Investigating The Performance of A Steam Power Plant

Transcription

1 Internatinal OPEN ACCESS Jurnal Of Mdern Engineering Research (IJMER) Investigating The Perfrmance f A Steam Pwer Plant * Ahmed Rashad 1, A. Elmaihy *2 1 Department f Mechanical Pwer and Energy, Military Technical Cllege, Kbry El Kbba, Cair, Egypt 2 Department f Mechanical Pwer and Energy, Military Technical Cllege, Kbry El Kbba, Cair, Egypt Crrespnding authr: *Ahmed Rashad ABSTRACT: The perfrmance analysis f Shbra El-Khima pwer plant in Cair, Egypt is presented based n energy and exergy analysis t determine the causes, the sites with high exergy destructin, lsses and the pssibilities f imprving the plant perfrmance. The perfrmance f the plant was evaluated at different lads (Full, 75% and, 50 %). The calculated thermal efficiency based n the heat added t the steam was fund t be 41.9 %, 41.7 %, 43.9%, while the exergetic efficiency f the pwer cycle was fund t be 44.8%, 45.5% and 48.8% at max, 75% and, 50 % lad respectively. The cndenser was fund t have the largest energy lsses where (54.3%, 55.1% and 56.3% at max, 75% and, 50 % lad respectively) f the added energy t the steam is lst t the envirnment. The maximum exergy destructin was fund t be in the turbine where the percentage f the exergy destructin was fund t be (42%, 59% and 46.1% at max, 75% and, 50 % lad respectively). The pump was fund t have the minimum exergy destructin. It was als fund that the exergy destructin in feed water heaters and in the cndenser tgether represents the maximum exergy destructin in the plant (abut 52%). This means that the irreversibilities in the heat transfer devices in the plant have a significant rle n the exergy destructin. S, it is thught that the imprvement in the pwer plant will be limited due t the heat transfer devices. Keywrds : 2nd law efficiency; Dead state; Steam pwer plant I. INTRODUCTION Efficient utilizatin f the energy resurces is f a majr interest fr system designers and scientists. Thermal analysis is the way t evaluate the perfrmance f the energy systems (pwer generatin thermal systems). Thermal analysis includes energy and exergy analysis. Energy analysis fllws the energy thrugh the system and measures the capability f the system in cnverting the input energy int the desired utput (thermal efficiency). Where exergy analysis gives a measure hw far the system perfrmance is frm the ideality [1-3]. In energy analysis, the term thermal efficiency which is knwn as a cnversin efficiency is used fr the evaluatin. Thermal efficiency is used t evaluate the perfrmance f the verall system. Fr that reasn; first lw analysis r the cnversin efficiency is nt enugh t evaluate the system perfrmance. Exergy analysis r secnd law analysis has been used in evaluating the energy system design t ptimize and imprve the system [4-7]. As a result f the exergy analysis, a term secnd law efficiency r exergetic efficiency is used. Exergetic efficiency can be determined fr the verall system as well as fr the individual cmpnents f the system. Energy and exergy analysis f energy systems are used t get a cmplete picture f the system perfrmance. The perfrmance f pwer plants as energy systems is evaluated using energy and exergy analysis. Exergy analysis f pwer plants is a helpful tl helps in determining the magnitudes, causes, and lcatins f lsses as well as imprving the efficiency f the verall system and its cmpnents. Effrts were dne t analyze and lcate the sites f maximum lsses in thermal pwer systems. The effrts fcused als n the ways f imprving the perfrmance. Aguilar et al [8] cncerned with the lss factr t be used in energy audits fr the turbine. Kwak et al [9] evaluated the perfrmance f a cmbined cycle plant by analyzing each cmpnent in the plant as well as the whle cycle. They intrduced an ecnmic evaluatin fr the plant as well Khaliq et al, [10] used the exergetic analyses t evaluate the perfrmance f a cmbined gas turbine-steam pwer. Sciubba et al [11] highlighted the imprtance f the cncept f exergy and its usage in evaluating and ptimizatin f the perfrmance f pwer plants. Aljundi [12], implemented the first law and secnd law analysis t evaluate the perfrmance f a steam pwer plant. Studied the effect f the envirnmental cnditin n the plant perfrmance. Yamini et al [13] fund that increasing the number f feedwater heaters in the Rankine cycle imprved the energy and exergy efficiency IJMER ISSN: Vl. 7 Iss. 7 July

