Agglomerate nucleation and growth

Beyond the nucleation stage, size change in the system can occur by a number of mechanisms as depicted in Fig. 3.2. The prevailing mechanism depends on such factors as the feed particle size and other solid properties, liquid surface tension and viscosity and the mode of operation (batch or continuous). After nucleation has occurred, the predominating growth mechanisms are  

Both coalescence and layering can occur simultaneously in a system but, in general, one mechanism will predominate. 

In continuous systems, recycled undersize material or agglomerates formed by coalescence of the fresh feed act as nuclei. However, since the fine feed particles can form stronger bonds with the nuclei particles than with each other, the majority of the feed material would be expected to simply layer onto the established agglomerates rather than to coalesce with other fine particles. 

Agglomerates formed by coalescence and by layering can usually be distinguished by their appearance. Layered granules tend to a smooth spherical shape and examination of their interior cross sections reveals a layered onion skin construction. Coalesced granules tend to a more irregular spheroidal shape and often exhibit a rough raspberry -type surface. 

Influence of agglomerate strength maximum feed particle size 

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