EP0722521B1 - Device for forming a plane liquid jet - Google Patents

Abstract

PCT No. PCT/FR95/01028 Sec. 371 Date Apr. 5, 1996 Sec. 102(e) Date Apr. 5, 1996 PCT Filed Jul. 31, 1995 PCT Pub. No. WO96/05369 PCT Pub. Date Feb. 22, 1996Device for the formation of a fan jet (J) of liquid, of the type comprising: means (3) for supplying a liquid; means for distributing the delivery and for controlling the turbulence of the liquid supplied; outlet means (4) for the fan jet (J) formed, characterized in that the means for distributing the delivery and for controlling the turbulence of the liquid supplied are formed: from a first fixed curved conduit (15) for the flow of the liquid; from a second curved conduit (25) having an axis parallel to that of the first conduit (15); from means (26) for forming calibrated vortices having an axis parallel to the curved flow, so as to bring about a harmonic transverse distribution of the speeds and pressures and to control the scale and level of the vortices. Planned uses: headbox of a paper machine or installation for the couching of paper.

Description

Technical area

The invention relates to a device for forming a plane jet. a liquid; it relates more particularly to the formation of such jet plan in the field of mixing, coating, coating and manufacture of sheet or plate materials from particles in suspension in a fluid, in particular suspension of fibers in water (see US-A-2,451,305).

The invention is particularly suitable for the paper industry in level of leaf formation from fibrous suspensions; she also finds different applications in the field of coating and in the coating of paper and cardboard.

If in the following description, the invention is particularly described in its application to the manufacture of papers, it can also find other applications in mixtures with or without heat exchange in the chemical and agro-food industries, pharmaceuticals or water treatment, as well as in manufacturing films from polymers or molten metals, or in the fiber cement manufacturing.

Previous techniques

In the manufacture of paper and cardboard, the fibrous suspension turns into a jet of dough coming out of the headbox.

• uniformité de l'épaisseur du jet ;
• vitesse constante à la buse de sortie ;
• homogénéité de la concentration en fibres ;
• et si possible, contrôle de la floculation.

As is known, a headbox must essentially ensure a uniform and homogeneous jet in the outlet nozzle, while attenuating the irregularities in speed, pressure and concentration coming from the distributor for the arrival of the dough. Whatever the dough arrival system, a headbox must essentially ensure the following main properties:

• uniformity of spray thickness;
• constant speed at the outlet nozzle;
• homogeneity of the fiber concentration;
• and if possible, flocculation control.

These properties must be stable in space, especially in the crosswise, and in time (i.e. in the direction of travel of the jet), so that the grammage of the sheet remains constant and homogeneous.

For constant lip opening, any local variation in sheet weight comes from either a local speed variation, either the concentration caused by the flocculation, or both at the time.

When the speed in the jet varies, it causes a variation in the quantity of material, which can introduce variations of the order of 1 to 5% over time and across the width of the sheet formed.

The speed variations in the cross direction are of origin not turbulent. They can be random if the surface finish of the output is perfect, if not stationary. We thus sought to standardize the pressure in the outlet nozzle to obtain a uniform distribution of the speed field. However, this setting is difficult to obtain on nozzle widths of the order or more than three meters.

As is known, the fluctuations in fiber concentration are linked to flocculation, the intensity of which depends essentially on the hydrodynamic turbulence generated in the headbox. This turbulence causes dislocation of the flocs. So the vortices of small size, i.e. whose size is smaller than that of the flocs, dislocate the flocs into individual fibers, while the large vortices drive the flocs in their movement. So there is an interaction of these two types of vortices between them, which can cause refloculation.

Head boxes designed for high concentration training must be effective at low concentrations. Indeed, power deflocculate a concentrated system and maintain it in the free jet, must allow perfectly homogeneous flows to be achieved with commonly used concentrations.

To obtain this result, the principle of classic turbulence generation, with more or less variances for dislocate the flocs. However, conventional turbulence is not sufficient to a total dislocation of the flocs. In addition, the boundary layer hydrodynamics in the outlet nozzle, which is involved in particular in the distribution of the speeds in the jet, is not taken into account in the design of head boxes.

The invention overcomes these drawbacks.

It targets a device of the type in question, making it possible to generate a particular turbulence where the size of the vortices is calibrated while following a discrete law throughout the flow in the device.

