Sensitivity analysis of exergy destruction in a real combined cycle power plant based on advanced exergy method

Abstract

The advanced exergy analysis extends engineering knowledge beyond the respective conventional methods by improving the design and operation of energy conversion systems. In advanced exergy analysis, the exergy destruction is splitting into endogenous/exogenous and avoidable/unavoidable parts. In this study, an advanced exergy analysis of a real combined cycle power plant (CCPP) with supplementary firing is done. The endogenous/exogenous irreversibilities of each component as well as their combination with avoidable/unavoidable irreversibilities are determined. A parametric study is presented discussing the sensitivity of various performance indicators to the turbine inlet temperature (TIT), and compressor pressure ratio (rc). It is observed that the thermal and exergy efficiencies increase when TIT and rc rise. Results show that combustion chamber (CC) concentrates most of the exergy destruction (more than 62%), dominantly in unavoidable endogenous form which is decreased by 11.89% and 13.12% while the avoidable endogenous exergy destruction increase and is multiplied by the factors of 1.3 and 8.6 with increasing TIT and rc, respectively. In addition, TIT growth strongly increases the endogenous avoidable exergy destruction in high pressure superheater (HP.SUP), CC and low pressure evaporator (LP.EVAP). It, also, increases the exogenous avoidable exergy destruction of HP.SUP and low pressure steam turbine (LP.ST) and leads to the high decrement in the endogenous exergy destruction of the preheater (PRE) by about 98.8%. Furthermore, rc growth extremely rises the endogenous avoidable exergy destruction of gas turbine (GT), CC and high pressure evaporator (HP.EVAP); it also increases the exogenous exergy destruction in LP.EVAP, GT, air compressor (AC) and PRE and causes the most increment in endogenous exergy destruction of GT by about 28.4%. Therefore, an increase in TIT and rc has positive effect on most of the component’s potential improvements to have a CCPP with higher efficiency and lower exergy destruction.