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.

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.

A Study on Fluidized Bed-Type Particulate Filter for Diesel Engines

2007 ◽  
Vol 129 (4) ◽  
pp. 1072-1078 ◽  
Author(s):  
Sung-Sub Kee ◽  
Ali Mohammadi ◽  
Takuji Ishiyama ◽  
Takaaki Kakuta
Keyword(s):  
Particle Size ◽  
Diesel Engine ◽  
Pressure Drop ◽  
Fluidized Bed ◽  
Particle Diameter ◽  
Filtration Efficiency ◽  
Particulate Filter ◽  
Design Parameters ◽  
Gas Velocity ◽  
Bed Height

A fluidized bed-type diesel particulate filter (DPF) was applied to filter particulate matter (PM) in diesel engine exhaust gas. The effects of the fluidized bed design parameters, such as gas velocity, bed particle size, and height, on PM and smoke filtration efficiencies, and pressure drop were experimentally investigated using a single-cylinder direct injection (DI) diesel engine. High PM filtration efficiency and low pressure drop were achieved with the DPF, especially at a lower gas velocity. The PM filtration efficiency was higher with a smaller bed particle size at the lower gas velocity; however, it drastically decreased with an increase in gas velocity due to excessive fluidization of the bed particles. Increase in bed height led to higher PM filtration efficiency while causing an increase in pressure drop. The theoretical work was also conducted for further investigation of the effects of the above-mentioned parameters on PM filtration. These results indicated that diffusion filtration was the dominant mechanism for PM filtration under the conditions of this study and that the decrease in PM filtration efficiency at high gas velocity was caused by a deterioration in the diffusion filtration. The bed particle diameter and the bed height should be optimized in order to obtain a high filtration efficiency without increasing the DPF size.

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.

Monitoring Fluidization Dynamics for Detection of Changes in Fluidized Bed Composition and Operating Conditions

1999 ◽  
Vol 121 (4) ◽  
pp. 887-894 ◽  
Author(s):  
J. Ruud van Ommen ◽  
Jaap C. Schouten ◽  
Cor M. van den Bleek
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Fluidized Bed ◽  
Pressure Fluctuations ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Gradual Change ◽  
Monitoring Method ◽  
Superficial Gas Velocity

In many industrial applications of gas-solids fluidized beds, it is worthwhile to have an on-line monitoring method for detecting changes in the hydrodynamics of the bed (due for example to agglomeration) quickly. In this paper, such a method, based on the short-term predictability of fluidized bed pressure fluctuations, is examined. Its sensitivity is shown by experiments with small step changes in the superficial gas velocity and by experiments with a gradual change in the particle size distribution of the solids in the bed. Furthermore, it is demonstrated that the method is well able to indicate if a stationary hydrodynamic state has been reached after a change in the particle size distribution (a ‘grade change’).

scholarly journals Effect of Solid Particles on the Gas Hold Up in the Fluidized Bed Columns: Experimental and Mathematical Studies

2021 ◽  
Vol 12 (4) ◽  
pp. 5004-5011
Keyword(s):  
Particle Density ◽  
Tap Water ◽  
Particle Diameter ◽  
Gas Holdup ◽  
Operating Conditions ◽  
Solid Particles ◽  
Bubble Columns ◽  
Solid Concentration ◽  
Gas Velocity ◽  
Superficial Gas Velocity

The present research investigated the effect of solid properties on the gas holdup of the fluidization bed bubble columns (FBCS). All experiments were performed in the constant clear tap water of 80 cm height. The range of solid particle diameters was 0.7 – 2 mm with two different densities of 1075 and 1200 kg/m3, superficial air velocities 4 – 7 cm/s. It was observed that there are proportional relationships between superficial gas velocity and particle diameter with the gas holdup. While an inverse relationship between solid concentration and particle density with the gas holdup. Mathematical and statistical analysis was also used as a powerful way to represent the gas hold up as a function of different operating conditions.

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.

