Initial Static Bed Height Research Articles

Effects of initial static bed height on fractional conversion and bed pressure drop in tapered-in and tapered-out fluidized bed reactors

In this article, a standard 2D Two-Fluid Model (TFM) closed by the kinetic theory of granular flow (KTGF) has been applied to simulate the behavior of tapered-in and tapered-out fluidized bed reactors. In this regard, two types of chemical reactions with gas volume reduction and increase were considered to investigate the effects of initial static bed height on the fractional conversion and bed pressure drop. To validate the CFD model predictions, the results of hydrodynamic simulations concerning bed pressure drop and bed expansion ratio were compared against experimental data reported in the literature and excellent agreement was observed. The obtained simulation results clearly indicate that there is an appropriate static bed height in a tapered-in reactor in which the fractional conversion becomes maximum at this height; whereas variations of static bed height in a tapered-out reactor have insignificant influences on the fractional conversion. Moreover, it was found that the residence time, temperature, and intensity of turbulence of the gas phase are three important factors affecting the fractional conversion in tapered fluidized bed reactors. In addition, it was observed that increasing the static bed height increases the bed pressure drop for both the tapered-in and tapered-out fluidized bed reactors.

Prediction of Pressure Drop and Holdup for Homogeneous Ternary Mixtures of Spherical Glass Bead Particles in a Three-Phase Fluidized Bed

Hydrodynamic characteristics, viz. bed pressure drop and gas holdup, have been studied for ternary mixtures of homogeneous regular particles in a co-current three-phase fluidized bed. For this, a series of experiments have been carried out in a 5-cm diameter column with air as the gas phase, water as the liquid phase, and ternary mixtures of glass beads (1.54, 1.3, and 1.1 mm) as the solid phase. The dependence of bed pressure drop on the average particle diameter, superficial gas velocity, and initial static bed height has been discussed. Based on the dimensional and statistical analyses, correlations have been developed with the system parameters, for both bed pressure drop and gas holdup. Experimental values of bed pressure drop and gas holdup have been found to agree well with those calculated from developed correlations.

Hydrodynamics of Liquid-Solid Semi-fluidized Bed with Regular Homogenous Ternary Mixture

Hydrodynamics studies in Semi-fluidized bed relating to bed pressure drop, height of top packed bed, minimum and maximum semi-fluidization velocities with regular (spherical glass beads) homogeneous ternary mixtures, have been made in 0.01, 0.025, 0.037, 0.05, and 0.065 m internal diameter Perspex columns, with water as the fluidizing medium. Ternary mixtures of glass beads of different sizes (-8+10, -10+12 and -12+14 BSS) have been used as the semi-fluidized solids. Experimental studies relate to establish the effect of system parameters viz. column diameter, average particle size of semi-fluidized solid and initial static bed height and operating parameters viz. superficial liquid velocity and bed expansion ratio on the above mentioned system variables. Empirical and semi-empirical models have been developed using dimensional as well as statistical analyses. The calculated values from the predicted models have been compared with their experimental counterparts and fairly good agreement has been obtained. The results have also been compared with those available in the literature for irregular homogenous ternary mixtures.

Hydrodynamics of gas–solid fluidization of a homogeneous ternary mixture in a conical bed: Prediction of bed expansion and bed fluctuation ratios

Hydrodynamic characteristics of fluidization in a conical or tapered bed differ from those in a columnar bed because the superficial velocity in the bed varies in the axial direction. Fixed and fluidized regions could coexist and sharp variations in pressure drop could occur, thereby giving rise to a noticeable pressure drop-flow rate hysteresis loop under incipient fluidization conditions. To explore these unique properties, several experiments were carried out using homogeneous, well-mixed, ternary mixtures with three different particle sizes at varying composition in gas–solid conical fluidized beds with varying cone angles. The hydrodynamic characteristics determined include the minimum fluidization velocity, bed fluctuation, and bed expansion ratios. The dependence of these quantities on average particle diameter, mass fraction of the fines in the mixture, initial static bed height, and cone angle is discussed. Based on dimensional analysis and factorial design, correlations are developed using the system parameters, i.e. geometry of the bed (cone angle), particle diameter, initial static bed height, density of the solid, and superficial velocity of the fluidizing medium. Experimental values of minimum fluidization velocity, bed fluctuation, and bed expansion ratios were found to agree well with the developed correlations.

