Exergy analysis of wet compression gas turbine cycle with recuperator and turbine blade cooling

In this work, exergy analysis of the wet-compression gas turbine cycle with recuperator and turbine blade cooling is performed. The exergy destructions in the system components and cycle exergy efficiency are estimated for varying pressure ratios and water injection ratios.
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Exergy analysis of wet compression gas turbine cycle with recuperator and turbine blade coolingJournal of Automation and Control Engineering, Vol. 1, No. 2, June 2013Exergy Analysis of Wet-Compression GasTurbine Cycle with Recuperator and TurbineBlade CoolingKyoung Hoon Kim and Hyung Jong KoKumoh National Institute of Technology/Department of Mechanical Engineering, Gumi, KoreaEmail: {khkim, kohj}@kumoh.ac.krAbstract—Turbine blade cooling has been considered as themost effective way for maintaining high operatingtemperatures while making use of the available componentmaterial and has been a challenging area for improving theperformance of gas turbine systems. In this work, exergyanalysis of the wet-compression gas turbine cycle withrecuperator and turbine blade cooling is performed. Theexergy destructions in the system components and cycleexergy efficiency are estimated for varying pressure ratiosand water injection ratios. Exergy destruction in thecombustor and exergy loss due to exhaust gas are dominantand larger for higher pressure ratios and lower waterinjection ratios. Consequently the exergy efficiencydecreases with pressure ratio but can be improved byinjecting more water. ratio leads to a better system performance. However,employment of high temperature gas in gas turbinesrequires materials which can withstand the effects of hightemperature operation [8]. One of the ways to overcomethe problems resulting from high temperature is tomaintain the temperature of the blade at a level lowenough to preserve the desired material properties byblade cooling. For a variety of method of turbine bladecooling, there have been many studies modeling theturbine blade cooling process [9]-[13].The exergy analysis is well suited for furthering thegoal of more effective energy resource use, since itenables the location, cause, and true magnitude of wasteand loss to be determined [14]. Kim et al. [15] carried outexergy analysis of simple and regenerative gas turbinecycles with wet compression. In this study exergyanalysis of the wet-compression gas turbine system withrecuperator and turbine blade cooling is carried out.Effects of pressure ratio and water injection ratio areinvestigated parametrically on the exergy destructionsand the exergy efficiency of the cycle.Index Terms—water injection, wet compression, gas turbine,turbine blade cooling, exergyI.INTRODUCTIONThe humidified gas turbines in which water or steam isinjected at various positions have been attracted muchattention, since they have the potential to enhance thepower output with low cost. In these systems, evaporativecooling is a key process which can be classified as inletfogging, after fogging and wet compression [1]-[3]. Wetcompression is a process in which water droplets areinjected into the air at the compressor inlet and allowed tobe carried into the compressor. Since the dropletevaporation in the front stages of the compressor reducesthe air temperature, the amount of compression work isreduced [4], [5]. Kim et al. [6], [7] studied on theperformance of gas turbine cycles with wet compressionand developed a model analyzing the transport operationsfor the non-equilibrium wet compression process basedon droplet evaporation.It is important in a gas turbine design to increase thepower output and to reduce the fuel consumption.Improvement in the thermal efficiency of a power plantcan be obtained by operating with higher turbine inlettemperatures. The maximum temperature of a gas turbineplant occurs at the entry of the first stage of the turbine.The employment of high temperature for given pressure6exhaust2 fuel7ACFC3 CC8air film cooling4ATair waterFigure 1. Schematic diagram of the system.II.SYSTEM ANALYSISThe schematic diagram of the system is shown in Fig.1. Air enters the compressor at temperature T1, pressureP1 and relative humidity RH1. At the same time liquidwater droplets are injected into the air with initialdiameter of D1 at a rate such that the ratio of mass ofliquid water to dry air is equal to f1. For the convenienceof analysis the injected water droplets are assumed tohave uniform size. Fuel is assumed to be pure methaneand enters the combustion chamber with air. TheManuscript received November 9, 2012; revised December 22, 2012.©2013 Engineering and Technology Publishingdoi: 10.12720/joace.1.2.140-1435HE140Journal of Automation and Control Engineering, Vol. 1, No. 2, June 2013combustion occurs at constant pressure until the flameadiabatic temperature is reached. The hot gas is thenexpanded to state 5 and exhausts the turbine. The fuelmass is determined such that the turbine inlet temperaturereaches a predetermined value. The recuperation ofexhaust heat and the cooling of turbine blade also takeplace.By considering the combustion process, total fivekinds of gases, namely O ...