EP0305251A1 - Injector mixer under pressure - Google Patents

Abstract

The invention relates to a multiple liquid injector composed of several identical elementary injection tubes 2, arranged in a ring around a central tube. Each tube 2 comprises an inlet pipe 3 itself comprising a converging truncated cone 6 and a cylinder 7, followed by an aeration zone 4 comprising an aeration chamber 8 fed tangentially by a pipe 9 perpendicular to the tubes 2, a funnel 10 for centering the jet, followed by a mixing cylinder 11, and finally a divergent outlet pipe 12.

Description

In the paper industry, paper pulp undergoes numerous purification, separation and various filtration, decontamination and de-inking treatments.

The present invention relates to devices for injecting liquid and air under pressure mixture, and in particular to devices for mixing paper pulp and air, used in decontamination and deinking cells by flotation.

One of the known techniques of decontamination and deinking consists in injecting air into the dough to be treated, at the entry of the cell. The air traps the charges and the ink particles in bubbles, and entrains them towards the surface to form a foam which is then sucked towards a separator.

The quality of deinking depends in particular on the quality of the mixture obtained in the injector: it is indeed necessary that the dough is very aerated in order to retain the maximum quantity of particles in the air bubbles and this aeration must be the most homogeneous and the most evenly distributed in the dough: the bubbles must be very small; and avoid even the irregular presence of large bubbles.

In the technique of liquid-gas mixtures, very many injectors have been studied, each giving particular results corresponding to the specific problem to be solved.

In practice, the flow of fluids being done at high speed in these injectors, it is enough a slight variation either of dimensions, or of arrangement of the elements, or even of structure for that the results be significantly changed. In addition, it is usually impossible to predict the operating results of an injector placed under conditions different from those for which it was designed. In particular, the results of a gas-gas injector-mixer cannot be transposed to those of a liquid-liquid injector-mixer, and even less to those of a liquid-gas injector-mixer.

In the field of aeration of paper pulp before deinking, it is not a question of mixing two bodies of identical phases, nor only of introducing air into a liquid comprising ink and a large quantity of fibers, it is above all a question of forming bubbles, in very great number, and all of similar size.

Injectors are generally used comprising a pressurized liquid inlet and a nozzle-shaped outlet; between the inlet and the outlet there is an air inlet and a cylinder in which the air, sucked in by the flow of the liquid, mixes there before reaching the conical part of the outlet. A device of this kind is described in patent CH-A-581,493.

These injectors usually have an air inlet tube whose end is coaxial with the liquid supply. In operation, we actually observe around the end of the air tube, the formation of an air ring, the air mixing with water at the downstream end of the ring. However, the mixture is not always of good quality because the ring is too short or too thin, or the mixture is unevenly distributed. It follows that the formation of bubbles is irregular and the deinking obtained is poor.

There are also injector-mixers in which the dough flows in a tubular pipe in the form of a nozzle. In the narrowest part is housed a profile of longitudinal section in the shape of a wing. The air is introduced approximately radially into the narrowest part. Such a device is described in patent WO-A-85 01888.

However, such types of injectors still give only poor results.

The amount of air drawn into this type of injector is mainly a function of the supply pressure; it can for example be of the order of 150% of the volume of liquid; however, the problem is not so much to obtain a large flow of aspirated air but rather to ensure a large and constant homogeneity of the liquid-air mixture.

It also turns out that the quantity of liquid itself cannot exceed a certain limit because the exit speed would be too high, and the impact of the bubbles, on exit, against the ambient air, would cause them to burst and the ink would then return to the liquid phase.

The liquid flow rate accepted by an injector cannot be increased indefinitely, by enlarging the section of the mixing cylinder: there is a maximum section. For example, it turns out that for a diameter greater than about 8mm, the aeration becomes irregular: formation of large bubbles, variable air flow, lower quality inking.

This problem is generally solved by using several conventional injectors supplied in parallel. However, these injectors are small in cross-section and therefore have the drawback of clogging easily: during stops in operation, the impurities are deposited in the pipes, upstream of the injectors, agglomerate and dry fairly quickly. At the next start, they come off and cause the injectors to become blocked. These injectors which are generally formed in a single block must be completely dismantled in order to unblock them.

GB-A-1,582,898 describes another injection and mixing device in which the liquid supply line is divided into a plurality of small nozzles, opening into a common chamber supplied with air. Opposite each of these nozzles, there is a venturi-shaped outlet.

