scholarly journals Simulation of Coal and Biomass Cofiring with Different Particle Density and Diameter in Bubbling Fluidized Bed under O2/CO2 Atmospheres

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Chao Chen ◽  
Xuan Wu ◽  
Lingling Zhao
Keyword(s):  
Fluidized Bed ◽  
Mass Fraction ◽  
Volume Fraction ◽  
Solid Phase ◽  
Particle Density ◽  
Reaction Rates ◽  
High Mass ◽  
Species Concentration ◽  
Bubbling Fluidized Bed ◽  
Biomass Cofiring

A 2D dynamic model for a bubbling fluidized bed (BFB) combustor has been developed for simulating the coal and biomass cofiring process under 21% O2/79% CO2 atmosphere in a 6 kWth bubbling fluidized bed, coupled with the Euler-Euler two-phase flow model. The kinetic theory of binary granular mixtures is employed for the solid phase in order to map the effect of particle size and density. The distribution of temperature, volume fraction, velocity, gas species concentration, and reaction rates are studied with numerical calculations. The simulated temperature distribution along the height of the combustor and outlet gas concentrations show good agreement with experimental data, validating the accuracy and reliability of the developed cofiring simulation model. As indicated in the results, there are two high temperature zones in the combustor, which separately exist at the fuel inlet and dilute phase. The reaction rates are related to the species concentration and temperature. The higher concentration and temperature lead to the larger reaction rates. It can be seen that all of the homogeneous reaction rates are larger at the fuel inlet region because of rich O2 and volatiles. High mass fraction of volatile gas is found at the fuel inlet, and the main reburning gas at the dilute phase is CH4. The mass fraction distribution of CO is related to the volume fraction of fuel which is due to the fact that the source of CO is not only from the devolatilization but also from the gasification. On the basis of this theoretical study, a better understanding of flow and combustion characteristics in biomass and coal cofiring under oxy-fuel atmospheres could be achieved.

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.

Study on Black Liquor Low-temperature Gasification in Fluidized Bed by Eulerian Multiphase Computationally Fluid Dynamics Modeling

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Weiling Li ◽  
Wenqi Zhong ◽  
Baosheng Jin ◽  
Rui Xiao ◽  
Yingjuan Shao ◽  
...  
Keyword(s):  
Low Temperature ◽  
Fluidized Bed ◽  
Reaction Rate ◽  
Solid Phase ◽  
Heterogeneous Reaction ◽  
Black Liquor ◽  
Molar Fraction ◽  
Reaction Rates ◽  
Operating Conditions ◽  
Heterogeneous Reactions

Abstract A three-dimensional Eulerian multiphase based computational model was developed to simulate the black liquor gasification processes in a fluidized bed gasifier (FBG) at low temperature. The standard k-e model and kinetic theory of granular model were used to simulate the gas phase and solid phase, respectively. Black liquor pyrolysis, homogeneous reactions and heterogeneous reactions were taken into account in chemical model. The reaction rates of homogeneous and heterogeneous reaction were determined by Arrhenius–Eddy dissipation reaction rate and kinetic reaction rate. Simulations were carried out at four different operating conditions, i.e. reactor temperature was kept at 550 degree centigrade or 600 degree centigrade, and nitrogen or air was used as fluidizing medium. The calculated results were in well agreement with the experiment used as calibration. Base on the simulation, gas-sold flow patterns and gas species molar fraction distributions were obtained, the relationship of gas composition profiles with the temperature and the fluidizing media were discussed.

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.

Minimum Air Fluidization Velocity Study of Specific 2-D Bubbling Fluidized Bed Reactor

2014 ◽  
Vol 699 ◽  
pp. 660-665
Author(s):  
M. Fadhil ◽  
M.S. Aris ◽  
A.H. Abbas ◽  
A.B.A. Ibrahim ◽  
N. Aniza
Keyword(s):  
Fluidized Bed ◽  
Particle Density ◽  
Flow Behavior ◽  
Numerical Approach ◽  
Combustion Efficiency ◽  
Fluidized Bed Combustion ◽  
Fluidization Velocity ◽  
Bubbling Fluidized Bed ◽  
Flow Through ◽  
Bed Expansion

