Energy Conversion and Management 45 (2004) 3017–3031 www.elsevier.com/locate/enconman
Energy and exergy analyses in a rotary burner with pre-calcinations in cement production € Unal C ß amdali
a,* ,
Ali Er_isßen b, F€ usun C ß elen
c
a Development Bank of Turkey, Necatibey Cad., No: 98, Bakanliklar, 06100 Ankara, Turkey Kırıkkale University, Engineering Faculty, Mechanical Engineering Department, 71100 Kırıkkale, Turkey Metropolitan Municipality, General Directorate of EGO, Gas Department, Maltepe, 06570 Ankara, Turkey
b c
Received 31 May 2003; received in revised form 27 September 2003; accepted 9 December 2003 Available online 24 January 2004
Abstract Cement production facilities are often located in rural areas and close to quarries, where the raw materials required for cement production are present, i.e. limestone and shale. Although energy analysis, based on the first law of thermodynamics, is used to reduce heat losses or enhance heat recovery, it does not give any information on the degradation of energy that occurs in the process. Exergy analysis, based on the first and second laws of thermodynamics, facilitates improvement of the operation or technology by clearly indicating the locations of energy degradation in the process. In this study, the applications of energy and exergy analyses are examined for a dry system rotary burner (RB) with pre-calcinations in a cement plant of an important cement producer in Turkey. The RB includes thermal and chemical processes. Besides, real figures of the cement factory have been used in this work. In conclusion, the values of the first and second law efficiencies have been found and compared. 2004 Elsevier Ltd. All rights reserved. Keywords: Energy analysis; Exergy analysis; Cement production; Rotary burner
1. Introduction By the mid 1970s, the increase in energy resource consumption that occurred in each passing year was not a source of general concern. However, recurrent fuel shortages, electricity blackouts
*
Corresponding author. Tel.: +90-312-2318400; fax: +90-312-2302394. ¨. C E-mail addresses:
[email protected],
[email protected] (U ß amdali).
0196-8904/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2003.12.002
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Nomenclature A C cp E Eex Ein EL EO EQ Es EW g gG h h0f h I k l m P Q QL r RB S s T Tin Tsur V W z0 l g w e
surface area (m2 ) flow velocity (m/s) specific heat capacity at constant pressure (kJ/kg K) exergy (kJ), energy (kJ) exit exergy (kJ) inlet exergy (kJ) lost exergy due to irreversibilities (kJ) outlet exergy (kJ) exergy of heat transfer (kJ) exergy of a system (kJ) exergy of work transfer (kJ) specific Gibbs function (kJ/kg) gravitational acceleration (m/s2 ) specific enthalpy (kJ/kg) specific enthalpy of formation (kJ/kg) convective heat transfer coefficient (kJ/h m2 K) irreversibility (kJ) thermal conductivity (kJ/h m K) length of RB (m) mass (kg) pressure (kPa) heat transfer (kJ) heat loss (kJ) radius (m) rotary burner entropy (kJ/K) specific entropy (kJ/kgK) temperature (K) inner temperature of RB (K) surface temperature of RB (K) volume (m3 ), velocity (m/s) work (kJ) height of flow (m) chemical potential (kJ/kmol) energy efficiency (%) exergy efficiency (%) specific exergy (kJ/kg)
Subscripts anz anzast layer br bricks
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cond conduction conv convection cv control volume ex exit f flow gen generation i ith component in inlet L loss rad radiation S-gases stack gases sts steel sheet 0 environmental state 00 chemical potential at chemical equilibrium with environment Superscripts CH chemical KN kinetic PH physical PT potential TM thermomechanical Æ rate – per mole 0 standard reference conditions and brownouts, rising prices and so on began to alter perceptions. Many individuals voiced concern that unless corrective steps were undertaken, difficulties would be encountered in providing energy for future needs [1]. So, energy analyses