Abstract
Particulate bed expansion and its collapse were investigated for binary powder-particle mixtures of FCC particles (Geldart A) and a small amount of cohesive Al(OH)3 powders (Geldart C) up to 15 ?m in mean size with starting fractions of fine powders in the bed no larger than 5 wt%. The column of a fluidized bed was a transparent vinyl chloride column of 0.104 m i.d. with a porous metal-sintered distributor. Superficial gas velocities at incipient fluidization and bubbling were also investigated. The effects of size and hold-up of fine powder on the particulate bed expansion and its collapse were investigated.
When the hold-up of fine powder in the bed was less than the maximum value (1wt% for 1-?m fines and 3wt% for 3-µm fines) to avoid segregation or aggregation during fluidization, bed expansion as well as de-aeration rate increased with increasing the hold-up of fine powders. Thus, the difference between superficial gas velocities at incipient fluidization and bubbling got larger with increasing the hold-up of fine powder in the bed. When the size of Al(OH)3 powder was 1µm, a small hold-up of fine powder such as 1 wt% was still effective to increase the minimum bubbling velocity and the dense phase expansion as compared to FCC particles alone.
