Pilot-scale investigation of a convective fixed-bed reactor for CaO/Ca(OH)2 thermochemical energy storage

The CaO/Ca(OH) 2 system is considered as one of the most promising thermochemical energy storage systems due to its high energy storage density and low material cost. However, existing studies are mainly limited to numerical simulations or laboratory-scale reactors, while pilot-scale investigations remain scarce. In addition, the high decomposition temperature of Ca(OH) 2 aggravates material sintering and limits the utilization of low- and medium-temperature heat sources. In this study, a pilot-scale convective fixed-bed reactor capable of loading 334.14 kg of CaO is proposed. During the heat storage stage, high-temperature N 2 directly transfers heat by convection while simultaneously removing reaction steam to reduce the decomposition temperature, whereas during the heat release stage, heat is indirectly extracted by heat transfer oil flowing inside finned tubes. Total 4 cyclic performance tests have been conducted with the max and final conversion ratio of 98.18% and 91.75%, respectively. For a typical heat release stage, it lasts for 105 min with maximum/average heat release powers of 75.03/52.89 kW and 318.17 MJ of energy is released. The overall/particle-side heat transfer coefficients are 97/107 W/(m 2 ·K). During the heat storage stage, it lasts for 1135 min with maximum/average reaction heat storage powers of 7.97/4.68 kW and 321.03 MJ of energy is stored. In addition, the decomposition temperature decreases to 420 °C. Based on energy balance analysis, the heat release, heat storage, and cycle efficiencies are 95.85%, 79.11% and 76.65%, respectively. This work demonstrates significant advantages in storage scale, conversion performance, and decomposition temperature, promoting practical applications of thermochemical energy storage technology.