2 Investigating The Perfrmance Of A Steam Pwer Plant f the cycle. Sinha et al studied the effect f the ship external factrs n the verall energy efficiency perfrmance f a steam pwer plant. [14] Lalatendu et al studied the perfrmance f a cal-fired biler at the design and ff-design cnditins. Ozdil et al [15] fund that the maximum exergy destructin ccurs in the fluidized bed cal cmbustr f the steam pwer plant. Navid et al [16] studied the thermdynamic and exergecnmic perfrmance f a cmbined steam-rganic Rankine cycle. The bjective f this wrk is t make a detailed analysis f a steam pwer plant in Shbra El-Khima, Cair, Egypt. The plant cnsists f fur units. The energy and exegy analysis were implemented n ne unit at different lads. Causes f irreversibilities in each cmpnent will be discussed. Sites f majr energy lss and exergy destructin will be determined. The pssibilities f imprving the exergetic efficiency are examined. II. PLANT DESCRIPTION The pwer capacity f the plant is (1260) MW. The fuel used is Natural gas and heavy fuel il. It has fur steam turbines with a rated pwer 315 MW fr each ne at full lad. Each unit has seven stages f regenerative feed water heating systems. The bleeding water t the regenerative heaters is taken frm the highpressure turbine, the intermediate turbine, and the lw-pressure turbine. The lcatins, type and the number f feedwater heaters are shwn in Figure 1. The steam generatr prduces superheated steam t the high-pressure turbine at (811) K and (16.64) MPa with a mass flw rate f kg/s at full lad. The exhaust steam at 3.75 MPa frm the high-pressure turbine is reheated t 811 K and enters the intermediate pressure turbine at MPa. The steam enters the lw-pressure turbine at MPa. The cndenser pressure is kpa. At 75% lad, the steam enters the high-pressure turbine at a rate f kg/s and exhausts frm the turbine at a pressure f 2.72 MPa where it is reheated t 811 K and enters the intermediate pressure turbine at 2.45 MPa. The steam enters the lw-pressure turbine at MPa. The cndenser pressure is 8.36 kpa. At 50% lad, the steam enters the high-pressure turbine at a rate f kg/s and exhausts frm the turbine at a pressure f 2.37MPa where it is reheated t 811 K and enters the intermediate pressure turbine at 2.13 MPa. The steam enters the lwpressure turbine at 0.822MPa. The cndenser pressure is kpa. Tab. 1 shws the perating cnditins f the plant. III. THERMODYNAMIC ANALYSIS Exergy and availability are identical terms and they can be defined as measure f the maximum capacity f a system t perfrm useful wrk as it prceeds t a specified final state in equilibrium with its surrundings. Exergy is nt cnserved where it is destructed in the system due t the irreversibilities in the system. By exergy analysis, the magnitudes, surces, and lcatins f thermdynamic inefficiencies can be identified. 3.1 Energy Analysis Neglecting the ptential and kinetic energy effects f the flwing streams the first law calculatins at steady state peratin f the plant were dne. The cnservatin equatin f energy can be expressed as fllws: The thermal efficiency f the plant: Q -W me h - mi h (1) W th Q 3.2 Exergy Analysis Exergy can be transferred in the frm f heat, wrk, and mass flw. The general equatin f exergy balance fr a steady state prcess; e i (2) X heat -W me e -mi i I (3) IJMER ISSN: Vl. 7 Iss. 7 July

3 Investigating The Perfrmance Of A Steam Pwer Plant Figure 1: Cycle Scheme and perating cnditins at 50 % lad Table 1 The perating peratin cnditins f the pwer plant Operating Cnditin Value The fllwing equatins represent the exergy f varius frms f energy: The net exergy transfer by heat ( X And the specific exergy is given by heat X heat ) at temperature T is given by T 1 Q (4) T h h T (s s ) (5) Then the ttal exergy rate assciated with a fluid stream becmes X m m h h T s s ) (6) Max. Lad 75% Lad 50% Lad Feedwater inlet temperature t biler K K K Steam Flw rate tn/h 693 tn/h 607 tn/h Steam temperature, HPT inlet 811K 811K 811K Steam pressure, HPT inlet bar bar bar Pwer utput 320 MW 236 MW 208 MW ( IJMER ISSN: Vl. 7 Iss. 7 July

