Research Article Thermodynamic Analysis of a Steam Power Plant with Double Reheat and Feed Water Heaters

Transcription

1 Hindawi Publishing Corporation Advances in Mechanical Engineering Volume 2014, Article ID , 11 pages Research Article Thermodynamic Analysis of a Steam Power Plant with Double Reheat and Feed Water Heaters M M Rashidi, 1,2 A Aghagoli, 1 and M Ali 3 1 Mechanical Engineering Department, Engineering Faculty, Bu-Ali Sina University, PO Box , Hamedan, Iran 2 University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai, China 3 Mechanical Engineering Department, College of Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia Correspondence should be addressed to M Ali; mali@ksuedusa Received 4 September 2013; Revised 27 December 2013; Accepted 2 January 2014; Published 9 March 2014 Academic Editor: Moran Wang Copyright 2014 M M Rashidi et al This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited A steam cycle with double reheat and turbine extraction is presented Six heaters are used, three of them at high pressure and the other three at low pressure with deaerator The first and second law analysis for the cycle and optimization of the thermal and exergy efficiencies are investigated An exergy analysis is performed to guide the thermodynamic improvement for this cycle The exergy and irreversibility analyses of each component of the cycle are determined Effects of turbine inlet pressure, boiler exit steam temperature, and condenser pressure on the first and second laws efficiencies are investigated Also the best turbine extraction pressure on the first law efficiency is obtained The results show that the biggest exergy loss occurs in the boiler followed by the turbine The results also show that the overall thermal efficiency and the second law efficiency decrease as the condenser pressure increases for any fixed outlet boiler temperature, however, they increase as the boiler temperature increases for any condenser pressure Furthermore, the best values of extraction pressure from high, intermediate, and low pressure turbine which give the maximum first law efficiencies are obtained based on the required heat load corresponding to each exit boiler temperature 1 Introduction Steam power plants are widely utilized throughout the world for electricity generation, and coal is often used to fuel these plants Energy consumption is one of the most important indicators showing the development stages of countries and living standard of communities Currently, 80% of electricity in the world is approximately produced from fossil fuels (coal, petroleum, fuel oil, and natural gas) fired thermal power plants, whereas 20% of the electricity is compensated from different sources such as hydraulic, nuclear, wind, solar, geothermal,and biogas [1] Many techniques are being used to increase the efficiency of the steam cycle The most outstanding of these techniques are reheating in order to reduce the irreversibility of the cycle Reheating increases the efficiency by raising the mean temperature of the heat addition process, by increasing the steam temperature at the turbine inlet and also by increasing the efficiency of the expansion process in the steam turbine With reheat, a power plant can take advantage of the increased efficiency that results in higher boiler pressure and yet avoid lowquality steam at the turbine exhaust [2] Habib and Zubair [3] conducted a second law analysis of regenerative Rankine power plants with reheat Chiesa and Macchi [4], Gambini et al [5], Bhargava and Peretto [6], and Poullikkas [7] have studied and predicted the performance of reheat gas turbine using air as a coolant Srinivas [8] showed that the deaerator placed in between the LP