Sparged Systems Research Articles

Effects of Equipment and Process Variables on the Suspension of Buoyant Particles in Gas-Sparged Vessels

Previous work (Bao et al., 2005) reported the influence of solid concentration and agitator selection on the just-drawdown agitation speed and gas holdup in three-phase reactors containing nonwetting buoyant solids. This paper reports experimental results for the unaerated and aerated aqueous suspension of buoyant (polypropylene and polyethylene) particles in a tall vessel of 0.476 m diameter. The composite agitators used a concave blade dispersing impeller surmounted by one or two up-pumping wide-blade hydrofoils. To find the influence of the density and size of particles on the drawdown of particles, all solids were cleaned up to four times with pure alcohol until they were hydrophilic. The influence on suspension and gas retention of solid density (900-955 kg.m -3 ) and size (0.5-4 mm), baffle width, and agitator centering have been studied. There is little difference in the gas retention behavior in the presence of similarly sized different particles. Gas holdup is relatively unaffected by particle size, though particles <1 mm tend to reduce gas retention. Baffle width has significant effects: drawdown is easier with either narrow-or full-width baffles than with midwidth baffles, which need higher agitator speeds. In a fully baffled three-phase system, the drawdown of buoyant particles results from the bulk velocity and turbulence intensity, while with narrow baffles, conditions appear to be controlled by the development of a central vortex. However, gas dispersion in such a partially baffled system is not as effective as when fully baffled, so the fully baffled conditions are recommended for the sparged drawdown of buoyant particles. Despite the possible mechanical drawbacks, off-centered agitators achieve effective drawdown of buoyant particles in both sparged and unaerated systems. Off-centering the agitator does not affect the retained void fraction except at low gassing rates and specific power input.

Gas/Liquid Mass Transfer in Hot Sparged Systems

AbstractUnderstanding the effect of temperature on the volumetric mass transfer rate is of vital importance for the design of chemical reactors operated at elevated temperatures. The present study is motivated by a poor understanding of this effect due to previous limited investigations. Such an effect has been studied at the CSIRO Energy &amp; Thermofluids Engineering Laboratory in a mechanically agitated air‐water mixing tank with operating temperatures in the range of 20‐80d̀C at atmospheric pressure. The oxygen concentration of the liquid is measured by a dissolved oxygen probe. The volumetric mass transfer rate is estimated using a dynamic method. It has been found that the saturated oxygen concentration of the liquid does not change significantly with the gas sparging rate and impeller speed. The change of temperature affects the saturated oxygen concentration significantly. The volumetric mass transfer rate increases with the increase of liquid temperature in the range of 18‐60d̀C. Beyond 60d̀C, the transfer rate decreases. Such a decrease is mainly due to the dramatic drop in the gas void fraction.

Advances in biotreatment of acid mine drainage and biorecovery of metals: 2. Membrane bioreactor system for sulfate reduction.

Several biotreatmemt techniques for sulfate conversion by the sulfate reducing bacteria (SRB) have been proposed in the past, however few of them have been practically applied to treat sulfate containing acid mine drainage (AMD). This research deals with development of an innovative polypropylene hollow fiber membrane bioreactor system for the treatment of acid mine water from the Berkeley Pit, Butte, MT, using hydrogen consuming SRB biofilms. The advantages of using the membrane bioreactor over the conventional tall liquid phase sparged gas bioreactor systems are: large microporous membrane surface to the liquid phase; formation of hydrogen sulfide outside the membrane, preventing the mixing with the pressurized hydrogen gas inside the membrane; no requirement of gas recycle compressor; membrane surface is suitable for immobilization of active SRB, resulting in the formation of biofilms, thus preventing washout problems associated with suspended culture reactors; and lower operating costs in membrane bioreactors, eliminating gas recompression and gas recycle costs. Information is provided on sulfate reduction rate studies and on biokinetic tests with suspended SRB in anaerobic digester sludge and sediment master culture reactors and with SRB biofilms in bench-scale SRB membrane bioreactors. Biokinetic parameters have been determined using biokinetic models for the master culture and membrane bioreactor systems. Data are presented on the effect of acid mine water sulfate loading at 25, 50, 75 and 100 ml/min in scale-up SRB membrane units, under varied temperatures (25, 35 and 40 degrees C) to determine and optimize sulfate conversions for an effective AMD biotreatment. Pilot-scale studies have generated data on the effect of flow rates of acid mine water (MGD) and varied inlet sulfate concentrations in the influents on the resultant outlet sulfate concentration in the effluents and on the number of SRB membrane modules needed for the desired sulfate conversion in those systems. The pilot-scale data indicate that the SRB membrane bioreactors systems can be applied toward field-scale biotreatment of AMD and for recovery of high purity metals and an agriculturally usable water.

