(480f) CFD Study of Drag Model on Simulating Bubbling Fluidized Bed of Geldart A Particles

Fluidized beds are widely used in chemical, petrochemical, metallurgical, and energy industries. Hydrodynamic understanding of gas-solid multiphase flow is critical in the success of fluidized bed design.

A two fluid model with kinetic theory is commonly used in computational fluid dynamics (CFD) models to simulate the gas-solid flows. Interaction between gas and solid phase is described by a drag model, which plays an important role in predicting the hydrodynamic behavior in the fluidized bed. However, few successful simulations were reported on a bubbling fluidized bed of Geldart A particles. Overestimated bed expansion comparing to experimental data was reported by Zimmermann and Taghipour [1], which attributed to overestimated drag from classic drag models of Syamlal–O’Brien [2] and Gidaspow [3]. Most classic drag models were developed based on homogenous flow and weighted by solids volume fraction. Energy minimization multi-scale theory based drag models (EMMS) were reported for better representing the heterogeneous nature in a bubbling bed and having better agreement of bed expansion with experimental measurement [4][5]. The EMMS drag model intentionally resolves the heterogeneous structures by seeking the minimum energy consumption for particles suspension and transport.

In this research, a 3D CFD model is constructed based on PSRI’s bubbling bed for the NETL challenge problem III (2010) [6]. A two fluid model incorporating kinetic theory is used in the simulation. A commercial CFD software, Ansys FLUENT 19.0, is chosen for simulation. The effect of different drag models of Gidaspow, Wen-Yu with factor of 0.7 and EMMS on the simulation results are evaluated and compared to experimental data. The EMMS model was implemented into FLUENT by a user defined function (UDF). Two sets of experiments on 3% content of fine particles with different superficial gas velocity are modeled for validating the drag model’s wide application on the bubbling regime. The results showed that both Gidaspow and modified Wen-Yu drag model over-predict the bed expansion comparing to the EMMS drag model. The heterogeneous structure in the bottom dense region is better resolved by the EMMS model.

[1] Zimmermann, S. and F. Taghipour, CFD Modeling of the Hydrodynamics and Reaction Kinetics of FCC Fluidized Bed Reactors, Ind Eng Chem J..44, 9818–9827. 2005.

[2] Syamlal, M. and T.J. O’Brien, Computation of flow patterns in circulating fluidized bed. A.I.Ch.E. Symposium Series 85 (270), 22–31, 1989.

[3] Gidaspow, D., 1994. Multiphase Flow and Fluidization: Continuum and Kinetic Theory Description. Academic Press, Boston.

[4] Yang, N, W. Wang and W. Ge, J. Li, CFD simulation of concurrent-up gas-solid flow in circulating fluidized beds with structure-dependent drag coefficient, Chem.Eng J. 96, 71–80. 2003.

[5] Benzarti, S., H. Mhiri, and H. Bournot, Drag models for Simulation Gas-Solid Flow in the Bubbling Fluidized Bed of FCC Particles, International Journal of Chemical and Molecular Engineering 6, 111-116, 2012.

[6] NETL Multiphase Flow Science, Challenge problem III, 2010, https://mfix.netl.doe.gov/challenge-problem-iii-2010/