and IP heaters gives high efficiency compared to a deaerator-condenser arrangement Analyses of power generation systems are of scientific interest and also essential for the efficient utilization of energy resources The most commonly used method for analysis of an energy-conversion process is the first law of thermodynamics Furthermore, exergetic analysis provides a tool for a clear distinction between energy losses to the environment and internal irreversibility in the process [9] As energy analysis is based on the first law of thermodynamics, it has some inherent limitations like not accounting for properties of the system environment or degradation of the energy quality through dissipative processes An energy analysis

2 2 Advances in Mechanical Engineering Table 1: The main parameters for analyzing the steam cycle P 0 (kpa) [16] 1013 T 0 ( C) [16] 25 Condenser pressure (kpa) [10] Deaerator pressure (kpa) Boiler exit steam temperature ( C) [31, 32] 600 HP turbine pressure (kpa) [31] η LPT [8] 09 η HPT [33] 085 η P [34] 08 T in ( C) 25 T out ( C) 35 Pinch point ( C) [29] 2 Approach 1 ( C) [29] 8 m 10 (kg s 1 ) 1 1 Approach point is used for the heaters For example, temperature difference between T 23 and T 9 is defined as the approach point does not characterize the irreversibility of processes within the system In contrast, exergy analysis will characterize the work potential of a system Exergy is the maximum work thatcanbeobtainedfromthesystem,whenitsstateis brought to the reference or dead state [10] Ozgener et al [11] illustrated that the overall energy and exergy efficiencies of the SGDHS (Salihli geothermal district heating system) components were also studied to evaluate their individual performance and obtained to be 555 and 594%, respectively Ameri et al [12] showed that the greatest exergy loss in the gas turbine occurs in the combustion chamber due to its high irreversibility Rosen [13] evaluated the performance of coalfired and nuclear power plants via exergy analyses Dincer and Muslim [14] performed a thermodynamic analysis of reheat cycle power plants Medina-Flores and Picón-Núñez [15] proposed algorithms to predict power production for single and multiple extraction steam turbines Aljundi [16] studied the energy and exergy analysis of Al-Hussein power plant in Jordan and reported that the chemical reaction is the most significant source of exergy destruction in the boiler system Oktay [17] presented exergy loss and proposed improving methods for a fluidized bed power plant in Turkey Ahmadi et al [18] have shown the results of both exergy and exergoeconomic analyses Their results showed that the largest exergy destruction occurs in the CCPP (combined cycle power plant) combustion chamber and that increasing the gas turbine inlet temperature decreases the CCPP cost of exergy destruction In the present study, the energy and exergy analysis are conducted to evaluate the performance of the above suggested steam power plant cycle using 6 closed feed water heaters with double reheat and with different extracting pressure Sources of exergy destruction in the power plant are identified and a parametric study is performed to determine the first and second law efficiencies with different operating conditions Maximum first law efficiencies are obtained at the optimal extraction pressure 2 Energy and Exergy Analysis This cycle consists of boiler, turbine, condenser, feed water heaters, deaerator, feed water pump, and the condensate extraction pump The schematic of cycle and the T-s diagram are shown in Figures 1 and 2,respectively For an open system at steady state, the first law of thermodynamicscanbewrittenas[19 21] Q+ m(h i + V2 i 2 +gz i)= m(h o + V2 o 2 +gz