EP1817453A1

EP1817453A1 - Method for degassing and supplying a fibrous suspension to a headbox or a filter device, and degassing device

Info

Publication number: EP1817453A1
Application number: EP05785578A
Authority: EP
Inventors: Axel Gommel; Erwin Binder
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2004-10-21
Filing date: 2005-09-20
Publication date: 2007-08-15
Also published as: WO2006045378A1; CN101040081A; US7807020B2; US20070267156A1; DE102004051327B4; US8025772B2; US20110061829A1; US20110056636A1; US8025761B2; DE102004051327A1

Abstract

The invention relates to a method for supplying a fibrous suspension (S) to a headbox (1) of a paper or cardboard machine (2) or to a filter device. The fibrous suspension (S) can, for example, be formed by mixing a thick matter suspension (4) with a thinning liquid (5). Said method uses at least one degassing device (6), the action of said device corresponding to that of a centrifuge. The inventive method can be carried out in a compact manner and enables, for example, the use of large degassing containers to be omitted.

Description

RPS12086 WO

VOITH PAPER PATENT GmbH

Method for degassing and feeding a pulp suspension to a headbox or a filter device and Entqasungsvorrichtung

The invention relates to a method for feeding a pulp suspension according to the preamble of claim 1, 3 or 14 and a degassing device according to the preamble of claim 26.

Such methods are e.g. used to supply paper or board machines with pulp suspension. The headbox brings a layer of fibrous material on a passing sieve, the u.a. also performs the function of thickening. The required Stoffzuführsysteme are basically known. The pulp suspension to be supplied receives most of the fibers from a thick stock suspension provided in the stock preparation plant. The latter has e.g. a typical consistency between 2.5 and 5%. By admixing dilution liquid, e.g. White water of the paper machine, the consistency is lowered to a value that is favorable for the operation of the headbox of the paper machine. Although the white water is optimally suitable for this dilution task, but there are problems because of the high gas content, the majority being air. The largest proportion of these gases escapes very quickly, on the other hand, the residual gases often have to be removed consuming. Otherwise, the quality of the paper produced would be unduly reduced. Known solutions are large degassing, in which by evacuation a constant negative pressure is maintained, which corresponds to the vapor pressure of the suspension to be degassed. This is effective but expensive.

From US 6,723,205 B1 a degassing pump for paper production is known, which is provided with a rotor forming a cylindrical interior, in which the supplied liquid can be degassed by centrifugal force. The white water supplied from the paper machine at high speed delivers the drive power for the rotor via a turbine integrated into the degassing pump. After exiting the degassing pump, the liquid is passed directly to mixing stations, in which the fiber raw material (thick matter) is added. Another application of this type of process takes place in the reprocessing plant ("stock preparation") for the pulp suspension intended for processing on the paper or board machine. For suspensions with a relatively low consistency, for example between 0.5% and 1.5%, filter devices, in particular disc filters, are used to increase the consistency. The pulp suspension to be thickened may have an air content of several percent, for example if it has been previously floated, in order to eliminate impurities with the flotation foam. The operation of disc filters and pumps is adversely affected by higher air content.

The invention is based on the object to provide a method of the type mentioned above, with which a flow of material to the fabric casserole or is guided to a filter device, which is sufficiently degassed. It should get along with relatively little effort and be reliable.

To achieve the object, a method with the features of the independent claims is provided.

The material feed system according to the invention is characterized in particular by the fact that a degassing device is used for the degassing of the white water or the pulp suspension, which is of compact construction and nevertheless allows a good degassing. In particular, it is generally not necessary to use large, elaborate containers which, because of their high weight, put a heavy load on the building during operation. Such containers are operated with the vapor pressure of the suspension to be degassed, so are under extreme vacuum with the resulting strength requirements. Also, vacuum systems with high energy consumption are not required for the inventive method.

It is particularly advantageous to use the method in paper machines whose wire speed is between 800 and 1600 m / min. The amount of air contained in the white water strongly depends on the sieving speed.

The method can also be used when a pulp suspension - as known per se - is passed over a disc filter in order to thicken it. Such a disc filter leaves a significantly higher throughput, when the Luftge stop the incoming liquid is lowered.

