EP3113867B1 - Process and device for dispersing gas in a liquid - Google Patents

Description

The invention relates to a method and a device for dispersing gas in a downward flow of liquid.

The invention more particularly relates to a method and a dispersing device with hybrid liquid gas jet mixer and jet injector. The method is intended to homogeneously disperse the gas in the form of fine bubbles in a liquid engine for contacting liquid gas or for subsequent contact with the mass of liquid in a surrounding contactor in which the device is implanted. The device is composed of an injection head comprising a liquid-jet mixing chamber at the top and a vertical coaxial tube with diphasic jet at the bottom, forming a nozzle. Said homogeneous liquid gas dispersion is produced for a gas retention of between 5 and 70%, preferably between 30 and 50%.

The invention relates more particularly to a method and a device for injecting ozone or a mixture of ozone and oxygen and / or air into a stream of water, to purify it.

The performance of the gas dispersion can be expressed on the one hand as a function of the size of the gas bubbles produced and on the other hand as a function of a gas / liquid volume ratio of the two-phase gas-liquid mixture resulting from the dispersion. , ratio related to the gas retention defined as the ratio of the volume of the gas phase relative to the total volume of the contactor equal to the sum of the volumes of gas and liquid that it contains or as the ratio of the volumetric flow rate of the gaseous phase reported the sum of the volume flow rates of gas and liquid. The methods and injection devices of the state of the art make it possible to obtain a homogeneous dispersion of gas in the form of bubbles at an acceptable energy consumption for a relatively low gas / liquid volume ratio, not exceeding 0, 5 in general.

The two-phase liquid gas contactors correspond to many industrial applications, such as liquid phase oxidation and hydrogenation or gas absorption by a liquid with or without a chemical reaction.

The gaseous and liquid phase contacting devices are designed to respond as efficiently as possible to the requirement to ensure the transfer of the quantities of material required, at the best cost, including furthermore notions related to the operation such as flexibility with regard to the quantities of material to be used, safety and stability of operation, speed of execution of the start-up and start-up steps, potential duration of operation (corrosion, maintenance, .... ).

Ainsi les contacteurs gaz liquide sont conçus pour offrir la surface d'échange la plus importante compatible avec des conditions hydrodynamiques relatives aux débits circulants des fluides et des propriétés physico-chimiques de ces derniers. Il est de plus primordial que la perte de charge côté gaz soit aussi modérée que possible afin d'éviter des dépenses énergétiques rédhibitoires ou des conditions de pression incompatibles avec les conditions d'application.In all cases, the quantity of material exchanged within a two-phase apparatus, denoted N, can be evaluated by: $$\begin{array}{l}\mathrm{NOT}=\mathrm{Coefficient\; of\; transfer\; of\; material}\times \mathrm{Interface\; area\; of\; exchange}\times \mathrm{Potential}\\ \mathrm{exchange}\end{array}$$

Thus the liquid gas contactors are designed to offer the largest exchange surface compatible with hydrodynamic conditions relating to the circulating flow rates of the fluids and the physicochemical properties of the latter. It is also essential that the pressure drop on the gas side is as moderate as possible in order to avoid unacceptable energy expenditure or pressure conditions that are incompatible with the application conditions.

The contactors in which the gas is dispersed in the form of bubbles in a liquid cover the bubble column, mechanically stirred tank, perforated plate column, co-current tubular contactor such as static mixer, submerged jet ejector and venturi ejector. engine liquid ( M. Roustan, Gas-liquid transfers in water and waste gas treatment processes, Editions Lavoisier 2003 ; Pierre Trambouze, Chemical Reactors - Technology, J4020, Editions Techniques de l'Ingénieur, 1993 ). These different contactors are characterized by variable levels of fluid retention and interfacial area. Among these tubular contactors operating at co-current of gas and liquid offer the advantages of admitting a wider operating range both in gaseous dispersed phase retention (defined as the ratio of gaseous phase volume reported to the total volume of the contactor equal to the sum of the volumes of gas and liquid contained therein or as the ratio of the volume flow rate of the gaseous phase to the sum of the volume flow rates of gas and liquid) and to generate a very important interfacial area. Their main disadvantage lies in the loss of charge caused to produce the dispersion of the gas, which then limits the retention of the dispersed gas phase to 30% at best in the case of systems with static mixer, submerged jet ejector and ejector venturi liquid engine, the immersion height less than a few meters at most for submerged jet thrusters operating with gas hold-ups greater than 50% because a gas injection installation at a greater depth may have the major disadvantage of requiring a source of pressurized gas, for example example a compressor and its associated piping.

