1996 Volume 82 Issue 10 Pages 823-828
In the case that particles of several different diameters exist in a fluidized bed, the segregation of particles is occasionally observed in the bed. Therefore, a mathematical model for the rate analysis of gaseous reduction considering the segregation in the bed was developed. The applicability of this model was confirmed by the following experiment.
Hematite powder, which was the mixture of particles of different sizes, i.e. large particle (0.50mm in diameter) and small one (0.15mm in diameter), was reduced to magnetite in the fluidized bed (21mm in tube diameter) at 700°C by 10%CO-90%CO2 gas mixture. The gas flow rates were 4.7×10-5m3/s (STP) and 8.0×10-5m3/s (STP). The ratios of the superficial velocity, U, to the minimum fluidized velocity Umf 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 8.0×10-5m3/s (STP), the bubbles were observed and the particles were fully mixed in the bed. The measured fractional reduction curve agreed well with the calculated one by the bubble assemblage model, in which it was assumed that the particle was mixed perfectly in the bed. In the case of 4.7×10-5m3/s (STP), the bubbles were not observed and the particles were not mixed in the lower part of the bed. Under this condition, the measured fractional reduction curve agreed well with the calculated one by the model considering the segregation of the particles in the bed.