(189o) Three-Dimensional Gas-Solid Fluidized Bed Cfd Simulation Using a Lattice Boltzmann Based Drag Correlation

From the pool of industrial gas-solid fluidization processes those using circulating fluidized bed (CFB) technology are implemented in a wide variety of fields, including fluid catalytic cracking (FCC), combustors, powder generation and mineral processing. As this process requires a huge economical investment for building a new or upgrading an existing unit, there is an especial interest in understanding the fluid dynamic behavior of CFB. Unfortunately there is no sufficiently accurate analytical model that describes all the complex phenomena that occur in such units. In this context the computational fluid dynamic (CFD) is a very promising tool, allowing the simultaneous modeling and resolution of mass, energy and momentum transfer as well as the hidrodynamics and collisional phase interactions on even very complex geometries. This work has as aim to study the implementation of a drag force correlation in three-dimensional gas-solid CFD simulations, performed with the commercial Ansys CFX 10.0 CFD code, in a laboratory scale. This correlation was developed by Hill et al. (2001), which was obtained not by the usual empirical data, but was instead formulated on lattice Boltzmann simulations data, and was later extended by Benyahia et al. (2006). It was added to the software in the form of a Fortran subroutine. The laboratory scale CFB experimental work of Samuelsberg et al. (1996) was used for the validation of the numerical results. The apparatus consist of a vertical 1 m column with an internal diameter of 0.032 m. There is a main air entrance at the bottom and a secondary one at 0.05 m above the gas distributor, orthogonal to the column, through which the particles are re-injected. The particles density is 1600 kg m-3 and with a Sauter mean diameter of 60 10-6 m. Three different superficial gas velocities were used in the experiment, 0.36, 0.71 and 1.42 m s-1, all at ambient temperature. A constant velocity of 0.05 m s-1 was held at the secondary entrance. The initial bed height of the solid was 0.05 m. Results for radial profiles of axial velocity were reported for three different heights of the column, namely 0.16, 0.32, 0.48 m. For the numerical mathematical modeling, the Eulerian-Eulerian approach was used, which consider both phases as fluids. For the gas phase, the κ-e model was used to represent the turbulence, and a laminar model was used for the particles phase. The wall contact was considered ?no-slip' for the gas and ?free-slip' for the solids. Also, the results of this work were compared with the hybrid drag correlation suggested by Gidaspow(1994).

Keywords: gas/solid fluidization, CFD, lattice Boltzmann drag correlation

References:

1.HILL, R. J.; KOCH, D. L.; LADD, A. J. C. The first effects of fluid inertia on flows on ordered and random arrays of spheres. Journal of Fluid Mechanics, v. 448, p. 213-241, 2001.

2.BENYAHIA, S.; SYAMLAL, M.; O'BRIEN, T. J. Extension of Hill-Koch-Ladd drag correlation ovel all ranges of Reynolds number and solids volume fraction. Powder Technology, v. 162, p. 166-174, 2006.

3.SAMUELSBERG, A.; HJERTAGER, B. H. An experimental and numerical study of flow patterns in a circulating fludized bed reactor. International Journal of Multiphase Flow, v. 22, p. 575?591, 1996.