Thermochemical materials, particularly salt hydrates, have a significant potential of use in storage systems. When a salt hydrate is heated to a critical temperature, a chemical reaction is initiated to dissociate it into its anhydrous form and water vapour. The anhydrous salt stores the sensible energy that was supplied for dehydration, which can be later extracted by allowing cooler water or water vapour to flow through the salt, transforming the stored energy into higher sensible heat. This work presents the modelling during the thermochemical hydration reaction in the reactive porous bed based MgCl2 in a closed system. An analytical sharp front model is also developed in order to determine the required hydration time and bed size. A sensitivity analysis helps identifying optimal parameters that more significantly influence the performance of the heat release process. Numerical heat and mass transfer through principal system components are studied using Comsol Multiphysics Software. Results show good concordance with the experiment. In this closed system, the inlet vapour pressure into the bed has no influence on the process conversion. The optimal porosity of around 0.76 has been taken based on the heat and mass transfer dilemma analysis. Optimal heat exchanger design reveals critical values to enhance the mass transfer issue in the reactive bed.