Experimental studies on distributions of granule size, binder content and porosity in batch drum granulation: Inferences on process modelling requirements and process sensitivities

Abstract

Batch granulation experiments on a lab-scale drum granulator for a Calcite/Polyvinyl alcohol in water (Calcite/PVOH–H 2O) system are presented in this study. Experimental studies were carried out to study the aggregation kinetics and mechanism for this granulation recipe, whilst investigating the effects of binder-to-solids ratio and drum load on the granule size, binder content and porosity distributions. In particular, the effect of formulation properties and the granulation operating conditions on the batch process dynamics and the end-granule properties are studied. The formulation properties considered include liquid surface tension, powder-liquid contact angle, dynamic yield stress, powder shape and liquid viscosity. The operating variables include the binder-to-solids ratio, binder addition duration and the binder addition mode. The sensitivity in the process and the non-homogeneity of key particle attributes (size, binder content, and porosity) is evident. The important process manipulations for feedback control and potential disturbances are identified, formulating a comprehensive control configuration for batch and continuous granulation, with the latter case being exemplified in Glaser et al. [T., Glaser, C.F.W., Sanders, F.Y., Wang, I.T., Cameron, R., Ramachandran, J.D., Litster, J.M.-H., Poon, C.D., Immanuel, F.J. Doyle, III, 2007. Model predictive control of drum granulation. Manuscript in preparation.]. The importance of multi-scale process models that link fundamental material properties with the granulation mechanisms and end-granule properties is also evident from the experiments. A three-dimensional population balance equation structure in terms of the particle size, binder content and porosity is confirmed to be an ideal framework for the process model.