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To avoid compaction problems in random laminar contactors, new supports covering a wide variety of specific surface areas and porosity have been developed reducing the pressure drop problems in these systems. An interesting laminar contactor that prevents the formation of heterogeneities with minimal power consumption is the capillary reactor when operated under Taylor flow and is discussed later in this paper.

As technologies for biological gas treatment are applied mostly at relatively low gas concentrations, we estimate that they are nearly always subject to at least partial mass transfer limitation. Biotechnology for gas treatment is accepted as an economical and reliable air pollution control technology for treating gases contaminated mainly with relatively low concentrations. The extension of its application field is limited in many cases by the mass transfer of especially hydrophobic target compounds. Below we briefly review some of the strategies which we have shown to be technical feasible to overcome mass transfer limitation.

Fungi have the advantage that their aerial mycelia form a larger surface area see Eq. Wosten et al. Filamentous fungi secrete hydrophobins at hydrophobic—hydrophilic interfaces such as gas—water to form an amphipathic coating that lowers the surface tension, which enables hyphae to breach the water—gas interface.

This mechanism can be used by fungi for direct pollutant consumption from the gas phase avoiding the mass transfer resistance in the liquid. The results indicated that partition coefficient of hexane was nearly an order of magnitude lower for fungal more absorption than bacteria films, and it was lower for dry fungal samples than for the wet samples.

This proves also that direct gas—biofilm mass transfer is preferred, minimizing the gas—liquid—biofilm path for the transfer of the target compound. Vergara-Fernandez et al. Besides relatively higher mass transfer rates of hydrophobic compounds in fungal biofilters than in bacterial biofilters, another advantage is that fungi are more resistant to drying out and acidification.

Fungi biofilters have shown to be significantly more robust to poor moisture control in the biofilter Cox ; Kraakman et al. Different authors Groenestijn et al. High conversion rates come with increased biomass growth in biofilters and high pressure losses are reached sooner with filamentous fungi than with non-filamentous microorganisms, eventually causing clogging and channeling problems in the biofilter.

Innovative solutions, such as the addition of higher organisms, are explored and described by Groenestijn et al. Simultaneously, the performance of the fungal biofilter was significantly higher compared to the control fungal biofilter without mites. The addition of a non-aqueous phase liquid NAPL such as for instance an organic solvent can overcome design and operational limitations of biological systems.

The so-called two-phase partitioning bioreactors make use of an extra phase solvent to enhance the productivity or facilitate the downstream processing from bioprocesses. The concept is applied either to control the delivery of a sometimes toxic substrate dissolved in the non-aqueous phase or to continuously extract a bio-product Ratledge ; Wubbolts et al. This technology has now been researched for the treatment of poorly water soluble gaseous compounds Yeom and Daugulis ; Davison and Daugulis ; Arriaga et al. The non-aqueous phase for example a large branched alkane, silicone oil or a plastic polymer , which is selected as immiscible, non-volatile, non-toxic, non-biodegradable, and with high affinity by the target compound Quijano et al.

Resistance of the diffusion through the liquid boundary layer is counteracted both by the increase in the interfacial area for mass transfer and the enhanced accumulation of the target compound in the organic phase, which acts as a reservoir. It is also known that many microorganisms are also capable of producing biosurfactants that can solubilize the hydrophobic compounds and possibly improve uptake Hamme et al.

With the addition of a solvent, the overall change in volumetric mass transfer coefficient k L a depends on the relative magnitudes of effects on a new resistance organic phase added to the overall system, which is usually higher than that of water due to a higher viscosity of the NAPL, and the different interfacial contact areas that can be present gas—water, gas—oil, oil—water, cell—gas, cell—water, cell—oil.

Studies on bioreactor systems with a non-aqueous phase addition to increase mass transfer and consumption of poorly water soluble compounds. In turbulent reactors, for the organic phase addition to be effective, the increase in the different interfacial contact areas must overcome the general increase in the mass transfer resistance by the organic phase addition Clarke and Correia ; Quijano et al. It has been shown in stirred tank reactors that silicone oil drops can increase the gas—water interfacial contact area through two effects, first, colliding with the gas bubbles and breaking them Galindo et al.