Micromixing in Boiling and Hot Sparged Systems: Development of a New Reaction Pair

The relevance of micromixing in fast reactions can be characterized by measuring the product distribution of a known test reaction. Although several test reaction systems have been published none is suitable for boiling or nearly boiling conditions. This paper presents details of a new test reaction system suitable for sparged aqueous systems at temperatures up to 100°C. This system, which is easy to use, provides the basis for experiments carried out in a standard semi-batch stirred tank reactor (STR) agitated with a Chemineer CD-6 hollow-blade impeller. The quantitative characterization provided by liquid micromixing sheds light on the effect of temperature, and hence vapour pressure, in the operation of gas–liquid reactors.

Gas Dispersion in Sparged and Boiling Reactors

Gas holdup measurements in cold gassed, hot sparged and boiling systems using different agitators with multiple modern hollow blade and up-pumping wide-blade hydrofoil impellers are reported. In a cold gassed system with given gas flow rates and power input, the different multiple impeller configurations generate very similar gas holdup. The gas holdup in a hot sparged system, between 70°C and 90°C, is only about half that in a cold system with the same total gas flow rate and power input. Moreover, at the higher temperatures there are unexpected and very significant differences between the gas holdup achieved by the different agitators. With most vapour generation occurring near the liquid surface, the vapour holdup in an unsparged boiling system is much lower than that for either cold gassed or hot sparged systems with similar total gas flow rate and power input. These results are of particular relevance to the design and operation of reactors with hot sparging or boiling liquids.

Void fraction distribution in sparged and boiling reactors with modern impeller configuration

Vertical void fraction distributions in cold gassed, hot sparged and boiling systems using different agitators with multiple modern hollow blade and up-pumping wide-blade hydrofoil impellers are reported. The void fraction in boiling systems is dramatically different from that in cold gassed or hot sparged systems whether in terms of value or distribution. Under the same gas phase output conditions, the void fraction is much smaller in boiling systems than in cold gassed or hot sparging systems. Hot sparged systems have similar vertical void fraction distributions, with maxima in similar locations but with smaller void fractions overall, like those of cold gassed systems. The results are of particular relevance to the design and operation of reactors with hot sparging or boiling liquids.

Passive acoustic bubble sizing in sparged systems

Passive acoustic bubble sizing was investigated in both controlled tests and in a stirred, sparged tank typical of the biotechnology or minerals processing industries. Acoustic techniques have promise for industrial systems where other bubble analysis methods are impractical. Acoustic signals were studied for bubbles precisely formed at higher airflow rates. Acoustic pulses varied with bubble production rate as well as with bubble size. A technique of windowing pulses is proposed. Two alternative versions of this windowing technique were applied to a stirred, sparged tank, giving good agreement. It was shown that, in some cases, it may also be possible to acoustically estimate the spatial distribution of void fraction.

Application of membrane tubing aeration and perfluorocarbon To improve oxygen delivery to hairy root cultures

Growth and atropine production by Atropa belladonna hairy roots were studied in bioreactor cultures using porous polypropylene membrane tubing as a supplementary aeration device and with FC-43 perfluorocarbon emulsion added to the medium. Both these treatments were applied to improve oxygen transfer to the roots. Membrane tubing aeration allowed direct delivery of oxygen within the root clump, thus overcoming mass transfer resistances associated with poor intraclump penetration of liquid convective currents. Combined air sparging and membrane tubing aeration in a gas-driven bioreactor supported biomass levels 32-65% higher than sparging only of air or oxygen-enriched air at the same total gas flow rate. The optimal air flow rate ratio between the sparger and membrane tubing giving the maximum final biomass concentration was 0.2:0.4 L min-1. Intraclump dissolved oxygen tensions at high biomass densities were generally greater using air delivered by combined sparger-membrane tubing aeration than with sparging only of air or oxygen-enriched air. Specific atropine levels were not significantly affected by membrane tubing aeration. Indicators of anaerobic metabolism, such as lactic acid, ethanol, and ADH activity levels, were not significantly different in sparged and membrane-aerated systems; A. belladonna hairy roots also did not produce aerenchyma in response to oxygen limitations. Addition of perfluorocarbon emulsion to Murashige and Skoog medium in sparged stirred tank bioreactors did not improve growth, even when the emulsion was continuously recycled for re-aeration in an external vessel. Perfluorocarbons are associated with enhancement of gas-liquid oxygen transfer, so their ineffectiveness in this work most likely reflects the dominance of liquid-solid transfer resistances in hairy root cultures. The results of this investigation highlight the importance of developing new approaches for site-directed aeration of hairy root cultures, targeting oxygen delivery into the zones of highest root density.

