Experimental study of gas hold-up and bubble behavior in gas-liquid bubble column (original) (raw)
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Effect of gas properties on the characteristics of a bubble column equipped with fine porous sparger
2016
The purpose of this work is to check the validity of previously proposed correlations concerning the parameters that affect the operation of bubble columns by conducting experiments with various gases. The effect of gas properties on the performance of a bubble column reactor with fine pore sparger is investigated by employing various gases (i.e., air, CO2, He) that cover a wide range of physical property values, while the liquid phase is de-ionized water. A fast video technique is employed for visual observations and, combined with image processing, is used for collecting data regarding gas holdup and bubble size distribution. Previously proposed correlations for predicting the transition point from the homogeneous to the heterogeneous regime, the gas holdup and the Sauter mean bubble diameter are slightly modified to include the effect of gas phase properties. It is found that the new correlations can predict the aforementioned quantities with reasonable accuracy.
Review of Gas Holdup Characteristics of Bubble Column Reactors
International Journal of Chemical Engineering Research
Gas-liquid bubble columns are used extensively in the process industries. The gas-liquid two phase flow prevailing in this type of process equipment is extremely complex, inherently unsteady and dominated by phenomena with widely varying time-and length-scales. It is for this reason that many important fluid dynamical aspects of gas-liquid bubble columns are still poorly understood and difficult to predict a priori. This paper aims to contribute to our understanding of the gas holdup characteristics of gas-liquid bubble column reactors by reviewing recently published studies. Three-phase bubble column reactors are widely employed in reaction engineering, i.e. in the presence of a catalyst and in biochemical applications where microorganisms are utilized as solid suspensions in order to manufacture industrially valuable bioproducts. Investigation of design parameters characterizing the operation and transport phenomena of bubble columns have led to better understanding of the hydrodynamic properties, heat and mass transfer mechanisms and flow regime characteristics ongoing during the operation. Moreover, experimental studies are supported with computational fluid dynamics (CFDs) simulations and developed mathematical models to describe better the phenomena taking place in a bubble column reactor. This review focuses on bubble column reactors, their description, design and operation, application areas, fluid dynamics and regime analysis encountered and parameters characterizing the operation are presented together with the findings of published studies. This work is the extension of work done by Kuntlu O Ulgen et al.,(2005).
Effect of liquid properties on the performance of bubble column reactors with fine pore spargers
Chemical Engineering Science, 2005
This work is a study of the effect of liquid properties on the performance of bubble column reactors with fine pore spargers. Various liquids covering a range of surface tension and viscosity values are employed, while the gas phase is atmospheric air. A fast video technique is used for visual observations and, combined with image processing, is used for gas holdup and bubble size measurements. New data on average gas holdup values, bubble size distributions and Sauter diameters are presented and are consistent with existing physical models on coalescence/breakage. A correlation based on dimensionless groups for the prediction of gas holdup in the homogeneous regime is proposed and found to be in good agreement with available data.
Study on the Gas Holdup of Triangular Pitch and Square Pitch Sparger Geometry in Bubble Column
Gas holdup in a bubble column has been studied for triangular and square geometries of a pitch sparger. The investigation was carried out in a bubble col-umn characterized by an aspect ratio equal to four. The column was made up of plexiglas, equipped with sparger. The top of the column was open to atmo-sphere. The column was also equipped with appropriate rotameters for gas phase flow measurement and control. The liquids used in experiments were: deionised water, glycerin (50 %) and butanol (1.5 %) with atmospheric air representing the gas phase. A high-speed digital video camera was employed for the measuring of bubble rise velocity. The recorded images are also used to obtain an insight into the coalescence/breakage mechanisms occurring during bubble formation at the vicinity of the sparger. Using the appropriate software, rise velocity of the bubbles after their detachment from the triangular and square pitch spargers can be obtained from recorded images for examined liquid and ...
Chemical Engineering Journal, 2006
A comprehensive literature search was conducted to obtain the holdup data for different gases in various liquids and slurries using bubble and slurry bubble column reactors operating under wide ranges of conditions in different size reactors provided with a variety of gas spargers. The data were used to develop two novel correlations, one for the total gas holdup and the other for the holdup of large gas bubbles. The total gas holdup correlation is capable of predicting the experimental data within an absolute average relative error (AARE) and standard deviation (σ) of 20%, whereas the correlation of the holdup of large bubbles is capable of predicting the experimental values within AARE and σ of about 25 and 27%, respectively. The novel correlations were used to predict the effects of pressure, temperature, gas velocity, solid concentration, rector size, and distributor type on the holdup of syngas (H 2 /CO = 2) in various slurry bubble column reactors (SBCRs) operating under typical Fischer-Tropsch conditions.
