EP1598477B1 - Pressure screen for screening a fibrous suspension - Google Patents

Abstract

In a paper making process foreign bodies with fibres in suspension (S) are removed in a pressure sorting assembly with a housing (2) containing a sieve (1) and a moving sieve scraper (5). The sieve scraper moves in opposite direction to the tangential inlet (8). The upper part of the inlet chamber (4, 4') has an outlet (11, 11') for lightweight fractions. The pressure sorting assembly has a sieve (1) separating the radial inlet chamber from the interior fibre chamber (3). The inlet chamber (4, 4') has a chamber outlet (7) for heavy fractions. The inlet chamber (4) has a conical zone (15) between the inlet (8) and the outlet (10) for rejected fractions. Also claimed is a process to employ the pressure sorting assembly for the recovery of recycled paper.

Description

The invention relates to a pressure sorter according to the preamble of claim 1 and to a use of a pressure sorter according to claims 13 and 15.

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

The separation effect of a pressure sorter is therefore attributable to the fact that at least some of the impurities contained in the paper pulp suspension fed can not pass through the sieve, that is to say it is separated from the paper fibers due to its size, shape or flexibility. There are also pressure sorters are known in which additionally targeted to the density of the impurities separation is made by the different forces of the impurities are used in a centrifugal field. Although the separation effect can only be optimally achieved in hydrocyclones and centrifuges, it can still be useful in pressure sorters. Although a large part of the heavy parts would not pass through the screen openings usually used, so be rejected there, but there is a risk of damage or wear when they come into contact with the sieve. This risk is aggravated by the fact that almost always used are Siebräumer that move very close to the screen at a relatively high speed.

It is easily possible, pressure graders, which in highly contaminated paper fiber suspensions be used by upstream hydrocyclones, so-called thicker scavenger, to protect against coarse heavy particles. This is effective, but with additional effort.

Another way to reduce wear on the screen of the sorter is to place the sifter on the accept side of the screen. As a result, the rejected parts on the screen have a lower speed and can not be detected by the sieve scraper. In particular, the damage caused by pinching of metal parts between the sieve and Siebräumern is very unlikely.

When designed with cylindrical screen baskets pressure sorters of the type considered here is often a centripetal procedure used, in which the suspension passes radially from outside to inside the sieve openings. Heavy parts can not easily reach the sieve due to the centrifugal forces.

From the DE-A-28 30 386 as well as from the DE 12 31 539 B Drucksortierer are known in which the suspension to be cleaned centripetally is passed through a cylindrical screen basket and where the Siebräumer run in the accepts. It is in an embodiment according to the DE 12 31 539 B the rotor is driven so that its peripheral speed is opposite to that of the inflowing suspension. This sorter discharges both heavy and light contaminants downwards.

Despite these advances, the operation of pressure sorters of this type is very problematic. Thus, it can not be ruled out that scrapings, eg pieces of metal, broken glass and stones still scrape along the wire and lead to increased wear, especially in the case of suspensions containing a lot of contaminants, such as must be treated immediately after the waste paper is dissolved in the presorting. Even lightweight parts, especially foams (polystyrene) are not, at least not optimal and quickly excreted. With these, there is a risk that they are crushed in the pressure sorter so far that they get into the accept and can be deposited in the subsequent separation stages only poorly. Or they concentrate in the pressure sorter and block the inflow paths to the sieve or sieve openings themselves.

The invention is based on the object of further improving the known pressure sorters, so that even a considerable part of the contaminants can be removed from the paper fiber suspension before they strike the screen. In particular wear-promoting heavy parts and sensitive lightweight parts should be removed early.

This object is achieved in a pressure sorter according to claim 1 by the feature mentioned in the characterizing part of claim 1.

In the pressure sorter of the specified type significantly more favorable flow conditions can be generated by the inventive measures, which is particularly true for the inlet chamber. This is generally annular and is supplied by a tangentially attached inlet with the pulp suspension to be sorted, whereby a rotational flow is formed. As a result of the centrifugal forces generated thereby, the heavy parts are thrown radially outward, so that they can not or hardly come into contact with the sieve. They drive in the direction of the inner wall of the housing and are partly further dragged by the suspension flow and partly transported by gravity into a part of the Zulaufraumes, from which they can be easily removed. The radial inside of the screen - so good material - rotating Siebräumer generated in Acceptance space pressure and suction pulses to keep free the screen openings. In this case, the Siebräumer has a direction of rotation, which is opposite to the direction of rotation of the located in the Zulaufraum rotating liquid ring. This is advantageous because the Räumerflügel produce in cooperation with the screen an opposing rotational flow in the inlet space, so driving the suspension located in Zulaufraum in the direction that it already has from the inlet ago. The lightweight parts are separated by the centrifugal forces of the heavy parts and move up the sieve up and can be easily removed. Due to the pronounced rotational flow also directly on the screen, the tendency of the light parts is low to stick to it. In this way, the separation efficiency of heavy parts and lightweight parts in the inlet space is substantially improved without additional equipment and at about the same energy consumption.

