Three-Phase Sorption Process for Thermal Energy Storage: Theoretical Analysis and Implementation Solutions with Porous Matrix

摘要

Thermal energy storage systems based on the sorption technology are attracting the attention of many researchers in the recent decade, mainly owing to the benefits of high storage density and no significant heat loss to the environment during the storage. First, the principle of the three-phase process of salt-water system was illustrated in theory. Three-phase TES cycles for three working pairs, namely LiCl/H_2O, CaCl_2/H_2O and LiBr/H_2O, were theoretically investigated based on their pressure-temperature-phase diagrams. Calculation results shows that a remarkably high storage density is potentially available with the thorough transformation from solid salt to liquid solution. To implement the cycle in real systems, possible concepts were presented and discussed. Two porous matrices have been proposed and tested to support the liquid solution. Optimization of silica gel-based and expanded graphite-based matrices shows that the SLi30 sample with 35 wt.% LiCl and the ELi250 sample with 54 wt.% LiCl are the best options. Distributing LiCl into porous structure could greatly improve the water sorption kinetics. Approximate evaluation suggests that ELi250 could realize a heat storage potential of 375 kWh/m~3 and SLi30 possesses a heat storage potential of 280 kWh/m~3.