WO2014137274A1

WO2014137274A1 - Arrangement and method for dewatering a fibrous web to high dry solids content

Info

Publication number: WO2014137274A1
Application number: PCT/SE2014/050259
Authority: WO
Inventors: Ingvar Klerelid
Original assignee: Valmet Aktiebolag
Priority date: 2013-03-04
Filing date: 2014-03-04
Publication date: 2014-09-12
Also published as: SE1350254A1

Abstract

An arrangement for dewatering a fibrous web (w) being manufactured in a paper or board machine, wherein the arrangement comprises a press roll (3) adapted to bear against a counter roll (2), whereby a press nip (N2) is formed by said bearing contact, wherein said counter roll (2) is a drying cylinder (2) heated from within by hot steam and that said fibrous web (w) is brought into contact with a shell surface of said drying cylinder (2) at a distance (D1) upstream of an entrance (E1) to said press nip (N2) as viewed in the machine direction (MD) of the paper or board machine. A method for dewatering a fibrous web (w) being manufactured in a paper or board machine, wherein the arrangement comprises a press roll (3) adapted to bear against a counter roll (2), whereby a press nip N2 is formed by said bearing contact, wherein the counter roll (2) is a drying cylinder (2) heated from within by hot steam and that the fibrous web (w) is transported on a shell surface of the drying cylinder (2) over a distance (D1), said transport caused by the rotation (R) of the drying cylinder (2) in the machine direction (MD) of the paper or board machine, before the fibrous web (w) arrives at an entrance (E1) to said press nip (N2).

Description

ARRANGEMENT AND METHOD FOR DEWATERING A FIBROUS WEB TO

HIGH DRY SOLIDS CONTENT

TECHNICAL FIELD

The present invention relates to an arrangement in a machine for manufacturing paper, especially soft crepe paper.

Furthermore, the invention relates to a method for dewatering a paper web.

STATE OF THE ART

It is known since long to seek to minimize the energy consumption when manufacturing different types of paper and paperboard. The energy for drying the paper or paperboard is the largest energy-consuming operation when manufacturing paper and paperboard. It is therefore preferred to increase the dry solids content of the paper web before the paper web is guided into the drying section in order to contribute to the reduction of energy consumption.

At present, when manufacturing soft crepe paper, so-called tissue, there are various known methods of achieving as high dry solids content as possible in the paper web before entry into the drying section. One known solution is a press configuration with two press rolls bearing against a drying cylinder and where the first press roll may be a suction roll. One example of such a configuration is disclosed in US Patent publication No. 3691010. Another example of a configuration of this type is disclosed in US Patent publication No. 4911791. Typical linear loads in this type of configuration can be up to 120 kN/m. Another known solution is to use an extended nip roll having a flexible press body and a lower linear load, or a shoe press having a short nip and a high linear load, as a press roll bearing against the drying cylinder. An example of a solution where an extended nip roll having a flexible press body is allowed to bear against a drying cylinder is disclosed, for example, in US Patent publication No. 7527708, and is described with reference to, inter alia, Figure 1 of that publication. Another example of a solution where an extended nip roll having a flexible press body is allowed to bear against a drying cylinder is disclosed in EP 2085513 Al .

It has also been suggested to allow a shoe press with a rigid shoe having a concave surface to bear against a drying cylinder. One example of such a configuration is disclosed, for example, in DE 100 32 251. Accordingly, dewatenng of tissue by means of pressing out water contained in the tissue web takes place by pressing the tissue web (i.e. the soft crepe paper web) bearing against the drying cylinder, and wherein the drying cylinder constitutes a hot counter roll. It is primarily the maximum nip pressure between the press roll and the counter roll which determines the dry solids content which can be obtained in the paper web before final drying takes place in contact with the drying cylinder. Since there is

simultaneously a transfer of heat from the drying cylinder to the paper web in the nip, also the time in the press nip has a significance for the increase in dry solids content. The total linear load which can be applied depends on the dimensions of the drying cylinder. This has the consequence that the shoe press body should be narrow in order to maximize the pressure and thereby the dry solids content, but on the other hand a narrow shoe press body means that the time in the nip becomes short, which limits the heat transfer and thereby also the dry solids content.

