scholarly journals A Validation Study for the Hydrodynamics of Biomass in a Fluidized Bed

2008 ◽  
Author(s):  
Mirka Deza ◽  
Francine Battaglia ◽  
Theodore J. Heindel
Keyword(s):  
Experimental Data ◽  
Fluidized Bed ◽  
Validation Study ◽  
Fluidized Beds ◽  
Coefficient Of Restitution ◽  
Computational Simulations ◽  
Eulerian Model ◽  
X Ray ◽  
Solid Phases ◽  
Interpenetrating Continua

Computational modeling of fluidized beds can be used to predict operation of biomass gasifiers after extensive validation with experimental data. The present work focused on computational simulations of a fluidized bed using a multifluid Eulerian-Eulerian model to represent the gas and solid phases as interpenetrating continua. Hydrodynamic results from the simulations were quantitatively compared with X-ray flow visualization studies of a similar bed. It was found that the Gidaspow model can accurately predict the hydrodynamics of the biomass in a fluidized bed. The coefficient of restitution of biomass was fairly high and did not affect the hydrodynamics of the bed; however, the model was more sensitive to particle sphericity variation.

Computational Modeling of Biomass in a Fluidized Bed Gasifier

2007 ◽  
Author(s):  
Mirka Deza ◽  
Francine Battaglia ◽  
Theodore J. Heindel
Keyword(s):  
Computational Modeling ◽  
Fluidized Bed ◽  
Coefficient Of Restitution ◽  
Computational Simulations ◽  
Eulerian Model ◽  
X Ray ◽  
Cold Flow ◽  
Solid Phases ◽  
Fluidized Bed Gasifier ◽  
Interpenetrating Continua

Computational modeling of fluidized beds can be used to predict operation of biomass gasifiers after extensive validation with experimental data. The present work will focus on computational simulations of a fluidized bed gasifier with a multifluid Eulerian-Eulerian model to represent the gas and solid phases as interpenetrating continua. The simulations described in this paper will model cold-flow fluidized bed experiments, and consider factors such as particle sphericity, coefficient of restitution, and drag coefficient calibration. Hydrodynamic results from the simulations will be qualitatively compared with X-ray flow visualization studies of a similar bed.

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

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Mirka Deza ◽  
Nathan P. Franka ◽  
Theodore J. Heindel ◽  
Francine Battaglia
Keyword(s):  
Fluidized Bed ◽  
Coefficient Of Restitution ◽  
Cfd Modeling ◽  
Eulerian Model ◽  
X Ray ◽  
Particle Properties ◽  
Cold Flow ◽  
X Ray Imaging ◽  
Drag Models ◽  
Interpenetrating Continua

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.

Prediction of the Flotsam Component in a Gas-Fluidized Bed of Two Dissimilar Solids

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Alberto Di Renzo ◽  
Francesco P. Di Maio ◽  
Vincenzino Vivacqua
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Simple Model ◽  
Discrete Element Method ◽  
Fluidized Bed ◽  
Fluidized Beds ◽  
Computational Simulations ◽  
The Difference ◽  
Gas Fluidized Beds

In the present paper the segregating behaviour of solids of different size and density in gas-fluidized beds is studied. In particular, the attention is focussed on pairs composed of a bigger/less dense species and a smaller/denser species. Typical industrial examples of such combinations are encountered in fluidized beds of biomass/sand mixtures. Their behaviour is not easily predictable, as the segregation tendency promoted by the difference in density is counteracted by the difference in size. While typically the denser component is expected to appear predominantly at the bottom of the fluidized bed, experiments on mixtures exhibiting the reverse behaviour have been reported (e.g. Chiba et al., 1980).A simple model to predict the segregation direction of the components, i.e. which species will segregate to the top of the bed (the flotsam), depending upon their difference in properties (size, density) and the mixture composition, is discussed. The predicted behaviour is compared with experimental data available in the literature and agreement is found for the majority of them. For one mixture, experiments are conducted as well as computational simulations based on the combined Discrete Element Method and Computational Fluid Dynamics (DEM-CFD) approach. This allows investigating how an initially mixed bed upon suspension evolves as a result of the segregation prevalence in the bed.

