Reduction and carburization of iron-ore in a fluidized bed by CO,H2 and CH4

The reduction and carburization of fine iron-ore (100 - 200 μm, Fe₂O₃ mass content of 98%) by gas mixtures containing CO, H₂ and CH₄ was investigated in a fluidized bed at temperatures of 400 up to 700°C. In this temperature range carbon is formed from CO via the Boudouard reaction as well as by the decomposition of methane. Yet, both reactions only occur in the presence of metallic iron and therefore only at reduction degrees of the DRI (direct-reduced iron) of more than 33%. As a contribution to the development of a DRI process without a costly hot briquetting, the influence of the C- and O-content of the DRI on its tendency to reoxidize was also investigated by means of the ignition point method. It was found that reoxidation (at 20°C) of a totally reduced DRI can be suppressed by carbon mass contents of more than 7%. With decreasing reduction degrees, this value decreases, until for reduction degrees of less than 80% no carbon is needed to suppress reoxidation. With regard to the final reduction of the DRI in the electric arc furnace, the molar C to O ratio should be one. The maximal reduction degree is then about 86% to stabilize carbon rich DRI (C mass content of 4%) against reoxidation.