Research On Sticking And Defluidization During Iron Ore Reduction In Fluidized Bed

Among many non-blast furnace iron-making processes, the fluidized technologyis likely to be an important future development direction of direct iron reduction for itsdirect use of fine ores, and the typical process is FINEX at present. But the fluidizedreduction technology has its own defects, which is defluidization problem, leading toreduce the fluidization efficiency, then to form the fixed bed. The way that is used toprevent defluidization is reducing the temperature and improving the gas velocity.Although it can prevent the defluidization problem, the production efficiency and therate of reduction gas will be reduced, which eventually leads to the whole process ofcoal consumption increased and the advantages of fluidized reduction technologygreatly reduced. Therefore the defluidization problem has acted as a barrier to thefluidized reduction technology reaching its full potential. This paper introduced testson defluidization and then conducted the theoretical analyses and discussion, to studythe influencing factors and the mechanism of defluidization.There were two steps in this experiment. Research on the influencing factors ofdefluidization was the first one, which depended on comparing the time at the stickingpoint to study effects of temperature, reduction gas concentration and the type, the sizeof iron ore. Research on the mechanism of defluidization was the second one. Thespecimens after defluidization have been analyzed by the electron microscope tocompare with the specimens before reduction to discuss the mechanism ofdefluidization.Through the research on the influencing factors of defluidization came to thefollowing conclusions: there is a critical temperature during iron ore reduction influidized bed, which below this temperature the defluidization can not occur. Inaddition, the higher the temperature, the greater the tendency of defluidization occurs.,and the higher the reduction gas concentration, the greater the tendency ofdefluidization occurs. Besides the kind of reduction gas has a great impact on thedefluidization, It comes to defluidization, when the hydrogen as the reduction gas itcan occur only in the high temperature of1123K, while the carbon monoxide as thereduction gas it can occur at923K. The larger the size of iron ore, the the greater thetendency of defluidization occurs when the hydrogen as the reduction gas. While thesmaller the size of iron ore, the the greater the tendency of defluidization occurs when the carbon monoxide as the reduction gas.There were two different types of defluidization phenomenon by contrast thesurface morphology of specimens before and after defluidization under variousoperating conditions. One is due to whisker connected to each other when thereduction gas is carbon monoxide, the other is caused by softening or melting of ironunder high temperature when the reduction gas is hydrogen.