WO2003057981A1

WO2003057981A1 - Broke system for a paper machine or an equivalent fibrous web machine

Info

Publication number: WO2003057981A1
Application number: PCT/FI2002/001026
Authority: WO
Inventors: Jouko Hautala; Antti Lukka
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2001-12-19
Filing date: 2002-12-16
Publication date: 2003-07-17
Anticipated expiration: 2004-06-19
Also published as: FI120551B; AT501331B1; FI20012513L; AT501331A1; DE10297530T5; AU2002350786A1; FI20012513A0

Abstract

A broke system for a paper machine or the like, particularly for the wet end of a paper machine, in which the dry solids content of the web is < 60 % and which comprises at least a forming section (WS) and a press section (PS1, PS2) and advantageously the beginning of a drying section (DS). According to the invention the broke system is arranged between a broke discharge point and a broke tower and the broke system comprises at least collecting means (l, 2) arranged below the paper machine for receiving broke, a broke conveying line (3) for transporting the broke past the forming section (WP) to the beginning of the paper machine or the like, and a broke tower (6) for receiving the broke either directly or via an intermediate conveyor (4) from the broke conveying line (3).

Description

Broke system for a paper machine or an equivalent fibrous web machine

The present invention relates to a broke system for a paper machine or an equiva- lent fibrous web machine, particularly for the wet end of a fibrous web machine, in which the dry solids content of the web is < 60 % and which comprises at least a forming section and a press section and advantageously part of a drying section.

A paper machine or a corresponding fibrous web machine refers in this applica- tion to a paper, board or soft tissue machine or a chemical pulp dryer.

At the wet end of a paper machine broke generally discharges from several broke discharge points, e.g. in the wire section i.e. the forming section during trimming, in connection with web breaks in the press section and at the beginning of the dry- ing section, in open draws between different sections of the paper machine and generally when the web is not supported from below.

Known broke systems have the principle of mixing the broke with water in a pulper located under the paper machine so that the consistency of the stock formed is typically about 3 %. After this the stock is pumped into a broke tower, from where it is taken back to the paper machine either as part of the stock or, in an extreme situation, broke alone is used.

The broke is typically disintegrated at the production rate of the machine in a pulper located under the machine to a pumpable consistency, which is normally in the range of 4...5 %. The disintegrated stock is normally pumped via the pulper of the wire section into the broke tower and the trim broke from the wire section is normally pumped in continuous operation via a broke thickener into the broke tower or a thickener. Coated broke, containing coating-derived ash, the amount of which in the paper is desired to be controlled, is kept separate from the base paper broke and stored in a broke tower of coated paper. The broke is screened for in- stance due to poor disintegrability of coated broke. The screening can be performed on all broke, whereby, in order to control the ash amount coming from the broke into the base paper, uncoated and coated broke are first proportioned into a broke dosage chest, from where they are pumped via screening to stock dosage. Before dosage to the paper machine the broke is thickened with a gravity thickener, which may be located in the base broke main line or as a separate thickening circulation in connection with the broke tower. Broke is usually dosed to a paper machine in an amount of 5...20 % of the machine's output. When the broke towers are being run to empty them, e.g. before a shutdown, the dosage may, at times, be up to 50...60 % of the machine's production.

A substantial problem related to known broke systems is that it is not possible to make the use of broke take place at the best possible time regarding the production. Problematic are also big broke towers, the large water volume of the broke system and time delays affecting the production. As to problems it can also be stated that since the broke occurring at the wet and dry end of the paper machine is caused by running problems related to pulp properties or chemistry, it would be most advantageous to run the paper machine with fresh pulps. This, however, is not possible if the broke cannot be recovered. In addition to running problems the provision for broke increases costs, since storage chests and dilution water tanks have to be built for storing broke. What is more, paper pulp does not keep for a long period of time at chest consistency and, on the other hand, the chests should be emptied as quickly as possible to maintain preparedness for dealing with the next break.