The first effect is increased by the stirring rate power consumption in the system as demonstrated by Rocha-Rios et al. Obtaining a mathematical model to describe the effect of a NAPL in these systems is still a challenge. The first attempt to model the degradation of a gaseous pollutant hexane in a two-phase partition bioreactor was developed by Bordel et al.

This assumption cannot be valid for more hydrophobic compounds like methane as Han et al. Rocha-Rios et al. Contrasting results were reported by Quijano et al. Therefore, more studies are required to clarify this particular finding. Although Dorado et al. Experiments by Heymes et al. This behavior has also been observed by the few authors who have used viscous fluids in their experiments and is contrary to all the authors who have worked on low-viscosity fluids.

The physical characterization of the liquid phase plays an important role in hydrodynamics and mass transfer kinetics. Gomez-Diaz and Navaza showed, for example, that the presence of polymers carboxymethyl cellulose influences the viscosity and thereby the mass transfer. It is therefore clear that the influence of viscosity on the mass transfer phenomenon is considerable and should be taken into account at the addition of a solvent.

The stability of a non-aqueous solvent under long-term operation is, in general, unclear and its application could be limited by the fact that the solvent can be slightly volatile. To overcome this, highly stable solid polymers based on copolymers of polyurethane, vinyl acetate, and ethylene e. Although slower to respond to sudden changes in pollutant concentration compared with the liquid—liquid systems Boudreau and Daugulis , the overall biological system can be more stable and possibly more cost effective. In laminar reactors, different heterogeneities are produced in the package of biofilters and biotrickling filters during the operation biomass, humidity, air canalization, etc.

When an organic phase like silicone oil is added, its distribution through the package is affected by these heterogeneities generating zones in the package with higher oil content this effect is enhanced by the higher viscosity of the oil than water.

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A strategy to avoid the addition of an organic phase in laminar contactors is selecting a packing material with similar properties fundamentally high affinity by the pollutant and oxygen Montes et al. Another strategy to avoid the formation of heterogeneities caused by a random distribution of the packed particles, is changing to a structured package capillary bioreactor as proposed by Kreutzer et al. Often a non-aqueous phase liquid like silicone oil does not mix well with water due to differences in hydrophobicity and density, which induces partitioning between the two phases.

If not controlled, phase separation could very well induce a reduction of the overall biodegradation efficiency. Stable emulsions are required and might require additional mixing. We have seen that the stability of a silicone oil and water emulsion improves over time in the presence of microorganisms Rocha-Rios et al. The non-aqueous phase should be selected based on its cost, enhanced partitioning properties towards the target compound s , immiscibility, viscosity, volatility, safety, non-toxicity, and non-biodegradability.

Although data on costs, immiscibility, viscosity, toxicity, volatility, safety, and biodegradability are available for different solvents and solid polymers Quijano et al. The traditionally used biological gas treatment methods biofilters and biotrickling filters can be called laminar contactors. Laminar flow occurs when a gas or liquid flows in parallel layers, with minimal disruption between the layers. Laminar flow is a flow regime characterized by high diffusion and low advection and is the opposite of turbulent flow. The mass transfer rate through a water film by diffusion is relatively slow when compared to diffusion through gas in general by a factor of approximately 10, Therefore improved convection by advection for example through mixing will improve mass transfer through a water film.

Considerable effort has been expended in the search of less energy-intensive reactors to further enhance mass transfer rate. Capillary reactors combine good mass transfer with low pressure drop, two important factors affecting cost effectiveness for many industrial applications. Capillary reactors are structures of parallel straight microchannels capillary channels separated by a thin wall. The hydrodynamics of gas—liquid flow in capillary channels have been studied within the context of chemical reaction engineering Nijhuis et al.

