High surface temperature gas-solid (Fe3O4 and H2O/CO2) interfacial reaction characteristics

Radiation heat transfer and temperature distributions are the important factors that affect solar to chemical energy conversion in the solar thermochemical reactor. In this paper, high surface temperature gas-solid (Fe₃O₄ and H₂O/CO₂) interfacial chemical reaction characteristics were investigated. It was found that the reaction kinetics and mechanisms of species conversion were strongly affected by the thermal energy changes and the contact time between gas and solid species in the reacting medium. The species reactivity was limited to the formation of H₂ and CO which are important feedstocks for the fuel cells and synthetic fuels production such as synthetic solar hydrocarbon fuels, methanol, and other chemical products. Moreover, H₂ and CO formation were essentially based on oxygen exchanges capability and the reactivity of short-lived radical species such as H, O, C and OH at the interface of iron oxide surface. Besides, during the process of solar thermochemical reacting systems (STRS), the reaction extent was favored by large axial temperature gradient and the convective heat flux which enhanced gas-solid contacting time thereby resulting in higher heat and mass transport. The surrounding species reactivity toward product gases formation was improved due to the thermal expansion of heat released from the species reaction by thermal conduction, radiative heat exchange, and heat transfer via advection. However, the rates of lattice oxygen extraction and diffusion from gas-to-iron oxide species were highly controlled by the surface temperature and pressure. Therefore, an accurate determination of reaction temperature and pressure of STRS is necessary for solar reactor geometry optimization for hydrogen production, as well as solar fuels synthesis.