Grid-Zone Particle Hydrodynamics and Solid Circulation in a Multiple Jet Fluidized Bed

2012 ◽  
Author(s):  
Gaurav Agarwal ◽  
Brian Lattimer ◽  
Srinath Ekkad ◽  
Uri Vandsburger
Keyword(s):  
Fluidized Bed ◽  
Sudden Change ◽  
Particle Diameter ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Orifice Diameter ◽  
Circulation Rate ◽  
Optimum Operating Condition ◽  
Fluidization Velocity ◽  
Solid Circulation Rate

Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA) were used to investigate the evolution of multiple inlet gas jets located at the distributor base of a two-dimensional fluidized bed setup. Experiments were conducted with varying distributor orifice diameter, orifice pitch, particle density, particle diameter, and fluidization velocity to understand the motion of particles in the grid-zone region of a fluidized bed. Results were used to develop a phenomenological model that quantifies the conditions throughout the entire grid-zone. The results and the model were further analyzed to understand the effect of operating conditions on the solid circulation dynamics of a multiple jet system fluidized bed. It was determined that the solid circulation rate increased linearly with an increase in the fluidization velocity until the jet system transitioned from isolated to an interacting system. The solid circulation increased at a much lower rate in the interacting system of jets. This sudden change in the solid circulation rate has not been reported in the literature possibly due to the lack of multiple jet studies. For multiple jet systems, this phenomenon may indicate the presence of an optimum operating condition with high circulation rate and low air input in the bed.

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 Effect of Bed Particle Size on Thermal Performance of a Directly-Irradiated Fluidized Bed Gas Heater

Processes ◽  
2020 ◽  
Vol 8 (8) ◽  
pp. 967
Author(s):  
Sae Han Park ◽  
Chae Eun Yeo ◽  
Min Ji Lee ◽  
Sung Won Kim
Keyword(s):  
Particle Size ◽  
Fluidized Bed ◽  
Thermal Performance ◽  
Thermal Efficiency ◽  
Gas Velocity ◽  
Bubble Behavior ◽  
Heat Transfer Characteristics ◽  
Maximum Value ◽  
Solar Thermal Collector ◽  
Sic Particle

There is a growing interest in a fluidized bed particle receiver that directly irradiates sunlight to particles in the fluidized bed as a solar thermal collector for heating. Thermal performance of directly-irradiated fluidized bed gas heater is strongly affected by the physical properties of the particles. The effect of SiC particle size on heat transfer characteristics in the solar fluidized bed gas heater (50 mm-ID × 100 mm high) has been determined. The outlet gas temperatures showed a maximum value with increasing gas velocity due to the particles motion by bubble behavior in the bed, and the maximum values were found at 3.6 times of Umf for fine SiC and less than 2.0 times of Umf for coarse SiC. Heat absorption from the receiver increased with increasing gas velocity, showing with maximum 18 W for the fine SiC and 23 W for the coarse SiC at 4.5 times of Umf. The thermal efficiency of the receiver increased with increasing gas velocity, but was affected by the content of finer particles. The maximum thermal efficiency of the receiver was 14% for fine SiC and 20% for coarse SiC within the experimental range, but showing higher for the fine SiC at the same gas velocity. A design consideration was proposed to improve the thermal efficiency of the system.

scholarly journals Effect of Fines Content on Fluidity of FCC Catalysts for Stable Operation of Fluid Catalytic Cracking Unit

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 293 ◽  
Author(s):  
Sung Kim ◽  
Chae Yeo ◽  
Do Lee
Keyword(s):  
Fluidized Bed ◽  
Catalytic Cracking ◽  
Particle Diameter ◽  
Fluidized Bed Reactor ◽  
Fluid Catalytic Cracking ◽  
Stable Operation ◽  
Minimum Fluidization Velocity ◽  
Fines Content ◽  
Fluidization Velocity ◽  
Fcc Catalysts

Effect of fines content (weight % of particles with diameter less than 45 μm) on bed fluidity was determined to get a base for good fluidization quality in the fluid catalytic cracking (FCC) unit. The fines content in equilibrium FCC catalysts (Ecat) from commercial units were controlled by adding or removing the fines to simulate commercial situation. To get the fluidity values (Umb/Umf) of seven different FCC catalysts (2 Ecats and 5 fresh catalysts) and their mixture, minimum fluidization velocity (Umf) and minimum bubbling velocity (Umb) were measured in a fluidized bed reactor (0.05 m ID). The fluidity decreased with loss of fines content and increased with increments of makeup of fresh catalysts or additive with the controlled fines content. The fluidities of catalysts increase with increases of normalized particle diameter variation by the fines addition. The obtained fluidities have been correlated with the fines contents and the catalyst and gas properties. The proposed correlation could guide to keep good catalyst fluidity in the FCC unit.

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