Particles In Gas-solid Fluidized Bed Research Articles

Segregation of binary particles in gas-solid fluidized bed

Segregation of binary particles in gas-solid fluidized bed

A study on fluidization of activated carbon particles in gas-solid fluidized bed

ABSTRACT In this paper, the minimum fluidisation velocity () of activated carbon particles in a gas–solid fluidised bed was experimentally determined using dry air as the fluidising medium. The effect of particle size and temperature on the minimum fluidisation velocity of the fluidised activated carbon particles was analysed. The particle sizes 212, 425, and 710 µm and bed temperatures of 30°C, 100°C, 200°C, and 300°C were studied. From the experimental results, it was found that the decreased with a decrease in particle size of the activated carbon particles and decreased with an increase in the temperature. Based on the experimental results, a new correlation was developed to predict at higher temperatures, since at higher temperatures, the deviation of experimental values was higher when compared with the values estimated using previously published correlations. The present study will be useful for the design of an experimental system to study the continuous adsorption and desorption of organic vapours at higher temperatures in the fluidised bed of activated carbon particles. The details of the experimental study and analysis of results are discussed in this paper.

Characterization of flow pattern of cohesive particles in gas-solid fluidized bed via axial distribution of particle motions

Flow pattern of cohesive particles in gas-solid fluidized bed is complex, and particles in different regions exhibit various flow patterns. Characterization methods in literatures are deficient in detecting local motions of particles. In this work, particle motions distribution along the axial direction was investigated by acoustic emission detection and pressure fluctuation. The axial distribution of particle motions proved the “stratified fluidization” of cohesive particles and further investigation showed that the stratified fluidization was affected by both the superficial gas velocity and the initial height-to-diameter ratio (H0/D). Increasing the operating gas velocity, the fluidization of the fluidized bed with a relatively low H0/D changed from fixed bed with stable channeling to the two-layer stratified fluidization consisted of the fixed bed layer in the lower part and the bubbling fluidized bed layer in the upper part. While for the fluidized bed with a large H0/D, the fluidization transmitted from fixed bed with unstable channeling to two-layer stratified fluidization, then to multi-layer stratified fluidization with an inflatable fluidized bed layer appeared above the bubbling bed layer. Moreover, a flow pattern map of the fluidization of cohesive particles was established which could show guidance for the selection of optimized operation conditions for fluidization of cohesive particles.

Enrichment effect of coal and quartz particles in gas-solid fluidized bed with applied electrical field

Electrostatic effects are commonly found in gas-solid fluidized beds. With an electrical field applied in a gas-solid fluidized bed, the charged particles there would be separated according to the opposite charge polarity. A charge-to-mass ratio test showed that quartz can easily be given a negative charge when tribo-charging with coal. A binary particle mixture was employed to explore the enrichment effect in an electrical-field fluidized bed unit. The results showed that the mass fraction of quartz in the products decrease gradually from negative plate to positive plate. The increase of fluidization time, plate voltage and gas velocity, along with low bed height, were beneficial to the improvement of the enrichment effect. The mass fraction of quartz close to the positive plate was >40%, while that of negative was around 10%. This work demonstrates the possibility of separating fine coal using a fluidized bed with applied electrical field.

Simulated pulsed flow of gas and particles in a horizontal oppose-pulsed gas jets of bubbling fluidized bed

Flow behavior of gas and particles with a horizontal oppose-pulsed gas jets are simulated by means of a three dimensional Computational Fluid Dynamics (CFD) model with the kinetic theory of granular flow in a gas-particles bubbling fluidized bed. The effects of amplitudes and frequencies on the hydrodynamics of gas and particles are analyzed. The simulation results are presented in terms of phase velocity vector plot, volume fraction of phases, granular temperature, power spectrum and Reynolds stresses in the bed. Results show that the impingement caused by the oppose-pulsed gas jets oscillates with the variation of pulsed gas velocity. The impingement zone with the high solid volume fraction reciprocates from the left side to the right side through the bed center with the variation of pulsed jet gas velocities. The lateral velocity and gas turbulent kinetic energy, granular temperature and Reynolds stresses of gas and particles are larger near the pulsed gas jets than that at the center of the bed. The large dispersion coefficients of particles using the horizontal oppose-pulsed gas jets enhance the mixing of particles in gas-solid fluidized bed.

CFD modeling to determine the minimum fluidization velocity of particles in gas-solid fluidized bed at different temperatures

It is often important to know minimum fluidization velocity of particles in gas-solid fluidized bed at different temperatures and with different fluidizing gases. Generally, carrying out such experiments are often time consuming as well as very expensive. Computational fluid dynamic (CFD) modeling is presently an important tool that can be extended to solve these problems. The present work demonstrates the use and advantages of CFD modeling to study the effect of temperature on fluidization velocity for lithium titanate (Li2TiO3) particles which fall under Geldart B type and air as fluidizing media. 2D simulation of fluidized bed was performed using Eulerian-Eulerian approach. The inlet superficial air velocity was varied and pressure drop across the bed was predicted at different temperatures from 30 to 600°C for spherical particles of diameter from 231 to 780μm. Minimum fluidization velocity was also determined using experiments for validation for different temperatures and diameter of particles. CFD predicts the minimum fluidization velocity with 95% accuracy when compared to experimental observations. The minimum fluidization velocity decreases with increase in temperature which is confirmed with validated model. The data from simulations was also compared with correlations reported in literature.

Hydrodynamic modeling of the entrainment of Geldart A group particles in gas-solid fluidized bed: The effect of column diameter

A multi-fluid Eulerian computational fluid dynamics (CFD) model is used to simulate the entrainment of fluid catalytic cracking (FCC) particles in gas-solid fluidized beds. Entrainment of Geldart A group particles was studied because of their wide range of industrial use. The model was based on the kinetic theory of granular flow. The CFD model was used to investigate the effect of column diameter on the entrainment flux of particles in a binary mixture. Two different sizes of particles were used because many engineering applications deal with binary mixture of particles in fluidized beds. Various column diameters, including 38 mm, 76 mm, 114 mm, 152 mm, and 190 mm, were investigated. The entrainment flux of particles was increased with decreasing column diameter. The effect of column diameter was not significant for column diameters larger than 114 mm. Furthermore, increasing the superficial gas velocity increased the entrainment flux of particles. Model predictions were also compared with experimental findings.

A new measuring system for flow patterns of solid particles in gas-solid fluidized bed.

A new system was developed to measure the flows of solid particles in fluidized beds. Porous particles, which were coated with a water-soluble fluorescent dye, emitted a strong visible light upon excitation by UV light. The illuminating UV light and the fluorescent visible light passed through clear silica fibers and plastic fibers, respectively. By using bifurcate optical probes and fluorescent tracer particles, pulse response curves at arbitrary locations were demonstratively measured. The output signals were processed by a microcomputer, and flow patterns of solid particles were visualized on CRT. The results show that the present system is useful in many situations of gas-solid contactors requiring observation of particle flows.