Initial Static Bed Height Research Articles

Particle motion analysis of a new three-phase fluidized bed flotation column with glass sphere particles

Analysis of the particle movement within the unit vessel is necessary for the design, optimization and scale-up of the new three-phase fluidized bed flotation column (TFC). This work aimed to examine the motion and distribution of assisted fluidized particle-glass spheres in the TFC and to provide a better assessment of particle collision and dispersion behavior by quantifying particle velocities. Tracer particles were analyzed by high-speed camera techniques to determine particle velocity fluctuations in a three-phase fluidized bed consisting of glass spheres, water, and bubbles. A correlation model for determining the particle velocity in a three-phase fluidized bed is proposed after a systematic analysis of the particle velocity. The model covers a wide range of superficial gas velocities (0–0.339 m/s), superficial liquid velocities (0.169–0.425 m/s) and initial static bed heights (0.162–0.262 m). Aiming to evaluate particle collisions in the TFC, this paper derives the particle collision frequencies using a modified collision model and investigates the effect of a wide range of operating parameters on particle collisions. Finally, a new method for estimating dispersion due to particle motion is developed based on the study of particle dispersion coefficients.

Prediction of Fluctuation, Expansion Ratios and Gas Hold Up in a Three Stage Gas-solid Fluidized Bed – A Statistical Approach

Multistage fluidized bed has shown greater performance than the single stage in terms adsorption efficiency, recovery efficiency etc. Thus, experiments have been carried out in a three stage gas-solid fluidized bed. The hydrodynamic characteristicssuch as fluctuation ratio, expansion ratio and gas holdups have been studied. The dependency of these quantities with the system variables like particle size, initial static bed height and superficial gas velocity in each stage of a three-stage fluidized bed have been analyzed. It has been found that both fluctuation and expansion ratios are inverse functions of particle size and static bed height whereas a direct function of superficial gas velocity. However the gas holdup is a direct function of all the three operating parameter.It has also been observed that bed fluctuation and expansion goes on decreasing from lower bed to the upper bed. Further correlations have been developed for all the three stages for fluctuation ratio, expansion ratio and gas holdup using statistical analysis. It has been found that the experimental values of the responses agree well with the values predicted from the models.

Bed hydrodynamics of a new three-phase fluidized bed flotation column with steel ball particles

The new three-phase fluidized bed flotation column (TFC) hydrodynamics characteristics, such as gas holdup, bubble diameter and bubble surface area flux have been carried out, and this study focuses on bed fluid hydrodynamic parameters of the TFC. The bed hydrodynamic characteristics viz., bed fluctuation ratio (r), bed expansion ratio (R) and bed voidage (ε) of the TFC have been studied using air as the discontinuous phase and water as the continuous phase, respectively. The effects of the system parameters studied include superficial gas, liquid velocities and initial static bed height (H0). Experimental studies based on the Response surface methodology (RSM) have been made to investigate the mathematical model of hydrodynamic parameters (r, R, ε) and bubble diameter (Db) of the TFC. The results show that the models which were established by operating variables can predict the r, R, ε and Db of the TFC well. Based on the previous investigation of the optimization of bubble performance parameters which has been caried out by Liu et al. (2020), the correlation of Db has been carried out, and the result shows that H0 is the boundary condition that determines the variation of Db. The optimization of Db by RSM shows that relatively small bubbles can be obtained when H0 is greater than 0.290 m within the range of parameters studied. The values of the experiment have been compared with those predicted by the proposed models and have been found to agree well.

Modeling and Optimization of Gas-Solid Fluidization of Binary Mixtures using Box-Behnken Experimental Design

The influence of different factors on the fluidization of a binary mixture of red mud and aluminum was investigated. A new model was developed for predicting pressure drop through the solid bed using experimental data of other work. Statistical analysis based on response surface methodology has been used to develop correlations for bed pressure drop with three independent factors, minimum fluidization velocity (Umf), red mud to aluminum ratio (R/A), and static head (Hs). The design of experiments offers a best alternative to study the effect of factors and their response with the minimum number of experiments. The hydrodynamic characteristics of fluidization, bed pressure drop, superficial gas velocity (Umf), red mud to aluminum ratio (R/A), and initial static bed height (Hs) were modeled and optimized. ANOVA has been used to analyze the system parameters on bed pressure drop. A model of bed pressure drop was found to have a correlation coefficient of 0.98. The measured values of bed pressure drop from RSM were found to match the experimental values very well.