A capillary reactor is a reactor where the capillary forces, created by the capillary channel, become dominant over other forces as such gravity and viscosity. The preferred flow patron, called segmented flow or Taylor flow, is a bubble train of alternating liquid slugs and air bubbles with gas and liquid flowing downwards or upwards co-currently. Although the airflow seems to be laminar, the internal liquid circulation increases the mass transfer from the gas phase to the liquid phase where a plug flow no macromixing and axial dispersion is combined with good mass transfer local mixing and low pressure drop Kreutzer et al.

A bioreactor using a monolith support operated under Taylor flow conditions is an example of a capillary bioreactor. The rate of transport of the compounds through a medium is characterized by resistance to the medium. Input of energy can overcome resistance, such as, for example, mixing in bubble-tank bioreactor to break up air bubbles and thereby increasing the interfacial surface area of the gas bubble with the liquid. The physical input of energy in a system is always limited by the equipment required for the energy input, which will operate with a specific optimal efficiency dependent on its operating conditions.

Increased energy consumption results in increased cost of operation, which should be minimized for industrial applications. The mass transfer using Taylor flow is relatively energy efficient, mainly because no energy is required to maintain the small gas bubble size. Mass transfer and power consumption in monolithic reactors compared to biotrickling filtration.

The data for capillary reactors were obtained from Kreutzer et al. The data for the biotrickling filter were obtained from Kim and Deshusses , who were the first to conduct a systematic study to actually measure mass transfer rates in the most common used biotechnologies for gas treatment biofiltration and biotrickling filtration.

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Capillary reactors are becoming increasingly significant as multiphase reactors, considering the advantages that they offer, in comparison with conventionally used trickle beds or biofilters for a host of processes Liu et al. These advantages, which include low pressure drop, high gas—liquid mass transfer rates, and minimum axial dispersion plug flow , stem from the uniquely structured multichannel configuration of capillary channels. Some studies have shown that the use of capillary reactors, in lieu of trickle beds, results in higher productivities and a very significant reduction in reactor size for specified chemical processes Nijhuis et al.

Ebrahimi et al. Understanding the mass transfer behavior in bioreactors for gas treatment is highly relevant to obtain improved modeling tools and more advanced reactor operations. Different aspects have been discussed and it shows that work is still needed to fully understand the phenomena of mass transfer in a bioreactor for gas treatment.

Studies to determine mass transfer coefficients in biological gas treatment reactors are rare and mass transfer estimates are therefore often derived from studies on packing materials in systems e. The influence of biomass on the partitioning coefficient of the target compound in a gas—liquid and gas—biofilm interface in biological gas treatment processes also needs more detailed study. Some of the strategies that have shown to be technical feasible to overcome mass transfer limitation have been reviewed. Although the mechanisms of mass transfer enhancement are not fully elucidated and different technical challenges need to be resolved before they can be used at full-scale, several promising strategies to improve mass transfer while minimizing power consumption mark the future trend.

In random package contactors, these strategies include the use of inorganic supports with high specific surface areas and high porosities, the action of fungi and the addition of a liquid organic phase. Nevertheless, the addition of an organic phase, more viscous than water, may increase the formation of heterogeneities through the bed affecting the pollutant transfer rate. This could explain why different authors have reported either positive or negative effects of the organic phase on mass transfer in these systems.

An interesting alternative is the absorption of the pollutant in a solid polymer which can be used as support in a biofilter or biotrickling filter. Finally, a promising strategy to increase mass transfer of poorly water soluble compounds with minimal power requirements is the capillary bioreactor, but more study is necessary to scale-up this system to commercial applications. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author s and source are credited.

National Center for Biotechnology Information , U. Applied Microbiology and Biotechnology. Appl Microbiol Biotechnol. Published online Jun Norbertus J. Mark C. Author information Article notes Copyright and License information Disclaimer. Kraakman, Email: ln. Corresponding author. This article has been cited by other articles in PMC. Abstract This contribution reviews the mass transfer aspects of biotechnological processes for gas treatment, with an emphasis on the underlying principles and technical feasible methods for mass transfer enhancements. Keywords: Mass transfer limitation, Bioavailability, Biofiltration, Biotrickling filters, Biofilters, Partitioning bioreactor, Capillary channels, Taylor flow.

