Seasonal variation on the performance of the dry cooled supercritical CO2 recompression cycle

Abstract

The dry cooling unit is integrated with a 25 MW recompression super-critical CO2 (sCO2) cycle for solar energy application. Based on the optimal operating condition, a natural draft dry cooling tower (NDDCT) is modelled for an ambient temperature of 20 °C and sCO2 inlet condition of 67 °C and 7.96 MPa. The Kroger’s detailed working principle of NDDCT is adapted in the simulation processes. The sCO2 property variation with the change of bulk temperature is considered while modelling the heat exchanger unit inside the tower. The draft equation of the tower is solved by including various air-flow resistances at different parts of the tower. The heat input to the cycle is assumed to be supplied by the solar field with sufficient capacity of thermal storage. The seasonal effect on the performance of a dry-cooled sCO2 recompression cycle is performed in Alice Spring, NT, Australia by using the daily meteorological data. The daily net power generation fluctuates in the range of 2.4% to 22.4% of the design value for the consecutive days. The year-round mean net power generation is 24.66 MW which corresponds to 50.9% cycle efficiency. The weekly and monthly seasonal variation of the plant performance in summer, autumn, winter, and spring is performed based on the mean maximum and minimum temperature data. The mean net power produced in summer and winter is 22.9 MW and 26.4 MW respectively. The fluctuation of heat input to the cycle, heat rejected by the cycle and air mass flow rate in NDDCT are demonstrated. Seven performance indicators (Thermal efficiency, exergetic performance criteria, exergy efficiency, maximum available work, ecological coefficient of performance, cooling efficiency, and ecological function criteria) are determined to evaluate the plant performance for the period of 1941 to 2018 using the mean temperature data.