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Wet agglomeration processes have predominantly been investigated by changing operation variables of process-scale experiments. So far, most fundamental work concentrated on the strength of the liquid bonds in the agglomerate and its relation to the process. Previous studies on the relationship between droplet size and agglomerate size in fluid bed agglomeration indicated that, besides agglomerate strength, liquid distribution determines the agglomerate properties to a large extent. This paper focuses on the mechanism of growth of a single agglomerate originating from one droplet of binder liquid. A model is introduced which describes agglomerate growth as a function of time. We discern two stages of growth of an agglomerate. Initially, fast growth takes I,lace by wetting of the powder particles by a droplet, which result in the formation of an initial agglomerate. This stage of fast growth is followed by a second stage of slower growth, which results from drainage of binder liquid from the initial agglomerate to the outer layers of the growing agglomerate. This model predicts agglomerate growth and the final agglomerate size by taking into account the particle sie distribution, the viscosity, the surface tension, the contact angle, the porosity, the wetting saturation and the residual saturation. Experimental results were in good agreement with the model. (C) 1998 Elsevier Science S.A. All rights reserved. |
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