Modeling and Predicting Gas-Solid Fluidized Bed Dynamics to Capture Nonuniform Inlet Conditions

Abstract

The hydrodynamics of fluidized beds involving gas-solids interactions are very complex, and modeling such a system using computational fluid dynamics (CFD) modeling is even more challenging for mixtures composed of nonuniform particle characteristics such as diameter or density. Another issue is the presence of dead-zones, regions of particles that do not fluidize and accumulate at the bottom of the bed, affecting uniform fluidization of the material. The dead zones typically form between the gas jets and depend on the spacing of the distributor holes and gas velocity. Conventionally, in Eulerian–Eulerian modeling for gas-solid mixtures, the solid phase is assumed to behave like a fluid, and the presence of dead zones are not typically captured in a CFD simulation. Instead, the entire bed mass present in an experiment is usually modeled in the simulations assuming complete fluidization of the bed mass. A different modeling approach was presented that accounts for only the fluidizing mass by adjusting the initial mass present in the bed using the measured pressure drop and minimum fluidization velocity from the experiments. In order to demonstrate the fidelity of the new modeling approach, three different bed materials were examined that can be classified as Geldart B particles. Glass beads and ceramic beads of the same mean particle diameter were used, as well as larger-sized ceramic particles. Binary mixture models were also validated for two types of bed mixtures consisting of glass-ceramic and ceramic-ceramic compositions. It was found that adjusting the amount of fluidizing mass in the modeling of fluidized beds best predicted the fluidization dynamics of an experiment for both single phase and binary mixture fluidized beds.

On the Computational Modeling of Unfluidized and Fluidized Bed Dynamics

“…[16]). The continuity and momentum equations are solved for both the gas phase and the solids phase, and the Gidaspow model is used for the interphase drag force.…”

“…The purpose of this paper is to find the best possible approach to model the ground walnut shell bed in the unfluidized and fluidized regimes using FLUENT based on the recommendations of Gavi et al [20] and Battaglia et al [16,22]. Gavi et al [20] did not show results in both the unfluidized bed regime for the STD and NEW approaches.…”

“…In both studies [19,22] MFIX was employed to predict the fluidization dynamics, and analyzed how best to capture pressure drop, minimum fluidization velocity, and mean void fraction, simultaneously. These studies [16,22] considered two adjustments in system parameters in order to match the experimentally measured pressure drop: modifying void fraction and modifying bed height. Adjusting only the bed mass and subsequently the bed height provided the best predictions, which matched with the experiments for all desired criteria.…”

“…Battaglia et al [22] and Kanholy et al [16] proposed a new approach to model the ground walnut shell experiments [20]. In both studies [19,22] MFIX was employed to predict the fluidization dynamics, and analyzed how best to capture pressure drop, minimum fluidization velocity, and mean void fraction, simultaneously.…”

“…The equations and models employed will be briefly discussed as extensive details by the second author can be found in Refs. [15,16].…”