The Effect of Superficial Gas Velocity and Aerated Liquid Height on the Spatial Distribution of Local Liquid-Phase Axial Dispersion Coefficients in a Bubble Column

Abstract Industrial gas-liquid processes such as oxidation, hydrogenation, Fischer-Trospch synthesis, liquid-phase methanol synthesis, and nuclear fission are exothermic in nature; the reactor of choice for such processes is, therefore, a bubble column equipped with heat exchanging internals. In addition to maintaining the desired process temperature, the heat exchanging vertical tube internals are used to control flow structures and liquid back mixing. The present work reports the experimentally measured gas hold-up, mean liquid velocity and liquid phase turbulent kinetic energy, using the Radioactive Particle Tracking (RPT) technique, in a 120 mm diameter bubble column equipped with dense vertical tube internals covering 23 % of the total cross-sectional area of the column. The effect of superficial gas velocity (44–265 mm/s) on gas hold-up, mean liquid velocity and turbulent kinetic energy is presented and discussed. It has been inferred from the experimental results that the vertical tube internal located at the center of the column plays a vital role in affecting the hydrodynamics when compared to the conventional internal configurations reported in the literature. For the chosen dense internal configuration, the cross-sectional distribution of the gas holdup, mean liquid velocity and turbulent kinetic energy show asymmetry for all the superficial gas velocities investigated. The overall gas holdup and the liquid turbulence increases with an increase in the superficial gas velocity. The strong liquid circulation velocities have been seen upon the insertion of the dense internals.

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Effect of Surfactants on Gas Holdup in Shear-Thinning Fluids

International Journal of Chemical Engineering ◽

10.1155/2017/9062649 ◽

2017 ◽

Vol 2017 ◽

pp. 1-7 ◽

Cited By ~ 1

Author(s):

Shaobai Li ◽

Siyuan Huang ◽

Jungeng Fan

Keyword(s):

Experimental Data ◽

Liquid Phase ◽

Sodium Dodecyl ◽

Shear Thinning ◽

Gas Holdup ◽

Bubble Columns ◽

Gas Velocity ◽

Shear Thinning Fluids ◽

Liquid Surface Tension ◽

Superficial Gas Velocity

In this study, the gas holdup of bubble swarms in shear-thinning fluids was experimentally studied at superficial gas velocities ranging from 0.001 to 0.02 m·s−1. Carboxylmethyl cellulose (CMC) solutions of 0.2 wt%, 0.6 wt%, and 1.0 wt% with sodium dodecyl sulfate (SDS) as the surfactant were used as the power-law (liquid phase), and nitrogen was used as the gas phase. Effects of SDS concentration, rheological behavior, and physical properties of the liquid phase and superficial gas velocity on gas holdup were investigated. Results indicated that gas holdup increases with increasing superficial gas velocity and decreasing CMC concentration. Moreover, the addition of SDS in CMC solutions increased gas holdup, and the degree increased with the surfactant concentration. An empirical correlation was proposed for evaluating gas holdup as a function of liquid surface tension, density, effective viscosity, rheological property, superficial gas velocity, and geometric characteristics of bubble columns using the experimental data obtained for the different superficial gas velocities and CMC solution concentrations with different surfactant solutions. These proposed correlations reasonably fitted the experimental data obtained for gas holdup in this system.

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The gas holdup in a multiphase reciprocating plate column filled with carboxymethylcellulose solutions

Journal of the Serbian Chemical Society ◽

10.2298/jsc0512533s ◽

2005 ◽

Vol 70 (12) ◽

pp. 1533-1544 ◽

Cited By ~ 3

Author(s):

Ivica Stamenkovic ◽

Olivera Stamenkovic ◽

Ivana Bankovic-Ilic ◽

Miodrag Lazic ◽

Vlada Veljkovic ◽

...

