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Computational modeling of fluidized beds can be used to predict the operation of biomass gasifiers after extensive validation with experimental data. The present work focused on validating computational simulations of a fluidized bed using a multifluid Eulerian-Eulerian model to represent the gas and solid phases as interpenetrating continua. Simulations of a cold-flow glass bead fluidized bed, using two different drag models, were compared with experimental results for model validation. The validated numerical model was then used to complete a parametric study for the coefficient of restitution and particle sphericity, which are unknown properties of biomass. Biomass is not well characterized, and so this study attempts to demonstrate how particle properties affect the hydrodynamics of a fluidized bed. Hydrodynamic results from the simulations were compared with X-ray flow visualization computed tomography studies of a similar bed. It was found that the Gidaspow (blending) model can accurately predict the hydrodynamics of a biomass fluidized bed. The coefficient of restitution of biomass did not affect the hydrodynamics of the bed for the conditions of this study; however, the bed hydrodynamics were more sensitive to particle sphericity variation.

Glass beads or sand particles are typically used as bed materials in fluidized beds due to their high sphericity, uniform properties, and resistance to breaking. X-ray imaging can be used to visualize these complex flows. Glass attenuates X-rays much more than the surrounding air and, consequently, the images may be nearly saturated in order to resolve the internal flow of a large diameter bed. This paper focuses on the use of alternative bed materials to increase X-ray penetration and resolution to enhance flow visualization in a 9.5 cm diameter fluidized bed. Melamine plastic, ground walnut shell, and ground corncob particles are qualitatively compared to glass beads using X-ray computer tomography (CT) imaging and X-ray radiography. The various beds are compared at three different flow rates and the ratio of superficial gas velocity to minimum fluidization velocity is constant for each bed material. X-ray CT imaging is used to provide a qualitative view of the local time-averaged solids concentration, and clearly shows differences in fluidization between the materials. Channeling is shown in melamine, walnut shells and corncob at low flow rates, however, the beds fluidize more uniformly as gas flow rate increases. In all cases, glass beads fluidize most uniformly and flow rate does not significantly affect fluidization uniformity. Radiographic movies confirm that visualizing internal flow structures of the glass bed is much more difficult than for other materials.

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Fluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. Knowing how the fluidized bed hydrodynamics vary as reactor dimensions are scaled up is vital for improving reactor efficiency. This study utilizes 10.2 cm and 15.2 cm diameter fluidized beds with added side port air injection to investigate column diameter effects on fluidized bed hydrodynamics. Both inert (glass beads) and biomass (ground walnut shell and ground corncob) bed materials are used and the hydrodynamic differences with side port air injection are recorded. Minimum fluidization velocity is determined through pressure drop measurements. Time-averaged local and global gas holdup are recorded using X-ray computed tomography imaging. Results show that by varying the side port air flow rate as a percentage of the minimum fluidization flow rate, partial and complete fluidization is observed in both fluidized beds. Local gas holdup trends are also similar in both fluidized beds. These results will be used in future studies to validate computational fluid dynamics models of fluidized beds.Keywords fluidized bed, gasification, minimum fluidization velocity, particle injection, x-ray computed tomography ABSTRACTFluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. Knowing how the fluidized bed hydrodynamics vary as reactor dimensions are scaled up is vital for improving reactor efficiency. This study utilizes 10.2 em and 15.2 em diameter fluidized beds with added side port air injection to investigate column diameter effects on fluidized bed hydrodynamics. Both inert (glass beads) and biomass (ground walnut shell and ground corncob) bed materials are used and the hydrodynamic differences with side port air injection are recorded. Minimum fluidization velocity is determined through pressure drop measurements. Timeaveraged local and global gas holdup are recorded using X-ray computed tomography imaging. Results show that by varying the side port air flow rate as a percentage of the minimum fluidization flow rate, partial and complete fluidization is observed in both fluidized beds. Local gas holdup trends are also similar in both fluidized beds. These results will be used in future studies to validate computational fluid dynamics models of fluidized beds.