Combined cycle power plant performance evaluation using exergy and energy analysis

Abstract

Performance evaluation of a combined cycle power plant (CCPP) is generally attempted using first law of thermodynamics based on energy and mass balance methodology. For detailed component wise performance analysis, exergy‐based evaluation based on second law of thermodynamics is gaining increasing importance. In this study, a CCPP consisting of triple pressure steam cycle with reheat is analyzed using both energy and exergy. Effect of ambient temperature, inlet and exhaust pressure loss, CCPP load, excess air percentage, cooling water temperature, and condenser vacuum has been investigated. Energy and exergy‐based performances are compared and presented. The simulation results show that efficiency of CCPP decreases with increase in the inlet and exhaust pressure loss and with increase in inlet air temperature to compressor. The total power output of CCPP decreases at higher inlet air temperature with increase of steam flow rate in bottoming cycle and increase in compressor power consumption. The exergy efficiency of combustion chamber, heat recovery steam generator, and condenser are found to be 77.48%, 87.20%, and 29%, respectively; and the overall exergy and energy efficiency of the unit at 100% design and operating condition is found to be 54.09%, 58.26% and 53.92%, 57.10%, respectively. The overall exergetic efficiency of the CCPP can be improved by reducing the losses in bottoming cycle. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1180–1186, 2017