Enhancing conventional steam power plant performance through feed water heating repowering

ABSTRACTRepowering of old steam power plants is a viable solution to increase power and improve efficiency. This study investigates the feasibility of feed water heating repowering for the Neka steam power plant by considering the influences of steam mass flow rate on the condenser performance and the heat rate of the new cycle. Energy and exergy analyses were conducted using the first and second laws of thermodynamics and heat transfer relations in each scheme. The effect of increasing the steam mass flow rate on the performance of the condenser and the cycle was also investigated. The repowered cycle was simulated using Thermoflow software, and the results were validated with small errors. The results showed that replacing low and high-pressure heaters with new heat exchangers increased the power of the steam unit and the repowered cycle, energy, and exergy efficiencies by 15.7%, 49.3%, 5.93%, and 2.17%, respectively. Although the condenser pressure increased by 19 millibars, leading to a 0.63% increase in the heat rate, the total heat rate of the repowered cycle improved by 4.62%. Overall, the findings demonstrate that feed water heating repowering can be an effective strategy to increase the efficiency and power of conventional steam power plants.KEYWORDS: Repoweringthermodynamic analysisheat ratecondenser performancesteam power plant Nomenclature Symbols=DefinitionsAC=Air Compressoraux.cond=Auxiliary CondenserBFPT=Boiler Feed Pump Turbinec=Specific HeatCCh=Combustion Chambercond=CondenserCP=Condensate Pumpdea=DeaeratorE=EnergyEff=EfficiencyĖx=Exergy Flow Rateex=Specific Exergyēx=Molar Specific ExergyFR=Full RepoweringFWH=Feed Water HeaterFWHR=Feed Water Heating RepoweringFWP=Feed Water PumpGT=Gas Turbineh=Specific EnthalpyHPFWH=High-Pressure Feed water HeaterHPHEX=High-Pressure Heat ExchangerHPT=High-Pressure TurbineHR=Heat RateHWBR=Hot Wind Box RepoweringIPT=Intermediate-Pressure TurbineLHV=Lower Heating ValueLPFWH=Low-Pressure Feed water HeaterLPHEX=Low-Pressure Heat ExchangerLPT=Low-Pressure Turbineṁ=Mass Flow RateP=PressurePFWHR=Parallel Feed Water Heating RepoweringPR=Partial RepoweringRC=Repowered CycleQ˙=Heat Flow Rater=Pressure RatioQ˙=Heat Flow Rates=Specific EntropySBR=Supplementary Boiler RepoweringST=Steam TurbineT=TemperatureTET=Turbine Exit TemperatureTIT=Turbine Inlet TemperatureẆ=Powerx=Molar FractionGreek Letters=ρ=Densityη=Energy Efficiencyε=Exergy EfficiencySuperscripts=CH=ChemicalPH=PhysicalSubscripts=o=Reference Conditiona=Airb=System BoundaryB=Boilerc=Compressorc.c=Combustion Chamberc.v.=Control VolumeD=Destructione, out=OutletF, f=Fuelf.g, g=Flue Gasgen=Generationi, in=Inletl=Lossesliq=LiquidP=Production, Pressuret=TurbineAcknowledgementsThe authors are thankful to the deputy of engineering and planning of the Neka steam power plant for cooperating in recording the real data of the steam unit cycle.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationNotes on contributorsJamshid NaeimiJamshid Naeimi received his bachelor's degree in mechanical engineering with a focus on heat and fluids from K.N. Toosi University of Technology in 1990. After that he worked at the Neka thermal power plant. After retiring, he obtained his master's degree in mechanical engineering majoring in energy conversion from Semnan University in 2017. He is currently a Ph.D. student in mechanical engineering at Semnan University. His fields of interests are energy, applied thermodynamics, and power plant technology.Mojtaba BiglariMojtaba Biglari is associate professor of mechanical engineering at Semnan University. He received his B.S. degree from Sharif University of Technology and M.S. degree from Tehran University both in mechanical engineering and received his Ph.D. degree in cryogenic engineering from Moscow Power Engineering Institute (Technical University). His areas of interests are thermodynamics, refrigeration and cryogenics, direct energy conversion and renewable energies.Saadat ZirakSaadat Zirak is assistant professor of department of heat, fluid and energy conversion at Semnan University. In 1989, he received a bachelor's degree in mechanical engineering from Chamran University in Ahvaz. Then he received a master's degree in 1992 and a Ph.D. degree in mechanical engineering in 1999 from Isfahan University of Technology.Iraj Jafari GavzanIraj Jafari Gavzan is assistant professor of department of heat, fluid and energy conversion at Semnan University. In 1992, he received a bachelor's degree in mechanical engineering from Iran University of Science and Technology. Then in 1998 he received a master's degree from Tarbiat Modares University and in 2009 he received a Ph.D. in mechanical engineering from Sharif University of Technology.