Quantitative Analysis of Powder-Binder Agglomeration

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J.D. Litster, R. Smith, H. Wildeboer, IT Cameron
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Particle Formation
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This report summarises progress in IFPRI project 37 in 2001/2. The breakage of wet granules in a granulator environment is being studied by Rachel Smith (UQ PhD student). Preliminary results from the dynamic compression of single wet pellets using an Instron Dynamite load frame are reported. The methodology developed by Iveson and Page is used with sone improvements. Fast frame video is used to capture in detail the deformation of the pellets.

The deformation behaviour of the pellets varied widely from very plastic behaviour to failure by brittle crack propagation. Brittle or semi-brittle behaviour was more likely at high strain rate and with high viscosity binders. Pellets made from non-spherical, broad size distribution lactose powder were also more likely to fail in a brittle mode than closely sized glass ballotini pellets. Preliminary results suggest the failure mode can be related to a critical capillary number. The fast frame video analysis of the compression is a very useful tool for understanding the failure behaviour of these partially saturated materials. A hypothesis for wet granule breakage in mixer granulators is suggested and a plan for testing the hypothesis using a specially designed breakage only granulator is presented.

A summary of the PhD studies of Hans Wildeboer on regime separated granulation is given. This work proposes that to optimise granulator design, the key rate processes for granulation should be separated. A conceptual design for a two stage granulator – nucleation only, followed by consolidation and layered growth - is presented. Mathematical models for both stages are developed. The models are compared to results from a partly regime separated continuous drum granulator. The models are very promising in predicting and understanding the granulation behaviour.

A new granulator design is developed which completely separates the nucleation regime from consolidation and growth. A novel nucleation device is tested which gives near mono-sized nuclei at a required size. Further details of Wildeboer’s work are given in his PhD thesis, which will be sent to IFPRI members in early 2003.