Introduction Biological gas treatment can be defined as the transformation of gaseous compounds to less harmful or more valuable products through the action of microorganisms. Mass transfer or kinetically limited Understanding the rate-limiting steps in a system generates opportunities to optimize the design and operations of the system for a specific application. Defining mass transfer Mass transfer of the target compounds pollutant and oxygen from a gas phase into the liquid phase in biological gas treatment systems is often described with the two film theory from Lewis and Whitman Open in a separate window.

An illustration of mass transfer typical for biological waste gas treatment processes. Determining mass transfer rates A biological gas treatment system contains typically a gas phase, a liquid phase, and a biofilm phase. Factors influencing mass transfer The intrinsic mass transfer coefficient is a function of the pollutant physical—chemical properties, the medium properties e.

Bioreactor configurations and mass transfer enhancement strategies Basically, we can divide the bioreactors for gas treatment operations in two groups: turbulent and laminar contactors. The action of fungi Fungi have the advantage that their aerial mycelia form a larger surface area see Eq. Table 1 Studies on bioreactor systems for gas treatment with fungi. Non-aqueous phase addition The addition of a non-aqueous phase liquid NAPL such as for instance an organic solvent can overcome design and operational limitations of biological systems.

Table 2 Studies on bioreactor systems with a non-aqueous phase addition to increase mass transfer and consumption of poorly water soluble compounds. Taylor flow turbulence The traditionally used biological gas treatment methods biofilters and biotrickling filters can be called laminar contactors. Conclusions Understanding the mass transfer behavior in bioreactors for gas treatment is highly relevant to obtain improved modeling tools and more advanced reactor operations. References Adler SF Biofiltration a primer. Removal of n-hexane by Fusarium solani with a gas phase bioreactor.

J Ind Microbiol Biotechnol. Improving hexane removal by enhancing fungal development in a microbial consortium biofilter. Biotechnol Bioeng. Mathematical modeling and simulation of hexane degradation in fungal and bacterial biofilters: effective diffusivity and partition aspects. Can J Civil Eng. Gaseous hexane biodegradation by Fusarium solani in two liquid phase packed-bed and stirred tank bioreactors.

Environ Sci Technol. Removal of dichloromethane from waste gases in one- and two-liquid-phase stirred tank bioreactors and biotrickling filters. Water Res. Estimation of mass transfer and kinetics in operating trickle-bed bioreactors for removal of VOCs. Environ Prog. Partitioning of BTEX constituents and chloroorganics in high-biomass systems. Solubility of toluene, benzene and TCE in high-microbial concentraion systems. Prediction of mass transfer columns with dumped and arranged packings — updated summary of the calculation method of Billet and Shultes.

Chem Eng Res Des. Modelling gas—liquid VOCs transport in two-liquid phase partitioning bioreactors. Int J Heat Mass Transfer. Mass transfer limitation of biotransformation: quantifying bioavailability. Transient performance in two-phase partitioning bioreactors treating a toluene contaminated gas stream. Characterization of compost biofiltration media. J Air Waste Manag Assoc. Oxygen transfer in hydrocarbon-aqueous dispersions and its applicability to alkane bioprocesses: a review.

Biochem Eng J. Mass-transfer and kinetic aspects in continuous bioreactors using Rhodospirillum rubrum. Appl Biochem Biotechnol. Toluene degradation in the recycle liquid of biotrickling filters for air pollution control. Delivery of benzene to Alcaligenes xylosoxidans by solid polymers in a two-phase partitioning bioreactor. Biotechnol Lett. The treatment of gaseous benzene by two-phase partitioning bioreactors: a high performance alternative to the use of biofilters.

Influence of high biomass concentrations on alkane solubilities. The influence of viscosity on the liquid-phase mass transfer resistance in packed columns. Chem Eng J. A phenomenological review of biofilter models. Removal of styrene from waste gas using a biological trickling filter. Eng Life Sci. Evaluation of mass transfer coefficients in biotrickling filters: experimental determination and comparison to correlations.

