EP1036879B1 - Pressure screen for fibre suspensions and a cleaning rotor for such a screen - Google Patents

Abstract

The pressure sorting assembly, to pass a fiber suspension (S) through a sieve, has a sieve cleaner (8) with different structures according to its position in relation to the suspension carrier flow (T). It gives a number of clearing zones (9-12) where the clearing elements have differing and increasing cleaning effects in the flow direction (T). The sieve cleaning elements differ in their geometric shape and in their type. In one cleaning zone (9,10), the cleaning elements have a ball section shape (13) mounted directly to the body (8') of the sieve cleaner (8). In one section (9-12), the cleaning elements have a hydrodynamic flow profile (14), mounted to the body (8') of the cleaner (8), at a radial gap from it. In one zone (10-12), the cleaning elements have wedge-shaped projections (15) mounted directly to the cleaner body (8'). The sieve (2) is cylindrical, and the cleaning elements in one zone (11,12) are formed by at least one rotating rounded polygon (16), with an outer contour giving different gaps between its periphery and the center of the sieve cleaner (8). The rounded polygon (16) is composed of a number of cylinder segments, fitted together to give an irregular rotating outer contour. The pressure tendency in the cleaning zones (9-12) increases in the flow direction (T). The ball sections (13) are at the zone (9) nearest to the suspension inflow (5), with the hydrodynamic flow profiles (14) in the second zone (10), the wedge-shaped projections (15) in the third zone (11) and the polygon (16) in the final zone (12), in the flow direction (T). The sieve (2) has openings which are smaller in the downstream flow direction (T) than in the upstream section. The sieve (2) can also have slits, narrowing downstream. The round holes in the sieve (2) have the smallest diameter smaller downstream. The sieve cleaner (8) is composed of a number of modules, assembled together by release mountings, where each module has at least one sieve clearing zone (9-12). The modules can be fitted in a variety of successive structures.

Description

The invention relates to a pressure sorter according to the preamble of claim 1.

Pressure sorters are used in the processing of pulp suspensions used, namely to process the fiber suspension in a wet sieving. For this purpose, such a pressure sorter contains a sieve element, which has a large number of Openings are provided. The fibers contained in the suspension should pass through the Open openings while keeping unwanted solid components on it rejected and routed out of the sorter. That is also conceivable Use to separate different fiber components, i.e. the shorter from the longer fibers. Round holes are generally used as sorting openings or Slots. In most cases, pressure sorters of the type considered here are included Provide screen clearers which have clearing surfaces moved past the screen. Thereby clogging of the screen openings is prevented in a manner known per se.

From WO 98/53135 a screen clearer has become known, that with wing elements for clearing the sieve. These wing elements have a hydrodynamic profile, which extends over the entire length of the sieve element Strainer, extends. This is due to the relative movement to the surrounding suspension Wing element in front a pressure and behind it a suction impulse on the one to be cleared Strainer. This will remove part of the suspension that has been rejected on the sieve or has already passed the sieve as a good substance, sucked back, causing the sieve openings be kept free or cleared. To the different known per se Solid content ("consistency") of the fiber suspension in different zones of the Taking the sieve element into account is the cross-section of the wing elements designed differently. The influence of this measure is however very limited.

The US 3,586,172 shows a pressure sorter, the rotor in four different zones is divided. After a first zone that only serves to accelerate the substance, the suspension reaches a sorting zone, in which the rotor with elevations is equipped that fluidize the fiber suspension and the formation of fiber flakes ("clusters") should prevent. The following sorting zone shows similar to the first Zone indentations in the rotor, which ensure the maintenance of speed and thereby to prevent plugging. The clearing effect of such However, there is little indentation in the present material.

WO 93/22494 A also shows a pressure sorter, the rotor of which is in different types Zones is divided. As a result, a drum-shaped rotor has a number of Projections on which are provided with surfaces for the axial transport of the suspension between rotor and screen basket. The axial transport is from Inflow to the sieve up to the reject outlet is promoted and in the last zone slowed down.

