CFD Simulations of bubbling/collapsing fluidized beds for three Geldart Groups

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Abstract

A multiphase computational fluid dynamics (CFD) model was applied to a commonly used industrial experiment known as the collapsing fluidized-bed experiment. The experiment involves several hydrodynamic regimes including the bed expansion, bubbling, sedimentation, and consolidation of the fluidized bed. The CFD model is capable of predicting all four of these regimes. The three Geldart Groups, C, A, and B were simulated in a bubbling and subsequently collapsing fluidized bed. Results show that hydrodynamic Models A and B, the use of the modified Ergun equation or the MFIX code drag models, and solids rheology have limited impact on the bubbling- and collapsing-bed simulations. The major finding of this study is that the solids modulus, G, is the controlling parameter during the consolidation regime. The simulated bubble sizes and bed collapse rates for all three Geldart groups were found to be within reported experimental error. The computed high turbulent intensity of Geldart Group A particles also agrees with data in the literature measured using an acoustic shot noise probe. It is also demonstrated that the traditional interpretation of the collapsing bed as consisting of separate bubble escape and sedimentation regimes is incorrect and that, in fact, they occur simultaneously.

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