EP0045705B1 - Method and apparatus for separating suspensions of solid particles in a liquid, particularly for treating fibrous suspensions in the paper-making industry - Google Patents

Abstract

A process for fractionating a suspension of solid particles in a liquid, of the type wherein said suspension is made to pass through a filtering screen, characterized in that said suspension is directed in a direction parallel to the longitudinal axis of an elastically deforming, flexible, perforated sleeve forming a filtering screen, and in that a sequence of high and low pressures is continuously created within this sleeve and travels at least predominantly opposite the direction of the suspension flow. The invention also applies to equipment.

Description

The invention relates to a method and a device for the fractionation of suspensions of solid particles in a liquid; it relates more particularly, but not specifically, to a method and a device for treating fibrous suspensions in the paper industry.

In the following description, the invention will be more particularly described in its preferred application to the paper industry.

In papermaking, it is well known to try to recover the fibers in the suspensions rejected in the sewers. However, the low concentration of these suspensions, which is of the order of 0.2 and 1 g of solids per liter, requires treating very large quantities of water.

However, the hitherto known methods which make it possible to economically treat very large quantities of suspensions at low concentration do not make it possible simultaneously to carry out the fractionation of the solid phase contained in the effluents in order to recover the recoverable part thereof.

It is possible, for example to decant or "float" the effluents before discharging them, which makes it possible to purify the water, but does not make it possible to selectively recover the fibers from the thickened suspension which is then entirely rejected at the discharge.

We thus lose significant quantities of raw materials which, moreover, become more and more expensive.

In US patent US-A-3,833,468, it has been suggested to purify suspensions by means of an inclined screen formed by a curved and rigid grid. This solution suitable for retaining large impurities, such as sticks and gravel, is however not effective for selectively recovering the fibers, because, in the long run, the grids are clogged by said fibers which have the annoying tendency to crash. perpendicular to the filter grid.

In British patent GB-A-485,553, an apparatus has been described for the filtration of paper pulps formed by a rectilinear series of sieves with inclined rigid slots through which the suspension to be purified and in which the filtrate of each sieve is collected in separate chambers where a diaphragm applies pressure pulses to it. Thus, the unclogging is carried out by a back and forth of the filtrate through the sieve, which risks on the one hand, to reintroduce a part of the "fines" and of water in the suspension to be treated, and d 'on the other hand, is insufficient to disrupt the fibrous mattress retained by the sieve.

In German patent DE-C-366,127, a horizontal sieve with slots has been associated with fins arranged in the filtrate collection chamber and, rotating in the direction of flow of the suspension to be purified. In addition to the drawbacks mentioned above, this device suitable for extracting fiber agglomerates does not make it possible to economically split more individual fibers, by the very fact of the slotted sieve, namely; low flow rates and significant fiber losses, therefore unsuitable for the treatment of very dilute suspensions.

In French patent FR-A-1,145,263, a process for draining fine-grained products with a high water content has been described, in which the filter cloth is subjected to mechanical fiberizing. These vibrations of the fabric allow the release of liquid particles, but are unfortunately insufficient to disorganize the cake formed, which, moreover, is not sought after. In this way, this technique cannot be used effectively for the fractionation of a fibrous suspension.

Document FR-A-2,232,345 describes a process for draining the milk curd by passing it through a conical filter sleeve which rests on a rigid sole and pressing this sleeve by means of a train of rollers which moves in the direction of flow of the curd and thus ensures its progression. This technique cannot be used to fractionate suspensions, particularly fibrous, because first of all, under the effect of compression, solid particles which one wishes to keep in the retentate would pass through the sleeve, thus preventing separation. selective, and then quickly the particles will agglomerate to form a compact mattress which will then oppose filtration and clog the whole.

• - soit, parce qu'ils se colmatent en cours de traitement,
• - soit, qu'ils ne permettent pas d'obtenir une séparation sélective de la fraction fibreuse.