o)+ W (1) Exergy is defined as the maximum work that can be achieved by bringing a system into equilibrium with its environment The concept of exergy is supported by the consideration of the temperature level, which is based on the energy conversion from thermal to power Exergy analysis is a useful method for complementing but not for replacing the energy analysis It is becoming the most appropriate tool for thermodynamic analysis The exergy efficiency of the power cycle may be defined in two ways The first one is the physical exergy and the second one is the chemical exergy In this study, the kinetic and potential parts of exergy are considered negligiblethechemicalexergyofgaseousfuelsiscomputed from the stoichiometric combustion chemical reactions The chemical exergy is associated with the departure of the chemical composition of a system from its chemical equilibrium which is important in processes involving combustion Equations (2) and (6) show in general the exergy destroyed rate and the exergy at any state of an open system: Ex Q + in m i ex i = m o ex o + Ex W + Ex D, (2) out Ex Q = (1 T 0 ) Q T k, k (3) Ex W = W, (4) Ex = Ex ph + Ex ch, (5) Ex ch = mex ch mix, (6) Ex ph = m[(h h 0 ) T 0 (s s 0 )], (7) where Ex Q, Ex W,andEx D are the corresponding exergy of heat transfer, work, and the exergy destruction which crosses the boundaries of the control volume, T is the absolute temperature (K), and (0) refers to the ambient conditions The mixture chemical exergy is defined as follows: ex ch n mix =[ i=1 X i ex ch n i +RT 0 X i LnX i ] (8) i=1 The physical exergy of the fuels is negligible when compared to the chemical exergy For the evaluation of the fuel exergy, the above equation cannot be used [22, 23] Thus, the corresponding ratio of simplified exergy is defined as follows [24]: ex f =γ LHV, (9)

3 Advances in Mechanical Engineering Boiler HP turbine IP turbine LP turbine Third LP Second LP First LP α heater heater 4 heater 19 Condenser Third HP Second HP First HP Deaerator α5 α6 α7 heater heater heater α 1 α 2 α 3 FWP 6 5 CEP Figure 1: The schematic of steam power plant cycle Hot water Cold water Table 2: Process parameters of the cycle Point T ( C) P (kpa) h (kj kg 1 ) s (kj K 1 kg 1 ) m (kg s 1 ) ψ (kj kg 1 ) Cold water Hot water

4 4 Advances in Mechanical Engineering Water where γ stands for the exergy factor and LHV denotes the lower heating value of the fuel material It should be noted that γ canbeestimatedforanyfuelc x H y by [23, 25, 26] T ( C) , , 7 24 Deaerator , Condenser Extraction line Turbine line s (kj/kg K) Figure 2: The T-s diagramofthecycle γ = ( y x ) (10) x The energy and exergy destroyed equations for all components of the cycle are given as follows The First Adiabatic Low Pressure Feed Water Heater ( m 10 α 1 α 2 α 3 α 4 )(h 3 h 2 ) +(α 5 +α 6 +α 7 )h 28 (α 5 +α 6 )h 27 α 7 h 22 =0, I FirstLPH = T 0 [( m 10 α 1 α 2 α 3 α 4 )(s 2 s 3 ) +(α 5 +α 6 )s 27 +α 7 s 22 (11) Table 3: Power balance of the power plant components Component Power balance (kw) based on Table 2 Power balance (kw) based on the optimal first law efficiency Boiler Condenser Turbine Feed water pump Condense extraction pump (α 5 +α 6 +α 7 )s 28 ], η Π,FirstLPH =1 I FirstLPH ψ in,firstlph, where α is the extraction mass flow rate The Second Adiabatic Low Pressure Feed Water Heater ( m 10 α 1 α 2 α 3 α 4 )(h 4 h 3 ) Table 4: Exergy destruction of the power plant components Component Exergy destruction (kw) Percent ratio (%) Exergy efficiency (%) Boiler Condenser Turbine Feed water pump Condensate extraction pump First LP heater Second LP heater Third LP heater Deaerator First HP heater Second HP heater Third HP heater Total Thermal efficiency 489 Exergy efficiency (α 5 +α 6 )h 27 α 5 h 26 α 6 h 21 =0, I SecondLPH = T 0 [( m 10 α 1 α 2 α 3 α 4 )(s 3 s 4 ) +α 5 s 26 +α 6 s 21 (α 5 +α 6 )s 27 ], η Π,SecondLPH =1 I SecondLPH ψ in,secondlph The Third Adiabatic Low Pressure Feed Water Heater ( m 10 α 1 α 2 α 3 α 4 )(h 5 h 4 )+α 5 (h 26 h 20 )=0, I ThirdLPH = T 0 [( m 10 α 1 α 2 α 3 α 4 )(s 4 s 5 ) +α 5 (s 20 s 26 )], η Π,ThirdLPH =1 I ThirdLPH ψ in,thirdlph (12) (13)

