EP1215335B1 - Pressure screen for cleaning paper pulp containing impurities - Google Patents

Abstract

Pressurized screen to remove contaminants from a contaminant-containing fibrous paper suspension. Pressurized screen includes a housing, a first screen element, essentially axially symmetric and rotatably mounted within housing, and a second screen element, which is essentially axially symmetric. First and second screen elements are successively arranged in suspension flow direction. At least one intake, coupled to housing, supplies suspension to housing, and at least one accepts outlet, coupled to housing, conveys a part of suspension that passes through the second screen element out of housing. At least one coarse reject outlet is located within housing to remove a part of suspension not passing through first screen element, and at least one fine reject outlet is located within housing to remove a part of suspension not passing through second screen element. First screen element includes conical shape with opening angle (alpha) between about 10° and 170°.

Description

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

Pressure sorters are used in the processing of paper fiber suspensions to process the pulp suspension in a wet sieving. For this purpose, such a pressure sorter contains at least one sieve element which is provided with a plurality of openings. The fibers contained in the suspension are to pass through the openings, while the unwanted solid constituents are rejected therefrom and are led out of the sorter again. As sorting holes round holes are usually used or slots. In most cases, pressure sorters of the type considered here are provided with screen scrapers having reaming surfaces moved past the screen. As a result, clogging of the screen openings is prevented in a manner known per se.

Since both the dissolving state of the paper pulp and the amount and structure of the contaminant load constantly change in the course of the stock preparation process, it is necessary in many cases to operate pressure screens in several stages with different openings. In this way, a good separation of most of the resulting contaminants can be achieved overall. Such contaminants, which differ significantly from the other contaminants due to their sinking behavior, can also be separated by hydrocyclones. This technique is also known, so that generally a series of hydrocyclones and pressure sorters is used for fabric cleaning.

From DE-C-197 02 044 is a vertical sifter for a pulp suspension known, which has two sieve elements in a single machine. In this sifter, the material flow to be sorted first reaches the area of a flat preliminary screen, which is kept free on the inlet side with a reamer. The passage through this flat pre-screen is then passed into the interior of a rotationally symmetrical screen basket, through the openings of the accepts passes, so that the suspended paper fibers can pass through this screen basket into the Gutstoffauslauf. Such a sorter should be used in particular when the supplied pulp suspension is mixed with a larger amount of coarse impurities. As is well known, this is very common in recovered paper processing, especially in the case of the substance which originates directly from the pulper or after passage of a cleaning device removing only the very largest impurities. However, in certain cases, this known sorter has the disadvantage that, in particular in the area of the flat pre-screen, high wear occurs and the coarse impurities can lead to malfunctions.

WO-A-00/58549 shows a sorter with a vertical housing, in which there are two sieve elements through which the paper fiber suspension to be cleaned flows in succession. In this case, the two sieve elements are at least partially pushed into each other axially, which allows a compact design. Other versions with two through-flow sieves are known from EP-A-0 955 406 and DE-A-21 40 904. The first sieve is cylindrical and is rotated. However, these devices are unfavorable in many applications. This is especially true when processing coarse materials. A cylindrical screen in particular has the disadvantage that the elongated, tending for spinning or winding impurities can easily create such a sieve and then be lashed in consequence of the rotation. They are then manually removable only after parking.

A flat disk-shaped sieve, as known, for example, from WO-A-00/52260, has a simple structure and requires little space. However, it has only a small one Sieve surface, which is disadvantageous.

The invention is based on the object to build a pressure sorter so that it is insensitive to clogging impurities and at the same time provides a good sorting quality. He should be used in particular for dissolved waste paper, which still contains a large part of the originally contained, little crushed impurities.

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

A pressure sorter of the type according to the invention is particularly suitable for being used at the beginning of pulping, that is, where - still - a relatively large proportion of coarser impurities in the suspension is entrained. If e.g. Waste paper in a pulper or a dissolving drum brought into suspension, this often has an impurity content of more than 2% of the solid. Part of this contaminant is relatively coarse, so it is also rejected at a 4mm hole to large proportion.

