Efficient storage of thermal energy can contribute significantly to a sustainable and cost-effective energy solution. Thermochemical storage, where heat is stored as reaction enthalpy of a reversible chemical reaction, has great potential as an economic option for thermal energy storage. This is especially due to the high specific storage densities associated with the chemical reactions. Suitable thermochemical storage materials are characterized by high reaction enthalpies, fast dynamics as well as cycling stability. Furthermore, sufficient heat and mass transfer through the reaction bed and within the particles is crucial.
A currently investigated reaction system for application at temperatures between 400 and 600 °C is the CaO/Ca(OH)2 system , where calcium oxide (CaO) reacts in an exothermic reaction with water vapour (H2O) to calcium hydroxide (Ca(OH)2). This system has already been studied in stationary bench- and pilot-scale reactors. In order to improve the storage’s efficiency a moving bed reactor is proposed, offering the advantage of separating the storage’s capacity from its power. However, due to the very fine particle size, the material is a Geldart C powder and therefore difficult to move. One approach for enhancing the flowability is the admixture of nanostructured additives in a dry mixing process, leading to a reduction of agglomeration effects during thermal cycling .
In contrast, the aim of this work is to stabilize the particle size during thermal cycling. Two options, namely the embedment in a water permeable matrix and the encapsulation of the storage material with a water permeable layer are presented. Important criteria for the selection of feasible matrix and encapsulation materials are discussed. The contribution is focused on material optimization and investigations concerning the mechanical stability and cyclability during thermal cycling in lab scale experiments. From the results a strategy for further material optimization is derived.