have been conducted widely in many industries. Energy can be transformed from one form to another and transferred by work and heat transfer. The total amount of energy is conserved in all transformations and transfers. The main aim in realizing energy analysis is to determine the used and lost energies. Wide application of exergy analysis can lead to reducing the use of natural resources and, as a result, to decreasing the pollution of the environment. The main purpose of exergy analysis is to detect and evaluate quantitatively the causes of the thermodynamic imperfections of thermal and chemical processes. The exergy method of thermodynamic analysis is based upon the first and second laws of thermodynamics together, whereas the energy balance is based upon the first law only, which is a conservation principle. It is a feature of the exergy concept to permit quantitative evaluation of energy degradation [2]. As a result, the energy and exergy concepts may be expressed in the following simple terms: (1) energy is the ability of producing change and (2) exergy is the work producing potential or quality of different energy forms for a given environment. The laws of thermodynamics may be formulated accordingly: (1) energy is always conserved in a process (first law) and (2) exergy is always
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conserved in a reversible process, but is always consumed in an irreversible process (second law, the law of exergy) [3]. In this study, the mass analysis is realized. Then, enthalpies going into and leaving the RB are calculated with heat losses from the RB by conduction, convection and radiation according to the first law of thermodynamics. Furthermore, exergy analysis is made based on the second law of thermodynamics. At the end of the present study, efficiencies depending on both the first and second laws are compared.
2. Cement production The cement industry has an important role in the economy based on its production. During the production of cement, natural resources are consumed in large amounts. The most important raw materials for the manufacture of cement are limestone (CaCO3 ) and clay or calcareous clay in which both components are already naturally mixed. The components are milled and dried with flue gases from the clinker kiln. Depending on the type of cement to be produced, the following products may be added to the dried limestone subsequently: pyrite ash, fly ash from coal fired power plants, sandy clay and filter ash from the electrostatic precipitator present. The mixture obtained is ground and subsequently fired in a rotary furnace to cement clinkers. For heating, various fuels and other combustible materials, e.g. coal dust, petroleum coke, etc., are used. Depending on the type of preheating of the material, it is differentiated between grate and cyclone preheating, whereby the starting materials are preheated to 700–800 C. The raw materials pass through the rotary furnace towards the flame. In the hottest zone, the material being fired reaches temperatures of around 1450 C. After fast cooling with ambient air, the clinkers are milled, together with gypsum, to give ready cement. A part of the process is given in Fig. 1 [4–6]. Materials going into and leaving the RB are seen in detail in Fig. 2, and those materials, the energy and exergy analysis are accomplished. The process has a two and half hour cycle. 2.1. Chemical analysis occurring in the rotary burner Chemical reactions occur in the RB by combustion of coal and forming clinker. These are given as standard reactions in the following [7]. 2.1.1. Chemical reactions in combustion of coal C þ 1=2O2 ! CO C þ O2 ! CO2 S þ O2 ! SO2
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Fig. 1. A part of cement production process (from Cemex Inc., USA).
Farine coming from pre-heater
QL
Gas Dust
Coal Secondary air Primary air Hot clinker
Fig. 2. Rotary burner (RB) and materials going into and leaving [7].
