Computational study of pressure-drop hysteresis in fluidized beds

Cohesive forces are implemented in a discrete-particle fluidized bed simulation using both a square-well potential and a Hamaker model for van der Waals forces. This simulation is used as a tool to gain greater understanding of the hysteresis behavior that has been observed experimentally during fluidization–defluidization cycles. For the parameters investigated, the results show that cohesive forces are significant in the pressure overshoot observed during the fluidization process. Furthermore, the mechanisms by which the specific cohesive mechanisms causing the pressure overshoot are different depending on the cohesion model being used. Although both models indicate that particle–particle cohesion dominates the overshoot, the square-well model predicts that cohesive interactions between particles and distributor plate also play a role, while the Hamaker model for van der Waals forces predicts that particle–sidewall friction may be enhanced by the presence of cohesion. The results are in accordance with a one-dimensional force balance on the system, and provide alternative explanations for trends in existing datasets.

This plot of pressure drop versus superficial velocity illustrates the effect of cohesion induced by the square-well model on the pressure overshoot during the fluidization cycle. The dotted line represents the normalized weight of the particles in the fluidized bed.Figure optionsDownload as PowerPoint slide