Bubble Column (bubble + column)

Distribution by Scientific Domains
Chemistry95%

Kinds of Bubble Column

  • airlift bubble column
  • external loop airlift bubble column
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  • loop airlift bubble column
  • slurry bubble column
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    Terms modified by Bubble Column

  • bubble column reactor
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    Selected Abstracts

    Energy Efficiency of Two-Phase Mixing in a Modified Bubble Column

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007
    Subrata Kumar Majumder
    Abstract Energy efficiency for gas liquid mixing in a modified downflow bubble column reactor has been analyzed in this paper. Efficiencies of the different parts of the bubble column have been assessed on the basis of energy dissipation. Prediction of the energy dissipation coefficient as well as energy utilization efficiency due to gas-liquid mixing as a function of different physical, geometric and dynamic variables of the system has been done by correlation method. The distribution of energy utilization in the different zones of the column has also been analyzed. Experiments were carried out with air-water and air-aqueous solutions of carboxy methyl cellulose with different concentrations. Dans cet article on a analysé l'efficacité énergétique pour le mélange gaz-liquide dans un réacteur à colonne à bulles à écoulement descendant modifié. Les efficacités des différentes régions de la colonne à bulles ont été évaluées sur la base de la dissipation d'énergie. On a utilisé une méthode de corrélation pour prédire le coefficient de dissipation d'énergie ainsi que l'efficacité d'utilisation de l'énergie due au mélange gaz-liquide en fonction des différentes variables physiques, géométriques et dynamiques du système. La distribution de l'utilisation de l'énergie dans les différentes régions de la colonne a également été analysée. Des expériences ont été menées avec des solutions air-eau et air-solutions aqueuses de carboxyméthylcellulose à différentes concentrations. [source]

    Mixing Time in a Short Bubble Column

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2003
    M Ravinath
    Abstract Mixing time measurements have been carried out in a 0.2m I.D. short bubble column (Hc/D , 5) with different spargers and for different clear liquid height to diameter (HC/D) ratios. Superficial gas velocity has been varied in the range of 0.01m/s to 0.1m/s. Effect of bulk fluid viscosity on the mixing time has also been studied. The circulation cell model, with two fitted parameters viz. number of circulation cells, S and the inter-cell exchange velocity, Ve, has been used to predict and explain the variation in mixing time and the flow pattern in the short bubble column for different types of spargers. On a effectué des mesures de temps de mélange dans une colonne à bulles courte de 0,2 m de diamètre intérieur (Hc/D , 5) munie de différents aérateurs et pour différents rapports entre la hauteur de liquide clair et le diamètre (HC/D). On a fait varier la vitesse de gaz superficielle dans la gamme de 0,01-0,1 m/s. L'effet de la viscosité en masse du fluide sur le temps de mélange est également étudié. On a utilisé le modèle de zones de circulation, comprenant deux paramètres calés, à savoir le nombre de zones de circulation, S, et la vitesse d'échange entre les zones, Ve, pour prédire et expliquer la variation du temps de mélange et le profil d'écoulement dans la colonne à bulles courte pour différents types d'aérateurs. [source]

    Gas-Liquid Mass Transfer Approach applied to the Modeling of Flotation in a Bubble Column

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2008
    J. Chahed
    Abstract A kinetic model developed to describe flotation in a bubble column is presented. This model, developed on the basis of the theory of mass transfer in gas-liquid flows, makes explicit in its formulation the effect of the superficial saturation of bubbles on the kinetics of flotation. The model is applied to the simulation of flotation column experiments for which the classical first-order models, commonly used in flotation modeling, are insufficient to represent the flotation kinetics. The results of the simulations obtained under different hypotheses of simplification and compared to experimental data show that the model succeeds in representing the flotation kinetics in these cases. [source]

    Effect of Suspended Liposomes on Hydrodynamic and Oxygen Transfer Properties in a Mini-Scale External Loop Airlift Bubble Column

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2006
    M. Yoshimoto
    Abstract The circulating liquid velocity, gas holdup, bubble size distribution, and liquid phase oxygen transfer coefficient were measured in a mini-scale external loop airlift bubble column (MELBC) with the liquid volume suspending enzyme-free liposomes of varying diameters. These values were compared to those for liposome-free MELBC, normal bubble column (NBC), and a larger scale airlift column. The liposomes suspended in the MELBC are incorporated into the liquid film around the bubbles, leading to the development of a foam layer, where the incorporated liposomes exert negligible effect on the oxygen transfer in the film. [source]

    Gas-Liquid Mass Transfer in a Slurry Bubble Column at High Slurry Concentrations and High Gas Velocities

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2005
    C. O. Vandu
    Abstract The volumetric mass transfer coefficient kLa in a 0.1,m-diameter bubble column was studied for an air-slurry system. A C9 -C11n -paraffin oil was employed as the liquid phase with fine alumina catalyst carrier particles used as the solid phase. The n -paraffin oil had properties similar to those of the liquid phase in a commercial Fischer-Tropsch reactor under reaction conditions. The superficial gas velocity UG was varied in the range of 0.01 to 0.8,m/s, spanning both the homogeneous and heterogeneous flow regimes. The slurry concentration ,S ranged from 0 to 0.5. The experimental results obtained show that the gas hold-up ,G decreases with an increase in slurry concentration, with this decrease being most significant when ,S < 0.2. kLa/,G was found to be practically independent of the superficial gas velocity when UG > 0.1,m/s is taking on values predominantly between 0.4 and 0.6,s,1 when ,S = 0.1 to 0.4, and 0.29,s,1, when ,S = 0.5. This study provides a practical means for estimating the volumetric mass transfer coefficient kLa in an industrial-size bubble column slurry reactor, with a particular focus on the Fischer-Tropsch process as well as high gas velocities and high slurry concentrations. [source]

