System Performance Analysis of a Coal-fired Unit Coupled with High- and Low-temperature Molten Salt Thermal Energy Storage

To effectively improve the peak-shaving performance and operational flexibility of coal-fired units, a scheme that combines a coal-fired unit with high- and low-temperature molten salt thermal energy storage was proposed. During the energy storage process, high-temperature molten salt (solar salt) and low-temperature molten salt (Hitec salt) were sequentially used to store the thermal energy of the main steam and reheat steam from the coal-fired unit, while the electric heater was employed to further increase the temperature of the molten salt. During the energy release process, high-temperature molten salt was used to heat the feedwater to main steam conditions, and low-temperature molten salt was used to heat the feedwater at the feedwater pump outlet to final feedwater conditions. Results show that the peak range of the coal-fired unit can be increased to 14.25%THA-108.03%THA, and the equivalent round-trip efficiency of the energy storage system can reach 50.95%. The exergy efficiency of the integrated system is 34.70%. Furthermore, the total investment cost of the molten salt thermal energy storage system is 151.663 4 million CNY, with a dynamic payback period of 3.36 a.