Performance Analysis of a Combined Cycle Power Plant with Simultaneous Cooling of Inlet Air Streams to the Compressor and Condenser

Abstract: This paper presents the thermodynamic performance analysis of an existing combined cycle power plant to be retrofitted with a waste heat driven aqua lithium bromide absorption refrigerator for cooling the inlet air streams to the compressor and air-cooled steam condenser. The power plant is located in the hot and humid tropical region of Nigeria, latitude 4°45′N and longitude 7°00′E. This was achieved by performing energy and exergy analysis of the integrated system. Using the operating data of the existing combined cycle power plant, the results of the analysis showed that by cooling the inlet air streams to 15oC at the compressors, and to 29oC at the air-cooled steam condenser, the net power output, thermal and exergy efficiencies of the combined cycle plant increased by 7.7%, 8.1% and 7.5% respectively while the plant total exergy destruction rate and specific fuel consumption dropped by 10.8% and 7.0% respectively. The stack flue gas exit temperature reduced from 126oC to 84oC in the absorption refrigerator, thus reducing the environmental thermal pollution. The COP and exergy efficiency of the refrigeration cycle was 0.60 and 27.0%, respectively. Results also show that the highest rate of exergy destruction in the combined cycle power plant occurred in the combustion chamber while the highest rate of exergy destruction in the absorption refrigeration cycle occurred in the evaporator followed by the absorber.