Fluidization of micron-size ceramic powders in a small-diameter fluidized bed

Abstract

Fluidization characteristics of nine micron-size ceramic powders (Group C powders in Geldart's classification) have been investigated in a small-diameter transparent column. Three types of fluidization were observed. Type I fluidization was similar to that observed by Chaouki et al., J. Powder Technol., 43 (1985) 117, and Morooka et al., J. Chem. Eng. Jpn., 21 (1988) 41. In type II fluidization, two regimes of flow patterns were distinguished with increasing gas velocity. Initially, solid powder with channels was observed in the bed, and within the channels, powder moved as very small agglomerates forming spouts in the freeboard from the top surface of the bed. With an increase in superficial velocity, the channels enlarged and powder from the channels spouted much higher from the top surface of the bed. In the second flow regime, two layers were formed in the fluidized bed: the top layer was well fluidized, and the bottom layer consisted of bigger agglomerates. Type III fluidization was for those powders which had small agglomerates before fluidization started. The process of fluidization of these materials was very similar to that of Group A powders. Experiments showed that even with drying and vibration, some powders could never be fluidized stably and reproducibly.