WO 2012025214 discloses a device and method for absorbing ozone in a tubular contactor for treating liquids in which the ozonated gas injection takes place in the circulating liquid stream by means of at least two static mixers spaced from contact zones .

WO 2013082132 relates to a method and apparatus for injecting a gas into a liquid, wherein a rotating helical helix located inside a suction tube immersed in the liquid creates a downward flow of liquid inside the tube suction nozzle fed by gas through nozzles arranged either above or below or along the helical helix. The liquid is sucked into the suction tube at a superficial velocity greater than a terminal rate of rise of the gas bubbles, so as to allow undissolved gas bubbles to be entrained in the bulk of the liquid within the liquid that is sucked into the suction tube. A transfer efficiency of 90% is obtained in the contactor for a gas retention of 5% in the tube of less than one meter in length.

EP 0 086 019 relates to a two-stage hybrid contactor combining a rain column and a bubble column for dissolving a gas in a liquid, preferably for the ozonation of water, in which the gas injection is carried out by means of a submerged tube. According to this method, a fraction of the liquid flow is used to inject the gas in the form of bubbles by means of a submerged tube which introduces the two-phase mixture into a downward flow of the main flow of liquid fed by runoff into the annular portion upper outer of the contactor. This device thus involves a free space of significant volume runoff that promotes degassing so that the yield of dissolution of the gas is reduced. Gaseous retention in the injection tube is indicated as 13% maximum.

FR 2,762,232 also describes a method and a device for contacting ozone in liquids, in particular water, according to which a two-phase mixture of the partial flow of the liquid to be treated and a gas charged with ozone under pressure is formed in a downwardly co-current tube of gas and liquid optionally containing bubble shearing devices, all of which constitute part of an ozone absorption contactor in the U-shaped tube-shaped liquid as described in FR 2 545 732 . The dispersion of the gas in the form of bubbles is obtained in the descending tube under the effect of the liquid velocity of about 1.5 m / s. The height of the contactor is between 20 and 35 m. This type of contactor involves operating with a gas retention of less than 20% to control the two-phase water and gas mixture ( Degrémont, Memento Technique of water, Editions Lavoisier, 2005 ).

US6001247 still exposes a contactor composed of a diffusion compartment equipped with a submerged vertical tube cocurrent descending ozonated gas and water to uniformly introduce the gas. The inside of the tube contains coaxial porous elements to distribute the ozonated gas in the form of bubbles in the water flowing through it.

• La perte de charge importante occasionnée pour produire la dispersion du gaz,
• La limitation de fonctionnement de ces contacteurs à des rétentions de la phase gazeuse dispersée à 30 % ou à des rapports volumiques gaz/liquide de 0,5 au mieux dans le cas des systèmes à mélangeur statique, éjecteur à jet immergé et éjecteur venturi à liquide moteur en application à taille industrielle,
• La limitation de la hauteur d'immersion à moins de quelques mètres au maximum pour les éjecteurs à jet immergé fonctionnant avec des rétentions gazeuses supérieures à 50 % correspondant à des rapports volumiques gaz/liquide supérieurs à 1 alors que la pression statique est bénéfique au transfert de matière gaz liquide,
• La limitation de conception des jets immergés à des volumes et des hauteurs de contacteur réduits sous l'effet de probables difficultés d'ingénierie pour l'extrapolation des systèmes à plus grande échelle,
• L'utilisation d'éléments de construction tels qu'éléments de mélangeurs statiques, éléments hélicoïdaux, buses d'éjection de liquide sensibles au colmatage par des dépôts et nécessitant une maintenance accrue,
• Des conditions de fonctionnement en vitesse liquide supérieure à 10 m/s inacceptables vis-à-vis de la durée de vie des équipements,
• La faible flexibilité des systèmes vis-à-vis de la variation des conditions de fonctionnement.

L'invention a aussi pour but de permettre d'obtenir un mélange diphasique avec un rapport volumique gaz/liquide supérieur à 0,3, sans toutefois consommer trop d'énergie et sans mettre en jeu des pressions de liquide élevées, de l'ordre de 4 bars. Il est souhaitable en outre que le procédé et le dispositif de dispersion soient simples à mettre en oeuvre, et que leur maintenance ne soit pas rendue difficile par la présence de particules dans le liquide. L'invention est définie par les caractéristiques des revendications 1 et 9. Selon l'invention, le procédé de dispersion de gaz dans un courant descendant de liquide, est caractérisé en ce que :

• le liquide est distribué selon au moins un jet dirigé vers le bas, de préférence selon une pluralité de jets,
• le gaz est distribué radialement vers le ou les jets de liquide pour être entraîné par le liquide,
• et le mélange liquide gaz est canalisé dans un tube vertical d'écoulement descendant.

