Agglomeration Behavior of Calcium Hydroxide/Calcium Oxide as Thermochemical Heat Storage Material: A Reactive Molecular Dynamics Study

Thermochemical energy storage is a promising alternation in heat recovery application compared to phase change energy storage. However, cycling instability caused by agglomeration of the reactant particles is the main problem that hinders the application of this system. The present paper focuses on the agglomeration behavior of the calcium hydroxide/calcium oxide particles as a thermochemical energy storage material at the molecular level. Molecular dynamics simulations with the reactive force field were carried out to investigate the agglomeration of two nano-CaO/Ca(OH)2 particles. The results indicated that the agglomeration rate of two Ca(OH)2 particles was faster than that of two CaO particles in the presence of H2O, which was attributed to the greater spatial displacements of atoms in the reactant particles when thermochemical reaction occurred. The present of H2O could accelerate the agglomeration of the CaO particles. Moreover, the hydration of the CaO agglomeration lump was more difficult than that of fresh particles. The agglomeration of reactant particles had a negative effect on cycling stability. Finally, SiO2 particle was introduced to prevent the CaO/Ca(OH)2 particles from agglomerating during reaction. The results revealed that the presence of silica particles could reduce the agglomeration of reactant particles. This study might provide the guidelines on synthesizing or selecting themochemical energy storage materials with less agglomeration for the Ca(OH)2/CaO reaction cycle.