EP1155185B1 - Method and means for paper pulp filtering - Google Patents

Abstract

Process for the filtration of paper pulp with a device that comprises a rotor and a stator; one of the two, filter (1), has perforations of slot or hole types, and the other, the backwashing element, includes means that are intended to generate pressure pulses that consist in combatting the gradual clogging of the perforations of the filter and the gradual flocculation of the pulp during the creep of the pulp between the rotor and the stator by creating deflocculation zones and/or increasing the relative speed between the pulp and the backwashing elements.

Description

The present invention relates to the problems of pulp filtration at paper and more particularly pulp from pulping old papers.

It is known, in the technology of the pulp to employ various filtration apparatus either to remove foreign matter or to classify pulp fibers according to their length is again to increase the concentration of the pulp by partial removal of water.

Among the known filtration apparatus are filters comprising a rotor and a stator, one of two, hereinafter referred to as sieves fulfilling the function of filtering with holes such as slots or holes, the other below called decolator, fulfilling the declogging function with means for generating pressure pulsations to prevent clogging holes. The sieve can therefore be fixed or rotating and, conversely, the decolator is rotating with a fixed sieve and fixed with a rotating sieve. Of the more the liquid can either flow through the sieve from the outside to the inside (towards the axis), so-called centripetal operation, either from the inside to the outside, said centrifugal operation.

In this type of apparatus, the dough arrives at one end of the cylindrical sieve, flows in the space between the cylindrical sieve and the decolator, and spring at the other end.

As the dough progresses in the filter, it becomes more in thicker.

This gradual thickening of the dough produces several effects: an effect of flocculation of the dough and a clogging effect of the sieve.

Even if the admixed pulp has been previously deflocculated, there is a risk of appearance of flocks as it progresses; the more flocculation is important, the more clogging is important.

If the decolator turns, it tends to drive the dough with him in rotation. If the decolator is fixed, it is the filter that tends to cause the dough in rotation. In both cases, as the effect of declogging by the pulsations of pressure caused by the decolator is directly related to the speed difference between the decolator and the dough, the dough progresses towards the end of the sieve, less unclogging is effective and this while the sieve is more likely to seal.

In addition, with a sieve with fine slits the long fibers have more trouble in pass that short fibers and therefore the proportion of long fibers compared short fibers increases as the dough progresses, which accelerates both the flocculation process and the clogging process.

It results from this accumulation of phenomena a progressive reduction production per unit area of the sieve as and when progress of the dough in the filter.

Many patents have aimed to counter this reduction of filter productivity by intervening during the journey along the sieves, in order to create areas of high deflocculation, and / or slow down dough.

In particular, from 1968 in his French patent 1,539,846 the plaintiff proposed to have obstacles to break the component parallel to the surface of the sieve of the velocity of the liquid.

In US Pat. No. 4,383,918 it has been proposed to arrange between the sieve and the rotor obstructions causing turbulence.

In patent FR 2,613,390, also in the name of the applicant, proposed to separate the sieve into several portions and to introduce water from dilution between the portions of the sieve.

In British Patent GB 2,222,967 it has been proposed to install two screens separated by fixed vanes placed between the sieve surface and the rotor.

All these devices have gradually improved the operation of the devices filtration systems consisting of a sieve and a decolator but still insufficient.

• la zone d'augmentation de l'écart de vitesse peut comprendre une ou plusieurs chicanes ;
• les zones de défloculation et d'augmentation de l'écart de vitesse peuvent être combinées.

According to the present invention:

• the speed difference increasing zone may comprise one or more baffles;
• areas of defloculation and speed gap increase can be combined.