5 Advances in Mechanical Engineering 5 The Adiabatic Deaerator α 4 h 19 +(α 1 +α 2 +α 3 )h 25 +( m 10 α 1 α 2 α 3 α 4 )h 5 m 6 h 6 =0, I deaerator = T 0 [α 4 s 19 +(α 1 +α 2 +α 3 )s 25 +( m 10 α 1 α 2 α 3 α 4 )s 5 m 6 s 6 ], I C ={( m 10 α 1 α 2 α 3 α 4 α 5 α 6 α 7 )h 16 +(α 5 +α 6 +α 7 )h 28 ( m 10 α 1 α 2 α 3 α 4 )h 1 } T 0 {( m 10 α 1 α 2 α 3 α 4 α 5 α 6 α 7 )s 16 +(α 5 +α 6 +α 7 )s 28 ( m 10 α 1 α 2 α 3 α 4 )s 1 } η Π,deaerator =1 I deaerator ψ in,deaerator (14) + m win {(h win h wout ) T 0 (s win s wout )}, η Π,C =1 I C ψ in,c The First Adiabatic High Pressure Feed Water Heater (18) m 7 h 7 m 8 h 8 +α 3 h 14 +(α 1 +α 2 )h 24 The Adiabatic Feed Water Pump (α 1 +α 2 +α 3 )h 25 =0, I FirstHPH = T 0 [ m 7 s 7 +α 3 s 14 +(α 1 +α 2 )s 24 (α 1 +α 2 +α 3 )s 25 ], η Π,FirstHPH =1 I FirstHPH ψ in,firsthph The Second Adiabatic High Pressure Feed Water Heater m 8 s 8 (15) w FWP = m 7 (h 7 h 6 ), I FWP = m 7 [(h 6 h 7 ) T 0 (s 6 s 7 )] + w FWP, η Π,FWP =1 I FWP w FWP The Adiabatic Condensate Extraction Pump (19) m 8 h 8 m 9 h 9 +α 1 h 23 +α 2 h 12 (α 1 +α 2 )h 24 =0, w CEP =( m 10 α 1 α 2 α 3 α 4 )(h 2 h 1 ), I SecondHPH = T 0 [ m 8 s 8 +α 1 s 23 +α 2 s 12 m 9 s 9 I CEP =( m 10 α 1 α 2 α 3 α 4 ) (α 1 +α 2 )s 24 ], (16) [(h 1 h 2 ) T 0 (s 1 s 2 )] + w CEP, (20) η Π,SecondHPH =1 I SecondHPH ψ in,secondhph η Π,CEP =1 I CEP w CEP The Third Adiabatic High Pressure Feed Water Heater The Adiabatic Turbine m 10 h 10 m 9 h 9 α 1 (h 17 h 23 ) =0, I ThirdHPH = T 0 [ m 9 s 9 m 10 s 10 +α 1 (s 17 s 23 )], w t ={ m 11 (h 11 h 17 )+( m 10 α 1 )(h 17 h 12 ) η Π,ThirdHPH =1 I ThirdHPH ψ in,thirdhph (17) +( m 10 α 1 α 2 )(h 13 h 14 ) +( m 10 α 1 α 2 α 3 )(h 14 h 18 ) +( m 10 α 1 α 2 α 3 α 4 )(h 15 h 20 ) The Condenser +( m 10 α 1 α 2 α 3 α 4 α 5 )(h 20 h 21 ) q C =( m 10 α 1 α 2 α 3 α 4 α 5 α 6 α 7 )h 16 +( m 10 α 1 α 2 α 3 α 4 α 5 α 6 )(h 21 h 22 ) +(α 5 +α 6 +α 7 )h 28 ( m 10 α 1 α 2 α 3 α 4 )h 1, +( m 10 α 1 α 2 α 3 α 4 α 5 α 6 α 7 )(h 22 h 16 )},

6 6 Advances in Mechanical Engineering I t ={ T 0 [ m 11 (s 11 s 17 )+( m 10 α 1 )(s 17 s 12 ) The Boiler q B = +( m 10 α 1 α 2 )(s 13 s 14 ) +( m 10 α 1 α 2 α 3 )(s 14 s 18 ) +( m 10 α 1 α 2 α 3 α 4 )(s 15 s 20 ) +( m 10 α 1 α 2 α 3 α 4 α 5 )(s 20 s 21 ) +( m 10 α 1 α 2 α 3 α 4 α 5 α 6 )(s 21 s 22 ) +( m 10 α 1 α 2 α 3 α 4 α 5 α 6 α 7 ) (s 22 s 16 )]}, w η Π,t = t I t + w t m 11 h 11 m 10 h 10 +( m 10 α 1 α 2 )(h 13 h 12 ) +( m 10 α 1 α 2 α 3 α 4 )(h 15 h 18 ), I B ={ m 10 (h 10 h 11 )+( m 10 α 1 α 2 )(h 12 h 13 ) +( m 10 α 1 α 2 α 3 α 4 )(h 18 h 15 ) T 0 [(s 10 s 11 )+( m 10 α 1 α 2 )(s 12 s 13 ) + q B (1 T 0 ), T B +( m 10 α 1 α 2 α 3 α 4 )(s 18 s 15 )]} η Π,B =1 I B ex f Energy efficiency (thermal efficiency) is defined as [27] It is obvious that W Net = η thermal = (21) (22) W Net Q B (23) W T W CEP W FWP, (24) whereas exergy efficiency (the second law efficiency) is defined as It is obvious that [28] η exe = W Net ex f (25) η exe = η thermal (26) γ Boiler heat load (kw) Condenser heat load T B =550( C) Condenser pressure (kpa) Boiler heat load T B =550( C) Figure 3: The effect of condenser pressure on the boiler and condenser heat loads at T B = 500 C, 550 C, and 600 C 3 Results and Discussion The main parameters for analyzing this steam cycle are shown in Table 1 It should be noted that the main parameters in Table 1 are chosen following some references as