    Possibilities and Limits of Application of Electrical Resistance Tomography in Hydrodynamics of Bubble Columns

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2005
    Dominique Toye
    Abstract Knowing the hydrodynamic regime in which is working a bubble column is of great importance because the regime affects strongly the mass transfer between the phases. To this end, we examine the potentialities of an Electrical Resistance Tomography (ERT) device. We analyse cross correlation of electrode pair measurements, of neighbouring pixels and power spectra of averaged pixels within a single plane as well as cross correlations of averaged pixels between two planes, without finding a clear signature of the churn turbulent flow. Variable gas flow rate inputs are used to determine the time resolution of the ERT. L'objet du présent travail est de déterminer dans quelle mesure la Tomographie Électrique Résistive (ERT) peut être utilisée pour détecter le régime hydrodynamique dans lequel fonctionne une colonne à bulles. La connaissance de ce régime est extrêmement importante, en raison notamment de son influence sur les valeurs des paramètres de transfert. Dans ce but, nous avons analysé les spectres de puissance de la valeur moyenne des pixels dans un plan de mesure donné, ainsi que la corrélation temporelle existant entre les mesures de différence de potentiel, entre les pixels voisins d'un plan de mesure donné et entre les valeurs moyennes des pixels appartenant à deux plans de mesure différents. Nous n'avons trouvé aucune signature claire du régime hétérogène. La résolution temporelle de l'ERT a par ailleurs été évaluée en utilisant une alimentation de gaz variable. [source]

    Local Bubble Dynamics and Macroscopic Flow Structure in Bubble Columns with Different Scales

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2003
    Wei Chen
    Abstract Local bubble behaviours were investigated in three bubble columns with different diameters of 200, 400 and 800 mm. By means of a novel single-tip optical fibre probe employing laser Doppler technique, the local gas holdup, bubble frequency, bubble size and velocity were measured simultaneously at different locations of the columns. Measurements were performed in air-water system at superficial gas velocities up to 90 mm/s. The averaged profiles and instantaneous measurements were analyzed and compared for different columns. The presence of a coherent gross circulation structure spanning the entire column diameter in the larger column rather than a pair of symmetrical circulation cells observed in the smaller columns has been confirmed. Les comportements locaux des bulles ont été étudiés dans trois colonnes à bulles de diamètres différents, soient 200, 400 et 800 mm. Au moyen d'une nouvelle sonde à fibre optique à embout unique employant la technique laser Doppler, des mesures locales de la rétention de gaz, de la fréquence des bulles, de la taille des bulles et de la vitesse ont été effectuées simultanément à différents endroits dans les colonnes. Ces mesures ont été effectuées pour un système air-eau à des vitesses de gaz superficielles atteignant 90 mm/s. Les profils moyennés et les mesures instantanées ont été analysés puis comparés pour différentes colonnes. La présence d'une structure de circulation unique cohérente occupant tout le diamètre de la colonne dans la colonne la plus large plutôt qu'une paire de cellules de circulation symétriques observées dans les colonnes plus petites est confirmée. [source]

    Liquid Dispersion in Large Diameter Bubble Columns, with and without Internals

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Ann Forret
    Abstract Liquid mixing has been studied in a 1 m diameter bubble column, with and without internals (vertical cooling tubes). The presence of internals significantly affects both large scale recirculation and local dispersion. The most common approach to model liquid mixing is the one-dimensional axial dispersion model, validated many times in small bubble columns without internals. This paper shows that this model is still appropriate to large columns, but without internals. A two-dimensional model, taking into account a radially dependent axial velocity profile, and both axial and radial dispersion, is required to account for the internals on liquid mixing. Le mélange du liquide dans une colonne à bulles de 1 m de diamètre a été étudié, avec et sans internes (tubes verticaux simulant des échangeurs de chaleur). La présence d'internes affecte de manière significative à la fois la recirculation globale du liquide ainsi que la dispersion locale. L'approche la plus couramment employée pour modéliser le mélange du liquide est le modèle de dispersion axiale mono dimensionnel, validé maintes fois pour les petites colonnes à bulles sans internes. Cet article montre que ce modèle reste valable pour les colonnes de grande taille, sans internes. Par contre, la prise en compte des effets des internes sur le mélange liquide passe par l'utilisation d'un modèle bidimensionnel, prenant en compte le profile radiale de la vitesse axiale ainsi que les dispersions axiale et radiale. [source]

    Measurement and Correlation of Critical Gas and Liquid Velocities for Complete Circulation of Solid Particles in External Loop Airlift Bubble Columns