4 Investigating The Perfrmance Of A Steam Pwer Plant Table II shws the definitin f the exergy destructin rate and the 2nd law efficiency fr each cmpnent in Figure 1 in case f a steady state peratin. Table 2: Definitin f the exergy destructin rate and the 2nd law IV. RESULTS AND DISCUSSIONS The perfrmance f the pwer plant was analyzed with the reference ambient temperature and pressure as K and kpa, respectively.katt sftware[17] was used t indicate the thermdynamic prperties f water at the indicated state pints f Figure 1 Appendix A shws a summary f the prperties f the state pints at different lads. Figure 2 shws that the plant has highest thermal efficiency at 50% lad ( 44%). This efficiency was based n steam inlet cnditins at HPT. Figure 3 shws that the plant has highest exergetic efficiency at 50% lad (ηii 48.8%), while the lwest exergetic efficiency was fund t be at full lad (η II 44.8%).Frm figure 2 and 3 it can be cncluded that the plant has the best perfrmance at ff-design cnditin (part lad cnditins). The figures shw that, the thermal efficiency was fund t be 41.9 %, 41.7 %, 43.9% at max lad, 75% lad and, 50 % lad respectively, while the pwer cycle exergetic efficiency was fund t be 44.8%, 45.5% and 48.8% at max lad, 75% lad and, 50 % lad respectively.figure 4 shws that the maximum exergy destructin was fund t be in the turbine, and the maximum exergy destructin in the turbine ccurs at 75% lad while perating the plant at maximum lad results in lwest exergy destructin. Frm this; it culd be cncluded that the irreversibilities in the turbine are dminant ver all ther irreversibilities in the cycle. The percentage f exergy destructin in the turbine is (42% - 46%) f lsses in the plant. Als, this indicates that fcus shuld be n the turbine t make significant imprvements [18], [19]. Figure 4 shws als that the minimum exergy destructin was fund t be at the pump. The causes f the exergy destructin include frictin, mixing, chemical reactins, heat transfer thrugh a finite temperature difference, unrestrained expansin, nn-quasi equilibrium cmpressin r expansin [4].The pumping prcess f the feed water t the biler has fewer causes f exergy destructin where the heat transfer during the prcess is cnsidered t be neglected; the perating fluid is a single phase (liquid). Fr these reasns it is thught that the pump has the minimum exergy destructin.on the ther hand, the peratin f steam expansin in the turbine has many causes f exergy destructin such as high frictin between steam and turbine blades due t the high velcity f steam, the deviatin f the steam expansin prcess frm the quasi-equilibrium expansin and the heat transfer f steam at a temperature and the surrunding. Fr these reasns it is believed that the turbine has the maximum exergy destructin. In the fllwing the results f each sectr f the plant will be analyzed: 4.1 Turbine: Figure 5 shws that the high-pressure turbine stage has the maximum exergy destructin. This may be because f the irreversibilities arise frm the interactin between the steam flw and the turbine blades; where at this stage the steam has the highest pressure, temperature, and velcity which cause high interactin between the steam flw and the turbine blades. The figure shws als that the exergy destructin in this stage increases with decreasing the lad where it has its maximum value at 50% lad.figure 5 shws that the third stage f the lw- IJMER ISSN: Vl. 7 Iss. 7 July

5 Investigating The Perfrmance Of A Steam Pwer Plant pressure turbine has the lwest exergy destructin at all lads. Als, amng the three lads f peratin, the 75% lad has the highest exergy destructin. 4.2 Cndenser: Frm the first law analysis, energy lsses assciated with the cndenser are significant because they represent abut (55%) f the energy input t the plant. The exergy analysis shwed that nly abut (20% - 28 %) f the exergy was lst in the cndenser. A large amunt f heat energy is remved frm the plant via the cndenser. Due t the lw grade f this heat energy, it is thermdynamically insignificant and frm an ecnmic pint f view; it is difficult t regenerate this energy [18], [20]. Figure 4 shws that the exergy destructin in the cndenser decreases with decreasing plant lad. The majr factr f irreversibility in the cndenser is the heat transfer thrugh a finite temperature difference. 4.3 Feed water heaters: Figure 6 shws that the maximum exergy destructin in the feed water heaters ccurs at a full lad f peratin. Cmbining the exergy destructin in feed water heaters and the cndenser (figure 7) it reveals that the exergy destructin in the cndenser and heaters represent the maximum exergy destructin in the plant. This means that the irreversibilities due t the heat transfer prcesses in the heaters and the cndenser have a majr influence n the exergy destructin in the plant. Figure 2: Thermal efficiency at different lads Figure 3: 2 nd law efficiency at different lads IJMER ISSN: Vl. 7 Iss. 7 July

