Thermodynamic analysis of the air separation unit and CO2 purification unit in the semi-closed supercritical CO2 cycle with nearly zero emission

The natural gas-fired semi-closed supercritical CO2 cycle is an efficient oxyfuel combustion power generation technology featuring nearly zero emissions. This study investigated the interaction of the semi-closed supercritical CO2 power unit with the air separation unit (ASU), which supplies O2 for combustion and adiabatic compression heat for the heat recovery process in the power unit, and the CO2 purification unit (CPU), which refines the CO2 in the exhaust gas to 99.97% for enhanced oil recovery (EOR) applications. The detailed thermodynamic models of the power unit, ASU, and CPU have been constructed to explore the impact of variations in oxygen purity and excess oxygen coefficient on the overall thermodynamic performance of the system. The results demonstrate that the net electric efficiency peaks at an oxygen purity of 98%, and a one percent decrease in oxygen purity reduces the net electrical efficiency by approximately 0.36% to 0.97% points. Moreover, the net electric efficiency decreased by 0.10% points when the excess oxygen coefficient increased from 3.00% to 13.67%. These findings may offer valuable guidance for developing oxyfuel combustion power generation technologies.