Simulation of Geldart Group A Particles in Fluidized Beds by Computational Fluid Dynamics
Date Issued
2009
Date
2009
Author(s)
Hsu, Sheng-Jie
Abstract
Gas–solid flow behavior in fluidized beds with Geldart Group A particles was numerically simulated by using a computational fluid dynamics (CFD) package FLUENT which is based on the two–fluid model (TFM). Due to the fine nature of Geldart Group A particles, cohesive interparticle forces are significant in comparison to the particle weight and drag force. This effect is very difficult to model in TFM because the continuum basis of the model makes it difficult to consider cohesive forces between individual particles. In this study, five different particles and ambient air were used to simulate.These particles are the glass beads with the diameter 50 μm and the density 2500 kg/m3 for System–1, the glass beads with the diameter 60 μm and the density 2510 kg/m3 for System–2, the FCC (fluid catalytic cracking) particles with the diameter 78 μm and the density 1880 kg/m3 for System–3 and System–4, and the FCC particles with the diameter 58 μm and the density 1780 kg/m3 for System–5. The gas–solid drag models used are Gidaspow drag model and Syamlal–O’Brien drag model for System–1 and System–2, modified Gibilaro drag model for System–3, and Yang drag model for System–4 and System–5.The minimum fluidization velocity and the minimum bubbling velocity was obtained by using the relation between the computed time–averaged solid void fraction and the superficial gas velocity for System–1 and System–2. The simulation results were in agreement with the literature data. The computed time–averaged axial particle velocity in the radial profile at the different bed heights in the bubbling fluidization regime (System–3) and the fast fluidization regime (System–4) were in good agreement with the literature experimental results. The results showed that the particles flow upward in the center of the bed and downward near the wall. For System–5, the axial voidage distribution in the fast fluidization regime were calculated with different superficial gas velocities but at the same solid circulating rate. The simulation results showed that the solid phase void fraction distribution along the bed was the S-curve, and it does not change with the superficial gas velocity changed. It was different from the literature experiment data. Yang drag model was derived from the EMMS model at = 1.52 m/s and = 14.3 kg/m2–s. Therefore, if the simulation conditions were different from the above condition, the drag model would be derived again from the EMMS model at specific simulation conditions.
Subjects
gas-solid fluidized bed
CFD
gas-solid drag model
Type
thesis
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