The present invention relates to a filtration apparatus of the type comprising a cylindrical sieve and a decolator equipped with blades that produce pressure fluctuations to fight against the clogging of said sieve, the latter being in at least two parts of substantially equal diameter from each other by means intended to break the component of the velocity of the liquid, which is parallel to the surface of the sieve and to create turbulence, characterized in that said means are baffles formed on the one hand by cavities formed in an annular ring of the sieve disposed between said sieve parts and secondly by a deflector annular carried by the decolator in front of each crown of the sieve bearing the cavities, so that the majority of the liquid flow is forced to cross the cavities.

a - le tamis comprend un empilage d'anneaux,

b - le tamis comprend un empilage de grilles, chaque grille étant obtenue par la juxtaposition de fils soit sensiblement parallèles à l'axe de rotation du rotor soit perpendiculaires à cet axe, soit inclinés,

c - le tamis comprend un empilage de tôles cylindriques à trous ou à fentes,

d - les différentes parties du tamis sont constituées de façons différentes les unes des autres,

e - les cavités sont parallélépipédiques,

f - les cavités sont des volumes creux cylindriques,

g - certaines cavités sont reliées à un conduit de dilution,

h - le nombre, le type, l'épaisseur et l'inclinaison des pales portées par le décolmateur peuvent varier entre les déflecteurs annulaires,

i - l'appareil comprend en outre une zone d'agitation violente disposée à l'entrée du tamis.

j - les turbulences dans la zone d'agitation violente disposée à l'entrée du tamis sont créées par des ailettes fixées sur le décolmateur et des ailettes fixées sur le tamis.

The present invention may further comprise all or part of the following provisions, taken together or separately:

a - the sieve comprises a stack of rings,

b - the screen comprises a stack of grids, each grid being obtained by the juxtaposition of wires either substantially parallel to the axis of rotation of the rotor or perpendicular to this axis, or inclined,

c - the screen comprises a stack of cylindrical sheets with holes or slits,

d - the different parts of the sieve are constituted in different ways from each other,

e - the cavities are parallelepipedic,

f - the cavities are cylindrical hollow volumes,

g - certain cavities are connected to a dilution duct,

h - the number, type, thickness and inclination of the blades carried by the decolator may vary between the annular baffles,

the apparatus further comprises a violent stirring zone arranged at the inlet of the sieve.

the turbulence in the zone of violent agitation arranged at the inlet of the sieve is created by fins fixed on the decolator and fins fixed on the sieve.

The present invention also provides a method of using this apparatus for the treatment of paper pulp according to which each part of the apparatus of filtration includes an output of accepted products and each annular ring of the sieve optionally has a dilution inlet the filtration apparatus further comprising an input and an output of the rejects, and according to which by playing on the settings of the accepted product exits, the release of the rejects and the arrivals dilution of the pipes reduces the rotation speed of the decolator so that it is as low as possible in order to save energy, while maintaining a low discharge rate.

a) soit ajuster la vitesse du décolmateur en fonction du différentiel de pression de la pâte entre l'entrée de l'appareil et l'une au moins des sorties acceptées ;

b) soit ajuster la vitesse du décolmateur en fonction du ou des débits dans l'une au moins des sorties de produits acceptés ;

c) soit ajuster le taux des refus d'une ou plusieurs parties du tamis en ajustant le débit de sortie des refus de l'appareil en tenant compte des débits de sortie des produits acceptés et des débits des arrivées de dilution ;

d) soit combiner deux ou trois de ces moyens de régulation.

The method according to the invention may comprise the following phases consisting of:

a) adjust the speed of the decolator according to the differential pressure of the dough between the inlet of the apparatus and at least one of the accepted outlets;

b) adjust the speed of the decolator according to the flow rate (s) in at least one of the accepted product outlets;

c) adjust the refusal rate of one or more parts of the sieve by adjusting the exit rate of the appliance refusals, taking into account the outflow rates of the accepted products and the flow rates of the dilution inlets;

d) combine two or three of these control means.

The present invention also aims at the implementation of the above means described for filtering pulp.

Figure 1 : un premier exemple de réalisation comportant une zone de ralentissement obtenue au moyen de chicanes.

Figure 2 : une vue en coupe selon AA de la figure 1.

Figure 3 : une variante de réalisation de la figure 1.