Prediction of particle circulation rate in an internally circulating fluidized bed with a central draft tube

Controlling the internal particle circulation rate quantitatively is of great importance to the operation of the internally circulating fluidized bed with a central draft tube used in the biomass gasification field. In this work, the effects of the operating parameters on the internal particle circulation rate were investigated on a laboratory experimental apparatus. The results indicated that the internal particle circulation rate increased with the increasing air velocity in the central draft tube, and gently increased with the air velocity in the annular bubbling bed. The internal particle circulation rate increased with the increasing initial static bed height in the annular bubbling bed and decreased with the increasing particle size. The correlation formula was obtained through the regression of experimental data. Furthermore, a dynamic prediction model was established based on the theory of fluid mechanics, and the matching degree between the predicted values and experimental data was larger than 80%.

Rate of CO2 adsorbent attrition induced by gas jets on perforated plate distributors in bubbling fluidized beds

Particle attrition is a major challenge when handling bulk solid materials with fluidized beds due to its ability to cause particle loss. Herein, the particle attrition induced by the gas jets on a perforated plate distributor in a bubbling fluidized bed was investigated for CO2 adsorbent particles. An attrition tube, which used air as the fluidizing gas, was used as the fluidized bed. At a constant fluidizing velocity, the initial static bed height and orifice gas velocity were considered as variables. It was confirmed that abrasion dominated the particle attrition. The trend indicating the change in the maximum size of the particles (dpm,a) formed by attrition followed that of the attrition rate (i.e., the formation rate of fine particles via attrition). A new stirring factor that combined the model developed by Werther and Xi with the original stirring factor adequately explained the effect of the static bed height on both the attrition rate and dpm,a when the initial static bed height was greater than the length of the orifice gas jet that penetrated the bed. The attrition rate increased linearly with the new stirring factor. However, dpm,a increased exponentially with the new stirring factor. Relationships were successfully proposed to enable the estimation of the attrition rate and dpm,a for the CO2 adsorbent particles. This study provided the evidence indicating the significance of the effect of bed height on particle attrition induced by the gas jet on the distributor. Moreover, proper models for correlating the attrition rate and the maximum size of the fine particles formed by attrition in the bubbling fluidized bed were provided.

Removal of Tetracycline from Wastewater Using Circulating Fluidized Bed

In this study, the circulating fluidized bed was used to remove the Tetracycline from wastewater utilizing a pistachio shell coated with ZnO nanoparticles. Several parameters including, Tetracycline solution flowrate, initial static bed height, Tetracycline initial concentration and airflow rate were systematically examined to show their effect on the breakthrough curve and the required time to reach the adsorption capacity and thus draw the fully saturated curve of the adsorbent. Results showed that using ZnO nanoparticles will increase the adsorbent surface area and pores and as a result the adsorption increased, also the required time for adsorbent saturation increased and thus the removal efficiency may be achieved at minimum antibiotic flowrate, maximum bed height, higher antibiotic concentration, and higher airflow rate. Also, a minimum fluidization velocity correlation was developed in this study. This correlation was found to be a function of liquid velocity, bed height, particle size, and particle density. The results showed that circulating fluidized bed has a better performance and last more than two hours before the bed biomass exhausted in comparison with traditional fluidized bed.

Optimization of gas parameters in a three-phase fluidized bed flotation column

The gas parameters, including gas holdup, bubble diameter and bubble specific surface area flux, of a three-phase fluidized bed flotation column (TFC) have been systematically studied. According to the characteristics of each stage of flotation the TFC is designed into three parts, the fluidized mineralization area, the buffer zone and the circulation section, and the solid particles are introduced into the fluidized mineralization area as regulatory factor. The gas holdup was calculated by measuring bed pressure drop, and the bubble diameter was measured by the conductivity probe method. Experimental parameters, including superficial gas velocity, superficial liquid velocity, solid particle type, frother concentration and initial static bed height, were studied. Experimental results show that the gas parameters can be optimized by changing experimental parameters. The models of gas parameters of the TFC have been derived. Experimental results have been compared with those in the relevant literature.

