Computational Fluid Dynamics-Discrete Element Method Investigation of Solid Mixing Characteristics in an Internally Circulating Fluidized Bed

Abstract

Solid mixing dynamics is of vital important to the processing rate, achievable homogeneity and product quality in the related industries of granular material. In this paper, solid mixing behaviors within a baffle-type internally circulating fluidized bed (ICFB) are numerically investigated using a three-dimensional computational fluid dynamics-discrete element method (CFD-DEM), in which the gas motion is modeled by means of large eddy simulation (LES) while the solid kinematics is handled by a soft-sphere model. On the basis of the simulation results, typical snapshots of granular mixing dynamics in the bed are extracted to reveal the mixing process of different initial segregation conditions. The mixing quality, which is described by Lacey mixing index, is evaluated. Meanwhile, the solid circulation pattern is illustrated by tracking tracer positions both in the three-dimensional bed and along the horizontal and vertical directions as simulation time advances. Furthermore, the influence of different parameters, such as sampling grid dimension, bed aeration setup, diameter and density of the solid, and the gap height beneath the baffle, on the mixing behaviors are also investigated. The results show that macroscopic circulation of solid plays a dominate role in the mixing process of the bed. Judging by the tracer trajectory with time, a better transverse mixing can be obtained, and the mixing mechanisms are further analyzed. Besides, it is found that mixing rate and degree are insensitive to the sampling grid size and a nice mixing level can be obtained within seconds providing enough aeration to the bed and a proper gap height. Meanwhile, lighter and smaller particles possess better mixing ability, as they are easier to fluidize. Furthermore, this ICFB exhibits additional potentials in solid mixing compared with the corresponding fluidized bed.

Numerical investigation of mixing and orientation of non-spherical particles in a model type fluidized bed

“…Liu et al [41] derived a DEM/CFD-framework relying on a coupling of the commercial CFD-code Fluent with a non-commercial DEM-scheme, focusing on bubble/particle interaction and its influence on mixing. A fluidized bed with internal recirculation was addressed by Fang et al [42]. Within the fluidized bed different mixing stages were identified over time.…”

Experimental and numerical investigation of sands and Geldart A biomass co‐fluidization

“…Xiong et al reviewed the widely used CFD models such as multifluid modeling, in which gas–sands–biomass are all treated as continuum phases; Euler–Lagrange–Lagrange modeling, in which gas phase is treated as continuum phase while sands and biomass are treated as discrete phase; Euler–Euler–Lagrange modeling, in which the gas phase and sands are treated as continuum phase while biomass is treated as discrete phase. The Lagrange‐based methods directly tracked the positions of particles and is convenient for the analysis of mixing . In gas–solid CFD simulation, the drag model which describes the gas–solids interactions plays a key role.…”

Parallel CFD–DEM modeling of the hydrodynamics in a lab-scale double slot-rectangular spouted bed with a partition plate

“…Besides the experimental work, numerical simulation has been used in the modeling of two-phase dense flow with the development of the computational technology [14][15][16][17][18]. The methods adopted to model the two-phase dense flow can be mainly divided into two types: the Eulerian-Eulerian method and the Eulerian-Lagrangian method.…”