A Rate Equation for the Reduction of Iron Ore

Abstract

A rate equation has been derived for the gaseous reduction of iron are pellets on the assumption that both chemical reaction and diffusion contribute to the overall reduction rate. It was assumed that there is no resistance of diffusion through the boundary layer outside the pellet and chemical reaction takes place only at the interface between reduced and unreduced layers. Under these conditions the rate equation is given as follows:
(1/k)[1-(1-R) ^1.3] + (r₀/D)[1/2-R/3-(1-R) ^2/3/2] = (C₀-C_c) t/r₀d₀
whereR: fractional reduction k: chemical reaction rate constant
t: time D: effective diffusion coefficient: radius of pellet C₀: gas concenration in the bulk gas phase
d₀: density of pellet C_c: equilibrium gas concentration
The two terms on the left side of the equation show the relative contribution by chemical reaction and by diffusion of the reducing gas through the reduced metal layer. It was found that the equation agrees with experimental data except towards the completion of reduction.
Equation for the reduction controlled either by chemical reaction or by diffusion could be derived as the limitimg cases of the above-mentioned equation.