The main object of the present invention is to provide, particularly for the wet end of the paper machine, a novel broke system with which the above-mentioned problems and disadvantages related to traditional broke systems could be eliminated or at least essentially reduced. It is a special object of the present invention to reduce the mixing of broke with water. A further object according to an additional aspect of the present invention is to do away with the need to use a pulper and to provide broke pre-treatment by means of which all broke from the wet end of the machine can be passed into a broke tower at a constant consistency and after that be disintegrated and diluted in the broke tower to a pumping consistency, which is usually 4...5 %.

These objects have been achieved with the above-mentioned broke system generally characterized, according to its new and inventive basic idea, in that the broke system, arranged between a broke discharge point and a broke tower, comprises: at least one set of collecting means arranged below a paper machine or the like for receiving broke from broke discharge points, a broke conveying line for receiving and conveying broke from each broke collecting means and for transporting it either directly or via an intermediate conveyor away from the broke conveying line.

The broke conveying line extends, according to an advantageous embodiment of the invention, at least over the length of the wet end of the paper machine and discharges the broke either directly or via an intermediate conveyor into the broke tower. The broke tower can, what comes to the operativeness of the invention, be placed freely; it is, however, advantageous to place it near the paper machine.

It is also advantageous to a preferable embodiment of the invention that a first set of broke collecting means is disposed below the final end of the forming section and that a second set of collecting means is arranged at least under the press section. It is then advantageous that each collecting means comprises at least one conveying means for moving the broke discharging from the broke discharge point below and to the middle of the paper machine or to one or both sides of the machine.

To provide a substantially uniform consistency regardless of the broke discharge point it is characteristic of the invention that in the intermediate conveyor and/or in each conveying means belonging to each collecting means dilution water is mixed with the broke so that the consistency of the broke is diluted to a range of 6-20%, preferably to a range of 10-15 %, at which consistency the broke conveying line or the intermediate conveyor discharges the diluted wet broke into the broke tower. According to the invention the dilution water is in that case taken from a first dilution water pipe.

To stabilize the consistency in the broke tower to the range of 6-20%, preferably to the range of 10-15 %, the dilution water can, according to the invention, be also fed directly into the broke tower.

According to an application of an advantageous embodiment of the invention it is advantageous that, in order to move the broke with a collecting means in the lateral direction below and to the middle or to both sides of the paper machine or the like, the conveying means belonging to the collecting means comprises two parts so that the centre lines, parallel to the transport direction of broke, of the parts of the conveying means run at a right angle to or obliquely crosswise relative to the MD direction. The set of collecting means then discharges the broke through ends facing each other onto the broke conveying line located in the middle of the paper machine or the like or through ends facing away from each other onto the broke conveying lines located on the sides of the paper machine or the like.

According to another application of a preferred embodiment of the invention in order to move the broke by means of the collecting means in the lateral direction to a side of the paper machine the conveying means belonging to the collecting means comprises one part so that its centre line in the transport direction of broke runs at a right angle to or obliquely crosswise relative to the MD direction.

To enhance the mixing of dilution water with broke and to store, at the broke discharge points, wet brokes having different consistencies at a substantially uniform consistency in the broke tower it is advantageous, according to the invention, that the broke conveying line, being a belt conveyor or the like, transports the wet brokes to the intermediate conveyor, being a screw conveyor that mixes wet broke and dilution water. For the same purpose, i.e. to mix dilution water with wet broke and to provide the desired consistency, it is also advantageous that the conveying means of the collecting means are screw conveyors.