Avantageusement, le gaz est distribué sous une pression inférieure à 2 bars, de préférence inférieure à 1,5 bar.
La vitesse des jets de liquide peut être comprise entre 4 et 10 m/s, de préférence entre 6 et 8 m/s.
La section transversale du tube vertical est au moins égale à la surface totale d'émission des jets de liquide, et au plus égale à 2 fois cette même surface, ladite section transversale étant de préférence comprise entre 1,2 et 1,5 fois la surface totale d'émission des jets.
Avantageusement, le liquide est dirigé au-dessus d'une plaque horizontale comportant une pluralité d'orifices à l'intérieur d'une zone, pour s'écouler vers le bas selon une pluralité de jets,

• le gaz est distribué radialement vers l'intérieur de ladite zone d'orifices pour le liquide,
• le mélange liquide gaz est canalisé selon une section décroissante jusqu'à rejoindre le tube vertical d'écoulement descendant.

De préférence, le mélange liquide gaz est canalisé dans le tube vertical descendant pendant au moins 0,2 seconde. FR 2,776,942 also details a device for dispersing a gas in a liquid by submerged jet. The dispersing device consists of a single emitting nozzle of a downward directed liquid jet, a coaxial jet tube, and an impact plate located near the lower end of the tube. . The level of the dispersion is maintained as close as possible to the outlet of the nozzle by maintaining the level in the surrounding contactor. The jet produced by the nozzle draws the gas admitted laterally to the nozzle and the vehicle in the tube simultaneously with the dispersion which penetrates from the outside to the inside of the tube through submerged holes. The assembly is dispersed in the mass of the surrounding contactor by impact on the plate. No bubble reaches the volume below the plate from which is taken the liquid that feeds the nozzle through a pump. As is readily understood, this single emitter nozzle device is suitable for dispersing gas in a reduced volume contactor, typically less than one cubic meter as presented. This device is also difficult to build on a large scale due to the fragility provided to the structure by the recirculation orifices to be made in the down tube. Finally the high speed limit ejection given at 12 m / s is unacceptable vis-à-vis the abrasion of materials for the construction of the down tube. DE 20 2006002983 describes a method and a device according to the preambles of claims 1 and 9. The method according to the invention aims, above all, to avoid the many disadvantages of tubular contactors operating at co-current of gas and liquid capable of producing a important interfacial area and described in the state of the prior art. The main disadvantages are recalled below:

• The significant loss of pressure caused to produce the dispersion of the gas,
• The operating limitation of these contactors to 30% dispersed gas phase retentions or to gas / liquid volume ratios of at best 0.5 in the case of static mixer systems, submerged jet ejector and liquid venturi ejector motor in application to industrial size,
• The limitation of the immersion height to less than a few meters maximum for submerged jet thrusters operating with gas retentions greater than 50% corresponding to gas / liquid volumetric ratios greater than 1 while the static pressure is beneficial to the transfer of liquid gas material,
• The design limitation of submerged jets at reduced contactor volumes and heights under the effect of probable engineering difficulties for the extrapolation of larger-scale systems,
• The use of building elements such as static mixer elements, helical elements, liquid ejectors sensitive to clogging by deposits and requiring increased maintenance,
• Operating conditions in liquid velocity greater than 10 m / s unacceptable with respect to the service life of the equipment,
• The low flexibility of the systems vis-à-vis the variation of the operating conditions.

The invention also aims to provide a two-phase mixture with a gaseous / liquid volume ratio greater than 0.3, without however consuming too much energy and without bringing into play high liquid pressures, of the order 4 bars. It is further desirable that the method and the dispersing device are simple to implement, and that their maintenance is not made difficult by the presence of particles in the liquid. The invention is defined by the features of claims 1 and 9. According to the invention, the method of dispersing gas in a downward flow of liquid, is characterized in that:

• the liquid is distributed in at least one jet directed downwards, preferably in a plurality of jets,
• the gas is distributed radially towards the jets or liquid to be driven by the liquid,
• and the liquid gas mixture is channeled into a vertical downflow tube.