Research on the thermodynamic behavior of sand beds was carried out using a commercial computational dynamic package. The work involved simulating, with the use of the Ergun equation, the air flow through a two-dimensional bubbling bed reactor to predict the bed character whilst considering the major effective function (particle size, particle density, bed height and reactor width). The Minimum Fluidization Velocity (Umf) values were then calculated before the optimum value of Umfneeded to ensure a workable Bubbling Fluidize Bed Combustor (BFBC) system. The effects of using different Umfvalues on the flow behavior were also investigated using the numerical approach at different times. The results from these investigations indicate that the bubbling region in the fluidized bed combustion can be correlated to the sand bed expansion with minimum errors and assist in enhancing the combustion efficiency by supplying the required volume of oxygen into the system.

Numerical Study of the Influence of Horizontal Tube Banks on the Hydrodynamics of a Dense Gas-Solid Bubbling Fluidized Bed

2003 ◽  
Vol 1 (1) ◽  
Author(s):  
Sanjib K. Das Sharma ◽  
Ratan Mohan
Keyword(s):  
Fluidized Bed ◽  
Solid Phase ◽  
Numerical Study ◽  
Horizontal Tube ◽  
Particle Interactions ◽  
Tube Bank ◽  
Bubbling Fluidized Bed ◽  
Tube Banks ◽  
Fluidizing Medium ◽  
Good Agreement

Numerical study of the influence of tube-bank on the hydrodynamics of a freely bubbling fluidized bed is relatively less reported in the literature. In this paper, results obtained from CFD study of a two dimensional gas-solid fluidized beds with horizontal tube-bank are compared with the published experimental data (Hull et. al., 1999). A 2-D bed, 1 m high and 0.2 m wide with tubes of diameter 0.026 m was taken for the calculations. Two different tube arrangements of staggered and inline pitch with center-to-center distance of 0.05 m were considered. Air was used as the fluidizing medium and ballotini glass (diameter: 230 mm and density: 2723 kg/m3) was the fluidized material. Air velocities used were 0.15 m/s and 0.187 m/s. The Eulerian-Eularian Two-Fluid CFD model was employed for modeling the momentum equations for both the gas and the solid phase with kinetic theory modification for the solid phase to account for the inter-particle interactions. Hydrodynamic features, such as, bubble size and bubble rise velocity and their variation with height within and outside the tube bank showed good agreement with the data of Hull et al.(1999)

Comparing ANSYS Fluent® and OpenFOAM® simulations of Geldart A, B and D bubbling fluidized bed hydrodynamics

2019 ◽  
Vol 30 (1) ◽  
pp. 93-118 ◽  
Author(s):  
Cesar Martin Venier ◽  
Andrés Reyes Urrutia ◽  
Juan Pablo Capossio ◽  
Jan Baeyens ◽  
Germán Mazza
Keyword(s):  
Fluidized Bed ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Internal Diameter ◽  
Ansys Fluent ◽  
Content Type ◽  
Current State ◽  
Bubbling Fluidized Bed ◽  
Bubble Sizes

Purpose The purpose of this study is to assess the performance of ANSYS Fluent® and OpenFOAM®, at their current state of development, to study the relevant bubbling fluidized bed (BFB) characteristics with Geldart A, B and D particles. Design/methodology/approach For typical Geldart B and D particles, both a three-dimensional cylindrical and a pseudo-two-dimensional arrangement were used to measure the bed pressure drop and solids volume fraction, the latter by digital image analysis techniques. For a typical Geldart A particle, specifically to examine bubbling and slugging phenomena, a 2 m high three-dimensional cylindrical arrangement of small internal diameter was used. The hydrodynamics of the experimentally investigated BFB cases were also simulated for identical geometries and operating conditions using OpenFOAM® v6.0 and ANSYS Fluent® v19.2 at identical mesh and numerical setups. Findings The comparison between experimental and simulated results showed that both ANSYS Fluent® and OpenFOAM® provide a fair qualitative prediction of the bubble sizes and solids fraction for freely-bubbling Geldart B and D particles. For Geldart A particles, operated in a slugging mode, the qualitative predictions are again quite fair, but numerical values of relevant slug characteristics (length, velocity and frequency) slightly favor the use of OpenFOAM®, despite some deviations of predicted slug velocities. Originality/value A useful comparison of computational fluid dynamics (CFD) software performance for different fluidized regimes is presented. The results are discussed and recommendations are formulated for the selection of the CFD software and models involved.

