INFLUENCE OF THE PARTICLE SIZE AND SUPERFICIAL GAS VELOCITY ON THE SUBLIMATION OF PURE SUBSTANCES IN FLUIDIZED BEDS OF DIFFERENT SIZES

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.

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On the superficial gas velocity in deep gas–solids fluidized beds

Chemical Engineering Science ◽

10.1016/j.ces.2011.08.002 ◽

2011 ◽

Vol 66 (22) ◽

pp. 5735-5738 ◽

Cited By ~ 7

Author(s):

Tingwen Li ◽

John Grace ◽

Lawrence Shadle ◽

Chris Guenther

Keyword(s):

Fluidized Beds ◽

Gas Velocity ◽

Superficial Gas Velocity

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

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.396-398.322 ◽

2011 ◽

Vol 396-398 ◽

pp. 322-325 ◽

Cited By ~ 1

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.

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Effect of Superficial Gas Velocity on the Solid Temperature Distribution in Gas Fluidized Beds with Heat Production

Industrial & Engineering Chemistry Research ◽

10.1021/acs.iecr.7b00338 ◽

2017 ◽

Vol 56 (30) ◽

pp. 8729-8737 ◽

Cited By ~ 4

Author(s):

Mohammad Banaei ◽

Jeroen Jegers ◽

Martin van Sint Annaland ◽

Johannes A.M. Kuipers ◽

Niels G. Deen

Keyword(s):

Temperature Distribution ◽

Heat Production ◽

Fluidized Beds ◽

Gas Velocity ◽

Gas Fluidized Beds ◽

Superficial Gas Velocity ◽

Solid Temperature

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Magneto-Stabilization of Fluidized Beds as due to Short Ranged Interparticle Forces

International Journal of Chemical Reactor Engineering ◽

10.1515/1542-6580.2988 ◽

2012 ◽

Vol 10 (1) ◽

Author(s):

M. J. Espin ◽

Jose Manuel Valverde ◽

M. A S. Quintanilla

Keyword(s):

Particle Size ◽

Yield Stress ◽

Fluidized Beds ◽

Gas Flow ◽

Fine Particles ◽

Marginal Stability ◽

Chain Model ◽

Gas Velocity ◽

Interparticle Forces ◽

Magnetic Stabilization

We present an experimental study on the stabilization of bubbling gas-fluidized beds of magnetic powders by interparticle forces induced by an externally applied magnetic field in the cross-flow configuration. The samples tested consist of magnetite and steel powders in a range of particle size dp between 35 and 110 microns, allowing us to investigate the effect of particle size and material properties on magnetic stabilization. According to our observations, the stabilization physical mechanism is ruled by the jamming of particle chains created due to attractive forces induced between the magnetized particles. Even in the case of the horizontally applied field, these chains are mechanically stable at orientations close to the gas flow direction in agreement with the prediction of a chain model based on the balance between gas flow shear and interparticle magnetic force fm. Since fm is increased as dp is increased, the critical gas velocity at marginal stability vc for a fixed field strength B is seen to increase with dp. The yield stress of the stabilized bed s increases steadily as the gas velocity v0 is decreased below vc. Thus, s is increased with dp for fixed v0 and B. It is inferred also from our results that natural aggregation of fine particles due to the universal van der Waals interaction enhances the yield stress of the magnetically stabilized bed. A main conclusion is that interparticle short ranged attractive forces play an essential role on magnetic stabilization of fluidized beds.

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Parametric effects of particle size and gas velocity on cluster characteristics in fast fluidized beds

Powder Technology ◽

10.1016/s0032-5910(00)00247-3 ◽

2000 ◽

Vol 111 (1-2) ◽

pp. 114-122 ◽

Cited By ~ 110

Author(s):

Arun K Sharma ◽

Kemal Tuzla ◽

John Matsen ◽

John C Chen

Keyword(s):

Particle Size ◽

Fluidized Beds ◽

Gas Velocity ◽

Parametric Effects

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

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2017-0138 ◽

2018 ◽

Vol 16 (6) ◽

Cited By ~ 2

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.