A CFD Study of Existing Drag Models for Geldart A Particles in Bubbling Fluidized Beds

2014 ◽  
Author(s):  
Bahareh Estejab ◽  
Francine Battaglia
Keyword(s):  
Experimental Data ◽  
Fluidized Beds ◽  
Fine Particles ◽  
The Other ◽  
Particle Interactions ◽  
Model Group ◽  
Drag Model ◽  
Numerical Studies ◽  
Solid Phases ◽  
Drag Models

In this study, seven drag models are examined to determine how they affect fluidization behavior of Geldart A particles of biomass and coal. Notwithstanding the notable number of numerical studies to find the best drag model for larger particles, there is a dearth of information related to drag models for finer Geldart A particles. Additionally, to our knowledge, these drag models have not been tested with a binary mixture of Geldart A particles. Computational fluid dynamics was used to model the gas and solid phases in an Eulerian-Eulerain approach to simulate the particle-particle interactions of coal-biomass mixtures and compare the predictions with experimental data. In spite of the previous findings that bode badly for using predominately Geldart B drag models for fine particles, the results of our study reveal that if static regions of mass in the fluidized beds are considered, these drag models work well with Geldart A particles. It was found that the seven drag models could be divided into two categories based on their performance. One category included the Gidaspow family of drag models (Gidaspow, Gidaspow-Blend, and Wen-Yu) and the Syamlal-O’Brien drag model; these models closely predicted the experiments for single solids phase fluidization. For binary mixtures, however, the other drag model group (BVK, HYS, Koch and Hill) yielded better predictions.

CFD Modeling of the Fast Pyrolysis of Coal in Cold Flow Fluidized Bed

2011 ◽  
Vol 396-398 ◽  
pp. 209-212
Author(s):  
An Ning Zhou ◽  
Tie Shuan Zhang ◽  
Xiu Bin Ren ◽  
Li Zhen Zheng
Keyword(s):  
Fluidized Bed ◽  
Fluidized Beds ◽  
Two Phase Flow ◽  
Fast Pyrolysis ◽  
Cfd Modeling ◽  
Phase Flow ◽  
Two Phase ◽  
Cold Flow ◽  
Solid Phases ◽  
2D Model

Abstract. Gas-solid fluidized beds are widely applied in many industries as reactors or heat/mass transferring units because of their good heterogeneous mixing behaviors and large transferring area between the gas and solid phases. In this study, based on the Eulerian-Eulerian approach, 2D model of gas-solid flow field in fluidized bed is simulated, and the drag force models of Gidaspow and Syamlal-O’Brien have been used to simulate and analyze the two-phase flow for exploring mechanism and interaction laws of two-phase flow.

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

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Joshua B. Drake ◽  
Theodore J. Heindel
Keyword(s):  
Computed Tomography ◽  
Fluidized Bed ◽  
Annular Flow ◽  
Fluidized Beds ◽  
Local Scale ◽  
Gas Holdup ◽  
Ct Imaging ◽  
X Ray ◽  
X Ray Computed ◽  
Time Average

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 for the direct comparisons of 2D models, assuming axisymmetric annular flow.

scholarly journals Repeatability of Gas Holdup in a Fluidized Bed Using X-Ray Computed Tomography

2009 ◽  
Author(s):  
Joshua B. Drake ◽  
Theodore J. Heindel
Keyword(s):  
Computed Tomography ◽  
Fluidized Bed ◽  
Fluidized Beds ◽  
Gas Holdup ◽  
X Ray ◽  
Calibration Methods ◽  
Multiphase Systems ◽  
X Ray Computed ◽  
Bed Material ◽  
High Degree

Characterizing the hydrodynamics in fluidized beds is important to many processes from producing biofuels to coating pharmaceuticals. X-ray computed tomography (CT) can quantify local time-averaged phase fractions in multiphase systems that are highly dynamic, like fluidized beds. This paper describes the calibration methods used to produced CT images of a 15.24 cm diameter fluidized bed, how in-house software used these CTs to calculate gas holdup, and how well multiple CTs of a dynamic fluidized bed produced repeatable results while varying bed material and superficial gas velocities. It was concluded there is a very high degree of repeatability using the calibration methods and in-house software developed.

