as Tables and figures. r1-r2 gives the thickness of the steel mantle. The energy and exergy calculations are done using MS Excel Professional Plus 2013 which is a commercial software. In dry process. r3 and r4 are the inner radiuses of the rotary kiln. Tin is the inner temperature of the rotary kiln and Tsurf is the surface temperature of the mantle of the kiln. The refractory brick arrangement and anzast layer in rotary kiln are presented in Fig. The software makes it possible to analyze the whole system by considering their interactions with each other.3). r2-r3 is the thickness of the refractory bricks and r4 is the average radius of the anzast layer. and they are discussed in this chapter. The type and length of refractory materials used are presented in Fig. The surface of the kiln is divided into 4 sections with different surface temperature values. Fig. AC C Fig. Presentation of refractory arrangement and anzast layer in rotary kiln. The rotary kiln surface temperature zones and brick arrangement. 3. 4. Rotary kiln zones. 7 EP TE D M AN U SC RI PT . 5.ACCEPTED MANUSCRIPT Fig. It is generally lined with alkali resistant refractories such as 40 to 50 % alumina bricks. and average ambient air temperature (To) are given in Table 3. This zone is about 20 % of the burning zone length. Calcining: Higher in temperature than the chain and pre-heating zones it is High Alumina commonly lined with higher alumina refractory materials. The results of the energy and exergy analysis for the rotary kiln unit are presented in Table 3. The work transfer due to electricity and heat lost values are calculated. electricity consumed and the combustion of pulverized lignite coal.Table 2 Kiln zones and refractory materials. it is typically lined with coarse aggregate Coarse aggregate monolithic. 4. clinker fluids are also present. Preheating: Usually the longest zone as the name suggests this section is the pre. The specific heat capacity of the each input and output material has been calculated using the empiric correlation below which practices upon the Kirchhoff law [19]. The discharge zone is commonly lined with basic or high alumina refractories [18]. Temperatures here are at the highest and the coating is often unstable and thin. The clinker discharges into firing hood.Mid/High Alumina heating section of the kiln. The material and energy balance for the unit is presented in Table 4. Results obtained from a case study can be given to explain energy analysis for the kiln. constant pressure specific heats (cp). The three sections are commonly determined by different clinker coating conditions.1 Upper Transition: In the upper transition zone the coating is usually thin or nonexistent. a stable coating is essential for extended refractory life. High wear often occurs at the ring end of the discharge zone.1. The given and calculated values including mass flow rates (ṁ). Energy and exergy analysis of the kiln Energy balance for the kiln is defined that energy input is equal to energy output for the steady state operation. TE D RI PT MagnesiaAlumina-Spinel MagnesiaAlumina-Spinel MagnesiaAlumina-Spinel MagnesiaAlumina-Spinel MagnesiaAlumina-Spinel and/or Mid/High Alumina .2 Sintering: Coatings in sintering zone are usually thick and stable. energy and exergy values of the raw materials. This zone is about the 50 % of the burning zone length. SC 5. About 30 % of the length of the burning zone is called as the upper transition zone. 4. The relevant data and constants are obtained from on site measurements. 3 4 M AN U 8 Burning zone: The eutectic temperature between the “free” lime in the calcined feed and alumina-silica materials is in the region of 1100 to 1300 ˚C. temperatures are generally in the region of 1250 ˚C. Total energy output consists of the energy absorbed by raw materials. first law (ηI) and second law (ηII) efficiencies. enthalpy (∆h) and entropy (∆s) changes. 