SIZE DISTRIBUTION OF PARTICLES ENTRAINED FROM FLUIDIZED-BEDS - ELECTROSTATIC EFFECTS

Experimental results obtained with solids ranging from 69-mu-m cracking catalyst to 400-mu-m polyethylene showed that the smallest particles were not the most easily elutriated from fluidized beds of mixed size particles. This is in contradiction with the assumption made by existing models for the prediction of the flux and size distribution of particles elutriated from a fluidized bed. The smallest particles cannot be removed by elutriation from a mixture of particles of various sizes. The smallest particles may be agglomerated with larger particles. Reducing or eliminating particle electrostatic charges by injecting counteracting charges or increasing the gas humidity did not greatly affect the size distribution of the elutriated particles. Electrostatic forces were, thus, not responsible for particle agglomeration. Electrostatic effects, on the other hand, greatly reduced the flux of elutriated particles by creating an extra electrostatic pressure drop in the fluidized bed freeboard. They also changed the fluidization quality of the bed of polyethylene particles.