scholarly journals Effect of Superficial Gas Velocity on Bubbling Fluidized Bed Behaviour in a Biomass Gasifier

2020 ◽  
Author(s):  
Cornelius Agu ◽  
Britt M.E. Moldestad
Keyword(s):  
Fluidized Bed ◽  
Gas Velocity ◽  
Bubbling Fluidized Bed ◽  
Superficial Gas Velocity

Sesame and Broad Bean Stalks: Mixing Characteristics of Chips as a Biomass Fuel for Bubbling Fluidized Bed Combustor

2018 ◽  
Vol 16 (6) ◽  
Author(s):  
Saad A. El-Sayed ◽  
Amro A. El-baz ◽  
Emad H. Noseir
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Mass Fraction ◽  
Broad Bean ◽  
Sand Particle ◽  
Gas Velocity ◽  
Mixing Index ◽  
Bubbling Fluidized Bed ◽  
Superficial Gas Velocity ◽  
Fluidized Bed Combustor

Abstract Mixing and segregation characteristics of biomass particles are of practical importance because the in-bed combustion efficiency of volatile matter affects the vertical location of biomass in bubbling fluidized bed combustor. Sesame and broad bean stalk biomass materials mixed with sand used in this study. The superficial gas velocity, biomass chip length, sand particle size and mass fraction of biomass varied as experimental variables. The mixing and segregation behavior of mixtures were analyzed in terms of mixing index. It was found that the variability in the chip-shape made the sesame chips is quantitatively and qualitatively higher homogeneity and mixedness than the broad bean chips. The optimum overall mixing index for the sesame and the broad bean is around 0.96 and 0.84 at dimensionless superficial gas velocity (U/Umf) of 2.0 (1.40 m/sec) and 2.1 (1.25 m/sec), respectively. It was found that as the mean diameter increased and the sphericity decreased, the mixing quality decreased. The average sand particle size of 371 µm can keep good mixing with biomass chips of both materials, compared with average particle sizes of sand 550 and 700 µm. Increasing the initial biomass mass fraction yields a poor mixing of the investigated biomass stalks.

CFD-DEM Numerical Simulation and Experimental Validation of Heat Transfer and Two-Component Flow in Fluidized Bed

2017 ◽  
Vol 16 (1) ◽  
Author(s):  
Feihong Guo ◽  
Zhaoping Zhong
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Fluidized Bed ◽  
Quartz Sand ◽  
Thermal Imager ◽  
Gas Velocity ◽  
Bed Height ◽  
Two Component ◽  
Superficial Gas Velocity ◽  
Infrared Thermal Imager

AbstractBased on the improved computational fluid dynamics and discrete element method (CFD-DEM), heat transfer and two-component flow of biomass and quartz sand have been studied from experiments and numerical simulation in this paper. During experiments, the particle temperature and moving images are respectively recorded by infrared thermal imager and high speed camera. With the increase of the velocity, the mixing index (MI) and the cooling rate of the particles are rising. Due to larger heat capacity and mass, the temperature of biomass drops slower than that of quartz sand. Fictitious element method is employed to solve the incompatibility of the traditional CFD-DEM where the cylindrical biomass are considered as an aggregation of numerous fictitious sphere particles arranged in certain sequence. By the comparison of data collected by infrared thermal imager and the simulated results, it can be concluded that experimental data is basically agreement with numerical simulation results. Directly affected by inflow air (25℃), the average temperature of particles in the bed height area (h>30 mm) is about 3 degrees lower than that of the other heights. When the superficial gas velocity is larger, the fluidization is good, and the gas temperature distribution is more uniform in the whole area. On the contrary, bubbles are not easy to produce and the fluidization is restricted at lower superficial gas velocity. Gas-solid heat transfer mainly exists under the bed height of 10 mm, and decreases rapidly on fluidized bed height. The mixing index (MI) is employed to quantitatively discuss the mixing effectiveness, which first rises accelerate, then rising speed decreases, finally tends to a upper limit.

scholarly journals Mixing Characteristics of Binary Mixture with Biomass in a Gas-Solid Rectangular Fluidized Bed