Advantageously, the gas is distributed under a pressure of less than 2 bar, preferably less than 1.5 bar.
The speed of the liquid jets can be between 4 and 10 m / s, preferably between 6 and 8 m / s.
The cross section of the vertical tube is at least equal to the total emission surface of the liquid jets, and at most equal to twice the same surface, said cross section preferably being between 1.2 and 1.5 times the total emission area of the jets.
Advantageously, the liquid is directed above a horizontal plate having a plurality of orifices within an area, to flow downwards in a plurality of jets,

• the gas is distributed radially inward of said orifice zone for the liquid,
• the liquid gas mixture is channeled in a decreasing section to join the downward vertical tube.

Preferably, the liquid gas mixture is channeled in the descending vertical tube for at least 0.2 seconds.

• en partie haute, une tête d'injection reliée au conduit d'arrivée et comportant une chambre de mélange à jet liquide,
• et en partie inférieure un tube vertical, de préférence coaxial, à écoulement diphasique.

La tête d'injection comprend un compartiment avec, en partie inférieure, une plaque horizontale de distribution pour le liquide percée d'au moins un orifice, et une chambre annulaire prévue sous la plaque à sa périphérie et comportant au moins une ouverture de distribution du gaz suivant une direction radiale centripète,

• la chambre de mélange, située au-dessous de la plaque, étant sous forme d'un convergent de raccordement au tube vertical descendant.

Avantageusement, le diamètre des orifices de la plaque est suffisant, en particulier au moins égal à 10 mm, pour éviter un colmatage dû à des particules contenues dans le liquide, en particulier des eaux usées.The injected gas may be selected from air, oxygen, ozone, carbon dioxide, these gases being injected alone or in mixtures.
Preferably, the liquid is aqueous including natural fresh or saline water, wastewater and more generally aqueous effluents, process water in industry including the drinking water production sector.
The invention also relates to a device for dispersing gas in a liquid according to claim 9, in particular for the implementation of a method as defined above, comprising an inlet conduit for the liquid to be treated. The device comprises:

• in the upper part, an injection head connected to the inlet duct and comprising a liquid jet mixing chamber,
• and in the lower part a vertical tube, preferably coaxial, two-phase flow.

The injection head comprises a compartment with, in the lower part, a horizontal distribution plate for the liquid pierced with at least one orifice, and an annular chamber provided under the plate at its periphery and comprising at least one dispensing opening of the gas in a centripetal radial direction,

• the mixing chamber, located below the plate, being in the form of a converging connection to the downward vertical tube.

Advantageously, the diameter of the orifices of the plate is sufficient, in particular at least equal to 10 mm, to prevent clogging due to particles contained in the liquid, in particular wastewater.

The device comprises a radial inlet of the gas in the annular distributing chamber, from a gas pipe extending beyond the radial inlet for possible venting to the atmosphere.
Such venting is particularly advantageous, in particular because it improves the safety during the operation of such a device, in particular during a stop sequence of the device. During such a sequence stopping, it typically begins by evacuating the gas contained in the device by replacing it with outside air, through the extension, or vent pipe, of said gas pipe. Typically, a vent valve is gradually opened so as to introduce outside air into the mixing chamber through this vent pipe, and then a gas inlet valve is closed so as to interrupt the arrival. of gas in the mixing chamber through said gas conduit. The venting thus makes it possible to avoid any phenomenon of implosion of the device. This is particularly advantageous in cases where the gas introduced into the mixing chamber through the gas pipe is dangerous, typically ozone.
In addition, such venting makes it possible to comply with such safety constraints, particularly when the device performs an injection of gas into a water level situated at a relatively low altitude relative to the altitude of the injection head. , that is to say when said downward vertical tube has a relatively long length before submersion, for example 10 meters.

The venting also makes it possible to improve the flexibility of the device during a start-up sequence during which a liquid is injected into the mixing chamber via said inlet duct for the liquid to be treated. Typically, during such a start sequence, the vent valve is opened, allowing at least a portion of the gas present in the mixing chamber to be evacuated. Venting also allows the gas supply to be closed until the desired hydraulic speed is achieved. The gas inlet is then opened and the vent valve is closed.

The cross section of the vertical tube is at least equal to the total surface of the holes of the plate, and at most equal to twice the same surface, and is preferably between 1.2 and 1.5 times the total surface of the orifices. of the plate.

The length of the descending tube may be between 1 and 30 meters, and is preferably between 1 and 15 meters.

The convergent of the mixing chamber may be frustoconical, the angle of inclination of the generatrices of the truncated cone relative to the axis being between 15 ° and 45 °.