Fig. 1

schematisch geschnitten in Seitenansicht dargestellt, einen erfindungsgemäßen Drucksortierer;

Fig. 2

schematisch geschnitten in Aufsicht dargestellt, einen erfindungsgemäßen Drucksortierer;

Fig. 3+4

je eine Variation in Seitenansicht;

Fig. 5

Schema mit einer vorteilhaften Verwendung des erfindungsgemäßen Drucksortierers.

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

Fig. 1

shown schematically in side view, a pressure sorter according to the invention;

Fig. 2

schematically shown in plan view, a pressure sorter according to the invention;

Fig. 3 + 4

one variation each in side view;

Fig. 5

Scheme with an advantageous use of the pressure sorter according to the invention.

A typical embodiment of the pressure sorter according to the invention is shown in FIG. 1. This contains in a housing 2 a sieve 1 in the form of a cylindrical screen basket. The center line of the screen 1 is perpendicular here in the position of use of the device. One speaks therefore of a vertical sorter. The sieve openings are advantageously cylindrical along their entire length with a diameter between one and three millimeters. The pulp suspension S to be screened is introduced into the housing 2 through an inlet 8. In the process, it first passes into the inlet space 4, which extends substantially annularly and radially outside the screen 1 as part of the housing 2. As can be seen from FIG. 2, the inlet 8 is connected tangentially to the inlet chamber 4, so that a rotational flow forms during operation of the machine in the inlet chamber 4, which runs in the clockwise direction in this illustration.

The supplied pulp suspension S moves in the inlet space 4 helically downwards, with a considerable part of this suspension pass through the sieve opening of the sieve 1 and can reach into the accepts space 3 located radially inside the sieve 1. By a conically tapering portion 15 of the inlet chamber 4, the peripheral velocity of the suspension is maintained or increased, even if their amount decreases due to the outflow through the wire 1.

In Gutgutraum 3 is the Siebräumer 5, which is provided here with a number of wings 6, which are preferably driven at a peripheral speed of at least 15 m / s. By relative movement to the surrounding liquid they produce pressure and suction surges, with which the screen openings are kept free. The Siebräumer 5 is mounted on the fly in the lower part of the housing 2 (bearing and sealing unit 16) and is driven in rotation. As shown in FIG. 2, the sifter 5 is driven so that its peripheral speed opposite tangential inflow direction at the inlet 8. The advantages of this contradiction have already been mentioned. As a result of the rotational flow formed in the feed space 4, centrifugal forces act on the pulp suspension S. These result in heavy parts being thrown outwards, ie towards the housing wall. As a result, they are effectively prevented from contact with the wire 1. They collect in the lower part of the inlet chamber 4 and are derived, for example via the Schwerteilauslass 7 in the heavy part lock 13, with hardly any fiber losses. In typical cases, the fibrous suspension S to be screened is contaminated not only with heavy but also with light parts, which include, in particular, polystyrene or other light foams. These are quickly separated from the heavy parts due to the centrifugal forces and can be removed early because they move due to their tendency to rise in the liquid-filled feed space 4 in the upper part. There they are discharged through the Leichtteilauslass 11. This can, as here, lead vertically upwards or obliquely upwards, or also tangentially connected. It may be advantageous to provide an impermeable cylinder wall 14 lying above the screen 1 for the purpose of separating the inlet space 4 and the accepts space 3, so that a lightweight part collecting space is formed in the upper part of the inlet space 4. This can cause a significant calming of the flow, whereby the lightweight parts and possibly air can be separated even better. The axial length of this cylinder wall 14 is only a fraction of the axial length of the screen 1, for example, about 20%. The climbing effect of the lightweight parts can be additionally supported in this area by a fixed helix, which deflects the circumferential movement into a rising motion.

The largest part of the suspension rejected at the sieve 1, in particular the contaminants entrained by flow forces, are removed from the housing 2 at the reject outlet 10 as reject R. It is usually sorted to avoid fiber loss.

The accepts space 3 has here at its uppermost part a vent line 12 through which air and possibly also very fine lightweight parts can be removed from the accepts.

Figures 3 and 4 serve to show even more solutions with specific details. Thus, the device according to FIG. 3 has a modified flow guidance in that the accept A from the accept chamber 3 is not discharged downwards, as in FIG. 1, but upwards, ie, that the Gutstoffauslass 9 'is centrally connected to the upper wall of Acceptance space 3. The deducted accepts A then contains in addition to the sorted fibers and air, which is why a further vent line can be omitted. The ejected in the inlet space 4 to the outside heavy parts are guided by a vertical or oblique on the housing 2 radially projecting Schwerteilkanal 18 directly down to the heavy section lock 13. This embodiment ("Schwerteilfalle") prevents longer rotation of heavy parts in the housing and is also possible in the sorters shown in Figures 1 and 4. In addition, the device according to FIG. 3 has a possibility to better guide rejected heavy parts by means of a bevel 17 at a continuation of the inlet space 4 located below the accepts space 3 into the heavy-duty sluice 13. The inlet space 4 is closed at the top by a bevel 20, at the highest point of the lightweight outlet 11 'is connected.