5 Discharge: There is a chamber between the rotary kiln and the clinker cooler. heat loss and hot gas leaving from the kiln.3 Lower Transition: The lower transition zone encounters the most severe conditions in the kiln. ACCEPTED MANUSCRIPT Refractory materials Kiln Zones 1 2 Chain zone: The “front end” of the kiln. AC C EP 4. input (Tin) and output (Tout) temperatures. that is why the burning section of the kiln is lined with basic refractories such as magnesia-chrome or magnesia-spinel as these materials form no eutectics with lime at the temperatures encountered in the “hot” zones. Total energy input to the kiln consists of energy entering by raw materials. 000 4788 1468.64 3.6 7200 7200 7675.61 0.55 2566.102 0.7 5.2 % of the inlet energy. electricity. combustion process has the greatest contribution of input energy and input exergy. leaking dust and ash and the energy consumed during the formation of clinker which are the unavoidable waste of burning process.8 1648.43 2914.18 0.3 % and hot gas leaving the system accounts for 32.15 0.22 0. The output includes thermal energies contained in clinker and hot gas as well as energy losses with heat losses.52 15. [20.93 2.311. Input material Content CaO SiO2 Al2O3 Fe2O3 MgO K 2O H 2O Na2O SO3 C2 Ash O2 H2 H 2O N2 S2 N2 O2 ṁ (kg/h) 75.1 % of the total energy input (Fig. Operation of the system involves thermal energy inputs in the form of hot gas. 8 shows that most of the exergy input to the system is due to combustion of fuel (69.62 70.18 4.543 5145 2709 1312.3 0.5 901.089.45 0.31 4.62 0.49 kW = 0.96 1.01 4.68 12.2 303.85 0.71 0.75 (23) C p = a + bT + cT 2 + dT 3 Here.541.6 3575.8 %. Based on the calculated values given in Table 3.61 885.34 62.58 0.18 1.38 0.7 %.92 112.60 63.03 1.9 %) followed by the exergy of primary and secondary air streams (13.37 4.558 or 55.47 2.3 % of the all output exergies.78 55. The exergy flow diagram in Fig.11 465. ACCEPTED MANUSCRIPT SC ∆s (kJ/kgK) 0.18 MW.3 % in the unit. The second law efficiency of the rotary kiln is calculated from Eq. b.93 1237.18 4. c and d are the constants for raw material.76 1.5 5.849 Total Coal Total Combustion of coal Primary air AC C EP Farine Σ ṁ ∆ψ (kW) 5410. An examination of output exergies shows that exergy loss is responsible for 61.6 % of the output energies (Table 4).5 MW which accounts for the 11.2 249.79 5.93 110. the first law efficiency of the kiln is calculated from Eq.369 18.62 1.65 66.2 93.Table 3 Energy and exergy analysis of the kiln unit.69 2.64 1.68 773. The energy lost account to 44.72 56.16 20.18 2. (4) to be 62.1 cp (kJ/kgK) 0.31 4.19 10.553.64 T0 (K) 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 M AN U Tin (K) 1110 1110 1110 1110 1110 1110 1110 1110 1110 344 344 344 344 344 344 344 ∆h (kJ/kg) 492 565.649 MW / 89. Heat loss from the surface of the kiln accounts for 11.92 TE D 290 290 290 9 .2 492 1.387 or 38.16 304.10 MW/111. 8 shows a Grassmann diagram with the corresponding data for exergy.39 1348.9 % of the input energy is lost during the formation of clinker.15 28. Heat lost from the surface of the kiln is equal to 12.14 369.7 2056.33 0.28 225.95 739.05 0.56 920 320 320 31655.32 4.825 31.66 9.22 0.16 2.9 30.2 201.81 248.6 3. Total energy input to the kiln is calculated to be 111.43 58.15 0.6 259. Fig.01 0.81 0.4 3534.18 MW = 0. (7) to be 34. 7 shows a Sankey diagram indicating magnitudes and percentages of energy flows and losses while Fig. and thermal energies of burning coal and raw materials.8 %). 32.61 5.2 49.9 % and precalcined farine accounts for 18. a.16 0. The input energy is dominated by the combustion of pulverized lignite coal with a 56.92 14.36 0.5 %) and the precalcined farine (11. 8).81 0.2 3411.04 0.37 2. 21].45 105. This corresponds to an exergy loss of 61. The constants of each component of the input and output materials are taken from Ref.6 115. As a result.71 130.80 7.091 RI PT Σ ṁ ∆h (kW) 10300.9 % contribution while inlet air accounts for 20.46 703.8 273.34 2355. and T represents temperature of each material.04 5.15 1.3 % of the total energy input to the unit.89 1530.2 3427.2 27. 