Formation of iron carbide in fluidized bed by the reactions of partially pre-reduced iron ore with CO-H2-H2S mixtures:: Influence of the reduction degree

In our previous studies of the iron carbide formation, the iron ore particles were completely reduced to metallic iron and then the reduced iron was carburized with CO-H-2-H2S mixtures. However, the reactivity of the reduced iron seems to definitely influence the rate of the iron carbide formation. Therefore, in this study, at the atmospheric pressure and 873K, iron ore particles of hematite were first reduced to various reduction degrees with 50% N-2-H-2-H2S mixture and second exposed to CO-H-2-H2S mixtures with alphas = 0.5. The remained iron oxides are reduced and then the fresh reduced iron ore of somewhat low sulfur contents is immediately carburized. It was experimentally confirmed that the lower the pre-reduction degree, the faster the carburization rate and the easier the formation of Fe5C2 and free carbon. The recommended condition for the fast and stable carbide formation is to be a low pre-reduction degree and the CO-H-2-H2S mixtures containing less than 60% CO. From the microscopic observation of cross sections of samples, a new knowledge was obtained that the remained wustite and reduced iron are open to the reaction gas access through the pore of particles.