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Katsumi Nakao
    Abstract The external loop airlift bubble column provides an easy way of good contacting among gas, liquid and solid phases due to a relatively high recirculating liquid velocity UL. The critical gas and liquid velocities for complete circulation of solid particles, UG,C and UL,C, were measured in two different scales of columns with air, tap water and aqueous CMC solutions, and ion exchange resin and glass beads (155,3834 µm) were employed. The UG,C was determined as the inflection point on the plot of the pressure drop due to the suspended solid particles in the downcomer as a function of the gas velocity UG. The critical liquid velocity UL,C corresponding to the UG,C was obtained from the measured relationship between UL and UG. As a result, a unified dimensionless empirical correlation of UL,C was obtained within an error of ±20% and a dimensionless empirical relationship between UL and UG was developed within an error of ±15%. La colonne à bulles de type airlift à boucle externe offre un moyen facile pour le contact entre les phases gazeuse, liquide et solide grâce à la vitesse de liquide en recirculation UL relativement élevée. Les vitesses de gaz et de liquide critiques pour la circulation complète des particules solides, UG,C et UL,C, ont été mesurées dans deux colonnes d'échelle différente avec de l'air, de l'eau du robinet et des solutions aqueuses de CMC, et des billes de verre et de résine échandeuse d'ions (155,3834 µm) ont été employées. La vitesse UG,C est déterminée comme étant le point d'inflexion sur la courbe de la perte de chgarge causée par les particules solides suspendues dans le déversoir en fonction de la vitesse de gaz UG. La vitesse de liquide critique UL.C correspondant à la vitesse UG.C est obtenue à partir de la relation mesurée entre UL et UG. Ainsi, on obtient une corrélation empirique adimensionnelle unifiée de UL.C avec une erreur de ± 20% et une relation empirique adimensionnelle entre UL et UG est établie avec une erreur de ±15%. [source]

    A Method for the Detection of Defluidized Zones in Slurry Bubble Columns

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Ahad Emami
    Abstract The formation of defluidized zones was studied in a laboratory slurry bubble column equipped with heat transfer probes. The probes were small thermistors 2.4 mm in diameter. Dionized water and air were used as a liquid and gas phase, respectively. Solids were fine ceramic particles with mean size of 19.2 ,m and density of 2244 kg/m3. The effects of solids holdup (up to 30 wt% on gas free basis), gas superficial velocity (0.01-0.09 m/s), sparger height (0.01-0.09 m) on defluidized zones formation was studied. Cycle analysis of the local heat transfer fluctuations reliably detected the local formation of defluidized zones for each condition. La formation de zones défluidisées a été étudiée dans une colonne à bulles avec bouillie, équipée de sondes de transfert de chaleur. Les sondes étaient des petits thermistors de 2.4 mm de diamètre. De l'eau déionisée et de l'air constituaient les phases liquide et gazeuse. Les solides étaient des fines particules en céramique avec une taille moyenne de 19.2 µm et une densité de 2244 kg/m3. Les effets de la rétention solide (jusqu'à 30 % en masses sur base sans gaz), de la vitesse superficielle du gaz (0.01-0.09 m/s) et de la hauteur du distributeur de gaz ont été étudiés. L'analyse de cycle du transfert de local de chaleur a détecté de façon fiable la formation locale de zones défluidisées pour chaque condition. [source]

    Intensification of Slurry Bubble Columns by Vibration Excitement

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Jürg Ellenberger
    Abstract We show that application of low-frequency vibrations, in the 30 to 60 Hz range, to the liquid phase of an air , water , silica catalyst slurry bubble column causes significant enhancement of both gas holdup and volumetric mass transfer coefficient over a wide range of superficial gas velocities. The increase in the gas holdup is attributed mainly to a significant reduction in the rise velocity of the bubble swarm due to the generation of standing waves in the column. Furthermore, application of vibrations to the liquid phase serves to stabilize the homogenous bubbly flow regime and delay the onset of the churn-turbulent flow regime. On montre que l'application de vibrations de faibles fréquences (entre 30 et 60 Hz) à la phase liquide d'une colonne à bulles à suspensions de catalyseur air-eau-silice, permet une amélioration significative à la fois du coefficient de rétention de gaz et du coefficient du transfert de matière volumétrique pour une vaste gamme de vitesses de gaz superficielles. L'augmentation de la rétention de gaz est imputée principalement à une réduction importante de la vitesse de montée de l'essaim de bulles qui est due à la création de vagues stationnaires dans la colonne. En outre, l'application des vibrations à la phase liquide sert à stabiliser le régime d'écoulement à bulles homogène et retarde l'apparition du régime d'écoulement agité-pistonnant. [source]

    Comparison, Combination and Validation of Measuring Techniques for Local Flow and Turbulence Analysis in Bubble Columns and Airlift Reactors

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Christophe Vial
    Abstract The applicability of velocimetry techniques based on the Doppler effect , such as laser and ultrasound Doppler velocimetry , for investigating local hydrodynamics in bubble columns and airlift reactors have been extended to non-coalescing media. Their limitations are highlighted, especially as a function of gas sparger and reactor type. The ultrasound technique was shown to be able to measure either bubble or liquid velocity. Differences in local hydrodynamics due to coalescence behaviour were used to support the analysis. Data validation was carried out both by mass balance and by comparison with other techniques, such as electrochemical probes, Pavlov tubes and optical probes. L'applicabilité des techniques de vélocimétrie laser Doppler et de vélocimétrie ultrasonore pour décrire l'hydrodynamique locale dans les colonnes à bulles et les airlifts est étendue aux milieux non-coalescents. On étudie leurs limitations, notamment en fonction du type de distributeur et de réacteur. On montre que la technique ultrasonore permet à la fois la mesure de la vitesse locale des bulles et du liquide. Les différences dues à l'aptitude à la coalescence du milieu sont démontrées. Les résultats sont validés par des bilans et par la comparaison avec d'autres techniques (sonde électrochimique, tube de Pavlov et sonde optique). [source]

    Effect of Gas Density on the Hydrodynamics of Bubble Columns and Three-Phase Fluidized Beds

