A three-interface random pore model: the reduction of iron oxide in chemical looping and green steel technologies

Abstract

Accurate modelling of the gaseous reduction of porous iron oxide powders or fines is important in industry for (i) reinventing the carbon intensive production of iron and steel and (ii) chemical looping technologies in the sphere of carbon capture and storage. A new three-interface random pore model is derived and applied to the gaseous reduction of hematite (Fe2⁢O3 ) to iron (Fe). The structural reaction–diffusion model is able to describe three simultaneously reacting oxide layers, Fe2⁢O3 , magnetite (Fe3⁢O4 ) and wustite (Fe𝑤⁢O ). The geometric nature of the model encodes structural information about the particles (porosity, surface area, pore length and size distribution), measured here by experiment. The model is usefully able to separate structural particle properties from individual rates of reaction and product layer diffusion. The results have been compared and fitted to thermogravimetric experiments between 800–1000∘⁢C and three CO/CO2 gas mixtures. Rate constants for each indvidual reaction have been obtained and fit well to Arrhenius plots. The reduction of Fe2⁢O3–Fe3⁢O4 was controlled by diffusion and reaction kinetics, while the reduction of Fe3⁢O4–Fe𝑤⁢O and Fe𝑤⁢O –Fe was limited by reaction kinetics. Metallization rates of the iron oxide powders were rapid, showing promise for both hydrogen-based direct reduced iron and chemical looping processes.