Study on long-term thermochemical thermal storage performance based on SrBr2-expanded vermiculite composite materials

Abstract

Strontium bromide hexahydrate (SrBr2·6H2O) is one of the most promising storage materials of thermochemical energy storage for space heating. In this study, four different SrBr2/expanded vermiculite composites (SrBr2/EVMs) were prepared by the impregnation method. After that, the micro and macro-structural characteristics of those composites were characterized by Scanning Electron Microscopy (SEM) and X-ray Energy Dispersive Analysis (EDX). Moreover, the composites’ dynamical desorption behaviors were tested by Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Meanwhile, the composites’ dynamical adsorption behaviors were investigated in a constant temperature and humidity chamber. Lastly and most importantly, the kinetic models for the adsorption and desorption processes of SrBr2·6H2O were first deduced based on the above experimental data. The results showed that the carrying capacity of SrBr2/EVM composite linearly increased with the concentration of SrBr2 solution. And the composite can likely achieve a higher water uptake amount and better adsorption performance than pure salt. However, the composite loaded with more salt would deliquesce at high humidity and reduce the adsorption performance. It was found that SrBr2·6H2O in the composite could be well desorbed and achieve a reaction enthalpy as high as 644.9 J/g. The developed conversion rate function can reasonably predict the hydration reaction of SrBr2. Besides, six different kinetic equations of the solid-state decomposition were established to calculate the desorption reaction. The findings are useful to the design and operation of the thermochemical energy storage system with SrBr2·6H2O.