Bubbling Behaviour of Geldart Group B Particles in Pulsed Fluidization Mode: Experimental and Simulation Study

Authors: 
Akhavan, A., CPFD Software
Clark, R., CPFD Software
van Ommen, J. R., Delft University of Technology
Rhodes, M., Monash University
Coppens, M. O., University College London
Pulsed fluidization is a special mode of fluidization in which the flowrate of the fluidizing medium is intermittently changing. Pulsed fluidization has been proven to offer some unique advantages compared to steady-flow fluidization. These advantages include better mixing for cohesive particles [1], improved drying of wet particles in fluidized beds [2] and a more controlled bubble pattern in some bubbling fluidized beds [3].

Bubbling behaviour of group B particles in a two-dimensional column was studied experimentally. Solenoid valves were used to generate pulsation in the gas flow. Unlike the conventional concept of pulsed fluidization, total gas flow was not subjected to pulsation; a pulsing gas flow was imposed on a constant steady gas flow to the bed. In this paper, we are presenting the CFD simulation results of the system alongside the experimental findings. Barracuda VR was used for the CFD simulation. Glass beads with density of 2520 kg/m3 were used for particles. Air was used as the fluidizing medium and Wen-Yu was the drag model applied in most simulation cases. Effects of flow pulsation in general, and pulsation conditions such as frequency in particular, on bubbling characteristics were studied.

We found that pulsation in general leads to an increase in average bubble size, especially at lower pulsation frequencies; Up to 100% increase in average bubble size could be observed. The bubble size decreases with increasing pulsation frequency. This demonstrates that pulsation gives additional degrees of freedom to control fluidized-bed hydrodynamics.

[1] Hadi, B., van Ommen, J. R., & Coppens, M.-O. (2011). Enhanced particle mixing in pulsed fluidized beds and the effect of internals. Industrial & Engineering Chemistry Research, 51(4), 1713-1720.

[2] Akhavan, A., van Ommen, J. R., Nijenhuis, J., Wang, X. S., Coppens, M.-O., & Rhodes, M. J. (2008). Improved drying in a pulsation-assisted fluidized bed. Industrial & Engineering Chemistry Research, 48(1), 302-309.

[3] Wu, K., de Martín, L., & Coppens, M.-O. (2017). Pattern formation in pulsed gas-solid fluidized beds - the role of granular solid mechanics. Chemical Engineering Journal 329, 4-14.

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