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 2011
Author(s):  
Guiying Wu ◽  
Bangting Yu ◽  
Yanjun Guan ◽  
Xuehui Wu ◽  
Kai Zhang ◽  
...  
Keyword(s):  
Binary Mixture ◽  
Fluidized Bed ◽  
Binary Mixtures ◽  
Silica Sand ◽  
Mixture Composition ◽  
Inert Material ◽  
Gas Velocity ◽  
Mixing Characteristics ◽  
Superficial Gas Velocity ◽  
Initial Packing

Aiming to better understand the biomass pyrolysis and gasification processes, a detailed experimental study of the mixing characteristics is conducted in a fluidized bed with binary mixtures. Rapeseed is used as biomass, and silica sand or resin as inert material. The effect of mixture composition, initial packing manner, and superficial gas velocity on the concentration distribution is investigated in a rectangular fluidized bed by means of photography and sampling methods. The results show that the mixture composition plays an important role in the axial solids profile of binary mixtures. The mixing behavior of binary mixture is dominated by the bubble movement. The axial distribution of binary mixtures becomes uniform with increasing superficial gas velocity, whilst no obvious effect of initial packing manner is observed in this study.

Detailed Description of the Fluidized Bed Mixing and Heat Transfer by Means of Eulerian Multi-Fluid Numerical Simulations

2020 ◽  
Author(s):  
Muhammad Ali Uzair ◽  
Francesco Fornarelli ◽  
Sergio Mario Camporeale ◽  
Marco Torresi
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Granular Flow ◽  
Fluid Model ◽  
Gas Velocity ◽  
Uniform Temperature ◽  
Temperature Dependent ◽  
Commercial Code ◽  
Temperature Dependent Properties ◽  
Superficial Gas Velocity

Abstract The hydrodynamics and heat transfer of a binary mixture of sand and biomass in a fluidized bed have been numerically investigated. The Eulerian multi-fluid model MFM incorporating kinetic theory of granular flow was used to numerically investigate fluidized bed. A commercial code has been used together with user-defined functions to correctly predict the hydrodynamics and the heat transfer. Numerical results were validated against the experiment in terms of pressure drop across the bed and concentration of biomass at different heights of the bed. Influence of additional parameters, such as superficial gas velocity and sand sizes on hydrodynamics were investigated. Additionally, heat transfer in the fluidized bed was also studied highlighting the influence of the temperature dependent properties of air on the results. The present results reveal that better mixing is achieved for smallest sand size, also promoting more uniform temperature of biomass.

Influence of Fluidization Velocity on Bed Defluidization in Fluidized Bed Combustors

2005 ◽  
Author(s):  
Mohammad R. Golriz ◽  
Morgan Eriksson ◽  
Marcus O¨hman ◽  
Anders Nordin ◽  
Rainer Backman
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Large Scale ◽  
Particle Diameter ◽  
Operating Conditions ◽  
Biomass Combustion ◽  
Gas Velocity ◽  
Fluidization Velocity ◽  
Significant Difference ◽  
Superficial Gas Velocity

Effects of superficial gas velocity and bed particle size on bed defluidization during biomass combustion were investigated. Sampled bed particles from four different large-scale circulating- and bubbling fluidized bed combustors, using biomass as fuel, were collected and analyzed. The bed particles from each fluidized bed unit were divided into small and large particle size fractions. The results indicate no significant difference in elemental compositions between small and large coated bed particles but the ratio of coating thickness to the mean particle diameter was higher for the small particles compared to the large ones. Controlled fluidized bed agglomeration tests revealed strong influence from fluidization velocity on initial defluidization temperatures at lower velocities, but little effect at higher velocities. Influence of bed particle size on initial defluidization temperature varied depending on operating conditions. Finally, a model based on viscous flow sintering is proposed for the relation between agglomeration temperature and superficial gas velocity. The model predictions are in good agreement with experimental data.