Figure 4 : une deuxième variante de réalisation de la figure 1.

Figure 5 : un deuxième exemple de réalisation selon l'invention combinant une zone de défloculation et une zone de ralentissement selon la figure 1.

Figure 6 : un troisième mode de réalisation utilisant les moyens de ralentissement de la figure 1, dans un filtre centripète.

Figure 7 : une vue en perspective illustrant un tamis selon l'invention.

Figure 8 : une vue en perspective illustrant le rotor destiné à être placé à l'intérieur du tamis de la figure 7.

Figure 9 : une vue partielle en perspective montrant l'intérieur du tamis de la figure 7.

Figures 10 et 11 : deux vues partielles et à grande échelle de la figure 9.

Figure 12 : une vue partielle de l'intérieur d'une variante de réalisation du tamis des figures 7, 9, 10 et 11.

Figure 13 : une vue partielle d'une variante de réalisation d'un élément filtrant selon l'invention.

Figure 14 : une vue partielle d'une autre variante de réalisation d'un tamis d'élément filtrant selon l'invention.

Figure 15 : une vue en coupe verticale d'un élément filtrant selon l'invention.

Figure 16 : un exemple de réalisation d'un appareil de filtration.

As non-limiting examples and to facilitate the understanding of the invention, there is shown in the accompanying drawings:

Figure 1: a first embodiment having a slowing zone obtained by means of baffles.

Figure 2: a sectional view along AA of Figure 1.

Figure 3: an alternative embodiment of Figure 1.

Figure 4: a second alternative embodiment of Figure 1.

FIG. 5: a second exemplary embodiment according to the invention combining a defloculation zone and a slowing zone according to FIG.

Figure 6: a third embodiment using the slowing means of Figure 1, in a centripetal filter.

Figure 7 is a perspective view illustrating a sieve according to the invention.

8 is a perspective view illustrating the rotor intended to be placed inside the sieve of FIG.

Figure 9 is a partial perspective view showing the interior of the sieve of Figure 7.

Figures 10 and 11: two partial and large-scale views of Figure 9.

Figure 12: a partial view of the interior of an embodiment of the sieve of Figures 7, 9, 10 and 11.

Figure 13 is a partial view of an alternative embodiment of a filter element according to the invention.

Figure 14 is a partial view of another alternative embodiment of a filter element screen according to the invention.

Figure 15 is a vertical sectional view of a filter element according to the invention.

Figure 16: an exemplary embodiment of a filtration apparatus.

In all of Figures 1 to 6, the sieve is constituted, as has been described in patent EP 0 707 109 by a stack of circles 1 with U section, pressed against each other by means of two end crowns 2 and 3 assembled to each other by tie rods 4 which make it possible to establish a prestressing. The bases of the U are provided with holes (whether they are slots or holes).

The dough arrives in the filter by its end to the left of the figure (on the side of the crown 2) and emerges by its opposite end (on the side of the 3) circulating in the space 6 located between the decolator 5 and the sieve as indicated by the arrow f1.

It should be noted, however, that the invention is not limited to this structure particular sieve but is applicable to any cylindrical sieve as it will described below.

According to the invention, a slowdown zone is created for the speed at which the dough is driven.

For this purpose, as illustrated in FIGS. 1 and 2, there is available in the sieve a series of baffles that slow down the rotating motion of the dough.

Referring to these figures we see that we replace one or more circles 1 by a plurality of partitions 20, parallel to the axis of the filter which with the edges of the two rings 1 which surround it constitute a plurality of cavities parallelepiped C disposed all around the sieve.

In front of these partitions 20 is arranged an annular partition 21 perpendicular to the filter axis and carried by the rotor 5.

Thus, as represented by the arrow f2, the flow of dough is diverted by the annular partition 21 and strikes the partitions 20 which are connected to the sieve and passes through cavities C to return to space 6.

This causes a slowing of the speed of rotation of the dough and, in same time, a stirring of the dough which has a deflocculation effect and fluidization.