For the press configuration with two press rolls, the nip pressure is limited by a combination of linear load, roll diameter and hardness of the roll coating. In practice, this means that it is more difficult to achieve the same high specific pressure as with a shoe press. Consequently, the magnitude of the dry solids content which can be obtained by means of a two-press method is limited.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to save energy when manufacturing soft crepe paper (tissue paper) by increasing the dry solids content achieved by pressing.

This is accomplished by means of an arrangement for dewatering a fibrous web

(especially a web of tissue paper) being manufactured in a paper or board machine, wherein the arrangement comprises a press roll adapted to bear against a counter roll, whereby a press nip N2 is formed by said bearing contact. The counter roll is constituted by a drying cylinder which can be heated from inside by steam, preferably a Yankee cylinder. According to the invention, the fibrous web is brought into contact with the shell surface of said counter roll at a distance upstream of an entrance to said press nip as viewed in the machine direction MD of the paper or board machine.

According to the invention, said press roll is constituted by an extended nip roll having an internal press body, preferably an extended nip roll having a flexible press body. The fibrous web can be brought into contact with the shell surface of said counter roll at a distance from the press nip N2 which distance is in the range of 0.5 m - 2.5 m, wherein the distance is calculated along the surface of the counter roll. Thanks to an arrangement according to the invention, the paper web can achieve a substantially higher dry solids content than conventionally achieved in the paper or paperboard web in a press section before final drying in contact with the drying cylinder in a drying section, which results in great energy savings in the final drying process performed by means of the drying cylinder in the drying section. The drying cylinder is hence being both part of the press section as well as being arranged as the drying section for final drying afterwards the pressing step/-s in the press section, i.e. the press section and the drying section are integrally arranged, which indeed leads to energy savings instead of using separately arranged press section and drying section. According to a preferred aspect of the invention, the fibrous web is brought into contact with the counter roll in that an additional press roll brings the fibrous web to bear against the counter roll. This additional press roll can be constituted by a suction roll.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows a cross-section of the arrangement according to a preferred but non- limiting embodiment of the invention.

DETAILED DESCRIPTION OF THE FIGURES

Fig. 1 schematically shows a non-limiting embodiment of the arrangement according to the invention in a cross-section in the machine direction of the paper or board machine. The invention is primarily intended for a paper machine of the tissue machine type, but is not limited exclusively to tissue machines. In this context, tissue should be understood as such paper grades as for example toilet paper and kitchen paper, and wherein the finally dried fibrous web preferably has a grammage in the range of 10 g/m² - 40 g/m², and usually a grammage in the range of 12 g/m² - 35 g/m². Many times, the grammage can be in the range of 15 g/m² - 30 g/m² or in the range of 20 g/m² - 30 g/m². The grammage can, for example, be 25 g/m². However, the machine according to the invention could also be used for other paper grades with higher grammages.

A formed wet fibrous web w, formed in a forming section in which there is at least one headbox (not shown), which headbox for example may be a multilayer headbox, is supported by a blanket or felt F during the transport thereof through the forming section. The web w is guided by one or several guide rolls 4 toward the arrangement according to the invention, hereinafter called a press section, included in the paper machine. The press section preferably comprises a first press roll 1, a drying cylinder 2 and a second press roll 3. At least one guide roll 4 is disposed between the first press roll 1 and the second press roll 3. The drying cylinder 2 is furthermore arranged as a drying section after the second press nip N2 as viewed in the machine direction MD. A doctor blade 5, preferably a creping doctor, is disposed against the drying cylinder 2. Downstream of the doctor blade 5, there is a reel-up (not shown) for reeling up a formed and dried paper web. It is also conceivable to dispose equipment between the drying cylinder and the reel-up, such as measuring equipment for measuring different properties of the paper web, e.g. moisture content/dry solids content and/or grammage.