Prediction of bed fluctuation and expansion ratios for homogeneous ternary mixtures of spherical glass bead particles in a three‐phase fluidised bed

AbstractThe prediction of the fluctuation and expansion ratios in three‐phase fluidised beds of homogeneous particles is of prime importance in designing the equipments and evaluating the efficiency of a number of physical and/or chemical operations of industrial importance. A clear knowledge of the hydrodynamic behaviour in a three‐phase fluidised bed is a prerequisite for this purpose. To explore this, a series of experiments have been carried out for homogeneous well‐mixed ternary mixtures of three different sizes of glass beads of varying compositions in a three‐phase fluidised bed. The hydrodynamic characteristics determined include the bed fluctuation and expansion ratios. The dependence of these quantities on the average particle diameter, superficial gas velocity and initial static bed height has been discussed. Based on dimensional and statistical analyses, correlations have been developed with the system parameters, viz., average particle diameter, initial static bed height and superficial velocity of the fluidising medium. Experimental values of bed fluctuation and expansion ratios have been found to agree well with those calculated from developed correlations.

Adsorption studies of As(III) from wastewater with a novel adsorbent in a three-phase fluidized bed by using response surface method

Existing overviews of arsenic removal include technologies that have traditionally been used (oxidation, precipitation/coagulation/membrane separation/adsorption) in static bed, with far less attention paid to fluidized bed. The objective of this study is to investigate the possibility of using cashew nut shale waste as an alternative adsorbent for the removal of arsenic (III) ions from aqueous solutions by using gas–liquid–solid fluidized bed. The effect of gas velocity, liquid velocity, initial static bed height and average particle size on the adsorption of arsenic (III) by cashew nut shale waste is investigated using batch methods. The single and combined effects of operating parameters such as gas velocity, liquid velocity, initial static bed height and average particle size on the adsorption of arsenic (III) from wastewater are analyzed using response surface methodology (RSM). A 24 full factorial central composite experimental design was employed. Analysis of variance (ANOVA) showed a high coefficient of determination value (R2=0.9611) and satisfactory prediction second-order regression model was derived. The optimum operating conditions were determined as gas velocity, 12.5m/s; liquid velocity, 0.04m/s; initial static bed height, 0.1m and average particle size of 1.27mm. At optimum adsorption conditions, the adsorption of arsenic (III) from wastewater in a three phase fluidized bed is found to be 92.5464%.

Hydrodynamics of three-phase fluidization of a homogeneous ternary mixture of regular particles—Experimental and statistical analysis

Abstract In the present study, a series of experiments were carried out for homogeneous well-mixed ternary mixtures of glass beads of varying compositions in a three-phase fluidized bed. The hydrodynamic characteristics determined included the bed pressure drop, bed fluctuation and bed expansion ratios. The individual and combined effects of operating parameters such as superficial gas velocity, superficial liquid velocity, initial static bed height, average particle size and column diameter 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 value coefficient of determination and a satisfactory prediction of second-order regression model. The synergetic and antagonistic effect of the system parameters on the above three responses are analyzed from the developed regression models. The coefficient of correlations for bed pressure drop, bed expansion and fluctuation ratios are found to be 0.9642, 0.9483 and 0.9423 respectively. Thus, the experimental values of the above three hydrodynamic parameters have been found to agree well with those calculated from the developed correlations.

