CFD Modeling and X-Ray Imaging of Biomass in a Fluidized Bed

Deza, Mirka; Franka, Nathan P.; Heindel, Theodore J.; Battaglia, Francine

doi:10.1115/1.4000257

Cited by 38 publications

(24 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The literature on this topic is abundant; from the earlier works of Boemer et al (1998), and Van Wachem et al (1998), to the more recent studies comprising image analysis (Busciglio et al, 2009), particle drag optimisation procedures (Mahinpey et al, 2007;Vejahati et al, 2009), and time averaged volume fraction (Deza et al, 2009;Min et al, 2010;. Particularly, the works of Deza et al (2009) and Min et al (2010) show a reasonable agreement between two dimensional (2D) and three dimensional (3D) simulations and X ray imaging experiments of cylindrical fluidized beds of internal diameter of 0.095 and 0.152 m, respectively. compared their 3D simulation results of time average solids volume fraction in a bubbling bed with experimental data from g ray absorption, capa citance probe and differential pressure measurements, and showed that industrial scale fluidized beds can be reasonable predicted with acceptable computational cost.…”

Section: Introductionmentioning

confidence: 99%

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

Hernández-Jiménez

Sánchez-Delgado

Gómez-García

et al. 2011

Chemical Engineering Science

108

View full text Add to dashboard Cite

a b s t r a c tThis work compares simulation and experimental results of the hydrodynamics of a two dimensional, bubbling air fluidized bed. The simulation in this study has been conducted using an Eulerian Eulerian two fluid approach based on two different and well known closure models for the gas particle interaction: the drag models due to Gidaspow and Syamlal & O'Brien. The experimental results have been obtained by means of Digital Image Analysis (DIA) and Particle Image Velocimetry (PIV) techniques applied on a real bubbling fluidized bed of 0.005 m thickness to ensure its two dimensional behaviour. Several results have been obtained in this work from both simulation and experiments and mutually compared. Previous studies in literature devoted to the comparison between two fluid models and experiments are usually focused on bubble behaviour (i.e. bubble velocity and diameter) and dense phase distribution. However, the present work examines and compares not only the bubble hydrodynamics and dense phase probability within the bed, but also the time averaged vertical and horizontal component of the dense phase velocity, the air throughflow and the instantaneous interaction between bubbles and dense phase. Besides, quantitative comparison of the time averaged dense phase probability as well as the velocity profiles at various distances from the distributor has been undertaken in this study by means of the definition of a discrepancy factor, which accounts for the quadratic difference between simulation and experiments The resulting comparison shows and acceptable resemblance between simulation and experiments for dense phase probability, and good agreement for bubble diameter and velocity in two dimensional beds, which is in harmony with other previous studies. However, regarding the time averaged velocity of the dense phase, the present study clearly reveals that simulation and experiments only agree qualitatively in the two dimensional bed tested, the vertical component of the simulated dense phase velocity being nearly an order of magnitude larger than the one obtained from the PIV experiments. This discrepancy increases with the height above the distributor of the two dimensional bed, and it is even larger for the horizontal component of the time averaged dense phase velocity. In other words, the results presented in this work indicate that the fine agreement commonly encountered between simulated and real beds on bubble hydrodynamics is not a sufficient condition to ensure that the dense phase velocity obtained with two fluid models is similar to that from experimental measurements on two dimensional beds.

show abstract

Section: Introductionmentioning

confidence: 99%

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

Hernández-Jiménez

Sánchez-Delgado

Gómez-García

et al. 2011

Chemical Engineering Science

108

View full text Add to dashboard Cite

show abstract

“…The use of CFD to model fluidized beds is highly dependent on the boundary conditions and validation through experimentation. Deza et al [8,9] and Min et al [10] have shown that X-ray visualization techniques can be used as a validation tool for fluidized bed hydrodynamic simulations.…”

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

Self Cite

View full text Add to dashboard Cite

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...

show abstract

“…The grid resolution study by Deza et al [30] identified a sufficient number of cells that would produce an estimated numerical error less than 1%. The study was for a 2D domain, where a total of 2400 grid cells provided adequate resolution of the domain.…”

Section: Resultsmentioning

confidence: 99%

“…Table 1 summarizes the ground walnut shell particle properties and flow conditions. To account for the non-spherical nature of the ground walnut shell (it is more chunk-like), the sphericity and coefficient of restitution were numerically estimated based on previous work by Deza et al [30], whereas the other properties were provided from the experiments. Two inlet gas velocities are examined; the lower velocity of U g ¼ 1:5U mf represents a mild bubbling bed and the higher velocity of U g ¼ 3:0U mf represents a moderate industrial reactor flow rate [34], where U mf is the minimum fluidization velocity.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Effects of Mixing Using Side Port Air Injection on a Biomass Fluidized Bed

Deza

Heindel

Battaglia

2011

Journal of Fluids Engineering

View full text Add to dashboard Cite

Fluidized beds are being used in practice to gasify biomass to create producer gas, a flammable gas that can be used for process heating. However, recent literature has identified the need to better understand and characterize biomass fluidization hydrodynamics, and has motivated the combined experimental-numerical effort in this work. A cylindrical reactor is considered and a side port is introduced to inject air and promote mixing within the bed. Comparisons between the computational fluid dynamics (CFD) simulations with experiments indicate that three-dimensional simulations are necessary to capture the fluidization behavior of the more complex geometry. This paper considers the effects of increasing side port air flow on the homogeneity of the bed material in a 10.2 cm diameter fluidized bed filled with 500-600 μmground walnut shell particles. The use of two air injection ports diametrically opposed to each other is also modeled using CFD to determine their effects on fluidization hydrodynamics. Whenever possible, the simulations are compared to experimental data of time-average local gas holdup obtained using X-ray computed tomography. This study will show that increasing the fluidization and side port air flows contribute to a more homogeneous bed. Furthermore, the introduction of two side ports results in a more symmetric gas-solid distribution.

show abstract

CFD Modeling and X-Ray Imaging of Biomass in a Fluidized Bed

Cited by 38 publications

References 24 publications

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

Comparison between two-fluid model simulations and particle image analysis & velocimetry (PIV) results for a two-dimensional gas–solid fluidized bed

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

Effects of Mixing Using Side Port Air Injection on a Biomass Fluidized Bed

Contact Info

Product

Resources

About