Thermodynamic performance analysis and advanced exergy analysis of a transcritical CO₂ energy storage system coupled with methanol production

Growing human activity demands have driven a drastic rise in global energy consumption, increasing global CO₂ emissions while spurring the development of CO₂ utilization technologies to mitigate such emissions. Specifically, this paper couples a transcritical CO₂-based energy storage system with the CO₂-to-methanol process, conducting thermodynamic, traditional exergy, and advanced exergy analyses on the proposed system.The results show that under standard operating conditions, the round-trip efficiency of the energy storage system is 136.63% with an energy storage density of 19.48 kWh/m3; the round-trip efficiency (RTE) of the system is quite sensitive to the reaction pressure in the methanol production process. As the pressure increases, the RTE rises from 140.01% to 176.66%. when the primary methanol yield reaches 27%, the energy storage density can attain 21.60 kWh/m3. Traditional exergy analysis results show that Reheater B (REHB), Evaporator (EVA), and Intercooler A (CLA) account for the highest exergy destruction, representing 27.2%, 26.6%, and 9.4% of the total system exergy destruction respectively. Subsequent advanced exergy analysis indicates that EVA, REHB, and CLA have the largest avoidable exergy destruction, with proportions of 32.4%, 29.8%, and 11.3% respectively. Based on the above results, priority should be given to optimizing EVA, REHB, and CLA.