Preferably, said first press roll 1 is constituted by a suction roll having a suction zone S disposed on at least a portion of the shell surface of the suction roll. At least a portion of the suction surface S of the suction roll 1, preferably the entire extension thereof in the cross direction CD of the paper machine, is adapted to bear against the counter roll, i.e. the drying cylinder 2, wherein the bearing contact results in a first press nip Nl . An example of such an assembly is disclosed, for example, in US Patent publication No. 3691010. The linear load in the first press nip Nl can be low if the nip Nl is primarily a pure transfer nip, which only serves for transferring the fibrous web w to the drying cylinder 2. It is appreciated that, in the transfer of the fibrous web, there is also a separation between the fibrous web and the felt F, and that the felt is thereby not transferred to the drying cylinder, but is guided into another direction. For a pure transfer nip, the linear load in the press nip Nl can then, for example, be in the range of 2 kN/m - 60 kN/m, 5 kN/m - 60 kN/m or 20 kN/m - 60 kN/m. As previously mentioned, low linear loads can be used if the nip Nl is primarily intended for transferring the fibrous web w from the felt F to the drying cylinder 2 and if the purpose of the press nip is not primarily to dewater the fibrous web. However, also higher linear loads in the first press nip Nl between the suction roll 1 and the drying cylinder 2 are conceivable. Linear loads up to 120 kN/m can be used, especially if it is desired to cause water to be pressed out to some extent of the fibrous web in the nip Nl . Linear loads above 120 kN/m in the press nip Nl, in some cases up to 150 kN/m, or even 170 kN/m, may also be conceivable in some cases. The highest possible load is limited by the mechanical strength of the drying cylinder 2. In principle, the strength of the drying cylinder 2 can be increased by making the shell wall thereof thicker, but in that case the heat transferring ability of the drying cylinder would be reduced. Therefore, in practice, the upper limit of the linear load in the first press nip Nl may in most cases be considered to be about 170 kN/m. The length of the the first press nip Nl in the cross direction of the machine is ultimately limited by the width of the drying cylinder 2. Typical values for the width of the drying cylinder 2 can be in the range of 2 m - 6 m, but there are also machines where drying cylinders, such as Yankee cylinders, can be wider than 6 m. Machine widths of up to 8 m, 9 m, or up to 10 m are entirely conceivable. In some cases, even machine widths exceeding 10 m might be conceivable for soft crepe paper machines. There are also some small machines where the machine width may be below 2 m. For instance, so-called pilot machines may have a machine width of only about 0.5 m. The drying cylinder 2 is typically filled within with hot steam which may have a temperature of up to 180°C or even more. The hot steam heats the drying cylinder such that the external surface/shell surface of the drying cylinder 2 reaches a temperature suitable for effective evaporation of water in a wet fibrous web such as a tissue paper web.

Normally, the length of the first press nip Nl in the machine direction MD between the suction roll 1 and the drying cylinder 2 can be in the range of 30 mm - 80 mm, depending on, inter alia, the diameter of the rolls, the linear load and the thickness and characteristics of the felt F. In many cases, the length of the nip Nl can be in the order of 35 mm - 60 mm.

The drying cylinder 2 is preferably constituted by a Yankee cylinder. The Yankee cylinder can be designed in several different ways without departing from the inventive idea. The drying cylinder may, for example, be a Yankee cylinder of cast iron, but it can also be a Yankee of the type disclosed in WO2008/105005. Normally, the Yankee cylinder will have a diameter in the range of 3 m - 6 m, but Yankee cylinders with a greater diameter than 6 m, or a smaller diameter than 3 m, are conceivable.

Also the second press roll 3 is disposed with a small bearing contact against the counter roll, i.e. the drying cylinder 2, while forming a second press nip N2.

