Numerical simulation of counter-current flow field in the downcomer of a liquid–solid circulating fluidized bed

• A CFD model was developed to simulate counter-current two-phase flow in the downcomer of LSCFB.
• Model was adapted to predict the residence time distribution of the solids in the downcomer.
• Increasing superficial liquid velocity decreased solids dispersion in the downcomer.

A comprehensive study on the hydrodynamics in the downcomer of a liquid–solid circulating fluidized bed (LSCFB) is crucial in the control and optimization of the extraction process using an ion exchange LSCFB. A computational fluid dynamics model is proposed in this study to simulate the counter-current two-phase flow in the downcomer of the LSCFB. The model is based on the Eulerian–Eulerian approach incorporating the kinetic theory of granular flow. The predicted results agree well with our earlier experimental data. Furthermore, it is shown that the bed expansion of the particles in the downcomer is directly affected by the superficial liquid velocity in downcomer and solids circulation rate. The model also predicts the residence time of solid particles in the downcomer using a pulse technique. It is demonstrated that the increase in the superficial liquid velocity decreases the solids dispersion in the downcomer of the LSCFB.

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