Comparative analysis of heat–power decoupling technologies and hot-water tank optimization for deep peak shaving of a 350 MW supercritical combined heat and power unit

To improve the deep peak-shaving capability of combined heat and power (CHP) units under high-penetration renewable energy integration while maintaining heating security and operational economy, this study investigates a 350 MW supercritical extraction heating unit. An off-design thermodynamic model is established in EBSILON and validated against design data. Five heat–power decoupling schemes, namely low-pressure turbine zero-output renovation, hot-water thermal energy storage tank, electric boiler, molten-salt thermal energy storage, and compressed air energy storage, are constructed and compared under a unified framework in terms of the heat–power feasible operating region, energy utilization efficiency, exergy efficiency, and standard coal consumption rate for power generation. On this basis, the hot-water tank scheme, which features bidirectional regulation, low disturbance to the original thermal system, and relatively low investment, is selected for capacity optimization and economic evaluation. The results show that the hot-water tank shifts heat on the district-heating side, reconstructs the actual heating load undertaken by the CHP unit, and moves operating points toward the low-coal-consumption region. For the typical-day dispatch, the optimal tank capacity is 163.986 MWh, corresponding to a volume of 3513.979 m 3 . Compared with the original CHP unit, the cumulative upward peak-regulation capability, downward valley-load reduction capability, and total operating-range expansion increase by 263.220, 618.162, and 881.382 MWh, respectively. The total energy utilization efficiency increases from 64.50% to 69.24%, and the typical-day net profit increases from 4.231 × 10 6 CNY/day to 4.306 × 10 6 CNY/day. On an annual basis, the hot-water tank scheme yields an incremental annual net cash flow of 1.128 × 10 7 CNY/a, an incremental net present value of 2.160 × 10 8 CNY, and a discounted payback period of 0.225 a. These results indicate that the hot-water tank is a heat–power decoupling option with low investment, a short payback period, and stable operating benefits, and can provide a quantitative reference for flexibility retrofits of existing CHP units and the capacity optimization of district-heating-side hot-water storage systems.