The injection system which is the subject of the invention is a dispersion system with a hybrid liquid gas jet mixer and a jet injector. Said system is composed of an injection head comprising a liquid-jet mixing chamber at the top and a vertical coaxial tube with diphasic jet at the bottom, forming a nozzle. Its function is to homogeneously disperse the gas in the form of fine bubbles in the engine liquid as a liquid gas contactor or for subsequent contact with the mass of liquid in a surrounding contactor. Said liquid gas dispersion is produced for a gas retention of between 5 and 70%, preferably between 30 and 50%.

The injection head is designed to pre-mix the liquid and the gas upstream of the nozzle, the mixture being made homogeneous along the descent into the nozzle.

The gas and the liquid may be those involved in any operation requiring the formation of a liquid gas dispersion.

Preferably, the injected gas will be selected from air, oxygen, ozone, carbon dioxide, these gases being injected alone or in mixtures.

Preferably, the liquid will be aqueous including natural fresh or saline water, wastewater and more generally aqueous effluents, industrial process water in the industry including the drinking water production sector.

According to a preferred embodiment, the injection head is fed by the liquid discharged by a pumping system and the gas from the distribution system is at a pressure equal to or greater than atmospheric pressure. The injection head performs a premixing of the liquid and the gas under the effect of one to several turbulent streams of liquid emitted into the radially admitted gas stream. The jets of liquid are produced by means of a liquid distribution member in the form of jets at high speed, typically between 4 and 10 m / s, preferably between 6 and 8 m / s.

The dispensing member is preferably an orifice distribution plate. A mixing chamber located below the dispenser member has the shape of the section of the dispensing plate as an upper section. The mixing chamber is tulip-shaped or frustoconical convergent or cylindrical or parallelepipedal.

The turbulence of the jets is demonstrated by Reynolds numbers greater than 10 ⁵ . The emission of the liquid jets produces an interfacial friction rate in the gas, which can thus reach more than 0.3 m / s, ie a speed greater than the terminal gas bubble speed of the order of 3 mm. A liquid flow diagram shows the liquid flow lines and highlights the areas of liquid recirculation within the mixing chamber also filled with gas. The high speed liquid jets thus shear the gas and suck up the produced gas pockets towards the down tube. In addition, the liquid jets initiate the transfer of liquid gas material. Considering an average contact time of the liquid jets of 0.15 s, the transfer coefficient is of the order of 1.10 ^-4 m / s according to the nature of the gas. The exchange potential is equal to the equilibrium concentration between the gas and the liquid. For example, in the case of carbon dioxide as a gas to be dispersed in water and liquid distribution jets at the rate of 10 m / s over a total area of 0.3 m ² and 1 m in height, the quantity The amount of carbon dioxide transferred is 0.3 kg / s.

The mixing chamber is followed downstream of a preferably cylindrical coaxial tube. The section of the tube is at least equal to the total emission surface of the liquid jets in the mixing chamber and at most equal to twice the same surface. The ratio of these surfaces is preferably between 1.2 and 1.5.

• L'écoulement à bulles apparaît pour de faibles valeurs du rapport des débits gaz et liquide. Il est caractérisé par une phase liquide continue fortement turbulente avec une dispersion homogène de bulles de gaz de taille relativement uniforme,
• Pour des rapports des débits gaz et liquide plus élevés, les régimes intermittents à bulles et à poches et agités se mettent en place en place,
• Les régimes à film et annulaire apparaissent pour des rapports volumiques de gaz et de liquide très élevés.

La carte d'écoulement en conduite verticale dépend, par ordre d'importance : des vitesses superficielles de gaz et de liquide, du diamètre de la conduite et des propriétés des fluides.It is known from the state of the prior art that vertical pipe flow can take many forms depending on the operating conditions and dimensions of the pipe. The transition between the different regimes operates according to the ratio of gas and liquid flow rates:

• The bubble flow appears at low values of the ratio of gas and liquid flow rates. It is characterized by a highly turbulent continuous liquid phase with homogeneous dispersion of gas-sized bubbles relatively uniform,
• For higher gas and liquid flow ratios, the intermittent bubble and bagged and stirred regimes are put in place,
• The film and ring regimes appear for very high volume ratios of gas and liquid.

The flow chart in vertical pipe depends, in order of importance: superficial velocities of gas and liquid, the diameter of the pipe and the properties of the fluids.

In the present case, the dispersion device according to the invention makes the two-phase mixture homogeneous during the downward co-flow flow in the coaxial tube to the liquid distributor, as has been observed for a 40% gas retention. %.