Experimental investigation of fountain height in a shallow rectangular spouted bed using digital image analysis

The formation of a fountain is a unique phenomenon of spouted beds, which plays a significant role in the reactor design as well as the physical and chemical efficiency of the whole system. The present work investigates the fountain height (Hf) behavior in a rectangular spouted bed (30.2 mm × 101.6 mm) using four different kinds of particles classified in both Geldart groups D (Nylon and Alumina) and B (Glass beads (GB) and High density polyethylene (HDPE)), which is intended as a gap-bridging attempt, given the fact that most of the published fountain height studies were conducted in the cylindrical bed geometry. First, with the determination of Hf by systematic image processing methods, the effects of different variables including, superficial gas velocity (Ug), nozzle size (Deqn), and initial static bed height (H0) on Hf of the Geldart D and B particles are addressed. Secondly, because of the intrinsic periodical behavior of the absolute fountain height (Hfa, i.e. the vertical distance between the fountain surface to the bed bottom), the Fast Fourier Transform (FFT) is applied to characterize the variation of the Hfa for the four particle types. The period of particles’ entry into the spout and the “residence time” of particles in the fountain region are proposed as two possible factors that affect the fountain frequency. Finally, correlations to predict the Hf for both Geldart D and B particles are developed respectively, based on the discussion of different influence factors and frequency analysis. The correlation developed for Geldart B particles indicates that the effect of the nozzle size (Di) can be neglected when the ratio of particle size (dp) to nozzle size (Di) is less than 0.1. The predicted values show good agreement with the experimental data in the present study. In addition, the employment of the equivalent cross-sectional area diameters of the nozzle and rectangular column, namely Di and Dc, ensures the potential extension of the application of the developed correlations to cylindrical spouted beds.

Effect of tapered angle on hydrodynamics of homogenous ternary mixture of regular particles in a three-phase tapered fluidized bed

ABSTRACTHydrodynamics characteristics, namely bed pressure drop, bed fluctuation and expansion ratios have been studied for regular particles in a three-phase tapered fluidised bed. For this, experiments have been carried out in different tapered columns with glass beads as solid phase, compressed air as gas phase and water as the liquid phase. The effect of tapered angle, initial static bed height, average particle size and superficial gas velocity on the hydrodynamic characteristics has been studied. Correlations have been developed for the three hydrodynamic characteristics using both dimensional and statistical analysis. Experimental values of bed expansion and fluctuation ratios have been found to agree well with those calculated from developed correlations.

Effect of plasma irradiation on the fine particle behavior in a spouted bed

The combination of a spouted bed with non-thermal plasma has been used widely in industrial chemical processes. However, the detailed behavior of particles in a spouted bed with irradiation of plasma is still unknown. In this study, a fluidization experiment of fine white fused alumina particles under the irradiation of a dielectric barrier discharge (DBD) plasma generator was performed, and the effect of the plasma irradiation on the particle behavior in a spouted bed was evaluated. Essential operation parameters, such as static bed height, gas velocity, applied voltage, and working gases were changed, and the minimum spouted velocity, pressure drop, bed void fraction and spouted bed temperature with plasma enhancement were measured to understand the fluidization behavior of fine particles. As the results, the minimum spouted velocity decreased as the applied voltage increased to a high voltage, irrespective of the initial static bed height, while the void fraction of the solid bed before the fluidization point increased with an increase in the applied voltage. Fluidization behavior varied with the working gas, and the minimum spouted velocity with N2 was much higher than that of Ar. The temperature of the bed and particle surface did not show apparent changes when the plasma was applied. The proposed mechanism shows that the ionization of gas improves the interaction between particles and may cause the minimum spouted velocity to decrease.

Spouting behavior of binary particle mixtures of different densities: Fluid dynamics and particle segregation

Numerous industrial applications of spouted beds involve a mixture of granular particles, where differences in particle size, density, and shape can cause particle segregation, affecting the quality of flow and decreasing product homogeneity. The aim of this study was to investigate the particle segregation and fluid dynamics of a conical spouted bed operating with a binary mixture of particles of different densities. Using glass beads and polyethylene particles with a diameter of 4mm, we determined the effects of the mass fraction of denser particles and static bed height on the minimum spouting condition and mixture index. The pressure drop and airflow in the minimum spouting condition increased with an increase in bed height or jetsam concentration. Regarding particle segregation, the jetsam particles tended to concentrate near the bottom, at the spout–annulus interface because they have a shorter trajectory than the lighter particles in the fountain region. Jetsam-rich mixtures with high initial static bed heights exhibited more efficient particle mixing, excluding those at the bottom of the bed.

