(563d) Particle Clump Formation and Its Effect on Entrainment

Three cases are presented on the entrainment of various materials from fluidized beds in which particle clumps, resembling agglomeration, affected the measured entrainment rates. In the first case, direct evidence of ?agglomeration? is observed in the freeboard of a fluidized bed of 20 µm particles in that large clusters are visible at sizes exceeding 1000 µm. In the second and third cases, the effects of agglomeration are seen indirectly by the measured entrainment fluxes. For the second case, fines from a secondary cyclone of a fluidized catalytic cracking unit were measured at different fluidized bed heights. Higher entrainment fluxes were observed with lower bed heights (and subsequently higher disengaging heights). The third case comes from replication of a phenomenon observed in an industrial scale process where loading into the solids recovery system was highly variable and led to flooding of the recovery system. It was found that with an initial high concentration of fines in the fluidized bed that the entrainment flux was very low, but that as the fines were gradually elutriated away, the entrainment flux increased dramatically. Following the dramatic increase, the entrainment flux then exhibited classical exponential decay as the fines were further elutriated from the fluidized bed.

Evidence suggest that fines of many materials may be clumping and resulting in a lower entrainment rate. These clumps appear to be formed in the fluidized bed and can be ejected into the freeboard intact. Thus, entrainment rates may be influenced by fines levels, bed heights, baffles, jet velocities, etc. Details of this mechanism and its implementation will be discussed.