WO2008029430A1

WO2008029430A1 - Papermaking machine with felt washing devices and felt washing method

Info

Publication number: WO2008029430A1
Application number: PCT/IT2007/000609
Authority: WO
Inventors: Marco Celli
Original assignee: A. Celli Paper S.P.A.
Priority date: 2006-09-08
Filing date: 2007-09-04
Publication date: 2008-03-13
Also published as: ITFI20060221A1

Abstract

The machine comprises at least one continuous flexible member (13), such as a felt or a fabric or the like, movable along a closed path. Along a first portion of the path the continuous flexible member is in contact with a layer of aqueous slurry of cellulose fibers. In a second portion of the path the continuous flexible member is not in contact with the layer of cellulose slurry and along said second portion there is disposed a water distributor (41) to wash the continuous flexible member. In proximity of the water distributor the continuous flexible member is diverted around a centrifugal roller (27) to cause discharge by centrifugation of at least part of the water contained in the continuous flexible member.

Description

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PAPERMAKING MACHINE WITH FELT WASHING DEVICES AND FELT WASHING METHOD

DESCRIPTION Technical Field The present invention relates to a papermaking machine and in particular to a wet forming paper machine, i.e. using a slurry of cellulose fibers and water. More in particular, the invention relates to improvements to systems for washing the felt of a machine of this type.

The invention also relates to a method for washing a felt in a continuous papermaking machine. State of the Art

Wet methods and machinery are widely used in papermaking, i.e. methods and machinery wherein using headboxes, plies of a slurry of cellulose fibers and water are formed in a forming area normally defined between a form- ing fabric and a felt. The web formed by said slurry, containing a high percentage of water and a low percentage of cellulose fibers, is drained to eliminate water and increase the percentage in weight of fibers (dry percentage) and finally dried, for example on a Yankee cylinder or the like.

In particular, on the felt located in the web forming area cellulose fibers can deposit, which must be eliminated in an appropriate position along the closed path followed by the felt.

For this purpose, it is known to dispose nozzles that spray water on the felt, followed by suction boxes, by means of which the wash water is drained from the felt with entrainment and removal of the fibers and any other debris that may have deposited on the felt. In this manner, the felt reaches the forming area always substantially clean.

These wash systems present the drawback of consuming large amounts of energy, due to the noteworthy power required to supply the vacuum pumps that maintain the vacuum inside the suction boxes, which remove the wash wa- ter from the felt.

Object and Summary of the Invention

An object of the present invention is to provide a wet forming paper machine, which allows more efficient washing of the felt or other continuous forming member for forming the paper ply. According to a different aspect, an object of the present invention is to provide a new method for washing a continuous member, for example and in particular a felt, inside the wet forming paper machine.

In substance, according to a first aspect, the machine comprises a con- tinuous flexible member, movable along a closed path with a first portion, wherein a layer formed of said slurry is in contact with a first surface of the continuous flexible member, and a second portion wherein the continuous flexible member is not in contact with said layer, a water distributor being arranged along said second portion to wash the continuous flexible member. Characteris- tically, in proximity of the water distributor the path of the continuous flexible member presents a diversion such as to cause discharge by centrifugation of at least part of the water contained in the continuous flexible member.

The higher the feed speed of the flexible member is, the more efficient the effect of discharge of the water by centrifugation, and consequently of washing of the felt or other continuous flexible member, will be. Remarkable effects are obtained in particular with speeds of 600 m/min or higher.

According to an advantageous embodiment, the continuous flexible member is preferably a felt, although it would also be possible to apply the washing and water draining system according to the invention to other types of continuous flexible members, such as a fabric. Below, for the sake of brevity, reference will always be made to a continuous flexible member in the form of a felt, but it must be understood that the invention can have a more general application.

With the invention it is thus possible to eliminate at least part of the wash water contained in the felt by centrifugation with a substantial saving in the energy required for suction of said water. It may be possible to remove an adequate quantity of wash water by centrifugation, eliminating the suction system entirely. In any case, the suction system will require less power than the power normally installed for this purpose. In a practical embodiment, diversion of the path of the felt is defined by at least one diverter or centrifugal roller. It would also be possible to use several diverter rollers in series, to increase the effect of drainage by centrifugal force.

Advantageously, to obtain better elimination of the wash water from the felt by centrifugal force, the centrifugal roller is structured to allow air to pass _ _

through the felt in correspondence of the contact area between felt and centrifugal roller. This can be obtained, for example, by designing the roller with a perforated surface, which allows air to pass from the inside of the roller towards the outside, thereby avoiding the adhesive effect (suction effect) which occurs with normal rollers for feeding the felt or fabric.

Alternatively, or in combination, the roller can be provided with a grooved surface, wherein the grooves allow air to pass between the surface of the roller and the surface of the felt in contact with the centrifugal roller. In one embodiment, on the grooved surface a mesh structure can be applied, for example a sort of net, on which the felt or other flexible member is placed and which allows air to pass from the grooves of the roller towards the outside of the net, between this and the felt or other continuous flexible member fed around the centrifugal roller.

