Two- and three-dimensional CFD modeling of Geldart A particles in a thin bubbling fluidized bed: Comparison of turbulence and dispersion coefficients

A comprehensive understanding of turbulence and dispersion is essential for the efficient design of a conventional fluidized bed reactor. However, the available information is restricted to that in a two-dimensional (2-D) plane, because of the experimental and simulation limitations. It is, therefore, of importance to evaluate the remaining third dimension of the system and compare these results with the corresponding data obtained from the 2-D analysis for validation. In this study, computational fluid dynamics (CFD) based upon the kinetic theory of granular flow with a modified interphase exchange coefficient was successfully used to compute the system hydrodynamics of fluid catalytic cracking (FCC) particles in a thin bubbling fluidized bed with 2-D and three-dimensional (3-D) computational domains. In addition, the shortcoming of the current CFD model was evaluated. With respect to the bed height, the bed expansion ratio and solid volume fraction revealed similar results from both 2-D and 3-D computational domains. The turbulent granular temperature was higher than that of the laminar ones in the lower section of the bed while the laminar granular temperature dominates the system in the upper section. However, the granular temperatures obtained from the 3-D computational domain were slightly lower than that from the 2-D computational domain. The computation also showed that the dispersion coefficients are in good agreement with the literature measurements and so the 2-D computational domain can be used to simulate the bubbling fluidized bed system. Finally, all the evaluated system hydrodynamic values in the thin radial system direction were lower in the 3-D computational domain than in the thick radial system direction.

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