2.1.2. Main chemical reactions in formation of clinker 2CaO þ SiO2 ! ðCaOÞ2 SiO2 CaOAl2 O3 þ 2CaO ! ðCaOÞ3 Al2 O3 CaOAl2 O3 þ 3CaO þ Fe2 O3 ! ðCaOÞ4 Al2 O3 Fe2 O3 ðCaOÞ2 SiO2 þ CaO ! ðCaOÞ3 SiO2 MgO ! MgO K2 O ! K2 O Na2 O ! Na2 O
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3. Mass analysis in the rotary burner (RB) The mass balance of the RB, which is performed according to the chemical reactions, is given in their chemical components in Table 1. This balance is formed based on the law of conservation of mass in Eqs. (1)–(1b). X X min ¼ mex ð1Þ where X X
min ¼ mfarine þ mcoal þ mair
ð1aÞ
mex ¼ mclinker þ mDust þ mSgases
ð1bÞ
Table 1 Chemical analysis of materials going into and leaving RB [7–9] Materials going into RB
Materials leaving RB
Farine CaO CO2 SiO2 Al2 O3 Fe2 O3 MgO K2 O SO3 Na2 O Total Coal C S N2 H2 O2 H2 O CaO SiO2 Al2 O3 Fe2 O3 MgO K2 O SO3 Total Air O2 ðÞ N2 ðÞ Total
(kg/h) 68 948.80 20 467.70 18 924.80 5520.70 3676.50 1735.80 843.80 241.10 180.80 120 540.00 (kg/h) 5668.25 389.50 164.00 451.00 461.25 1610.27 38.95 831.28 297.25 215.25 32.80 20.50 69.70 10 250.00 (kg/h) 56 654.78 186 394.22 243 049.00
Clinker C3 S C2 S C3 A C4 AF MgO SO3 K2 O Na2 O Total Dust CaO SiO2 Al2 O3 Fe2 O3 MgO SO3 K2 O Na2 O Total Stack gases CO2 CO SO2 H2 O O2 ðÞ N2 ðÞ Total
(kg/h) 57 111.30 13 438.50 9104.70 10 955.40 1357.80 232.50 660.30 139.50 93 000.00 (kg/h) 7427.79 40.30 83.75 291.79 410.8 78.30 204.00 41.30 8578.03 (kg/h) 40 693.43 355.00 779.00 5669.30 38 206.02 186 558.22 272 260.97
Overall
373 839.00
Overall
373 839.00
(*): primary air + secondary air; (**): waste air; C3 S: 3CaO Æ SiO2 ; C2 S: 2CaO Æ SiO2 ; C3 A: 3CaO Æ Al2 O3 ; C4 AF: 4CaO Æ Al2 O3 Æ Fe2 O3 .
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4. Energy analysis in the rotary burner (RB) The first law of thermodynamics, which is called the law of conservation of energy, is used for the energy analysis for the RB. When this law is applied to a system in which chemical reactions are occurring, the following equation can be written: Qcv þ
X
min ðh0f þ Dh þ Vin2 =2 þ gG zin Þ ¼ Wcv þ
X
mex ðh0f þ Dh þ Vex2 =2 þ gG zex Þ þ QL
ð2Þ
ex
in
The following assumptions are made for the energy analysis: • Heat ðQcv Þ is not given out of the system. • Electrical energy ðWcv Þ used for the RB to rotate is not included in the analysis. • Kinetic and potential energies of materials going into and leaving the system are neglected. Eq. (2) can be written as Eq. (3) when the assumptions above are taken into consideration. X
min hT;P ¼
X
mex hT;P þ
X
ð3Þ
QL
ex
in
where hT;P ¼ h0f þ Dh Dh ¼
Z
ð4Þ
T
ð5Þ
cp dT 298
cp ¼ a þ bT þ cT 2
ð6Þ
The a, b and c coefficients in Eq. (6) change with material types. The coefficients of some materials used in the RB are listed in Table 2. Table 2 Constant pressure specific heat and its coefficients of some substances used in the RB [10] Substance
a
b
c
cp ¼ a þ b T þ c T 2 (kcal/kmol K)
CaO ÆSiO2 æ ÆSiO2 æ Al2 O3 a b
11.86 3.27 13.64 25.48 23.5 36
1.08 · 103 24.8 · 103 2.64 · 103 4.25 · 103 18.6 · 103 –
)1.66 · 105 – – )6.82 · 105 )3.55 · 105 –
d
31.7
1.76 · 103
–
11:86 þ 1:08 103 T 1:66 105 T 2 3:27 þ 24:8 103 T ð298 < T < 390Þ 13:64 þ 2:64 103 T ð390 < T < 2000Þ 25:48 þ 4:25 103 T 6:82105 T 2 ð298 < T < 1800Þ 23:5 þ 18:6 103 T 3:55105 T 2 ð298 < T < 950Þ 36 ð950 < T < 1050Þ 31:7 þ 1:76 103 T ð1050 < T < 1873Þ
T ¼ T ðKÞ; Æ æ: solid phase; h ia : a-phase; h ib : b-phase; h id : d-phase.