Hydrodynamics of liquid–solid semi-fluidized bed with irregular homogenous ternary mixture

Abstract Hydrodynamics of semi-fluidized bed relating to minimum and maximum semi-fluidization velocities, packed bed formation and bed pressure drop with irregular homogeneous ternary mixtures, have been studied in a 0.05 m internal diameter Perspex column, with water as the fluidizing medium. Stainless steel screen of 40 mesh (BSS) with special design is used as bottom grid as well as the top movable restraint with negligible pressure drop. Experimental parameters studied include superficial liquid velocity, average particle size and density, initial static bed height, mixture composition and expansion ratio. Empirical and semi-empirical models have been developed. The calculated values from predicted models have been compared with the experimental values and fairly good agreement has been obtained. The results have also been compared with those available in the literature for irregular single and binary homogenous mixtures.

Experimental flow behaviors of irregular particles with silica sand in solid waste fluidized bed

Co-fluidization characteristics of irregular particles with bed material have been investigated. Experiments were carried out in a solid waste fluidized bed with cross section of 0.2 m × 0.2 m and height of 2 m. Four particles differing in shapes, sizes and densities were used as simulative solid waste, and silica sand was employed as fluidization medium. The pressure drop, flow pattern and minimum fluidization velocity (Umf) under different operating conditions were investigated by recording pressure differential signals and fluidization images. A correlation of Umf was also developed. The results showed that during the fluidization of irregular particles with the bed material of silica sand, the pressure drop curve measured with increasing fluidization gas flow rate was visibly fluctuant and always underestimated the Umf value; while the pressure drop curve measured with decreasing fluidization gas flow rate was smooth and adequate to determine the value of Umf. The Umf was found to be increased with increasing volume proportion and effective particle density, while the initial static bed height has no significant effect on the minimum fluidization velocity. By comparing the Umf values predicted by the developed correlation with the present experimental data and those from literature, it was found that the correlation was quite satisfactory on predicting the Umf value for the fluidization of irregular particles with the bed material of silica sand. The correlation was also found to be applicable to the prediction of Umf values of a solid waste fluidized bed with a single kind or multi-kinds of irregular particles.

Fluidization Behavior of Mixtures of Nanoparticles in Vibrated Fluidized Beds

The experiments of mixtures of SiO2 and ZnO nanoparticles in a vibrated fluidized bed were carried out. The effects of ratio of initial static bed height to diameter (h0/D), vibration amplitude (A), frequency (f) and mass ratio of mixed SiO2 and ZnO nanoparticles on the behavior of mixtures of SiO2 and ZnO nanoparticles were studied. The experimental results proved that the fluidization quality of mixed nanoparticles can be enhanced under h0/D=1, A=3.0 mm, f =45Hz, leading to larger bed pressure drops at low superficial gas velocities. The bed height decreases with increase in the mass ratio of ZnO component of the mixture.

Hydrodynamics of three-phase fluidization of a homogeneous ternary mixture of irregular particles

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 were carried out for homogeneous well-mixed ternary mixtures of five different materials of varying compositions of three different particle sizes in a three-phase fluidized bed. The hydrodynamic characteristics determined included the bed pressure drop, bed fluctuation and bed expansion ratios. The dependence of these quantities on average particle diameter, mass fraction of the fines in the mixture, initial static bed height and material density has been discussed. Based on dimensional analysis and statistical analysis, correlations have been developed with the system parameters, viz., average particle diameter, initial static bed height, density of solid and superficial velocity of the fluidizing medium. Experimental values of bed pressure drop, bed fluctuation and bed expansion ratios have been found to agree well with the developed correlations.