EP 0 289 020 proposes thickening the residue too quickly to prevent or reduce by a rotor that the axial transport along the Sieve basket accelerated. For this purpose, the rotor has a large number of projections ("bulges") with inclined surfaces for the production of axial components. there the axial impulses are of different strength depending on the axial position of the considered projection generated.

The invention has for its object to provide a pressure sorter with a special screen clearer on the entire screen element has a good sorting effect favored and particularly robust, i.e. enables a high throughput and is also suitable for suspensions with a consistency of more than 2%.

This object is achieved by the features mentioned in the characterizing part of claim 1 completely solved.

The subject of the invention develops its particularly advantageous effect in that the screen clearer used therein is provided with a number of clearing elements, which differ depending on their position. Although the shape is the used clearing elements known per se from the prior art. Surrender however, considerable advantages from their combination in the manner indicated. New is, that in the course of the transport flow, that is, on the path that it has flowed in Fibrous suspension runs along the sieve element until it does not pass through the Portions of the reject outlet that have passed through the sieve element leave the apparatus again, the screen clearing is carried out with increasing clearing effect, namely by differently designed clearing elements. For the sorting effect are not only the size and shape of the sorting openings in the sieve element are important, but also that Shape of the clearing elements, which keep the sieve element free. Broaching elements generate pressure and suction impulses at the screen openings Suction impulses are used for clearing, i.e. keeping the sieve free. The clearing elements can one differentiates several types, which have a fundamentally different structure to have. For example, hydrodynamically effective air flow in the wing The space between the rotor and the screen element is moved relative to the suspension, which specifically causes such pressure and suction phenomena that increase the throughput favor. Another option is to put on essentially spherical segment-shaped elevations, so-called "bumps", on one Basic rotor body or the placement of elevations, which a more or less have a pronounced wedge shape. There is also the possibility of the basic rotor body not with a round cross-section, but oval or in the form of a rounded polygons, e.g. Triangle, so to provide it with an outer contour, which has a different distance from the center of the rotor ("lobed rotor"). The influence that the different clearing elements have on sorting characteristics and Throughput describes e.g. the technical paper R. Rienecker: "Sorting - a Tool for sticky removal: machines "(weekly paper production, Book 17 and 18, 1997, pages 787 to 793, 855 to 859). This one based on Cleared design baskets described course exist also for screen clearers, which should keep flat screens clear.

In the rotor of the pressure sorter according to the invention, the different ones Broaching elements arranged so that the screen clearing effect in the different Clearing zones is increased in the course of the transport flow. The Paper fiber suspension is relative immediately after entering the pressure sorter thin and has a high content of fine and fillers. Hence the requirements the clearing of the screen less than in the later course. Less clearing effect is usually used for sorting quality, that is, for selectivity. More fibers get in the accepted substance. Would, however, in this first zone too much of these fine and Fillers flow through the sieve, so they were missing as a lubricant and carrier material in the following sorting zones. The sorting effect is thus achieved by the invention equalized in that in larger areas of the sorter an inexpensive Mixture of fibers and fines is present. This is important for the "rescue" of the Long fibers that are otherwise too easily permanently rejected, i.e. in the reject of the Pressure sorter would arrive.

With the invention, the push-through tendency in the transport direction can also be increased become. This means the following: The boundary between the rejected and Permitted proportions of a sieve element increases with the clearing effect shifted such that portions lagging behind with weaker push through tendency remain, get into the passage with a stronger tendency. In this context it is favorable that the broaching elements, which have a high push-through tendency, e.g. those with wedge-shaped elevations or a triangular contour, only in a small one Area of the strainer basket are used, i.e. where the achievable advantages are greater than the disadvantages. They are also particularly robust and call in turn, only a small part at this particularly vulnerable point on the screen element Stress caused by alternating bending stresses. It can also be useful that to combine increasing clearing action with decreasing push through tendency, e.g. if Too much dirt accumulation occurs in the downstream clearing zones.

