Multi-stage Zone-reaction Model for the Gaseous Reduction of Porous Hematite Pellets

A mathematical model is presented for describing the multi-stage reaction of a porous hematite pellet with a reducing gas on the basis of the ISHIDA and WEN'S intermediate model. This model represents non-topochemical behavior; cross section of a pellet is devided into four layers-iron layer and the three reaction zones of hematite-magnetite, magnetite-wüstite, and wüstite-iron layers, in which chemical reaction and gaseous diffusion proceed simultaneously. Semi-analytical solutions to reducing gas and oxygen concentrations in a pellet are derived and fractional reduction and boundary radii are calculated numerically. Acid and basic hematite pellets (porosity_??_0.23) were reduced with hydrogen of 5 Nl/min over a temperature range 700° to 1000°C. Calculated reduction curves and boundary radii agreed well with experimental data except in the final stage of reduction of the basic pellet at 1000°C.