Design and performance comparison of coupling a coal-fired power plant with molten salt thermal storage system using different heat sources

Driven by low-carbon targets, renewable energy has developed rapidly, which places higher demands on the peak regulation capability of coal-fired power plants (CFPPs). Molten salt thermal storage (MSTS) systems provide a potentially feasible solution for improving the peak regulation flexibility of CFPPs. This study designs four MSTS-assisted peak regulation schemes for CFPPs, with heat supplied by four different heat sources: flue gas, main steam, reheat steam, and electric energy, and two types of molten salt with different parameters are used for thermal energy storage. The high-low temperature molten salt thermal storage system overcomes the constraint of the limited operating temperature range of a single molten salt, effectively enhancing the peak-shaving capability of the CFPP and the efficiency of the entire system. Taking a 630 MW CFPP as the research object, detailed evaluations of the thermodynamic performance, peak-shaving capability, and economic performance of each scheme are conducted. The results show that, at a unified peak-shaving depth of 10.0%, the scheme using extracted flue gas and main steam for thermal storage achieves the highest equivalent round-trip efficiency (77.96%) and exergy efficiency (38.34%). Although this scheme has a relatively high initial investment (43,122.89 k$), it features a short dynamic payback period (4.22 years) and the highest net present value (132,965.15 k$). This study can provide practical theoretical and technical support for the design of MSTS systems and the improvement of operational flexibility in CFPPs.