Thermochemical Storage Using Composite Materials: From the Material To the System
Abstract
A seasonal chemical heat store, based on the hydration/dehydration cycle of a magnesium sulphate (MgSO4) composite material, is under development. During the summer, the material stores heat by an endothermic dehydration reaction and heat used for space heating is released in winter by rehydrating the material. For that specific purpose, a new thermal energy storage composite material is developed. The active material needs to be dispersed to optimise the gas-solid reaction kinetics and the thermal power released/absorbed. Zeolite has proved to be a favourable porous expanded structure for MgSO4, with energy densities of 150-400 kWh/m3 at a storage temperature compatible with solar thermal collectors. Characterisation by Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) on 10 mg samples show that almost 80% of the total energy density can be stored at 150°C although the material is not fully dehydrated. At a greater scale, during hydration tests on 200g samples, an energy density of 0.18Wh/g is achieved, i.e. 45% of the theoretical energy density of the form-stable zeolite-MgSO4 composite sorbent. Keywords: thermal energy storage, thermochemical storage, magnesium sulphate, zeolite, composite sorbent.