6 Investigating The Perfrmance Of A Steam Pwer Plant Figure 4: Percent exergy destructin at different lads Figure 5: Percent exergy destructin in the turbine stages at different lads Figure 6: Percent exergy destructin in the feed water heaters at different lads IJMER ISSN: Vl. 7 Iss. 7 July

7 Investigating The Perfrmance Of A Steam Pwer Plant Figure 7: Cmparisn f % exergy destructin at different lads V. CONCLUSION In the present study, the first law and the secnd law f thermdynamics were used t evaluate the perfrmance f a steam pwer plant. The main bjective f this paper was t analyze the plant main cmpnents separately and t identify and quantify the sites having largest energy and exergy lsses at different lads. The calculated thermal efficiency f the cycle based n specific heat input t the steam was 41.9%, 41.7% and 43.9% at 50%, 75%, and full lad respectively. The calculated exergy efficiency f the pwer cycle is (45% - 49%), which is lw. The best mde f peratin f the plant was fund t be at 50% lad where; the plant has highest thermal and exergetic efficiencies at this mde f peratin. The maximum energy lss ccurs in the cndenser where 56.4%, 55.2% and 54.4% f the input energy was lst t the envirnment at 50%, 75%, and full lad respectively. But this energy is thermdynamically insignificant due t its lw-grade energy. The exergy destructin in feed water heaters and in the cndenser tgether represents the maximum exergy destructin in the plant (abut 52%). This means that the irreversibilities in the heat transfer devices in the plant have a significant rle in the exergy destructin in the plant. But it is thught that the pprtunities t imprve the exergy destructin in these heat transfer devices are lw due t the nature f the heat transfer prcess itself which shuld be dne at finite temperature difference (physical cnstraints). The secnd law analysis f the plant shwed that the turbine is the majr surce f lsses where 46.1%, 59.6% and 42% f the fuel exergy input t the cycle was destryed at 50%, 75%, and full lad respectively. The turbine has the maximum exergy destructin while the pump has the minimum exergy destructin. In cntrast t the case f heat transfer devices; it is thught that the pprtunities t imprve the irreversibilities in the turbine are high. In general, part f the irreversibility in the plant can nt be avided due t physical, technlgical, and ecnmic cnstraints. IJMER ISSN: Vl. 7 Iss. 7 July

