On iron reduction from magnetite by gaseous reducing agents

Abstract

The chemical process of iron reduction from magnetite by gaseous reducing agents is the basis of MIDREX technology implemented at the Oskol Electrometallurgical Plant (OEMK). In the paper, this process was modeled using the TERRA software package developed at the Bauman Moscow State Technical University. During the simulation, thermodynamic system Fe‒С‒О‒Н was analyzed at constant temperature (900  °C) and gas pressure (0.2026 MPa). Mixtures of carbon monoxide and hydrogen in different ratios, as well as individual components of natural hydrocarbon gases, were used as reducing agents. The chemical compositions of reducing agents were estimated by the gross formula СрОrHq , where p, r and q are stoichiometric coefficients. The results of the calculations were the expenses of the reducing gas m, necessary for the complete iron reduction from magnetite, which corresponded to the degree of iron metallization φ  =  1. In the future, the values m were used to evaluate the reducing abilities of various gas mixtures, and the values of φm – to determine the required expenses of these mixtures for iron reduction. Subsequent analysis showed that the machine calculation of the value m can be approximated with a small error (up to 0.001) by the formula where mC and mH are the partial costs of carbon and hydrogen for iron reduction, respectively, and mO is the partial oxygen consumption for iron oxidation. It was also established that the parameters of mC and mH depend on the process temperature and are interrelated in accordance with the equation where K is the chemical equilibrium constant of the “water gas reaction” CO + H2 O = CO2 + H2 , simultaneously occurring in the gas phase. The mO parameter is actually a constant independent of temperature and numerically equal to the value of (–4/3) moles per 1 mole of iron. The arguments of partial costs can also be characteristic molecular compounds accompanied with appropriate stoichiometric coefficients. In the practice of OEMK, natural gas consumption V is taken into account, measured in cubic meters per ton of sponge iron. The forecast of this value can be performed using the formula: In general, the proposed calculation algorithm of the chemical process can be correctly applied in the temperature range of 800 – 900 °C. Possible variations in the gas working pressure will not require significant adjustments in the calculation results.