The wash water distributor is appropriately disposed upstream of the centrifugal roller and preferably directly upstream thereof, so as to feed the wash water to the felt in proximity of the initial contact area between the felt and the centrifugal roller. For example, the wash water distributor can comprise pressurized water nozzles oriented towards the volume defined by the felt and by the centrifugal roller, upstream of the contact area between the centrifugal roller and the felt with respect to the direction of feed of said felt.

To obtain an optimal washing effect, the water is sprayed onto the felt from the side thereof that does not come into contact with the web being formed, and the diversion imposed on the path of the felt is such that the centrifugal force tends to eliminate the wash water from the surface that comes into contact with the slurry of water and cellulose fibers. This allows maximum efficiency to be obtained in removing the fibers and any other debris that may have deposited on the felt.

In front of the diversion in the path of the felt where at least part of the wash water is eliminated a recovering member can be arranged for recovering the eliminated water, so as to collect the water and any fibers entrained thereby.

If necessary, downstream of the diversion in the path of the felt, in correspondence of which the wash water is eliminated, one or more suction boxes can be disposed in sequence, advisably and preferably on the side of the felt facing the outside of the path and consequently from which the wash water is eliminated by centrifugal force.

According to a different aspect, a method is provided for washing a continuous flexible member, such as a felt, in a wet forming paper machine, com- prising the steps of: feeding wash water to said continuous flexible member; at least partially eliminating said wash water from the continuous flexible member by applying a centrifugal force.

Further advantageous characteristics and embodiments of the method and of the machine according to the invention are indicated in the appended claims and will be described below with reference to a preferred but non-limiting embodiment of the invention. Brief description of the drawings

The invention will be better understood by following the description and accompanying drawing, which shows a non-limiting practical embodiment of the invention. More in particular, in the drawing: figure 1 shows a general diagram of the machine for wet forming a paper web, in particular a machine called crescent former, typically utilized to produce tissue paper, to which the present invention is applied; figure 2 shows an enlargement of a portion of path of the felt of the machine in figure 1; and figures 3A and 3B diagrammatically show ways of implementing the centrifugal roller.

Detailed description of an embodiment of the invention With reference to figure 1, numeral 1 indicates the forming area in which the paper web is formed by means of a headbox 3, which cooperates with a forming cylinder 5. Around the forming cylinder 5 a forming fabric 7 is fed, which moves along a closed path defined, as well as by the forming cylinder 5, by the rollers 11, 12, 14 and 16. Besides being defined by the forming fabric 7, the forming area is also defined by a felt 13 that follows a closed path fed, as well as around the forming cylinder 5, around further diverter rollers 24, 25, 26, 27, 28, 29, 30 and 32.

The paper web C, formed in the forming area between fabric 7 and felt _ .

13, is transferred to a drying roller 31 (so called Yankee roller) around which it is dried and from which it is detached by a creping blade 33 to be wound on a reel B.

The machine described above is known per se and does not require fur- ther detailed descriptions. It must be understood that the configuration of the machine illustrated herein is given by way of example and that the invention can be applied to a plurality of continuous wet forming paper machines, each time it is necessary to wash a felt or other continuous flexible element arranged along the forming path of the paper. With reference to figure 2, in the area of the drive roller 17, and downstream thereof with respect to the direction f13 of feed of the felt 13, a system of nozzles 41 is arranged, which spray jets of water A towards the surface of the felt 13 facing the inside of the closed path followed thereby. The water sprayed by the nozzles 41 impregnates the felt 13 to allow the washing and consequently the removal of debris, in particular paper fibers, which remain adhering thereto after the web has been transferred to the drying roller 31.

To remove the majority of the wash water sprayed by the nozzles 41 , the felt 13 is diverted around the centrifugal roller 17 directly downstream of the area in which it is impregnated with the water A. The arc of contact, the radius of the roller 17 and the speed of the felt (typically between 1000 and 2000 m/min) are such as to cause projection by centrifugal force of the majority of the water A sprayed by the nozzles 41 and also of water still contained in the felt 13 after the web has been transferred to the drying roller 31. Downstream of the centrifugal roller 17, therefore, the quantity of water that remains in the felt 13 is very limited and could even be such that no further measures are required for removal thereof.

In the embodiment shown, however, downstream of the centrifugal roller 17 a suction system is arranged, comprising a suction box 43 in front of which the felt 13 runs. Suction through the mouth of the box 43, the extension of which is substantially the same as the width of the felt 13, removes any residual water (or part thereof) in the felt 13 from the same side from which the majority of the wash water was eliminated by centrifugal force in the diversion area around the centrifugal roller 17. This side is the one that comes into contact with the web being formed in the forming area in front of the headbox 3. To recover the water projected by centrifugal force, around the centrifugal roller 17 a trough 45 is disposed, into which the water is sprayed through centrifugal force and from which it is recovered to allow also recycling of any fibers collected. Figures 3A and 3B schematically show two embodiments of the centrifugal roller. In one case the roller is designed with a perforated cylindrical shell, wherein the perforations allow air to pass between the outer surface of the cylindrical shell of the roller and the felt. In the other case the roller presents a surface with grooves and annular ridges and a net made of metal, plastic or another suitable material, for example with a mesh dimension approximately between 5 and 10 mesh, e.g. approximately 2-4 mesh per linear centimeter. The net structure allows air to pass between the outer surface of the net and the felt fed thereon.

