Thermo-economic analysis of a multi-pressure supercritical CO₂ pumped thermal energy storage system integrated with waste heat recovery

Pumped thermal energy storage (PTES) is a large-scale, long-duration physical energy storage technology for achieving stable operation of high-proportional renewable energy power systems, while advancing the large-scale application of efficient energy storage and enhancing the deep peak regulation capability of thermal power plants are vital pathways for both maximizing renewable energy integration and facilitating the low-carbon transition of coal-fired power. To this end, a novel multi-pressure supercritical CO₂ PTES system integrated with waste heat recovery is developed. This system achieves efficient recovery and utilization of low-grade flue gas waste heat from thermal power plants. Furthermore, by incorporating a multi-stage thermal storage topology and distributed regenerative devices, it significantly mitigates irreversible losses caused by temperature glide during heat exchange processes within the PTES system. Consequently, the proposed system enhances the flexible peak shaving capability of thermal power units and ensures the secure grid integration of renewable energy sources. Based on the establishment of thermodynamic and economic models, sensitivity analysis was employed to study the influence of key operating parameters on the system's thermodynamic and economic performance. Furthermore, a genetic algorithm was applied to conduct thermo-economic multi-objective optimization. The results show that the performance indicators of the system under the design condition are exergy efficiency of 53.83% and levelized cost of energy(LCOE) of 2063.26 CNY·MWh^-1. Among the key parameters, the isentropic efficiency of the discharge expander has the most significant impact on the thermodynamic performance, while the isentropic efficiency of the charging turbine has the most significant impact on economic performance. According to the TOPSIS method, the optimal exergy efficiency obtained in the Pareto optimal frontier solution set is 58.20% and the levelized cost of electricity is 1142.24 CNY·MWh^-1, which are 8.12% higher and 44.64% lower than the design condition, respectively.