Characteristics of Mixing/Segregation in a Bubbling/Slugging Fluidized Bed with Binary Mixtures

2011 ◽  
Vol 396-398 ◽  
pp. 322-325 ◽  
Author(s):  
Heng Zhi Chen ◽  
Zheng Kui Guo
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Binary Mixtures ◽  
Fixed Bed ◽  
Size Difference ◽  
Gas Velocity ◽  
Carbon Particles ◽  
Fluidization Regime ◽  
Superficial Gas Velocity

Fluidization behavior of binary mixtures with titanic slag particles and carbon particles had been investigated. Three solids states in the bed: fixed bed, transient fluidization and steady fluidization, emerges as increasing gas velocity. The extent of segregation of solids mixture in transient fluidization regime depended on the size difference between jetsam particles and flotsam particles. The effects of flotsam particle size, initial jetsam concentration and the superficial gas velocity on the segregation of binary solids had been measured.

scholarly journals Prediction of gas holdup in a combined loop air lift fluidized bed reactor using Newtonian and non-Newtonian liquids

2011 ◽  
Vol 17 (3) ◽  
pp. 375-383
Author(s):  
Sivakumar Venkatachalam ◽  
Akilamudhan Palaniappan ◽  
Senthilkumar Kandasamy ◽  
Kannan Kandasamy
Keyword(s):  
Fluidized Bed ◽  
Particle Diameter ◽  
Fluidized Bed Reactor ◽  
Gas Holdup ◽  
Operating Conditions ◽  
Experimental Results ◽  
Gas Velocity ◽  
Wide Range ◽  
Newtonian Liquids ◽  
Superficial Gas Velocity

Many experiments have been conducted to study the hydrodynamic characteristics of column reactors and loop reactors. In this present work a novel combined loop airlift fluidized bed reactor was developed to study, the effect of superficial gas and liquid velocities, particle diameter, fluid properties on gas holdup by using Newtonian and non-Newtonian liquids. Compressed air was used as gas phase. Water, 5% n-butanol, various concentrations of glycerol (60 % and 80 %) were used as Newtonian liquids, different concentrations of Carboxy Methyl Cellulose (0.25 %, 0.6 % and 1.0 %) aqueous solutions were used as non-Newtonian liquids. Different sizes of Spheres, Bearl saddles and Raschig rings were used as solid phases. From the experimental results it was found that the increase in superficial gas velocity increases the gas holdup, but it decreases with increase in superficial liquid velocity and viscosity of liquids. Based on the experimental results a correlation was developed to predict the gas holdup for Newtonian and non-Newtonian liquids for a wide range of operating conditions at a homogeneous flow regime where the superficial gas velocity is approximately less than 5 cm/s.

scholarly journals Simulation of Three-dimensional Vibrated Fluidized Bed Dryer Using Distinct Element Method

2019 ◽  
Vol 7 (2) ◽  
Author(s):  
S. Wongsiriwan ◽  
Thongchai Rohitatisha Srinophakun ◽  
Pakon Laopreecha
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Particle Motion ◽  
Distinct Element ◽  
Distinct Element Method ◽  
Drying Rate ◽  
Gas Velocity ◽  
Fluidized Bed Dryer ◽  
Vibrated Fluidized Bed ◽  
Superficial Gas Velocity

The particle motion, temperature behavior, and drying rate of particle inside a vibrated fluidized bed dryer were numerically investigated in this work. In the simulation, the Distinct Element Method (DEM) based on the Newton’s second law of motion was used to solve the particle motion. The physical aspects of fluid motion and heat transfer were obtained by applying Computational Fluid Dynamics (CFD) technique. For the drying of particle, only the constant rate period was considered in order to save the computational time. Programming was developed in Standard-C language and using MATLAB to visualize the results. In the simulation, 2,000 particles with stiffness 800 N m-1 were simulated in a rectangular bed. The developed model was validated with an experimental result of Gupta et al. [1]. The program was then used to study the effect of superficial gas velocity (U0), frequency of vibration (f) and amplitude of vibration (a) in fluidized bed dryer. At low velocities and no vibration of bed,  articles in the bed were not fluidized but smoothly circulated. Thus, the heat transfer occurred only near the orifice. When superficial gas velocity increased, the fluidization of the particles was observed. The fluidization and drying rate improved with increased in superficial velocity for both vibrated fluidized bed and stationary bed. With introducing of vibration, the fluidization behavior of the particle was improved. The particles in the bed were well mixed and also increased the drying rate. From the simulation results, increasing of frequency and amplitude could not significantly improve rate of drying.

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