Another significant advantage of the invention is that not only the further transport of the exiting from the degassing vented fiber suspension is secured by the connected to the degassing material pump, but that can be set in the degassing a degassing promoting lower pressure, since the pump Exercises.

In an advantageous embodiment, the rotor of the degassing device is driven by a motor, e.g. Electric motor, driven. As a result, the circumferential speed of the rotor can be easily adjusted to the value required by the requirements.

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

Fig. 1 is a simplified process scheme;

Fig. 2 shows a variant;

FIG. 3 shows a degassing device according to the invention; FIG.

4 shows a degassing device according to the invention with sorting function;

Fig. 5 shows another embodiment of the method;

Fig. 6 shows an application of the method in stock preparation.

The diagram of FIG. 1 shows a first example for carrying out the method according to the invention. A pulp suspension S is produced in the usual manner by mixing a thick stock suspension 4 with a diluting liquid 5 and thereafter essentially has the consistency desired for the operation of the headbox 1 of the paper or board machine 2 at this point. It is known that headbox consistencies range between 0.5 and 2%, usually around 1%. The dilution liquid 5, which is supplied at a mixing point 8, originates in the example shown here from the first white water 12, that is, the water incurred in the forming area of the paper or board machine 2. It is often referred to as white water I (SW I) in contrast to the later on the paper machine resulting second white water 12 '(SW II), which contains much less fines. It is known that such white water is inter alia mixed with a considerable proportion of air and possibly other gases. The white water is collected below the paper machine sieve and discharged laterally. In the open channels used for this purpose, a large part of the air contained can already escape. Nevertheless, it often makes sense to eliminate a further proportion of gas T in a special container 11, as is known, for example, from DE 199 38 799. To assist the container 11 may be under a moderate negative pressure. After mixing thick matter suspension 4 and diluting liquid 5, a degassing device 6 is used. This is constructed as a cylindrical or conical container and provided according to the invention with a rotor 13. To drive the rotor 13 is a motor 34, which is not fed from the hydraulic energy of the degassed suspension flow, such as an electric motor. The pulp suspension S enters the substantially cylindrical inner space 14 of the rotor 13 and is set in rapid rotation. This principle corresponds to that of a solid bowl centrifuge. The gases contained 7 migrate inwardly as a result of the centrifugal forces and are sucked out of the center by a - only roughly indicated - vacuum device 1 0. In this case, a phase boundary forms liquid / gaseous in the container. The centrifugal forces may be at least 5 times, preferably 10 times the gravitational acceleration. The vacuum device 10 does not require a negative pressure which corresponds to the vapor pressure of the suspension or is in the vicinity thereof. Conventional values for the negative pressure of a vacuum device 10 used here are 0.8 to 0.9 bar.

After leaving the degassing device 6, the suspension is passed through a fuel pump 9 here in a closed system (ie without open containers or laid paper) to the headbox 1. Here, in the usual way, the remainder of remaining impurities are eliminated by a cleaner 17 and a sorting system 18. In order not to let the pressure in the cleaner unit 17 become too high, a pump 22 ("booster pump") can be installed between accepting the cleaner unit 17 and feed to the sorting unit 18 for increasing the pressure. Alternatively, it is also possible to provide an open intermediate chest 20 for the material guide downstream of the material pump 9, e.g. to reduce pulsations. This is shown in FIG. 2, but can also be realized in a system according to FIG. Of course, the effort that must be done for these hydrocyclones and sorters will depend on the raw materials as well as the quality requirements of the paper produced. If e.g. the thick matter suspension 4 was formed from waste paper, sand and small plastic parts may still be present.

The invention can also be embodied such that, as FIG. 2 shows, the white water 12 of the paper or board machine 2 in a Entgasungsvorrichtu ng 6 ^'is degassed, whose function corresponds to that already described in connection with FIG. The degassed white water is passed through the outlet 15 directly into a dilution water pump 19. Because of the much lower solids content of the white water 12 compared to the pulp suspension S, the degassing can be performed easily. However, this requires a maximum of only low gas content in the added at the mixing point 8 Dickstoffsuspensϊon 4 in order to avoid quality losses.

