Thermodynamic analysis and optimization of a novel semi-closed supercritical CO2 power cycle integrated with an air separation unit incorporating LNG cold energy utilization

This study investigated a novel semi-closed supercritical CO2 power cycle integrated with an air separation unit (ASU) integrating liquified natural gas (LNG) cold energy utilization. A part of the compression waste heat of the ASU is injected into the cycle, enhancing heat recovery. An advanced ASU producing high-pressure liquid oxygen has been developed by utilizing LNG cold energy in the compression and refrigeration sections. The remaining LNG cold energy condenses CO2 in the cycle, reducing the recycle flow compression shaft work. Energy and exergy analyses of the cycle were conducted, along with a sensitivity analysis of key parameters affecting thermodynamic performance. The single objective optimization is carried out to maximize exergy efficiency. The results denote that the ASU achieves a specific energy consumption of 0.165 kWh/kg LO2, representing about a 33 % reduction compared to a similar ASU. The initial parameters of the turbine significantly influence system efficiency. Decreasing turbine outlet pressure and recycle flow subcooling degree in a certain range can substantially reduce CO2 condensation-related heat transfer irreversibility, enhancing thermodynamic efficiency. The optimization results indicate that the highest exergy efficiency and net electric power efficiency are 49.90 % and 70.07 %, which are 3.21 % and 5.86 % higher than the base case, respectively.