It is understood that the drawing only shows an example provided by way of practical arrangement of the invention, and that said invention can vary in forms and arrangement without however departing from the scope of the concept on which the invention is based. Any reference numerals in the appended claims are provided to facilitate reading of the claims with reference to the description and to the drawing, and do not limit the scope of protection repre- sented by the claims.

Claims

1. A papermaking machine for making paper from a slurry of water and cellulose fibers, comprising at least one continuous flexible member, movable along a closed path with a first portion, wherein a layer formed of said slurry is in contact with a first surface of the continuous flexible member, and a second portion, wherein the continuous flexible member is not in contact with said layer, a water distributor to wash the continuous flexible member being arranged along said second portion, characterized in that in proximity of said water distributor the path of the continuous flexible member presents a diversion such as to cause discharge by centrifugation of at least part of the water contained in the continuous flexible member.

2. Machine as claimed in claim 1 , characterized in that said continuous flexible member is a felt.

3. Machine as claimed in claim 1 or 2, characterized in that said diver- sion in the path of the continuous flexible member is defined by at least one centrifugal roller.

4. Machine as claimed in claim 3, characterized in that said centrifugal roller is structured to allow air to pass through said continuous flexible member in correspondence of the contact area of the continuous flexible member with the roller.

5. Machine as claimed in claim 4, characterized in that said centrifugal roller presents an apertured surface.

6. Machine as claimed in claim 4, characterized in that said centrifugal roller presents a grooved surface, preferably covered with a net structure.

7. Machine as claimed in one or more of claims 3 to 6, characterized in that said water distributor is arranged and configured to feed water towards said continuous flexible member in proximity of the initial contact area between said continuous flexible member and said centrifugal roller.

8. Machine as claimed in claim 7, characterized in that said distributor comprises nozzles oriented towards the volume defined between the continuous flexible member and the centrifugal roller, upstream of the contact area between centrifugal roller and continuous flexible member, with respect to the direction of movement of said continuous flexible member.

9. Machine as claimed in one or more of the preceding claims, charac- _

terized in that said diversion is configured so that the centrifugal force generated on the water contained in the continuous flexible member pushes the water towards the outside of the continuous flexible member through said first surface of the continuous flexible member which comes into contact with the layer of slurry of water and cellulose fibers.

10. Machine as claimed in one or more of claims 3 to 8, characterized in that said centrifugal roller is in contact with a second surface of the continuous flexible member opposite to the first surface of the continuous flexible member, which comes into contact with the layer of slurry of water and cellulose fibers.

11. Machine as claimed in one or more of the preceding claims, characterized by including a device to recover the water eliminated from the continuous flexible member by centrifugation, positioned in front of said diversion.

12. Machine as claimed in one or more of the preceding claims, characterized in that said continuous flexible member is fed around a forming cylinder defining, with a further continuous flexible member such as a fabric, a forming area for forming the layer of slurry of cellulose fibers and water.

13. Machine as claimed in one or more of the preceding claims, characterized in that it comprises a suction box downstream of said diversion with respect to the direction of movement of the continuous flexible member.

14. Machine as claimed in claim 13, characterized in that said suction box is positioned in front of said first surface of the continuous flexible member.

15. Method for washing a continuous flexible member in a wet forming paper machine, comprising the steps of: feeding wash water to said continuous flexible member; - at least partially eliminating said wash water from the continuous flexible member by applying a centrifugal force.

16. Method as claimed in claim 15, wherein the wash water is fed to the continuous flexible member on the surface opposite to the surface from which the water is eliminated by centrifugal force.

17. Method as claimed in claim 15 or 16, wherein said continuous flexible member presents a first surface, which comes into contact with the slurry of cellulose fibers and water to form the paper, and wherein said wash water is eliminated by centrifugal force through said first surface. _

18. Method as claimed in one or more of claims 15 to 17, wherein said centrifugal force is generated by imposing a diversion on the path of the continuous flexible member.

19. Method as claimed in claim 18, wherein said diversion is imposed by entraining the continuous flexible member around a centrifugal roller.

20. Method as claimed in claim 19, wherein in correspondence of the contact area between the continuous flexible member and the centrifugal roller a flow of air is generated through the continuous flexible member as a result of elimination of the water from the continuous flexible member.

21. Method as claimed in claim 18, 19 or 20, wherein the wash water is fed to the continuous flexible member directly upstream of said diversion.

22. Method as claimed in one or more of claims 15 to 21 , wherein suction is applied to said continuous flexible member to remove at least part of the wash water not eliminated by centrifugal force.

23. Method as claimed in one or more of claims 15 to 22, wherein said continuous flexible member is a felt.