Determination of mass transfer parameters in surface aerated bioreactors with bubble entrainment

The volumetric oxygen mass transfer coefficient k L a is a critical design parameter for most bioreactors and has been extensively studied. However, few reliable correlations are available for its estimation. In this context, the k L a and specific interfacial area a of 3.5 1 and 16 1 surface-baffled and aerated double-helical-ribbon impeller (HRI) bioreactors were evaluated. The bioreactor configuration is characterized by significant surface bubble generation and entrainment into the liquid phase and has been shown to be highly efficient in the culture of fragile plant, mammalian and insect cells. The k L a and a parameters were determined independently using the dynamic gassing-in method and a modified sulphite method respectively. A second order model with proper validity criteria was developed to account for the effect (up to 90% underestimation) of headspace gas mixing dynamics on the k L a determination of surface-aerated bioreactors. For a 3.5 bioreactor stirred at 250 rev min −1 a surface k L a value of 52 h − was observed while the value for the 16 1 bioreactor mixed at 150 rev min −1 was 44 h −1. The liquid mass transfer coefficients k L obtained by dividing the measured k L a by the corresponding measured specific interfacial area are within the ranges reported in the literature for surface aerated (2.0–3.2×10 −5 m s −1) and sparged (9/23;7×10 −5 m s −1) conventional systems.

Interactions between animal cells and gas bubbles: The influence of serum and pluronic F68 on the physical properties of the bubble surface

We describe a method by which the degree of bubble saturation can be determined by measuring the velocity of single bubbles at different heights from the bubble source in pure water containing increasing concentrations of surfactants. The highest rising velocities were measured in pure water. Addition of surfactants caused a concentration-dependent and height-dependent decrease in bubble velocity; thus, bubbles are covered with surfactants as they rise, and the distance traveled until saturation is reached decreases with increased concentration of surfactant. Pluronic F68 is a potent effector of bubble saturation, 500 times more active than serum. At Pluronic F68 concentrations of 0.1% (w/v), bubbles are saturated essentially at their source. The effect of bubble saturation on the interactions between animal cells and gas bubbles was investigated by using light microscopy and a micromanipulator. In the absence of surfactants, bubbles had a killing effect on cells; hybridoma cells and Chinese hamster ovary (CHO) cells were ruptured when coming into contact with a bubble. Bubbles only partially covered by surfactants adsorbed the cells. The adsorbed cells were not damaged and they also could survive subsequent detachment. Saturated bubbles, on the other hand, did not show any interactions with cells. It is concluded that the protective effect of serum and Pluronic F68 in sparged cultivation systems is based on covering the medium-bubble interface with surfaceactive components and that cell death occurs either after contact of cells with an uncovered bubble or by adsorption of cells through partially saturated bubbles and subsequent transport of cells into the foam region. (c) 1994 John Wiley & Sons, Inc.

Electrowinning of zinc from electrolytes containing anti-acid mist surfactant

A series of experiments were conducted to measure the current efficiency of synthetic zinc electrolytes containing additions of nonyl-phenol oxyethylene surfactant. The values of cell voltage were also measured and the energy consumptions were calculated. The surfactant was added in order to prevent the acid mist problem. The experiments were carried out for non-sparged and sparged systems with various surfactant concentrations and with changes in several operating conditions such as current density and zinc/acid ratio. The zinc current efficiency values varied from 56.0 to 90.0 and energy consumptions were in the range of 2900–5200 kWh/t according to operating conditions, surfactant concentrations and system type.

Effect of gas sparging on mass transfer in zinc electrolytes

The effect of sparging on mass transfer is reported for zinc electrolytes containing antimony and antimony-free electrolytes. Comparative results with non-sparged electrolytes show, an enhancement in mass transfer. In the sparged electrolyte, the mass transfer coefficients,KZn, increase with increasing current density, antimony additions, and sulphuric acid concentration. The deposition morphology is consistent with the mass transfer results. A relationship between the mass transfer coefficients for sparged and non-sparged systems is obtained. The relationship correlates satisfactorily with the data and provides a quantitative method for determining the degree of enhancement in mass transfer coefficients due to sparging. The correlation which best represents the mass transfer data for sparged zinc electrolytes is $$Sh = 105(ReSc)^{0.23} $$ whereSh, Re, andSc are the Sherwood, Reynolds, and Schmidt numbers, respectively. The correlation represents the case where sparging is applied to a gas evolving electrode, hydrogen in this case.

