Exergy Analysis and Optimization of Combined Brayton and Rankine Cycles

Abstract

There are many energy sources on the World that can be classified as renewable and non-renewable energies. The non-renewable energies which are exhaustible and often harmful to the environment. The usage of all these renewable and non-renewable energies efficiently is very important in technology and industry. The concept of exergy and exergy analysis is very important methods to show the inefficiencies and the irreversibility’s in a system and its devices. In this study, exergy analysis methods are applied to efficient combine cycle and cogeneration systems. The destruction of exergy has been examined for combined cycles and cogeneration system to find the optimum working conditions. It is found that as the pump pressure of the Rankine cycle increases from 400 kPa to 7600 kPa, the exergy efficiency increases from 76% to 85%, and as the compression pressure of the Brayton cycle increases from 400 kPa to 2200 kPa, the exergy efficiency increases from 72% to 79%. When these operating conditions, where the two cycles will operate at their optimum, are applied together, the exergy efficiency of the all cycle exceeds 86%. When the operating conditions, where the Brayton and Rankine cycles are at their maximum efficiency, are applied together, the optimum operating conditions of the system are obtained.