shown in Table 1 Furthermore, low values of both pinch and approach points are chosen following [29] such that the thermal efficiency of the cycle has a maximum The thermodynamic properties of water were calculated using EES software [30] and summarized in Table 2 The energy consumption based on the dead state of P 0 = 101 (kpa) and T 0 =25( C) for each component is shown in Tables 3 and 4, respectivelytable 3 shows the power balance of the power plant components at two states One of these is based on the data from Table 2 and the other is from the power plant at the optimal first law efficiency In other words, to obtain the optimum first law efficiency and then the power balance of other parts of cycle such as boiler and turbine, should vary as seen in Table 3 The optimum first law efficiency is shown, for example, in Figures 9, 11, 12, and 13 for some different extraction pressure The exergy destruction, exergy efficiency of each component, and percent exergy destruction rate are also shown in Table 4 following the equations defined earlier for each component The thermal efficiencies for boiler, heaters, and condenser are 100%, since the heat losses for these components are neglected The efficiencies in the case of the turbine, feed water pump and, condensate extraction pump are 9283%, 80%, and 80%, respectively The first and second law efficiencies of this power cycle based on (23)and(26)are 489% and 4613%, respectively 31 Effect of Condenser Pressure The effect of condenser pressure on the boiler and condenser heat load and also on Condenser heat load (kw)

7 Advances in Mechanical Engineering 7 Turbine power (kw) Condenser pressure (kpa) Figure 4: The effect of condenser pressure on the turbine power at T B = 500 C, 550 C, and 600 C Second law efficiency (%) Condenser pressure (kpa) T B =550( C) Figure 6: The effect of condenser pressure on the second law efficiency at T B = 500 C, 550 C, and 600 C First law efficiency (%) Condenser pressure (kpa) Figure 5: The effect of condenser pressure on the first law efficiency at T B = 500 C, 550 C, and 600 C the turbine power for three boiler exit steam temperatures isshowninfigures3 and 4, respectivelyitisclearthatas the condenser pressure increases, the condenser saturation temperature increases too which means that more heat has to be removed by the condenser for fixed boiler exit steam temperature as seen in Figure 3 Furthermore, the condenser heat load increases for fixed condenser pressure as the boiler Boiler heat load (kw) HP turbine pressure (kpa) 4 Boiler heat load Condenser heat load Figure7:TheeffectofHPturbineinletpressureontheboilerand condenser heat loads at T B = 500 C, 550 C, and 600 C exit steam temperature increases However, the boiler heat load is independent of the condenser pressure Figure 4 shows that the turbine power is affected by both the boiler exit steam temperature and the condenser pressure Therefore, as the condenser pressure increases, more heat load will be removed through the condenser which leads to a decrease Condenser heat load (kw)

8 8 Advances in Mechanical Engineering Turbine power (kw) Second law efficiency (%) HP turbine pressure (kpa) 10 4 Figure 8: The effect of HP turbine inlet pressure on the turbine power at T B = 500 C, 550 C, and 600 C HP turbine pressure (kpa) 10 4 T B =550( C) Figure 10: The effect of HP turbine inlet pressure on the second law efficiency at T B = 500 C, 550 C, and 600 C First law efficiency (%) First law efficiency (%) HP turbine pressure (kpa) HP turbine extraction pressure (kpa) 10 3 P 17 P 12 Figure9:TheeffectofHPturbineinletpressureonthefirstlaw efficiency at T B = 500 C, 550 C, and 600 C in the turbine power for fixed T B andviceversaitisalso noted