The second press roll 3 is preferably constituted by an extended nip roll having an internal press body, and can, in a particularly advantageous embodiment of the invention, be constituted by an extended nip roll having a flexible press body. The extended nip rolls having a flexible press body which are described in the patent publication US 7,527,708 can advantageously be used as a second press roll 3 according to the present invention, however the invention is not limited to this type of extended nip rolls, but also other types of extended nip rolls having a flexible press body are conceivable, for example the type of extended nip rolls according to the teaching of EP 2,085,513. In this context, the term 'flexible press body' refers to such press bodies that are capable of conforming to the shape of the counter roll in the cross direction of the machine (usually called the CD direction). By using an extended nip roll 3, a so-called extended second press nip N2 is obtained. A press body 6 inserted into the extended nip roll 3 is adapted to determine the length of the extended press nip N2, as viewed in the machine direction. A preferred length range for the extended press nip N2 is 40 mm - 300 mm, more preferably 50 mm - 150 mm, and even more preferably 50 mm - 80 mm. In one conceivable embodiment, the length of the extended press nip N2 can be for example 60 mm. The press body 6 is preferably elastically deformable, and has its pressing surface conformable to the counter pressure surface of the counter roll 2 in cooperation therewith. This adaptation takes place under the influence of a load, which is produced by a loading means for the press body 6 included in the extended nip device, and which acts on the press body 6 in a direction toward the counter pressure surface in order to load the entire extended press nip N2 correspondingly. The load in the nip N2 can suitably be in the range of 100 kN/m - 170 kN/m, preferably 120 kN/m - 150 kN/m. The linear load in the extended press nip N2 can, for example, be 130 kN/m.

In a another embodiment, the press roll 3 is constituted by a such an extended nip roll that is a conventional shoe press roll 3 where the press body 6 is not a flexible press body, but a substantially rigid shoe. Examples of such rolls are disclosed in several patent publications, for example US 5,662,777 and US 6,083,352. Examples of suppliers of shoe press rolls are Metso Paper Inc. in Finland, who market a shoe press roll under the name SymBelt. Such shoe presses normally have a shoe, or press body, which is not flexible, but has a concave surface facing outward toward the counter roll. The press body (shoe) in such an extended nip roll can, for example, be made of steel or aluminium. Also for such an extended nip roll 3, the length of the nip can be in the range of 40 mm - 300 mm in many realistic embodiments, and the linear load in the range of 100 kN/m - 170 kN/m.

While supported by the felt F, the fibrous web w, in the preferred embodiment a tissue web w, is passed over one or several guide rolls 4 into the press section and is brought to bear against the suction roll 1, and with the felt F disposed between the shell surface of the suction roll 1 and said fibrous web w. The fibrous web is transported in the machine direction MD and arrives at the portion of the suction roll 1 which is provided with a suction zone S. As the fibrous web passes over the suction zone S, a