Keyword(s):

Liquid Phase ◽

Power Consumption ◽

Rheological Properties ◽

Gas Holdup ◽

Gas Velocity ◽

Vibration Intensity ◽

Three Phase ◽

Solids Content ◽

Superficial Gas Velocity ◽

Plate Column

Gas holdup was investigated in a gas-liquid and gas-liquid-solid reciprocating plate column (RPC) under various operation conditions. Aqueous carboxymethyl cellulose (sodium salt, CMC) solutions were used as the liquid phase, the solid phase was spheres placed into interplate spaces, and the gas phase was air. The gas holdup in the RPC was influenced by: the vibration intensity, i.e., the power consumption, the superficial gas velocity, the solids content and the rheological properties of the liquid phase. The gas holdup increased with increasing vibration intensity and superficial gas velocity in both the two- and three-phase system. With increasing concentration of the CMC PP 50 solution (Newtonian fluid), the gas holdup decreased, because the coalescence of the bubbles was favored by the higher liquid viscosity. In the case of the CMC PP 200 solutions (non-Newtonian liquids), the gas holdup depends on the combined influence of the rheological properties of the liquid phase, the vibration intensity and the superficial gas velocity. The gas holdup in the three-phase systems was greater than that in the two-phase ones under the same operating conditions. Increasing the solids content has little influence on the gas holdup. The gas holdup was correlated with the power consumption (either the time-averaged or total power consumption) and the superficial gas velocity.

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Mass Transfer Studies in a Novel Perforated Plate Bubble Column

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.2340 ◽

2010 ◽

Vol 8 (1) ◽

Author(s):

S. Dhanasekaran ◽

T. Karunanithi

Keyword(s):

Mass Transfer ◽

Liquid Velocity ◽

Bubble Column ◽

Perforated Plate ◽

Gas Velocity ◽

Plate Spacing ◽

Mass Transfer Studies ◽

Superficial Gas Velocity ◽

Superficial Liquid Velocity

This investigation reports the experimental and theoretical results carried out to evaluate the volumetric mass transfer coefficient (kLa) in a novel hybrid rotating and reciprocating perforated plate bubble column. Countercurrent condition is performed. kLa is studied by the absorption of oxygen from air into deoxygenated water at room temperature (27 ± 1°C). Effects of agitation level, superficial gas velocity, superficial liquid velocity and plate spacing on kLa were analyzed and found to be significant. With an increase in agitation level at a constant superficial gas and liquid velocities, the breakage process of gas bubbles starts to be more pronounced and intensive oxygen mass transfer occurs. Hence, kLa increases sharply. kLa increases with an increase in superficial gas velocity, due to higher gas holdup and the enhanced breakup of bubbles. Similarly, kLa increases with an increase in superficial liquid velocity and the effect is found to be significant. When plate spacing is decreased (by increasing the number of plates), it is observed that the kLa increases at higher superficial gas velocity and agitation level. Correlation is developed for the determination of kLa and found to concur with experimental results. This correlation can be used for the determination of kLa for this hybrid column with 95% accuracy within the range of variables investigated in this present study.

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Hydrodynamic Study of a Gas–liquid–solid Bubble Column Employing CFD–BPBM Method

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2016-0197 ◽

2017 ◽

Vol 15 (4) ◽

Author(s):

Weiling Li ◽

Chuanwen Zhao ◽

Ping Lu

Keyword(s):

Bubble Size ◽

Volume Fraction ◽

Bubble Column ◽

Particle Density ◽

Solid Volume Fraction ◽

Experimental Result ◽

Bubble Coalescence ◽

Phase System ◽

Gas Velocity ◽

Superficial Gas Velocity

Abstract The computational fluid dynamics – bubble population balance model (CFD–BPBM) was employed to predict the hydrodynamic characteristics of a gas–liquid–solid bubble column. A 3D time dependent numerical study was performed and the bubble size distributions at the conditions of different superficial gas velocity (0.089 m/s–0.22 m/s), solid volume fraction (0.03–0.30) and particle density (2500 kg/m3–4800 kg/m3) in the three–phase system were investigated, and the simulation results were compared with the experimental results. The bubble diameters ranging from 1 mm to 64 mm were divided into ten classes. The predicted pressure changing with the bed height had a good agreemeet with the experimental result. The bubble number density predicted decreased when the bubble size increased at each superficial gas velocity, and the bubble coalescence rate became greater than the breakup rate when Ug shifted from 0.089 m/s to 0.16 m/s. The bubble interaction was similar at 0.16 m/s and 0.22 m/s both at particle size dp = 75 μm and 150 μm. The bubble size corresponding to the maximum of the bubble volume fraction increased as Ug increased. The particles can make the bubble break up and coalesce simultaneously when the solid volume fraction was larger than 0.20, and therefore the particles had a contribution to both of the bubble coalescence and breakup in the bubble coalescence regime (Ug = 0.16 m/s). The effect of the particle density was similar with that of the solid volume fraction. Increasing the particle density can enhance the breakup rate of the large bubbles.