8 Investigating The Perfrmance Of A Steam Pwer Plant Nmenclature h Specific enthalpy (J/kg) s Specific entrpy (J/kg.K) I Exergy destructin rate (W) T Temperature (K) m P Mass flw rate (kg/s) Pressure (Pa) W X Wrk dne rate r pwer dne by the system (W) Ttal exergy rate (W) Q Heat transfer rate t the system kj/s Greek Symbls Abbreviatins η th First law efficiency HPT High-pressure turbine η II 2 nd law efficiency IPT Intermediate pressure turbine ψ Specific exergy (J/kg) LPT Lw-pressure turbine Subscripts e exit i inlet Dead state cnditin REFERENCES [1]. Y.A. Cengel, M. A. Bles, "Thermdynamics: An Engineering Apprach", fifth ed. McGraw-Hill, New Yrk [2]. N. A. Musa, M. S. Adam, "Analysis f Steam Pwer Plant at Kaduna Refining and Petrchemical Cmpany frm Exergetic Perspective", British Jurnal f Applied Science & Technlgy, Vl. 8, n. 6, pp , 2015 [3]. R. Dang, S.K. Manga, Gaurav, " Energy & Exergy Analysis f Thermal Pwer Plant at Design and ff Design Lad, Internatinal Advanced Research Jurnal in Science, Engineering and Technlgy Vl. 3, n. 5, pp , 2016 [4]. M. A. Rajper, A. G. Memn, K. Harijan, "Energy and Exergy Analysis f 210 MW Jamshr Thermal Pwer Plant", Mehran University Research Jurnal f Engineering & Technlgy, Vl. 35, n. 2, pp , 2016 [5]. M. A. Rajper, A. G. Memn, K. Harijan "Exergy Analysis f a Subcritical Reheat Steam Pwer Plant with Regressin Mdeling and Optimizatin", Mehran University Research Jurnal f Engineering & Technlgy, Vl. 35, n. 3, pp , 2016 [6]. R. Parimal, Pati, Hemish A. Vaidya, Nilesh R. Sheth, " Exergy Analysis f Steam System Cmpnents f Pwer Plant at S&PG Dept. f GNFC BHARUCH", Internatinal Jurnal f Advance Research In Science And Engineering, Vl. 3, n. 5, pp , 2014 [7]. A. Bejan, " Advanced Engineering Thermdynamics", third ed. Wiley, New Yrk [8]. A. Z. Aguilar, L.V. Vega, A. G. Munz and A. H. Guerrer, " Thermdynamic characterizatin f the pwer lss factr in steam turbines" Energy Cnversin and Management vl. 43 pp , 2002 [9]. H. Y. Kwak, D. J. Kim, J. S. Jen. " Exergetic and therm-ecnmic analyses f pwer plants "Energy, Vl. 28 pp , 2003 [10]. A. Khaliqa, S. C. Kaushikb, "Secnd-law based thermdynamic analysis f Braytn/Rankine cmbined pwer cycle with reheat", Applied Energy Vl. 78 pp , 2004 [11]. E. Sciubba, G. Wall, "A brief Cmmented Histry f Exergy Frm the Beginnings t 2004", Int. J. f Thermdynamics, Vl. 10 n. 1, pp. 1-26, [12]. I.H.Aljundi " Energy and exergy analysis f a steam pwer plant in Jrdan", Applied Thermal Engineering, Vl. 29, n. 2-3,, pp , 2009 [13]. Y. Verma, K. P. Kaurase, "Exergy Analysis f Thermal Pwer Plant", Internatinal Jurnal f Engineering & Science Research, vl. 4, n. 12, pp , 2014 [14]. L. Pattanayak, S. K. Ayyagari, " Use f Energy and Exergy Analysis in Cal Fired Biler" Internatinal Jurnal f Multidisciplinary Sciences and Engineering, Vl. 5, n. 3, pp , 2014 [15]. N. F. T. Ozdil, A. Tantekin, Z. Erbay " Energy and exergy analyses f a fluidized bed cal cmbustr steamplant in textile industry" Fuel, Vl. 183, n. 1, pp , 2016 [16]. N. Nazari, P. Heidarnejad, S. Prkhial," Multi-bjective ptimizatin f a cmbined steam-rganic Rankine cycle based n exergy and exerg-ecnmic analysis fr waste heat recvery applicatin" Energy Cnversin and Management, Vl. 127, n. 1, pp , 2016 [17]. KATT sftware " Cmputer Aided Thermdynamic Tables" Jhn Wiley & Sns Inc [18]. M. Yunus, M. Asadullah, H. A. Ghulman, J. F. Rahman, M. Irfan, "Energy Based Analysis f a Thermal Pwer Statin fr Energy Efficiency Imprvement" Internatinal Jurnal f Mdern Engineering Research, Vl. 4, n. 3,,pp , 2014 [19]. L. Pattanayak, " The Influence f Operatinal Parameters n Biler Perfrmance: An Exergy Analysis", Internatinal Jurnal f Advances in Engineering & Technlgy, Vl. 7, n. 5, pp , 2014 IJMER ISSN: Vl. 7 Iss. 7 July

9 Investigating The Perfrmance Of A Steam Pwer Plant [20]. H. R. Kulkarni, P.P.Revankar, S.G. Hadaga, " Energy and Exergy Analysis f Cal Fired Pwer Plant",Internatinal Jurnal f Innvative Research in Technlgy & Science, Vl. 1 n. 3, pp , APPENDIX The thermdynamic prperties f water at indicated state pints shwn in Fig. 1Full Lad: nde T (K) P (MPa) m (kg/s) h (kj/kg) s (kj/kg K) Ψ(kJ/kg) X (MW) nde T (K) P (MPa) 75 % Lad: m (kg/s) h (kj/kg) s (kj/kg K) Ψ(kJ/kg) X (MW) nde T (K) P (MPa) 50 % Lad: m h (kj/kg) s (kj/kg K) Ψ(kJ/kg) (kg/s) X (MW) IJMER ISSN: Vl. 7 Iss. 7 July