Mechanistic modelling of fluid bed granulation, Part II: Eased process development via degree of wetness

The performance of a fluid bed granulator was investigated through experimental and numerical study to develop a stand-alone fluid bed granulation model. The single-compartment model proposed in part I (for agglomeration modeling) was extended to account for i) evaporation of freely-flowing droplets, and ii) particle drying. This model enables us to predict the granule liquid content and temperature besides the granule size. Accurately, the equations of heat and mass conservation were solved in parallel to the population balance calculation of the agglomeration. In the same manner as for the agglomeration model, the model parameters associated with the drying model were estimated and correlated to the relevant quantities. The analysis of the experimental results revealed the significant contribution of the system “degree of wetness” to the bed performance, i.e., granule size and loss on drying (LoD). As the agglomeration model parameters were partially correlated to LoD in Part I, the presented model was revisited by inclusion of the degree of wetness. The reliability of the developed model in predicting the temporal evolution of granule size, liquid content, and temperature was proven through comparing the bed performance between simulation and experiment. Subsequently, to lowering the costs associated with experimental run, an approach was proposed based on the degree of wetness, aimed at reducing the number of experiments required for the design of experiment (DoE). The results of our simulation using reduced experiments demonstrated that the degree of wetness can be a promising indicator for the performance of the fluid bed granulator as well as for more efficient design of experiment.