CFD Modelling of a Fluidized Bed Gasifier; Effects of Drag Model and Bed Heights

2014 ◽  
Vol 699 ◽  
pp. 730-735
Author(s):  
Kamariah Md Isa ◽  
Kahar Osman ◽  
Nik Rosli Abdullah ◽  
Azfarizal Mukhtar ◽  
Nor Fadzilah Othman
Keyword(s):  
Fluidized Bed ◽  
Volume Fraction ◽  
Solid Phase ◽  
Multiphase Model ◽  
Cfd Modelling ◽  
Drag Model ◽  
Bed Height ◽  
Representative Unit Cell ◽  
Fluidized Bed Gasifier ◽  
Drag Models

One of the unresolved issues in using the gasifier is the inability to determine the occurrence of the transition regime of fluidized bed. In modeling gas-solid phase, drag force is one of the main mechanisms for inter-phase momentum transfer. Thus, a simulation of fluidized bed was developed to study the effect of using various drag models over different bed height of H/D ratio such as 0.5, 1 and 2. A two dimensional model using Eulerian-Granular Multiphase Model (EGM) based on two fluid models have been used to simulate hydrodynamics of a bubbling fluidized beds. Gas-solid interactions are modeled via inter-phase of a drag model. The drag correlations of Gidaspow, Wen Yu, Syamlal-O'Brien, Hill Koch Ladd (HKL) and Representative Unit Cell (RUC) were implemented to simulate the interaction between phases. From this study, we found that different H/D ratio such as 0.5, 1 and 2 yields different volume fraction as increasing bed height slows kinetic transport of particle sand to the upper side of the bed. Besides that, different H/D ratio also resulted in different velocity vector. The results also show that Wen Yu and Syamlal-O'Brien are sufficient enough in detecting the change from one regime to another regardless of the bed height.

Numerical Simulation on the Preparation of Vinyl Acetate Catalyst in Fluidized Bed

2013 ◽  
Vol 750-752 ◽  
pp. 1704-1707
Author(s):  
Pan Zhang ◽  
Kun Cui ◽  
Ning Xu ◽  
Guang Jian Wang
Keyword(s):  
Activated Carbon ◽  
Fluidized Bed ◽  
Zinc Acetate ◽  
Volume Fraction ◽  
Hydrodynamic Characteristics ◽  
Multiphase Model ◽  
Carbon Catalyst ◽  
Solid Flow ◽  
Phase Volume Fraction ◽  
Mode Of Operation

Based on the preparation of zinc acetate/activated carbon catalyst in the fluidized bed reactor, the Eulerian multiphase model in Fluent was used to numerically simulate the gas-liquid-solid flow and the gas-solid-solid flow hydrodynamic characteristics in fluidized beds. The instantaneous phase volume fraction and the flow hydrodynamic characteristics of the three phases were analyzed, and in view of the zinc acetate/activated carbon catalyst with bad uniformity prepared by present method, a new mode of operation with dynamic rules was proposed. The simulation results show that activated carbon particles with different density can realize layer inversion using this mode of operation, and the uniformity of zinc acetate/activated carbon catalyst will be effectively improved.

CFD Simulation of a Bubbling Fluidized Bed Gasifier Using a Bubble-Based Drag Model

2014 ◽  
Vol 28 (10) ◽  
pp. 6351-6360 ◽  
Author(s):  
Juhui Chen ◽  
Guangbin Yu ◽  
Bing Dai ◽  
Di Liu ◽  
Lei Zhao
Keyword(s):  
Fluidized Bed ◽  
Cfd Simulation ◽  
Drag Model ◽  
Bubbling Fluidized Bed ◽  
Fluidized Bed Gasifier

Analysis of Solid Structures and Stresses in a Gas Fluidized Bed

2007 ◽  
Author(s):  
Jin Sun ◽  
Francine Battaglia
Keyword(s):  
Kinetic Theory ◽  
Normal Stress ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Solid Phase ◽  
Coarse Graining ◽  
Contact Forces ◽  
Normal Contact ◽  
Stress Components ◽  
Force Network

Structures and stresses for the solid phase in a gas-solid fluidized bed are analyzed using results from hybrid simulations. The hybrid method couples the discrete element method (DEM) for particle dynamics with the averaged two-fluid (TF) equations for the gas phase. The coupling between the two phases is modeled using an interphase momentum transfer term. Structure information is characterized using force network size distribution, which shows no large force network existing in the fluidized bed. The normal contact forces have an exponentially decaying distribution. Solid phase continuum fields (local volume fraction, strain rate, stress tensor, and granular temperature) are computed using a coarse-graining process. The results show that the stress has difference in normal stress components. The collisional contribution is larger than the kinetic contribution and spatially correlated to force networks. Stresses are also computed using a kinetic theory stress model. It is demonstrated that the kinetic theory model predicts no difference in normal stress components and larger normal stresses than those computed from the coarse-graining process.