Study on gas holdup in a fluidized flotation column from bed pressure drop

ABSTRACTThis paper investigated the overall gas holdup characteristics in a cocurrent three-phase fluidized flotation column with liquid as the continuous phase. The air, water, and glass beads with a diameter of 3 mm were, respectively, used as the gas, liquid, and solid phases in the flotation column. The gas holdup studies were carried out in a plexiglass column with 0.05 m in internal diameter and 2.2 m in height. Bed pressure drop measurements were used to calculate the fractional gas holdup. During the measurements, the superficial gas and liquid velocities, respectively, varied from 0.42 to 2.55 cm/s and from 6.47 to 10.82 cm/s. Detailed experimental investigations were carried out to study the effects of static liquid height, initial static bed height, gas velocity, liquid velocity, and frother concentration on gas holdup in a cocurrent three-phase fluidized flotation column. It was found that the gas holdup increased with the flow rate of air and decreased with an increase in the water flow rate. Certain effect of the static bed height on gas holdup was observed when the gas velocity varied. But the increase in the static liquid height resulted in the decrease in gas holdup when the gas velocity varied.

Experimental and modeling studies on mixing behavior of binary mixtures in a spout-fluid bed

ABSTRACTExperimental and modeling studies have been performed to determine mixing characteristics of binary mixtures in a spout-fluid bed. Spherical glass beads of diameters (3.075, 1.7, 1.2, and 0.75 mm) and air as fluidizing medium have been used in the study. Effect of various system parameters, namely, initial static bed height, gas velocity, diameter ratio, mixture composition, and sampling time on mixing of binary particles has been experimentally investigated. A dimensionless correlation has been developed for mixing index. Mixing behavior has been modeled using artificial neural networks (ANNs). Training of ANN was performed using the Levenberg–Marquardt (LM) backpropagation algorithm to predict the mixing index. The predictions of the ANN were found to be in good agreement with the experimental results and predictions from developed correlations.

CFD-DEM modeling the effect of column size and bed height on minimum fluidization velocity in micro fluidized beds with Geldart B particles

The fluidization behavior of Geldart B particles in micro fluidized beds is investigated numerically using Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) available in the open-source Multiphase Flow with Interphase eXchanges (MFIX) code. The effects of different bed inner diameters (D) of 8mm, 12mm, 16mm and various initial static bed heights (H) were examined. It is found that both decreasing the column diameter and increasing the bed height in a micro fluidized bed increases the minimum fluidization velocity (Umf). The observed overshoot in pressure drop that occurs before the onset of fluidization decreases in magnitude with increasing column diameter, however there is less sensitivity to bed height. Overall, the numerical results agree qualitatively with existing theoretical correlations and experimental studies. The simulations show that both column diameter and particle-wall friction contribute to the variation in minimum fluidization velocity. These two factors are coupled and hard to separate. The detailed influences of wall friction on minimum fluidization velocity are then investigated for a prescribed column diameter of 8mm by varying the wall friction from 0 to 0.4.

Experimental study on gas-solid flow characteristics in an internally circulating fluidized bed cold test apparatus

A self-designed internally circulating fluidized bed cold test apparatus was built to investigate the gas-solid flow characteristics in a new kind of internally circulating fluidized bed furnace. The test material was circulating ash from a power plant CFB boiler. Optical fiber probes and differential pressure transmitters were employed for the measurements. The particle internal circulation rate and the solids holdup in the upper space of the furnace were studied by changing the fluidization air velocity in the main chamber, the height of partition wall and the initial static bed height. The results showed that with the increase of fluidization air velocity in the main chamber, the particle internal circulation rate increased at first then decreased. Meanwhile, the particle internal circulation rate decreased with the increase of the partition wall height and increased with the increase of initial static bed height in the main chamber. The solids holdup in the upper space of the internally CFB cold test apparatus was 1–4% of that in the normal CFB cold test apparatus. The proportion of particle external circulation rate was relatively low in the circulating system.

