APPARATUS, SYSTEM AND METHOD FOR REMOVING LIQUID FROM A MOVING WEB

Field of the invention

The invention relates to an apparatus for removing liquid from a moving web. The invention relates to a system for removing liquid from a moving web. The invention relates to a method for removing liquid from a moving web.

Background of the invention

For example paper machines comprise a running endless wire, on which there is pulp consisting of liquid and fibres required for papermaking, also called a web in this application. Water is removed from the web at several different steps by means of devices placed under the wire, including, for example, various rotating rolls whose perforated shell is permeable to air. The roll is placed in a box, in which a negative pressure is arranged, wherein the term suction roll can be used. A suction roll is disclosed in document EP 0 639 667 A1 , which also presents the use of overpressure to intensify the dewatering.

A particularly efficient suction roll is disclosed in document WO 2006/090012 A1. With this device, it is possible to support a moving wire. In an opening in the upper surface of the device, against the moving wire, a perforated rotating roll is provided, through which a negative pressure is effective on the wire. The device is used to provide a sufficient suction effect and high- capacity dewatering, wherein it can also be applied on wires with a high speed.

Summary of the invention

The requirements for the efficiency of dewatering are constantly increasing. It is an aim of the invention to improve the operation of apparatuses according to prior art. It is another aim of the invention to provide an efficient unit with various suction rolls and particularly with the apparatus of document WO ™06/090012 A1.

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The apparatus according to the invention is presented in claim 1. The system according to the invention is presented in claim 10. The method according to the invention is presented in claim 14. The other claims present some embodiments of the invention.

The arrangement according to the invention for making the operation of the dewatering apparatus more efficient comprises an apparatus, in which overpressure is effective on the side of the wire and the web opposite to the effect of negative pressure. The overpressure intensifies, for example, dewatering of the wire and the web and improves the operation of the apparatus. The overpressure moves liquid from the web to the range of action of the negative pressure, and the negative pressure removes the liquid further away from the wire and the web. The overpressure is effective on an area which is also subjected to the negative pressure produced by a suction apparatus.

The solution can be applied especially in situations of using one wire, the web lying on top of the same. The overpressure apparatus is not directly against the web, but a second wire runs between the overpressure apparatus and the web and is also mechanically effective on the web. The wire belonging to the overpressure device, which preferably forms an endless loop, is permeable to air, so that air supplied into the overpressure apparatus would be transferred by the effect of overpressure through the wire and the web and further through the suction roll, conveying liquid and moisture with it. The suction apparatus is provided on one side of the web on the web path, that is, underneath the wire, and the overpressure apparatus is provided on the other side, that is, above the web, and implemented e.g. by means of a pressure box. Furthermore, a moving wire of the overpressure apparatus is introduced between the web and the pressure box.

If necessary, the wire of the overpressure apparatus is also mechanically effective on the web, wherein the web can be flattened or compressed by a desired force. The apparatus that moves the wire is preferably arranged to be adjustable so that its distance from the web and its skew in the plane of the running direction of the web can be set. Compression will intensify dewatering, but above all, the contact between the wire and the web will affect the surface quality and the texture of the web. In particular, the surface

of the web can be levelled out with the wire, which has favourable effects, for example, in view of the further processing of the web.

Self-purification of the wire of the overpressure apparatus is efficient, because an overpressure is effective through the wire, transferring any material or liquid adhered from the web back to the web. For this reason, it will not be necessary to use a separate wire washing apparatus, and the structure becomes simpler. The properties of the wire with respect to air permeability remain unaltered, because the wire is constantly purified, whereby the web quality can also be kept uniform. The wire has the property of permeability to air, and preferably, the wire is as dense as possible.

Preferably, the wire is of a single-layer and flat string type.

Brief description of the drawings

In the following, the invention will be described by means of examples and with reference to the appended drawings.

Figure 1 shows an apparatus according to the invention, seen from the ends.

Figure 2 shows the apparatus according to Fig. 1 , seen from the side.

Detailed description of the invention

In Fig. 1 , the apparatus according to the invention for dewatering a material web is shown in a reduced view and only for the essential parts. The apparatus 1 is shown as seen from the end. In Fig. 1 , the apparatus is horizontal, and the wire 4 preferably forms a horizontal plane. The apparatus 1 is shown without the front end 2 (see Fig. 2), to expose the other structures. Figure 1 shows the rear end 3. The ends 2 and 3 are, for example, vertical plate structures, and their shape may differ from the triangular shape.

As a part of the whole system and as the dewatering apparatus, for example an apparatus according to the document WO 2006/090012 A1 is also used, which directs a suction to the wire and the web by means of a vacuum.