The invention relates more particularly to a headbox capable of generate vortices to ensure the dislocation of flocs in better conditions, in particular by a stretching effect rotational, known by the English term "swirling".

Statement of the invention

• des moyens d'alimentation d'un liquide ;
• des moyens de répartition du débit et de contrôle de la turbulence du liquide alimenté ;
• des moyens de sortie du jet plan formé se caractérise en ce que les moyens de répartition du débit et de contrôle de la turbulence du liquide alimenté sont formés :
• d'un premier canal incurvé fixe pour l'écoulement du liquide ;
• d'un second canal d'écoulement incurvé, d'axe parallèle à celui du premier canal;
• et de moyens pour former des vortex calibrés d'axe parallèle à celui des canaux incurvés, de manière à créer une répartition transversale harmonique des vitesses et des pressions, et à contrôler l'échelle et le niveau des vortex.

This device for the formation of a plane jet of liquid of the type comprising:

• means for supplying a liquid;
• means for distributing the flow rate and controlling the turbulence of the liquid supplied;
• means for outputting the plane jet formed is characterized in that the means for distributing the flow rate and for controlling the turbulence of the liquid supplied are formed:
• a first fixed curved channel for the flow of the liquid;
• a second curved flow channel, with an axis parallel to that of the first channel;
• and means for forming calibrated vortices with an axis parallel to that of the curved channels, so as to create a harmonic transverse distribution of speeds and pressures, and to control the scale and level of the vortices.

This device is particularly suitable for the treatment of fibrous suspensions in the paper industry.

In a preferred embodiment, the invention consists, in a headbox of a paper machine, to introduce the suspension fibrous in two successive curved channels with parallel axis, coaxial in particular, so as to form calibrated vortices with an axis parallel to the flow, therefore to the channels, to create a transverse distribution harmonic of velocities and pressures, and consequently form a homogeneous jet in speed and reduced flocculation, even at high concentration.

• le moyen pour former des vortex calibrés est constitué par au moins un cylindre rotatif d'axe parallèle à celui des deux canaux incurvés ;
• les deux canaux incurvés sont disposés en série de manière à produire une succession d'échelles et de niveaux de turbulence adaptée à la défloculation progressive de la suspension fibreuse.

Advantageously in practice;

• the means for forming calibrated vortices consists of at least one rotary cylinder with an axis parallel to that of the two curved channels;
• the two curved channels are arranged in series so as to produce a succession of scales and turbulence levels adapted to the progressive deflocculation of the fibrous suspension.

The first external fixed flow channel produces vortices calibrated on a large scale adapted to the dispersion of the largest flocs.

The second internal flow channel with an axis parallel to the first, associated with the rotating cylinder, produces small-scale calibrated vortices suitable for dispersing the smallest flocs of fibers.

The rotary cylinder rotates in the same direction as the flow of the suspension, and the peripheral speed of the rotary cylinder is approximately three to four times that of the flow velocity, if we wants to minimize pressure losses.

The rotary cylinder has a non-uniform surface condition, for example example of which the generator follows a broken or wavy line, regular preference.

Advantageously, the generator of the cylinder follows the shape of a radial sine groove with a wavelength of about two to ten times (preferably three to five times) the average length of the fibers.

If more generally, the device comprises a single cylinder rotary, it can also have two parallel axes.

In another embodiment, the device also comprises a deflector member arranged between the rotary cylinder and the outlet jet to separate the flow between the supply and the outlet in the channel curved.

In another form of execution, the device has means for introducing water, solutions or suspensions, arranged along a generator of at least one of the curved channels, so as to regulate the concentration and composition of the dough at the level of the jet.

In a variant, a composition is introduced into this means different (retention agents, fine elements, etc.) from the suspension main, so as to create an effective mixture of the different suspensions in the jet.

In another advantageous form of execution, at least two head boxes according to the invention, possibly with a or several conventional head boxes (multijet paper and cardboard).

Thus, the new headbox according to the invention aims to generate a particular turbulence where the size of the vortices is calibrated. The size of these vortexes varies discreetly or continuously throughout the flow. So, at the cash register entrance, we start by generating large Dean vortex in the first curved channel, so to dislocate large flocs into smaller flocs. In the second channel curved coaxial to the first, we again reduce these flocs by vortices of Taylor modified more and more small, until total dislocation.

In the version with two rotary parallel cylinders, we further reduce plus the size of these Taylor vortices to disperse the smallest flocs.