The length of the down tube can reach 30 meters to promote the transfer of material inside the tube and possibly in the surrounding contactor whose height corresponds to the useful height of the dispersion system. The height is preferably between 1 and 25 m. A gas retention in the two-phase volume equal to 50% corresponds to the compact stack of the gas inclusions in the liquid. Therefore, the attainment of a homogeneous bubble size in the descending tube requires shearing again the volume of gas sucked under the effect of the turbulence of the mixture while the frequency of coalescence of the bubbles is all the more important than the gas retention is high. The turbulence of the mixture is demonstrated by Reynolds number levels of the diphasic mixture greater than 10 ⁴ . This turbulence is maintained by applying a relative liquid velocity equal to the liquid velocity of the distribution jets in the mixing chamber for the best continuity of flow, ie typically between 4 and 10 m / s. This velocity tends to decrease slightly during the descent under the effect of the compression of the gas under the effect of the column of liquid and under the effect of the transfer of material which takes place. The regime is established in the area of bubble flow from the top of the tube. The quality of the mixture at the beginning of the descending tube determines the pressure required for the injected gas.

Indeed, the pressure of the liquid gas mixture is a function of the outlet pressure of the nozzle (mainly a function of the immersion height), the pressure drops and the weight of the liquid column in the injection system (which can be considered as the static component). It turns out that an annular liquid film type flow regime such as that observed in the first meters of a tube equipped with a nozzle and without premixing of the gas and liquid operating with gaseous retention of 40% prevents the transmission of static pressure downwards.

The loss of liquid height is reflected directly by the need to increase the pressure of the gas injection. The device of the invention allows on the contrary a regular transmission of the pressure because it provides a good quality of dispersion from the beginning of the descent into the tube. The size of the bubbles produced is correlated with the dissipated energy itself, which is dependent on the local retention rates and on the physicochemical properties of the fluids composing the dispersion. A dispersion of oxygen in water at 40% gas is characterized by bubbles of average diameter equal to 2.5 mm at the end of the tube 10 m in length.

The highly concentrated two-phase jet of dissolved gas produced at the outlet of the tube can then be dispersed in a surrounding contactor or relaxed towards the outlet of the reactor according to the contact time necessary for the absorption and possibly the reaction involved in the application. The surrounding contactor may be any contactor known from the state of the art with a gas updraft.

• Fig.1 est une vue schématique de dessus en perspective du dispositif de dispersion selon l'invention.
• Fig.2 est une vue schématique en perspective selon un autre angle de vue et avec parties coupées du dispositif de Fig.1, et
• Fig.3 est une vue en perspective du dessous du dispositif de Fig.1.

The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed below with reference to an example embodiment described with reference to the appended drawing, but which is in no way limiting. On this drawing :

• Fig.1 is a schematic view from above in perspective of the dispersion device according to the invention.
• Fig.2 is a schematic view in perspective according to another angle of view and with cut parts of the device of Fig.1 , and
• Fig.3 is a perspective view of the bottom of the device Fig.1 .

Referring to the drawing, it can be seen that the dispersing device D comprises two sets: an injection head H and a jet dispersion tube P, forming a nozzle. The injection head H is the structure that connects the liquid and gas inlets, mixes these fluids and directs the resulting mixture into the down tube P.

The injection head H is connected to the inlet pipe 1 of liquid and comprises a compartment B with, in the lower part, a liquid distribution member, preferably a horizontal distribution plate 2 for the liquid, pierced with orifices. 2a. The liquid flows vertically below the plate, following jets schematized by arrows A on Fig.2 .

An inlet pipe 4 of the gas to be injected is connected, by a radial box 4a, to an annular chamber 5 located under the plate 2, the lower periphery of which it surrounds. A wall E limiting radially inwards the chamber 5 comprises nozzles or openings O of gas distribution in centripetal radial directions represented by arrows F on Fig.2 .

A mixing chamber 3 is located under the plate 2. The mixing chamber 3 is preferably convergent tulip or frustoconical shape, but could be of cylindrical or parallelepipedal shape.

In the case where the chamber 3 is in the form of a frustoconical convergent downwards, the inclination of the generatrices of the convergent with respect to the geometric axis is preferably between 15 ° and 45 °. The chamber 3 provides the connection to the downward vertical tube P, preferably coaxial and cylindrical.

A venting system 6 for the start-up phase is provided at the end of the pipe 4 beyond the connection with the annular chamber 5. A vent valve, not shown, is provided in the system 6, and a gas inlet valve not shown.