Study of Parameters Effect on Hydrodynamics of a Gas-Solid Chamber Experimentally and Numerically

2 Abstract: In this research, gas velocity, initial static bed height and particle size effect on hydrodynamics of a non-reactive gas-solid fluidized bed chamber were studied experimentally and computationally. A multi fluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this chamber and momentum exchange coefficients were calculated by using the Syamlal- O'Brien drag functions. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops predicted by the simulations at different particle sizes and initial static bed height were in good agreement with experimental measurements at superficial gas velocity higher than the minimum fluidization velocity. Simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Furthermore, this comparison showed that the model can predict hydrodynamic behavior of gas solid fluidized bed chambers reasonably well. Fluidized bed driers and chambers are used in a wide range of applications in various industrial operations, including chemical, mechanical, petroleum, mineral, and pharmaceutical industries. Understanding the hydrodynamics of fluidized bed chambers is essential for choosing the correct operating parameters for the appropriate fluidization regime (1-4). Computational fluid dynamics (CFD) offers an approach to understanding the complex phenomena that occur between the gas phase and the particles. The Eulerian-Lagrangian and Eulerian-Eulerian models have been applied to the CFD modeling of multiphase systems. For gas-solid flows modeling, usually, Eulerian- Lagrangian are called discrete particle models and Eulerian-Eulerian models are called granular flow models. Granular flow models (GFM) are continuum based and are more suitable for simulating large and complex industrial fluidized bed chambers containing billions of solid particles. These models, however, require information about solid phase rheology and particle-particle interaction laws. In principle, discrete particle models (DPM) can supply such information (5-8). DPMs in turn need closure laws to model fluid- particle interactions and particle-particle interaction parameters based on contact theory and material properties. In principle, it is possible to work our way upwards from direct solution of Navier-Stokes equations. Lattice-Boltzmann models and contact theory to obtain all the necessary closure laws and other parameters required for granular flow

Modeling of Chemical Vapor Deposition of Pyrolytic Carbon in a Gas-Spouted Bed Reactor

Spouted beds are used in chemical vapor deposition as they provide good solid mixing, thereby enhancing high mass and heat transfer rates. In the present study, investigations on the kinetics of a coating process by chemical vapor deposition were carried out in a spouted-bed reactor. Pyrolytic carbon coatings were studied by thermal cracking of acetylene mixed with carrier gas argon at 1350 °C. A theoretical model was proposed based on the mass balance of the precursor in the spout and annulus zones at isothermal condition, and the model equations were solved using MATLAB (version 7.1) software. The effect of the operating gas velocity, initial static bed height, and acetylene concentration on the coating rate was examined experimentally and also by simulation results. The simulated results agreed well with the experimental results. Model equations used for simulation were utilized to evaluate the reaction rate constant and radial gas diffusion coefficient and then to study the effect of spout diameter, operating gas velocity, and precursor concentration on the overall conversion of the precursor.

Hydrodynamics of Coarse Coal Slime and Quartz Particles in a Liquid-Solid Fluidized Bed Separator

The hydrodynamics of particles of coarse coal slime and quartz of different sizes in a liquid-solid fluidized bed separator were investigated experimentally, including minimum fluidization velocities, bed expansion ratios, and segregation of mixed particles with two methods. Experimental parameters studied included density and size of particle, superficial water velocity and initial static bed height. The results provide a reference for choice of size scope on coarse coal slime separation by liquid-solid fluidized bed separators.

Effect of Distributor-Orifice on Drying Kineticsin a Fluidized Bed Drier (EDODKFBD)

The drying characteristics of tea-particles have been analyzed in a fluidized bed drier with different orifice sizes while keeping the number of orifices constant. The experiment has been conducted in a fluidized bed drier having 5 cm inner diameter and 80 cm height with four number of distributors of different orifice sizes. In each experimental run the tea-particles have initial moisture content of 13.38 % on dry weight basis. The initial static bed height and air flow rate are kept constant. Hot air is used as the heating medium, air temperatures are varied for 40, 50 and 60 degree centigrade in the present study. The weight of the tea-particles is measured in 10 minute time interval for total drying time of 130 minutes. The amounts of moisture removed are calculated each time. The drying constants are calculated for different distributors for different temperatures. The experimental results show that the drying rate increases with the orifice size up to a specific limit, after which it starts to fall thereby indicating the effect of other pre-dominant parameters.

