Thermochemical characterizations of high-stable activated alumina/LiCl composites with multistage sorption process for thermal storage

High-stable activated alumina/LiCl composites with multistage sorption process were fabricated to store low-temperature heat below 120 °C. The worried issue of solution leakage was solved by controlling its salt content below the threshold value. The microstructure was observed by transmission electron microscopy (TEM). Research on nitrogen adsorption suggested that because of the impregnated salt, composite sorbents presented different pore structure from pure activated alumina. Based on the measured results of water isotherms, the sorption equilibrium states represented by the mass concentration of the inside LiCl solution were evaluated. Moreover, the multistage sorption process-physical adsorption, chemical adsorption and liquid-gas solution absorption were quantitative analyzed based on the capillary condensation mechanism and hydrous reaction equation. Sorption kinetics proved that the sorption capacity of composite sorbents was significantly improved compared with pure activated alumina. Sorption energy storage density was obtained by the TGA/DSC measurement. Overall, AA/LiCl composite sorbent with salt content of 14.68% was selected as the optimistic AA/LiCl composite sorbent with a sorption capacity of 0.45 g/cm3 (0.41 g/g) and an energy storage density of 318.3 kWh/m3 (1041.5 kJ/kg) at the condition of 20 °C, 80% RH with a charging temperature of 120 °C.