Collision dynamics in fluidised bed granulators: A DEM-CFD study

The fluid, particle and collision dynamics inside a fluidised bed granulator are described in detail using coupled DEM-CFD simulations. Three different granulator configurations are compared in terms of their particle–particle interactions, using criteria such as the average particle velocity, angular velocity, average particle–particle and particle–wall collision velocity and the collision frequency. From these measures the agglomeration probability, the breakage and growth rate and the agglomerate strength can be assessed. Depending on the required product properties the results highlight advantages of specific granulator geometries.The top-spray granulator is the simplest device and is often used for large-scale granulation processes in the food and fertilizer industries, but wetting intensity and growth rate are relatively low compared to the other configurations investigated in this work. The spouted bed has the most intensive gas–liquid–solid contact and produces compact and dense agglomerates. Both the agglomeration probability and the breakage rate are very high. The Wurster-coater achieves the fastest growth rate for the applied process conditions and is characterised by homogeneous cyclic particle wetting and a low breakage rate.The simulation results are confirmed by lab scale batch agglomeration experiments using maltodextrin DE21, a model substance for amorphous food powders. It can be concluded that the DEM model offers large potential for process intensification by investigating the effect of geometry modifications on the fluid and particle dynamics and on the homogeneity of particle wetting. This is shown exemplarily for fluidised bed agglomeration.

► DEM-CFD simulation of particle and collision dynamics in a fluidised bed granulator.
► Identical geometry is used in simulation and experiment.
► Influence of granulator geometry on structure and strength of the agglomerates.
► Model can predict growth rate and width of the size distribution of the product.