Kinetics of fluidised bed melt granulationIV. Selecting the breakage model

Abstract

The main purpose of this paper is to develop and verify a suitable breakage model to describe the breakage kinetics in fluidised bed melt granulation (FBMG), by means of population balance modelling. A two internal coordinate population balance equation (PBE) [AIChE J. 47 (2001) 1984] that describes the granule size and tracer mass is employed in the modelling process. In addition, a new analytical PBE and discretized population balance equation was developed for the tracer mass distribution for the growth and nucleation process. Three physically plausible breakage models (fragmentation, attrition and random binary breakage) were also implemented in a discretized population balance model (PBM) to describe the breakage process in FBMG. Three phases of the modelling procedures were performed. In Phase 0, the equipartition of kinetic energy (EKE) kernel is fitted to the mass-based granule size distributions to extract an aggregation rate constant to represent the net growth process. In Phase I, a fitting exercise to the different breakage models was performed, and the best fit model is that by random binary breakage with a size-independent selection rate constant. In Phase II, a refined two-parameter breakage model was developed to account for granule breakage by a combination of random binary breakage and attrition processes. A new error-weighted integral fit technique was also developed to extract the aggregation and breakage rate constant simultaneously. For this purpose, we have conducted experiments with and without the presence of tracer granules. Each of these models is quite effective at describing the granule size distribution to which they are fitted, although the Phase 0 model gives a poor description of the numbers of granules. These same models are then used to predict the results of the tracer experiments. From this, we are able to show that the Phase 2 model is the most effective.