A thermodynamic and kinetic study of the de- and rehydration of Ca(OH)2 at high H2O partial pressures for thermo-chemical heat storage

Heat storage technologies are used to improve energy efficiency of power plants and recovery of process heat. Storing thermal energy by reversible thermo-chemical reactions offers a promising option for high storage capacities especially at high temperatures. Due to its low material cost, the use of the reversible reaction Ca(OH)2 ⇌ CaO + H2O has been proposed. This paper reports on the physical properties such as heat capacity, thermodynamic equilibrium, reaction enthalpy and kinetics. To achieve high reaction temperatures, high H2O partial pressures are required. Therefore the cycling stability is confirmed for H2O partial pressures up to 95.6 kPa and the dehydration and hydration kinetics are studied. Quantitative data are collected and expressions are derived which are in good agreement with the presented measurements. At 1 bar H2O partial pressure the expected equilibrium temperature is 505 °C and the reaction enthalpy is 104.4 kJ/mol.