DEM-CFD modeling of a fluidized bed spray granulator

Coupled DEM-CFD simulations have been performed to study the fluid and particle dynamics in a fluidized bed spray granulator on the scale of individual particles. The aim of this study is to develop a model of a fluidized bed granulator by combining the gas and particle dynamics with a simple model of particle wetting. Based on material tests, the collision behavior of gamma-Al2O3 particles was characterized and incorporated into the contact model. For two different granulator configurations, a bubbling fluidized bed with top-spray injection and a Wurster-coater, wetting of the particle surface is estimated based on the residence time distribution inside a biconical spray zone. The effect of the geometry of the apparatus on the homogeneity of wetting is analyzed in order to understand the performance and specificity of different granulator configurations. Compared to the top-spray granulator, the Wurster-coater has a narrow residence time distribution of the particles in the spray zone, which corresponds to more homogeneous particle wetting. For the Wurster-coater, the effect of process parameters like air flow rate and geometry details like the position of the Wurster tube is studied using the model. A stable circulating fluidization regime is established by keeping the jet velocity above 100 m/s and the gap distance between bottom plate and Wurster tube below 15 times the particle diameter Based on a description of the physical material properties, an effective modeling tool for design and scale-up of a fluidized bed spray granulator is obtained. Modeling the interactions of the individual particles, a step forward is taken towards a description of the micro-processes in granulation, which also considers the material properties. (C) 2011 Elsevier Ltd. All rights reserved.