Mapping of regimes for the key processes in wet granulation: Foam vs. spray

The evaluation of foam and spray granulation mechanisms and their performances in achieving uniform liquid distribution in a high-shear mixer-granulator is presented. A regime map is presented to describe the granulation mechanisms for the foam and spray systems. Foam and spray granulation are shown to successfully create granules of well-distributed moisture at the end of wet massing despite there was a deviation from the theoretical moisture content at the end of binder addition. In the wetting and nucleation regime, spray granulation involves drop penetration nucleation outside of the drop-controlled regime, whereas foam granulation operates favorably in the mechanical dispersion regime. For foam granulation, mechanical dispersion produces more uniform granule-size distributions below the overwetting limit. Spray granulation exhibits steady granule growth, whereas foam granulation shows induction granule growth followed by rapid granule growth. The regime map provides a basis to customize formulations and compare the different foam and spray granulation mechanisms. © 2013 American Institute of Chemical Engineers AIChE J, 2013