Design and performance comparison of stepwise and staged molten salt thermal storage systems integrated within a coal-fired power plant

The swift advancement of renewable energy demands greater flexibility and enhanced peak-shaving capabilities from coal-fired power plants (CFPPs). Molten salt thermal energy storage (MSTES) is considered a potential solution. In this study, a CFPP integrated steam and flue gas stepwise/staged heating MSTES system is proposed. The proportion of steam heat energy allocated to the molten salt and feed water is adjusted. The thermodynamic and economic performance of two configurations under different thermal load distribution ratios are compared and studied. Results show that, under the same molten salt thermal load distribution ratio, the stepwise configuration achieves an average energy storage density that is 2.53 kWh/m³ greater than the staged configuration. Furthermore, it demonstrates a 3.82 % improvement in average denitration efficiency and a 1.28 MW reduction in average charging exergy loss. Economic analysis reveals that the integrated system performs best when the molten salt thermal load distribution ratio is minimized. At this time, the stepwise configuration demonstrates a 9.3 % lower life cycle cost, a 9 % lower equivalence levelized cost of electricity, and a 9.5 % lower equivalence levelized cost of thermal storage compared to the staged configuration.