The screen clearer can advantageously be modular. It then consists of several parts releasably connected to each other, each of which e.g. forms a clearing zone. So clearing zones can be meaningfully combined and tailored to the application, e.g. by changing the order of clearing zones. Worn parts can can be easily replaced.

It is also possible to configure the inventive design of the Siebräumers to combine with a special characteristic of the sieve element. Such as. is described in DE 44 32 842, a sieve element with sieve openings be provided, which in the direction of the transport direction continuously or batchwise be made smaller. This increases the size as it passes through the sorter are taken into account. It can be best this way Combine sorting quality, high throughput and operational reliability.

Fig. 1

den Erfindungsgegenstand in schematischer, perspektivischer Darstellung;

Fig. 2 bis 5

jeweils Varianten eines im Erfindungsgegenstand verwendbaren Siebräumers;

Fig. 6 und 7

jeweils eine andere Form eines geeigneten Siebräumers.

The invention and its advantages are explained with reference to drawings. Show:

Fig. 1

the subject of the invention in a schematic, perspective representation;

2 to 5

in each case variants of a screen clearer which can be used in the subject of the invention;

6 and 7

a different form of a suitable screen clearer.

1 shows a pressure sorter according to the invention with a sieve element 2, here in the form of a cylindrical screen basket, which the interior of the Pressure sorter divides into an inlet space 3 and an accept material space 4. In the Inlet 3 can the fiber suspension S via a suspension inlet 5 are fed. With the pressure sorter used here it receives one Angular momentum that sets it in a circumferential motion. In addition to this, in a row of the applied pressure gradient between the suspension inlet 5 and the bottom reject outlet 7, a transport flow T, through a vertical symbolizes downward arrow, created. On the way of the transport flow T is a large part of the fiber suspension S as intended by the Sieve element 2 derived in the accepted substance room 4. At least a big one occurs Part of the paper fibers contained in the fibrous stock suspension S into the accepted stock room 4 about. To prevent the openings of the sieve element 2 from becoming blocked a sieve clearer 8 known per se is used, which is relative to the sieve element 2 can move. According to the invention, the clearing elements used on the screen clearer 8 designed so that, viewed in the direction of the transport flow T, several Form clearing zones 9, 10, 11 and 12, each of which has different clearing elements exhibit. The screen clearer 8 of the embodiment shown here contains a total four different clearing zones, the first clearing zone 9 having spherical sections 13 which second clearing zone 10 with hydrodynamic flow profiles 14, the third clearing zone 11 with wedge-shaped elevations 15 and the last clearing zone 12 with a circumferential one Polygon 16 is provided. The order shown here is true in many cases particularly advantageous, but in the form not the only way to the invention realize. In addition, e.g. the number of clearing zones can also be varied. It is important that the clearing effect that the clearing elements exert from level to level Level is increased. Then there is a relatively high throughput through the pressure sorter possible because the increasing resistance on the way of the transport flow T at Convey the suspension through the sieve element with a correspondingly stronger one Effectiveness of the clearing elements can be balanced.

Fig. 2 shows a schematic representation of a clearing zone from above, in the Ball sections 13 are placed directly on a base body 8 '. It should be noted that these spherical sections operated here at a lower peripheral speed are considered common because they are on the same rotor as the other clearing elements. By reducing the clearing effect again, they support the solution of the task.

Another version is shown in FIG. 3 with wedge-shaped elevations 15, which also are attached to the base body 8 'without clearance. 4 are hydrodynamic Flow profiles 14 can be used, the radial spacing on the base body 8 'of Siebräumers 8 are attached. There is only a certain form of such hydrodynamic flow profile shown; as is well known, there are also others here Possibilities, e.g. with a greater length in the circumferential direction. Fig. 5 shows as Another variant is a so-called "lobed rotor", in which a rounded polygon 16 is used, which e.g. - as shown here - from two cylinder segments is formed, each having an ellipse section as the base. Here is the Transition point of adjacent cylinder segments on the outer contour is discontinuous.