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Stabilization of gas-fluidized beds of magnetic powders by a cross-flow magnetic field

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.151 ◽

2011 ◽

Vol 680 ◽

pp. 80-113 ◽

Cited By ~ 15

Author(s):

M. J. ESPIN ◽

J. M. VALVERDE ◽

M. A. S. QUINTANILLA ◽

A. CASTELLANOS

Keyword(s):

Magnetic Field ◽

Particle Size ◽

Yield Stress ◽

Material Properties ◽

Fluidized Beds ◽

Gas Flow ◽

Cross Flow ◽

Gas Velocity ◽

Gas Fluidized Beds ◽

The Magnetic Field

In this paper we present an experimental study of the stabilization of gas-fluidized beds of magnetic powders by application of a cross-flow magnetic field. The powders tested consist of magnetite and steel powders in a range of particle size dp between 35 and 110 μm, allowing us to investigate the effect of particle size and material properties on magnetic stabilization. In the operation mode employed by us the magnetic field is applied to the unstable bubbling bed and the gas velocity is slowly decreased. According to our observations, the bed is stabilized at a critical gas velocity by the jamming of particle chains formed during bubbling because of the attractive forces induced between the magnetized particles, which are thus responsible for stabilization. Although the magnetic field is applied in the horizontal direction, these chains are mechanically stable at orientations close to the gas flow direction, in agreement with the prediction of an unconfined chain model based on the balance between gas flow shear and interparticle magnetic force fm. Since fm is increased as dp is increased, the critical gas velocity at marginal stability vc for a fixed field strength B is seen to increase with dp. As the gas velocity v0 is decreased below vc, there is a rearrangement of the structure depending on particle size. Restructuring of the bed depends on particle size as derived from measurements of its permeability to the gas flow, which causes the yield stress to be a function of particle size. It is also inferred from our results that natural agglomeration of fine particles (in the absence of a magnetic field) due to van der Waals forces enhances the yield stress of the magnetically stabilized bed. From our experimental results it is concluded that structural effects, as affected by operating conditions and material properties, play a main role in the rheology of the stabilized magnetofluidized bed (MFB).

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Hydrodynamics and Mass Transfer in a Concentric Internal Jet-Loop Airlift Bioreactor Equipped with a Deflector

Energies ◽

10.3390/en14144329 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4329

Author(s):

Radek Šulc ◽

Jan Dymák

Keyword(s):

Mass Transfer ◽

Transfer Coefficient ◽

Mass Transfer Coefficient ◽

Liquid System ◽

Gas Holdup ◽

Gas Velocity ◽

Liquid Phase Mass Transfer ◽

Homogenization Time ◽

Standard Design ◽

Superficial Gas Velocity

The gas–liquid hydrodynamics and mass transfer were studied in a concentric tube internal jet-loop airlift reactor with a conical bottom. Comparing with a standard design, the gas separator was equipped with an adjustable deflector placed above the riser. The effect of riser superficial gas velocity uSGR on the total gas holdup εGT, homogenization time tH, and overall volumetric liquid-phase mass transfer coefficient kLa was investigated in a laboratory bioreactor, of 300 mm in inner diameter, in a two-phase air–water system and three-phase air–water–PVC–particle system with the volumetric solid fraction of 1% for various deflector clearances. The airlift was operated in the range of riser superficial gas velocity from 0.011 to 0.045 m/s. For the gas–liquid system, when reducing the deflector clearance, the total gas holdup decreased, the homogenization time increased twice compared to the highest deflector clearance tested, and the overall volumetric mass transfer coefficient slightly increased by 10–17%. The presence of a solid phase shortened the homogenization time, especially for lower uSGR and deflector clearance, and reduced the mass transfer coefficient by 15–35%. Compared to the gas–liquid system, the noticeable effect of deflector clearance was found for the kLa coefficient, which was found approx. 20–29% higher for the lowest tested deflector clearance.

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