Agglomeration processes compact density

FIG. 20-71 Classification of agglomeration processes by agitation intensity and compaction pressure. Relative density is with respect to primary particle density and equals (1 — e) where e is the solid volume fraction. Reprinted from Granulation and Coating Technologies for High-Value-Added Industties, Ennis and Litster (1996) with permission of E G Associates. All rights reserved. 

Pai+icle size enlargement equipment can be classified into several groups, with advantages, disadvantages, and applications summarized in Table 20-36. Comparisons of bed-agitation intensity, compaction pressures, and product bulk density for selected agglomeration processes are highlighted above in Fig. 20-71. 

The powder is characterized by chemical (purity), physical (grain size, size distribution, shape, agglomeration, etc.), and technological properties (fluidity, compaction density, etc.), which are influenced by the production process and which can be controlled—to a certain extent— by the process parameters. 

The particle size distribution also has an effect on the compaction behavior. For a powder with a wide distribution of sizes, a plot of the compact density versus the logarithm of the applied pressure has a steeper slope than that for a narrow size distribution (Fig. 6.28), indicating that the deformation process occurs more easily. As outlined earlier (Fig. 6.24), the type and amount of agglomerates in the powder influence its compaction behavior. The effect of the particle shape can sometimes be difficult to predict. The spherical (or equiaxial) shape is the commonly desired geometry, but flat particles with smooth surfaces can provide a higher compact density if they become aligned. 

A fundamental requirement in powder processing is characterization of the as-received powders (10—12). Many powder suppHers provide information on tap and pour densities, particle size distributions, specific surface areas, and chemical analyses. Characterization data provided by suppHers should be checked and further augmented where possible with in-house characterization. Uniaxial characterization compaction behavior, in particular, is easily measured and provides data on the nature of the agglomerates in a powder (13,14). 

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