As is known, there are many paper or board machines in which the headbox not only supplied with the already mentioned pulp suspension S \ / vird, but also with a dilution liquid, which is seen over the width of the fabric casserole 1 dosed at different locations. As a result, for example, the transverse profile of the fibrous material layer formed with the headbox can be influenced, in particular optimized. Such a possibility is shown in FIG. 2, in which the white water is not only used as diluting liquid 5 for the thick stock suspension 4. A portion of the degassed in the degassing 6 ^' white water is passed with the dilution water pump 19 as dilution liquid 5 ^' in a metering device 3 of the headbox 1 'in which it is divided and the pulp suspension S is added at various points. Often there are other places in a paper mill where additional dilution liquid 5 "vented by the process can be used, which is indicated here by a dashed arrow.

In Fig. 3 eϊ ne suitable for the process degassing 6 is shown in section without showing structural details. In a fixed housing 23, a rotor 13 is arranged, the interior 14 is supplied by the inlet f 16 with a liquid to be degassed. The inlet 16 can be arranged centric or eccentric as here. The liquid added by it is first greatly accelerated in the circumferential direction, for which purpose, for example, acceleration ribs 24 can serve. As a result of the centrifugal forces, the liquid is applied to the inner wall of the rotor 13, wherein the gas contained therein, in particular the air, migrates to the center of the rotor 13. In general, a separation surface between the liquid and the gas forms 7. By a central degassing tube 25, the gas 7 can be removed or sucked. In continuous operation of this degassing, for example, by an input throttle 26, the operating conditions are regulated so that a steady flow of liquid from the inlet 16 to the outlet 15 bi Idet. In this case, in the region of the outlet 15, the wall of the rotor 13 is made liquid-permeable, for example by attaching openings 27 in this area. The outlet 15 is advantageously mounted tangentially in such a way that the rotational flow of the degassed liquid leads to a pressure build-up in the outlet 15. The openings 27 in the wall of the rotor 13 are so large that they do not lead to a sorting of the degassed liquid.

The embodiment of a degassing device 6 ^' shown in FIG. 4 combines the function of degassing with the function of sorting. As already mentioned, when a paper machine is supplied, a final sorting stage is often switched in front of the headbox in order to prevent contaminants from entering it, which disturb the operation of the headbox or the paper machine. This sorting function can be performed in combination with the degassing function in the same device. For this purpose, a screen basket 28 is arranged so that the degassed liquid flowing radially outwards from the rotor 13 ^'is fed to the screen basket 28. In a manner known per se, a separation into accept 29 and reject 30 takes place at the screen openings 32 of the screen basket 28. The latter can be derived from the device through a reject outlet 31. Of the screen openings 32 in the screen basket 28, only a few are drawn by way of example and not to scale. The combination has the advantage that the rotor 13 ^'can also serve to keep the screen openings 32 clear. For this purpose, on its outer side clearing elements 33 are mounted, which are able to produce suitable suction and pressure pulses in the fiber suspension.

FIG. 5 shows a process diagram with the use of a degassing device 6 ^' according to FIG. 4. Then, the sorter shown in Fig. 1 for the pulp suspension S can be omitted. Eventually, a cleaner 17 between the degassing 6 ^' and the headbox 1 is still necessary; but this depends on the impurities present in the pulp suspension S.

In Fig. 6, a favorable application of the invention in the stock preparation of a paper mill is shown. A low-consistency pulp suspension S ^" is thickened, ie brought to a higher consistency, in a disc filter 35 which is indicated only The substance S ^'" thickened by the filter action can be further processed as raw material for paper production, while the filtrate 36 serves, for example, for dilution. The reason for such a measure is that the process steps in the Stoffaufbituituπg run optimally at low and partly at higher consistency.

In the plant shown in Fig. 6, a flotation plant 37 is operated, the one with impurities, For example, ink particles mixed pulp suspension S ^' at low consistency, for example, between 0.5 and 2%, cleans. From the flotation system 37 five sequentially flowed through flotation cells 38 are shown schematically. By several pumps 39 each of the accept of an upstream flotation cell is conveyed via a venting injector 40 in the next flotation cell. The formed reject R, ie the flotation foam, contains the separated impurities. The accepts of the last flotation cell 38 ^' , for example, has an air content between 3% and 6%, is deducted here by a downstream of the degassing pump 6 material pump 9. As a result, the pressure of the degassing device 6 is lowered, which further favors the degassing effect.