In other words, the purifying devices known and operated to date cannot be suitable:

• - either, because they clog up during treatment,
• - Or, that they do not make it possible to obtain a selective separation of the fibrous fraction.

The object of the invention is a method and a device for the selective separation of a fraction of solid particles in a fibrous suspension in a liquid which is rapid, economical, even at high flow rates and low concentration, for example between 0.2 and 2 g per liter.

More specifically, the invention is suitable for the treatment of paper mill effluents, upstream of the purification station, a treatment in which it is sought to selectively recover the recoverable fibers.

• - en ce que la suspension s'écoule librement dans une direction parallèle à l'axe longitudinal dudit manchon;
• - et en ce que, en continu, on déforme la section du manchon, de manière à créer dans la suspension au voisinage de la paroi interne de ce manchon, une succession de pressions et de dépressions qui se propagent dans un sens opposé à celui de l'écoulement du flux de la suspension.

This process for the fractionation of fibrous suspensions in a liquid, of the type in which said suspension is passed through a filtering sieve constituted by a flexible, flexible, elastically deformable sleeve, and pressure is exerted on said strut, is characterized:

• - in that the suspension flows freely in a direction parallel to the longitudinal axis of said sleeve;
• - And in that, continuously, the section of the sleeve is deformed, so as to create in the suspension at near the inner wall of this sleeve, a succession of pressures and depressions which propagate in a direction opposite to that of the flow of the suspension flow.

In a particular embodiment, the deformation of the section of the sleeve is propagated along a generator and on the external face of this sleeve.

• - un conduit d'amenée de la suspension liquide à traiter;
• - un élément filtrant constitué par un manchon fixe perforé, souple, élastiquement déformable, de forme générale tronconique, connecté à son extrémité la plus large au conduit d'amenée et à son extrémité la plus étroite à l'organe de récupération;
• - un organe d'extraction du filtrat;
• - un organe pour la récupération de la fraction des particules solides concentrée;

se caractérise:

• - en ce que ledit manchon filtrant est apte à canaliser le libre écoulement de la suspension à traiter dans l'axe longitudinal;
• - et en ce qu'il présente un moyen apte à déformer la section de ce manchon, de manière à créer à l'intérieur de celui-ci et au voisinage de sa paroi interne une succession de pressions et de dépressions qui se déplacent continuellement à contre-courant du flux de ladite suspension.

The invention also relates to a device for the separation of fibrous particles in a liquid suspension. This device of the type comprising:

• - a supply line for the liquid suspension to be treated;
• - a filter element consisting of a fixed perforated, flexible, elastically deformable sleeve, of generally frustoconical shape, connected at its widest end to the supply duct and at its narrowest end to the recovery member;
• - an organ for extracting the filtrate;
• - an organ for the recovery of the fraction of concentrated solid particles;

characterized:

• - in that said filter sleeve is able to channel the free flow of the suspension to be treated in the longitudinal axis;
• - And in that it has a means capable of deforming the section of this sleeve, so as to create inside of it and in the vicinity of its internal wall a succession of pressures and depressions which move continuously at against the flow of said suspension.

• - ce manchon est orientable et inclinable, notamment par rapport au moyen destiné à créer la succession de pressions et de dépressions, afin de pouvoir augmenter la déformation dudit manchon;
• - l'axe du conduit d'amenée de la suspension à épurer est généralement confondu avec l'axe longitudinal du manchon;
• -le moyen apte à créer à l'intérieur du manchon déformable une succession de pressions et de dépressions est formé par une spirale rigide hélicoïdale rotative qui s'appuie transversalement en permanence contre ledit manchon et le déforme, le point de contact entre ladite spirale et la paroi filtrante du manchon se déplaçant en sens inverse de l'écoulement du flux de la suspension;
• - le pas de cette spirale est inférieur à la longueur du manchon;

In practice:

• - This sleeve is orientable and tiltable, in particular relative to the means intended to create the succession of pressures and depressions, in order to be able to increase the deformation of said sleeve;
• - The axis of the supply line of the suspension to be purified is generally coincident with the longitudinal axis of the sleeve;
• the means capable of creating a succession of pressures and depressions inside the deformable sleeve is formed by a rigid rotary helical spiral which permanently leans transversely against said sleeve and deforms it, the point of contact between said spiral and the filter wall of the sleeve moving in the opposite direction to the flow of the suspension flow;
• - The pitch of this spiral is less than the length of the sleeve;

Advantageously, the means able to create inside the deformable sleeve a succession of pressures and depressions is formed by an endless belt moving in the opposite direction to the flow of the suspension flow and having rigid bars spaced along of said belt, part of said bars resting transversely and in turn on the flexible sleeve by deforming it. These rigid bars can have shapes and cross sections. Likewise, they can be mounted idly on their axis.

In practice, the purification device can have several parallel sleeves and a single means capable of creating inside these sleeves a succession of pressures and depressions which then acts simultaneously on said sleeves.

Similarly, the device may also include in the sleeve auxiliary introduction means for the suspension, these means, such as supply conduits, being substantially directed in the direction of the flow of the suspension, in order to compensate for the gradual fall velocities resulting from the reduction in flow rate as the filtrate is evacuated. This also makes it possible to carry out an additional purification of the fibrous fraction to be recovered.

The operation of this device can be explained as follows.

When (see FIG. 1) a fibrous suspension (2) is sent in a flexible filter sleeve (1), for example in a woven fabric, in the longitudinal direction of said sleeve (1) (direction indicated by arrow A), at the level of the wall (1), the elementary fibers (3) of said suspension are preferably oriented in this direction A.

When (see FIG. 2) a rigid member (4) which moves against the current in the direction indicated by arrow B is applied to this flexible sleeve (1), this rigid member (4) first exerts on the sleeve (1) deformation. In parallel, upstream of this member (4) (area indicated by reference 5), the suspension (2) is filtered and the fibers (3) form a fibrous mat (6) on the wall of the sleeve. If the fibers (3) were allowed to continuously deposit on the mattress (6), this mattress would in turn play the role of filtering media, thus opposing the passage of liquid and "fines" through the wall of the sleeve.

But, when the member (4), which advances against the current, meets the mattress (6), this mattress then destroys and peels off from the wall in the area (7).

Downstream of the member (4) (see FIG. 3), between the detached mattress (7) and the fabric (1), a depression (8) is then formed which in turn detaches the remainder (7) from the mattress (6) and puts the fibers back in the suspension (9). This suspension is then accelerated by the vortex created by the movement of the member (4) along the sleeve (1).

Thus, a series of pressures and depressions moving in the opposite direction to the flow of the flow of the suspension to be treated is indeed created, the pressure being exerted upstream with respect to the flow, that is to say in the zone (5), while the depression is exerted downstream, that is to say in zone (8).

• -l'utilisation d'un manchon perforé souple élastiquement déformable, ce qui permet de remettre efficacement les fibres en suspension lors de l'application de la succession de pressions-dépressions;
• - le déplacement de la suspension par rapport au manchon, ce qui favorise la mobilité des fibres et leur orientation longitudinale dans la couche limite de ci-saillement;
• - la déformation du manchon par application d'une succession de pressions-dépressions;
• - le déplacement continu de cette succession de pressions-dépressions:
  • - par rapport à la surface du manchon, ce qui conduit à un décolmatage uniforme et continu,
  • . par rapport à l'écoulement de la suspension et principalement en sens inverse de cet écoulement, ce qui, d'une part, augmente l'amplitude des pulsations de pression et' d'autre part favorise le retour dans la suspension des fibres partiellement engagées dans les mailles du manchon.

