Design and simulation of a solar chemical reactor for the thermal reduction of metal oxides: Case study of zinc oxide dissociation

A laboratory-scale solar reactor was designed and simulated for the thermal reduction of metal oxides involved in water-splitting thermochemical cycles for hydrogen production. This reactor features a cavity-receiver directly heated by concentrated solar energy, in which solid particles are continuously injected. A computational model was developed by coupling the fluid flow, heat and mass transfer, and the chemical reaction. The reactive particle-laden flow was simulated, accounting for a multiphase model (solid-gas flow). A discrete phase model based on a Lagrangian approach was developed. The kinetics of the chemical reaction was considered in the specific case of zinc oxide dissociation for which reliable data are available. The complete model predicts temperature and gas velocity distributions, species concentration profiles inside the reactor, particle trajectories and fates, and conversion rate assessing the reaction degree of completion. The reaction extent is highly dependent on temperature of the radiation-absorbing particles. Initial diameter of injected particles is also a key parameter because it determines the available surface area for a given particle mass feed rate. The higher the particle surface area, the higher the conversion rate. As a result, reaction completion can be achieved when particle temperature exceeds 2200 K for a initial particle diameter.