EP2391769B1 - Device for producing a material web - Google Patents

Description

The invention relates to a drying device for drying a material web, in particular a paper, board or tissue web, which has an upper side and a lower side. The drying device comprises at least a first drying section and a second drying section, wherein the first drying section is substantially rectilinear and has a first impingement hood for direct loading of the upper side of the material web with hot drying medium. The underside of the material web is assigned a first drying wire for guiding the material web through the first drying section. The second drying section has a second impingement flow hood for direct loading of the lower side of the material web with hot drying medium, wherein the upper side of the material web is assigned a second drying fabric for guiding the material web through the second drying section and the second drying fabric is guided over at least one support surface.

Such drying devices are used in modern paper machines for high production speeds. These high-performance dryers work according to the impact flow principle. The paper web is charged with hot air and dried intensively. As the speed increases, the importance and the rate of drying of such high-performance dryers increases more and more. Until the first free draw of the paper web in the subsequent dryer section with drying cylinders, a certain minimum dry content is required for each type of paper so that the paper web has sufficient strength and does not tear. It follows for the design of the dryer section of a paper machine, that the length of the high-performance drying section increases more and more in comparison to the subsequent conventional drying with drying cylinders.

In the document DE102007018378A1 a generic drying device is described. Following the press section, the upper side of the paper web is dried in a horizontally running impingement-flow dryer and then, for drying the paper web underside, transferred to a vertically arranged impingement-flow dryer. The paper web is supported by rollers in both impingement dryers.

In the execution according to EP 1 281 807 A2 If the material web is always guided between two screen belts in the first drying section, direct application of pressure is not possible, but only through the dryer wire belt. This applies analogously also to those in the document EP1 072 722 A2 described embodiment.

In these known arrangements, the drying capacity required for increasing the machine speed can be increased by extending the horizontal impingement flow path of the first high-performance dryer. However, a disadvantage is the runability of the paper web, which deteriorates with high machine speed. This is especially true in the second drying section in which the paper web underside is dried in impingement dryer. The respective drying wire is supported by rollers in the first and in the second drying section. As a result, narrowing and widening gaps between the drying wire and the rollers are produced on each roller. These lead to pressure pulses, which detach the web, especially at the edges of the dryer fabric. This can lead to web breaks and wrinkles, especially at high speeds.

It is therefore the object of the invention to provide a drying apparatus which enables intensive and efficient drying and flexible and economic adaptability of the drying capacity to the production requirements while ensuring improved, safe runability of the paper web at high speed.

The object is solved by the features of claim 1. A drying device is provided for drying a material web, in particular a paper, board or tissue web, which has an upper side and a lower side. The drying device comprises at least a first drying section and a second drying section, wherein the first drying section is substantially rectilinear and has a first impingement hood for direct loading of the upper side of the material web with hot drying medium. The underside of the material web is assigned a first drying wire for guiding the material web through the first drying section. The second drying section has a second impingement flow hood for direct loading of the lower side of the material web with hot drying medium, wherein the upper side of the material web is assigned a second drying fabric for guiding the material web through the second drying section and the second drying fabric is guided over at least one support surface. The solution according to the invention is characterized in that the at least one support surface is designed to be air-permeable and low-pulsation.

The inventive solution ensures that the bottom of the paper web safely and reliably rests on the dryer fabric, even at high speeds. This is particularly advantageous in the case of drying by means of impingement-flow dryers, in which the material web is not guided between two dryer fabrics, so that the hot drying medium can impinge directly on the underside of the material web and thus dry it efficiently. Due to the low-pulsation design of the support surface of the dryer fabric no pressure pulses which lead to the detachment of the web from the dryer fabric. An air-permeable support surface makes it possible to suction the support surface and thus to hold the material web even more firmly on the dryer fabric. This is especially true when drying the Bottom of the web important to keep the web against gravity on the drying wire.

Hot air and / or steam can be used as the drying medium.

The invention has a particularly advantageous effect at speeds of greater than 1700 m / min, in particular greater than 1800 m / min.

Due to the straight-line arrangement of the first drying section, the drying capacity can be flexibly adapted to the production requirements by the adaptation of the length of this first drying section during its design. There are, in contrast to an impingement flow drying on a support roller or a support cylinder, which can not be made arbitrarily large, long drying distances can be realized. Under straight is according to the invention, a straight and / or a slightly curved course of the drying section to understand. A slightly curved course has the advantage of better stabilization of the web on the dryer fabric. The curvature has a radius of greater than 10 m, preferably greater than 15 m.