Hydrodynamics of three-phase fluidization of homogeneous ternary mixture in a conical conduit — Experimental and statistical analysis

Hydrodynamics of conical fluidized bed differ from that of columnar beds by the fact that a velocity gradient exists along the axial direction of the bed. The gas–liquid–solid fluidized bed has emerged in recent years as one of the most promising devices for three-phase operations. Such a device is of considerable industrial importance as evident from its wide applications in chemical, refining, petrochemical, biochemical processing, pharmaceutical and food industries. To explore this, a series of experiments have been carried out for homogeneous well-mixed ternary mixtures of dolomite of varying compositions in a three-phase conical fluidized bed. The hydrodynamic characteristics determined included the bed pressure drop, bed fluctuation and bed expansion ratios. The single and combined effects of operating parameters such as superficial gas velocity, superficial liquid velocity, initial static bed height, average particle size and cone angle on the responses have been analyzed using response surface methodology (RSM). A 25 full factorial central composite experimental design has been employed. Analysis of variance (ANOVA) showed a high coefficient of determination value and satisfactory prediction second-order regression models have been derived. Experimental values of bed pressure drop, bed fluctuation and bed expansion ratios have been found to agree well with the developed correlations.

Prediction of bed pressure drop, fluctuation and expansion ratios for three-phase fluidization of ternary mixtures of dolomite in a conical conduit

AbstractHydrodynamics of conical fluidized bed differ from that of columnar beds by the fact that a velocity gradient exists along the axial direction of the bed. The gas–liquid–solid fluidized bed has emerged in recent years as one of the most promising devices for three-phase operations. Such a device is of considerable industrial importance as evident from its wide applications in chemical, refining, petrochemical, biochemical processing, pharmaceutical, and food industries. To explore this, experiments have been carried out to find the bed pressure drop, bed fluctuation, and expansion ratios for ternary mixtures of dolomite in a three-phase conical fluidized bed. The effect of superficial liquid and gas velocity, initial static bed height, average particle size, and cone angle on the above-mentioned three responses have been studied. Mathematical models have been developed for the responses using both dimensional and statistical analyses. The calculated values of the responses from the developed model...

Effect of Initial Static Bed Height and Liquid Superficial Velocity on the Minimum Fluidization Velocity (Umf) and Pressure Drop for the Bed of Semolina Particles in Liquid-Solid Fluidization

The successful and economical design, scale up and operation of a fluidized bed reactor depends upon the true prediction of its bed hydrodynamics. The present research has been carried out to study the hydrodynamics behavior of bed of semolina particles in liquid solid fluidization. The prime objective of this research work is to study the effect of liquid superficial velocity and variation in static bed height on the minimum fluidization velocity and pressure drop. Liquid-solid fluidization is characterized by the uniform expansion of bed particles; therefore, it is known as particulate fluidization. In liquid, solid fluidization, there is no bubbling phase, that is the main cause of uniform bed expansion. Liquid-solid fluidization has extensive field of applications, i.e., in hydrometallurgy, waste water treatment, biochemical processing and food technology. Minimum fluidization velocity and pressure drop are important hydrodynamic parameters in the design and scale up of fluidized bed reactors. The experimental work was carried out in a column made up of acrylic having 60 mm outer diameter and 2 mm wall thickness and was 1000 mm long. Manometers were used to observe the pressure drop variations across the bed. The minimum fluidization velocity was found to be 0.404 mm/sec. It has been found that the minimum fluidization velocity is not affected by the variations in the initial static bed height. Semolina particles being sticky solids offer slightly greater pressure drop. Pressure drop becomes constant when fluidization is achieved.

Numerical simulation of soot combustion process in a bubbling fluidized bed with segregation behavior

AbstractAlthough only about 1 wt.% soot is formed after asphalt gasification, it is generally recognized that handling of the soot places a considerable financial burden on the integrated deasphalting–gasification process, because the disposal of the filter soot to landfill or other destinations causes serious environment problems. The bubbling fluidized bed combustion process, which takes the advantage of segregation behavior, was proposed to solve soot handling problem. A multi‐fluid model based on an Eulerian–Eulerian approach was developed to reveal the characteristics of segregation and combustion behavior. The distributions of flow, temperature, and species concentration were obtained, and the simulation results demonstrate that the segregation behavior is beneficial to discharge particle mixtures with low soot content at the bottom of the bed, which will favor the following vanadium recovering process. The effects of several key operating conditions, such as excess air coefficient, superficial gas velocity and initial static bed height were also discussed. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.