Chem Eng Technol. Potential application of monlith packed columns as bioreactors, control of biofilm formation. Biofilm growth pattern in honeycomb monolith packings: effect of shear rate and substrate transport limitations. Catal Today. A comparative analysis of odour treatment technologies in wastewater treatment plants. The effect of silicone oil on biofiltration of hydrophobic compounds.

Environ Progr. Study of drop and bubble sizes in a simulated mycelial fermentation broth of up to four phases. Enhanced biofiltration using cell attachment promotors. Recent developments in biological waste gas purification in Europe. Elimination of alkanes from off-gases using biotrickling filters containing two liquid phases. Biofilters based on the action of fungi. Water Sci Technol.

Recent advances in petroleum microbiology. Microbiol Mol Biol Rev. Mass transfer limitation of microbial growth and pollutant degradation.

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A comparative study of solid and liquid non-aqueous phases for the degradation of hexane in two-phase partitioning bioreactors. Hydrodynamics and mass transfer in a packed column: case of toluene absorption with a viscous absorbent. Chem Eng Sci. Standardization of mass transfer measurements: a basis for the description of absorption processes.

Chemical reaction and effective interfacial areas in gas adsorption. Bioreactors for waste gas treatment. Dordrecht: Kluwer Acadamic Publicers; Determination of mass transfer coefficients for packing materials used in biofilters and biotrickling filters for air pollution control. Experimental results. Diffusion—the crucial process in many aspects of th biology of bacteria.

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In: Marcshall KC, editor. Adv Microbiol Ecol New York: Plenum Press; Proceedings of an international symposium on Biological Waste Gas Cleaning.

In the illustrated embodiment, vertical wall 11 of reactor vessel 2 is shown as extending upward from floor 12 of the vessel to a point at which the wall slopes upward and inward to form outer conical baffle Said outer conical baffle 13 is connected with generally vertical wall 14 of an upper cone shaped portion of the reactor vessel terminating at roof 15 and forming an enclosed space for the relatively quiescent portion 4 of the body of liquid and for overhead gas space 6.

Inert gas can be passed to said overhead gas space 6 through line 16 to assure against the creation of flammable conditions in said overhead gas space 6, with gases being vented therefrom through line Inner conical baffle 18 is positioned above impeller means 7, and above draft tube 9 in the illustrated embodiment, and co-acts with outer conical baffle 13 to enable the desirable benefits referred to above to be achieved in the operation of the LOR system of the invention.

Inner conical baffle 18 slopes downward and inward toward impeller shaft 8 from a point near the outer portion of the wall of reactor vessel 2, desirably in the region near the upper end of outer conical baffle Thus, a vent opening 19 is provided in the space between the upper end of inner conical baffle 18 and the upper end of outer conical baffle In order for a gas bubble to escape from under inner conical baffle 18, it must come in contact with a hole in or around said baffle, i.

Thus, the amount of gas that escapes is proportional to the probability that a gas bubble will hit a hole.

Description

If the gas bubble remains in the liquid flow field, shown by flow pattern A in the lower portion of reactor vessel 2, and by flow pattern B in the upper portion thereof, so that it flows downward into draft tube 9 upon contact with inner conical baffle 18, it can not escape from the recirculating body of liquid and pass into quiescent zone 4 and overhead gas space 6. Thus, the downward slope of inner conical baffle 18 is intended to maximize the flow velocity of liquid under said baffle, minimize the probability that a bubble will come into contact with a hole in or around said baffle, i.

Under normal flow conditions, the liquid flow velocity on the underside of inner conical baffle 18 is directed radially inward and downward toward impeller shaft 8 and impeller means 7 and away from vent opening This downward and inward liquid flow drags most gas which contacts the underside of inner conical baffle 18 into the downward impeller suction and away from vent opening When the recirculating flow of liquid is stopped, as when the drive motor for said impeller fails, gas bubbles rise through major portion 3 of body of liquid 1 to the underside of inner conical baffle The slope of said inner baffle directs the gas bubbles to vent opening 19, through which the gas bubbles pass to quiescent portion 4 of the body of liquid and to inerted overhead gas space 6.


