Thermodynamic and kinetic investigations of the SrBr2 hydration and dehydration reactions for thermochemical energy storage and heat transformation

Abstract

The potential of thermochemical energy storage and heat transformation has been soundly highlighted in literature. For applications in the temperature range from approximately 150 °C to 300 °C, the inorganic salt strontium bromide, which reacts with water vapor in an exothermic reaction, is a promising candidate: SrBr2 (s) + H2O (g) ⇌ SrBr2·H2O (s) + ΔRH. This chemical reaction offers a specific energy density of 291 kJ/kg SrBr2 (or 81 kWh/t). The feasibility of a thermochemical energy storage and heat transformer based on the SrBr2/H2O working pair has already been successfully demonstrated on a 1 kW scale in a lab-scale storage unit. Here, we report on the steam pressure-dependent reaction temperatures of the dehydration and hydration reactions as well as the reaction rate and the cycle stability of the reactive system over 100 reaction cycles using thermogravimetric analysis. For distinct operating points, e.g. running the hydration reaction at 180 °C and 69 kPa, specific thermal powers up to 4 kW/kg SrBr2 were experimentally determined. Running the dehydration reaction at 210 °C and 5 kPa steam pressure showed specific thermal powers of 2.5 kW/kg of SrBr2·H2O, thus proving the suitability of SrBr2/H2O as thermochemical working pair for high-power storage applications. Our results provide fundamental material-related data for the design of high-power reactor modules as well as for numerical studies on the potential of thermochemical energy storage and heat transformation based on SrBr2/H2O.