Statistic model for predicting cluster movement in circulating fluidized bed (CFB) risers

H. Kruggel-Emden, K. Vollmari
Powder Technology
CFD, DEM (Discrete Element Method), Dual-chamber fluidized bed, fluidization, Non-spherical particles, Particle residence times, RFID

Fluidized beds that consist of multiple chambers are used in various processes including granulation, drying or coating. As overly short or long particle residence times inside the vessel are undesirable, it is of high interest to measure and detect the influences of variations of the operational parameters on the particle residence times so that they can be adjusted accordingly to gain narrow particle residence time distributions. For this purpose, an ultra-high frequency (UHF) radio frequency identification system (RFID) has been developed, that is able to detect multiple particles without a direct line-of-sight at different positions inside the vessel. Furthermore, coupled discrete element method (DEM)/computational fluid dynamics (CFD) simulations have been carried out to study a continuously operated laboratory scale dual-chamber fluidized bed. To examine the influences of operational and particle parameters 10 different variations have been evaluated both numerically and experimentally. Results show good agreement between simulation and experiment for most cases. The highest change of the residence times could be achieved by changing the particle mass inflow and the fluidization velocity. The results for non-spherical particles showed some deviations in the longer residence times, as certain particle/wall effects were not fully recreated in the simulation. Nonetheless, it was proven that coupled DEM-CFD simulations can be a useful tool in the prediction of residence time which can greatly help to optimize continuously operated fluidized processes.

Keywords: Dual-chamber fluidized bed, DEM (discrete element method), CFD, RFID, Particle residence times, Fluidization, Non-spherical particles, 

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