simultaneous dewatering of both the fibrous web and the felt F takes place. In the suction zone S, preferably at the far end portion of thereof as viewed in the machine direction, the fibrous web w is transferred from the suction roll to the shell surface of the drying cylinder at a contact point P on the drying cylinder 2, which substantially coincides with an exit of the first press nip Nl . Thereafter, the fibrous web w is transported forward on the shell surface of the Yankee cylinder over a first distance Dl in the machine direction MD, and wherein the transport is caused by the rotation R of the drying cylinder 2 in the machine direction. Said first distance Dl substantially extends from the exit of the first press nip Nl, i.e. the contant point P, to an entrance El of the second press nip N2, again as viewed in the machine direction, whereas the felt F is separated from the fibrous web in the transfer of the fibrous web to the drying cylinder 2 and is guided to a guide roll 4 disposed between the suction roll 1 and the press roll 3. It is appreciated that the felt F in this embodiment is not in contact with the fibrous web w between the nips Nl and N2, but is guided away from the drying cylinder. Between the two nips, first nip Nl and second nip N2, the machine can be provided with additional devices for dewatering the felt F (not shown in Figure 1) in order to reduce the risk of moisture (water) being transferred from the felt F to the fibrous web w when the felt F once again meets with the fibrous web in the second nip N2. A possible magnitude of the distance Dl is suitably at least 0.5 m, but normally no more than 2.5 m. The distance Dl can, for example, be in the range of 0.9 m - 1.8 m. In one possible embodiment, the drying cylinder 2 can be a Yankee cylinder having a diameter of 5.5 m, and the distance (interval) Dl can be about 1.5 m. The distance Dl can suitably be determined based on the diameter S_D of the suction roll 1 in such a way that the distance Dl is determined according to the formula k*So, where k is a constant in the range of 1.0 - 1.5. The diameter S_D of the suction roll 1 can usually be selected with the machine width as a starting point, so that the diameter S_D increases slightly with the machine width. If the machine width is 2.8 m, the suction roll 1 can suitably have a diameter of (for example) 0.9 m. If instead the machine width is 5.5 m, the suction roll 1 should have a greater diameter, say 1.2 m. Accordingly, if the suction roll 1 has a diameter of 0.9 m, the distance Dl can suitably be 0.9 m - 1.35 m, and if the suction roll 1 has a diameter of 1.2 m, the distance Dl can suitably be in the range of 1.2 m - 1.8 m. After having travelled the distance Dl, the fibrous web w enters the entrance El of the second press nip N2, passes through the second press nip N2 and leaves the the second press nip N2 at an exit E2. It is further appreciated that the first press nip Nl constitutes a first nip serving as a transfer nip, and that the second press nip N2 constitutes a second press nip which is located downstream of first press nip Nl in the machine direction, so that the fibrous web first passes the first nip Nl and then the second nip N2 when operating the machine. In the same way, the roll 1 serving for transferring the fibrous web to the surface of the Yankee cylinder 2 can be regarded as a first press roll 1, and the press roll 3 can then be regarded as a second press roll 3.

During the transport of the fibrous web on the shell surface of the drying cylinder over the distance Dl, the fibrous web is heated by the heated drying cylinder all the way from the first press nip Nl to the second press nip N2 and the temperature of the heated web may be as high as almost 180 °C. During the transportation of the web w through the second nip N2 additional water is pressed out of the web w and due to the heating of the fibrous web upstream of the second press nip N2, maximum dewatering can be achieved in the second press nip N2. One possible reason why the improved dewatering of the fibrous web is obtained when the fibrous web is at a higher temperature than usual in the second press nip N2 could be that the viscosity of the heated water contained in the fibrous web has been changed, i.e. reduced, which consequently could be at least one contributing reason for the improved dewatering of the web w. In the embodiment where the second press roll is constituted by an extended nip roll having a flexible press body, a comparatively high linear load and a short press body can be used owing to the improved dewatering ability.

After the fibrous web has passed the exit E2 of the second press nip N2 and hence left the press nip N2, as viewed in the machine direction, the fibrous web continues along the shell surface of the heated drying cylinder, which drying cylinder now forms the drying section of the paper machine for final drying of the web. After the fibrous web has been transported over the distance D2 in the drying section, which transport again is caused by the rotation of the drying cylinder, the fibrous web meets with the doctor blade 5, which separates the fibrous web from the drying cylinder. This means that the distance D2 extends in the machine direction from the exit E2 of the second press nip N2 to the point at which the doctor blade 5 separates the web w from the drying cylinder. Said distance D2 constitutes the length of the drying section of the drying cylinder The length of the distance D2 may typically be at least half the circumferential length of the drying cylinder, i.e. 50 % of the circumferential length, preferably at least 67 % of the circumferential length of the drying cylinder. The fibrous web has now obtained a sufficiently high dry solids content to be self-supporting and continues on, possibly by passing some kind of equipment, such as measuring equipment, before the fibrous web may be rolled up in e.g. a reel-up.

Another conceivable embodiment could be that the suction roll 1 is replaced by a blind- drilled roll in combination with suction boxes for dewatering the paper web and the felt.

Yet another conceivable embodiment is to operate according to the concept, but wherein the press roll 1 is replaced by a guide roll, which could be seen as an additional roll 1 and which is disposed in bearing contact against the drying cylinder 2, whereby a transfer nip for transferring the fibrous web w to the drying cylinder is formed as a first nip Nl, whereas the felt F, which has been separated from the fibrous web in the transfer of the fibrous web to the drying cylinder, is guided by one or several guide rolls to the extended nip roll or shoe press, to once again meet with the fibrous web and dewater it. Dewatering equipment for dewatering the felt F may suitably be disposed somewhere downstream of the separation of the fibrous web w from the felt F, but upstream of the entry of the felt F into the extended nip roll 3.