Fluidization is understood to mean a stirred and floc-free state of the dough which favors the flow in the openings, holes or slots of the sieve.

As a result, the sieve is divided into two parts; a first part in upstream of the crown of cavities C and a second part downstream, these two parts being separated from each other by the crown of cavities C.

It also results that the rotor is divided into two parts by the partition circular 21.

In Figure 1, the baffle 20/21 is disposed in the middle of the sieve; in Figure 3 it is arranged near the end, that is to say where the effects of clogging are the most important because of the thickening of the dough.

Figure 4 combines the provisions of Figures 1 and 3.

According to the example shown in Figure 5 turbulence is also created by fins 10 fixed to the decolator and fins 11 fixed on the screen.

These fins 10 and 11 may be radial or inclined and may have inclinations in the opposite direction.

Preferably, as shown in FIG. fins 10/11 are such that they fit into each other.

Thus, in the zone where the said fins are located, a violent stirring which achieves a good deflocculation of the dough.

FIG. 6 represents a centripetal filter that uses the means of FIG. 1. The same elements bear the same references.

In this figure, the sieve 1 is inside the decolator 5. The dough arrives at the end of the sieve and circulates in the space 6 located between the sieve 1 and the decolator 5.

In a zone of the sieve 1, the U-section circles are replaced by partitions 20, parallel to the axis of the cylinder, and the decolator 5 comprises a annular partition 21.

As in the case of Figure 1, the paste is deflected by the annular partition 21 and hits the partitions 20.

Figures 7 to 17 show an alternative embodiment of the apparatus implementing the method according to the present invention.

FIG. 7 represents a cylindrical sieve 30 which consists of bars 31 arranged vertically next to each other with a slight clearance (included between 0.05 mm and 1 mm) and fixed on horizontal rings 32, 33, 34, 35, 36 and 37.

These rings 32 to 37 are crossed by tie rods 38, parallel to the axis of the cylinder, these rods 38 being fixed to the two end rings 32 and 37, so that the assembly is maintained by tightening the tie rods 38.

FIG. 8 shows the rotor 40 which is placed inside the sieve of the FIG. 7. This rotor is a cylinder which comprises three annular rings 41, 42, and 43. In the areas between the ring rings are arranged blades 45, commonly referred to as "foils" in the pulp industry.

The function of the foils 45 is to cause pulsations of pressure / depression which tend to prevent clogging of the sieve.

The rings 41 to 43 are arranged on the rotor so as to be opposite crowns 33, 34 and 35.

It will be explained hereinafter how the rings 33, 34 and 35 of the sieve 30, cooperate with the rings 41, 42 and 43 of the rotor to form baffles.

As can be seen in FIG. 8, the annular rings 41, 42 and 43 define four zones of the rotor 40.

The shape, number and inclination of the blades or foils 45 may vary from one area to another.

Figure 9 shows the screen of Figure 7 seen from the inside.

We see that the crowns 33, 34 and 35 are hollow so as to define cavities C.

In this example, as the screen 30 is made of bars 31 juxtaposed, the cavities C are not made as in the case of Figures 1 to 6 where the sieve was constituted by U.

As seen in FIG. 9, the rings 33, 34, 35 are constituted by a ring comprising a multitude of parallelepiped cavities having practically the same shape as the cavities C of Figures 1 to 6.

Some cavities C crowns 33 and / or 34 further comprise orifices which are connected to dilution inlet pipes 50.

Figures 10 and 11 are detail views, on a larger scale of the figure 9.

Figure 12 illustrates a variant according to which, instead of having parallelepiped cavities C cylindrical cavities or blind holes are available Some may be connected to conduits 50.

As shown in Figure 12 (blind holes D) and Figure 13 (parallelepiped cavities C) the annular ring of the rotor 41 (42,43) which cooperates with the ring 33 (34, 35) is arranged to be substantially at the middle of the cavities C or cylindrical holes D.

Arrow F illustrates how dough from the area below crowns 33, 41 is forced into a cavity C or D, this cavity and the crown 41 forming a baffle that significantly slows the speed of the dough.

