An Exergy Analysis of Recompression Supercritical CO2 Cycles with and without Reheating

Abstract

Concentrated Solar Power using supercritical CO2 (S-CO2) recompression Brayton cycles offer advantages of similar and even higher overall thermal efficiencies compared to power cycles using superheated or supercritical steam. The high efficiency and compactness of S-CO2, as compared with steam Rankine cycle at the same high temperature, make this cycle attractive for central receiver applications, since both attributes lead to decrease in levelized cost of energy and therefore make this technology economically feasible. The current research in S-CO2 is focused on thermodynamic analysis and system components. In this paper energy and exergy analyses of a supercritical CO2 Recompression Brayton cycle are presented. Energy, exergy and mass balance are carried out for each component and first law and exergy efficiencies are calculated with and without reheat scenarios. Optimization is then carried out by using Sequential Least SQuares Programming (SLSQP) and optimum operating conditions based on maximum first law efficiency are determined. The results showed that the exergy efficiency reaches a maximum value at 600°C while the first law efficiency increases monotonically with highest temperature of the cycle.