Embodiments are also conceivable where the suction roll 1 does not form a nip with the drying cylinder 2, but is disposed so that the felt F and the fibrous web w are caused to follow the surface of the drying cylinder 2 for a distance Dl upstream of the nip N2 with the extended nip press roll 3. In such an arrangement, there is then only one nip N2. The suction roll 1 is then disposed at a spatial distance from the drying cylinder 2, and the felt F travels together with the tissue web w over the suction roll 1, and then all the way to the shell surface of the drying cylinder 2. The felt F and tissue web w meet the shell surface of the drying cylinder 2, and with the web w on the drying cylinder side of the felt F, at a contact point PI, and is then bearing against the external surface of the drying cylinder 2 all the way to the press nip N2 thereby travelling said distance Dl from the contact point PI of the drying cylinder 2 to the entrance El of the press nip N2. It is appreciated that there is no guide roll 4 disposed between the suction roll 1 and the press nip N2 in such an embodiment. On the other hand, the felt F will still be guided away from the drying cylinder 2 after the felt F has passed the second press nip N2. It is appreciated that if the suction roll 1 is disposed at a spatial distance from the drying cylinder 2, it is positioned in such a way relative to the drying cylinder 2 and the extended nip roll 3 that the felt F and the tissue web w are urged into bearing contact against the drying cylinder 2 at a certain distance Dl before the felt F and the tissue web w have arrived at the second press nip N2, which, again is the only nip in this embodiment. Also in such an embodiment, the tissue web w will be heated before arriving at the press nip N2 between the extended nip roll 3 and the drying cylinder 2. Thereby, the heated water contained in the tissue web can be pressed out of the tissue web w in the nip N2 more easily and the web w may be maximally dewatered before final drying of the web w in the subsequent drying section of the drying cylinder 2.

Extended nip rolls having an internal press body are usually designed such that the pressure profile in the nip where the extended nip roll is operating can be controlled in the machine direction. Since an extended nip roll having an internal press body is used in the arrangement and the method according to the invention, the pressure profile can be controlled such that a comparatively high maximum pressure is obtained in the press nip. For example, the press body 6 can be a flexible body with internal chambers that can be pressurized separately in a way which is described in US Patent publication No. 7527708 with reference to Figures 12 - 16 of that publication. In the present invention, the extended nip roll 3 is preferably used in such a way that the pressure profile in the machine direction exhibits a maximum pressure (a "pressure spike") amounting to 2.5 MPa - 5 MPa. A high level of the maximum pressure in the nip N2 contributes to efficient dewatering.

Possible machine speeds for a machine comprising the press section according to the invention is 1000 m/minute - 2300 m/minute. In practice, the machine speed may usually be in the range of 1300 m/min - 2200 m/min. In many realistic embodiments, the machine speed can be in the range of 1800 m/min - 2000 m/min. It should be appreciated, however, that one generally seeks to increase the machine speed in order to increase the production and the productivity. Therefore, the invention could in the future be applied to machines where the machine speed exceeds 2300 m/minute. At higher machine speeds, the time during which the web travels the distance Dl between the two nips Nl and N2 will become smaller, for which reason it may be justified to increase the distance Dl or possibly to try to increase the surface temperature of the drying cylinder 2 in such a case. The grammage of soft crepe paper manufactured in a machine comprising said press section according to the invention is preferably 15 - 25 g/m², more preferably 18 - 22 g/m².

It is appreciated that, irrespective of whether the extended nip roll 3 is an extended nip roll having a flexible press body 6 or a rigid (shape permanent) shoe, the press body 6 is surrounded by a rotating flexible belt forming the external surface of the extended nip roll 3, preferably a belt made of polyurethane, or containing polyurethane. The drying cylinder 2 is suitably heated from inside by hot steam. The steam may be under positive pressure and can have a temperature of up to about 180 °C. The temperature is lower on the external surface of the drying cylinder, since the external surface is cooled by the moist fibrous web.