Figure 1 shows the dewatering vacuum apparatus 5 only in part and in a

cross-sectional view. The vacuum apparatus 5 comprises a box-like sealed chamber 6 which is used as a vat and in which a rotating roll 7 is placed. The upper surface 6a of the chamber 6, on top of and against which the wire 4 is placed, is substantially level. The chamber 6 is elongated, and it preferably extends underneath the wire 4 substantially over its whole width. The chamber 6 is arranged crosswise, preferably transversely to the running direction of the web 4, as is also an opening 6b in the upper surface 6a of the chamber 6. The opening 6b is uniform and continuous and extends over the whole width of the wire 4. The chamber 6 is closed by end parts, through which the shaft of the roll 7 extends. The shaft is mounted on bearings, and the motor of a rotating apparatus is coupled to it.

A roll 7 that is rotatable with the wire 4 is placed inside the chamber 6. An opening 6b exposes at least part of the outer shell 7a of the roll 7 so that the running wire 4 that touches the chamber 6 can be supported to the outer shell 7a. The wire 4 runs along the upper surface 6a, and the negative pressure effective on the wire 4 sucks, for example, water off the wire 4. The roll 7 is perforated, equipped with openings or a metal wire cloth, and the negative pressure prevailing inside it pulls the wire 4 against the outer shell 7a and the suction pulls the liquid to the inside of the roll 7 and into the chamber 6. Beams 8 and 9 on the outer surface 6a limit the suction area to the opening 6b; in other words, they define the range of action of the negative pressure. The sealing between the roll 7 and the wire 4 and the sealing and defining of the suction area to prevent air leaks at the ends of the roll 7 are implemented in an adequate way and, among other things, by suitable dimensioning of the length of the apparatus. Thus, for example the solution according to WO 2006/090012 A1 is used.

In the example of Fig. 1 , the overpressure apparatus 10 is installed as a pair to the vacuum apparatus 5, on the opposite side of the wire 4 and centrally with respect to the opening 6b. The overpressure apparatus 10 comprises a box or a structure that is also called a pressure box 11 in this description, wherein the wire 4 and the web 12 on top of the same are placed between the pressure box 11 and the roll 7. The distance between the pressure box 11 and the web 12 can be adjusted by adjusting means, for example threaded bars which are fixed, on one hand, for example to the chamber 6 and, on the other hand, to the frame of the overpressure apparatus 10 (for

example pressure box 11) or the ends 2 and 3 of the apparatus 1. The pressure box 11 and simultaneously the apparatus 1 can also be fixed to other structures of the vacuum apparatus 5 in a desired manner. Controllable actuators or motors can also be used for the adjustment.

The angular position of the pressure box 11 with respect to the web 12 can also be adjusted, for example, by means of a joint and a rod mechanism, by using a suitable adjusting means, for example a threaded rod. Controllable actuators or motors can also be used for the adjustment. By means of adjusting the skew, the distance between the pressure box 11 and the web 12 can be made larger or smaller on the inlet side than on the outlet side. The pressure box 11 may also be supported, for example, to structures above the vacuum apparatus 5 and the wire 4, or structures placed on both sides of the wire. In the fixing and the constructions of the details of the apparatus, it is possible to apply principles which are common or known as such for a man skilled in the art.

The pressure box 11 is placed at the suction area defined by the vacuum apparatus 5 (corresponding to the opening 6b), and the size of the pressure box 11 is selected so that the overpressure is effective on the suction area. The pressure box 11 is coupled by one or more connections 13 to a separate pressure system to achieve a pressure effect and an air flow into the pressure box 11. The pressure box can be constructed of, for example, metal or plastic. In the example of Fig. 1 , the pressure box 11 is made inside a semicircular frame which extends over the web 12 and simultaneously supports the structure 1. The frame is downwards open. The pressure box 11 is mounted to the ends 2 and 3 of the apparatus 1 which close the ends of the pressure box 11.

The pressure box 11 comprises at least one overpressure chamber 14 which is positioned at the suction area and extends transversely over the web 12. The cross section of the overpressure chamber 14 has the form of a narrowing slit or gorge. Preferably, the aim is to bring warm or hot air into an accelerating movement by means of the narrowing shape. The overpressure chamber 14 is open toward the web 12 and it narrows down in the direction towards the web 12. The opening of the overpressure chamber 14, left between the parts 15 and 16, corresponds substantially to the suction area.

