Numerical analyses are performed to study thermo-chemical energy storage in a three-dimensional reaction bed. This study is aimed at investigating heat and mass transfer characteristics of a rectangular shaped fixed reaction bed packed with Ca(OH)(2)/CaO powders. A reversible reaction with endothermic decomposition of Ca(OH)(2) and exothermic hydration of CaO is used to achieve charging and discharging of the module respectively. Heat is transferred indirectly to and from the bed through side walls using a flat plate heat exchanger. A set of coupled nonlinear equations governing reaction kinetics, heat and mass transports is solved numerically using a finite element based software. Mathematical models and the numerical method employed are validated by comparing present simulation results against experimental results. Our results agree reasonably well with results of experimental measurements. It is noted that the heat and mass transport within the reaction bed is strongly three-dimensional in case of low bed porosity. The results of this study provide detailed insight to the heat storage and heat release processes occurring in fixed bed of fine Ca(OH)(2)/CaO particles. The study helps designing and optimizing high temperature thermo-chemical energy storage modules for power generation applications. (C) 2017 Elsevier Ltd. All rights reserved.