The pressure sorter shown in Fig. 1 is a relatively complex embodiment of the submitted invention. It has four different clearing zones 9, 10, 11 and 12 on. It is not always necessary to go that far. 6 shows an example with only three different clearing zones 9, 10 and 11. Also one is in the direction the clearing effect of the transport flow T can be achieved.

It is also conceivable that the embodiment shown in FIG technical requirements are already fully met. In this the screen clearer 8 in the first clearing zone 9 hydrodynamic flow profiles 14 on and in the second clearing zone 10 wedge-shaped elevations 15. Act in many applications this embodiment is a technical-economic optimum of the invention.

Claims (16)

1. Pressure screen for filtering a fibre suspension (S), having at least one filter element (2), which divides the pressure screen into an intake chamber (3) and an accepted stock chamber (4),
   wherein the intake chamber (3) communicates at one end with a suspension intake (5) and at the other end with a reject outlet (7), generating a conveying stream (T), whilst the accepted stock chamber (4) is connected to an accepted stock tube (6),
   wherein the pressure screen further has a filter scraper (8) which in order to keep the filter clear is movable relative to the filter element (2) and is provided in the course of the conveying stream (T) with plural scraping elements, the scraping elements being differently formed according to their position in the conveying stream (T), characterised in that plural scraping zones (9, 10, 11, 12) are formed in which the scraping elements achieve an individually different scraping effect increasing in the conveying direction, and in that the scraping elements differ from one another not only in their geometric configuration but also in their type.
2. Pressure screen according to claim 1, characterised in that the scraping elements of one scraping zone (9, 10) are spherical sections (13), which are fixed direct to the base body (8') of the filter scraper (8).
3. Pressure screen according to one of the preceding claims, characterised in that the scraping elements of one scraping zone (9, 10, 11, 12) are hydrodynamic flow profiles (14), which are fixed with radial clearance to the base body (8') of the filter scraper (8).
4. Pressure screen according to one of the preceding claims, characterised in that the scraping elements of one scraping zone (10, 11, 12) are wedge-shaped projections (15), which are fixed direct to the base body (8') of the filter scraper (8).
5. Pressure screen according to one of the preceding claims, characterised in that the filter element (2) is cylindrical and the scraping elements of one scraping zone (11, 12) are formed by at least one revolving, rounded polygon (16), whose outer contour has a distance from the centre of the filter scraper (8) which varies according to the circumference.
6. Pressure screen according to claim 5, characterised in that the rounded polygon (16) consists of plural cylinder segments, which are so arranged relative to one another that their outer contour is discontinuous.
7. Pressure screen according to one of the preceding claims, characterised in that the push-through tendency of the scraping zones (9, 10, 11, 12) increases in the direction of the conveying stream (T).
8. Pressure screen according to claim 2, characterised in that the spherical sections (13) form the first scraping zone (9) lying closest to the suspension intake (5).
9. Pressure screen according to claim 3, characterised in that the hydrodynamic flow profiles (14) form the second scraping zone (10) in the direction of the conveying stream (T).
10. Pressure screen according to claim 4, characterised in that the wedge-shaped projections (15) form the third scraping zone (11) in the direction of the conveying stream (T).
11. Pressure screen according to claim 5 or 6, characterised in that the polygon (16) forms the last scraping zone (12) in the direction of the conveying stream (T).
12. Pressure screen according to one of the preceding claims, characterised in that the filter element (2) is provided with apertures, which are smaller in the downstream direction of the conveying stream (T) than in the upstream direction.
13. Pressure screen according to claim 12, characterised in that the filter element (2) has slots, whose width is narrower in the downstream direction.
14. Pressure screen according to claim 12, characterised in that the filter element (2) has round holes, whose smallest diameter is smaller in the downstream direction.
15. Pressure screen according to one of the preceding claims, characterised in that the filter scraper (8) consists of plural units connected detachably together, each unit comprising at least one scraping zone (9, 10, 11, 12).
16. Pressure screen according to claim 15, characterised in that the various units are interchangeable in their arrangement.

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