In an advantageous embodiment of the invention, the at least one support surface is evacuated. A small negative pressure is sufficient. It can be in the range between 1 hPa to 200 hPa, in particular between 1 hPa and 100 hPa.

According to the invention, the first drying section may be formed with a support surface corresponding to the support surface of the second drying section.

Advantageously, the support surface perforations or holes or openings. As a result, a good support effect and a low-pulsation stabilization of the material web is achieved at the same time.

According to a further embodiment with low pulsation, the support surface is designed as a stationary, flat and / or curved plate in the web running direction. This design is inexpensive to manufacture.

In a preferred practical low-pulsation embodiment, the support surface of the second drying section is formed by the jacket of a support roller. In contrast to the plate, this solution has the advantage that no relative movement between the dryer and the support surface occurs and thus no wear due to friction. The backup roll has a perforated, for example drilled coat. For a sufficient drying capacity, a diameter in the range between 3 m and 6 m is sufficient.

In a further practical embodiment, the inner surface of the jacket of the support roller, at least in a partial region of the loop through the second dryer wire, associated with a suction box, wherein the sealing strip is located upstream of the start of the suction box of the material web. This avoids that the pressure pulse generated by the sealing strip lifts the material web from the screen and thus causes runability problems. The suction box can be divided in the web running direction into several sections with different pressures.

Preferably, the second drying section immediately follows the first drying section. In this case, the material web is transferred from the first drying wire to the second drying wire with the assistance of a suction zone arranged in the second drying wire.

In a practical embodiment variant, the first impingement flow hood and / or the second impingement flow hood are / are formed in the web running direction and / or in the transverse direction by a plurality of part hoods.

Advantageously, the drying performance of the first impingement flow hood and / or the second impingement flow hood can be set or regulated in the web running direction and / or in the transverse direction.

In a practical embodiment, the first drying wire is also guided over at least one air-permeable and low-pulsation supporting surface, corresponding to the support surface for the second drying wire.

In a further aspect, the invention relates to a paper machine for producing a material web, in particular a paper, board or tissue web, comprising a press section and a drying section, wherein the drying section comprises at least one drying device according to the invention.

In a preferred embodiment, the drying device according to the invention is preceded by a press section consisting of at least one extended press nip. Such press sections are also referred to as Single NipcoFlex presses. For certain types of paper also press sections come into question, which consist of two consecutively arranged extended press nips. Such press sections are referred to as Tandem NipcoFlex presses. Prolonged press nips are preferably formed from a respective shoe roll with a counter roll, wherein the paper web is guided between two bands through the nips. The bands may consist of two felts or even of a felt and a smooth, air-permeable or impermeable band.

For paper grades with higher surface roughness requirements, such as for SC papers, in a further embodiment of the invention, the drying device is preceded by a press section with at least one extended press nip and a downstream smoothing device. The smoothing device is formed by a roller and / or belt with a smooth surface and an evacuated counter-roller. In this case, the material web is transferred from a lower clothing of the last press nip with a smooth surface to a transfer belt and from there to a counter-roller wraps around, air-permeable fabric and passed through the smoothing nip of the smoothing device.

In a further preferred embodiment of the paper machine, the drying device is preceded by a press section with a compact press and a downstream smoothing device. The smoothing device is formed by a roller and / or belt with a smooth surface and an evacuated counter-roller. In this case, the material web is transferred from a center belt with a smooth surface, which wraps around the central roller, onto a transfer belt and from there onto an air-permeable clothing wound around the counter-roller of the smoothing device and guided through the smoothing nip of the smoothing device.

In a further preferred embodiment, the material web is guided in a closed train through the press section and through the drying device.

The solution according to the invention, in addition to a stable web run during the production operation, also permits a web-width transfer of the paper web 100 after a demolition or when the paper machine is restarted. This is reliably possible only with pulsation running support surfaces.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings.

Figur 1

eine erste Ausführungsform einer Papiermaschine mit einer erfindungsgemäßen Trocknungsvorrichtung mit vor gelagerter Pressensektion

Figur 2

eine zweite Ausführungsform einer Papiermaschine mit einer erfindungsgemäßen Trocknungsvorrichtung mit vor gelagerter Pressensektion mit Glättvorrichtung

Figur 3

eine dritte Ausführungsform einer Papiermaschine mit einer erfindungsgemäßen Trocknungsvorrichtung mit vor gelagerter Pressensektion mit Glättvorrichtung

Show it:

FIG. 1

a first embodiment of a paper machine with a drying device according to the invention with pre-stored press section