Bed expansion and fluctuation in cylindrical gas solid fluidized beds with stirred promoters

A profound and fundamental understanding of bed dynamics such as bed expansion ratio and bed fluctuation ratio of irregular particles of binary mixtures has been made in a cylindrical fluidized column for gas solid systems, resulting in a predictive model for fluidized beds. In the present work attempt has been made to study the effect of various system parameters (viz. rotational speed of the promoter, initial static bed height, superficial velocity of the fluidizing medium, particle size and density) on the bed dynamics through experimentation. The correlations for the bed dynamics have been developed on the basis of dimensional analysis. It was observed that the calculated values of bed dynamics agree well with the experimental values in most of the cases.

Experimental and computational study of the bed dynamics of semi‐cylindrical gas–solid fluidized bed

AbstractWith computational fluid dynamics (CFD) it is possible to get a detailed view of the flow behaviour of the fluidized beds. A profound and fundamental understanding of bed dynamics such as bed pressure drop, bed expansion ratio, bed fluctuation ratio, and minimum fluidization velocity of homogeneous binary mixtures has been made in a semi‐cylindrical fluidized column for gas–solid systems, resulting in a predictive model for fluidized beds. In the present work attempt has been made to study the effect of different system parameters (viz., size and density of the bed materials and initial static bed height) on the bed dynamics. The correlations for the bed expansion and bed fluctuations have been developed on the basis of dimensional analysis using these system parameters. Computational study has also been carried out using a commercial CFD package Fluent (Fluent, Inc.). A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied in order to simulate the gas–solid flow. CFD simulated bed pressure drop has been compared with the experimental bed pressure drops under different conditions for which the results show good agreements.

Artificial Neural Network Approach to Segregation Characteristic of Binary Heterogeneous Mixtures in Promoted Gas-Solid Fluidized Beds

Binary mixtures of particles of the same size but of different densities are fluidized in a 15 cm diameter column with a perforated plate distributor and two coaxial promoters. In the present work an attempt has been made to study the fluidization and the segregation characteristic of density-variant solids of the same size in terms of segregation distance. The dimensionless segregation distance has been correlated with other dimensionless groups relating to various system parameters: ratio of the density of jetsam particles to that of flotsam, initial static bed height, height of layer of particles above the bottom grid, superficial gas velocity, and average density of the mixture on the basis of the dimensional analysis approach for both un-promoted and promoted beds. Correlations have also been developed with the above system parameters by using an artificial neural network approach for different types of fluidized beds, and the findings with respect to both approaches have been compared with each other. The values of segregation distance for promoted beds have also been compared with those for the un-promoted bed in this work.

Prediction of gas holdup in a three-phase fluidized bed from bed pressure drop measurement

Experiments were conducted to investigate the overall gas holdup characteristics in a co-current three-phase fluidized bed with liquid as the continuous phase using air, water and glass beads as the gas, liquid and solid phases, respectively. These studies were carried out in a 0.1 m internal diameter, 1.24 m height vertical Plexiglas column with an antenna type air sparger at different water and air flow rates using four different particle sizes and initial static bed heights. Bed pressure drop measurement was used as the basis for the calculation of fractional gas holdup. From the data obtained through a set of experimental runs, an empirical correlation was developed for the overall gas holdup using dimensional analysis and non-linear regression technique and was compared with some existing correlations. It was found that the gas holdup increased with the flow rate of air and decreased with an increase in the water flow rate.

New investigation in regime transition from bubbling to turbulent fluidization

AbstractThe regime transition velocity from bubbling to turbulent fluidization was investigated in a 0.267 m diameter fluidized bed with FCC particles. Different transition velocities and processes are found from the measurements of differential pressure fluctuations and local solids concentration. The measurements of differential pressure fluctuations shows a relatively quicker global regime transition, while the local regime transition obtained from the local solids concentration presents a more gradual process marked by two transition velocities. These transition velocities increase with initial static bed height. For the same initial static bed height, increasing the spacing between two pressure taps leads to lower pressure fluctuations and the appearance of two transition velocities.