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Bubble Diameter and Effective Interfacial Area in a Novel Hybrid Rotating and Reciprocating Perforated Plate Bubble Column

International Journal of Chemical Reactor Engineering ◽

10.1515/1542-6580.2914 ◽

2012 ◽

Vol 10 (1) ◽

Author(s):

Dhanasekaran S ◽

Karunanithi T

Keyword(s):

Liquid Velocity ◽

Bubble Column ◽

Bubble Diameter ◽

Perforated Plate ◽

Interfacial Area ◽

Gas Velocity ◽

The Mean ◽

Superficial Gas Velocity ◽

Plate Column

This investigation reports on the experimental and theoretical investigation carried out to evaluate the bubble diameter and effective interfacial area in a novel Hybrid Rotating and Reciprocating Perforated Plate Bubble Column. Air-water system is used in this investigation. Countercurrent mode is employed. The effects of agitation level, superficial gas velocity and superficial liquid velocity on the bubble size distribution are studied. The mean bubble diameter is predicted using photographic technique. A simple correlation is developed for the determination of mean bubble diameter. It is found that the mean bubble diameter values for hybrid column are 1.8 to 2.5 times smaller when compared with conventional reciprocating plate column. The interfacial area is calculated based on the experimental results of the gas holdup and bubble diameter. Effects of agitation level, superficial gas velocity, superficial liquid velocity and plate free area on the interfacial area have been investigated. Correlations are developed for the determination of interfacial area for both mixer-settler and emulsion regions. It could be noted that the interfacial area for the hybrid column is 3 to 6 times higher in both mixer-settler region and emulsion region than that of conventional reciprocating plate column which is quite large.

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Turbulent axial dispersion coefficients in the liquid in a two-phase bubble column

AIChE Journal ◽

10.1002/aic.690300421 ◽

1984 ◽

Vol 30 (4) ◽

pp. 654-657

Author(s):

I. H. Lehrer

Keyword(s):

Bubble Column ◽

Axial Dispersion ◽

Dispersion Coefficients ◽

Two Phase

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Effects of Chemical Reactions on the Local Hydrodynamics in Slurry Bubble Column Reactors Operating under Typical Fischer-Tropsch Process Conditions – Ii

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2018-0244 ◽

2019 ◽

Vol 17 (9) ◽

Cited By ~ 1

Author(s):

Omar M. Basha ◽

Badie I. Morsi

Keyword(s):

Chemical Reactions ◽

Catalyst Concentration ◽

Bubble Column ◽

Pilot Scale ◽

Catalyst Loading ◽

Cfd Model ◽

Gas Velocity ◽

Cfd Simulations ◽

Bubble Column Reactors ◽

Superficial Gas Velocity

AbstractOur rigorously validated Computational Fluid Dynamics (CFD) model (Basha et al. 2016) was previously used to predict the effects of gas sparger designs and internals configurations on the local hydrodynamics in a pilot-scale and a conceptual large-scale slurry bubble column reactors (SBCRs) (Basha and Morsi 2018). In this study, the CFD model was used to predict the effect of incorporating the F-T reaction kinetics on the local hydrodynamics in the pilot-scale (0.3-m ID, 3-m height) and the overall performance of the pilot-scale and an industrial-scale (5.8-m ID, 42-m height) SBCRS, both operating under F-T conditions with iron catalyst.In the pilot-scale SBCR, the CFD simulations were carried out with catalyst concentrations of 5, 10 and 15 vol% and three H2/Co ratios of 1, 1.5 and 2, at temperature of 443 K, pressure of 20.5 bar and a superficial gas velocity of 0.24 m/s. The predictions showed that the presence of chemical reactions decreased the gas holdup and the Sauter mean bubble diameters along the reactor height by an average of 15.4 % and 17.63 %, respectively and strengthened the liquid circulations near the reactor wall. The predictions also showed that the CO and H2conversions increased with increasing the catalyst concentration, and the pilot scale SBCR could produce a maximum of 1.87 tons/day of C5+products at a catalyst concentration of 15 vol%.In the commercial-scale SBCR, the CFD simulations were conducted at a catalyst loading of 10 vol% at a temperature of 528 K, pressure of 29 bar and four superficial gas velocities of 0.12, 0.24, 0.3 and 0.4 m/s. The calculations were completed, however, the contours of the local hydrodynamics were not extracted due to computational and memory limitations associated with generating graphics of such a large and complex reactor geometry. The predictions showed that the CO conversions were 48 %, 59 %, 58 % and 55 %; the H2conversions were 36 %, 51 %, 56 % and 54 % and the C5+products yields were are 275, 576, 627 and 654 ton/day at the superficial gas velocities of 0.12, 0.24, 0.3 and 0.4 m/s, respectively. When comparing the CFD model predictions with those of the 1-D empirical model developed by Sehabiague et al. (Sehabiague et al. 2015) at a superficial gas velocity of 0.24 m/s and catalyst loading of 10 %, the CFD model was found to predict lower CO conversion, higher H2conversion and higher C5+yield.

