Proposal of a pilot-scale prototype of ‘electricity-in-steam-out’ packed-bed reactor for thermochemical energy storage with Ca(OH)₂/CaO

To flexibly store the renewable and valley powers for green industrial steam supply, this work proposes a pilot-scale prototype of ‘electricity-in-steam-out’ packed-bed reactor with loading of 290.527 kg of spherical CaO pellets for thermochemical energy storage. The reactor core is designed as a stack of 9 units with high scalability. Fin-networks and electric heaters are innovatively integrated within the reactor, which enables the provision of high-efficient heat transfer and capability of high-flexible renewable and valley energy consumption. Moreover, the whole system is containerized for mobile energy storage scenario. Totally 10 cyclic performance tests have been conducted with the max and final conversions of 95.87 % and 87.28 %, respectively. For a typical ‘electricity-in’ charging stage, it lasts for 319 min with maximum/average charging power of 126.11/67.43 kW and 1290.63 MJ of energy is stored. For a typical ‘steam-out’ discharging stage, the HTF water is favorably evaporated through the reactor and exhausted as superheated steam at 166.63 ℃ initially and saturated steam at 100 ℃ afterwards at atmospheric pressure. The discharging stage lasts for 351 min with the maximum/average discharging power of 73.02/37.47 kW and the overall heat transfer coefficient of 20–140 W·m⁻²·K⁻¹. Based on energy balance analyses, the charging, discharging and round-trip energy efficiencies are 98.84 %, 91.80 % and 90.74 %, respectively. Distinct advantages in terms of energy storage scale, number of cycles, conversion and working mode have been demonstrated in this work, which has indeed promoted the thermochemical energy storage technology towards practical applications.