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It will be understood that various changes and modifications can be made in the details of the invention without departing from the scope of the invention as recited in the appended claims. Thus, outer conical baffle 13 desirably has an inwardly extending flap section 13A, conveniently horizontally, to facilitate the flow of liquid and dispersed gas bubbles away from vent opening Outer conical baffle extension 13A conveniently extends from the upper end of outer conical baffle 13 inward to a position under inner conical baffle 18, preferably at the outer, upper end thereof.

As will be seen from the drawing, such a positioning of outer conical baffle extension 13A serves to make vent opening 19 a slit positioned away from the generally inward and downward flow of liquid under said inner conical baffle 18, thereby minimizing the amount of gas venting through vent opening 19 under normal operating conditions in reactor vessel 2. It will be seen from the drawing that outer conical baffle 13, which is sloped upward and serves to eliminate dead spots outside draft tube 9 since gas cannot collect underneath it, is conveniently the sloping portion of the wall of reactor vessel 2 that extends upward and inward from the top of vertical wall 11 of said reactor vessel 2.

It should be noted that, while the illustrated embodiment is convenient and preferred, it is also within the scope of the invention for vertical wall 11 to extend to the upper part of reactor vessel 2, with a separate outer conical baffle 13 being positioned therein to create the desired upward and inward liquid flow path toward inner conical baffle 18 with the flow path of liquid on the underside of inner baffle 18 being downward and inward into the impeller suction above and in draft tube 9.

In this regard, it will be appreciated that the upper portion of reactor vessel 2, in which quiescent portion 4 and overhead gas space 6 are contained, need not be smaller diameter than the lower portion of said reactor vessel 2, although the illustrated embodiment is convenient to construct and operate for the subject gas-liquid mixing purposes of the invention.

Attention is called to the downwardly extending portion 18A of inner conical baffle Such portion 18A, generally in the center of reactor vessel 2 above draft tube 9, will be seen to further direct the downwardly and inwardly flowing liquid under said inner conical baffle 18 downward into the suction of impeller means 7 for the desired downward flow of the recirculating portion 3 of the body of liquid through draft tube 9. Drive shaft 8 for impeller means 7 will be seen to extend upward through opening 20 defined by said extension 18A of inner conical baffle 18 for connection to suitable drive means for impeller means 7.

Due to the downward flow of liquid above draft tube 9 and impeller means 7, the amount of gas that will escape upward through opening 19 will be negligible during operation of the gas-liquid mixing system. The feed gas stream is introduced into reaction vessel 2 through conduit means 20 directly into the recirculating portion of the body of liquid, i. For this purpose, conduit means 20 preferably extend into said major body of liquid in the vicinity of liquid flow pattern B near the top of major portion 3 of the body of liquid for enhanced mixing under the influence of the draft tube-impeller means configuration as enhanced by the inner and outer conical baffles of the invention.

It is within the scope of the invention, however, to introduce the feed gas stream to the reactor vessel at any other convenient point, as in liquid flow pattern A near the bottom of reactor vessel, or elsewhere in the recirculating flow of liquid. It will be noted in the drawing that hollow draft tube 9 contains a conically flared portion 9A at the upper end thereof. This generally preferred, but not essential feature, serves to further facilitate the flow of gas bubble-liquid mixture into said hollow draft tube 9 for downward passage therein.

Impeller means 7 positioned within said hollow draft tube 9 are illustrated as a simple impeller blade device adapted to pump liquid down through said draft tube 9 and upward in the annulus between said draft tube 9 and outer wall 11 of reactor vessel 2, and the outer conical baffle 13 portion thereof. Those skilled in the art will appreciate that other impeller means can be employed in the practice of the invention, such as commercially available axial flow helical impeller means for enhancing the desired liquid pumping action and the overall gas-liquid mixing achieved in the practice of the invention.