To the invention it is also advantageous, especially to ensure the collection of broke discharging from the broke discharge point and to facilitate after-treatment, that each collecting means comprises mechanical broke disintegration means disposed before the conveying means belonging to the collecting means, a broke re- ceiving vessel or tank, having an open upper part and comprising a continuous edge part and a slide bottom part, which is funnel-like and/or obliquely slanting towards the mechanical broke disintegration means, the slide bottom part comprising an outlet through which the broke falls onto the conveying means of the broke collecting means. According to an embodiment the mechanical broke disintegration means consist of a pair of broke-shredding or -tearing rolls, in which pair of rolls the axes of the rolls are at a right angle to or at an oblique angle to the MD direction and in which the outer surface of at least one roll is broke-cutting or -tearing in order to cut the broke advantageously into flake-like pieces. According to another embodiment of the invention the mechanical broke disintegration means consist of water sprays.

In order to provide wet broke of the desired consistency, which wet broke is passed onto a broke conveying line or an intermediate conveyor before passing it to a broke tower, the amount of dilution water to be passed to the conveying means of the collecting means or to the intermediate conveyor is determined according to the invention, and thus the control of the broke system is based on the position and width information of the broke at the broke discharge point.

The advantages of the invention include that it is possible to use the broke pro- duced in the paper machine at a time when it is sensible from the viewpoint of the runnability of the paper machine and/or the paper grade, and that the shredding device included in the broke system according to the invention makes the handling of broke easier and quicker. Thanks to the possibility of using fresh pulp running problems can be solved more promptly, thus significantly increasing the efficiency of the paper machine. If desired, it is possible to place the broke system according to the invention in a low cellar space, and the paper machine does not need large broke towers, meaning that the costs become lower and the broke system is substantially more compact compared to traditional broke systems. The control of the broke system according to the invention can also be carried out more rapidly and precisely thanks to smaller pulp quantities and continuous operation. The invention also opens up the possibility of using the produced broke as raw material in another paper machine or the like.

The invention will now be described in more detail by means of an advantageous embodiment with reference to the accompanying patent drawings, in which FIG.1 schematically shows a broke system according to the invention for handling broke at the wet end of the paper machine,

FIG.2 schematically shows an advantageous embodiment of the collecting means of the broke system, and

FIG.3 schematically shows another advantageous embodiment of the collecting means of the broke system.

Reference is made to Figure 1 , which illustrates the broke system according to the invention at the wet end of a paper machine for receiving broke from broke discharge points and for conveying the broke to a broke tower 6.

For the sake of clarity several different broke discharge points are represented in Figure 1 by a broke discharge point between a forming section i.e. wire section WS and a first press unit PSl of a press section; and a broke discharge point between the first press unit PSl and a second press unit PS2 of the press section or a broke discharge point between the first press unit PSl of the press section and a drying section DS. It can be stated, more generally, that broke is produced e.g. as a result of trimming or a web break, in all open draws, in any section of a paper machine where the web R is not supported from below, and in every intermediate zone between the different sections of the paper machine, such as between the above-mentioned forming section WS and the first press unit PS 1 of the press section, between the press units PSl, PS2 of the press section or between the first press unit PSl of the press section and the drying section DS.

In the embodiment according to Figure 1 the broke system according to the invention is arranged below the paper machine in connection with the forming section WS, the first press unit PSl of the press section following it and the second press unit PS2 of the press section or the beginning of the drying section DS. In a typical paper machine the dry solids content of the web after the forming section is normally < 20 %, typically between 10 and 20 %. It is common for a paper machine to have, in the forming section, a broke dropping shower, in which case the consistency of the broke is about 10 %. After the press section the dry solids content is usually < 60 %, typically between 40 and 55 %.

The broke system according to the invention comprises a first set of broke collecting means 1 arranged below the end of the forming section WS and a second set of collecting means 2 arranged below the press section PSl, PS2. According to the invention the collecting means 1, 2 discharge the broke onto a broke conveying line 3 extending substantially over the length of the wet end of the paper ma- chine WS, PSl, PS2/DS. The broke conveying line 3 in turn discharges the broke at the end of the broke conveying line 3 onto an intermediate broke conveyor 4. On the intermediate conveyor 4 the broke is mixed with dilution water from a first dilution water pipe 5, after which the wet broke diluted to the desired consistency, which is between 6 and 20 %, preferably between 10 and 15 %, is passed into the broke tower 6. To stabilize the consistency to a level between 6 and 20 %, pref- erably between 10 and 15 %, in the broke tower 6, dilution water can, according to the invention, also be passed directly into the broke tower.

