CFD-DEM Simulation of a Coating Process in a Fluidized Bed Rotor Granulator

Coating of particles is a widely used technique in order to obtain the desired surface modification of the final product, e.g., specific color or taste. Especially in the pharmaceutical industry, rotor granulators are used to produce round, coated pellets. In this work, the coating process in a rotor granulator is investigated numerically using computational fluid dynamics (CFD) coupled with the discrete element method (DEM). The droplets are generated as a second particulate phase in DEM. A liquid bridge model is implemented in the DEM model to take the capillary and viscous forces during the wet contact of the particles into account. A coating model is developed, where the drying of the liquid layer on the particles, as well as the particle growth, is considered. The simulation results of the dry process compared to the simulations with liquid injection show an important influence of the liquid on the particle dynamics. The formation of liquid bridges and the viscous forces in the liquid layer lead to an increase of the average particle velocity and contact time. Changing the injection rate of water has an influence on the contact duration but no significant effect on the particle dynamics. In contrast, the aqueous binder solution has an important influence on the particle movement.