DEGRADATION CHARACTERISTICS OF IRON-ORE FINES OF A WIDE SIZE DISTRIBUTION IN FLUIDIZED-BED REDUCTION

Three mechanisms of the degradation behavior of iron ore fines (IOF) s ized 1 to 5 mm during fluidized-bed reduction have been investigated: mechanical degradation (MD), thermal degradation (TD) and reactional d egradation (RD). The effects of operational parameters such as ore typ e, temperature, superficial gas velocity, and reducing gas composition have also been studied. The degradation in three mechanisms has been quantitatively evaluated by the amount of IOF smaller than 1 mm which was produced and by the weight change of IOF in the bed during fluidiz ation. The reactional degradation becomes the most predominant aspect among the three and the thermal degradation is the least when the IOF has a low water content, while the degradations of all three aspects a re not much different in contribution when the IOF has a high water co ntent. For the effect of operating parameters, the IOF of a lower sphe ricity showed a higher degradation in the cold fluidization under iner t atmosphere but this effect was lessened or negligible under a fluidi zed-bed reduction at a high temperature. A higher water content in the IOF demonstrated a higher degradation at a high temperature. In the f luidized-bed reduction, the degradation was little affected by the rea ction temperature, the superficial gas velocity, and the reducing gas composition. In addition, ail three aspects of degradation were mostly completed in the early stage, within 15 min, of the operations.