Investigation of thermodynamic performances for two-stage recompression supercritical CO_2 Brayton cycle with high temperature thermal energy storage system

摘要

The supercritical CO2 (S-CO2) Brayton cycle with high temperature thermal energy storage is proposed to efficiently utilize solar thermal energy. A molten halide salt (mixture of 8.1 wt.%NaCl + 31.3 wt.%KCl + 60.6 wt. %ZnCl2) that can operate at a relatively high temperature is selected as a heat transfer fluid (HTF) and a storage medium. The proposed two-stage recompression Brayton cycle is used as power block to make full use of high-level solar energy and reduce power consumption. The thermodynamic performances and economic assessments are investigated to illustrate the feasibility of the proposed system, and the comparison between halide salt and nitrate salt is conducted. Theoretical results show that the solar-to-electric efficiency in the system with halide salt reaches to 19.16-22.03% in four representative days, which is higher than existing concentrated solar power plants with the tower central receiver, and the monthly averaged solar-to-electric efficiency of the halide salt system is increased by 11% as compared with the nitrate salt system. Research findings introduce a promising approach for the efficient utilization of the abundant solar resources in western China.