The pressure sorter in Fig. 4 is provided with an inlet space 4 ', whose cross section over the axial height is kept substantially constant, since it was dispensed with a tapered portion. Also, a special separate light parts collection space above the screen 1 can be omitted if necessary, to save height. The lightweight parts are immediately dissipated by the Leichtteilauslass 11. In the lower part of the inlet chamber 4 'is a downwardly sloping end wall 19, which leads out there arrived heavy parts together with the reject R through the reject outlet 10 from the housing. Conveniently, the reject outlet 10 is connected at the lowest point. Another Schwerteilauslass can then be saved. The end wall 19 may have an arcuate shape.

As already mentioned, the preferred use case of this device is the pre or coarse sorting of dissolved pulp. This may typically be a recovered paper pulp suspension formed in a pulper 21 from recovered paper P and water W and withdrawn through a coarse pulp screen 22, as shown in FIG. Such a Pulpersieb 22 is kept free by a rotor 23 and usually has holes with a diameter between 10 and 25 mm. The withdrawn by this waste paper suspension is pumped without further screening device via fuel pump 24 into the inlet 8 of an inventively designed pressure sorter. Therefore, this suspension S may be mixed with a larger amount of impurities, which can easily be retained on screen openings whose diameter, for example, in a range between 1 and 3 mm lies.

In other applications, such soiled waste paper suspensions may be prepared in a high consistency pulper or in a downstream open wire disintegrating drum, such as an open sorting drum, and diluted. A dissolving drum that is suitable for the process, for example, shows the German patent application DE 197 36 143 ,

Claims (17)

1. Pressure grader for screening pulp suspension (S) having at least one cylindrical or conical screen (1), which is inserted in a housing (2, 2'), its centre line being substantially vertical in the operating position, and which is provided with a large number of screen apertures, through which a part of the pulp suspension (S) supplied to a supply chamber (4, 4') through a tangential supply (8) can pass into an accepted stock chamber (3), to which an accepted stock outlet (9, 9') is connected, whilst another part of the suspension is rejected at the screen apertures and is discharged from the pressure grader separately as reject (R) through at least one reject outlet (10), wherein in the accepted stock chamber (3) a driven screen clearing device (5) is located, which is so driven that its speed of rotation is opposite to the tangential inflow direction at the supply (8), characterised in that a light-particle outlet (11, 11') is connected to the upper part of the supply chamber (4, 4').
2. Pressure grader according to claim 1, characterised in that the pressure grader is provided with a screen (1), which separates the radially inner accepted stock chamber (3) from the radially outer supply chamber (4, 4').
3. Pressure grader according to claim 1 or 2, characterised in that the supply chamber (4, 4') is connected to a heavy-particle outlet (7).
4. Pressure grader according to claim 3, characterised in that the heavy-particle outlet (7) is connected to the lower part of the supply chamber (4, 4').
5. Pressure grader according to claim 3 or 4, characterised in that an intermittently actuatable heavy-particle sluice (13) is connected to the heavy-particle outlet (7).
6. Pressure grader according to one of the preceding claims, characterised in that the supply chamber (4) has a conically tapering section (15) between the supply (8) and the reject outlet (10).
7. Pressure grader according to one of the preceding claims, characterised in that the supply (8) lies geometrically above the reject outlet (10).
8. Pressure grader according to one of the preceding claims, characterised in that a ventilation line (12) is connected to the upper part of the accepted stock chamber (3).
9. Pressure grader according to one of the preceding claims, characterised in that the screen clearing device (5) is so formed that, by relative motion, it can impart pressure and suction pulses in the direction of the screen (1) to the surrounding liquid.
10. Pressure grader according to one of the preceding claims, characterised in that the supply chamber (4) is closed at the bottom by a slope (17), to whose lowest point the heavy-particle outlet (7) is connected.
11. Pressure grader according to one of claims 1 to 9, characterised in that the supply chamber (4) is closed at the bottom by an obliquely extending closing wall (19), to whose lowest point the reject outlet is connected.
12. Pressure grader according to one of the preceding claims, characterised in that the supply chamber (4) is closed at the top by a slope (20), to whose highest point the light-particle outlet (11') is connected.
13. Use of a pressure grader according to one of the preceding claims, for cleaning a suspension produced from waste paper, which has been produced by dissolving in a dissolving drum and contains the unwanted materials, which can be retained at round screen apertures according to size, type and shape, the diameter of the apertures being larger than 1 mm, preferably larger than 3 mm.
14. Use according to claim 13, characterised in that the suspension generated in a dissolving drum is graded and diluted in an open screening apparatus, in particular screening drum and is pumped into the pressure grader.
15. Use of a pressure grader according to one of the preceding claims, for cleaning a suspension produced from waste paper, which has been produced by dissolving in a stock pulper (21) and which contains the unwanted materials, which can be retained on round screen apertures according to size, type and shape, the diameter of the apertures being larger than 1 mm, preferably larger than 3 mm.
16. Use according to claim 15, characterised in that the suspension is pumped from the pulper (21) through a pulper screen (22) incorporated in the pulper direct into the pressure grader.
17. Use according to claim 13, 14, 15 or 16, characterised in that the suspension (S) is passed into the pressure grader with a consistency of between 2% and 4%.

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