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Arturo Macchi
    Abstract Experiments were performed at ambient temperature and pressure in a 127 mm inner diameter column with a 55% wt. aqueous glycerol solution, 6-mm spherical borosilicate beads and four gases , helium, air, carbon dioxide and sulphur hexafluoride , giving a 35-fold gas density range. The dispersed bubble flow regime was sustained to higher gas velocities and gas holdups for denser gases. This finding appears to be due to the reduction of the maximum stable bubble size (i.e. enhanced bubble break-up), rather than to formation of smaller bubbles at the distributor with increasing gas density. The effect of gas density was significant both with and without the particles present, with gas holdup increasing, bed voidage increasing and liquid holdup decreasing with increasing gas density. The holdup correlations of Han et al. (1990) have been modified to incorporate the effect of gas density. On a mené des expériences à la température et à la pression ambiante dans une colonne de 127 mm de diamètre intérieur avec une solution de glycérol aqueux de 55 % en poids, des billes de verre de borosilicate sphériques de 6 mm et quatre gaz , hélium, air, gaz carbonique et hexafluorure de soufre , donnant une gamme de densité gazeuse multipliée par 35. Le régime d'écoulement bouillonnant dispersé est maintenu jusqu'à des vitesses et des rétentions de gaz supérieures pour les gaz plus denses. Ce résultat semble être dû à la réduction de la taille de bulle stable maximum (c.-à-d. une rupture de bulles améliorée), plutôt qu'à la formation de bulles plus petites au distributeur avec l'augmentation de la densité gazeuse. L'effet de la densité gazeuse est significatif avec ou sans la présence des particules, avec l'augmentation de la rétention de gaz, l'augmentation du vide du lit et la diminution de la rétention de liquide avec l'augmentation de la densité gazeuse. Les corrélations de rétention de Han et al. (1990) sont modifiées de sorte à introduire l'effet de la densité gazeuse. [source]

    Bubble Size Distribution in Oil-Based Bubble Columns

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2008
    S.-S. Homayouni
    Abstract A practical population balance model was used to evaluate the bubble size distribution in a bubble column. In addition, the bubble size distribution in the bubble column was measured at different gas velocities by photography and analysis of the pictures. Four types of liquid, i.e., water and three petroleum-based liquids, were used in the experiments. The gas phase was air. It was found that the existing models in the literature are not able to satisfactorily predict the experimentally measured bubble size distribution. The model can be corrected by applying a correction factor to the energy dissipation rate. The corrected model fits the experimental bubble size distribution considerably better than the existing models. The variation of this correction factor is reported for different systems at different gas velocities. [source]

    The effect of gas-liquid counter-current operation on gas hold-up in bubble columns using electrical resistance tomography,

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2010
    Haibo Jin
    Abstract BACKGROUND: In order to improve the performance of a counter-current bubble column, radial variations of the gas hold-ups and mean hold-ups were investigated in a 0.160 m i.d. bubble column using electrical resistance tomography with two axial locations (Plane 1 and Plane 2). In all experiments the liquid phase was tap water and the gas phase air. The superficial gas velocity was varied from 0.02 to 0.25 m s,1, and the liquid velocity varied from 0 to 0.01 m s,1. The effect of liquid velocity on the distribution of mean hold-ups and radial gas hold-ups is discussed. RESULTS: The gas hold-up profile in a gas,liquid counter-current bubble column was determined by electrical resistance tomography. The liquid velocity slightly influences the mean hold-up and radial hold-up distribution under the selected operating conditions and the liquid flow improves the transition gas velocity from a homogeneous regime to a heterogeneous regime. Meanwhile, the radial gas hold-up profiles are steeper at the central region of the column with increasing gas velocity. Moreover, the gas hold-up in the centre of the column becomes steeper with increasing liquid velocity. CONCLUSIONS: The value of mean gas hold-ups slightly increases with increasing downward liquid velocity, and more than mean gas hold-ups in batch and co-current operation. According to the experimental results, an empirical correlation for the centreline gas hold-up is obtained based on the effects of gas velocity, liquid velocity, and ratio of axial height to column diameter. The values calculated in this way are in close agreement with experimental data, and compare with literature data on gas hold-ups at the centre of the column. Copyright © 2010 Society of Chemical Industry [source]

    Influence of light quality and intensity in the cultivation of Spirulina platensis from Toliara (Madagascar) in a closed system

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2008
    Pierre H Ravelonandro
    Abstract BACKROUND:Spirulina platensis (Toliara, Madagascar) provides a food supplement which can fight against malnutrition and food insufficiency in Madagascar. In this country, the current production from three open basins is not sufficient to cover needs, and presents drawbacks such as low productivity and possible contamination. Thus cultivation of S. platensis in a closed photobioreactor opens the possibility of extending this microalga production. In this study, the influence of colour and intensity of the light on S. platensis growth and protein content was investigated in a bubble column. RESULTS: Growth kinetics were obtained for four colours (green, white, red and blue) and four intensities (400, 800, 1000 and 1200 lux) of light. The influence of light colour on Spirulina growth was discussed. The highest productivity (183.6 mg L,1 d,1) and concentration (2643 mg L,1) were obtained for green light at 1200 lux. The protein content was 58%. CONCLUSION: Using green light allows improvement of S. platensis growth. Performance obtained with the closed system was higher than that reported in the literature. Copyright © 2008 Society of Chemical Industry [source]

    Enhanced production of lovastatin in a bubble column by Aspergillus terreus using a two-stage feeding strategy

    JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2007
    EM Rodríguez Porcel
    Abstract A two-stage feeding strategy is shown to improve the rate of production of lovastatin by Aspergillus terreus when compared with conventional batch fermentation. The feeding strategy consisted of an initial batch/fed-batch phase and a semi-continuous culture dilution phase with retention of pelleted biomass in a slurry bubble column reactor. The batch phase served only to build up the biomass for producing lovastatin, a secondary metabolite that inhibits its own synthesis in the producing microfungus. The semi-continuous dilution phase provided nutrients to sustain the fungus, but prevented biomass growth by limiting the supply of essential nitrogen. (Synthesis of lovastatin does not require nitrogen.) The preferred pelleted growth morphology that favors lovastatin synthesis was readily obtained and maintained in the 20 L bubble column used. In contrast, a stirred tank fermentation had a substantially lower production of lovastatin because mechanical agitation damaged the fungal pellets. The two-stage feeding method increased lovastatin production rate by more than 50% in comparison with the conventional batch operation. Rheological data for the fungal broth are presented. Copyright © 2007 Society of Chemical Industry [source]

    CFD simulations of hydrodynamic/thermal coupling phenomena in a bubble column with internals

    AICHE JOURNAL, Issue 9 2010
    Cédric Laborde-Boutet
    Abstract CFD simulations have been carried out in a full three-dimensional, unsteady, Eulerian framework to simulate hydrodynamic/thermal coupling in a bubble column with internals. A first part of the study, dedicated to the hydrodynamic/thermal coupling in liquid single-phase flows, showed that assuming constant wall temperature on the internals constitutes a reasonable approximation in lieu of comprehensive simulations encompassing shell flow and coolant flow together. A second part dealing with the hydrodynamics of gas,liquid flows in a bubble column with internals showed that a RNG k,, turbulence model formulation accounting for gas-induced turbulence was a relevant choice. The last part used these conclusions to build a hydrodynamic/thermal coupling model of a gas,liquid flow in a bubble column with internals. With a per-phase RNG k,, turbulence model and assuming constant wall temperature, it was possible to simulate heat transfer phenomena consistent with experimentally measured heat transfer coefficients. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

    Multiphase flow and mixing in dilute bubble swarms

    AICHE JOURNAL, Issue 9 2010
    Stefan Radl
    Abstract High-fidelity three-dimensional (3-D) simulations of multiphase flow and mixing in dilute bubble swarms were performed using the Euler-Lagrange simulation approach. Included was species transport, as well as complex chemical reactions in the simulations. It was found that the algebraic SGS model satisfactory predicts experimental data for the mean flow field. A detailed description of multiphase flow was used and developed to simulate the time evolution of scalar and reactive mixing in a bubble column. An analysis involving the scale of segregation ,, a metric that characterizes the mean driving force for mixing, is applied for the first time to multiphase flow. The study shows that , is inversely proportional to the bubble diameter at constant gas-feed rate, but only a weak function of the gas-feed rate. Also, we observed significant differences of mixing metrics in reactive and nonreactive systems. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

    Influence of elevated pressure and particle lyophobicity on hydrodynamics and gas,liquid mass transfer in slurry bubble columns

    AICHE JOURNAL, Issue 3 2010
    Vinit P. Chilekar
    Abstract This article reports on the influence of elevated pressure and catalyst particle lyophobicity at particle concentrations up to 3 vol % on the hydrodynamics and the gas-to-liquid mass transfer in a slurry bubble column. The study was done with demineralized water (aqueous phase) and Isopar-M oil (organic phase) slurries in a 0.15 m internal diameter bubble column operated at pressures ranging from 0.1 to 1.3 MPa. The overall gas hold-up, the flow regime transition point, the average large bubble diameter, and the centerline liquid velocity were measured along with the gas,liquid mass transfer coefficient. The gas hold-up and the flow regime transition point are not influenced by the presence of lyophilic particles. Lyophobic particles shift the regime transition to a higher gas velocity and cause foam formation. Increasing operating pressure significantly increases the gas hold-up and the regime transition velocity, irrespective of the particle lyophobicity. The gas,liquid mass transfer coefficient is proportional to the gas hold-up for all investigated slurries and is not affected by the particle lyophobicity, the particle concentration, and the operating pressure. A correlation is presented to estimate the gas,liquid mass transfer coefficient as a function of the measured gas hold-up: . © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

    Detecting regime transitions in slurry bubble columns using pressure time series

    AICHE JOURNAL, Issue 7 2005
    Keshav C. Ruthiya
    Abstract Changes in the coherent standard deviation and in the average frequency of measured pressure time series with gas velocity, are proposed, as unique and unambiguous criteria to mark flow regime transitions in slurry bubble columns. In a 2-dimensional (2-D) slurry bubble column, pressure time series are measured at different gas velocities simultaneously with high-speed video recording of the gas-liquid flow. The frequency of occurrence and the average diameter of the large bubbles are determined from video image analysis. The gas velocity where the first large bubbles are detected, with an average diameter of 1.5 cm, and with a frequency of occurrence of one bubble per s, is designated as the first regime transition point (transition from the homogeneous regime to the transition regime). At this point, the coherent standard deviation of the measured pressure fluctuations clearly increases from zero. The gas velocity where the average diameter and the frequency of occurrence of the large bubbles become constant, is designated as the second regime transition point (transition from the transition regime to the heterogeneous regime). From this point onward, the slope of the coherent standard deviation of the measured pressure fluctuations clearly decreases with gas velocity, while the average frequency becomes constant. These clear changes with gas velocity in the coherent standard deviation, and in the average frequency are also demonstrated in a 3-D slurry bubble column. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source]

