Carbidization Rate of Reduced Iron Ore in H₂-CO-CO₂ Gas Mixture

Abstract

The carbidization rate of iron ore was thermogravimetrically measured and analyzed in H₂-H₂S-CO-CO₂ gas mixtures from 873K to 1073K, after it was completely reduced in H₂-H₂S gas mixture. Both gases contained sulfur low enough not to form sulfide. The fractional carbidization, f_θ[-], is defined as the mass gain relative to the mass of carbon converting iron to cementite completely, θ-Fe₃C. It grew along a parabolic curve without such a nucleation period as the carbidization CO-CO₂ system. Then, it grew linearly forming percarbide, χ-Fe₅C₂ after f_θ=0.5. The authors considered that the nucleation resistance of cementite and percarbide was reduced by higher carbon supersaturation than that in CO-CO₂ system.
It assumed that the carbidization rate was controlled by carburization of metal with CO and the reaction interface decreased linearly with the amount of metal. Thus, the curve was analyzed using the equation of first order reaction: -1n(1-f_θ)=Rt, where the carbidization rate, R [s^-1] is constant with time. The maximum rate was obtained at about 20 vol% H₂ in H₂-CO system. This fact agreed with Turkdogan and his co-workers' previous work for carbon deposition. As the results, the author showed the adsorbed OH catalyzed carbidization in the following reaction:
CO(g)+OH(ad)=CO₂(g)+1/2 H₂.
Sulfur suppressed the reaction with OH(ad) more strongly than O(ad).