that as T B increases the turbine power increases for fixed condenser pressure Figures 5 and 6 show the effect of condenser pressure on the first and second law efficiencies, respectively Profiles showninthesefiguresareconfirmedby(23) and(26), since Figure 11: The best values of extraction pressure from HP turbine the first law efficiency depends on both the net power and theheataddedattheboilerbutsincetheboilerheatloadis constant then increasing the condenser pressure will reduce the net power which in turn will reduce the thermal efficiency Similar effects are obtained for the exergy since it depends on the thermal efficiency and the constant value of the exergy factor as seen in Figure 6 32 Effect of High Pressure Turbine Figures 7 and 8 show the effect of high pressure turbine on the boiler and condenser

9 Advances in Mechanical Engineering 9 First law efficiency (%) IP turbine extraction pressure (kpa) 10 3 P 14 P deaerator Figure 12: The best values of extraction pressure from IP turbine 4915 increases, so the turbine power output increases However, due to the change of gradient of the saturated vapor line, the turbine power decreases and this explains the behavior of the thermal efficiency which increases and then decreases as the turbine extraction pressure increases as shown in Figures 11, 12,and13 Figures 9 and 10 show the effect of HP turbine pressure on the first and second law efficiencies Since the first law efficiency depends on both the turbine power and the boiler heat and since both of them (as shown in Figures 7 and 8) reach a maximum then decrease, therefore the thermal efficiency profiles follow them as seen in Figure 9 Similar effects are obtained for the second law efficiency since it is a function of the first law efficiency so it should follow the same trend as seen in Figure 8 It is also clear that for both cases as the boiler exit steam temperature increases the boiler and condenser heat load, turbine power, and first and second law efficiencies increase for any fixed pressure Figures 11, 12, and13 show the best values of extraction pressure from high, intermediate, and low pressure turbine on the first law efficiency at T B = 600 C, respectively The maximum first law efficiency at optimum extraction pressure (P 17 = kpa, P 12 = kpa, P 14 = 4540 kpa, P 6 = 2073 kpa, P 20 = 4726 kpa, P 21 = 1717 kpa, and P 22 = 50 kpa) is 4916% First law efficiency (%) Conclusion In this study, a thermodynamic analysis of a reheat Rankine cycle steam power plant with three HP feed water heaters and three LP feed water heaters with deaerator is conducted, in terms of the first law of thermodynamic analysis and the second law analysis The main conclusions drawn from the present study are summarized as follows LP turbine extraction pressure (kpa) (i) When condenser pressure increases, the condenser rejected heat increases and the turbine power and first and second law efficiencies decrease but boiler heat transfer is independent of the condenser pressure P 20 P 21 P 22 Figure 13: The best values of extraction pressure from LP turbine heat load and also on the turbine power for three boiler exit steam temperatures, respectively When the HP turbine pressure increases, the turbine exit enthalpy decreases and the condenser heat load decreases because the inlet and the outlet enthalpies at condenser are constant and the mass flow rate decreases Also it can be seen that the turbine power and boiler heat increase first to maximum and then decrease as the HP turbine inlet pressure increases It should be noticed that the enthalpy drop across the turbine and extraction mass flow rate increase as HP turbine inlet pressure (ii) When the boiler exit steam temperature