scholarly journals Studi Fluidisasi dan Pembakaran Batubara Polydisperse di Dalam Fluidized Bed Berbasis Simulasi CFD (Computational Fluid Dynamic)

2018 ◽  
Vol 2 (1) ◽  
pp. 40
Author(s):  
Mochammad Agung Indra Iswara ◽  
Tantular Nurtono ◽  
Sugeng Winardi
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Mass Fraction ◽  
Cfd Simulation ◽  
Solid Phase ◽  
Fluid Dynamic ◽  
Data Retrieval ◽  
Pulverized Coal ◽  
Solid Mass ◽  
Time Step

Penelitian ini bertujuan untuk mengetahui fenomena pembakaran batubara dimana dimensi alat, distribusi ukuran partikel, dan jenis kualitas batubara menggunakan validasi dari penelitian Wang. Penelitian ini mengarahkan pada simulasi berbasis CFD. Kondisi operasi pada saat simulasi pembakaran dilakukan pada kecepatan bubbling. Metode yang digunakan sebelum melakukan simulasi pembakaran merupakan kelanjutan dari simulasi fluidisasi dimana masih menggunakan geometri 2-D fluidized bed lalu dilakukan meshing, selanjutnya memasukkan persamaan energi. Geometri fluidized bed yang digunakan berbentuk tabung dengan panjang silinder fluidized bed 1370 mm, diameter silinder 152 mm. Bahan yang digunakan pada penelitian ini berupa pulverized coal dengan jenis batubara Bituminous dimana ukuran partikel dianggap polydisperse dengan ukuran partikel 1 mm dan 1,86mm yang masing-masing sebesar 50% fraksi massa dengan kecepatan 0,2 Kg/s dan suhu 1200 K, dan udara luar yang diinjeksikan dengan kecepatan 0,8 m/s dan suhu 300 K. Analisa pengambilan data adalah berupa kontur fase padatan, kontur temperatur pada fase-1 dan fase padatan, fraksi massa produk pembakaran, massa padatan awal dan akhir simulasi dengan time step sebesar 0,0001 detik dan number of time step sebesar 300000. Selanjutnya data tersebut diplot menjadi grafik temperatur terhadap time step dan disajikan dalam setiap 1 menit simulasi selama 5 menit simulasi.This research aims to determine coal combustion’s phenomenon, where the device’s dimension, particle size distribution, and the quality of rank coal  which validated Wang’s reseach. This reseach leads on CFD simulation. The operation condition has did in bubbling velocity. This method is a continuation from fluidization simulation which is use 2-D Geometry and then used the meshing method, and enter the energy equation. The geometry of fluidized bed used was tubular cylinder with 1370 mm length and 152 mm. Materials used in this study was pulverized coal with Bituminous coal type which the particle size was considered as monodispers with particle size was 1.43 mm and polydispersed with particle size was 1 mm with 50% mass fraction and 1.86 mm with 50% mass fraction with flow rate 0,2 Kg/s and the temperature is 1200 K, and the outside air are injected in 0,8 m/s and 300 K. The analysis of data retrieval is solid phase contour, temperature contours in phase-1 and solid phase, mass fraction of combustion product, initial solid mass and final solid mass simulation with time step 0,0001 s and the numberof time step 300000. Then the data is plotted into a graph temperature vs time step and presented in 1 minute simulation for 5 minute simulation.

scholarly journals Application of Particle Imaging Method for Measurement of Solid Volume Fraction in Carbon Nanotube Particles Fluidized Bed

2018 ◽  
Vol 7 (3.33) ◽  
pp. 85 ◽  
Author(s):  
Sung Won Kim ◽  
. .
Keyword(s):  
Carbon Nanotube ◽  
Fluidized Bed ◽  
Volume Fraction ◽  
Particle Density ◽  
Solid Volume Fraction ◽  
Fixed Bed ◽  
Apparent Volume ◽  
Previous Method ◽  
Imaging Method ◽  
Particle Imaging