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CFD-PBM simulation of hydrodynamics of microbubble column with shear-thinning fluid

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2020-0172 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Xi Zhang ◽

Ping Zhu ◽

Shuaichao Li ◽

Wenyuan Fan ◽

Jingyan Lian

Keyword(s):

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Radial Direction ◽

Liquid Velocity ◽

Bubble Column ◽

Gas Holdup ◽

Gas Velocity ◽

Gas Distributor ◽

Superficial Gas Velocity ◽

The Right

Abstract A numerical simulation was performed to study the hydrodynamics of micro-bubble swarm in bubble column with polyacrylamide (PAM) aqueous solution by using computational fluid dynamics coupled with population balance models (CFD-PBM). By considering rheological characteristics of fluid, this approach was able to accurately predict the features of bubble swarm, and validated by comparing with the experimental results. The gas holdup, turbulent kinetic energy and liquid velocity of bubble column have been elucidated by considering the influences of superficial gas velocity and gas distributor size respectively. The results show that with the rise of the superficial gas velocity, the gas holdup and its peak width increase significantly. Especially, the curve peak corresponding to high gas velocity tends to drift obviously toward the right side. Except for the occurrence of a smooth holdup peak at the column center under the condition of the moderate distributor size, the gas holdups for the small and large distributor sizes become flat in the radial direction respectively. The distribution of turbulent kinetic energy presents an increasingly asymmetrical feature in the radial direction and also its variation amplitude enhances obviously with the rise of gas velocity. The increase in gas distributor size can enhance markedly turbulent kinetic energy as well as its overall influenced width. At the low and moderate superficial gas velocity, the curves of the liquid velocity in radial direction present the Gaussian distributions, whereas the perfect distribution always is broken in the symmetry for high gas velocity. Both liquid velocities around the bubble column center and the ones near both column walls go up consistently with the gas distributor size, especially near the walls at the large distributor size condition.

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Effect of Vibrating Sparger on Mass Transfer, Gas Holdup, and Bubble Size in a Bubble Column Reactor

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2012-0094 ◽

2013 ◽

Vol 11 (1) ◽

pp. 47-56 ◽

Cited By ~ 1

Author(s):

Laleh Hadavand ◽

Ali Fadavi

Keyword(s):

Mass Transfer ◽

Transfer Coefficient ◽

Mass Transfer Coefficient ◽

Vibration Frequency ◽

Bubble Size ◽

Bubble Column ◽

Gas Holdup ◽

Bubble Column Reactor ◽

Gas Velocity ◽

Superficial Gas Velocity

Abstract Bubble size has a key role in gas holdup and mass transfer in bubble column reactors. In order to have small and uniform bubbles, a new structure was designed; the reactor operates in two modes, with vibrating sparger and conventional bubble column in which sparger is fixed. In vibrating mode, the sparger vibrates gently during gas entering. The vibrating sparger performs like a paddle, resulting in a forced recirculation of gas–liquid inside the reactor; moreover, the bubble detachment is accelerated. The superficial gas velocity was between 0.003 and 0.013 ms− 1, and the vibration frequency was changed between 0 and 10.3 Hz. The bubble size was measured at three various positions of the reactor height by photographic method and using MATLAB 7.0.1 software. The mass transfer coefficient was determined by means of the dynamic gassing-out method. The results show that the bubbles were bigger in vibrating mode than those working without vibration. The bubble size decreases with increase in height from sparger. Gas holdup increased with increase in superficial gas velocity and vibration frequency. The effect of vibration increased the gas holdup with an average of 70% for all superficial gas velocities. Volumetric mass transfer coefficient was almost stable as vibration frequency increased.

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