After entering the pressure sorter according to the invention, the suspension hits the inlet side of the first sieve element. Its rotation generates a centrifugal force with which the impurities are thrown off the surface of this sieve element, if they are specifically heavier than the surrounding suspension. On the solid particles, which are located in the vicinity of the sieve inlet, so attack not only the resulting due to the applied pressure difference drag forces, but also centrifugal forces. The more the longitudinal direction of the screen opening is oriented radially (instead of axially), the stronger is the free-spinning effect and the lower the risk that the particles get stuck in the openings. Heavy parts, which are dismissed as intended on the screen element, leave its inlet area relatively quickly and are removed by the coarse reject spout from the housing. You may also be able to carry light, rejected due to their size impurities, especially plastic films. The sieve is not only less but it is not so easily clogged by pieces of wire, glass splinters and small stones.

Of course, the spin effect depends on the velocities and the radius at the point of interest. The particular advantage of the invention is that the first sieve element is at least partially conical. A conical shape combines the advantages of a large sieve surface with sufficient centrifugal effect from the sieve area.

The combination according to the invention of the two differently operating sieve elements in a housing creates a compact machine which operates reliably even with heavily soiled liquids. It is also advantageous to be able to provide the first screening element and the scrapers for the second screening element with a common drive.

The pressure sorter according to the invention is easy to equip with an effective Leichtschmutzaustrag. Styrofoam and foil pieces can already be concentrated and removed with the aid of centrifugal forces before they have passed the first sieve element. The same applies to air. This accumulation and discharge of light parts is favored by a flat or conical first sieve element.

Fig. 1

schematisch: Den funktionalen Aufbau eines erfindungsgemäßen Drucksortierers;

Fig. 2

Kraftverhältnisse am konischen Siebelement;

Fig. 3, 4, 5 + 6

jeweils eine Variante des Erfindungsgegenstandes;

Fig. 7

detaillierter den in Fig. 1 gezeigten Drucksortierer in geschnittener Seitenansicht.

The invention and its advantages will be explained with reference to drawings. Showing:

Fig. 1

schematically: The functional structure of a Drucksortierers invention;

Fig. 2

Force relationships on the conical sieve element;

Fig. 3, 4, 5 + 6

in each case a variant of the subject invention;

Fig. 7

in more detail the pressure sorter shown in Fig. 1 in a sectional side view.

Fig. 1 shows, albeit only schematically, the most important functional parts to Belong to the pressure sorter according to the invention. During operation of this device, the paper fiber suspension S is introduced into the housing through the inlet connection 3 and firstly reaches the inlet chamber 10. The conical first screen element 1 is located in this housing. Its opening angle α is adapted to the requirements and is generally between 60 and 120 °. An important feature of the invention is that in such a machine, the first screen element 1 can be set in rotation. To prevent clogging of the screen openings in the first screen element 1, fixed Siebräumer 8 are indicated, which are located on the accept side of this screen element, ie on the downstream side and generate pressure pulses. The effect of such sieve clearers is known and need not be explained in detail. The arrangement on the accept side leads to a considerable reduction in wear and prevents the pinching of substances rejected on the screen. Contaminants that are rejected due to their size or shape of the screen element, so this can not happen, flow together with a small part of the suspension as overflow R1 through the coarse reject spout 5 from the housing. The same applies to such contaminants that have not passed through the screen element 1 due to the centrifugal effect already described.

The housing of the pressure sorter is constructed so that the passage A1 of the first screen element 1 can pass directly to the inlet side of the second screen element 2. Passage A2 passing through this screen element 2 is led away through the fine reject outlet 6 by the accepts outlet 4 and the rejected overflow R2. To keep free the second screen element 2 moving scraper 9 are provided, which are connected here to the rotor 24, that are driven at the same speed as the screen element 1. But it is quite conceivable that different speeds are beneficial. Then the first screen element 1 is to be driven by a further shaft (24 'in Fig. 3), e.g. would be within a rotor 26 to lead.

As a second screening element 2, a cylindrical sieve, also called a sieve basket, is particularly advantageously chosen. Such baskets provide both a large screen area, as well as high stability and easy clearing. In the inventive Pressure graders are no longer to be expected at this point by rough impurities. Therefore, a small screen perforation can be selected.