Solid volume fraction in the carbon nanotube (CNT) fluidized bed reactors is an important parameter which is responsible of fluidization quality and the design of reactor. The solid volume fraction can be obtained from the pressure drop across the bed with the information of gas and particle densities. However, previous method such as the Hg-porosimetry for the measurement of the particle density did not adequately draw the solid volume fraction of the CNT aggregates with entangled nanotubes network. A new method to measure the apparent particle density of the CNT aggregates was proposed to calculate the solid volume fraction in the CNT fluidized bed. The density of the vertically aligned CNT particle was measured based on the apparent volume by shape analysis using two dimensional imaging. The solid fraction based on imaging method showed a significant value of 0.69 for the fixed bed, which describes well the entangled structure of the CNT aggregates. The distribution of solid volume fraction in the CNT fluidized bed with variation of gas velocity was determined based on the imaging method. The method was verified by applying the obtained values to the Richardson-Zaki equation on the bed expansion in the fluidized bed.  

Dry beneficiation of +0.5mm-5.6mm South African coal using an air dense medium fluidization bed

2021 ◽  
Author(s):  
Elmarie Sunette Diedericks ◽  
Marco Le Roux ◽  
Quentin Peter Campbell
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Separation Efficiency ◽  
Solid Phase ◽  
Poor Performance ◽  
Operating Conditions ◽  
High Mass ◽  
Dense Medium ◽  
Separation Performance ◽  
Coal Particles

Abstract The separation performance of solid phase bed material, at various particle size ranges, in an air dense medium fluidized bed (ADMFB), were evaluated during this study. The coal particles were separated into +0.5mm-1mm, +1mm-2mm, +2mm-2.8mm, +2.8mm-4mm, +4mm-4.75mm and +4.75mm-5.6mm particle size ranges and fed to the fluidized bed in these fractions. Along with the six coal particle size ranges, three dense media to coal ratios and the addition of vibration was tested to identify the best operating conditions. Adequate results were obtained for larger particle size ranges down to and including +2.0mm-2.8mm coal particles, after which the separation performance decreased significantly. Density stratification was irregular and not obvious for coal particles below 2.0mm and maintaining a consistent fluidization state also proved to be challenging, especially when dense medium was added. The coal particles separated vertically along the bed height because of differences in particle and bed density, while particle size proved to have a notable influence on the degree of separation. An air fluidization velocity of between 1.1 to 1.4Umf was shown as the best performing velocity, which yielded the maximum ash differential between the top and bottom layers of the bed for all the particle size ranges tested. For +2.0mm-5.6mm coal particles, low cumulative ash yields were obtained at high mass yields, however the ash yields increased for -2mm coal. Vibration and dense medium have, in some cases, enhanced the separation efficiency of the ADMFB. The -2.0mm particles experienced stronger particle-particle interactions as well as elevated levels of bubbling and back mixing than that of the +2.0mm particles, which explains the poor performance of the small particle sizes.

The effect of ring baffles on the hydrodynamics of a gas—solid bubbling fluidized bed using computational fluid dynamics

2009 ◽  
Vol 223 (10) ◽  
pp. 2281-2289 ◽  
Author(s):  
S H Hosseini ◽  
R Rahimi ◽  
M Zivdar ◽  
A Samimi
Keyword(s):  
Fluidized Bed ◽  
Volume Fraction ◽  
Fluid Model ◽  
Expansion Ratio ◽  
Bubbling Fluidized Bed ◽  
Gas Volume Fraction ◽  
Two Fluid Model ◽  
Particle Velocities ◽  
Bed Expansion ◽  
Gas Volume

An Eulerian—Eulerian two-fluid model (TFM) integrating the kinetic theory for emulsion phase was used to simulate gas—solid fluidized beds. Validation of the model was investigated based on hydrodynamic parameters such as bed expansion ratio, H/ H0, gas volume fraction profile, bubble behaviour, and motion of the particles. A good agreement was found between numerical results and experimental values. The model was used to study a bubbling fluidized bed (BFB) including the ring baffles. Predicted results show that the ring baffles have an important role in the flow pattern of the bed. Baffles increase the bed expansion height and particle velocities at axial locations on the top of the highest baffle as well as uniform distribution of gas volume fraction between the baffles area. In spite of increasing the dead zones in the bed, ring baffles cause the improvement of mixing and heat transfer in the bed. The present study provides a useful basis for further works on the effect of baffles in BFBs.

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