However, if this device can function as a pump, it does not give satisfactory results in this deinking: the bubbles are irregular and burst, allowing the ink to escape.

The present invention aims to inject a liquid-air mixture at high flow rate, strong and regular aeration of the liquid and which solves the problems of clogging.

Its subject is an injector mixing liquid and air of the type comprising a supply of pressurized liquid, an air supply at atmospheric pressure, at least one injection tube, each tube successively comprising a converging inlet pipe, a ventilation space, a cylindrical mixing pipe, and a divergent conical outlet and drawing pipe, characterized in that in combination:
the aeration space is flat and perpendicular to the longitudinal axis of the injector, and it is limited by the walls of a cylindrical chamber with an axis parallel to said axis of the injector, and supplied tangentially so as to forming a rotating air current in the chamber;
- the diameter of the mixing line is constant and slightly greater than that of the inlet line,
- the length of the mixing pipe is much greater than its diameter, of the order of 4 to 9 times;
- The length of the outlet pipe is at least equal to that of the mixing pipe and the opening angle α of the cone is of the order of 1 to 3 °.

The injector is also remarkable for the following characteristics:
- the air inlet is arranged horizontally at the bottom of the injector;
- The injector comprises a plurality of parallel injection tubes, arranged in a ring around a central injection tube, and all have the same dimensions;
- The mixing pipe of each tube includes a funnel for receiving and centering the jet, converging on said mixing pipe;
the inlet diameter of the funnel is at most 1.5 times that of the inlet pipe, and the length of the funnel is substantially equal to its diameter;
- The ventilation space has the shape of a circular disc in which perpendicularly opening the dough inlet pipes.
- Said disc being of thickness substantially close to the diameter of an inlet pipe, and it comprises a tangential air inlet;
- The thickness of the aeration disc is between 5 and 15 mm, preferably between 10 and 12 mm.
the injector consists of two parts, one comprising the inlet pipe or pipes and a tangential air inlet pipe, the other comprising the funnels for receiving and centering the jets, the mixing pipes, the divergent outlet cones, the two parts being assembled by screwing or other known means, so that the assembly forms between the two parts, a space, communicating with the air intake duct, in the form of a flat disc or cylinder, separating the liquid inlet pipes from the mixture outlet pipes.

• 1°- l'aération du liquide est améliorée en qualité et en régularité : débit d'air aspiré élevé suivi d'un désencrage important. L'amélioration est remarquable même avec des pourcentages d'air importants, de l'ordre de 150%.
• 2°- L'installation est simplifiée car il est possible de remplacer par exemple, les 16 injecteurs unitaires répartis actuellement sur la périphérie de la cellule, par un ou deux injecteurs multiples selon l'invention.
• 3°- Le nettoyage est aisé du fait de la conception en deux parties facilement démontables.

The injector according to the invention provides the following advantages:

• 1 ° - the aeration of the liquid is improved in quality and regularity: high suction air flow rate followed by significant deinking. The improvement is remarkable even with large percentages of air, of the order of 150%.
• 2 ° - The installation is simplified because it is possible to replace for example, the 16 unit injectors currently distributed on the periphery of the cell, by one or two multiple injectors according to the invention.
• 3 ° - Cleaning is easy due to the design in two easily removable parts.

• Figure 1 une vue schématique de face d'un injecteur selon l'invention;
• Figure 2 une vue en coupe A-A longitudinale de l'injecteur de la figure 1.

By way of example and to better understand the invention, the following drawing shows:

• Figure 1 a schematic front view of an injector according to the invention;
• Figure 2 a longitudinal sectional view AA of the injector of Figure 1.

As shown in the drawing, the injector 1 is generally cylindrical in shape and comprises a plurality of parallel and preferably identical injection tubes 2: six peripheral tubes 2 regularly distributed in a ring around a central tube, each being equal distance from its immediate neighbors.

However, the invention is not limited to this exemplary embodiment and the injector 1 can comprise a greater or lesser number of tubes, or even comprise only one.

Each tube has an inlet pipe 3 for the liquid, an aeration zone 4 for mixing the liquid and the air, and an outlet pipe 5.