In Fig. 2, the forces are qualitatively represented, which act on a solid particle 14, which is located in the vicinity of the sieve opening 12. The centrifugal force 15 acts radially outwards and the drag force 16 in the direction of the sieve opening. For heavy parts, the centrifugal force 15 is large enough to produce a resultant 17 which removes the particulate matter 14 from the screen element 1. Important for the sorting effect is the smallest diameter 13 of the sorting opening 12. In typical applications of the subject invention, this diameter is at least 4 mm, since this is a relatively coarse material. A phase in the inlet region of the sorting openings 12 can improve the clogging behavior of the rotating screen element 1. Under certain circumstances, it makes sense to make the sorting openings of different sizes. Because of the shape of the first sieve element 1, different sorting conditions (inflow angle at the inlet into the sorting opening and centrifugal forces) are possible depending on the radial distance from the center, which is often undesirable. By the measure mentioned such disadvantages can be compensated.

In principle, as shown by way of example in FIG. 3, the pressure sorter according to the invention can also be a horizontal sorter, ie have a horizontal axis. This sometimes brings space advantages and can improve the discharge of heavy parts through the coarse reject spout 5, since gravity is supportive here.

The shape of the first sieve element, in particular the opening angle α, plays, as already stated, an important role in determining the properties of the pressure sorter. In addition, as shown in FIGS. 4 and 5, the first screen element 1 'may have a plurality of sections whose opening angles α are different.

Also with respect to the second screen element, there are a number of known design options. Optimal should be the cylindrical shape. As a scraper to Sieve free are wing, Foils (Fig. 1, 3, 5) or provided with projections drum rotors (see Fig. 4 and 7) used.

It may also be expedient to adapt the contour on the inlet space 10 approximately to the contour of the first sieve element 1. 6 shows an example of the type in which a conical upper part of the housing was also selected for the conical first sieve element 1.

The pressure sorter according to the invention already indicated in FIG. 1 is drawn somewhat more in detail in FIG. 7, without that figure being understood as a construction drawing. The first sieve element 1, which is designed in a conical shape, divides the upper part of the housing into an inlet space 10, which communicates with the inlet connection 3 for the suspension. Of the screen openings 12 only part is shown. Centrally located within the first sieve element 1 are a number of fixed Siebräumern 8. These are connected at its bottom to the housing. The two sieve elements are arranged so that the first sieve element 1 divides the upper part of the housing into the inlet space 10 and the first accepts space 11. This first Gutstoffraum 11 located centrally within the first screen element 1 is in communication with the Zulaufraum to the second screen element 2. The second screen element 2 in turn divides from the lower part of the housing from the Gutstoffraum 20, which communicates with the Gutstoffauslauf 4. The inlet space of the second screen element 2 merges at its lower end into the reject space 22, which in turn is connected to the fine reject outlet 6. The second screen element 2 is thus kept free of blockages on the rotor 24, which also drives the first screen element 1 is a drum 19 with it placed on scrapers 9 are. The rotor 24 is expediently mounted on the fly, ie a strong, multi-part bearing 23 holds the rotor from below. In this way, the upper part of the rotor can remain free from storage, so that the spinning impurities located in the upper part of the sorter can not create, but can slide off centrally. In the upper part of the sorter is the Leichtrejektauslauf 7, which here open and closed by a valve 18 intermittently can be.

In the inlet space for the first filter element 1, a flow-guiding element 25 is indicated by way of example. Such guide elements serve to keep the suspension which has flowed through the inlet connection 3 into rotation and / or to guide it radially inwards towards the screen plate. Since the first screen element 1 rotates during operation of the pressure sorter, it is also necessary to set the suspension in rotation so that it can flow through the screen openings 12 of the screen element.

