Large-scale renewable energy integration into the power grid necessitates enhanced flexibility of coal-fired power units. This study introduces a coal-fired unit integrated with a molten salt energy storage system to bolster the adaptability of the power system. We have conducted a comprehensive screening of potential molten salt working fluids to optimize the system's performance. Focusing on a 350 MW flexible coal-fired unit

we have designed the molten salt energy storage system to achieve a targeted load ramp rate of 3% of the rated power (Pe) per minute. Based on physical properties of the Solar salt (60%NaNO3+40%KNO3) and the Hitec salt (53%KNO3+40%NaNO2+7%NaNO3)

the thermodynamics of the turbine and the heat transfer of key components are analyzed. Hence

the effects of the two molten salts on the power generation efficiency

the system complexity

and the investment cost of the MSSG are investigated. It is found that due to the higher decomposition temperature of Solar salt

the MSSG with Solar salt achieves an average power generation efficiency of 36.7%

which is higher than the value of 29.2% for the system with Hitec salt. On the contrary

due to the higher melting temperature of Solar salt

it is necessary to extract water vapor from the steam turbine to preheat the feedwater of the MSSG with Solar salt requires to preheat its feedwater through water vapor extracted from the steam turbine to prevent the salt from solidifying and blocking pipelines

which complicates the system. One the other hand

the higher operation temperature of the MSSG with Solar salt decreases the mass flow rate of the salt

the inventory amount of the salt

and the sizes of heat exchangers

compared with those of the system with Hitec salt. Comprehensively

the investment cost of the Solar salt system drops by 10.0 million RMB compared with the Hitec system. Based on this investigation

the Solar salt is recommended for adoption in the MSSG to ensure efficient and safe operation

supporting the coal-fired power plant to reach the ultra-flexibility target.