    The reaction of mixtures of [Rh4(CO)12] and triphenylphosphite with carbon monoxide or syngas as studied by high-resolution, high-pressure NMR spectroscopy,

    MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2008
    Gillian Overend
    Abstract The fragmentation and redistribution reactions of [Rh4(CO)12,x{P(OPh)3}x] (x = 1,4) with carbon monoxide have been studied using high-resolution, high-pressure NMR spectroscopy. Under the conditions of efficient gas mixing in a high-pressure NMR bubble column, [Rh4(CO)9{P(OPh)3}3] fragments to give mainly [Rh2(CO)6{P(OPh)3}2]; [Rh4(CO)11{P(OPh)3}] is also observed, implying redistribution of the phosphite ligand and/or recombination of the dimers to tetrameric clusters. Fragmentation of [Rh4(CO)10{P(OPh)3}2] is found to be pressure-dependent giving predominantly [Rh2(CO)6{P(OPh)3}2] at low CO pressure (1,40 bar), and increasing amounts of [Rh2(CO)7{P(OPh)3}] at higher (40,80 bar) pressure. Using Syngas (CO : H2 (1:1)) instead of CO in the above fragmentations, homolytic addition of H2 to the dimer [Rh2(CO)6{P(OPh)3}2] to give [RhH(CO)3{P(OPh3}] and [RhH(CO)2{P(OPh)3}2] is observed. The distribution of tetrameric species obtained is similar to that obtained under the same partial pressure of CO. On depressurisation/out-gassing of the sample, the original mixture of tetrameric clusters is obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Destabilisation of homogeneous bubbly flow in an annular gap bubble column

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
    Fahd M. Al-Oufi
    Abstract Experimental results are presented to show that there are very significant differences in the mean gas void fractions measured in an open tube and a annular gap bubble column, when operated at the same gas superficial velocity, using a porous sparger. Measurements were carried out in a vertical 0.102,m internal diameter column, with a range of concentric inner tubes to form an annular gap, giving diameter ratios from 0.25 to 0.69; gas superficial velocities in the range 0.014,0.200,m/s were investigated. The mean gas void fraction decreases with increasing ratio of the inner to outer diameter of the annular gap column and the transition to heterogeneous flow occurs at lower gas superficial velocities and lower void fractions. Two reasons are proposed and validated by experimental investigations: (1) the presence of the inner tube causes large bubbles to form near the sparger, which destabilise the homogeneous bubbly flow and reduce the mean void fraction; this was confirmed by deliberately injecting large bubbles into a homogeneous dispersion of smaller bubbles, and (2) the shape of the void fraction profiles changes with gap geometry and this affects the distribution parameter in the drift-flux model. Both of these effects serve to reduce the mean gas void fraction in an annular gap bubble column compared to an open tube at the same gas superficial velocity. Des résultats expérimentaux sont présentés pour montrer qu'il existe de très grandes différences dans les fractions de vide gazeux moyennes mesurées dans un tube ouvert et une colonne à bulles à espace annulaire, lorsqu'ils sont utilisés à la même vitesse superficielle de gaz, au moyen d'un aérateur poreux. On a effectué des mesures dans une colonne verticale avec un diamètre interne de 0.102,m, avec une portée de tubes internes concentriques pour former un espace annulaire, procurant des rapports de diamètre de 0.25 à 0.69; des vitesses superficielles de gaz de 0.014 à 0.200,m/s ont été étudiées. La fraction de vide gazeux moyenne diminue avec le rapport croissant du diamètre interne à externe de la colonne à espace annulaire et la transition à la circulation hétérogène se produit à des vitesses superficielles de gaz et fractions de vide plus basses. Deux raisons sont proposées et validés par les vérifications expérimentales: (1) la présence du tube interne provoque la formation de grandes bulles près de l'aérateur, ce qui déstabilize l'écoulement à bulles homogène et réduit la fraction de vide moyenne; cet état a été confirmé en injectant délibérément de grandes bulles dans une dispersion homogène de plus petites bulles et, (2) la forme des profils de fraction de vide change avec la géométrie de l'espace qui les sépare, ce qui a des conséquences sur le paramètre de distribution du modèle à flux de dérive. Ces deux effets servent à réduire la fraction de vide gazeux moyenne dans une colonne à bulles à espace annulaire, en comparaison avec un tube ouvert à la même vitesse superficielle de gaz. [source]