The jet dispersion tube P is hydraulically described as a straight vertical pipe length.

The operation of the device is as follows.

• Quand le dispositif ou système est arrêté, le niveau d'eau à l'intérieur du tube immergé P est égal au niveau d'eau à l'extérieur. Au-dessus de ce niveau, la chambre de mélange 3 et le tube P sont remplis de gaz.
• L'alimentation en liquide est démarrée selon un débit égal au tiers du débit de fonctionnement souhaité. Le liquide remplit la canalisation 1 d'alimentation du système.
• La plaque de distribution 2 produit des jets de liquide à faible vitesse.
• Le système de mise à l'atmosphère 6 permet de ourqer le gaz initialement contenu dans la tête d'injection et les poches de gaz entraînées au démarrage en amont dans le haut du tube P.
• Lorsque le débit de purge devient nul, la vanne du tuyau d'évent du système de mise à l'atmosphère 6 commute progressivement vers l'alimentation en gaz par la conduite 4 et le système peut entrer en production.
• Le débit de liquide est porté à sa valeur de fonctionnement.
• En régime stationnaire, le mélange de gaz et d'eau formé dans la chambre 3 circule vers le bas du tube.

The start-up sequence of the device, integrated into a surrounding contactor not shown, provides a better understanding of the overall design of the device in its entirety.

• When the device or system is stopped, the water level inside the submerged tube P is equal to the water level outside. Above this level, the mixing chamber 3 and the tube P are filled with gas.
• The liquid supply is started at a rate equal to one third of the desired operating flow. The liquid fills the supply line 1 of the system.
• The distribution plate 2 produces jets of liquid at low speed.
• The venting system 6 allows the gas initially contained in the injection head and the entrained gas pockets to start upstream upstream of the top of the tube P.
• When the purge flow becomes zero, the vent pipe valve of the venting system 6 progressively switches to the gas supply via line 4 and the system can come into production.
• The liquid flow rate is brought to its operating value.
• In steady state, the mixture of gas and water formed in the chamber 3 flows down the tube.

• La première étape consiste à évacuer le gaz contenu dans le dispositif en le remplaçant par de l'air extérieur ou un gaz inerte. Pour cela, la vanne d'évent du système 6 est ouverte progressivement sur de l'air extérieur ou un gaz inerte, après quoi la vanne d'entrée de gaz du système 6 se ferme.
• Le dispositif continue de fonctionner, la totalité du gaz présent est remplacée.
• Après une courte période correspondant au renouvellement par 5 fois du volume total du dispositif, le dispositif peut être arrêté dans des conditions entièrement sécuritaires, en diminuant progressivement le débit d'eau.

The shutdown sequence of the dispersing device is as follows:

• The first step is to evacuate the gas contained in the device by replacing it with outside air or an inert gas. For this, the vent valve of the system 6 is progressively open on outside air or an inert gas, after which the gas inlet valve of the system 6 closes.
• The device continues to operate, all of the present gas is replaced.
• After a short period corresponding to the renewal by 5 times of the total volume of the device, the device can be stopped under completely safe conditions, gradually decreasing the flow of water.

Although the foregoing descriptions of the start-up and shutdown of the device more than once mention the gradual change in operating conditions in gas and liquid flow, it should be noted that the device is capable of responding correctly to abrupt changes in conditions. , resulting, for example, from a power failure or any other event that could lead to an unscheduled shutdown.

This device makes it possible to ensure an eminently variable gaseous engagement of between 0.01 and 2 (if expressed in relation to gas and liquid flow rates), at the best cost under the effect of the necessary pressure reduction, to produce a homogeneous dispersion of gas in the liquid suitable for transferring the quantities of material required.

• La sécurité et stabilité de fonctionnement ;
• La rapidité d'exécution des étapes de démarrage et mise en régime ;
• La durée potentielle de fonctionnement (corrosion, maintenance,....).

At the same time, it offers the following advantages:

• Security and stability of operation;
• The speed of execution of the start-up and start-up steps;
• The potential duration of operation (corrosion, maintenance, ....).

This device solves the disadvantages of the systems described in the state of the prior art and is also capable of replacing all or part of the gas injection and diffusion systems of the bubble column contactors, injection systems of gas and agitation of the agitated contactors. The resulting contactors are much more efficient both technically and economically.