increases, condenser rejected heat load, boiler heat load, turbine power, and first and second laws efficiencies increase (iii) As the high pressure turbine increases, the first and second laws efficiencies have similar profiles with maximum values depending on the HP turbine and the boiler temperature (iv) The maximum first law efficiencies are obtained for the optimal extraction pressure at high, intermediate, and low pressure turbine as 4915% (v) The maximum value of exergy loss occurs in the boiler followed by the turbine and the minimum value of exergy loss occurs in the condensate extraction pump

10 10 Advances in Mechanical Engineering Nomenclature ex: Specific exergy (kj kg 1 ) Ex: Exergy rate (kw) g: Gravitational constant (m s 2 ) h: Specific enthalpy (kj kg 1 ) LHV: Low heating value (kj kg 1 ) m: Mass flow rate (kg s 1 ) P: Pressure (kpa) Q: Heat transfer (kw) s: Specific entropy (kj K 1 kg 1 ) T: Temperature( C) V: Velocity(m s 1 ) W: Work rate (kw) z: Elevation (m) Greek Letters η: Efficiency (%) α: Extraction mass flow rate (kg s 1 ) γ: Exergyfactor Subscript 0: Reference point 1 28: Points B: Boiler C: Condenser H: Heater HP: High pressure i: Inlet IP: Intermediate pressure LP: Low pressure o: Outlet p: Pump t: Turbine Conflict of Interests The authors declare that there is no conflict of interests regarding the publication of this paper Acknowledgments The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through the research group Project no RGP-VPP- 080 They also express their gratitude to the anonymous referees for their constructive review of the paper and helpful comments References [1] H H Erdem, A V Akkaya, B Cetin et al, Comparative energetic and exergetic performance analyses for coal-fired thermal power plants in Turkey, International Journal of Thermal Sciences, vol 48, no 11, pp , 2009 [2]MJMoranandHNShapiro,Fundamentals of Engineering Thermodynamics, John Wiley & Sons, New York, NY, USA, 5th edition, 2006 [3]MAHabibandSMZubair, Second-law-basedthermodynamic analysis of regenerative-reheat Rankine-cycle power plants, Energy, vol 17,no 3, pp , 1992 [4] P Chiesa and E Macchi, A thermodynamic analysis of different options to break 60% electric efficiency in combined cycle power plants, Journal of Engineering for Gas Turbines and Power,vol126,no4,pp ,2004 [5] M Gambini, G L Guizzi, and M Vellini, H 2 /O 2 cycles: thermodynamic potentialities and limits, Journal of Engineering for Gas Turbines and Power,vol127,no3,pp ,2005 [6] R Bhargava and A Peretto, A unique approach for thermoeconomic optimization of an intercooled, reheat, and recuperated gas turbine for cogeneration applications, Journal of EngineeringforGasTurbinesandPower,vol124,no4,pp ,2002 [7] A Poullikkas, An overview of current and future sustainable gas turbine technologies, Renewable and Sustainable Energy Reviews,vol9,no5,pp ,2005 [8] T Srinivas, Study of a deaerator location in triple-pressure reheat combined power cycle, Energy, vol34,no9,pp , 2009 [9] M Kopac and A Hilalci, Effect of ambient temperature on the efficiency of the regenerative and reheat Çatalağzı power plant in Turkey, Applied Thermal Engineering, vol 27, no 8-9, pp , 2007 [10] P Regulagadda, I Dincer, and G F Naterer, Exergy analysis of a thermal power plant with measured boiler and turbine losses, AppliedThermalEngineering, vol 30, no 8-9, pp , 2010 [11] L Ozgener, A Hepbasli, and I Dincer, Energy and exergy analysis of Salihli geothermal district heating system in Manisa, Turkey, International Journal of Energy Research,vol29, no5, pp , 2005 [12] M Ameri, P Ahmadi, and S Khanmohammadi, Exergy analysis of a 420 MW combined cycle power plant, International Journal of Energy Research, vol 32, no 2, pp , 2008 [13] M A