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4.1. Enthalpies of materials going into and leaving RB The enthalpies of the materials going into and leaving the RB are given for the chemical components in Table 3. Eqs. (5) and (6) and Ref. [11] are used to obtain these values.
Table 3 Enthalpies of materials going into and leaving RB Materials going into RB
Materials leaving RB
Farine (1065 K) CaO CO2 SiO2 Al2 O3 Fe2 O3 MgzO K2 O SO3 Na2 O Total Coal (318 K) C S N2 H2 O2 H2 O CaO SiO2 Al2 O3 Fe2 O3 MgO K2 O SO3 Total Air (1373 and 298 K) O2 ðÞ N2 ðÞ Total Reaction energy C (for CO2 ) H2 (for H2 O) S (for SO2 ) Total
min hin (kJ/h) 733 180 854.56 165 814 978.01 271 205 631.36 86 066 608.86 16 449 763.95 24 324 806.88 2 399 007.78 1 035 186.96 1 021 031.84 1 301 497 870.20 min hin (kJ/h) 95 396.65 5639.96 3409.56 129 152.87 8570.03 21 561 515.30 440 481.66 12 589 378.15 4 880 170.24 1 108 035.97 488 581.26 78 338.70 343 622.39 41 247 954.60 (kJ/h) 59 888 721.99 212 642 102.89 272 530 824.88 E_ (kJ/h) 185 879 172 56 247 620 3 618 141 245 744 933
Clinker (1423 K) C3 S C2 S C3 A 9 ðCaOÞ4 = Al2 O3 C AF ; 4 Fe2 O3 MgO SO3 K2 O Na2 O Total Dust (1320 K) CaO SiO2 Al2 O3 Fe2 O3 MgO SO3 K2 O Na2 O Total Stack gases (1373 K) CO2 CO SO2 H2 O O2 ðÞ N2 ðÞ Total
mex hex (kJ/h) 654 910 126.04 159 973 113.47 110 598 796.97 85 641 719.1 34 793 961.43 14 961 104.20 18 399 058.99 917 059.05 1 608 781.33 574 236.41 1 082 377 956.99 mex hex (kJ/h) 77 148 740.83 563 990.44 1 278 828.16 1 239 515.17 5 622 233.45 316 804.15 520 901.76 208 668.66 86 899 682.62 mex hex (kJ/h) 313 599 035.08 964 822.55 2 941 659.80 62 819 585.74 42 982 918.68 226 509 662.81 110 832 521.68
Overall
1 315 959 932.92 (365 544 kW)
Overall
1 280 110 161 (355 586 kW)
(*): primary air + secondary air; (**): waste air; C3 S: 3CaO Æ SiO2 ; C2 S: 2CaO Æ SiO2 ; C3 A: 3CaO Æ Al2 O3 ; C4 AF: 4CaO Æ Al2 O3 Æ Fe2 O3 .