Experimental Measurement on Bubble Parameters During Fluidized Bed Scaling

2005 ◽  
Author(s):  
Xin Wang ◽  
Junfu Lu ◽  
Jiansheng Zhang ◽  
Hairui Yang ◽  
Hai Zhang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Fluidized Bed ◽  
Fluidized Beds ◽  
Bubble Diameter ◽  
Behavior Prediction ◽  
Analysis Method ◽  
Cold Model ◽  
Scaling Method ◽  
Bubble Rising ◽  
Bubble Rising Velocity

An experimental verification is reported on the bubble parameter similarity during fluidized bed scaling. Two bubbling fluidized beds were designed according to Horio’s scaling method, and bubble size and mean bubble rising velocity were measured and compared. It can be concluded from the results that with the increment of u/umf, the similarity between two beds increases with respect to the bubble diameter and rising velocity. The analysis of the experimental data confirms the applicability of Horio’s method on bubble fluidized bed. When given dynamic behavior prediction of a real boiler is desired, the Horio’s law is valid to establish a cold model and the analysis method introduced in the present paper can be used.

Mass Transfer in Oil Sand Fluidized Beds—A Simplified Model

1988 ◽  
Vol 110 (4) ◽  
pp. 279-283
Author(s):  
M. A. Abdrabboh ◽  
G. A. Karim
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Closed Form ◽  
Fluidized Bed ◽  
Oil Sands ◽  
Fluidized Beds ◽  
Spherical Particles ◽  
Simplified Model ◽  
Oil Sand ◽  
Uniform Velocity

Experimental data obtained previously relating to the behavior of single spherical particles of oil sands in hot uniform velocity oxidizing gaseous streams were employed and extended to estimate in a preliminary fashion the extent of mass transfer from oil sand fragments in a fluidized bed. This has been done through employing experimental correlations published in the literature on fluidization. A simple closed-form analytical expression was derived for estimating the transient rates of mass transfer in fluidized beds of oil sands in terms of the main controlling parameters.

Developing X-Ray Particle Tracking Velocimetry for Applications in Fluidized Beds

2008 ◽  
Author(s):  
Joshua B. Drake ◽  
Nathan P. Franka ◽  
Theodore J. Heindel
Keyword(s):  
Fluidized Bed ◽  
Particle Tracking ◽  
Particle Tracking Velocimetry ◽  
Fluidized Beds ◽  
Tracer Particle ◽  
Scale Up ◽  
Solid Particles ◽  
X Rays ◽  
X Ray ◽  
High Heat Transfer

Fluidized beds utilize a gas stream to fluidize solid particles and are used in the process industries because they provide a low pressure drop, uniform temperature distribution, and high heat transfer rates. Knowledge of fluidized bed hydrodynamics is necessary in the design and scale up of such devices. However, fluidized bed hydrodynamics are difficult to visualize and quantify because the systems are opaque and intrusive probes do not provide satisfactory measurements. This paper describes the development of X-ray particle tracking velocimetry (XPTV) to study fluidized bed hydrodynamics. XPTV utilizes X-rays to track specially designed tracer particles in a fluidized bed to noninvasively determine particle velocities. Stereoscopic X-ray imaging is used to locate the 3D position of the tracer particle as a function of time within a fluidized bed, from which particle velocity can be determined. An example of particle tracking will be shown and the automation of this process will be described.

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