scholarly journals Experimental study and transient CFD/DEM simulation in a fluidized bed based on different drag models

RSC Advances ◽  
2017 ◽  
Vol 7 (21) ◽  
pp. 12764-12774 ◽  
Author(s):  
Ling Zhou ◽  
Lingjie Zhang ◽  
Ling Bai ◽  
Weidong Shi ◽  
Wei Li ◽  
...  
Keyword(s):  
Experimental Study ◽  
Fluidized Bed ◽  
Dense Gas ◽  
Dem Simulation ◽  
Drag Model ◽  
Drag Models

Under the architecture of CFD/DEM, Gidaspow drag model gives the better prediction of the inner flow in the dense gas–solid fluidized bed.

Two-fluid Modeling of Geldart A Particles in Gas-solid Bubbling Fluidized Bed: Assessment of Drag Models and Solid Viscosity Correlations

2017 ◽  
Vol 16 (3) ◽  
Author(s):  
Tian Tian ◽  
Zhengrui Jia ◽  
Shujun Geng ◽  
Xiaoxing Liu
Keyword(s):  
Fluidized Bed ◽  
Viscosity Model ◽  
Frictional Stress ◽  
Concentration Profiles ◽  
Solid Concentration ◽  
Drag Model ◽  
Bubbling Fluidized Bed ◽  
Drag Models ◽  
Bed Expansion ◽  
Two Fluid

AbstractIn this work the influences of solid viscosity and the way to scale-down traditional drag models on the predicted hydrodynamics of Geldart A particles in a lab-scale gas-solid bubbling fluidized bed are investigated. To evaluate the effects of drag models, the modified Gibilaro et al. drag model (constant correction factor) and the EMMS drag model (non-constant correction factor) are tested. And the influences of solid viscosity are assessed by considering the empirical model proposed by Gidaspow et al. (1997, Turbulence, Viscosity and Numerical Simulation of FCC Particles in CFB. Fluidization and Fluid-particle Systems, AIChE Annual Meeting, Los Angeles, 58–62) and the models based on kinetic theory of granular flow (KTGF) with or without frictional stress. The resulting hydrodynamics by incorporating the different combinations of the drag model and solid viscosity model into two-fluid model (TFM) simulations are compared with the experimental data of Zhu et al. (2008, Detailed Measurements of Flow Structure inside a Dense Gas-Solids Fluidized Bed.”Powder Technological180:339–349). The simulation results show that the predicted hydrodynamics closely depends on the setting of solid viscosity. When solid viscosity is calculated from the empirical model of Gidaspow et al., both drag models can reasonably predict the radial solid concentration profiles and particle velocity profiles. When the KTGF viscosity model without frictional stress is adopted, the EMMS drag model significantly over-estimates the bed expansion, whereas the modified Gibilaro et al. drag model can still give acceptable radial solid concentration profiles but over-estimate particle upwards and downwards velocity. When KTGF viscosity model with frictional stress is chosen, both drag models predict the occurrence of slugging. At this time, the particle velocity profiles predicted by EMMS drag model are still in well agreement with the experimental data, but the bed expansion is under-estimated.

scholarly journals An Assessment of Drag Models in Eulerian–Eulerian CFD Simulation of Gas–Solid Flow Hydrodynamics in Circulating Fluidized Bed Riser

2020 ◽  
Vol 4 (2) ◽  
pp. 37 ◽  
Author(s):  
Mukesh Upadhyay ◽  
Ayeon Kim ◽  
Heehyang Kim ◽  
Dongjun Lim ◽  
Hankwon Lim
Keyword(s):  
Fluidized Bed ◽  
Cfd Simulation ◽  
Circulating Fluidized Bed ◽  
Model Simulation ◽  
Scale Up ◽  
Radial Profile ◽  
Momentum Exchange ◽  
Drag Model ◽  
Solid Holdup ◽  
Drag Models

Accurate prediction of the hydrodynamic profile is important for circulating fluidized bed (CFB) reactor design and scale-up. Multiphase computational fluid dynamics (CFD) simulation with interphase momentum exchange is key to accurately predict the gas-solid profile along the height of the riser. The present work deals with the assessment of six different drag model capability to accurately predict the riser section axial solid holdup distribution in bench scale circulating fluidized bed. The difference between six drag model predictions were validated against the experiment data. Two-dimensional geometry, transient solver and Eulerian–Eulerian multiphase models were used. Six drag model simulation predictions were discussed with respect to axial and radial profile. The comparison between CFD simulation and experimental data shows that the Syamlal-O’Brien, Gidaspow, Wen-Yu and Huilin-Gidaspow drag models were successfully able to predict the riser upper section solid holdup distribution with better accuracy, however unable to predict the solid holdup transition region. On the other hand, the Gibilaro model and Helland drag model were successfully able to predict the bottom dense region, but the upper section solid holdup distribution was overpredicted. The CFD simulation comparison of different drag model has clearly shown the limitation of the drag model to accurately predict overall axial heterogeneity with accuracy.