In other words, the invention relates to a particularly effective fractionation process and device for suspensions with low solids concentration, calling upon the combination of four characteristics:

• the use of an elastically deformable flexible perforated sleeve, which makes it possible to effectively resuspend the fibers during the application of the succession of pressure-depressions;
• - The displacement of the suspension relative to the sleeve, which promotes the mobility of the fibers and their longitudinal orientation in the boundary layer of jutting;
• - deformation of the sleeve by application of a succession of pressure-depressions;
• - the continuous displacement of this succession of pressure-depressions:
  • - relative to the surface of the sleeve, which leads to a uniform and continuous unclogging,
  • . with respect to the flow of the suspension and mainly in the opposite direction to this flow, which, on the one hand, increases the amplitude of the pressure pulsations and on the other hand promotes the return in the suspension of the partially engaged fibers in the mesh of the sleeve.

More precisely, it is the mattress at the start of training, the return of which to the suspension is favored. Indeed, the return in the suspension of the fibers partially engaged in the meshes of the sleeve is due to the speed of the fluid relative to the fabric of the sleeve which creates a boundary layer in which the fine elements can flow through the fabric, while the fibers, one end of which is in front of a mesh generally have the other end in a layer of the fluid more distant from the fabric and whose speed relative to the sleeve is clearly greater than the speed of "crossing" of the fluid through the sleeve; this thus promotes the return of the fibers in the suspension.

In practice, as we know, when the fibrous mat (6) is formed at the inlet of the sleeve (1), it initially contains not only fibers (recoverable materials) but also "fines" (mineral fillers, fragments of fibers and other materials that are not very valuable) which are "trapped" in the structure of said mattress during its formation and can therefore no longer migrate to the filtering wall.

By deforming the sleeve (1) thanks to the translational movement of the member (4) against the flow of the suspension, the fibrous mat (6) is released and it is detached from the wall, which releases the "fines "and allows them to be entrained with the liquid through the filter cloth.

In a way, an unclogging of the filter cloth and a self-cleaning of the fibrous mat are simultaneously carried out without the introduction of additional water into the system.

Thus, as one advances along the generatrix of the sleeve (1), the fibrous mat (6) is more and more concentrated in fibers.

Because the flow of the suspension (2) is directed in the longitudinal direction of the sleeve (1) at the boundary layer, the fibers (3) are preferably arranged in this fibrous mat (6) parallel to the longitudinal axis and therefore will not tend to plant it in the canvas, which limits the tendency to clogging.

On the other hand, the preferential orientation of the fibers in the longitudinal direction allows the use of fabrics with larger mesh, which promotes both a better selectivity of the separation (easier evacuation of the "fines") and a more high speed of treatment (higher filtration speed).

The filtration effect is also favored by the displacement of the member (4) in contact with the outer wall of the sleeve (1), which "wipes" the drop of runoff which would oppose filtration.

In addition, by its very shape, the sleeve has neither a blind spot nor a stagnation zone.

The manner in which the invention can be implemented and the advantages which result therefrom will emerge more clearly from the following description and from the exemplary embodiments, with the support of the appended figures, the whole being given by way of non-limiting indication.

As said, Figures 1 to 3 illustrate a summary explanation of the phenomena in question.

Figures 4 and 5 schematically show a first device for implementing the invention, respectively seen in front section (Figure 4) and seen in longitudinal section (Figure 5). Figure (6) shows a detail of this device seen from above.

FIG. 7 represents another embodiment of the invention.

Figures 8 and 9 show respectively in longitudinal and cross section a preferred device of the invention.

FIG. 10 is a schematic summary view of an improved installation implementing this method.

Figures 4, 5 and 6 show a first device in which the succession of pressures and depressions is caused by deformation of the section of the filter sleeve from the outside and in which this deformation is propagated along a generator of the sleeve and this, in the opposite direction to the flow of the suspension flow.