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4.2. Heat loss from RB 4.2.1. Heat loss by conduction from wall of RB The geometric shapes of the RB and RB surface with the electrical analogy of the thermal conductivities of the RB wall are given in Figs. 3–5 in order to calculate the heat losses. Furthermore, the thermal values of the RB are tabulated in Table 4 [7]. These values are measured by the firm authorities. There are three regions based on the temperature in the RB as seen in Fig. 3. Heat loss by conduction from the surface of the RB is given by the following equation: Tin1 Tsur1 Tin2 Tsur2 þ lnðr =r Þ Q_ cond ¼ lnðr =r Þ lnðr =r Þ lnðr =r Þ 2 1 3 2 2 1 3 =r2 Þ 4 =r3 Þ þ 2pkbrAl2O3 þ 2pk4sts l31 þ 2pklnðr þ lnðr 2pkanz l1 2pkanz l2 2pksts l2 l1 brMgO l2 þ lnðr =r Þ 2
1
2pkanz l3
Tin3 Tsur3
ð7Þ
3 =r2 Þ 4 =r3 Þ þ 2pklnðr þ lnðr 2pksts l3 brAl2O3 l3
4.2.2. Heat loss by radiation from inlet of RB, by convection from surface of RB Heat loss by radiation from the left and right ends of the RB inlet can be calculated using Eq. (8), by convection from the surface using Eq. (9) and by the total heat loss using Eq. (10): Tsur1
Tsur2
Al2O3
MgO
Tin1
43 m
Tsur3 Al2O3
Tin2
Tin3
20 m
3m
Fig. 3. Geometric shape of RB.
r4 r3 r2 r1
Steel sheet (r 3-r4) Bricks with Al2O3 or MgO (r2-r3) Anzast layer (r1-r2)
Fig. 4. Physical construction of RB wall.
Steel sheet (r3-r4) Bricks (r2-r3) Anzast layer (r1-r2) r1 = 1700 mm r2 = 1768 mm r3 = 2168 mm r4 = 2200 mm
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Anzast Layer
Bricks with Al2O3 or MgO
1 2π kanz l
1 2π kbr l
Chrome -nickel Steel sheet 1 2π ksts l
Fig. 5. Electrical analogy of thermal conductivities for RB wall.
Table 4 Thermal values of RB Thermal properties
Numerical values
Thermal properties
Numerical values
Tin1 Tin2 Tin3 kanz
1423 K 1823 K 1473 K 0.3 kW/m K
ksts l2
36.4 kW/m K 20 m
Tsur1 Tsur2 Tsur3 kbr-Al2 O3 kbr-MgO l1 l3
423 K 393 K 473 K 2.09 kW/m K 2.32 kW/m K 43 m 3m
Q_ rad ¼ reðTin4 T04 ÞA
ð8Þ
Q_ conv ¼ hAðTsur T0 Þ
ð9Þ
X
Q_ L ¼ Q_ cond þ Q_ rad þ Q_ conv ¼ 9958 kW
ð10Þ
4.2.3. Energy efficiency The energy efficiency is expressed as the ratio of the energies leaving the RB to the energies entering the RB. So, the energy efficiency and its result can be written as Eq. (11): X X min ðhT;P Þ ¼ j 355 586j=j 365 544j ¼ 97% ð11Þ mex ðhT;P Þ g ¼
5. Exergy analysis for a control volume There are many studies applying second law analysis [12–19]. The concept of exergy has been appearing in the international thermodynamic world with increasing frequency for one or two decades. Nonetheless, the concept of exergy is uncommon in descriptions of industrial processes. This is unfortunate, particularly since the concept of exergy will be used routinely in process analysis in the near future. The concept is both readily understood and easy to apply [3]. The various kinds of energy display different qualities. These differences appear in their ability to feed energy driving processes and to be converted into other kinds of energy [8]. The standard of energy quality is called exergy. So, exergy analysis is a powerful concept for physical and chemical processes. Besides,
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• Exergy analysis provides an alternative view on the correct efficiency of a process. • Exergy analysis is very useful to find operations where efficiency improvements are the most suitable or useful [11]. There are three types of exergy transfer across the control surface of a system: 1. Exergy of work transfer. 2. Exergy of heat transfer. 3. Exergy associated with the steady stream of matter. 5.1. Exergy of work transfer The maximum work delivered by the system Wmax is only partly available for use. One part P0 DV is spent in order to displace the atmosphere. The remaining part is the exergy of the system. So, the exergy relation can be written as follows: EW ¼ Wmax P0 DV