71 124.240.68 936.618 0.3 - T0 (K) 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 290 - Tin (K) 1550 1550 1550 1550 1550 1550 1550 1550 1550 1550 1550 1550 1550 1120 1120 1120 1120 1120 1120 1120 710 710 710 710 710 710 710 710 710 710 ∆h (kJ/kg) 778.00 - AC C EP 10 SC ∆s (kJ/kgK) 1.06 1410.48 2.86 - RI PT 4341.25 1.92 5935.79 356.84 12.43 Σ ṁ ∆ψ (kW) 259.3 871.82 852.167 0.42 778.76 1.01 1.012 4.94 63.885 Clinker Total Hot gas Total Dust and ash Total 4CaO C4AF Al2O3 Fe2O3 2CaO C2S SiO2 3CaO C3A Al2O3 3CaO C3S SiO2 K 2O SO3 MgO Na2O N2 CO2 H 2O O2 Ar SO2 Other 4CaO C4AF Al2O3 Fe2O3 2CaO C2S SiO2 3CaO C3A Al2O3 C3S 3CaO SiO2 Ash - TE D M AN U 898.103 0.21 2.1 589.28 342.98 30035.63 0.497.23 1177.87 73 53.37 14.083 1.63 0.47 36.42 0.71 1.3 0.182.887 0.95 7.68 2730.92 734.39 309.3 4.028 0.18 6021.618 2.4 30.18 778.72 433.09 4329.093 2.1 1091.63 705.124.9 9866 69639.04 1581 Ar CO2 H 2O Other N2 O2 Ar CO2 H 2O Other - 118.6 4341.903 0.779 0.04 1.95 100.577 - cp (kJ/kgK) 0.64 7568.08 546.293.89 907.007 1.5 111.705 927.235 9123.93 12123.25 8.18 839.16 - .445 438.97 0.004 4.489 0.21 20.63 120.74 2290.42 1.1 35.63 2.63 1905.5 296.99 12.32 14.1 1091.743 0.743 4.04 1.55 1.97 1.83 0.29 9.1 388.05 24.411 0.08 1087.55 290 290 290 290 290 290 1084 1084 1084 1084 1084 1084 909.54 1468.16 2226 296.392 4.11 1579.618 2.41 98.9 80.75 0.1 1074.921.56 ṁ (kg/h) 1956 1434.9 1.71 2.46 1.87 668.5 89.001 0.96 1.4 3.15 54.63 7.167 4.28 2034.Total Secondary air Total Electrical work TOTAL Output material Content 211.33 0.41 1770.92 4545.68 2730.91 3652.21 200.2 0.45 25.4 610.94 22965.69 135.14 202.075 87.37 10.18 1.047.42 5576.1 388.74 38.23 2791.33 4.51 1.39 934.046 1.86 807.05 0.41 1334.511 4.7 7742.18 23.924 1.04 3.074 4.24 133.61 1529.24 1713.83 1.93 4418.598 0.14 2571.45 5076.1 25.97 0.481 17599.099 1.2 652 65.76 778.426 0.01 60.6 89.72 734.23 1249.39 2181.8 26.4 23472 11084 1304 652 717.68 936.13 0.96 4125.146 1.705 0.48 63.200 91975.06 50.83 Σ ṁ ∆h (kW) 423.74 960.54 1117.85 4.177 ACCEPTED MANUSCRIPT 290 290 290 290 320 320 320 320 149.36 1546.38 125.618 0.09 166.66 3945.91 23.04 3.45 3118.16 296.005 0.705 0.083 0.59 5.60 3.68 340.01 180.227.6 18654.492 463.4 3995.705 2.63 2.4 2934 6520 7824 3260 3390.57 20.86 180.33 60.58 1928.99 2882.21 140.16 1.19 1698.24 0.81 603.08 296.9 3 8.68 191.69 866.44 1339.55 14.4 1.49 0.63 1.2 2241.37 6.72 0.41 132.42 6.924 0.19 48.59 19.63 129.81 38.4 1075.66 7.44 660.62 493.43 4.711 1. 3 100 SC Σ Ėin (kW) 20. 11 M AN U Table 4 Mass and energy balance of the unit.65 111.9 56.74 1581.9 21.83 32.48 23.577 36.200 Hot gas 133.227.6 1. Input materials ṁ (kg/h) Farine 105.182.089.9 3.577 Output materials ṁ (kg/h) Formation of clinker Clinker 65.63 24. Energy balance of the RK.5 63.9 100 Percentage (%) RI PT .68 34.6 87.537.102.649.00 12.293.47 112.86 AC C EP TE D Fig.83 Σ Ėout (kW) Percentage (%) 18.885 Heat transfer from the kiln Total 211.1 0.577 ACCEPTED MANUSCRIPT - - 62.1 20.182.51 111.8 32.4 11.000 Pulvarized coal 7200 Primary air 9866 Secondary air 89. 6.13 4341.240.542.492 Dust and ash 12.94 36.1 0.511 Electrical work Combustion of coal Total 211.311.TOTAL - 211. Table 5 Monthly SEC of the rotary kiln under standard conditions. The energy band diagram (Sankey) of the rotary kiln. Thus.200 kg/h clinker.45 kJ/kg clinker.5)*3600/65. 5.5 kW of electricity and 63.ACCEPTED MANUSCRIPT Fig. 8.2. the average SEC is (63. 7.65 kW of energy by the combustion of pulverized lignite coal. Specific energy consumption (SEC) of the kiln The specific energy consumption (SEC) of the system is calculated by using the data taken from the factory area for one year (Table 5). For the production of 65. EP TE D M AN U SEC (kJ/kg clinker) SC RI PT .311.341.311.200 =3735. The exergy band diagram (Grassmann) of the rotary kiln. the factory consumes 4341.65+4. Electricity Coal Clinker production * consumption Months consumption (kg/month) (kg/month) (kWh/month) 12 AC C Fig. 125. the first law efficiency of the kiln is calculated to be 69419.89 kW / 116614.1 %.2.96 kW / 93151. 