In an embodiment, the overpressure chamber 14 is made of two parts 15 and 16 placed against each other, which are planar, extend over the web 12 in the cross direction and are bent, for example, in a narrow angle so that their one flank is parallel to the web 12 and their other flank forms one flank of the slit or gorge. The overpressure chamber 14 is defined between the parts 15 and 16 and under the frame of said pressure box 11. The parts 15 and 16 are also defined by said frame. A means 17 for levelling out the air flow is fixed between the parts 15 and 16, for example a perforated plate or mesh, extending over the web 12 and distributing the air flow coming from the connection 13 evenly over the area of the whole web 12. The overpressure chamber 14 can also be accessed via a connection 18, through which for example water is supplied for washing.

The apparatus 1 also comprises a moving wire 19 running between the web 12 and the pressure box 11 and having the same speed as the wire 4 that carries the web 12. The wire 19 is introduced between the web 12 and the pressure box 11 , and it is pulled off the top of the web 12 after the pressure box 11 , substantially immediately. Preferably, the wire 19 extends over the whole web 12 in the cross direction of the web 12. The wire 19 extends as an endless loop via, for example, reversing rolls 20 and 21 as well as via a turning roll 22. The turning roll 22 moves the wire 19 by friction. The reversing rolls 20 and 21 are placed next to the web 12, on both sides of the pressure box 11. The turning roll 22 is placed above the pressure box 11 , and the pressure box 11 is placed inside the loop of the wire 19. The pressure box 11 is placed close to the web 12, from which it is separated by the wire 19. To the pressure box 11 , it is possible to fix bearing means, against which the wire 19 can be pressed when it moves past the pressure box 11 and when the web 12 presses the wire 19. The turning roll 22 and the pressure box 11 are placed preferably centrally in relation to the suction area and the reversing rolls 20 and 21. A motor 23 is coupled to the turning roll 22 to rotate the turning roll 22 by transmission. The turning roll 22 and the reversing rolls 20, 21 are mounted on bearings in a way known as such at the ends 2 and 3, and with respect to the motor drive of the turning roll 22, it is possible to apply principles known as such. At least the distance from one reversing roll to the other reversing roll is adjustable, wherein the tension of the wire 19 can be adjusted by changing said distance.

The apparatus 1 constitutes an integrated structure, comprising the overpressure apparatus 10 and the wire 19. When the position of the wire 19 is changed, the position of the pressure box 11 , among other things, is also changed. The reversing rolls 20 and 21 and the turning roll 22 belong to the same structure, and they are moved together with the wire 19. The structure enables an easy adjustment, because the overpressure apparatus 10 and the wire 19 are in the same apparatus 1 , and also an easy installation.

In the presented embodiment, the wire 19 extends uniformly over the whole suction area and, to some extent, also to the range of both beams 8 and 9, covering at least part of the upper surface 6a on both the inlet side and the outlet side of the web 12. Preferably, the wire 19 extends straight between the reversing rolls 20 and 21 , as does the web 12 which runs along the planar upper surface 6a of the vacuum apparatus 5.

The reversing rolls 20, 21 and particularly the wire 19 have a mechanical effect on the web 12, nipping and compressing it when necessary. Thanks to the mechanical compression, the dewatering of the web 12 can be intensified. Liquid is transferred, among other things, to the wire 4 underneath the web 12, from which it is transferred by vacuum into the chamber 6. At the same time, the overpressure that is effective through the wire 19 transfers liquid from the web 12 through the wire 4 into the chamber 6. Due to the air flow, the overpressure is also effective on the wire 19, from which the liquid is transferred to the web 12, and simultaneously the material adhered to the wire 19 from the web is transferred back to the web 12. Thus, the overpressure is effective on the wire 19 and purifies it constantly.

The air permeability of wires suitable for the purpose is typically from about 5500 to 7500 m ³ /m ² h (permeability, 317 to 475 CFM). According to a suitable embodiment of the invention, particularly a wire that is only little permeable to air is used, having an air permeability of about 5000 to 5500 m ³ /m ² h.

The invention can be applied to a variety of material webs. In addition to a paper mill, the invention can also be applied in other types of processing mills. By means of the wire and the rolls, the material web can be compressed mechanically, simultaneously dewatering it. At the same time,

the material web can be subjected to suction and pressure, intensifying the removal of liquid from the material.

The apparatus and the system are suitable for the removal of liquid as well as solids, for example dust, from a wire, a felt or various other fabrics which are used, for example, in a paper machine. Consequently, the apparatus and the system can be used, in general, as a cleaning apparatus or a dewatering apparatus for removing liquid or solids from moving pulp, a web or a fabric, which are sufficiently permeable to air or liquid.

The invention is not limited solely to the above examples, but it may vary within the scope of the appended claims.