ð12Þ
5.2. Exergy of heat transfer Since heat cannot be totally converted into work, heat has a lower exergy compared with work. The exergy of heat at the control surface can be defined as follows: EQ ¼ Qcv ð1 T0 =T Þ
ð13Þ
5.3. Exergy associated with a steady stream of matter (flow exergy) The exergy of a stream of matter is equal to the maximum amount of work obtainable when the stream is brought from its initial state to the dead state by reversible processes. The specific exergy of a stream of matter (specific form) can be divided into distinct components. These components are written in two forms [20,21]: 1. Thermomechanical exergy ðeTM f Þ CH 2. Chemical exergy ðef Þ These are: etot ¼ eTM þ eCH f f
ð14Þ
where ¼ ePH þ eKN þ ePT eTM f f f f ¼ ðh T0 sÞ ðh0 T0 s0 Þ þ eCH ¼ ðli0 li00 Þ f
C2 þ gG z0 2
ð15Þ ð16Þ
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li0 and li00 can be given by the following Eqs. (16a) and (16b) for reference substances, assumed as ideal gases. li0 ¼ gi0 þ R T0 LnðPi0 =P0 Þ
ð16aÞ
li00 ¼ gi0 þ R T0 LnðPi00 =P0 Þ
ð16bÞ
gi0 ¼ hi0 T0 si0
ð16cÞ
If some of the species i of the system or of streams do not exist in the environment, li00 will be determined by one of the known methods for a gaseous fuel and a mixture [22,23]. 5.4. Exergy analysis in RB The exergy balance for a steady flow system is given by the following equation: Ein Eex EQ EL ¼ Es
ð17Þ
Eq. (17) shows that exergy losses are caused by irreversibilities. If this equation is applied for the RB as seen in Fig. 6, Eqs. (18)–(21) can be obtained. The following assumptions are made to obtain these equations: 1. The system is assumed as a steady state, steady flow process. 2. Electrical energy used for the RB to rotate is not included in the analysis in obtaining exergy equation. 3. Stack gases are assumed as ideal gases. 4. Pressure effects on enthalpy and entropy of solids are neglected. ¼ ePT 5. Variations of the potential and kinetic energies are neglected (i.e. eKN f f ¼ 0). 6. Chemical exergies of the substances are neglected. X X X PH min ePH ¼ m e þ EQ þ EL ð18Þ ex in ex in
ex
where ePH ¼ ðh h0 Þ T0 ðs s0 Þ
ð19Þ
EQ ¼ QL ð1 T0 =Tsur Þ
ð20Þ
PH Σ min ε in
in
RB
PH Σ mex εex
ex
Σ EQ
Fig. 6. Exergies going into and leaving rotary burner.
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EL ¼ T0 Sgen
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ð21Þ
Numerical results of this analysis are given in Table 5. Table 5 Numerical results of exergy analysis Materials going into RB
Materials leaving RB
Farin CaO CO2 SiO2 Al2 O3 Fe2 O3 MgO K2 O SO3 Na2 O Total Coal C S N2 H2 O2 H2 O CaO SiO2 Al2 O3 Fe2 O3 MgO K2 O SO3 Total Air O2 ðÞ N2 ðÞ Total Exergy after reaction of coal C H2 S Total
E_ PH (kJ/h) 24 813 983.63 9 123 681.95 8 340 159.36 2 459 361.43 1 340 304.84 820 755.67 482 780.17 82 451.37 104 498.78 47 567 977.20 E_ PH (kJ/h) 15 187.18 982.64 516.67 16 527.34 2 067.35 4 948.47 138.50 3561.51 1492.00 892.53 258.86 43.30 249.36 46 865.71 E_ PH (kJ/h) 35 342 985.70 125 003 748.25 160 346 733.95 E_ PHðÞ (kJ/h)
Overall
442 859 423.39
Clinker C3 S C2 S C3 A 9 ðCaOÞ4 = Al2 O3 C AF ; 4 Fe2 O3 MgO SO3 K2 O Na2 O Total Dust CaO SiO2 Al2 O3 Fe2 O3 MgO SO3 K2 O Na2 O Total Stack gases CO2 CO SO2 H2 O O2 ðÞ N2 ðÞ Total Lost exergy