The used between the flotation system 37 and disc filter 35 degassing device 6 removes a large part of z. B. in the flotation 37 recorded air. The disk filter 35 leaves e.g. if the air content is reduced by one percentage point, this will increase the throughput by 10%. If e.g. a reduction of 6% to 1%, the possible throughput is about 50% higher. Also other problems associated with the relatively high air content, e.g. at the fuel pump 9, are effectively and economically eliminated. The described degassing device 6 is particularly economical for those tasks in which it does not depend on the last percentage fraction of the air content in the degassed liquid.

Often, after flotation and thickening, fine sorting 41 is performed which is particularly effective at low consistency (e.g., 0.5 to 2%).

Claims

claims:

1. A method for feeding a pulp suspension to at least one headbox (1, 1 ^' ) of a paper or board machine (2) with at least one dilution device in which the pulp suspension (S) by mixing a thick stock suspension (4) with a dilution liquid (5) , in particular water, and at least one means for removing gas from liquid, characterized in that the pulp suspension (S) after mixing with the diluting liquid (5) in at least one degassing device (6) is guided, in which they Inner space (14) of a rotating rotor (13, 13 ') passes and is set in rotation, so that the gases contained (7) are deposited due to centrifugal forces and that the degassed dilution liquid (5) from the degassing device (6) in a separate fuel pump (9) is guided.

2. The method according to claim 1, characterized in that the pulp suspension (S) after the degassing device (6) by a material pump (9) in a closed system for Stoffaufiauf (1, Y) is performed and that the degassing device (6) in Strömungsrestriction of the pulp suspension seen directly in front of the fuel pump (9) is arranged.

3. A method for feeding a pulp suspension (S) to at least one headbox

(1, Y) of a paper or board machine C 2) with at least one dilution device, in which the pulp suspension (S) is produced by mixing a thick matter suspension (4) with a diluting liquid (5), in particular water, and at least one device for removal gas from liquid, wherein the dilution liquid (5) before being mixed with the thick stock suspension (4) in at least one degassing device (6} is guided, in which it enters the interior (14) of a rotating rotor (13, 13 ^' ) and is rotated so that the contained gases (7) are deposited due to centrifugal forces, characterized in that the degassed dilution liquid (5) is led out of the degassing device (6) into a separate dilution water pump (19).

4. The method according to claim 3, characterized in that the headbox (1 ^' ) is provided with a metering device (3), with which the Stoffaufia uf (1 ^' ) with dilution liquid (5 ^' ) is supplied to control the cross profile of the produced web , for the provision of which the degassing device (6 ^' ) is used for the dilution liquid.

5. The method according to claim 3 or 4, characterized in that in the degassing (6 ^' ) further dilution liquid (5 ") is degassed for supplying further dilution points.

6. The method according to any one of the preceding claims, characterized in that in the degassing (6 ^' ) a Nasssiebung to remove contaminants from the pulp suspension (S) is made by the degassed liquid from the interior (14 ^' ) to a in the degassing device (6 ^' ) built-in screen basket (28) is guided.

7. The method according to claim 6, characterized in that the rotor (13 ^' ) is also used to keep the screen basket (28) free.

8. The method according to claim 6 or 7, characterized in that the screen basket (28) radially outside the rotor (13 ') is inserted.

9. Method according to one of the preceding claims, characterized in that the dilution liquid (5) is white water (12) of the paper or board machine (2).

10. The method according to claim 9, characterized in that the white water (12) is vorentgast before entering the degassing device (6 ^' ) or in the mixing point (8) in open channels.

11. The method according to any one of the preceding claims, characterized in that the pulp suspension (S) by means of a fuel pump (9) in a closed system to the headbox (1, 1 ^' ) is performed without being degassed by re-applying vacuum becomes.

