The operation of prereduction fluidized bed combined with an in-bath smelting reduction furnace was performed in NKKFukuyama Works, Iron ore fines, such as sinter feed are directly charged into the fluidized bed. This fluidized bed was so designed as to form a dense bed and equip the circulating device. The reduction characteristics of iron ore fines were clarified through the operation in the integrated test plant. According to the above results and the simulation model based on the

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... behavior, the appropriate residence time of coarse became30-60min to reduce the iron ore to 20-25'/• reduction degree in 800"C bed temperature. The effect of circulation of fines was not quantitatively clear in the test, but the favorable circu]ation ratio was estimated with a mathematical model. Moreover, it was found that the collection efficiency of cyclone was closely related to the yields of prereduced ore and the circulation ratio influenced on the losses of products. Therefore, the circulation ratio was considered to be determined from the viewpoints of the effect on the reduction degree of fines and the losses of products.