In the broke tower 6 the wet broke is disintegrated and diluted in a bottom part 9 of the broke tower 6 with dilution water fed via a second dilution water pipe 7 to a pumping consistency, which is typically about 4-5 %. To eliminate the need for a pulper the wet broke to be pumped out of an outlet pipe of the bottom part 9 of the broke tower 6 is diluted further via a third dilution water pipe 8 so that a consistency suited for stock, about 3 %, is obtained.

Dilution water suited for the first, second and third dilution water pipes 5, 7 and 8 is advantageously taken from a filtrate water tower.

The first set of broke collecting means 1 extends in the running direction of the web, i.e. in the MD direction, backwards below the forming section WS and in the

CD direction transverse to the MD direction over the width of the paper machine. The second set of broke collecting means 2 also extends in the MD direction backwards below the press section PSl, PS2 and in the CD direction transverse to the MD direction over the width of the paper machine.

Both collecting means 1, 2 comprise advantageously at least one conveying means, e.g. a belt conveyor or the like, enabling the receiving of broke of the width of the paper machine web and passing the broke to after-treatment in the broke system according to the invention. Both collecting means 1, 2 may alterna- tively comprise at least one screw conveyor or the like enabling the receiving of broke of the width of the paper machine web and passing the broke to after- treatment in the broke system according to the invention.

According to the invention an object is to transport the broke discharging from the broke discharge point with the collecting means 1, 2 below and to the middle of the paper machine or, provided there is enough space in the machine hall, from under the machine to both sides or only one side of the machine.

In order to move the broke in the lateral direction either to the middle or to both sides of the machine a conveying means 11 belonging to the collecting means 1 , 2 comprises two parts such that the centre lines, parallel to the transport direction of broke, of the parts of the conveying means 11 run at a right angle to or obliquely crosswise relative to the MD direction, the parts of the conveying means discharging the broke - via its ends facing each other, via its ends facing away from each other onto the broke conveying line 3 located in the middle of the machine or correspondingly onto broke conveying lines 3 on the sides of the machine.

In order to move the broke in the lateral direction to only one side of the paper machine the conveying means belonging to the collecting means 1, 2 can comprise one part so that its centre line, in the transport direction of broke, runs at a right angle to or obliquely crosswise relative to the MD direction.

This way the broke, even of the width of the paper machine web, produced in the paper machine can, with the collecting means 1, 2, be collected below the paper machine, advantageously to the middle of the paper machine, or, provided there is enough space in the paper machine hall, to one side or both sides of the paper machine, and the broke can then be moved from the collecting means onto the broke conveying line 3, advantageously being a belt, a compartment or equivalent conveyor suited for conveying broke. The broke conveying line 3 and its transport direction advantageously extend at least from the end of the press section PSl, PS2 or from the beginning of the drying section DS in a direction opposite to the MD direction past the beginning of the forming section WS of the paper machine. At the end of the broke conveying line 3 the broke can be passed directly into the broke storage tower 6 below the end of the broke conveying line 3. To carry out the basic principle of the invention the end of the broke conveying line 3 extends, however, above the intermediate broke conveyor 4, whereby, at the end of the broke conveying line 3, the broke is passed onto the intermediate broke conveyor

4.