Chemical Engineering Science, 2007
New experimental data concerning the gas holdup in bubble columns equipped with porous sparger were acquired. The effect of liquid properties and sparger characteristic (i.e., pore size, dimensions) on gas holdup at the pseudo-homogeneous regime has been studied and a correlation regarding the prediction of the transition point from the pseudo-homogeneous to the heterogeneous regime has been proposed and found to be in good agreement with available data. Moreover, a previously proposed correlation [Mouza, A.A., Dalakoglou, G.K., Paras, S.V., 2005. Effect of liquid properties on the performance of bubble column reactors with fine pore spargers. Chemical Engineering Science 60(5), 1465-1475], for the prediction of gas holdup at the homogeneous regime for this type of equipment, has been modified to take into account the effect of the mean pore diameter and it is also found to be in good agreement with published data. ᭧
Industrial & Engineering Chemistry Research, 1999
The effects of gas velocity, system pressure, and catalyst loading on gas holdup of H 2 , N 2 , CO, and CH 4 in an organic mixture of hexanes were investigated in a 0.316 m diameter, 2.8 m height slurry bubble column reactor operating with a commercial Fischer-Tropsch iron-based catalyst. The data were obtained in the churn-turbulent flow regime with catalyst loading up to 50 wt % and a system pressure up to 8 bar. The hydrostatic pressure head method and the dynamic gas disengagement technique were employed to obtain the gas holdup profile and the values corresponding to different gas bubble sizes in the reactor. The experimental data showed that the gas holdup consists mainly of two classes of gas bubbles, small and large. The gas holdup data for the gases used were found to increase with pressure and superficial gas velocity due to the increase of the volume fraction of the small and large gas bubbles, respectively. The increase of catalyst loading, however, appeared to decrease the gas holdup values, due to the decrease of the volume fraction of the small gas bubbles. Statistical and empirical correlations for gas holdup data were proposed.
IMPROVED GAS HOLDUP IN NOVEL BUBBLE COLUMN
This investigation reports the experimental and theoretical results carried out to evaluate the gas holdup for air-water system in a novel hybrid rotating and reciprocating perforated plate bubble column under countercurrent condition. The response of this hybrid column is found to be similar to that of reciprocating plate column (RPC) showing mixer-settler, transition, and emulsion regions. The effect of agitation level, superficial gas velocity, superficial liquid velocity, perforation diameter, and plate spacing on gas holdup is studied and found to be significant. The gas holdup is found to be least in the range of agitation level of 1.3-1.5 cm/s. For all the superficial gas and liquid velocities considered in this present investigation, the critical agitation level at minimum gas holdup remains nearly same. The gas holdup in this hybrid column is 1.2-1.7 times higher in mixer-settler region and 2.1-2.7 times higher in emulsion region than that of RPC. Correlations have been developed and found to concur with the experimental values. It can be used with 95% accuracy.
CFD Analysis of Phase Holdup Behaviour in a Gas-Liquid Bubble Column
2021
Experimental works on bubble column hydrodynamic are normally carried out on a laboratory scale less than 0.3 m with holes number less than 10. In this paper, we discuss several approaches to bubble column scale-up, relying on variables of parameters. Two spargers with different hole diameters (0.5 mm and 1.25 mm) and superficial gas velocities (0.0125 m/s and 0.0501 m/s) are used to determine the distribution of gas holdup and liquid flow pattern. An Insignificant level of bed heights is investigated for the efficiency of hydrodynamic performance. Computational Fluid Dynamic (CFD) is used as the realistic representation of the actual reactor. The flow of the gas-liquid interface is implemented using the VOF model using the finite volume method by tracking the volume fraction of each of the fluids throughout the domain. It is observed that the initial bed heights, superficial gas velocity, and hole diameter of the sparger influence the overall gas holdup. Although the difference in ...
Korean Journal of Chemical Engineering, 2009
Flow properties of gas phase reactants such as size, rising velocity and frequency were investigated in simulated three-phase slurry bubble column reactors. Effects of gas velocity, reactor pressure, liquid viscosity, solid content in the slurry phase and column diameter on the flow properties of a gas reactant were determined. The multiple effects of operating variables on the bubble properties were well visualized by means of contour maps. The effects of operating variables on the flow properties of bubbles changed with changing column diameter of the reactor. The size, rising velocity and frequency of reactant gas bubbles were well correlated in terms of operating variables including column diameter of the reactor.