• -d'un conduit d'amenée (10) pour la suspension liquide à traiter;
• -d'un manchon (11), par exemple en toile de polyester souple, à maille rectangulaire de dimensions courantes pour cet usage en papèterie; grâce à deux plaques de serrage (12) et des écrous (13), cette toile prend la forme générale d'un corps cylindrique tronconique;
• - de deux supports règlables (14) et (15) grâce auxquels on peut faire varier l'inclinaison de cette toile (11);
• - d'un tube rigide (16) spiralé en hélice et raccordé par des rayons (17) à un axe longitudinal (18), entraîné en rotation par le jeu d'une poulie (19), d'une courroie (20), d'une seconde poulie (21) et d'un moteur (22); l'axe (18) est sensiblement parallèle à l'axe longitudinal du manchon (11);
• - d'un montant vertical (23) sur lequel se déplace le porte-manchon (24), ce qui permet ainsi de régler la distance entre le manchon (11) et l'hélice (16) et en d'autres termes, la pression de cette hélice (16) sur le manchon (11), mais également l'inclinaison de ce manchon (11) par rapport à cette hélice (16);
• - d'un bac de récupération (25);
• -d'une goulotte (26) pour l'évacuation du filtrat, c'est-à-dire de l'eau filtrée et des "fines";
• - d'un organe (27) pour récupérer la fraction concentrée disposée à l'extrémité basse du manchon (11); ce peut être par exemple un plan incliné, avantageusement filtrant relié à une goulotte de récupération.

Referring to these Figures 4 to 6, the device consists of:

• -a supply pipe (10) for the liquid suspension to be treated;
• -a sleeve (11), for example in flexible polyester fabric, with rectangular mesh of current dimensions for this use in stationery; thanks to two clamping plates (12) and nuts (13), this fabric takes the general form of a frustoconical cylindrical body;
• - two adjustable supports (14) and (15) by which the inclination of this fabric (11) can be varied;
• - a rigid tube (16) spiraled into a helix and connected by spokes (17) to a longitudinal axis (18), driven in rotation by the play of a pulley (19), a belt (20), a second pulley (21) and a motor (22); the axis (18) is substantially parallel to the longitudinal axis of the sleeve (11);
• - a vertical upright (23) on which the sleeve holder (24) moves, which thus makes it possible to adjust the distance between the sleeve (11) and the propeller (16) and in other words, the pressure of this propeller (16) on the sleeve (11), but also the inclination of this sleeve (11) relative to this propeller (16);
• - a recovery tank (25);
• -a chute (26) for the discharge of the filtrate, that is to say filtered water and "fines";
• - a member (27) for recovering the concentrated fraction disposed at the lower end of the sleeve (11); it may for example be an inclined plane, advantageously filtering, connected to a recovery chute.

FIG. 6 shows seen from above a detail (deformed to facilitate understanding) of the sleeve (11) fixed by the nuts (14) on the clamping plates (12) on the exterior side and bearing on the interior side on a support (28) tapered in the direction of flow A. In this way, this tapered shape gives the sleeve (11) a generally frusto-conical shape that tapers in the direction of flow and this, in order to compensate for the progressive fall in resulting speeds the decrease in flow rate as the filtrate is evacuated.

The inclination of the entire system also helps to maintain the speed of the flow by taking advantage of gravity to reduce the effect of the pressure drop.

FIG. 7 illustrates another embodiment with a flexible sleeve (11) and deformation from the outside. Here, the deformation is caused by a set of successive parallel rollers (40) spaced along an endless belt (42) driven in continuous rotation by two drive pulleys s (43) and (44) synchronized. These rollers are mounted idly around the axis (41) in order to reduce the friction on the sleeve (11) and thus reduce the wear of this fabric (11) and the energy consumption. A succession of pressures and depressions is thus formed inside the sleeve thanks to these rollers moving in the opposite direction to the flow of the flow of the suspension, only part of said rollers being supported transversely and in turn on the flexible sleeve by deforming it.