Since it is an object of the basic principle of the invention to store the broke originating from different parts of the paper machine into the broke storage tower 6 at a uniform dry solids content, according to an advantageous application of the invention dilution water is mixed in the intermediate conveyor 4 with the wet broke, which dilution water can be pumped e.g. from the filtrate water tower (not shown in the figure) via the dilution water pipe 5, whereby the consistency i.e. dry solids content of the wet broke can be diluted to a range of 6-20%, preferably to a range of 10-15%. To facilitate the mixing of water the intermediate broke conveyor 4 is, for example, a broke-mixing screw conveyor. According to a second advantageous application of the invention dilution water can be passed directly into the broke tower 6 to stabilize the consistency in the broke tower to a range of 6-20 %, preferably to a range of 10-15 %.

Since, in a paper machine process or the like, substantially all fibre suspension is fed to the process through a head box; since the development of the dry solids content of the web in the process, i.e. position information, is known essentially precisely in advance; since, on the other hand, trim-type broke is only produced at a location determined precisely in advance, i.e. width and/or position information; and since, as a result of a web break of a continuous web, broke of the width of the web can only be produced in one place, i.e. width and/or position information, the determining of the dry solids content of the broke being produced presents no problems. The feed volume of dilution water can thus be determined quickly and precisely to the desired consistency, i.e. 6-20 %, preferably 10-15 %, in order to produce diluted wet broke in the conveying means 11 of the collecting means 1, 2 or in the intermediate conveyor 4, whereby the wet broke diluted to the desired consistency can be fed into the broke tower 6.

Reference is made to Figure 2. To facilitate the handling of broke in the handling system it is also advisable to equip the collecting means 1, 2 with mechanical broke disintegration means 12, 12'. The disintegration means are advantageously located before the conveying means 11 belonging to the collecting means 1, 2.

The mechanical broke disintegration means 12 advantageously comprise a pair of broke-shredding or -tearing rolls, in which pair of rolls the axes of the rolls are at a right angle or an oblique angle to the MD direction and in which the outer surface of at least one roll is broke-cutting or -tearing in order to cut the broke advantageously into flake-like pieces. To ensure the recovery of all broke discharging from the broke discharge point it is advantageous that the broke collecting means 1, 2 also comprise a broke receiving vessel 13, having an open upper part and comprising a continuous edge part 14 and a slide bottom part 15, which is funnellike and/or obliquely slanting towards the mechanical broke disintegration means 12, the slide bottom part comprising an outlet 16 through which the broke falls onto the conveying means 11 belonging to the broke collecting means 1, 2.

The shredding or tearing pair of rolls of the shredding device according to Figure 2 can naturally be replaced with another device producing an equivalent result. Figure 3 illustrates one such embodiment. For the disintegration of broke, instead of a pair of rolls, water sprays 12' are illustrated, which, as they flow, cut and dis- integrate the web. This embodiment has the advantage that together with the conveying means 11 , advantageously being a screw conveyor, the water volume used for tearing the web can be adjusted so that it is no longer necessary to feed dilution water 5 or to arrange an intermediate conveyor 4, such as a screw conveyor between the broke conveying line 3 and the broke tower 6. The invention has been described above only in an exemplifying manner by means of some of its advantageous embodiments and applications. It is naturally not intended that this limit the invention in any way, but instead, as is clear to a person skilled in the art, many alternative arrangements and modifications are possible within the inventive idea and its scope of protection defined in the accompanying claims.

Claims

1. A broke system for a paper machine or the like, particularly for the wet end of a paper machine, in which the dry solids content of the web is < 60 % and which comprises at least a forming section (WS) and a press section (PSl,

PS2) and advantageously part of a drying section (DS), characterized in that the broke system, arranged between a broke discharge point and a broke tower, comprises: at least one set of collecting means (1, 2) arranged underneath a paper ma- chine or the like (WP, PSl, PS2, DS) for receiving broke from broke discharge points, a broke conveying line (3) for receiving broke from each broke collecting means (1, 2) and for transporting it past the forming section (WP) to the beginning of a paper machine or the like, and a broke tower (6) for receiving the broke transported by the broke conveying line (3) either directly or via an intermediate conveyor (4) from the broke conveying line (3).

