Numerical investigations of a continuous thermochemical heat storage reactor

Thermochemical systems are a good alternative to current technologies for long-term heat storage, since the energy is stored as a chemical potential and there is no heat loss during the storage phase. A large number of studies have now been conducted on the development of integrated thermochemical reactors, but fewer studies have investigated separate reactor technologies. The latter present the advantage of dissociating the thermal power and storage capacity of the system, which also increases the energy storage density of the process. This paper investigates the functioning of an open continuous thermochemical reactor with falling solid flow and humid air cross-flow. A 2D model was developed and set up with the finite element simulation software COMSOL Multiphysics to represent heat and mass transfer phenomena in the reactor. This study focuses on the influence of the inlet pressure and vapour fraction of the air on the reaction behaviour and the reactor performance (power, temperature). This study also investigates the influence of the reaction front on the pressure drop in the reactor. It highlights the presence of a sharp reaction front between one part of the reactor (bottom) where the solid is completely hydrated and the other part (top) where the solid has not reacted yet. This sharp front is strongly dependent on the inlet air conditions. Also, there is an inertia phenomenon at the entrance of the unreacted solid, which is influenced by inlet air pressure, creating a particular air velocity field.