It can be seen in these figures that the bars 31 are held by strapping 31a.

FIG. 14 illustrates another variant embodiment in which the same elements bear the same references.

In this example, the screen 30 is fixed and placed outside the rotor 40 which 45. The ring 41 of the rotor 40 is in front of the ring 33 of the sieve 30 so that the cavities C of said ring 33 form with the annular ring 41 a series of baffles.

In this figure, in the bottom of the cavity C arrives a pipe 50 which is a water pipe.

This makes it possible to combine the slowdown action caused by baffles C to a dilution action of the dough, which tends to thicken as and when as it passes through the filtration apparatus.

• une couronne d'extrémité supérieure 32 pour le tamis 30,
• une couronne intermédiaire 33 comportant une pluralité de cavités C, dont certaines sont reliées à des conduites 50 de dilution,
• une deuxième couronne intermédiaire 34, analogue à la couronne 33,
• une couronne d'extrémité inférieure 37, reliée à la couronne 32 par des tirants, non représentés,
• une couronne annulaire 41, portée par le rotor, et située en face des cavités C de la couronne 33 pour définir avec elle une pluralité de chicanes,
• une deuxième couronne annulaire 42, portée par le rotor, située en face des cavités C de la couronne 34.

Referring to FIG. 16, it can be seen that the filtration element according to the invention can comprise, from top to bottom:

• an upper end ring 32 for the sieve 30,
• an intermediate ring 33 comprising a plurality of cavities C, some of which are connected to dilution pipes 50,
• a second intermediate ring 34, similar to the ring gear 33,
• a lower end ring 37, connected to the ring 32 by tie rods, not shown,
• an annular ring 41, carried by the rotor, and located in front of the cavities C of the ring 33 to define with it a plurality of baffles,
• a second annular ring 42, borne by the rotor, situated in front of the cavities C of the ring 34.

The filter element constituted by the screen 30 and the rotor 40 is thus divided in three areas X, Y and Z from the bottom.

The pulp to be purified arrives at Q at the base of the device.

Zone X has an output 60 for the so-called "accepted" products, that is to say who passed through the sieve 30; zone Y has an output 61 for Accepted products and Zone Z an exit 62 for accepted products.

It is obvious that the dough will tend to thicken and flocculate at as it moves from one area to another.

As has been said, thickening causes a decrease in the efficiency of the declogging which must be compensated for example by a higher speed and therefore a higher energy consumption. The introduction of water into ducts 50 which open into certain cavities C or D of the crown 34 and the ring 33 makes it possible to counter this thickening and thus makes it possible to reduce the rotor speed and thus save energy.

At its upper part the apparatus comprises a cover 63, an output R for the rejects.

The speed of the rotor 40 can be adjusted according to the pressure differential between the entry Q in the apparatus and at least one of the pressures prevailing in the outlet ducts of accepted products 60, 61, 62.

It is also possible to adjust the speed of the rotor 40 according to one or several of the flows in the pipes 60, 61 or 62.

In either case it reduces the rotation speed of the rotor 40 and therefore to achieve energy savings.

The sieve can be made in many ways either by stacking rings to U-section of Figures 1 to 6, either by stacking grids obtained by juxtaposition of bars of Figures 12 and 13, or by stacking the sheets perforated cylindrical holes or slits of Figure 15.

Thus, for example, they may be constituted by plates 70, in the mass of which were hollowed with circular milling grooves 71, the slots are then machined with circular saws.

It should be noted that by disposing the blades 45 unclogging tilted a kind of pumping is obtained which accelerates the circulation in the apparatus.

It should also be noted that the rotor 40 being divided into as many portions as the sieve 30 can at each portion of the rotor have different blades 45 as to their number, their form, and their inclination.

In the same way the different portions of the sieve can be different constitutions.

In all the examples shown, the edges of the cavities C or D are exactly at the same level as that of the inner wall of the sieve 30.