2. A broke system according to claim 1, characterized in that the broke convey- ing line (3) extends substantially over the length of the wet end of the paper machine (WS, PSl, PS2, DS), and that the broke conveying line (3) discharges the broke either directly or via the intermediate conveyor (4) into the broke tower (6).

3. A broke system according to claim 1 and/or 2, characterized in that the first broke collecting means (1) are arranged below the end of the forming section (WS), and that the second collecting means (2) are arranged below the press section (PSl, PS2).

4. A broke system according to claim 3, characterized in that each collecting means (1, 2) comprises at least one conveying means (11) for moving the broke discharging from a broke discharge point below and to the middle of the paper machine or to one or both sides of the machine.

5. A broke system according to claim 2 and/or 4, characterized in that in the intermediate conveyor (4) and/or in each conveying means (11) belonging to each collecting means (1, 2) dilution water is mixed with the broke so that the consistency of the broke is diluted to a range of 6-20%, preferably to a range of 10-15 %, at which consistency the broke conveying line (3) or the intermediate conveyor (4) discharges the diluted wet broke into the broke tower (6).

6. A broke system according to claim 5, characterized in that dilution water is fed directly into the broke tower (6) to stabilize the consistency in the broke tower.

7. A broke system according to claim 5, characterized in that dilution water is passed to the collecting means (1, 2), the conveying means (11) or the intermediate conveyor (4) from a first dilution water pipe (5).

8. A broke system according to any one of claims 1-7, characterized in that in order to move the broke with a collecting means (1, 2) in the lateral direction from the broke discharge point below and to the middle or to both sides of the paper machine or the like, the conveying means (11) belonging to the collecting means comprises two parts so that the centre lines, parallel to the transport direction of broke, of the parts of the conveying means run at a right angle to or obliquely crosswise relative to the MD direction, the conveying means discharging the broke through ends facing each other or through ends facing away from each other onto the broke conveying line (3) located in the middle of the paper machine or the like or correspondingly on the sides of the paper machine or the like.

9. A broke system according to any one of claims 1-7, characterized in that in order to move the broke by means of the collecting means (1, 2) in the lateral direction from the broke discharge point to a side of the paper machine or the like the conveying means (11) belonging to the collecting means comprises one part so that its centre line parallel to the transport direction of broke runs at a right angle to or obliquely crosswise relative to the MD direction.

10. A broke system according to any one of claims 1-9, characterized in that in order to store wet brokes having different consistencies at the broke discharge points into the broke tower (6) at a substantially uniform consistency, the broke conveying line (3), which is a belt conveyor or the like, passes the wet brokes to the intermediate conveyor (4), being, in order to facilitate the mixing of dilution water, a screw conveyor that mixes wet broke and dilution water.

11. A broke system according to any one of claims 1-10, characterized in that each collecting means (1, 2) comprises mechanical broke disintegration means (12, 12') arranged before the conveying means (11) belonging to the collecting means, a broke receiving vessel or tank (13) having an open upper part and comprising a continuous edge part 14 and a slide bottom part (15), which is funnel-like and/or obliquely slanting towards the mechanical broke disintegration means (12, 12'), the slide bottom part comprising an outlet (16) through which the broke falls onto the conveying means of the broke collecting means.

12. A broke system according to claim 11, characterized in that the mechanical broke disintegration means (12) consist of a pair of broke-shredding or broke- tearing rolls, in which pair of rolls the axes of the rolls are at a right angle to or at an oblique angle relative to the MD direction and in which the outer surface of at least one roll is broke-cutting or broke-tearing in order to cut the broke advantageously into flake-like pieces.

13. A broke system according to claim 11, characterized in that the mechanical broke disintegration means (12') consist of broke-disintegrating water sprays.

14. A broke system according to any one of claims 1-12, characterized in that the amount of the dilution water passed to the conveying means (11) of the collecting means (1, 2) or to the intermediate conveyor (4) is based on the position and width information of the broke at the broke discharge point.