Figures 8 and 9 show respectively in longitudinal section and in cross section a preferred device according to the invention. This device essentially comprises a frame (50) mounted on casters (51) which receives a motor (52) which, by means of a variator (53) drives a pulley (54). This motor pulley (54) drives an endless chain (55) which passes over two other return pulleys (56) and (57) carried by the cross-member (58). This horizontal crosspiece (58) also has a tensioning chain guide (59). The chain (55) carries rigid cylindrical bars (60) regularly spaced, so that there is always at least one point of contact between a bar (60) and the deformable sleeve (11).

On the top of the frame (50), adjustable supports (61) maintain in height and laterally a plate (62) which, seen from above, presents from left to right a generally tapered shape in order to give the sleeve (11) a general frustoconical shape. This assembly (62) is connected to the flexible perforated sleeve (11) produced as previously in a stationery fabric. The upstream end (63) of this fabric (11) is connected, when the time comes, to the conduit (10) for supplying the suspension to be purified, while its downstream end (64) opens into a box (65) where we will recover the concentrated fibers (similar to 27). (66) designates a conduit through which the filtrate will be discharged (similar to the chute 26).

Example 1:

• - manchon (11) en toile tissée de crin polyester de 320 pm de diamètre,
  • - maille de la toile du manchon (11) 250x600 pm
  • -longueur du manchon (11) 100 cm
  • - diamètre de l'hélice (16) 100 cm
  • - pas de l'hélice (16) 80 cm
  • - vitesse de rotation de l'hélice (16) 200 tours/minute.

A device is produced in accordance with FIGS. 4 to 6 having the following general characteristics;

• - sleeve (11) in woven polyester horsehair fabric, 320 μm in diameter,
  • - mesh of the sleeve fabric (11) 250x600 pm
  • -length of the sleeve (11) 100 cm
  • - propeller diameter (16) 100 cm
  • - no propeller (16) 80 cm
  • - propeller rotation speed (16) 200 revolutions / minute.

• - concentration en matières solides de
  la suspension amenée en (10) 0,45 g/litre
• - débit de la suspension 12,6 m3/heure
• -taux de cendres avant traitement 17%.

A suspension collected just downstream of a paper machine is treated in this device, before being discharged into the river. This suspension, which essentially contains long fibers and "fines", is treated under the following conditions:

• - solids concentration of
  the suspension supplied in (10) 0.45 g / liter
• - suspension flow 12.6 m3 / hour
• - ash rate before treatment 17%.

After treatment, a filtrate (in 26) is obtained having an average concentration of solid matter (the values indicated are obtained by the average of 20 measurements) of 0.11 g / liter, while the fibrous fraction accepted in (27) has an average concentration of 7.5 g / liter. The fibrous yield is approximately 75%.

Example 2:

• - concentration en matières solides 1,22 g/litre,
• -taux de cendres 58%.

Example 1 is repeated with another suspension more loaded with mineral matter (stationery sludge containing a high proportion of very short fibers) having the following characteristics:

• - solids concentration 1.22 g / liter,
• - ash rate 58%.

• - concentration en matières solides 4,1 g/litre,
• -taux de cendres 16%,
• - rendement fibreux 28%.

The following results are obtained (fibrous fraction accepted in 27):

• - solids concentration 4.1 g / liter,
• - ash rate 16%,
• - fiber yield 28%.

• - concentration en matières solides 1,0 g/litre,
• -taux de cendres 62,6%

Filtrate collected in (26):

• - solids concentration 1.0 g / liter,
• - ash rate 62.6%

Example 3:

Example 2 is repeated with a mud having a solids concentration of 1 g / liter, an ash rate of 45% and a drip index of 75 ° SR (Schopper-Riegler degrees).

• - en (27) des acceptés (concentration en matières solides: 15 g/litre-taux de cendres: 20%-rendement fibreux: 70%-incide d'égouttage: 20°SR),
• - en (26) des refusés (concentration en matières solides: 0,7 g/litre-taux de cendres: 77%-rendement fibreux: 30%).