Claims (25)

1. A pressure grader for removing anionic trash from a paper fibre suspension (S) containing anionic trash, comprising a vertical or horizontal housing which contains at least two substantially rotationally symmetrical screen elements which are arranged such that the pulp suspension introduced through at least one inlet pipe (3) into the housing can flow therethrough in succession,
   the upstream first screen element (1, 1') being rotatable,
   the portion of the paper fibre suspension (A2) which has also passed through the second screen element (2) being discharged from the housing again through at least one accepted-stock outlet (4) and
   the housing having at least one coarse reject outlet (5) for the overflow fraction (R1) produced at the first screen element (1,1') and at least one fine reject outlet (6) for the overflow fraction (R2) produced at the second screen element (2),
   characterised in that
   the first screen element (1,1') is of conical form with an opening angle (α) of between 10 and 170°, and the first screen element (1, 1') is arranged axially outside and in the case of a horizontal housing laterally next to, and in the case of a vertical housing above, the space in which the second screen element (2) is located.
2. A pressure grader according to Claim 1,
   characterised in that
   the housing is vertical.
3. A pressure grader according to Claim 1 or 2,
   characterised in that
   the opening angle (α) is between 60 and 120°.
4. A pressure grader according to Claim 1, 2 or 3,
   characterised in that
   the downstream second screen element (2) is fixed in the housing.
5. A pressure grader according to Claim 1, 2, 3 or 4,
   characterised in that
   a centrally arranged light reject outlet (7) is located in the inflow space (10) associated with the first screen element (1, 1').
6. A pressure grader according to Claim 5,
   characterised in that
   the light reject outlet (7) is closed off by a valve (18) which briefly opens automatically at intervals.
7. A pressure grader according to Claim 5 or 6,
   characterised in that
   the rotor (24) driving the first screen element (1, 1') has no bearing means on the axial end facing the light reject outlet (7).
8. A pressure grader according to one of the preceding claims,
   characterised in that
   the first screen element (1) is in the form of a dual cone, the greater diameters being located at the axially outer ends.
9. A pressure grader according to one of the preceding claims,
   characterised in that
   the side of the cone with the larger diameter is directed towards the second screen element (2).
10. A pressure grader according to one of the preceding claims,
    characterised in that
    fixed screen scrapers (8) are located on the throughflow side of the first screen element (1, 1').
11. A pressure grader according to one of Claims 1 to 9,
    characterised in that
    fixed scrapers are located on the inflow side of the first screen element (1, 1').
12. A pressure grader according to one of the preceding claims,
    characterised in that
    the inflow side of the first screen element (1, 1') has a profiled surface.
13. A pressure grader according to one of the preceding claims,
    characterised in that
    the inflow side of the first screen element (1, 1') is provided with bars.
14. A pressure grader according to one of the preceding claims,
    characterised in that
    the first screen element (1, 1') is provided with round holes, the diameter of which is at least two millimetres.
15. A pressure grader according to Claim 14,
    characterised in that
    the round holes have a diameter of at least four millimetres.
16. A pressure grader according to one of the preceding claims,
    characterised in that
    the first screen element (1, 1', 1 ") is provided with grading openings, which are of different sizes according to their radial position on the screen element.
17. A pressure grader according to Claim 16,
    characterised in that
    the grading openings located radially further to the outside are larger than those located further to the inside.
18. A pressure grader according to one of the preceding claims,
    characterised in that
    flow guidance elements (25) are located in the inflow space (10) associated with the first screen element (1, 1'), which elements influence the peripheral movement of the suspension located therein.
19. A pressure grader according to Claim 20,
    characterised in that
    the flow guidance elements (25) have curved surfaces on which the peripheral flow is deflected radially to the centre.
20. A pressure grader according to one of the preceding claims,
    characterised in that
    the second screen element (2) is a cylindrical screen basket.
21. A pressure grader according to one of the preceding claims,
    characterised in that
    the second screen element (2) is provided with round grading openings, the diameter of which is at most two millimetres.
22. A pressure grader according to one of the preceding claims,
    characterised in that
    the second screen element (2) is kept clear by moved scrapers (9) which are associated with the rotor (24), which also drives the first screen element (1,1').
23. A pressure grader according to one of Claims 1 to 21,
    characterised in that
    the second screen element (2) is kept clear by scrapers (9) moved by a rotor (26), and that the first screen element (1, 1') is driven at a speed which differs from that of this rotor (26).
24. A pressure grader according to one of the preceding claims,
    characterised in that
    the inlet pipe (3) opens tangentially into the housing.
25. A pressure grader according to one of the preceding claims,
    characterised in that
    the greatest internal diameter of the first screen element (1, 1') is larger than that of the second screen element (2).

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