65760.640 November 5320.2.157.14 3810.44 kW = 0.230.230.79 3702.880 43.125.81 3690.78 3636. The second quality old bricks with poor thermal properties are replaced with bricks which have higher Mg and Al content.076 44. The thickness of the anzast layer is measured in each section of the kiln.595 or 59. Content Mg0 (%) Al2O3 (%) Section 1 Magnesia Chromite 65-70 2-5 13 Section 2 Magnesia Spinel 80-84 10-14 Section 3 High alumina 10-20 75-80 Section 4 Alumina 12-16 65-70 AC C EP TE D 5.61 3797.076 45.6 3.5 %.8 3. magnesia and chrome (Table 6). there is only magnesia chromite and alumina bricks inside the kiln.090. M AN U SC RI PT January 5493.230.076 44.706. The experienced staff have an important role to maintain the desired conditions.56 3.02 3742.26 kJ/kg clinker. it is recognized that the thickness of the old bricks are reduced by half in some regions of the kiln. While replacing the bricks.84 3.200 October 5424.36 2. the service life of the bricks are increased considerably.87 * The specific combustion energy of the coal is calculated to be 31.21 3.979.8 3.13 3. Effect of the type and quality of the refractory bricks on the efficiency of the kiln Refractory materials play a critical role in the rotary kiln lining. and the average thickness of the layer is found to be 450 mm.684 42.88 3. ACCEPTED MANUSCRIPT 3813.076 45.45 .076 45.431 or 43. In this way.85 3735.568 July 5364. .788.5. alkali and sulphate attack. Some advantages of the anzast layer formation are summarized below: . .Supports bricks during continuous rotation of the kiln. The second law efficiency of the rotary kiln is calculated to be 40215.880 43.230.076 44.880 44.67 kJ/kg clinker.384 September 5199.788. It is seen that.39 3768.2 3. Silica has an abrasive effect on the bricks. Effect of anzast layer on the efficiency of the kiln The formation of an anzast layer inside the kiln has important effects on energy and exergy efficiency of the unit.2.22 3777.230.2 kW = 0.230.021.1.560 December 5475.076 45. After obtaining the thickness of the anzast layer.8 February 4791. The new chrome ore free bricks have resistance against high thermo-mechanical and thermochemical loads with redox conditions. the silicate module of the farine has kept as low as possible to provide easy sintering.384 April 5098.150. Therefore. the amount of free silica has been decreased by using iron oxide minerals instead of sand during production of farine. The SEC of the unit is found to be 3441.795.8 44.2 June 5212.8 Average 5305. Thus. the materials containing higher silica were able to melt easily under lower temperature values.100 kJ/kg coal.24 3.An anzast layer protects the refractory bricks against high temperature values.481.71 3.8 March 5501.926 39. .89 August 5386.37 3648.804 May 5399. In order to maintain appropriate anzast layer inside the kiln.86 3650.125.Reduces the heat transfer rate and coal consumption.38 3800. Table 6 Properties of new refractory bricks.99 kJ/s x 3600 / 66450 kg/h = 3562.Reduces the deformations on the bricks due to hot clinker flow. The main contents of these bricks are mainly based on alumina. SEC value is calculated from.230.84 3. 106 59.5 Total 211.4 19.65 kW = 0.4 60 300 4-7 2-8 20 2.784.7 100 Output materials ṁ (kg/h) Σ Ėout (kW) Percentage (%) Formation of clinker 35. The second law efficiency of the rotary kiln is calculated to be 42874.74 0. the first law efficiency of the kiln is calculated to be 72838.6 3.05 Secondary air 89.411.999.839.675.000 22.2 %.21 kJ/s x 3600 / 66750 kg/h = 3463.56 2.44 22.612 or 61.5 55 250 2-5 1-4 17 2.62 8. Based on the calculated values in Table 7. SC RI PT Cr2O3 (%) CaO (%) Fe2O3 (%) SiO2 (%) Apparent Porosity (%) Bulk Density (g/cm3) Thermal conductivity at 1000 ˚C (W/mK) Cold Crushing Strength (MPa ) Thickness (mm) ACCEPTED MANUSCRIPT 2-4 10-16 3-5 18 3.7 100 EP TE D M AN U The heat transfer losses from the surface of the unit and the coal consumption of the unit decreased considerably after replacing high quality refractory bricks inside the kiln.451 or 45.5 3.278.09 Primary air 10.14 37.47 Dust and ash 11.03 Electrical work 4341.65-3.08 3.2 3478.05 2.45 Clinker 66.9-3.105.25 Total 211. SEC value is calculated from.427 116.230.505.7-2.52 3488.68 kW = 0.1 3.076 47.2 61 250 .8 63 350 3-6 4-10 22 2.435 1703.59 Pulvarized coal 6810 106.880.05-3.4 kW / 118973. The