    Bubble shape, gas flow and gas,liquid mass transfer in pulp fibre suspensions

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010
    L. K. Ishkintana
    Abstract Gas,liquid mass transfer in pulp fibre suspensions in a batch-operated bubble column is explained by observations of bubble size and shape made in a 2D column. Two pulp fibre suspensions (hardwood and softwood kraft) were studied over a range of suspension mass concentrations and gas flow rates. For a given gas flow rate, bubble size was found to increase as suspension concentration increased, moving from smaller spherical/elliptical bubbles to larger spherical-capped/dimpled-elliptical bubbles. At relatively low mass concentrations (Cm,=,2,3% for the softwood and Cm,,,7% for the hardwood pulp) distinct bubbles were no longer observed in the suspension. Instead, a network of channels formed through which gas flowed. In the bubble column, the volumetric gas,liquid mass transfer rate, kLa, decreased with increasing suspension concentration. From the 2D studies, this occurred as bubble size and rise velocity increased, which would decrease overall bubble surface area and gas holdup in the column. A minimum in kLa occurred between Cm,=,2% and 4% which depended on pulp type and was reached near the mass concentration where the flow channels first formed. le transfert de masse gaz-liquide dans des suspensions de fibres de pulpe, dans une colonne à bulles de traitement en lot, est expliqué par des observations faites dans une colonne 2D de la taille et de la forme des bulles. Deux suspensions de fibres de pulpe (pulpes kraft de bois dur et de bois tendre) ont été étudiées sur un intervalle de concentrations en masse des suspensions et sur un intervalle de débits de gaz. Pour un débit de gaz donné, on a observé que la taille des bulles augmentait avec l'augmentation de la concentration de la suspension, passant de petites bulles sphériques/elliptiques à des bulles plus grosses de forme quasi-sphérique avec capuchon à elliptique avec dépression. À des concentrations en masse relativement basses (Cm,=,2,3% pour le bois tendre et Cm,=,,7% pour la pulpe de bois dur), des bulles distinctes n'étaient plus observées dans la suspension. Au lieu de cela, un réseau de canaux se formait, au travers duquel le gaz s'écoulait. Dans la colonne à bulles, le taux de transfert de masse volumétrique gaz-liquide, kLa, diminuait avec l'augmentation de la concentration de la suspension. À partir des études 2D, cela se produisait lorsque la taille des bulles et la vélocité ascendante augmentaient, ce qui devrait faire diminuer la surface d'ensemble des bulles et la retenue de gaz dans la colonne. Un minimum de kLa a été observé avec Cm,=,2% et 4% (selon le type de pulpe) et était atteint à proximité de la concentration en masse pour laquelle les canaux d'écoulement commençaient à se former. [source]

    Energy Efficiency of Two-Phase Mixing in a Modified Bubble Column

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007
    Subrata Kumar Majumder
    Abstract Energy efficiency for gas liquid mixing in a modified downflow bubble column reactor has been analyzed in this paper. Efficiencies of the different parts of the bubble column have been assessed on the basis of energy dissipation. Prediction of the energy dissipation coefficient as well as energy utilization efficiency due to gas-liquid mixing as a function of different physical, geometric and dynamic variables of the system has been done by correlation method. The distribution of energy utilization in the different zones of the column has also been analyzed. Experiments were carried out with air-water and air-aqueous solutions of carboxy methyl cellulose with different concentrations. Dans cet article on a analysé l'efficacité énergétique pour le mélange gaz-liquide dans un réacteur à colonne à bulles à écoulement descendant modifié. Les efficacités des différentes régions de la colonne à bulles ont été évaluées sur la base de la dissipation d'énergie. On a utilisé une méthode de corrélation pour prédire le coefficient de dissipation d'énergie ainsi que l'efficacité d'utilisation de l'énergie due au mélange gaz-liquide en fonction des différentes variables physiques, géométriques et dynamiques du système. La distribution de l'utilisation de l'énergie dans les différentes régions de la colonne a également été analysée. Des expériences ont été menées avec des solutions air-eau et air-solutions aqueuses de carboxyméthylcellulose à différentes concentrations. [source]

    A Study on Hydrodynamics and Heat Transfer in a Bubble Column Reactor with Yeast and Bacterial Cell Suspensions

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2005
    Nigar Kantarci
    Abstract Hydrodynamics and heat transfer experiments were carried out in a slurry bubble column with air-water-yeast cells and air-water-bacteria cells systems to investigate gas hold-up, bubble characteristics and heat transfer coefficients with cell concentrations of 0.1% w/w and 0.4% w/w and superficial gas velocity up to 0.20 m/s. The gas hold-ups and heat transfer coefficients were found to increase with increasing gas velocity and cell concentration. The heat transfer coefficients were higher at the centre of the column as compared to the near wall region. The development of empirical correlations to predict the heat transfer coefficient in two- and three-phase systems was carried out with ±15% confidence interval at most. On a réalisé des expériences d'hydrodynamique et de transfert de chaleur dans une colonne triphasique gaz-liquide-solide avec des systèmes de cellules air-eau-levure et de cellules air-eau-bactéries afin d'étudier la rétention de gaz, les caractéristiques des bulles et les coefficients de transfert de chaleur avec des concentrations de cellules de 0,1 % en poids et 0,4 % en poids et des vitesses de gaz superficielles jusqu'à 0,20 m/s. On a trouvé que les rétentions de gaz et les coefficients de transfert de chaleur augmentaient avec la vitesse de gaz et la concentration en cellules. Les coefficients de transfert de chaleur sont plus grands au centre de la colonne que dans la région proche de la paroi. Des corrélations empiriques pour prédire le coefficient de transfert de chaleur dans des systèmes bi et triphasiques ont été établies avec un écart de confiance inférieur ou égal à ± 15%. [source]

    Possibilities and Limits of Application of Electrical Resistance Tomography in Hydrodynamics of Bubble Columns

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2005
    Dominique Toye
    Abstract Knowing the hydrodynamic regime in which is working a bubble column is of great importance because the regime affects strongly the mass transfer between the phases. To this end, we examine the potentialities of an Electrical Resistance Tomography (ERT) device. We analyse cross correlation of electrode pair measurements, of neighbouring pixels and power spectra of averaged pixels within a single plane as well as cross correlations of averaged pixels between two planes, without finding a clear signature of the churn turbulent flow. Variable gas flow rate inputs are used to determine the time resolution of the ERT. L'objet du présent travail est de déterminer dans quelle mesure la Tomographie Électrique Résistive (ERT) peut être utilisée pour détecter le régime hydrodynamique dans lequel fonctionne une colonne à bulles. La connaissance de ce régime est extrêmement importante, en raison notamment de son influence sur les valeurs des paramètres de transfert. Dans ce but, nous avons analysé les spectres de puissance de la valeur moyenne des pixels dans un plan de mesure donné, ainsi que la corrélation temporelle existant entre les mesures de différence de potentiel, entre les pixels voisins d'un plan de mesure donné et entre les valeurs moyennes des pixels appartenant à deux plans de mesure différents. Nous n'avons trouvé aucune signature claire du régime hétérogène. La résolution temporelle de l'ERT a par ailleurs été évaluée en utilisant une alimentation de gaz variable. [source]

