Improved theory on the rate of reduction of single particles and fixed beds of iron oxide pellets with hydrogen.
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Single hematite pellets having not so large porosity are reduced over a temperature range 600-1000°C and a flow-rate range 0.1-20Nl/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. For these dilution processes, the dispersion model is introduced into the unreacted-core shrinking (UCS) models for one and three interfaces in consideration of the resistance due to the rate of gas flow proposed by Clair. With appropriate selection of kinetic constants, the modified models produce greatly improved fit to experimental data.Porous wustite pellets are reduced and their reduction rates are analyzed by using modified grain and intermediate models; for this case the latter analysis gives rather satisfactory results. Then, multi-stage diffusional (MSD) model is derived on the basis of the intermediate model, and the calculated results are compared with hematite-reduction data. Both reduction curves based on this model and the three interface UCS model reproduce experimental ones very well, while interface radii based on the MSD model simulate cross-sectional view much better than those based on the three interface model. When basic hematite pellets are reduced at 1000°C, the reduction rate decreases extremely in the final stage. An equation of solid-state diffusion is introduced into the MSD model; fairly good agreement is seen up to the final stage.Packed beds of Hamersley pellets are reduced over a temperature range 600-1000°C and a flow-rate range 1-45Nl/min. Not only reduction curves and exit hydrogen flow-rate but core radii and local fractional-reduction in beds reduced partially are measured. The equations of mass balance for a fixed bed are combined with the UCS models for one and three interfaces and numerical calculations are done by the method of characteristics or by an approximate approach; the results calculated by both methods are much the same. Calculated results based on the three interface model reproduce experimental data much better than those based on the Rist model or the one interface model.Porous pure-hematite pellets and basic pellets (fluxed pellets) are reduced at 800 and 1000°C, respectively, and their rates are analyzed by the approximate approach based on the MSD models with and without the solid-state diffusion; each analysis reproduces respective experimental data very well.
- The Iron and Steel Institute of Japanの論文
The Iron and Steel Institute of Japan | 論文
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