Experimental study of a novel multi-layer moving bed reactor for low-grade thermochemical energy storage

• A moving-bed thermochemical energy storage system is experimentally investigated. • Pumice-based salt-in-matrix composite sorbents are developed and implemented. • The system achieves an energy storage density of 189.7 kWh/m 3 . • Maximum effective energy and exergy efficiencies are 52.7% and 6.8%, respectively. • A correlation between air humidity difference and temperature lift is established. In the last decade, low-grade thermochemical energy storage systems have been gaining interest due to their long-term heat storage potential and high energy storage density. Despite the advantageous aspects of this heat storage method, previously investigated fixed-bed reactors suffer from low heat and mass transfer performance and offer limited process control. In order to overcome these challenges, a new multi-layer moving bed reactor was designed, manufactured, and tested in this study. The proposed reactor consists of reaction and storage sections where eight independent sorption beds have freedom of movement between the two sections. Such a design enables a modular concept, where each sorption bed could be charged or discharged individually, while the remaining sorption beds are stored inside their own hermetically insulated chambers. In the system, two different sizes of pumice stones, namely PM1 and PM2, were used as the host matrix, and three different thermochemical materials were synthesized by impregnation of the LiCl-CaCl 2 mixture and CaCl 2 as salts into pumice. During the experiments, comparative analyses of different materials, short-cycle full-system analyses, long-cycle energy density analyses, and multi-bed performance analyses have been performed. Additionally, the impact of air velocity was investigated. The evaluations were performed based on the First and Second Laws of Thermodynamics. Study results demonstrated that each sorption bed provides an average heat output between 0.58 and 1.07 kW depending on the inlet air conditions and the composition of thermochemical material. According to the study results, the energy storage density of the system was obtained as 189.7 kWh/m 3 with the use of PM2-CaCl 2 . On the other hand, 4.2 m/s was found as the most optimal air velocity, proving the highest average heat output during the discharging process and the highest moisture desorption rate per unit of heat consumed during the charging process. A linear correlation between the air absolute humidity difference and the air temperature lift for the discharging process was also obtained, which could provide useful insights for the performance prediction of thermochemical energy storage systems.