Fluid Beds: At Last, Challenging Two Entrenched Practices

Squires, Arthur M.; Kwauk, Mooson; Avidan, A.A.

doi:10.1126/science.230.4732.1329

Cited by 88 publications

(39 citation statements)

References 46 publications

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“…They are used in the oil industry to make gasoline from oil. Squires et al (1985) described FCC powder as somewhat like cement powder but much more freely flowing. The tests were conducted in the vertical tube of a two-story circulating fluidized bed (CFB) apparatus shown in Figure 1.…”

Section: Introductionmentioning

confidence: 97%

Equation of state and radial distribution functions of FCC particles in a CFB

1998

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Section: Introductionmentioning

confidence: 97%

Equation of state and radial distribution functions of FCC particles in a CFB

1998

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“…The hydrodynamic characterization of a fluidized bed requires a deep understanding of these dependencies, particularly in the design process when mistakes can become extremely expensive. In fact, system failures have been reported in commercial reactors designed from laboratory or pilot scale models due to hydrodynamic changes over reactor scale-up [6,7].…”

Section: Introductionmentioning

confidence: 99%

Comparisons of Annular Hydrodynamic Structures in 3D Fluidized Beds Using X-Ray Computed Tomography Imaging

Drake

Heindel

2012

Journal of Fluids Engineering

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Fluidized beds are common equipment in many process industries. Knowledge of the hydrodynamics within a fluidized bed on the local scale is important for the improvement of scale-up and process efficiencies. This knowledge is lacking due to limited observational technologies at the local scale. This paper uses X-ray computed tomography (CT) imaging to describe the local time-average gas holdup differences of annular hydrodynamic structures that arise through axisymmetric annular flow in a 10.2 cm and 15.2 cm diameter cold flow fluidized bed. The aeration scheme used is similar to that provided by a porous plate and hydrodynamic results can be directly compared. Geldart type B glass bead, ground walnut shell, and crushed corncob particles were studied at various superficial gas velocities. Assuming axisymmetry, the local 3D timeaverage gas holdup data acquired through X-ray CT imaging was averaged over concentric annuli, resulting in a 2D annular and time-average gas holdup map. These gas holdup maps show that four different types of annular hydrodynamic structures occur in the fluidized beds of this study: zones of (1) aeration jetting, (2) bubble coalescence, (3) bubble rise, and (4) particle shear. Changes in the superficial gas velocities, bed diameters, and bed material densities display changes in these zones. The 2D gas holdup maps provide a benchmark that can be used by computational fluid dynamic (CFD) users for the direct comparisons of 2D models, assuming axisymmetric annular flow.Keywords annular flow, fluidized bed, gas holdup, hydrodynamic structure, X-ray computed tomography Fluidized beds are common equipment in many process industries. Knowledge of the hydrodynamics within a fluidized bed on the local scale is important for the improvement of scale-up and process efficiencies. This knowledge is lacking due to limited observational technologies at the local scale. This paper uses X-ray computed tomography (CT) imaging to describe the local time-average gas holdup differences of annular hydrodynamic structures that arise through axisymmetric annular flow in a 10.2 cm and 15.2 cm diameter cold flow fluidized bed. The aeration scheme used is similar to that provided by a porous plate and hydrodynamic results can be directly compared. Geldart type B glass bead, ground walnut shell, and crushed corncob particles were studied at various superficial gas velocities. Assuming axisymmetry, the local 3D time-average gas holdup data acquired through X-ray CT imaging was averaged over concentric annuli, resulting in a 2D annular and time-average gas holdup map. These gas holdup maps show that four different types of annular hydrodynamic structures occur in the fluidized beds of this study: zones of (1) aeration jetting, (2) bubble coalescence, (3) bubble rise, and (4) particle shear. Changes in the superficial gas velocities, bed diameters, and bed material densities display changes in these zones. The 2D gas holdup maps provide a benchmark that can be used by computational fluid dynamic (CFD) users fo...

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“…Despite the ubiquity of fluidized bed units in the chemical process industry the effect of polydispersity on the hydrodynamic behavior of fluidized beds remains poorly understood. The addition of a small amount of fine particles to an otherwise monodisperse fluidized bed is known to promote uniform fluidization (Squires et al, 1985;. However, increasing the concentration of fine particles is known to result in macroscopic segregation between particles of different sizes when the superficial gas velocity is between the minimum fluidization velocity of the largest and smallest particle species Peeler and Huang, 1989;.…”

Section: Introductionmentioning

confidence: 99%

Development, Verification, and Validation of Multiphase Models for Polydisperse Flows

Hrenya¹,

Cocco²,

Fox³

et al. 2011

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This report describes in detail the technical findings of the DOE Award entitled "Development, Verification, and Validation of Multiphase Models for Polydisperse Flows." The focus was on high-velocity, gas-solid flows with a range of particle sizes. A complete mathematical model was developed based on first principles and incorporated into MFIX. The solid-phase description took two forms: the Kinetic Theory of Granular Flows (KTGF) and Discrete Quadrature Method of Moments (DQMOM). The gas-solid drag law for polydisperse flows was developed over a range of flow conditions using Discrete Numerical Simulations (DNS). These models were verified via examination of a range of limiting cases and comparison with Discrete Element Method (DEM) data. Validation took the form of comparison with both DEM and experimental data. Experiments were conducted in three separate circulating fluidized beds (CFB's), with emphasis on the riser section. Measurements included bulk quantities like pressure drop and elutriation, as well as axial and radial measurements of bubble characteristics, cluster characteristics, solids flux, and differential pressure drops (axial only). Monodisperse systems were compared to their binary and continuous particle size distribution (PSD) counterparts. The continuous distributions examined included Gaussian, lognormal, and NETLprovided data for a coal gasifier.FINAL TECHNICAL 4 DE-FC26-07NT43098 5 EXECUTIVE SUMMARYThis report is the final technical report for the award DE-FC26-07NT43098 entitled "Development, Verification, and Validation of Multiphase Models for Polydisperse Flows." Below is a summary of work completed under the grant for each of the major goals. Goal I: Continuum Theory for Solid PhaseTwo separate and complementary continuum theories were derived to model polydisperse solids: the kinetic theory of granular flow (KTGF) and the discrete quadrature method of moments (DQMOM). Both theories are based on first principles with no adjustable parameters. The polydisperse KTGF and DQMOM were then encoded in MFIX, and underwent a wide range of verification testing to ensure, to the best possible extent, that no coding errors were present. These verification tests included both granular and gas-solid flows, including cases where an analytical solution and/or DEM (discrete element method) data and/or simple test cases. For the case of KTGF, another set of constitutive equations were derived which rigorously incorporated the gas phase for a simplified case of monodisperse systems at low Reynolds numbers. This derivation used the acceleration model developed in Task 2 from direct numerical simulations (DNS) in the starting kinetic equation, and indicated the effect of the fluid phase on the resulting constitutive relations. Goal II: Improved Gas-Particle Drag Laws -effect of particle size distributionIn this portion of the effort, two types of direct numerical simulations (DNS) were used to extract the drag force experienced by particles in a polydisperse suspension. These two methods, na...

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Fluid Beds: At Last, Challenging Two Entrenched Practices

Cited by 88 publications

References 46 publications

Equation of state and radial distribution functions of FCC particles in a CFB

Equation of state and radial distribution functions of FCC particles in a CFB

Comparisons of Annular Hydrodynamic Structures in 3D Fluidized Beds Using X-Ray Computed Tomography Imaging

Development, Verification, and Validation of Multiphase Models for Polydisperse Flows

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