E_ PH (kJ/h) 38 982 444.96 9 460 417.06 6 064 725.29 22 041 142.08 2 447 395.14 2 179 805.72 1 120 945.36 141 315.82 581 374.34 246 000.31 83 265 566.08 E_ PH (kJ/h) 4 044 505.93 27 894.05 78 358.17 155 909.23 295 571.35 41 262.53 160 180.80 42 414.27 4 846 096.33 E_ PH (kJ/h) 30 088 733.78 256 417.74 394 416.60 7 900 863.40 25 366 122.86 133 155 929.53 197 162 483.91 157 585 277.07
Overall
442 859 423.39
186 284 202.13ðÞ 44 955 847.20ðÞ 3 657 797.20ðÞ 234 897 846.53
(*): primary air + secondary air; (**): waste air; (***): The exergies values are found by using Gibbs function for C, H2 ve S according to chemical reactions below. (****): C+O2 !CO2 ; (*****): H2 +1/2O2 !H2 O; (******): S+O2 !SO2 . e ¼ gCO2 gC gO2 ; e ¼ gH2 O gH2 1=2 gO2 ; e ¼ gSO2 gS gO2 . C3 S: 3CaO Æ SiO2 ; C2 S: 2CaO Æ SiO2 ; C3 A: 3CaO Æ Al2 O3 ; C4 AF:4CaO Æ Al2 O3 Æ Fe2 O3 .
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5.5. Exergy efficiency The exergy efficiency is a measure of how effectively the input exergy is converted into the exergy of the products. So, exergy efficiency is defined by the following equation: hX i X X X min ein ¼ 1 EL = min ein w¼ mex eex = ¼ 1 ½157 585 277:07=442 859 423:39 ¼ 0:644
ð22Þ
6. Conclusions • Heat losses by conduction, convection and radiation from the RB are about 3% of the heat coming into the system. Although this ratio is seen to be low, the total amount is very considerable from the viewpoint of process duration. So, it is significant to reduce heat losses by using insulation materials for the RB. • Dust and stack gases occurring in the system transport the most significant amount of energy out of the RB. Some of this energy is used in the pre-heater system. The amount of energy that is not used in the pre-heater system can be utilized in various sections of the plant as process heat. • Waste air also transfers a very important amount of energy from the RB. Accordingly, the amount of air coming into the RB should be controlled. • The percent of lost exergy is 35.6% of the total exergies. This is the highest ratio after the exergy percent of stack gases. The exergy losses in the RB are caused by chemical reactions, forming of clinker, heat transfer and other reasons. • Stack gases and the waste air in them have a considerable amount of exergy. It is possible to use the unused portion of this energy in other applications. • Although the energy efficiency is about 97%, the exergy efficiency is 64.4%. So, it is seen that exergy analysis accounts for the operation, indicating the locations of energy degradation in the process. • The exergy efficiency at another plant in Turkey was obtained to be 64.5% [5]. This value is close to the value obtained in this study.
References [1] Moran MJ. Availability analysis. New Jersey: Prentice-Hall, Inc.; 1982. [2] Morris DR, Szargut J. Standard chemical exergy of some elements and compounds on the planet earth. Exergy 1986;11(8):733–55. [3] Wall G. Exergy flows in industrial processes. Energy 1998;13(2):197–208. [4] C ß elen F. Exergy analysis in a Rotary Burner With Pre-Calcination In Dry System Cement Production. Kırıkkale University Institute of Science & Technology, M.S. Thesis, 1998. € urk IT, _ K€ [5] Kolip A, Uzt€ ose R, Arıkol M. Energy and exergy analysis for cement factory. In: Proceedings of the Workshop on the Second Law of Thermodynamics, Erciyes University and Turkish Soc. Thermal Scis. and Tech. (T.S.T.S.T), August 27–30, 1990, Kayseri, Turkey.
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