Effect of gas—liquid interfaces on the growth of suspended mammalian cells: mechanisms of cell damage by bubbles

The hypothesis is examined that cell death in sparged systems for suspended mammalian cell culture is associated only with the region of bubble disengagement at the medium surface. The effects of bubble diameter, superficial gas velocities, and the nonionic surfactant Pluronic F-68 on hybridoma viability have been reported previously. The work reported here extends these experimental studies to a range of bubble columns and for the culture of not only hybridoma but also myeloma, BHK-21, and lymphoblastoid (RAJI) cells lines. In short bubble columns, small bubbles and high bubble frequencies are more detrimental to hybridoma cells than BHK-21 suspension cells. Both fetal calf serum (FCS) and Pluronic F-68 have concentration-dependent protective effects on cells. In defined serum-free media, gross mechanical disruption of hybridoma cells and loss of cells and medium components at the medium surface occur on sparging. With increasing bubble column height, a progressively increasing retention of cell viability is observed for all cell types. By implication, this is because the proportion of time spent by cells in the “destructive zone” at the medium surface is reduced as the column height increases. Finally, two mechanisms of cell damage are proposed: damage due to rapid oscillations caused by bursting bubbles, and damage due to shearing in draining liquid films (or lamellae) in foams. It is proposed that Pluronic (and other polymers such as polyethylene glycol and polyvinyl pyrollidone) act as cell protective agents by stabilizing foams and thereby reducing film drainage and bubble bursting in the vicinity of cells.

Stripping in sparged fermentation systems. III. The acetic acid–water system

Stripping in sparged fermentation systems. III. The acetic acid–water system

Stripping in sparged fermentation systems. III. The acetic acid‐water system

Biotechnology and BioengineeringVolume 10, Issue 2 p. 243-246 Communications to the EditorFree Access Stripping in sparged fermentation systems. III. The acetic acid-water system G. Hamer, G. Hamer Bacteriological Bioengineering Research Unit, Karolinska Institutet, Stockholm, 60, SwedenSearch for more papers by this author G. Hamer, G. Hamer Bacteriological Bioengineering Research Unit, Karolinska Institutet, Stockholm, 60, SwedenSearch for more papers by this author First published: March 1968 https://doi.org/10.1002/bit.260100211Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL References 1 G. Hamer, Biotechnol. Bioeng., 7, 199, (1965). 2 F. H. MacDougall, J. Am. Chem. Soc., 58, 2585, (1936). 3 H. L. Ritter and J. H. Simons, J. Am. Chem. Soc., 67, 757, (1945). 4 E. W. Johnson and L. K. Nash, J. Am. Chem. Soc., 72, 547, (1950). 5 J. Marek, Collection Czechoslovak. Chem. Commun., 20, 1490, (1955). 6 E. Sebastiani and L. Lacquaniti, Chem. Eng. Sci., 22, 1155, (1967). Citing Literature Volume10, Issue2March 1968Pages 243-246 ReferencesRelatedInformation

Stripping in sparged fermentation systems. I. Two component model systems

AbstractA theoretical approach to the prediction of stripping or accumulation of minor components in solution with water by a sparged stream of dry air bubbles is developed and tested experimentally for two model systems, containing 1 mole‐% respectively, of ethanol, to represent situations where the minor component is more volatile than water, and of acetic acid, to represent the reverse. Close agreement between theory and practice is achieved in the former case, where an overall reduction in the liquid phase concentration of the minor component occurs, while in the latter, where overall accumulation occurs, there is some discrepancy. Considerations for an extension of the study are included.

Stripping in sparged fermentation systems. II. The effect of operating temperature and gas phase pre‐humidification in an ethanol‐water system

AbstractThe effect of operating temperature upon relative stripping of a two component (ethanol–water) mixture by dry air, with the aid of a previously derived equation,1 is considered. The variations encountered in the relative humidity of air sparged to fermentors are discussed. A general equation is developed for the stripping of a more volatile component from a solution in water by wet air. The theoretical results derived from this equation are tested experimentally at one particular level of prehumidity of the air sparged to an ethanol–water system.