Group C powders

Group C powders are of small particle size, cohesive by nature and hence, difficult to fluidize. Either the fluidized bed lifts as a solid plug of material or forms stable channels of air flow, which allows the fluidizing gas to escape. The latter phenomenon is referred to simply as channelling . It may be possible to fluidize such powders by mechanical agitation (e.g., stirring, vibration). 

Group C powders Very fine, cohesive powders are classified into this category, which are incapable of fluidization in the strict sense and tend to rise as a slug of solids. Their sizes are usually less than 30 pin, and they easily give rise to channeling. Examples of group C materials are talc, flour, and starch. 

Figure 13 Fluidisation behaviour of a group C powder an attempt to fluidise a group C powder produces channels or a discrete plug...

For fine Geldart Group C powders that defluidize slowly, it has been shown experimentally that solids continued to be transported through the downcomer even when the fluidizing gas to the dipleg was turned off. The particulate solids move in the dense phase. This operation will be designated self-flow (Kwauk, 1974a). Under this condition, the total gas rate is zero ... 

Group C. Powders in which surface forces become overwhelmingly important, e.g., all powders having a mean size less than about 30 /am. 

Group C powders are cohesive and fluidize with great difficulty. They generally have a lower particle density and/or particle size compared to Group A powders. 

Figure 7.8 Attempts to fluidize Group C powder producing cracks and channels or discrete solid plugs...

Molerus (1982) classified the powders by taking into account the interparticle cohesion forces. Free particle motion for Group C powder is suppressed by the... 

---