As we control the intensity and size of the vortices all along these channels, we completely change the flocculation-turbulence interaction by an action of turbulence on the flocculation. This device allows therefore to obtain very homogeneous suspensions, even at high concentration (four percent or more), regardless of the nature of the fibers.

Furthermore, the lifetime in the free jet of the generated vortices is much larger than that of a conventional turbulence, exploited until then.

This parameter is important in free jet, because relaxation is at say the reappearance of the flocs, strongly depends on it since the turbulence production no longer exists.

The manner in which the invention can be realized and the advantages which From this will emerge more clearly the examples of embodiment which follow, in support of the appended figures.

Brief description of the drawings

Figure 1 is a representation of a device according to the invention in its application to head boxes for the manufacture of paper.

Figure 2 is an alternative embodiment of Figure 1 with recyclag or dilution.

Figure 3 is another embodiment of the invention, in which three devices are associated.

Figure 4 is a schematic representation of the invention in application of paper coating.

Ways to realize the invention

The headbox according to the invention, designated by the reference general (1) comprises an enclosure (2) connected from below to a feeding (3) in fibrous suspension, commonly used in manufacture of paper or cardboard.

The enclosure (2) of parallelepiped shape, for example of section square, has an outlet orifice (4) from which the plane jet comes (J). The orifice outlet (4) is advantageously formed in a known manner by a lip fixed lower (5), and an upper lip (6), adjustable relative to the lower lip (5), to adjust the size of the outlet.

According to a first characteristic of the invention, the conduit supply (3) opens into a first space (10) formed between the rectilinear vertical wall (11) and a curved portion (12) so that that the thickness of the vein of the liquid fluid (F) decreases gradually.

According to a second characteristic of the invention, the liquid flow (F) enters a first fixed curved flow channel, designated by the general reference (15), formed by two curved coxial plates, respectively exterior (16) and interior (17) in the extension of (12). In this channel (15), large Dean vortices are generated which dislocate large flocs into small flocs. The curved area (16) does everything around the enclosure (2) and at the level of the wall (18) parallel to (11) is welded at (19) at the inlet (20) of the upper lip (6).

According to another characteristic of the invention, the device also includes a second channel, designated by the general reference (25) formed by the internal face of the curved plate (17), so that that the fibrous suspension (F2) be subjected to Taylor vortices modified more and more small, until total dislocation of the flocs.

According to another essential characteristic of the invention, the device also includes a rotating cylinder (26) about an axis (29) parallel to the axis of the channels (15 and 25), driven by a motor (27) at by means of a belt (28).

The treated suspension (F3) enters the outlet channel (4) to thus form the desired jet plane (J).

Thus, throughout the flow (F1, F2, F3), we control the intensity, level and size of the vortices, which causes a turbulence on the flocculation, instead of a flocculation-turbulence interaction.

According to another characteristic of the invention, the rotary cylinder (26) which forms the confined shear space with the curved plate (17) has a generator which is not a straight line, but varies from harmonically.

This generator can take various forms, such as by example of sawtooth, slots, arcs, and preferably sinusoid-shaped. As already said, the wavelength of these shapes, sinusoid for example, is on the order of three to five times the average length of the fibers of the suspension to be treated.

In a variant not illustrated but useful, the channels (15 and 25) have a thickness decreasing in the direction of flow.

In the improved embodiment shown in Figure 2, the outlet orifice (4) is associated with a parallel outlet (30) for recycling or dilution, arranged slightly downstream of (4) to allow increasing the flow in the device, and therefore the intensity of vorticity, while increasing the speed of the rotating cylinder (26), without modifying the flow of outlet (4) from the body.

When it is desired to dilute, the water injection points coincide spatially with the ripples of the generator of the rotating cylinder (26).

In practice, the speed of rotation of the characteristic cylinder (26) can vary from one to ten times the speed of flow (F) and this, one way or the other.

In the embodiment illustrated in FIG. 3, the device includes three jets (40-42), from three cases according to the invention (43,44,45) into which various suspensions containing fibers of different length and / or different concentration. The references (46,47) denote a canvas, and the references (48,49) two rotary cylinders of a paper machine.

The references (60,61,62) designate the dough feeders and references 63, 64, 65) the dilution organs.

