Investigation of the recompression pathway in the supercritical CO2 Brayton cycle: Cycle modification and thermodynamic study

Abstract

The recompression process in supercritical CO2 (S-CO2) Brayton cycle is highly energy-intensive, leading to significant temperature rises and complex interactions with internal regeneration and overall cycle performance. This paper aims to investigate the influence of recompression path selection on S-CO2 Brayton cycle and explores opportunities to improve cycle performance by varying the recompression intake position. To actively regulate recompression inlet temperature, two modified layouts based on the conventional recompression S-CO2 Brayton cycle are proposed. Detailed energy and exergy analyses are conducted for these cycles. Optimization is then conducted for modified cycles under different operation conditions to find the optimal recompression path. Thermal efficiency maps with variation of key variables are depicted among cycles to give a comparative evaluation for recompression path selection. The results show that the modified recompression cycles could overtake conventional cycle in thermal efficiency under various certain operation conditions. At split ratio lower than 0.5, further precooling before recompression enhances thermal efficiency. In a case study, thermal efficiency is improved from 39.1 % to 41.7 %. Efficiency of modified cycle becomes less sensitive to main compressor inlet parameters. The modification of three-stage recuperation is effective to eliminate inner pinch point during recuperation and enhance cycle efficiency, with a proper higher recompression inlet temperature. At higher split ratio, shifting recompression path could bring benefits, with a maximum thermal efficiency increasing from 41.6 % to 43.6 % in the case study. Efficiency deterioration could be mitigated by reasonably changing recompression path in off-design operation.