A systematic comparison of different S-CO2 Brayton cycle layouts based on multi-objective optimization for applications in solar power tower plants

Supercritical CO2 (S-CO2) Brayton cycles are recently proposed to be integrated into the solar power tower (SPT) due to their high efficiency and compactness. Comparison of different S-CO2 Brayton cycle layouts is of great significance for selecting a suitable one in the SPT plant. Both of the efficiency and specific work are important performance criteria for the SPT plant. However, previous studies compared only one individual criterion, or both of them just separately. This paper puts forward a systematic comparison of different S-CO2 Brayton cycle layouts based on multi-objective optimizations. The two performance criteria are compared simultaneously between different S-CO2 cycle layouts by comparing the Pareto optimal fronts obtained from multi-objective optimizations. The results suggest that the inter-cooling cycle layout and the partial-cooling cycle layout can generally yield the most excellent performances, and followed by the recompression cycle layout and the pre-compression cycle layout, while the simple recuperation cycle layout has the worst performances. The advantages of the partial-cooling cycle layout and the inter-cooling cycle layout are more prominent compared with the other cycle layouts in the case of high compressor inlet temperature. The provided systematic comparison can be helpful in selecting the most suitable cycle layout for the application in SPT when there are specified requirements for the efficiency and the specific work. In addition, novel salts with high upper limit temperature (higher than 650 °C) are recommended to be developed as the heat transfer fluid for improving system performances.