It is possible to arrange them so that they project slightly to inside the sieve 30, provided that this does not prevent the introduction of the rotor 40 in the screen 30, that is to say that the annular rings such as 41, 42 etc ... can pass.

Claims (17)

1. Filtration apparatus of the type comprising a sieve (30) of a cylindrical form and a scourer (40), provided with blades (45) which produce pressure fluctuations in order to combat clogging-up of said sieve, the latter being in at least two parts of a substantially equivalent diameter, separated from each other by means, the purpose of which is to break up the component of the speed of the liquid, which is parallel to the surface of the screen, and to create turbulences, characterised by the fact that said means are baffles formed on the one hand by cavities (C, D) provided in an annular ring (33, 34, 35) of the sieve, said ring being disposed between said parts of the sieve and, on the other hand, by an annular deflector (21, 41, 42, 43) which is carried by the scourer opposite each ring of the sieve carrying the cavities, in such a manner that the majority of the liquid flow is forced to pass through the cavities.
2. Filtration apparatus according to claim 1, in which the sieve (30) comprises a stack of rings.
3. Filtration apparatus according to claim 1, in which the sieve (30) comprises a stack of screens, each screen being obtained by the juxtaposition of wires (31), either substantially parallel to the axis of rotation of the rotor (40) or perpendicular to this axis, or inclined.
4. Filtration apparatus according to claim 1, in which the sieve (30) comprises a stack of cylindrical sheets with holes or slits.
5. Filtration apparatus according to claim 1, in which the various parts of the sieve (30) are formed in a different manner from each other.
6. Filtration apparatus according to any of the claims 1 to 5, in which the cavities are parallelepipeds (C).
7. Filtration apparatus according to any of the claims 1 to 5, in which the cavities are cylindrical hollow volumes (D).
8. Filtration apparatus according to any of the claims 6 or 7, in which certain cavities are connected to a dilution conduit (50).
9. Filtration apparatus according to one of the claims 1 to 8, in which the number, the type, the thickness and the inclination of the blades (45) carried by the scourer (40) can vary between the annular deflectors (41, 42....).
10. Filtration apparatus according to any of the preceding claims, characterised by the fact that it comprises furthermore a zone of violent agitation disposed at the inlet of the sieve.
11. Filtration apparatus according to claim 10, characterised by the fact that the turbulences in the zone of violent agitation disposed at the inlet of the sieve are created by vanes (10) which are fixed on the scourer and vanes (11) which are fixed on the sieve.
12. Method of using a filtration apparatus according to one of the preceding claims for the treatment of paper pulp.
13. Method of using a filtration apparatus according to claim 12, according to which each part (X, Y, Z) of the filtration apparatus comprises an outlet for accepted products, (60, 61, 62) and each annular ring (33, 34) of the sieve (30) possibly comprises a dilution intake, the filtration apparatus furthermore comprising an inlet (Q) and an outlet (R) for rejects, and according to which, by acting upon the controls of the outlets for accepted products, of the outlet for rejects and of the intakes for dilution through the channels (50), the speed of rotation of the scourer (40) is reduced in such a manner that it is either the lowest possible in order to economise on power, whilst maintaining a low yield of rejects.
14. Method of using a filtration apparatus according to claim 13, according to which the speed of the scourer (40) is adjusted as a function of the pressure differential between the inlet (Q) in the apparatus and one at least of the pressures prevailing in the outlet conduits (60, 61, 62) for the accepted products.
15. Method of using a filtration apparatus according to claim 13, according to which the speed of the scourer (40) is adjusted as a function of one at least of the yields in the outlet conduits (60, 61, 62) for accepted products.
16. Method of using a filtration apparatus according to claim 13, according to which the ratio of rejects from one or more parts of the sieve is adjusted by adjusting the yield of the outlet for rejects from the apparatus, taking into account the yields of the outlet for the accepted products and the yields of the intakes for dilution.
17. Method of using a filtration apparatus according to at least two of the claims 14, 15 and 16.

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