Degradation of Hematite Powder during the Fluidized Bed Reduction with CO-CO₂ Gas Mixture

Abstract

The degradation was observed during the reduction of hematite powder (70-140mesh) to magnetite with CO-CO₂ gas mixture by a fluidized bed. The effects of reduction temperature, gas velocity, reduction time by fluidized bed, and the other on the degradation were investigated. The degradation was not observed for sample without reduction. The degradation was most significant in the reduction at 700°C, and the amount of the degradation decreased during reduction at higher temperature than 700°C. The amount of degradation increased with an increase of gas velocity, but the amount of the degradation did not increase over the gas velocity 0.44m/s. Next, the amount of the degradation increased with an increase of the reduction time(the fractional reduction). The degradation was not observed only in the fixed bed reduction and the degradation increased with an increase of the fluidizing time after reduction by the fixed bed. It was noted that the degradation by the fluidized bed reduction was caused by the particle getting fragile by the reduction and fluidizing after the reduction.
Moreover, a mathematical model which considered the decreases of the particle size and the particle weight in the bed was developed for the rate analysis of the fluidized bed reduction. The reduction rate calculated by the model which considered those effects agreed well with the one measured in fluidized bed and was faster than the one calculated by the model which ignored the effects.