    Liquid Dispersion in Large Diameter Bubble Columns, with and without Internals

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Ann Forret
    Abstract Liquid mixing has been studied in a 1 m diameter bubble column, with and without internals (vertical cooling tubes). The presence of internals significantly affects both large scale recirculation and local dispersion. The most common approach to model liquid mixing is the one-dimensional axial dispersion model, validated many times in small bubble columns without internals. This paper shows that this model is still appropriate to large columns, but without internals. A two-dimensional model, taking into account a radially dependent axial velocity profile, and both axial and radial dispersion, is required to account for the internals on liquid mixing. Le mélange du liquide dans une colonne à bulles de 1 m de diamètre a été étudié, avec et sans internes (tubes verticaux simulant des échangeurs de chaleur). La présence d'internes affecte de manière significative à la fois la recirculation globale du liquide ainsi que la dispersion locale. L'approche la plus couramment employée pour modéliser le mélange du liquide est le modèle de dispersion axiale mono dimensionnel, validé maintes fois pour les petites colonnes à bulles sans internes. Cet article montre que ce modèle reste valable pour les colonnes de grande taille, sans internes. Par contre, la prise en compte des effets des internes sur le mélange liquide passe par l'utilisation d'un modèle bidimensionnel, prenant en compte le profile radiale de la vitesse axiale ainsi que les dispersions axiale et radiale. [source]

    A Method for the Detection of Defluidized Zones in Slurry Bubble Columns

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Ahad Emami
    Abstract The formation of defluidized zones was studied in a laboratory slurry bubble column equipped with heat transfer probes. The probes were small thermistors 2.4 mm in diameter. Dionized water and air were used as a liquid and gas phase, respectively. Solids were fine ceramic particles with mean size of 19.2 ,m and density of 2244 kg/m3. The effects of solids holdup (up to 30 wt% on gas free basis), gas superficial velocity (0.01-0.09 m/s), sparger height (0.01-0.09 m) on defluidized zones formation was studied. Cycle analysis of the local heat transfer fluctuations reliably detected the local formation of defluidized zones for each condition. La formation de zones défluidisées a été étudiée dans une colonne à bulles avec bouillie, équipée de sondes de transfert de chaleur. Les sondes étaient des petits thermistors de 2.4 mm de diamètre. De l'eau déionisée et de l'air constituaient les phases liquide et gazeuse. Les solides étaient des fines particules en céramique avec une taille moyenne de 19.2 µm et une densité de 2244 kg/m3. Les effets de la rétention solide (jusqu'à 30 % en masses sur base sans gaz), de la vitesse superficielle du gaz (0.01-0.09 m/s) et de la hauteur du distributeur de gaz ont été étudiés. L'analyse de cycle du transfert de local de chaleur a détecté de façon fiable la formation locale de zones défluidisées pour chaque condition. [source]

    2D Slurry Bubble Column Hydrodynamic Phenomena Clarified with a 3D Gas,Liquid Model

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2003
    Jeroen H. J. Kluytmans
    Abstract The gas hold-up in a 2D bubble column is modelled using a 3D gas hold-up model. The influence of the scale of 2D bubble columns on several parameters, for instance, transition gas hold-up, transition gas velocity, and bubble rise velocities, is investigated and related to 3D bubble columns. By adapting the rise velocity of the large bubbles of an existing 3D bubble column model (Krishna et al., 2001a), the gas hold-up in both the homogeneous and the heterogeneous regime can be described satisfactorily. By adjusting the transition points only, it is also possible to describe the gas hold-up in systems containing small amounts of carbon particles and electrolyte. The smallest dimension of the 2D slurry bubble column, the column thickness, influences the location of the regime transition point. In the heterogeneous regime, however, it is only the largest column dimension, the column width, that influences the gas hold-up. These observations together enable proper 2D/3D bubble column comparison in future studies. Dans cette étude, la rétention de gaz dans une colonne à bulles en 2D est modélisée à l'aide d'un modèle de rétention de gaz en 3D. L'influence de l'échelle des colonnes à bulles 2D sur plusieurs paramètres, comme la rétention de gaz de transition, la vitesse de gaz de transition et les vitesses de montée des bulles, est étudiée et reliée aux colonnes à bulles 3D. On montre qu'en adaptant la vitesse de montée des bulles larges fournie par un modèle de colonnes à bulles 3D existant (Krishna et al., 2001a), la rétention de gaz tant en régime homogène qu'hétérogène peut être décrite de manière satisfaisante. En ajustant seulement les points de transition, il est également possible de décrire la rétention de gaz dans des systèmes contenant de petites quantités de particules de carbone et d'électrolyte. On a trouvé que la plus petite dimension de la colonne à bulles à suspensions 2D, soit l'épaisseur de la colonne, influence la position du point de transition de régime. Cependant, dans le régime hétérogène, c'est seulement la plus grande dimension de la colonne, soit la largeur de la colonne, qui influence la rétention de gaz. Toutes ces observations vont permettre des comparaisons adéquates des colonnes 2D et 3D dans les prochaines études. [source]