METHOD FOR REMOVING IMPURITIES FROM A FIBROUS SUSPENSION

Abstract

Method and apparatus for removing impurities from a fibrous suspension. The method includes conducting a fibrous suspension stream into an inflow chamber of a pressurized screen, concentrating portions of the fibrous suspension stream to be removed in front of a screen basket, discharging the concentrated portions in an overflow stream, passing an other portion of the fibrous suspension stream through the pressurized screen as a throughput stream, and guiding gases out of a central region of the housing of the pressurized screen. The instant abstract is neither intended to define the invention disclosed in this specification nor intended to limit the scope of the invention in any way.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1 illustrates an exemplary process description for the removal of foreign particles according to the invention;

FIG. 2 illustrates a detail of a pressurized screen according to the invention with mounted recirculation adapter piece;

FIG. 3 illustrates a recirculation adapter piece for carrying out the method in a view from above;

FIG. 4 illustrates a side view of a variant of the piece depicted in FIG. 2; and

FIG. 5 illustrates an alternative use of the coupling.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

FIG. 1 shows a pressurized screen 1 in diagrammatic form. During the operation of a machine of this type, the fibrous suspension stream 2 flowing in is guided into the interior of the housing 11 and then passes radially from the inside outwardly, in part, through the cylindrical wire basket 7. This wire basket can be provided with slot-shaped wire openings, the width of which is, e.g., between 0.08 and 0.5 mm. A throughput stream 3 and an overflow stream 4 are formed at the wire basket 7. Both streams can then leave the housing 11 again through pipe connections. In order to prevent the wire clogging, a rotating scraper 13 is located radially inside the wire basket 7. Pressurized screens of this type are known in many variations and do not need to be described in further technical detail. In the example shown here, the overflow stream 4 is divided in a distribution device 8. Due to the rotary motion that is generated inside the wire basket 7 by the scraper 13, the overflow stream 4 leaves the housing with an overpressure that makes it possible to guide the return stream 5 diverted from the overflow stream 4 back into the housing again without a further pump. To this end, a recirculation adapter piece 14, the function of which is explained based on FIG. 2, is located in the center of the cover, i.e., where a relatively low pressure prevails.

The recirculation adapter piece 14 is mounted concentrically with the housing 11 on the cover 10 arranged above, preferably screwed thereto via flanges. The return line 18 opens in the center of the recirculation adapter piece 14. The return line is enclosed by a concentrically arranged pipe length 16 to which the deaeration line 15 is connected, preferably tangentially (see FIG. 3). The gases, possibly light particles as well, can thus flow off from the inflow chamber 17 of the pressurized screen 1. The pipe length 16 is open to the inflow chamber 17 of the pressurized screen 1. The pipe length 16 can advantageously terminate inside at the cover 10, while the return line 18 opens at a distance A from the cover 10, which distance corresponds, e.g., to 1 to 5 times the inside diameter of the return line 18.

As FIG. 4 shows, the deaeration line 15′ can have a connection angle α with respect to the horizontal, which angle is greater than 0, e.g., is between 5 and 30°, whereby the gases accumulating at the top can be drawn off more easily.

It can be particularly favorable in practice to be able to choose between operation with or without return stream 5. It would then be easier to retool the pressurized screen by, e.g., attaching one of the recirculation adapter pieces described above or optionally an adapter piece shown in FIG. 5 that contains only one deaeration line 15. The fitting dimensions on the cover 10 are the same as with the recirculation adapter piece 14.

The method was described in the figures based on the example of a curved cover 10. However, the method is largely independent of the cover shape, so it can also be used with screens with a conical or flat cover. A curved or conical form is generally preferable.

It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

Claims

1. A method for removing impurities from a fibrous suspension, comprising: conducting a fibrous suspension stream into an inflow chamber of a pressurized screen;concentrating portions of the fibrous suspension stream to be removed in front of a screen basket;discharging the concentrated portions in an overflow stream;passing an other portion of the fibrous suspension stream through the pressurized screen as a throughput stream; andguiding gases out of a central region of the housing of the pressurized screen.

2. The method in accordance with claim 1, wherein the gases are not guided through a center of the housing.

3. The method in accordance with claim 1, further comprising guiding a return stream into a center of the inflow chamber of the pressurized screen, such that the gases are not guided through a center of the housing.

4. The method in accordance with claim 1, wherein the return stream is composed of at least a part of the overflow stream.

5. The method in accordance with claim 4, further comprising: forming a reject stream with an other part of the overflow stream; andremoving reject stream and thereby undesirable foreign particles within the reject stream.

6. The method in accordance with claim 1, wherein, during operation of the pressurized screen, the overflow stream is thickened and the throughput stream becomes thinner.

7. The method in accordance with claim 6, wherein at least a portion of the overflow forms a return stream to be guided back into the pressurized screen, and the return stream is set to be at least large enough that the thickening of the overflow stream remains so slight in all operating conditions that it flows off unimpeded from the pressurized screen.

8. The method in accordance with claim 1, wherein a flow of gas is guided out of the central region of the housing.

9. The method in accordance with claim 8, wherein the gas comprises air

10. The method in accordance with claim 1, wherein the screen basket comprises a cylindrical wire basket with slot-shaped wire openings.

11. The method in accordance with claim 1, further comprising adjusting a division of the overflow stream with a regulator that controls a corresponding distribution device.

12. The method in accordance with claim 3, wherein the return stream is guided in a pipe arranged outside the housing.

13. The method in accordance with claim 1, wherein a recirculation adapter piece is mounted in a center of a cover of the housing and is composed of a central return line, a surrounding concentric pipe length, and a deaeration line attached to the pipe length, and wherein the central return line and the pipe length open into the inflow chamber.

14. The method in accordance with claim 13, wherein the gases are removed tangentially from the pipe length.

15. The method in accordance with claim 13, wherein the deaeration line is oriented at a connection angle (α) with respect to a horizontal axis between 50 and 30°.

16. The method in accordance with claim 13, wherein the central return line opens into the inflow chamber with an axial distance (A) of 1 to 10 times an interior diameter of the return line from the pipe length.

17. The method in accordance with claim 16, wherein the axial distance is between 2 and 5 times the interior diameter of the return line.

18. The method in accordance with claim 13, wherein an interior diameter of the pipe length is between 5% and 40% of an interior diameter of the housing in an area of the inflow chamber.

19. The method in accordance with claim 18, wherein the interior diameter of the pipe length is between 10% to 20% of the interior diameter of the housing in the area of the inflow chamber.

20. The method in accordance with claim 13, wherein an interior diameter of the pipe length is 150% to 400% of an interior diameter of the return line.

21. The method in accordance with claim 13, wherein an axial length of the pipe length is between 100 and 1000 mm.

22. An apparatus for removing impurities from a fibrous suspension, comprising: an inflow chamber of a pressurized screen;a housing surrounding the inflow chamber;a rejects discharge for a reject portion of the fibrous suspension with impurities to be removed;a throughput stream discharge for a portion of the fibrous suspension passing through the pressurized screen; anda gas discharge element arranged to guiding gases out of a central region of the housing.

23. The apparatus in accordance with claim 22, further comprising a return stream device structured and arranged to guide a portion of the reject portion into a center of the inflow chamber and the gas discharge element is arranged so the gases are not guided through a center of the housing.

24. The apparatus in accordance with claim 22, further comprising a recirculation adapter piece mountable in a center of a cover of the housing and composed of a central return line, a surrounding concentric pipe length, and a deaeration line attached to the pipe length, wherein the central return line and the pipe length open into the inflow chamber.