first and second law efficiency and SEC of the unit have been evaluated again.95 14 AC C Table 7 Mass and energy balance of the unit after installing refractory bricks with better thermal properties.71 51.73 Combustion of coal 59.242 43.566. The energy consumption and clinker production of the unit on a month basis is given in Table 8.Table 8 Monthly SEC of the rotary kiln after the application of anzast layer and new refractory bricks.75 30.1 2.96 1.47 Heat transfer from the kiln 9597. Coal Electricity Clinker production SEC Months consumption* consumption (t/month) (kJ/kg clinker) (t/month) (kWh/month) January 5349.75 1.8 3492.230.65 kW / 95089.427 116278.5 0.67 kJ/kg clinker.750 25.926 41.795. 64222.1 %.49 March 5353.62 February 4662.36 Hot gas 133.511 29.076 47. Input materials ṁ (kg/h) Σ Ėin (kW) Percentage (%) Farine 105.84 25. 41 5068.150. The amount of coal saved per year is 1736.06 3441.8 46.* The specific combustion energy of the coal is calculated to be 31.230.8 tons of coal in a year. 24].668.24 3495.230. 1.8 5215.4 45.614. Emissions reduction After obtaining a suitable anzast layer and using better quality refractory bricks inside the kiln.880 3.97 ACCEPTED MANUSCRIPT 3.2.33 5176. 9. Nitrogen oxides are formed during fuel combustion in rotary kilns. both the first and second law efficiencies increase.467. The average air temperatures for winter and summer can be taken as 5 ºC and 30 ºC.230.41 3420.080 47. respectively. coal consumption of the unit is lower in summer days.38 3450. Thus.67 . 5.8 5327.021.076 3.4 47.66 t/y.020.2 46. 9.683. Effect of ambient air temperature on the efficiency of the kiln The highest and lowest ambient air temperatures are obtained from Turkish State Meteorological Service [22].230.481.880 3.318. and less heat is lost.56 3428.318.327.8 44.125.46 t/y to 61.3.076 3.230.931.76 5055.21 3463.044 47. Standart conditions 3850 After efficiency enhancement studies 3750 SEC (kJ/kg clinker) 3550 3450 3350 Ja n Fe b M ar ch A pr il M ay Ju ne Ju ly A ug Se pt O ct N ov EP TE D 3650 M AN U 15 5.125. AC C Fig. As a result. the heat transfer from the surface and coal consumption of the kiln have been decreased considerably.360 47. The quantity of NOx D ec SC RI PT April May June July August September October November December Average 4959 5250. Clinker production has been increased at the same time.480 kg of CO2 emission has been prevented by saving 1736. The temperature difference between the mantle of the kiln and the surrounding air is lower in summer.684 3. The NOx emissions result from the oxidation of nitrogen in the fuel as well as in incoming combustion air.3.93 kg [23.84 5275. The monthly changes in SEC of the rotary kiln with respect to ambient air temperature are shown in Fig. the efficiencies are higher in summer than in winter.125. At the end of 2nd year.2 47.076 3.100 kJ/kg coal. The data indicates that at higher ambient temperatures (during summer months).17 3427.076 3. the average coal consumption of the unit has decreased from 63.44 5237.04 5160. The amount of carbon dioxide emission per kg of coal burned is 0. As a result.61 3488.880 3.56 3489. This corresponds to higher rates of clinker production.8 tons. SEC of the rotary kiln with respect to months.076 3.616 46.69 3465. where S is the sulfur content in the fuel in percent [25. Coal consumption of the kiln decreased by 2.668.8 % while the second law efficiency is 38. 2. that’s 1736. With decrease in coal consumption.5 tons to 555. The ambient air conditions affect efficiency and production capacity of the kiln. reducing the temperature of gases at the outlet by more effective heat transfer in the unit.66 tons. It is calculated that 32. respectively.46 tons to 61. NOx and SO2 emissions rates of the facility are decreased by 1.4 kg/t coal burned for both dry and wet process kilns. The emission factor for NOx in cement process is 1. The properties of the coal are presented in Table 3. combustion temperature. The rotary kiln operates for about 7750 hours in a year.formed depends on the type of fuels. Further studies on the topic may involve the investigation of the parameters effecting the system performance and optimization of them for best operation. With the help of efficiency enhancement studies. The quality and type of the refractory used inside the kiln affect the performance of the rotary kiln significantly.7 %. The energy lost from the system is calculated to be 12. annual clinker production of the kiln has been increased from 529. Thus. Reduction in fuel consumption in a rotary kiln operation can be achieved by minimizing various losses occurring in the unit [27]. 