A MATHEMATICAL-MODEL FOR THE RATE ANALYSI S OF GASEOUS REDUCTION OF HEMATITE POWDER IN A FLUIDIZED-BED WITH SEGREGATION

In the case that particles of several different diameters exist in a f luidized bed, the segregation of particles is occasionally observed in the bed. Therefore, a mathematical model for the rate analysis of gas eous reduction considering the segregation in the bed was developed. T he applicability of this model was confirmed by the following experime nt. Hematite powder, which was the mixture of particles of different s izes, i.e. large particle (0.50mm in diameter) and small one (0.15mm i n diameter), was reduced to magnetite in the fluidized bed (21mm in tu be diameter) at 700 degrees C by 10%CO-90%CO2 gas mixture. The gas flo w rates were 4.7x10(-5)m(3)/s (STP) and 8.0x10(-5)m(3)/s(STP). The rat ios of the superficial velocity, U, to the minimum fluidized velocity U-mf in the case of the large particle were 1.5 and 2.8 respectively. The fluidization phenomena of the bed were observed in the cold model experiment. In the case of 8.0x10(-5)m(3)/s (STP): the bubbles were ob served and the particles were fully mixed in the bed. The measured fra ctional reduction curve agreed well with the calculated one by the bub ble assemblage model, in which it was assumed that the particle was mi xed perfectly in the bed. In the case of 4.7x10(-5)m(3)/s (STP), the b ubbles were not observed and the particles were not mixed in the lower part of the bed. Under this condition, the measured fractional reduct ion curve agreed well with the calculated one by the model considering the segregation of the particles in the bed.