A Comparative Experimental Study On The Kinetics Of Iron Ore Fines Fluidization Reduction

Blast furnace process is highly capital and energy intensive, requiring large-scaleinfrastructure and operationg. The process requires the iron ore feed in the form ofsinters or prllets and coke produced from high-grade coking coal. Iron ore finesreduction in fluidised bed reactor systems is gaining more attraction due to theireconomic and ecological benefits. In order to optimize the kinetics of reduction of ironore fine with carbon monoxide in fluidized, increase reduction rate and productionefficiency, in this paper MFBRA and TGA are used to study Brazil iron ore finereduction behavior in different temperature and volum fraction of CO atmosphere. Thenthe fluidized bed was used to achieve the fluidization pre-reduction and final reductionof Brazil iron ore fine. This experimentation is used to investigate the effects ofpre-reduction stage temperature and residence time on the final reduction stage, andanalysis the effects of strucyural changes of product during reduction on Brazil iron orefine reduction behavior in entire reduction process.In TGA, the reaction rate of Fe₂O₃is increased as the temperature rises. However,Brazil iron ore fine can not be entriety reduction at same experiment condition, becauseof the rate of the reduction reactions are controlled by the CO diffuse thought theboundary layer to the external surface of the grain. The ore fine degree of reduction isincreased as the temoerature rise. But temperature has a small influence on the rate ofreduction. Highter concentrations of CO in the reducing gas gave higher rates ofreduction.In MFBRA, Increasing the reaction temperature and the volum fraction of CO led tohigher rates of reduction. However, this effect was less strong at small amount of CO.Temperature has a significant influence on the rate of reaction at the beginning ofreduction; this effect was less strong at later stage of reduction. The apparent activationenergy of model-free isoconversional and model-fitting approaches is similar. The rateof the reduction reactions are controlled by the diffusion of CO from product layers toreaction boundary. Comper MFBRA with TGA, in MFBRA, the rates of reaction is veryfast, effective inhibition of the external diffusion. The result of kinetic parameters issimilar with intrinsic reaction. It is indicating that the kinetic parameters by MFBRA aresuitable for the guidance of the fluidized bed reactor ironmaking process.In fluidized bed, the degree of pre-reduction is increased as the pre-temperatuer rises at the pre-reduction stage. When the pre-temperature of400℃,500℃,700℃, the drgreeof final reduction is increased significantly with the pre-temperature rises. When thepre-temperature of600℃,750℃, there has been an exception, the final reduction degreebelow500℃,700℃respectively. When the residence time of600℃from10min to8min, the final reduction degree has improved siginificantly.The SEM was uesd to analysis strucyural changes of product at pre-reduction andfinal reduction stage. We found that the reaction rate and residence time togetherdetermine the porosity of product layers. The higher temperature led to the faster therate of reaction, the more loss of the amount of oxygen within a unit time and the moreformation of voids and craks. As the reaction proceeded, the reaction rate is graduallyreduced, no further increase in the number of holes and cracks. At this point, if thereduction temperature is too high, the sintering effect will be significantly, result in ahole and crack closure. Dense sintered product layer prevents the diffusion of reducinggas to the reaction interface, resulting in a low degree of particles reduction.