Impact of different integration modes between an ultra-supercritical coal-fired power plant and molten salt thermal energy storage system on thermodynamic performance

The growing penetration of renewable energy in the power grid imposes high flexibility requirements on coal-fired power plants (CFPPs). Thermal energy storage (TES) is a promising option for improving the peak shaving potential of CFPPs. This study investigates a 660 MW ultra-supercritical CFPP integrated with a TES system, aiming to evaluate how different integration schemes of the TES system affect thermodynamic performance. Two integration modes are considered, namely the additional electric heating mode and the steam diversion mode. Five charging schemes using main steam, power-to-heat, and reheat steam as heat sources and three discharging schemes based on boiler feedwater heating and steam generation are proposed. The energy conversion performance of the TES system is quantified separately for charging and discharging by the power to heat coefficient and thermoelectric conversion efficiency under the same boundary conditions. The results show that the basic steam diversion scheme achieves the highest power to heat coefficient of 1.80. The heating boiler feedwater scheme achieves the highest thermoelectric conversion efficiency at low heat release power. Increasing peak shaving capacity during charging and decreasing heat release power during discharging both can improve the equivalent round-trip efficiency. The combination of the basic steam diversion scheme and the heating boiler feedwater scheme is the optimal configuration when the peak shaving capacity is below 75.66 MW and the heat release power is below 100 MW. In addition, at a 5 % heat loss rate of the heat exchangers, the reduction of the equivalent round-trip efficiency of integrated schemes is in the range of 8.26 % to 9.66 %. This study can provide a valuable reference for scheme selection in CFPP flexibility retrofits.