The inlet pipe 3 comprises a converging truncated cone 6, followed by a cylinder 7, both of circular sections. The cylindrical section 7 can be very short, it can even be nonexistent, its function is to stabilize the direction of flow after the inlet cone 6.

The aeration and mixing zone 4 of a tube 2 successively comprises:
- an aeration space 8 limited by the walls 25 of a chamber of circular section, communicating with the outside by an air inlet pipe 9, disposed tangentially to the chamber and perpendicular to the direction of flow of the liquid;
- A converging truncated cone, or centering funnel of the jet 10, of circular section, followed by a mixing cylinder 11 of circular section.
- The outlet pipe 5 of a tube 2 comprising a divergent 12, of circular section, of draft or expansion of the foam mixture.

The different frustoconical and cylindrical parts of each tube are coaxial.

The cylindrical chamber 8 is a single volume, common to all the injection tubes 2 so that the injector comprises a bundle of inlet tubes 3 which all open into the chamber 8, and a bundle of outlet tubes 5 , which leave from chamber 8 towards the outlet of injector 1.

The chamber 8 in fact has vis-a-vis the liquid an air layer 23 which the plane jet must pass through; this blade is preferably perpendicular to the longitudinal axis 24 of the injector. The jet in the space of the room is thus permanently entirely surrounded by air and it can aerate as much as possible. In the embodiment, the blade 23 is limited to a chamber-shaped space 8, but it is also possible not to limit the space to a chamber, by separating the inlet parts from the mixing and outlet parts , and keeping them aligned coaxially with a certain distance between them. With such a variant the jet would pass through an air space 23 not limited to the walls of a chamber.

The diameter 13 of the mixing cylinder is greater than the outlet diameter 14 of the inlet cylinder 7 in order to accept a flow of aerated liquid, which is greater than the flow of liquid alone, and the inlet diameter 15 of the funnel centering 10 is substantially greater than the diameter 14 of the inlet cylinder 7 in order to present a large surface for receiving the jet of liquid coming from the cylinder 7.

The operation of the injector 1 is as follows:
- The liquid is supplied under pressure in the inlet tubes 2; its speed increases in the tapered inlet section 6; it enters the air space 23 and passes through it in the form of a jet, then enters the centering funnel 10.

The passage of the liquid at high speed through the air gap 23 limited by the chamber 8 allows it to be perfectly ventilated.

The air inlet pipe 9 into the chamber 8 is arranged tangentially and perpendicular to the direction of the tubes 2 in order to create a rotating movement, promoting the mixing of the air in the liquid and above all promoting the cleaning of said chamber.

• 1°- d'évacuer immédiatement le liquide résiduel lorsque le fonctionnement de l'installation est arrêté, et d'éviter la formation de croûte;
• 2°- en cas d'obstruction d'une des conduites 10,11,12, de renvoyer le liquide provenant de la conduite d'entrée 3 correspondante, dans les autres conduites 10,11,12, et de briser les particules qui sont à l'origine de l'obstruction.

In addition, this pipe is arranged below the flow axis, this arrangement allows:

• 1 ° - to immediately evacuate the residual liquid when the operation of the installation is stopped, and to avoid the formation of crust;
• 2 ° - in the event of obstruction of one of the pipes 10,11,12, to return the liquid coming from the corresponding inlet pipe 3, in the other pipes 10,11,12, and to break the particles which are causing the obstruction.

The liquid then arrives in the cylindrical part 11 of the mixing zone 4 where the air-liquid mixture is produced in the form of bubbles of very small dimensions and where the ink and the contaminants are trapped.

At the end of the journey, the mixture enters and crosses the divergent outlet cone 12, which is a draw cone.

In order for this injector structure to function properly, it is important to observe the orders of magnitude of the following dimensions:
- the mixing line has a constant cross section slightly greater than that of the inlet line;
- the mixing line is much longer than its diameter, of the order of 4 to 8 times and more;
- The outlet pipe is of length at least equal to that of the mixing pipe, and the opening angle α of the drawing cone is very small, of the order of 1 ° to 3 °;
- the inlet section of the funnel is at most 1.5 times that of the section of the inlet pipe;
- the length of the funnel is very small; at most it is equal to its diameter.
- The thickness of the air gap 23 is close to the diameter 14 of an inlet pipe.
- The thickness of the air gap 23 is between 5 and 15 mm, preferably between 10 and 12 mm. This thickness is related to the length of the fibers. When there is a start of plugging, the fibers must be able to distribute themselves in chamber 25 and flow through an unclogged tube. The fact that the thickness of the air gap 23 is the same magnitude as the length of the fibers, thus avoids clogging of the injector, and ensures its unclogging.