Claims (13)

1. A process for dispersing gas in a downward flow of liquid, characterized in that:

   - the liquid is distributed as at least one downward-directed jet (A), preferably as a plurality of jets,

   - the gas is distributed radially (F) toward the liquid jet(s) in order to be entrained by the liquid,

   - and the liquid-gas mixture is channeled in a vertical tube (P) with downward flow,

   said process being implemented by a device comprising:

   - an inlet pipe (1) for the liquid to be treated

   - in the upper part, an injection head (H) connected to the inlet pipe and comprising a liquid-jet mixing chamber (3),

   - and in the lower part, a vertical, preferably coaxial, tube (P) with two-phase flow,

   - the injection head (H) comprising a compartment (B) with, in the lower part, a horizontal distribution plate (2) for the liquid perforated with at least one orifice (2a), and a distributing annular chamber (5) provided under the plate (2) over its periphery, and comprising at least one opening for distribution of the gas along a centripetal radial direction (F),

   - the mixing chamber (3), located under the plate, characterized in that the mixing chamber is in the form of a convergent section for coupling to the vertical down tube (P) and characterized in that the device comprises a radial inlet (4a) of the gas into the distributing annular chamber (5), from a gas pipe (4) that extends (6) beyond the radial inlet for possible venting to the atmosphere.
2. The process as claimed in claim 1, characterized in that the gas is distributed under a pressure of less than 2 bars, preferably less than 1.5 bar.
3. The process as claimed in claim 1 or 2, characterized in that the velocity of the liquid jet(s) (A) is between 4 and 10 m/s, preferably between 6 and 8 m/s.
4. The process as claimed in claim 1, characterized in that the cross section of the vertical tube (P) is at least equal to the total emission area of the liquid jets (A), and at most equal to 2 times this very area, said cross section preferably being between 1.2 and 1.5 times the total emission area of the jets.
5. The process as claimed in any one of the preceding claims, characterized in that:

   - the liquid is directed above a horizontal plate (2) comprising a plurality of orifices (2a) within a zone, in order to flow downward as a plurality of liquid jets,

   - the gas is distributed radially underneath and toward the interior of said zone of orifices for the liquid,

   - the liquid-gas mixture is channeled along a decreasing section until it reaches the vertical tube (P) with downward flow.
6. The process as claimed in any one of the preceding claims, characterized in that the liquid-gas mixture is channeled in the vertical down tube (P) for at least 0.2 second.
7. The process as claimed in any one of the preceding claims, characterized in that the gas injected is selected from air, oxygen, ozone and carbon dioxide, these gases being injected alone or as mixtures.
8. The process as claimed in any one of the preceding claims, characterized in that the liquid is aqueous including natural fresh waters or salt waters, wastewaters and more generally aqueous effluents, process waters in industry including in the sector for production of drinking water.
9. A device for injecting gas into a liquid, in particular for the implementation of a process as claimed in any one of the preceding claims, comprising an inlet pipe (1) for the liquid to be treated, characterized in that it comprises:

   - in the upper part, an injection head (H) connected to the inlet pipe and comprising a liquid-jet mixing chamber (3),

   - and in the lower part, a vertical, preferably coaxial, tube (P) with two-phase flow,

   - the injection head (H) comprises a compartment (B) with, in the lower part, a horizontal distribution plate (2) for the liquid perforated with at least one orifice (2a), and a distributing annular chamber (5) provided under the plate (2) over its periphery, and comprising at least one opening for distribution of the gas along a centripetal radial direction (F),

   - the mixing chamber (3), located under the plate, characterized in that the mixing chamber is in the form of a convergent section for coupling to the vertical down tube (P) and characterized in that the device comprises a radial inlet (4a) of the gas into the distributing annular chamber (5), from a gas pipe (4) that extends (6) beyond the radial inlet for possible venting to the atmosphere.
10. The device as claimed in claim 9, characterized in that the diameter of the orifices of the plate is sufficient, in particular at least equal to 10 mm, to prevent clogging due to particles contained in the liquid, in particular in wastewaters.
11. The device as claimed in any one of claims 9 or 10, characterized in that the cross section of the vertical tube is at least equal to the total area of the orifices (2a) of the plate, and at most equal to 2 times this very area, and is preferably between 1.2 and 1.5 times the total area of the orifices (2a) of the plate.
12. The device as claimed in any one of claims 9 to 11, characterized in that the length of the down tube (P) is between 1 and 25 meters.
13. The device as claimed in any one of claims 9 to 12, characterized in that the convergent section of the mixing chamber (3) is frustoconical, the angle of inclination of the generatrices of the frustum relative to the axis being between 15° and 45°.

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