Equilibrium parameters of gas mixtures H2–H2O–CO–CO2–CH4 in the absence and presence of carbon
DOI:
https://doi.org/10.14529/met160401Keywords:
water gas, oxygen potential, methane, reduction of oxidesAbstract
Cokeless direct iron-making outside the blast furnace (the “Midrex” process of) is carried out at 1000–1100 °C using natural gas. Processes of conversion of natural gas component, methane, namely
CH4 = C + 2H2, CH4 + CO2 = 2H2 + 2CO, CH4 + H2O = CO + 3H2
result in a reduction gas and sooty carbon at a certain ratio of mole fractions of CO and CO2. The thermodynamic possibility of reduction of the metal oxide in the complex gas mixture is determined by the ratio of the oxygen potential of the gas atmosphere and oxide: (po = RT ln pO2)oxide > (po = RT ln pO2)gas mixture.
The reduction potential of the gas mixture is estimated by equilibrium pressure of oxygen, and the oxygen potential of the oxide is estimated by its dissociation tension. The presence of a very small amount of oxygen in the gas phase is determined by reactions of dissociation of CO2 and H2O:
lg[pO2, atm] = 2 lg(xH2O / xH2) – 25708 / T + 5,653;
lg[pO2, atm] = 2 lg(xCO2 / xCO) – 29529 / T + 9,149.
The paper describes determination of oxygen potential of the gas mixtures H2–H2O–CO–CO2–CH4 depending on their composition in the temperature range of 800–1500 K. The obtained results allow to evaluate the effect of presence of methane in the gas mixtures on their reducing properties not only in relation to the iron oxides.