12. The method according to any one of the preceding claims, characterized in that the pulp suspension (S) after the degassing device (6, 6 ') by means of a directly following fuel pump (9) through a cleaner system (17) is guided and that the accepts this Cleaneranlage (17 ") is not further degassed by applying negative pressure.

13. Application of the method in the operation of a paper machine whose screening speed is between 800 and 1600 m / min.

14. A method for supplying a pulp suspension to at least one filter device, preferably a disc filter (35), wherein the pulp suspension (S) is thickened by a filtering process, wherein the pulp suspension has a consistency of not more than 4%, preferably between 0, 5 and 2% , characterized in that the pulp suspension (S) before thickening into at least one

Degassing device (6) is guided, in which they in the interior (14) of a rotating

Rotor (13, 13 ^' ) passes and is set in rotation, so that the gases contained (7)

Reason of centrifugal forces are deposited.

15. The method according to claim 14, characterized in that the degassed diluting liquid (5) from the degassing device (6) is guided in a separate fuel pump (9).

16. The method according to claim 14 or 15, characterized in that a pulp suspension (S '), in particular a waste paper suspension, cleaned in a flotation plant (37) discharged with the flotation foam impurities and then thickened.

17. The method according to claim 16, characterized in that in the flotation plant (37) purified pulp suspension (S) without intermediate pump in the degassing device (6) is guided.

18. The method according to any one of the preceding claims, characterized in that in the degassing device (6) guided pulp suspension (S) has a gas content above 1, 5%.

19. The method according to claim 18, characterized in that in the degassing device (6) guided pulp suspension (S) has a gas content; over 3%, preferably over 5%.

20. The method according to any one of the preceding claims, characterized in that the absolute pressure in the degassing device (6, 6 ') is set to at least 0.1 bar above the vapor pressure of the fibrous suspension contained therein.

21. The method according to any one of the preceding claims, characterized in that a degassing device (6, 6 ') is used with a cylindrical interior (14) having rotor (13) whose wall is liquid impermeable.

22. The method according to any one of claims 1 to 21, characterized in that a degassing device (6, 6 ') is used with a cylindrical interior (14) having a rotor (13) whose wall only in the region of the outlet (15), through which the degassed liquid is discharged, is liquid-permeable.

23. The method according to any one of the preceding claims, characterized in that the rotor (13, 13 ^' ) by a motor (34) is driven.

24. The method according to any one of the preceding claims, characterized in that the rotor (13, 13 ^' ) is driven dsss in its interior (14, 14') has a centrifugal field of at least 50 times, preferably at least 10 Fachen, the gravitational acceleration arises.

25. The method according to any one of the preceding claims, characterized in that the degassing device (6, 6 ^' ) is operated continuously.

26, degassing apparatus for performing a method according to one of the preceding claims, comprising a housing (23) in which an interior space (14) exhibiting rotor (13, 13 ') is arranged rotatably, with an inlet (16) for adding a to be degassed liquid, wherein the inlet (16) in

Interior (14) of the rotor (13, 13 ') opens, and with a preferably tangentially mounted outlet (15) for the degassed Liquid, as well as with a centrally located degassing pipe (25) to which a Vakuumeϊnrichtung

(10) for removing the gas escaped from the liquid (7) is connected, wherein the rotor (13) is provided with at least one opening (27) through which a hydraulic

Connection with the outlet (15) is produced, characterized in that the rotor (13) is connected to a motor (34) which drives it.

27. degassing device according to claim 26, characterized in that the rotor (13, 13 ^' ) by a strainer basket (28) is surrounded, the screen openings (32) produce a hydraulic connection between the rotor (13, 13') and outlet (15) and which are suitable for sorting a pulp suspension (S) so that most of the fibers pass through the screen openings (32) and can be discharged as accept (29), while the contaminants are retained as reject (30) and through a reject outlet ( 31) can be deduced.

28. degassing device according to claim 27, characterized in that the openings (27) in the strainer basket (28) are round holes with a diameter between 1 and 4 mm.

29. Degassing device according to claim 27 or 28, characterized in that the rotor (13 ^' ) is provided on its outer side with clearing elements (33) for keeping free the screen openings (32).