This arrangement which makes it possible to produce a multilayer structure composed of different types and / or kinds of fibers, is advantageous when using coarse to strong fiber suspensions concentrations in the central feeding device.

FIG. 4 schematically shows an embodiment in application to the coating of paper.

This device then constitutes a coating head which delivers a jet dosing plan of coating sauce (55) on a cylinder (56) having the role, either for supporting the sheet of paper (57), or transfer roller.

The coating sauce (E) is brought to (50) to be confined in a first curved channel (52) formed between a rotary cylinder (53) analogous to (26) and an outer sheet (54) coaxial to (53). The pipeline (52) curved has a constant section, for example rectangular.

This pipe leads into (55) in a confined space with the coating roller (56) rotating in the direction indicated by the arrow (R). The grater (51) makes it possible to control and limit the recirculation of the sauce in the channel (52).

In practice, the tangential speed of the cylinder (56) is of the order of three times the flow rate in the channel (52).

• la répartition uniforme de vitesse dans le jet, quel que soit le dispositif assurant l'arrivée de la pâte dans la caisse, du fait de l'absence de couche limite et de la répartition harmonique dans le sens travers de la pression relative, l'intensité et la longueur d'onde de cette variation harmonique étant parfaitement controlées ;
• une suspension homogène, même à haute concentration, grâce à la turbulence calibrée dont la taille des vortex est adaptée tout le long d'écoulement de la pâte dans la caisse de tête ;
• la durée de vie de la turbulence prolongée dans le jet libre du fait de l'intensité de la vorticité des vortex, parfaitement contrôlable.

The device according to the invention has many advantages, in particular compared to head boxes known to date at high, normal or low concentrations. We can cite :

• the uniform distribution of speed in the jet, whatever the device ensuring the arrival of the dough in the box, due to the absence of a boundary layer and the harmonic distribution in the cross direction of the relative pressure, the intensity and wavelength of this harmonic variation being perfectly controlled;
• a homogeneous suspension, even at high concentration, thanks to the calibrated turbulence whose vortex size is adapted throughout the flow of the dough in the headbox;
• the life of the turbulence prolonged in the free jet due to the intensity of the vorticity of the vortices, perfectly controllable.

In this way, this device can be successfully used in the manufacture of papers, in head boxes, and also for paper coating.

Claims (11)

1. Device for the formation of a fan jet (J) of liquid, of the type comprising:

   means (3) for supplying a liquid;

   means for distributing the delivery and for controlling the turbulence of the liquid supplied;

   outlet means (4) for the formed fan jet (J),

   characterized in that the means for distributing the delivery and for controlling the turbulence of the liquid supplied are formed:

   from a first fixed curved conduit (15) for the flow of the liquid;

   from a second curved flow conduit (25) having an axis parallel to that of the first conduit (15);

   and from means (26) for forming calibrated vortices having an axis parallel to that of the curved conduits (15, 25), so as to bring about a harmonic transverse distribution of the speeds and pressures and to control the scale and level of the vortices.
2. Device according to claim 1, characterized in that the means for forming the calibrated vortices consists of at least one rotary cylinder (26) having an axis parallel to that of the curved conduits (15, 25).
3. Device according to either one of claims 1 and 2, characterized in that the two curved conduits (15, 25) are fixed and are arranged in series.
4. Device according to any one of claims 1 to 3, characterized in that the rotary cylinder (26) rotates in the same direction as the direction of flow (F) of the liquid.
5. Device according to any one of claims 2 to 4, characterized in that the peripheral speed of the rotary cylinder (26) is three to four times the speed of flow of the liquid.
6. Device according to claim 2, characterized in that the generatrix of the rotary cylinder (26) follows the shape of a radial broken line selected from the group comprising sawteeth, crenelations, arcs of a circle and sinusoids.
7. Device according to claim 2, characterized in that it also comprises deflector members arranged between the rotary cylinder (26) and the outlet means (4).
8. Device according to one of claims 1 to 7, characterized in that the liquid to be processed is a fibrous suspension of a paper machine.
9. Device according to one of claims 6 and 8, in which the generatrix of the rotary cylinder (26) follows the shape of a radial sinusoid, characterized in that the wavelength of said sinusoid is three to five times the average length of the fibers of the suspension.
10. Headbox of a paper machine, comprising a device according to any one of claims 1 to 9.
11. Installation for the couching of paper, comprising a device according to any one of claims 1 to 9.

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