Thermocline in packed bed thermal energy storage during charge-discharge cycle using recycled ceramic materials - Commercial scale designs at high temperature

ReThink Seramic – Flora is an innovative ceramic material made from 100 % recycled materials. Due to its affordability, suitable thermal performance, and low pressure drop in packed bed thermal energy storage (TES), it is considered as a promising storage material option for high-temperature TES applications including concentrated solar power (CSP) plants. In the present study, a validated CFD model is used to analyze the thermal performance of the sustainable ceramic at high temperature (1000°C) for a commercial-scale packed bed. The paper focuses on modeling the charging/discharging processes and cyclic behavior based on threshold temperature, where dispersion thermal conductivity was considered. The effective thermal conductivity is affected when the dispersion thermal conductivity and the radiation heat transfer are taken into account in the model. The addition of dispersion conductivity leads to a variation in effective thermal conductivity in the range of 28.9–39.9 (W/m.K) for temperature range of 0–1000°C, while the addition of radiation heat transfer leads to a small variation in effective thermal conductivity based on two correlations from literature. The results show excellent thermal performance, with thermal exergy efficiency of 88 % for a full charge/discharge cycle. The net exergy efficiency for seven repeated cycles increased from 73.4 to 88.7 %, where thermal and pressure drop exergy losses are considered. The performance of ReThink Seramic – Flora is compared to the one of a commercial alumina-based TES material product. Thermal exergy efficiency for alumina is higher; however, the alumina-based product showed high pressure drop losses, leading to lower net exergy efficiency.