Rosen, Energy- and exergy-based comparison of coalfired and nuclear steam power plants, Exergy, vol1,no3,pp , 2001 [14] I Dincer and H A Muslim, Thermodynamic analysis of reheat cycle steam power plants, International Journal of Energy Research,vol25,no8,pp ,2001 [15] J M Medina-Flores and M Picón-Núñez, Modelling the power production of single and multiple extraction steam turbines, Chemical Engineering Science,vol65, no9,pp , 2010 [16] I H Aljundi, Energy and exergy analysis of a steam power plant in Jordan, Applied Thermal Engineering, vol29,no2-3, pp , 2009 [17] Z Oktay, Investigation of coal-fired power plants in Turkey and acasestudy:canplant, AppliedThermalEngineering,vol29,no 2-3, pp , 2009 [18] P Ahmadi, I Dincer, and M A Rosen, Exergy, exergoeconomic and environmental analyses and evolutionary algorithm based multi-objective optimization of combined cycle power plants, Energy,vol 36,no 10,pp , 2011 [19] Y A Cengel and M A Boles, Thermodynamics: An Engineering Approach,McGraw-Hill,NewYork,NY,USA,4thedition,2002 [20] A Bejan, G Tsatsaronis, and M Moran, Thermal Design and Optimization,Wiley,NewYork,NY,USA,1996

11 Advances in Mechanical Engineering 11 [21] S C Kaushik, V S Reddy, and S K Tyagi, Energy and exergy analyses of thermal power plants: a review, Renewable and Sustainable Energy Reviews, vol 15, no 4, pp , 2011 [22] M Ameri, P Ahmadi, and A Hamidi, Energy, exergy and exergoeconomic analysis of a steam power plant: a case study, International Journal of Energy Research,vol33,no5,pp , 2009 [23] AGKaviri,MNMJaafar,TMLazim,andHBarzegaravval, Exergoenvironmental optimization of Heat Recovery Steam Generators in combined cycle power plant through energy and exergy analysis, Energy Conversion and Management, vol 67, pp27 33,2013 [24] T J Kotas, The Exergy Method of Thermal Plant Analysis, Butterworths, London, UK, 1985 [25] M Ameri and N Enadi, Thermodynamic modeling and second law based performance analysis of a gas turbine power plant (exergy and exergoeconomic analysis), Journal of Power Technologies,vol92,no3,pp ,2012 [26] AGKaviri,MNMJaafar,andTMLazim, Modelingand multi-objective exergy based optimization of a combined cycle power plant using a genetic algorithm, Energy Conversion and Management,vol58,pp94 103,2012 [27] M M Rashidi, N Galanis, F Nazari, A Basiri Parsa, and L Shamekhi, Parametric analysis and optimization of regenerative Clausius and organic Rankine cycles with two feedwater heaters using artificial bees colony and artificial neural network, Energy, vol 36, no 9, pp , 2011 [28] C J Koroneos and E A Nanaki, Energy and exergy utilization assessment of the Greek transport sector, Resources, Conservation and Recycling,vol52,no5,pp ,2008 [29] M Valdés, M D Durán, and A Rovira, Thermoeconomic optimization of combined cycle gas turbine power plants using genetic algorithms, Applied Thermal Engineering, vol 23, no 17, pp ,2003 [30] S A Klein and F Alvarda, Engineering equation solver (EES), WI: F-chart Software, 2007 [31] J Franke and R Kral, Supercritical boiler technology for future market conditions, in Proceedings of the 6th International Charles Parsons Turbine Conference, Dublin, Ireland, 2003 [32] Y Ust, G Gonca, and H K Kayadelen, Determination of optimum reheat pressures for single and double reheat irreversible Rankine cycle, Journal of the Energy Institute,vol84,no4,pp , 2011 [33] F Hajabdollahi, Z Hajabdollahi, and H Hajabdollahi, Soft computing based multi-objective optimization of steam cycle power plant using NSGA-II and ANN, Applied Soft Computing, vol 12, no 11, pp , 2012 [34] R Chacartegui, D Sánchez, J M Muñoz, and T Sánchez, Alternative ORC bottoming cycles FOR combined cycle power plants, Applied Energy, vol 86, no 10,pp , 2009