Experimental Study of the Resistance due to the Rate of Gas Flow on the Hydrogen Reduction of an Iron Oxide Pellet

Abstract

Single basic hematite pellets (porosity 24%) have been reduced in two reactors of 54 and 156 mm I.D, over a temperature range 600 to 1000°C and a flow-rate range 0.1 to 20Nl/min. In the initial stage of reduction, hydrogen is diluted by nitrogen which flows through a reactor until it reaches a set temperature, and the reaction retards especially at low flow rates. In the course of reduction, hydrogen is also diluted by the product gas (H₂O). For these dilution processes, the dispersion model has been introduced into the unreacted-core shrinking model for one interface in consideration of the resistance due to the rate of gas flow proposed by Clair (1965).
Contribution of this resistance, denoted by k(0≤k≤1, k=0 and 1 imply the analyses without and with the resistance, respectively), has been examined by comparing calculated reduction curves with experimental ones: The value of k increases as the flow rate decreases. With appropriate selection of kinetic constants, the modified model produces a greatly improved fit to experimental data even at low flow rates, where sigmoidal reduction curves occur; such curves cannot be described by the analysis in which only time lag is taken into account on the assumption of plug flow.