CFD modeling of a typical fluidized bed column

Journal of Fluids Engineering, 2010

A two-dimensional transient Eulerian model integrating the kinetic theory for emulsion phase is used to simulate the bubbling and slugging gas-solid fluidized beds, including the Geldart B and D particles, respectively. CFD results show that utilizing an algebraic granular temperature equation, instead of a full granular temperature, one leads to a significant reduction in computational time without loosing accuracy. Different drag models have been examined in the current study. CFD results show that the Syamlal–O’Brien and Di Felice adjusted drag models, based on minimum fluidization velocity, are not suitable for the bed, including coarse particles (Geldart group B). The Gidaspow drag model displays better results in comparison with the others. A good agreement with the available experimental data and the researcher’s findings has been reached quantitatively and qualitatively. The proposed model can reasonably be used for simulation of slugging fluidized beds. This study reduces t...

2015

Expansion behaviour of a binary solid-liquid fluidised bed (SLFB) system with different initial mass of solids was studied both experimentally and numerically. Three different sizes (3, 5 & 8 mm diameter) of borosilicate glass beads of equal density (2230 kgm-3) were used as fluidised particles. Three different combinations of particle size pairs of both equal and unequal mass ratios were used using a constant liquid (water) superficial velocity of 0.17 ms-1 in all the cases. Numerically, a two dimensional Eulerian-Eulerian (E-E) CFD model incorporating kinetic theory of granular flow (KTGF) was developed to predict the bed expansion behaviour. It was observed that complete bed segregation occurred when the difference between the solid particle diameters was higher while lower difference in particle diameters led to partial bed segregation. The CFD model also predicted these behaviours which were in good agreement with the experimental data.

CFD simulation results of gas-solid fluidized bed using 2D Eulerian-Eulerian approach at high gas velocities integrating the kinetic theory of granular flow are presented. The range of gas velocities are from 0.35 to 2.19m/s. Predicted particle motion and bubble behavior in the bed are consistent with the literature data. Simulation results indicate that Arastoopour's drag model is the best choice for the current system. Laminar flow and turbulent models, standard k-and Simonin, are compared at Ug = 2.19m/s. CFD results show that Simonin model can be used at high gas velocities, reasonably. Current model reduces simulations errors compared with previous works. The minimum error is 6.5% and the maximum error is 13% in lower and upper part of the bed in radial direction, respectively.

Middle East Journal of Scientific Research

In this study, the multi fluid Eulerian computational fluid dynamics (CFD) model with granular flow extension was used to simulate a binary liquid-solid fluidized bed in the laminar flow, temperature among 20-25°C and below atmospheric pressure. The superficial water velocity was 0.0025 to 0.05 m/s. Governing equations were discredited by using the two-dimension finite volume method. It was concluded that the simulated data were in good agreement with the experimental ones obtained from the literature. In addition, the predicted values of bed voidage, obtained from CFD simulation, have been compared with the predicted value from the property average model and serial model. In addition, the results show that the simulation predicted bed voidage was in good agreement with the experimental data. The CFD simulation results and experimental data demonstrated also that the bed expansion increased by increasing superficial water velocity.

2016

The fluidization characteristics of fine particles i.e. Geldart–C and A particles are studied in a cylindrical fluidized column. The effects of different system parameters (viz. static bed height, particle density, size of particle, speed of promoter and superficial velocity of the fluidizing medium) on bed dynamics are analyzed. CFD simulation is carried out for the hydrodynamic behaviour of fine powders. The values of these bed dynamics obtained through CFD simulation are compared against the respective experimental values. The comparison results show very good agreement between the experimental and simulated results thereby indicating the possibility of smooth or proper fluidization for fine particles. Thus these findings will be helpful in designing a good fluidized bed reactor for fine particle system can optimize the processes very well.

