Gas/Solids Flow Patterns in a 30.5-CM-DIAMETER Circulating Fluidized Bed

Bader, Rolf; Findlay, John G.; Knowlton, T.M.

doi:10.1016/b978-0-08-036225-0.50016-2

Cited by 136 publications

(150 citation statements)

References 5 publications

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“…Neither Mouceaux et al [ 8 ] nor Bader et ul. [9 ] operated under isokiocfic conditions. They found that for sufficiently high aspiration rates the measured flux was independent of the extraction flow rate.…”

Section: Sampling or Ertracdon Probesmentioning

confidence: 99%

“…Despite their widespread application the fluid mechanics of CFBs is unfortunately not very well understood, This can be attributed on one hand to the very complex hydrodynamics of these systems which complicates a thorough theoretical description and understanding and on the other hand to the vet 5" significant difficulties encountered in measuring local fluid mechanic properties in dense gassolid two phase flows. Experimental studies clearly demonstrated the existence of inhomogeneous solids distribmions in both axial and radial directions and the occurrence of solids downflow in the wall region [1][2][3][4][5][6][7][8][9][10][11]. In this study existing techniques for the measurement of solids concentration and solids velocity in gas-solid two phase flows will he briefly reviewed.…”

Section: Introductionmentioning

confidence: 99%

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Measurements of solids concentration and axial solids velocity in gas-solid two-phase flows

et al. 1996

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Several techniques rep',med in the literature for measuring solids concentration and solids velocity in (dense) gas-selid two-phase flow have been briefly reviewed, An optical measuring system, based on detection of light reflected by Ihe suspended paRicles, has bece developed to measure local solids concentration and local axial solids velocity in dense gas-solid two phase flows. This system has bean applied to study hydrodynamics of a co)d-flow circulating fluidized bed unit operated in the dense flow regime (a": 7.:5-15 m s-i and G~ ~ 100-400 kg m-2 s I). With increaslng solids mass flux, at constant superficial gas velocity, lateud solids sngregation became more pronounced (i.e. extent of development of core-annulus structure) while the radial profiles of axial solids velocity hardly changed. A decre:,se in superficialgas velocity, at constant solids mass flux, also augmented the lateral solids segregation. The axial solids velocity decreased over the entire tube radius, although the shape of the profiles showed no strong dependence with respect to the superficial gas velocity. Average solids mass fluxes calculated from the measured local values of solids concentration and solids velocity exceeded the imposed solids mass flux. a finding which could be explained by the downflow observed visually of solid particles close to the tuba wall In addition, cross-sectional averaged solids concentrations obtained on the basis of the optical measuring system and those obtained from the pressure gradient measurements showed satisfactory agreement.

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Section: Sampling or Ertracdon Probesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Measurements of solids concentration and axial solids velocity in gas-solid two-phase flows

et al. 1996

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“…Experimental investigations clearly demonstrated an inhomogeneous solids distribution in both the axial and radial directions (Kwauk et al, 1986;Bader et al, 1988;Miller and Gidaspow, 1992). The inhomogeneous solids distribution in the axial direction can be attributed to the acceleration of particles which enter the column at the bottom of the bed with low velocity.…”

Section: Introductionmentioning

confidence: 97%

“…the system of interest. Gidaspow et al calculated this viscosity from the published experimental data of Bader et al (1988), using the following integral momentum balance:…”

Section: Constitutive Relations Lmentioning

confidence: 99%

Hydrodynamic modelling of circulating fluidised beds

Nieuwland

Huizenga

Kuipers

et al. 1994

Chemical Engineering Science

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Abstract-A one-dimensional model for the riser section of a circulating fluidised bed has been developed which describes the steady-state hydrodynamic key variables in the radial direction for fully developed axisymmetric flow. Both the gas and the solid phase are considered as two continuous media, fully penetrating each other. As a first approximation gas phase turbulence has been incorporated in our hydrodynamic model by applying a slightly modified version of the well-known Prandtl mixing length model. To solve the resulting set of transport equations, the solids distribution along the tube radius is required. Several strategies are given to obtain this information. In addition the effect of clusters on the momentum transfer between both phases has been modelled using an empirical correlation. Theoretically calculated results agree welt with reported experimental data of different authors.

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“…A stationary hydrodynamic model 7 is able to predict the particle phase stresses through the kinetic theory of granular flow as a function of the particle fluctuating energy (granular energy). A modified model 9 has been proposed and validated against experimental data, 10 showing a high sensitivity to the value of the restitution coefficient, whose reduction may lead to a wrong prediction of the particle segregation patterns inside the duct. In general, such sensitivity to model parameters points to a breakdown of the hydrodynamic description for relatively dilute flows.…”

Section: ■ Introductionmentioning

confidence: 99%

Simulation of Mono- and Bidisperse Gas-Particle Flow in a Riser with a Third-Order Quadrature-Based Moment Method

Passalacqua¹,

Fox²

2012

Ind. Eng. Chem. Res.

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Gas-particle flows can be described by a kinetic equation for the particle phase coupled with the Navier−Stokes equations for the fluid phase through a momentum exchange term. The direct solution of the kinetic equation is prohibitive for most applications due to the high dimensionality of the space of independent variables. A viable alternative is represented by moment methods, where moments of the velocity distribution function are transported in space and time. In this work, a fully coupled third-order, quadrature-based moment method is applied to the simulation of mono-and bidisperse gas-particle flows in the riser of a circulating fluidized bed. Gaussian quadrature formulas are used to model the unclosed terms in the moment transport equations. A Bhatnagar−Gross−Krook (BGK) collision model is used in the monodisperse case, while the full Boltzmann integral is adopted in the bidisperse case. The predicted values of mean local phase velocities, rms velocities, and particle volume fractions are compared with the Euler−Lagrange simulations and experimental data from the literature. The local values of the time-average Stokes, Mach, and Knudsen numbers predicted by the simulation are reported and analyzed to justify the adoption of high-order moment methods as opposed to models based on hydrodynamic closures. ABSTRACT: Gas-particle flows can be described by a kinetic equation for the particle phase coupled with the Navier−Stokes equations for the fluid phase through a momentum exchange term. The direct solution of the kinetic equation is prohibitive for most applications due to the high dimensionality of the space of independent variables. A viable alternative is represented by moment methods, where moments of the velocity distribution function are transported in space and time. In this work, a fully coupled third-order, quadrature-based moment method is applied to the simulation of mono-and bidisperse gas-particle flows in the riser of a circulating fluidized bed. Gaussian quadrature formulas are used to model the unclosed terms in the moment transport equations. A Bhatnagar−Gross−Krook (BGK) collision model is used in the monodisperse case, while the full Boltzmann integral is adopted in the bidisperse case. The predicted values of mean local phase velocities, rms velocities, and particle volume fractions are compared with the Euler−Lagrange simulations and experimental data from the literature. The local values of the time-average Stokes, Mach, and Knudsen numbers predicted by the simulation are reported and analyzed to justify the adoption of high-order moment methods as opposed to models based on hydrodynamic closures. Disciplines Biological Engineering | Chemical Engineering Comments

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Gas/Solids Flow Patterns in a 30.5-CM-DIAMETER Circulating Fluidized Bed

Cited by 136 publications

References 5 publications

Measurements of solids concentration and axial solids velocity in gas-solid two-phase flows

Measurements of solids concentration and axial solids velocity in gas-solid two-phase flows

Hydrodynamic modelling of circulating fluidised beds

Simulation of Mono- and Bidisperse Gas-Particle Flow in a Riser with a Third-Order Quadrature-Based Moment Method

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