Chemical reactions during iron reduction from oxides

The chemical process, accompanied by iron reduction from hematite, was modeled by computer program complex TERRA (product of MGTU im. N.E. Bauman). Carbon, hydrogen and methane were used as reducing agents. By varying the costs of reducing agents and process temperatures, equilibrium concentrations of the system components were determined. Change in these concentrations at the boundaries of individual temperature regions was regarded as a result of the passage of appropriate chemical reactions in them. At the same time, it was noted that the nonvariant type reactions begin and end at the same fixed temperatures. Calculations have shown that the conversion of Fe2O3 → Fe3O4 in all cases was thermodynamically possible at temperatures exceeding 65 °C. Therefore, at operating temperatures of the furnace it will be implemented without complications. The second stage of reduction also took place under a single scheme Fe3O4 → Fe, bypassing the participation of FeO oxide. The temperatures of beginning of iron reduction by components C, H2 and CH4 were respectively 680, 350 and 520 °C. In this case, there was only a direct reduction of iron by these components. An attempt to fix the fact of indirect reduction, using carbon monoxide as a reducing agent, was unsuccessful even with a large consumption of it. Carbon monoxide decomposed at low temperatures by the Bell-Boudoir reaction. Therefore, later iron was restored by means of “soot” carbon and that is also a direct method. In the final stage of the carbon thermal process, depending on the system composition, formation of iron carbide at 720 °C can occur with the possible subsequent conversion back to iron, as well as secondary oxidation of iron to form wustite. Carbon dioxide takes an active part in these reactions. Based on the results of calculations of chemical processes at high temperatures, a numerical assessment of the reducing (or oxidative) efficiency of all elements and components of the Fe – O – C – H system was given. This made it possible to predict with a high degree of reliability the phase composition of the reaction products at maximum process temperature (1500 °C).

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