FLUIDIZATION OF FINE AND VERY DENSE HARD-METAL POWDERS

The fluidisation characteristics of a hardmetal powder, of extremely high density and small primary particle size such that it belongs to Group C in Geldart's classification, has been investigated. Surprisingly, it was found that in this case the powder could be fluidised via self-agglomeration, though such behaviour is not predicted from the primary particle diameter and/or its density, or the Geldart classification. When the gas is flowing for the first time through a bed of this powder, three regimes of two phase flow patterns were distinguished with increasing gas velocity: gas-'solid powder'; gas-'solid powder' and agglomerates; gas-agglomerates. Subsequently, only the third condition is found with the agglomerate size dependent on gas velocity. A theoretical analysis of the first pattern is also presented, as well as a general qualitative description of the whole process. © 1990.