The example embodiment illustrated has the following dimensional characteristics:
the slope of the centering funnel 10 is of the order of 7%, as is that of the inlet cone 6,
- The opening ratio of the draft cone 12 is less than 2%, or an angle α of approximately 1 ° 30 ′, but these characteristics are not compulsory;
- for a diameter 14 of the inlet pipe, of 12 mm, the diameter 15 of the funnel is of the order of 16 mm, the length of the funnel of the order of 6 mm, the diameter 13 of the mixing pipe is of the order of 14 mm and its length from 60 to 120 mm, the length of the outlet cone is from 70 to 140 mm, the angle α of approximately 1 °, and the thickness of the blade of air is between 10 and 12 mm.

Such multiple injectors provide both the advantages of large injectors (large flow) and small injectors (maximum ventilation) without having the disadvantages (significant maintenance, expensive equipment: valves, ...)

In addition, in the illustrated variant, the injector 1 is produced in two parts 20, 21 assembled one against the other by screwing 22: the input part 20 comprises the input zone 3, the output part 21 comprises the centering funnel 10, the mixing cylinder 11, and the outlet cone 12. A cylindrical recess is provided on one of the parts 20 or 21 (in the example it is the part 20) to form the chamber 8 which defines a cavity in the form of an air knife 23. A cavity is dug laterally in the hollowed out room to form the tangential air inlet 9.

Claims (9)

1. Device for mixing liquid and air of the pressure injector type comprising a supply of pressurized liquid, an air supply at atmospheric pressure, at least one injection tube, each tube successively comprising a converging inlet pipe , an aeration space, a cylindrical mixing pipe, and a divergent conical outlet and drawing pipe, characterized in that in combination:
- The ventilation space (8) is plane and perpendicular to the longitudinal axis (24) of the injector, and it is limited by the walls (25) of a cylindrical chamber with an axis parallel to said axis of l 'injector, and fed tangentially so as to form a current of air rotating in the chamber;
the diameter (13) of the mixing pipe (11) is constant and slightly greater than that (14) of the inlet pipe (7),
- The length of the mixing pipe (11) is much greater than its diameter (13), of the order of 4 to 9 times;
- The length of the outlet pipe (5) is at least equal to that of the mixing pipe (11) and the opening angle α of the cone is of the order of 1 to 3 °. 2. Device for mixing liquid and air according to claim 1, characterized in that the air inlet (9) is arranged horizontally at the bottom of the injector (1). 3. Device for mixing liquid and air according to claim 1, characterized in that the injector (1) comprises a plurality of injection tubes (2) parallel, arranged in a ring around a central injection tube (2), and all have the same dimensions; 4. device for mixing liquid and air according to claim 1, characterized in that the mixing pipe (11) of each tube (2) comprises a funnel (10) for receiving and centering the jet, converging towards said pipe mixture ; 5. Device for mixing liquid and air according to claim 1, characterized in that the inlet diameter (15) of the funnel (10) is equal to a maximum of 1.5 times that of the line of inlet (7), and the length of the funnel is substantially equal to its diameter (15); 6. A device for mixing liquid and air according to claim 1, characterized in that the ventilation space (8) has the shape of a circular disc (23) into which the inlet pipes open perpendicularly transversely. paste. 7. Device for mixing liquid and air according to claim 1 characterized in that the thickness of the ventilation space (8) is between 5 and 15 mm. 8. Device for mixing liquid and air according to claim 6 characterized in that the disc (23) is of thickness substantially close to the diameter (14) of an inlet pipe (7). 9. Device for mixing liquid and air according to claim 1, characterized in that the injector consists of two parts (20,21) one (20) comprising the inlet pipe or pipes (3) and a tangential air supply line (9), the other (21) comprising the funnels (10) for receiving and centering the jets, the mixing lines (11), the cones of divergent outlet (12), the two parts being assembled by screwing (22) or other known means, so that the assembly forms between the two parts (20,21), a space (8), communicating with the pipe ( 9) air inlet, in the form of a flat disc (23) or cylinder, separating the liquid inlet pipes from the mixture outlet pipes.

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