A Method of Analysis for Reduction of Iron Oxide in Mixed-Control Kinetics

Abstract

Synopsis Various j)arameters included in the mixed-control rate equation for the gaseous reduction of an iron oxide j)ellet must be determined bifore the equation is applied to the analysis of processes in a blast furnace. I n this paper, a method is proposed to determine the reaction rate constant and the intraparticle dijJusivity from experimental reduction data by a simple graphical analysis. As an illustrative example, this method was applied to the present data for hydrogen reduction of dense hematite obtained by the authors. The rate constant k,., the intraparticle diffusivi0' D " and the tortuosity factor r of the reduced iron layer determined by this analysis are in reasonable agreement with those obtained by other investigators. When the mean pore radius of the reduced iron la.yer is comj)arable to or smaller than the mean)i'ee path of the gases, the total pressure gradient is expected in the layer because of the effect of Knudsen dijJusion. An equation was derived to estimate the ratio of the total pressure at the reaction ;nte/face to that at the exterior surface of a pellet. Its maximum value at 900°C for the situation q! the present experiment was calculated to be 1.07, which is fairly small.