457430 High Shear Granulation: An Investigation into the Granule Consolidation Mechanism

Monday, November 14, 2016: 9:35 AM
Bay View (Hotel Nikko San Francisco)
Stefan A. L. de Koster, Chemical and Biological Engineering, University of Sheffield, Sheffield, United Kingdom and Rachel Smith, Department of Chemical and Biological Engineering, The University of Sheffield, Sheffield, United Kingdom

High-shear granulation, the agglomeration of small particles in heavy mixers to produce agglomerates called granules, is extensively used by many industries. The key mechanisms taking place during the granulation process, wetting and nucleation; consolidation and growth; and breakage and attrition, however, are not yet fully understood.

The aim of this work is to compare a model for consolidation and layered growth to experimental data to allow for the prediction of the kinetics of the consolidation process in high-shear mixers. The model is based on deformation-driven diffusive growth, with small deformations causing a diffusion-like migration of binder liquid and powder, resulting in growth. The growth rate decays exponentially until the granule has reached a final size, which depends on the initial amount of liquid and the powder properties.

In order to properly monitor the growth of particles without the interference of other mechanisms such as breakage and attrition, a Consolidation-Only Granulator (COG) has been designed. Product granules were weighed, and the density of the granules was determined. In this way, the growth and density of the granules could be monitored over time.

Four different powder-binder systems were considered: lactose-silicone oil, lactose-hydroxypropyl methylcellulose (HPMC), glass beads-silicone oil and glass beads-HPMC. Binder liquids were used at varying viscosities to examine the effect of varying binder viscosity on the kinetics.

Here we present the results of granule growth behaviour and compare experimental findings to the proposed model. Growth behaviour is discussed in terms of the critical-packing liquid volume fraction, which is defined as the final liquid volume fraction of a granule.

Future work will include the incorporation of the kinetic model into population balance models, and the performance of DEM simulations to further increase the physical relevance of the model. In this way, consolidation and layered growth kernels for population balances can become more reliable.


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See more of this Session: Agglomeration and Granulation Processes I
See more of this Group/Topical: Particle Technology Forum