Development of a kinetic mechanism for the direct reduction of hematite pellets in CO-H2 atmospheres using a porous solid pellet model

Abstract

Increasing interest in the direct reduction of iron has revived investigations on gaseous iron oxides' kinetics. Despite extensive studies on the reduction of iron oxides with pure hydrogen or with syngas, the development of a generic reduction mechanism of iron oxides is still lacking. The conventional shrinking core model hardly distinguishes between transport processes and reaction processes, leading to biases in the kinetic model. In the present study, a porous solid model, which solves mass balances of the individual gas species and solid ones assuming spherical symmetry, is used for developing a heterogeneous kinetic mechanism accounting for different iron oxides (Fe2O3, Fe3O4, FeO). It also accounts for carbon accumulation and cementite (Fe3C) formation to model phenomena like carbon deposition and incomplete reduction of iron oxide using CO/-H2 mixtures. The proposed generic mechanism successfully reproduces 50 sets of experimental data by six different authors from the literature for single iron oxide pellet reduction with syngas of varying hydrogen content up to pure hydrogen without any adjustment of its parameters. The simulated results show a very good agreement with the experimental data. Finally, the effects of gas composition, temperature, and pellet characteristics on the reducing of iron oxide are investigated.