Thermo-economic comparison of three MW-scale S-CO2 recompression Brayton cycles

S-CO2 recompression Brayton cycle (SRBC) is considered to be one of the first choices to replace the steam Rankine cycle. Combining with nuclear or solar energy can achieve the goal of efficient, green energy conservation and emission reduction. To achieve higher efficiency and lower cost of MW-scale SRBC, this paper optimizes the cycle configuration and parameters by combining reheating, inter-cooling and pre-compression. The results show that reheating, inter-cooling and pre-compression can increase thermal efficiency by 1 %–1.65 %, 0.35 %–2.7 % and 0.16 %–0.2 %. Inter-cooling and pre-compression can increase exergy efficiency, but reheating reduces exergy efficiency. Under the condition of cycle maximum/minimum temperature of 600 °C/35 °C, the optimal value of compressor inlet and outlet pressure is 8.4 MPa and 24 MPa after consideration of system thermo-economic performance. And the expansion ratio of multi-stage turbines should be evenly distributed, the first-stage pressure ratio of multi-stage compressors should be as large as possible. SRBC can achieve optimal thermal efficiency and exergy efficiency can reach 42.62 % and 56.13 %. SRBC with staged expansion/compression and precompression can reduce investment costs. The levelized cost of energy of SRBC and its coupled pre-compression with cycle maximum pressure of 24 MPa is 2.86 % and 10 % lower than that of the conventional S-CO2 Brayton cycle.