Thermochemical Energy Storage Technologies Integrated with Coal-Fired Power Plants

With the global energy transition and the increasing use of renewable energy, coal-fired power plants are shifting from baseload generation toward flexible operation for load following and frequency regulation. However, low-load operation can destabilize boiler combustion, accelerate equipment wear, and complicate emissions control. Thermochemical energy storage offers high storage density, low heat loss during storage, and a wide operating temperature range. It may therefore support the flexible operation of coal-fired power plants. This narrative review compares six thermochemical energy storage systems: CaO/CaCO3, CaO/Ca(OH)2, ammonia decomposition and synthesis, metal hydrides, metal oxide redox systems, and methane dry reforming. The comparison considers reaction temperature, storage density, material cost, cyclic stability, safety, and compatibility with coal-fired power plants. Based on this qualitative comparison, CaO/CaCO3 appears to offer relatively favorable compatibility because of its low-cost raw materials, relatively high storage density, good temperature matching with high-temperature flue gas, and potential integration with CO2 capture. Three integration pathways are further reviewed: solar-driven CSP–CaL, calcium-looping carbon capture with sorbent storage, and flue-gas-driven calcination with carbonation-based flue-gas reheating. The first two pathways have received more extensive modeling and experimental investigation. The flue-gas-driven pathway remains mainly at the conceptual and component-validation stages. Its main constraints include CaO deactivation, flue-gas impurities, reactor scale-up, and coordination with variable boiler operation. Overall, the reviewed evidence suggests that CaO/CaCO3 may offer a favorable temperature and process match for integration with coal-fired power plants. However, the flue-gas-driven pathway is not yet ready for plant-scale application. Future research should focus on long-term testing under real flue gas, reactor scale-up, dynamic reactor–boiler demonstrations, and consistent techno-economic and life-cycle assessments.