Kinetic Analysis and Reduction Behavior Modeling of Multi-stage Hydrogen Reduction

In the multi-stage reduction process, the progress of reduction in each reactor affects the temperature and gas composition in other reactors due to interconnection among the reactors. The current study performed the kinetic analysis of the reduction in wustite to metallic iron, which is the most important reduction reaction of iron oxide in four-stage reduction process. The reduction in wustite to metallic iron progressed in the last two reduction stages (R3 and R4). Some wustite not fully reduced at R3 stage was further reduced at R4 stage by higher hydrogen partial pressure. The kinetic model analyses identified the first- and third-order chemical reactions to be the rate-controlling steps at R3 and R4 stages, respectively. In contrast, the reaction orders were evaluated to be 1.84 and 2.19 for R3 and R4, respectively. Although the results from different analytical methods showed slight difference, similar trend showed that R4 stage was more influenced by the hydrogen partial pressure, which involves reduction of residual wustite. The activation energies of the chemical reactions at two reduction stages were evaluated to be 150 and 68 kJ/mol, respectively. The derived equations were to predict the change in reduction degree with time at temperatures and hydrogen partial pressures using kinetic model, activation energies, and reaction order. The high consistency in both the measured and calculated reduction degrees at R3 and R4 stages might serve as fundamental data for determining operational conditions.