The Canadian Journal of Chemical Engineering, 2012

In this study, a two-dimensional mathematical model was developed considering the hydrodynamic behaviour of a circulating fluidised bed biomass gasifier (CFBBG), which is also applicable for other low-density particles. In the modelling, the CFB riser was divided into two regions: a dense region at the bottom and a dilute region at the top of the riser. Kunii and Levenspiel's [Kunii and Levenspiel, Powder Technol. 61, 193-206 (1990)] model was adopted to express the vertical solids distribution with some other assumptions. Radial distributions of bed voidage were taken into account in the upper zone by using Zhang et al.'s [Zhang et al., Chem. Eng. Sci. 46(12), 3045-3052 (1991)] correlation. For model validation purposes, a cold model CFB was employed, in which sawdust was transported with air as the fluidising agent. The column is 10 m in height and 280 mm in diameter, and is equipped with pressure transducers to measure axial pressure profile and with a reflective optical fibre probe to measure local solids holdup. A satisfactory agreement between the model predictions and experimental data was found.

International Journal of Advance Research and Innovative Ideas in Education, 2016

Experiment was conducted to analysis the hydrodynamics of a gas-liquid-solid fluidized bed containing low-density particles. Solid-Liquid-Gas fluidized beds are widely used in the environmental, pharmaceutical, petroleum, food and biotechnology plants. The three phase fluidization is strongly dependent on effective contact between the phases (solid-liquid-gas). Three-phase (solid-liquid-gas) fluidized beds are used to study the hydrodynamic characteristics of low density particles (solid wood) using air as the gas phase and water as liquid phase. The fluidized bed consists of three sections, the gas-liquid distributor section, the gas-liquid disengagement section, the test section. The hydrodynamic characteristics determined included the bed expansion ratios, bed pressure drop, and minimum fluidization velocity. The dependence of these quantities on liquid velocity, particle diameter, gas velocity initial, and static bed height, has been discussed. Results indicate that the minimum ...

2013

A multifluid Eulerian Computational Fluid Dynamics model incorporating the Kinetic Theory of Granular Flows was carried out to simulate the hydrodynamic of a 2D turbulent fluidized bed filled with Geldart B particles. Simulations were conducted using the commercial software package Ansys Fluent. In order to get an optimal modelization of the fluidized bed hydrodynamic, the effect of various drag models including those of Gidaspow, Syamlal & O'Brien, Wen & Yu and McKeen have been investigated. The numerical results obtained were compared to experimental data available in literature. Different specularity coefficients were also tested in the present work in a try to find out which fits better the handled case. The results showed that the Gidaspow drag model and the no slip boundary condition give a good prediction of experimental data.

Chemical Engineering Science, 2008

A computational fluid dynamics (CFD) model was developed to simulate the hydrodynamics of gas-solid flow in a circulating fluidized bed (CFB) riser at various fluidization conditions using the Eulerian-Granular multiphase model. The model was evaluated comprehensively by comparing its predictions with experimental results reported for a CFB riser operating at various solid mass fluxes and superficial gas velocities. The model was capable of predicting the main features of the complex gas-solids flow, including the cluster formation of the solid phase along the walls, for different operating conditions. The model also predicted the coexistence of up-flow in the lower regions and downward flow in the upper regions at the wall of the riser for high gas velocity and solid mass flux, as reported in the literature. The predicted solid volume fraction and axial particle velocity were in good agreement with the experimental data within the high density fast fluidization regime. However, the model showed some discrepancy in predicting the gas-solid flow behavior in the riser operating in dense suspension up-flow and low density fast fluidization regimes. ᭧

Progress in Natural Science, 2005

ABSTRACT Many computational fluid dynamics (CFD) models for describing the hydrodynamics of dense gas-solid flows in fluidized beds have been put forward in the past few decades. These models treat the solid phase as continuum or discrete particles, which leads to Eulerian-Eulerian or Eulerian-Lagrangian formulations, respectively. Different governing equations and closure relations essentially result from an insufficient understanding of the complex gas-particle and particle-particle interactions for gas-solid flows. The current status of these models is discussed briefly in this paper. All the approaches in the literature modify only the solid phase momentum balance equation introducing various forms of the solid phase stress tensor and the solid phase pressure drop in the Eulerian-Eulerian models. Taking them into consideration, a new model for predicting the fluid behavior of dense gas-solid flows in fluidized beds has been developed, which contains new terms in both the particle and gas phase momentum balance equations and requires only the use of an experimental drag force correlation. Several results are shown to verify the model's reliability, which include the homogeneous fluidization of Geldart type A particles, the bubbling and jetting fluidization of Geldart type B particles in rectangular beds, and fluid dynamics in a complicated geometry for a bubbling-bed of a fast internally circulating fluidized-bed biomass gasifier.