IRREVERSIBILITY AND EXERGY ANALYSIS OF A RECOMPRESSION SUPERCRITICAL CO2 CYCLE COUPLED WITH DRY COOLING SYSTEM

Abstract

In the present work, irreversibility and exergy analysis are performed for a recompression supercritical CO2 (sCO2) cycle coupled with the natural draft dry cooling tower (NDDCT). The dry cooling tower is modelled for a power plant of 25 MW electrical output applicable for concentrated solar power application. The influence of the main compressor inlet temperature on the cycle thermal efficiency, the net-work, and the exergy efficiency are performed under various cycle pressure ratio. Both the cycle efficiency and the exergy efficiency are maximum at the pseudocritical temperature of the respective operating pressure ratio. The total irreversibility of the cycle decreases with the increase of cycle pressure ratio and main compressor inlet temperature. Based on the optimum operating condition, the NDDCT is designed by adapting the Kroger’s one-dimensional model. The conventional method of modeling the heat exchanger is not applicable especially for supercritical fluids due to their non-linear property variation with the small change of the operating pressure and the bulk temperature. Hence, in the present work, the nodal method is applied to take account of the property variation of sCO2 with the change of bulk temperature while modelling the air-cooled heat exchanger bundles installed at the base of the NDDCT. The irreversibility analysis of the individual components of the power cycle like heat exchangers (recuperators and heat source heat exchanger), turbo-machineries and NDDCT are investigated over a wide range of air ambient temperature from 0C to 50C.