The invention is not limited by what has been described hereinabove, but can be varied within the scope of the following claims.

Claims

1. An arrangement for dewatering a fibrous web (w) being manufactured in a paper or board machine, wherein the arrangement comprises a press roll (3) adapted to bear against a counter roll (2), whereby a press nip (N2) is formed by said bearing contact, characterized in that said counter roll (2) is a drying cylinder (2) heated from within by hot steam and that said fibrous web (w) is brought into contact with a shell surface of said drying cylinder (2) at a distance (Dl) upstream of an entrance (El) to said press nip (N2) as viewed in the machine direction (MD) of the paper or board machine.

2. The arrangement according to claim 1, characterized in that said arrangement comprises an additional roll (1), which is adapted to bear against said drying cylinder (2) at a position upstream of said press roll (3) as viewed in the machine direction (MD) of the paper machine, whereby a transfer nip is formed by said bearing contact, said additional roll (1) is arranged to bring said fibrous web (w) into contact with the shell surface of said drying cylinder (2) by said transfer nip.

3. The arrangement according to claim 2, characterized in that said additional roll (1) is a first press roll (1) arranged to form a first press nip (Nl) by said bearing contact and that the bearing contact between said press roll (3), which forms a second press roll (3), and said counter roll (2) forms a second press nip (N2) downstream said first press nip (Nl).

4. The arrangement according to claim 1, characterized in that said arrangement comprises a suction roll (1) disposed at a spatial distance from the drying cylinder (2) and arranged to cause the fibrous web (w) to follow the surface of the drying cylinder (2) for a distance (Dl) upstream of the press nip (N2).

5. The arrangement according to claim 1, characterized in that said press roll (3) is an extended nip roll having an internal press body.

6. The arrangement according to claim 3, characterized in that said distance (Dl) is arranged to substantially extend from an exit of the first press nip (Nl) at a contact point (P) to an entrance (El) of the second press nip (N2), and that said distance (Dl) is at least 0.5 m.

7. The arrangement according to claim 5, characterized in that said extended nip roll (3) is constituted by an extended nip roll having a flexible press body.

8. The arrangement according to claim 5, characterized in that said extended nip roll (3) is constituted by a shoe press roll having a rigid shoe.

9. The arrangement according to claim 3, characterized in that said first press roll (1) is a suction roll.

10. The arrangement according to claim 3 or 9, characterized in that said first press roll (1), used for bringing the fibrous web into contact with the shell surface of the counter roll (2), is constituted by a blind-drilled roll in combination with suction boxes for dewatering the paper web and the felt.

11. A method for dewatering a fibrous web (w) being manufactured in a paper or board machine, wherein the arrangement comprises a press roll (3) adapted to bear against a counter roll (2), whereby a press nip N2 is formed by said bearing contact, characterized in that the counter roll (2) is a drying cylinder (2) heated from within by hot steam and that the fibrous web (w) is transported on a shell surface of the drying cylinder (2) over a distance (Dl), said transport caused by the rotation (R) of the drying cylinder (2) in the machine direction (MD) of the paper or board machine, before the fibrous web (w) arrives at an entrance (El) to said press nip (N2).

12. The method according to claim 11, characterized in that said fibrous web (w) is brought into contact with said shell surface of the drying cylinder (2) by a an additional roll (1), which is in bearing contact with said drying roll (2) at a position upstream of said press roll (3) as viewed in the machine direction (MD) of the paper machine, whereby a first press nip (Nl) is formed by said bearing contact and upstream said press nip (N2), and said fibrous web passes through said first press nip (Nl).

13. The method according to claim 11, characterized in that the press roll (3) is an extended nip roll having an internal press body (6).

14. The method according to claim 11, characterized in that the maximum pressure in the press nip (N2) between the press roll (3) and the drying cylinder (2) is in the range of 2.5 MPa - 5 MPa.