2. The emission of SO2 into the atmosphere is known to cause the formation of acid rain and smog.5 MW.928.9 % of the energy is lost during the formation of clinker and 32. without their continuous support and encouragement I never would have been able to achieve my goals.480 kg.2 %. 6. The emission factor for SO2 is calculated to be 0. The SEC of the kiln increase in winter months due to lower ambient temperatures. 45. the first and second law efficiency and SEC values of the system are calculated as 61. increase in combustion efficiency will be the main parameter on the system efficiency.5 kg of NOx / y emission has been prevented. According to the results. its nitrogen content. About 79 kg of SO2 emission is prevented yearly.931.68 % increase in production capacity of the unit. Special Thanks I would first like to thank my mother.894. Minimizing heat losses by effective insulation.614. Elif and my father Kemal Atmaca who have died in a terrible traffic accident in 27th of November 2013. After the application of anzast layer and new refractory bricks inside the kiln. The annual total coal consumption of the facility has been decreased from 63. 26]. Sulfur dioxide may come from the sulfur content in ores and in combusted fuel which will vary from plant to plant. There is 4. It appears that the losses (particularly heat losses) increase in winter months. etc.8 tons of coal per year has been saved after the application of anzast layer and new refractory bricks.67 kJ/kg clinker. annual CO2. and minimizing air and steam leak by effective sealing are some measures that can help reduce energy consumption.5S kg SO2 / ton of coal burned.431.1 % and 3463. The emission factors of dry kilns suggested by US EPA (US Environmental Protection Agency) is 3. Conclusions The analysis and performance assessment of the rotary kiln indicate that the clinker formation process involves energy and exergy losses.6 % of the total energy exits with hot gas streams.72 %.5 kg and 79 kg respectively.45 kJ/kg clinker. The specific energy consumption for clinker production is determined to be 3735. I would like to express my deepest appreciation to my parents.5 tons. Acknowledgment The authors acknowledge the support provided by the Scientific Research Unit (GUBAP) of the 16 ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT . and the process is affected by certain parameters.431. A thermoeconomic analysis of the system can also provide significant information indicating cost allocation in the system.0455 kg SO2/t coal burned. The main results of the study can be summarized as follows: The first law efficiency of the rotary kiln is determined to be 55. [3] E. Cement Manufacture and the Environment Part II: Environmental Challenges and Opportunities. A. Rotary Cement Kiln Simulator (RoCKS): Integrated modeling of pre-heater. [4] World cement production 2012. calciner. [6] K. Tsibouki. Dr. Ganesh Kulkarni.A. Chemical Engineering Science 62 (2007) 2590-2607.V. Characterization of various cement grinding aids and their impact on grindability and cement performance. Use of alternative fuels in the Polish cement industry. Applied Energy 74 (2003) 101–11. 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AC C EP TE D M AN U SC RI PT The anzast layer affect the efficiency and production capacity of the kiln.ACCEPTED MANUSCRIPT Highlights We analyzed a rotary kiln and investigated the first law and second law efficiency values. . Performance assessment of a kiln indicates that the burning process involves energy and exergy losses.