[Objective] To enhance the peak-shaving flexibility and operational economy of coal-fired power units and support the upgrading of next-generation coal power systems. 

[Methods] A multi-objective optimization is carried out using response surface methodology (RSM) for key parameters of a coupled system consisting of a compressed air energy storage (CAES) system and a 670 MW supercritical coal-fired unit. The coupled system model is built in EBSILON software, and an iterative solution strategy is employed to ensure heat balance convergence. During the charging process, the compression heat is recovered by condensed water from the coal-fired plant. During the discharging process, two extraction steam heating schemes (deaerator extraction and No.3 high -pressure heater extraction) are compared. Three design variables are selected: compressor isentropic efficiency, inlet air mass flow rate, and total pressure ratio. The two optimization objectives are downward peak-shaving capacity and annual 2 http ://rlfd.cbpt.cnki.net net electricity sales revenue. A quadratic regression model is established based on Box-Behnken experimental design. Under the optimal parameter combination, the off-design thermodynamic and peak-shaving performance over the load range of 30%–100% turbine heat acceptance (THA) is analyzed, and the economic indicators are evaluated using a life-cycle assessment method. 

[Results] The deaerator extraction scheme is found to be superior during the discharging stage. The optimal parameter combination is: compressor isentropic efficiency 0.91, inlet air flow rate 85.6 kg/s, and total pressure ratio 85.0. The regression model predicts a downward peak-shaving capacity of 41.08 MW and an annual net electricity sales revenue of 13.223 8 million yuan. The simulation validation shows a relative error of less than 4% for both objectives. The energy utilization coefficient of the coupled system increases with load, ranging from 46.97% at 30% THA to 48.67% at 100% THA, which is higher than that of the standalone CFPP. Under off-design conditions, at 100% THA, the round-trip efficiency of the coupled CAES system reaches 64.40%, which is 9.1 percentage points higher than that of a standalone CAES system (55.3%). At 30% THA, the downward peak-shaving capacity is 43.56 MW, corresponding to a peak-shaving depth of 6.5%. The economic analysis reveals a dynamic payback period of 11.56 years, an internal rate of return (IRR) of 13.34%, and a net present value of 119.61 million yuan. The sensitivity analysis shows that when the annual operating days are below 168, the project is not economically feasible; when the operating days reach 350, the dynamic payback period shortens to 9.6 years and the IRR increases to 15.4%. 

[Conclusion] This study provides optimized parameters and operation strategy references for the flexibility retrofitting of coal-fired power units, contributing to the transformation of next-generation coal power systems. An optimal operating strategy is recommended: storing energy during low load (30% 50% THA) and releasing energy during high load (above 75% THA) to maximize system benefits.