After treatment, we obtain:

• - in (27) of accepted (concentration in solids: 15 g / liter-rate of ash: 20% -fibrous yield: 70% -drying agent: 20 ° SR),
• - in (26) refusals (solids concentration: 0.7 g / liter-ash rate: 77% -fibrous yield: 30%).

Example 4:

By way of comparison, the same mud is used as in Example 3 in a purifier with rigid curved grids of the trade of the type of that described in the preambles.

• - acceptés (concentration en matières solides: 9,5 g/litre-taux de cendres: 7%-rendement fibreux: 42%),
• - refusés (concentration en matières solides: 0,77 g/litre-taux de cendres: 58%).

The following results are obtained:

• - accepted (solids concentration: 9.5 g / liter - ash rate: 7% - fiber yield: 42%),
• - refused (solids concentration: 0.77 g / liter ash rate: 58%).

Example 5:

A device is used in accordance with FIGS. 9 and 10 having the following general characteristics:

Using this device, the same suspension is treated as in Example 1. The same results are obtained, but with a flow rate of the order of 80 m ³ / h.

Example 6:

• - une tubulure d'amenée (70) de la suspension à épurer;
• - une vanne (71) et un organe de prélèvement d'échantillon (72);
• -une caisse de répartition (73) d'où partent trois conduits séparés (74) présentant chacun une vanne manuelle (75), des rotules (76) et (77), connecté au conduit d'amenée (10) placé juste en amont du manchon (11); on a donc trois manchons filtrants parallèles;
• - une chaîne (55) avec ses barres rectilignes (60);
• - de cette même caisse (73) partent également trois autres conduits auxiliares (78) qui débouche dans chacun des trois manchons (11) en aval de (10) par des injecteurs (79) dirigés vers l'aval du manchon (11); on peut avoir un ou plusieurs injecteurs dans le même manchon (11);
• - un conduit (80) pour l'évacuation vers l'égout du filtrat et un by-pass (81) connecté à ce même égout.

The device shown in FIG. 11 is used, which essentially comprises:

• - a supply tube (70) of the suspension to be purified;
• - a valve (71) and a sample collection member (72);
• -a distribution box (73) from which three separate conduits (74) leave each having a manual valve (75), ball joints (76) and (77), connected to the supply conduit (10) placed just upstream the sleeve (11); there are therefore three parallel filter sleeves;
• - A chain (55) with its rectilinear bars (60);
• - This same box (73) also leaves three other auxiliary conduits (78) which opens into each of the three sleeves (11) downstream of (10) by injectors (79) directed downstream of the sleeve (11); it is possible to have one or more injectors in the same sleeve (11);
• - A conduit (80) for the evacuation to the sewer of the filtrate and a by-pass (81) connected to this same sewer.

These auxiliary suspension feeds improve industrial operating safety by promoting unclogging and purification.

It goes without saying, taking into account the fractionation principle implemented by the invention, that it may happen that some large impurities are retained with the concentrated fibrous fraction. This is not very annoying, on the one hand because, if the manufacturing circuits are well designed, the large impurities are eliminated almost entirely upstream of the paper machine, on the other hand, because, at the concentration reached, the elimination of these impurities, if it turns out to be necessary, would not pose any problem.

• - la possibilité de traiter de gros débits par unité de surface filtrante de l'ordre de 150 m³/heure par m²;
• - la faible consommation d'énergie;
• - le faible encombrement de l'appareil et sont coût réduit;
• - la possibilité de mettre plusieurs manchons soit en parallèle, soit en série associés à un seul élément de déformation;
• - la possibilité de réaliser un effet d'égouttage-essuyage de la toile pour empêcher la formation de la goutte de ruissellement qui s'oppose à la filtration;
• - bref, la possibilité de réaliser, dans des conditions économiques la récupération des fibres valorisables dans des suspensions que jusqu'alors on rejetait en totalité.