Modeling and Simulation of a Pilot-Scale Bubbling Fluidized Bed Gasifier for the Gasification of High Ash Indian Coal Using Eulerian Granular Approach

2016 ◽  
Vol 14 (1) ◽  
pp. 417-431 ◽  
Author(s):  
G. K. Singh ◽  
B. Mohanty ◽  
P. Mondal ◽  
P. Chavan ◽  
S. Datta
Keyword(s):  
Experimental Data ◽  
Modeling And Simulation ◽  
Fluidized Bed ◽  
Gaseous Phase ◽  
Solid Phase ◽  
Pilot Scale ◽  
Indian Coal ◽  
Bubbling Fluidized Bed ◽  
Fluidized Bed Gasifier ◽  
Phase Phase

AbstractThe present work deals with modeling and simulation of a pilot-scale bubbling fluidized bed gasifier (BFBG) for the gasification of high ash Indian coal. Taking into account different stages of coal gasification, such as drying, volatilization, gasification and combustion processes, a two-dimensional model with quadrilateral cells is developed using FLUENT 12.0 software. The model incorporates exchange of mass, momentum and energy between gaseous phase (phase 1) and solid phase (phase 2) using Eulerian–Eulerian approach. The solid phase is described by kinetic theory of granular flows. Four heterogeneous and four homogeneous reactions covering six species in gaseous phase (CO, CO2, H2, N2, O2 and H2O) and coal in solid phase are considered for the above process. The kinetics for the homogeneous reactions are described using eddy dissipation model available in FLUENT while that for heterogeneous reactions, a user-defined function (UDF) with Arrhenius kinetics is written in C language. The validation of the above model has been done using experimental data generated in a pilot-scale BFBG at Center Institute of Mining and Fuel Research (CIMFR), Dhanbad, India. The computed exit gas compositions as well as temperature profile inside the gasifier are in good agreement (within an error band of ±10%) with experimental data. The flow behaviors and volume fraction profiles of gas and solid phases in the bed zone and freeboard zone of the gasifier have also been predicted using this model.

Three-dimensional computational fluid dynamics investigation of hydrodynamics behaviour of gas–solid flow in fluidized bed of Geldart D particles

2021 ◽  
pp. 095440892098769
Author(s):  
Fazia Aiche ◽  
Salah Belaadi ◽  
Adel Lalaoua ◽  
Abdallah Sofiane Berrouk ◽  
Abdelwahid Azzi
Keyword(s):  
Fluidized Bed ◽  
Gas Flow ◽  
Turbulence Modeling ◽  
Volume Fraction ◽  
Solid Phase ◽  
Fluid Model ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Industrial Processes ◽  
Cyclic Process

Fluidized beds are widely used in many industrial processes as they ensure the desirable high-intensity heat and mass transfers between gas and particles and offer the possibility to perform operations in a continuous mode and powders recycling. Some of these industrial processes use Geldart D type of powders and operate in the slugging mode. This paper presents a 3 D numerical model of gas-solid flows in a fluidized bed based on the Two-Fluid Model (TFM). Turbulence modeling (k- ε) was used to predict flow behavior in fluidized bed of Geldart D particles. The solid phase consists of Geldart D powders and the gas flow is in a slug regime. The numerical results are validated against the experimental work of Azzi et al. Model predictions on flow patterns, bed expansion, volume fraction time series and pressure drop fluctuations are presented and discussed in details in order to demonstrate the cyclic process of slug formation (onset, growth, rising and bursting of slugs) and its effects on the overall performance of beds fluidizing Geldart D type of powders.

Numerical Analysis on the Dynamic Behaviour of Fluidized Bed Reactor

2015 ◽  
Vol 813-814 ◽  
pp. 718-722
Author(s):  
P.M. Suhaile ◽  
S. Rupesh ◽  
C. Muraleedharan ◽  
P. Arun
Keyword(s):  
Fluid Dynamics ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Solid Phase ◽  
Fluid Model ◽  
Turbulence Models ◽  
Fluidized Bed Reactor ◽  
Two Fluid Model ◽  
Bed Expansion ◽  
Phase Transport

A gas-solid multiphase flow is simulated using CFD to investigate the fluid dynamics of a fluidized bed reactor. The simulation is based on Euler-Euler two fluid model where Kinetic Theory of Granular Flow is used for predicting the solid phase transport properties. The simulation procedure is validated by reproducing and comparing hydrodynamic parameters with those available in the literature. The effect of different turbulence models on bed fluid dynamics is analyzed and k-ε RNG per-phase model is found to have better prediction accuracy compared to other models. The minimum fluidization velocity, granular temperature, bed expansion, particle velocity and volume fraction are determined by the model.

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