Those skilled in the art will also appreciate that the draft tube-impeller means arrangement can be provided at different locations within reactor vessel 2, i. In various embodiments, flow pattern A in the lower portion of reactor vessel 2 may serve to create rolls cells of enhanced turbulence further facilitating the desired gas-liquid mixing operation. While downward pumping impeller means are herein described and claimed, it will be appreciated that upward pumping impeller means can also be employed for gas-liquid mixing operations, and baffle arrangements can be devised to accomplish the desirable results achieved using the invention.

However, such reverse flow operation is generally less convenient and less suited than the invention as herein described and illustrated. While the invention has been illustrated by an embodiment employing a desirable and advantageous hollow draft tube-impeller means configuration, it should be noted that the incorporation of a hollow draft tube, while highly preferred, can be omitted in various embodiments provided that the desired recirculating flow condition can be maintained sufficiently without the preferred use of said hollow draft tube.

Those skilled in the art will appreciate that the quiescent portion of the body of liquid can be of any suitable size to provide the desired separation of the recirculating portion of liquid from the overhead gas phase and to accommodate a change in liquid level in response to a change in volume of said body of liquid between the condition in which no gas bubble are in the body of liquid and the condition that exists when a desired gas bubble concentration is developed therein.

The liquid flow velocity into the draft tube section of the system should generally be about 1. For a given total flow rate, the desired flow velocity into the draft tube-impeller suction can be adjusted by properly setting the clearance between the draft tube and the inner and outer conical baffles of the invention, i. For advantageous operation of the invention, the outer diameter of inner conical baffle 18 should generally be from 0.

Extension 13A of outer conical baffle 13 will be seen as a flap that overlaps vent opening 19 opening so that there is no uncovered area under inner conical baffle 18 in the recirculating flow path. Said extension 13A and vent opening 19 will be seen to form a vent slit, with a gas bubble having to move against the liquid flow field to pass through the vent slit. The vent opening, and, in the illustrated embodiment, the vent slit, should desirably be located at the highest point of inner conical baffle Those skilled in the art will appreciate that any baffle configuration that meets the criteria referred to above, i.

In general, baffles with smooth contours that more closely follow the streamlines of the liquid flow field in the impeller suction zone that is accomplished by the use of flat baffle surfaces would generally be desirable from a hydrodynamic viewpoint. However, the cost of fabricating such a more complex shape must be weighed against the added benefits thereof.

It will be understood that any desired gas-liquid mixing operation in which the LOR approach is necessary or desirable can be benefited by the practice of the invention. The oxidation of an aliphatic aldehyde is an illustrative example of the type of reaction that can be carried out advantageously using an LOR system containing the desirable baffle arrangement herein described and claimed. The invention also provides a highly desirable improvement in LOR systems for use in other oxygen applications not involving the potential presence of flammable mixtures in the gas phase, and in other valuable hydrogenation, chlorination and other practical gas-liquid mixing operations.

By overcoming various practical operating problems encountered in the practice of the highly desirable and advantageous L0R system technology, the invention provides a significant improvement that enhances the ability of the LOR technology to satisfy the need for efficient, effective and economical gas-liquid mixing operations for a wide variety of desirable LOR applications. All rights reserved. A SumoBrain Solutions Company. Login Sign up. Search Expert Search Quick Search.

Advanced gas control in gas-liquid mixing systems. United States Patent Sloped inner and outer conical baffles are provided in a gas-liquid mixing system having a recirculating portion of a body of liquid, separated from a quiescent portion of the body of liquid and an overhead gas phase, precluding the collection of gas under the baffles, eliminating dead zones of gas, and minimizing the passage of gas to the overhead gas phase during normal operation, while facilitating the venting of gases during upset conditions.

Kingsley, Jeffrey P. Newburgh, NY. Click for automatic bibliography generation.

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Praxair Technology, Inc. Danbury, CT. I claim: 1. The system of claim 1 and including, at the upper end of the outer conical baffle, an inwardly extending flap section overlapping said vent opening so as to deflect any upwardly moving liquid away from the vent opening toward the inner conical baffle, said flat section and said vent opening forming a vent slit positioned opposite the direction of the liquid flow towards said inner conical baffle.

The system of claim 1 in which said impeller means comprises down pumping axial flow impeller means.