The invention has many advantages over the techniques used to date. We can cite:

• - the possibility of treating large flows per unit of filtering surface of the order of 150 m ³ / hour per m ² ;
• - low energy consumption;
• - the small footprint of the device and are reduced cost;
• - The possibility of putting several sleeves either in parallel or in series associated with a single deformation element;
• - The possibility of achieving a wiping-wiping effect of the fabric to prevent the formation of the drop of runoff which opposes filtration;
• - in short, the possibility of carrying out, under economic conditions, the recovery of recoverable fibers in suspensions which until then had been rejected entirely.

• - la filtration d'effluents urbains ou industriels;
• - le traitement de minerais ou d'aliments;
• - le traitement d'effluents de papèterie;
• - le fractionnement de suspensions de pâtes vierges, de vieux papiers de récupération et notamment dans le cas des opérations de désencrage.

This technique can therefore be used successfully for selective purification-filtration in all processes using particle size phenomena. We can cite:

• - filtration of urban or industrial effluents;
• - the processing of minerals or food;
• - the treatment of paper mill effluents;
• - the splitting of suspensions of virgin pulp, of old recovery paper and in particular in the case of deinking operations.

In stationery, the device is preferably placed on the final sewer, just before the treatment plant or at specific points in the production line.

Claims (10)

1. Process for fractionating fibrous particles suspended in a liquid of the type wherein said suspension is made to pass through a filtering screen comprising an elastically deformable, flexible, perforated sleeve, and where pressures are generated within this sleeve, characterized in that:

- said suspension can move freely in a parallel direction of the longitudinal axis of said sleeve;

- the sleeve cross-section is continuously deformed so as to generate in the suspension within the sleeve, near its internal side, a sequence of high and low pressures moving in a direction opposite to the direction of flow of said suspension.

2. Process according to claim 1, characterized in that sleeve cross-section deformation is propagated along a generatrix, on the external side of said sleeve.

3. Device for fractionating fibrous particles suspended in a liquid comprising:

- feed conduit (10) for the liquid suspension to be treated;

- filtering means (11) consisting in a fixed, flexible, perforated, elastically deforming sleeve of a generally frustum-of-cone shape connected by its wider end to the feed conduit (10) and by its narrower end to the recovery means (27-65);

- a filtrate extracting means (26­66);

- a means for recovering the concentrated solid fractions (27-65) characterized in that:

. said filtering sleeve is able to guide the suspension flow to be treated along the longitudinal axis;

. it comprises a means able to deform the sleeve cross-section for generating within said sleeve and near its internal wall a sequence of high and low pressures continuously travelling in counter-flow of said suspension.

4. Device according to claim 3 characterized in that the whole dispositive can be vertically oriented and inclined and as much as desired.

5. Device according to claims 3 and 4, characterized in that the sleeve can be oriented with respect to the means generating a sequence of high and low pressures.

6. Device according to one of the claims 3 to 5, characterized in that the axis of the feed conduit (10) of the suspension to be treated coincides with the longitudinal sleeve axis.

7. Device according to one of the claims 3 to 6, characterized in that said means for generating a sequence of high and low pressures within the deforming sleeve (11) consists in a rotating helicoidal rigid spiral (16) transversally resting permanently against external wall of said sleeve (11) and deforming it, the contact point between said spiral (16) and the filtering sleeve (11) moving in the opposite direction to the suspension flow.

8. Device according to one of the claims 3 to 6, characterized in that the means for generating a sequence of high and low pressures within the sleeve (11) consists in an endless belt (42-45) moving in the opposite direction to the suspension flow and comprising rigid parallel bars (40-60) spaced along and belt, part of these bars (40-60) pressing transversaly on the external side of said sleeve and deforming it.

9. Device according to one of the claims 3 to 8, characterized in that it comprises several parallel sleeves (11) linked with a single means for generating sequential high and low pressures within these sleeves (11).

10. Device according to one of the claims 3 to 9, characterized in that it comprises auxiliary introduction conduits of suspension (78) within the sleeve (11) downstream of principal feed conduit (10), which are directed substantially along sleeve axis.

Images