Fluidized Bed Spray Granulation: Nucleation Studies with Steady-State Experiments

Fluidized bed spray granulation is a technology for the production and formulation of coarse-grained granules from solutions, suspensions, or melts. In order to run the process continuously and stable, product particles removed from the process have to be replaced by new small granules. The nucleation rates have to be within certain limits; otherwise, the process behavior becomes unstable. In this work, steady-state experiments with a bottom-spray configuration were carried out to determine the influence of process parameters on internal nucleation rates. These investigations help to understand the nonlinear dependency of internal nucleation on process parameters and provide quantitative data of internal nucleation rates. It is shown that internal nucleation and dust integration are competitive mechanisms. Internal nucleation is enhanced by conditions that increase dust and drop concentrations in the spray resulting in agglomeration of the two disperse phases. On the other hand, parameters, for example, high binder concentration in the liquid or large granule holdup, that favor drop deposition on granules and dust integration of wet particles reduce the drop and dust concentrations and thus the internal nucleation.