The thermal energy storage system co-storing heat converted from power and transferred from flue gas and hot steam for coal-fired power plant: Proposal design and operation optimization

Integrating the molten salt thermal energy storage (TES) system into coal-fired power plants (CFPPs) is an effective method to enhance the CFPP's operational flexibility. It has been studied that high equivalent round-trip efficiency (ERTE) of TES systems and high operational flexibility of CFPPs can be co-achieved by storing the heat converted from power and transferred from hot steam simultaneously. If the heat of flue gas is used for the TES system, the ERTE may be further improved. However, the temperature match between molten salt and multiple heat sources significantly affects the overall TES performance. The optimal TES design is also complicated due to the limitations of boiler stable combustion, overheating of the reheater, and activity of denitrification catalysts. In this study, four TES configurations by co-storing the heat transferred from flue gas and hot steam and converted from power are proposed. The exergy and economic performance are evaluated, and the operation strategy is optimized. By storing the heat transferred from flue gas and live steam (or cold reheat steam), the minimum power load rate of CFPP can be reduced from 30 % to 12.48 % (or 17.30 %). Through the power-to-heat process, CFPP can realize zero electricity output. The TES configuration LSP (two types of molten salt are heated by flue gas, live steam, and electric heater in parallel) shows the highest ERTE of 73.32 % with the highest net present value at $161.7 million. Compared with the original CFPP, the optimized operation strategy increases the revenue in one day by about $13,670.