On the Modeling of Gas-Solid Fluidization: Which Physics Are Most Important to Capture?

Abstract

Recent studies to predict biomass fluidization hydrodynamics motivated a new study to reassess how to model gas-solid characteristics that capture the same physics as that measured in experiments. An Eulerian-Eulerian multifluid model was used to simulate and analyze gas-solid hydrodynamic behavior of the fluidized beds. The relations for the pressure drop measured at fluidization were used to correct for the bed mass by either adjusting the initial solids packing fraction or initial bed height, two parameters that must be specified in a CFD model. Simulations using sand as the bed medium were compared with experiments and it was found that adjusting the bulk density, or in other words, the initial solids volume packing, correctly predicted the pressure drop measured experimentally, but significantly under-predicted the minimum fluidization velocity. By adjusting the initial bed height to correct for the mass, both the pressure drop and minimum fluidization velocity were successfully predicted. Ground walnut shell and ground corncob were used as biomass media and simulations were performed for two reactor bed diameters by simply adjusting the initial bed height to match the measured pressure drop. All of the simulations correctly predicted the pressure drop curves of the experimental data. Further examination of the simulations and experimental data for walnut shell confirmed that adjusting the bed height was the best approach to model fluidization without artificially altering the physics and retaining the known characteristics of the bed material.

Computational fluid dynamics simulation of Lafia–Obi bituminous coal in a fluidized-bed chamber for air- and oxy-fuel combustion technologies

“…This study presents the CFD-modeling predictions of air-fuel and oxy-fuel for the flow, thermal transfer, and emissions characteristics of various sized Lafia-Obi coal particles in a laboratory scale fluidized-bed combustor. The model has been validated against the empirics from the experimental work; it demonstrates a maximum discrepancy of 16% and is within the estimates presented in [21,29]. The mesh-independence check reports the solution to be stable to within 10% and gives credence to the numerical stability of the CFD model.…”

“…Carbon oxide generation: The reaction rates R1-R9 and reaction-rate constants are given in Table 1; they are similar to those given in Zhou et al [19] and in CD-Adapco methodology [29].…”

On the Computational Modeling of Unfluidized and Fluidized Bed Dynamics

“…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.…”

“…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. 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.…”

“…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.…”