FIG. 2

a second embodiment of a paper machine with a drying device according to the invention with pre-stored press section with smoothing device

FIG. 3

a third embodiment of a paper machine with a drying device according to the invention with pre-stored press section with smoothing device

The FIG. 1 shows an embodiment of the drying device 1 of a paper machine. The drying device consists of a slightly curved first drying section 2 and an immediately following second drying section 3. The paper web 100 is transferred from a transfer belt 30 in the region of a suction roll 5 to the drying wire 20. This is supported in the region of the first drying section 2 by guide rollers 6. The arrangement of the guide rollers form a polygon, which corresponds to a radius of 15 m. As a result, the paper web 100 is securely guided. The top 101 of the paper web 100 is free and not covered by another sieve. The hot drying medium emerging from the impingement flow hood 4 can thus reach the paper surface 101 unhindered. At the end of the first drying section 2, the paper web 100 and the first drying wire 20 are guided around a suction roll 7. In the course of the paper web 100 passed to the second drying wire 22. In the transfer area, a suction element is arranged to transfer the paper web 100 from the first drying wire 20 to the second drying wire 22. The suction element can also be realized by a suction zone in the support cylinder 10. The second drying wire 22 partially wraps around a support cylinder 10, a steam-heated drying cylinder 11, a vacuumed deflection roller 12 and a further drying cylinder 13. On this, the second drying wire 3 is separated from the paper web and returned via the guide rollers 9. The paper web is guided in a free train to the next drying section. The support cylinder 10 has a drilled lateral surface 103, which is evacuated via a suction box in the wrap area of the second dryer fabric 3. The underside 102 of the paper web 100 is free and not covered by another sieve. The hot drying medium emerging from the impingement flow hood 8 can thus reach the paper surface 101 unhindered. The impingement flow hood 8 is divided into two in this example. A one-piece design but also possible. The air volume flow and the temperature can be adjusted separately in each part. In the case of a tear of the paper web 100, both hood parts 8 can be opened, so that the paper residues can fall into the machine cellar for disposal. In order to prevent the web run on the support cylinder 10 from becoming unstable due to gravity, the negative pressure in the suction box of the support cylinder 10 is 40 hPa.

The drying device 1 is preceded by a press section 200. The paper web 100 is transferred from a forming section to the top felt 50 of the first press nip and passed through the shoe press nip 201 together with another felt 51. This is formed by a shoe roll 52 and a counter roll 53. In the further course, the paper web is removed by the upper felt 40 and with the aid of a suction roll 44 from the lower felt 51 of the first press 201 and guided by the second shoe press nip 202. Subsequently, the web 100 is transferred through the transfer belt 30 from the lower belt 41 of the second press 202 and transferred to the drying device 1.

The paper machine in FIG. 2 is different from the one in FIG. 1 only by the execution of the press section 205. The press section 205 is composed of only one extended nip 203 and a downstream smoothing press 300 together. The paper web is removed by the upper felt 40 of the press 203 from the forming fabric 500 and guided by the press nip 203, which is formed by the shoe roll 42 and the backing roll 43. Thereafter, the web is transferred by the transfer belt 304 to the calender 300. This is formed from an evacuated counter roll 302, which is wrapped by an air-permeable, fine felt 303 and a smooth smoothing roll 301. This smoothing roll smoothes the top 101 of the paper web.

The FIG. 3 shows the drying device 1 according to the invention in combination with another variant of a press section 206. This press section 206 is by a so-called compact press 400 with three press nips and a smoothing press 300 analogous to FIG. 2 educated. The compact press 400 produces a two-sided paper web 100 with respect to the paper web smoothness. The top 101 after the press is rougher than the bottom 102. This roughness difference is compensated in the subsequent smoothing press 300 by smoothing the top 101.

LIST OF REFERENCE NUMBERS

1

drying device

2

first drying section

3

second drying section

4

first impingement hood

5, 7

suction roll

6

guide roll

8th

second impingement hood

9

guide roll

10

supporting cylinders

11

drying cylinders

12, 13

deflecting

14

Web direction

20

first drying wire

22

second drying wire

30

transfer tape

31

suction roll

40, 50

felt

41

press belt

42, 52

shoe roll

43, 53

backing roll

44

suction roll

54

suction roll

100

Material web, paper web

101

Top of the material web, paper web

102

Bottom of the web, paper web

103

support surface

200

Press section

205, 206

Press section

201, 202

extended press nip

203

extended press nip

300

smoothing device

301

smoothing roll

302

suctioned counter roll

303

breathable tape

304

transfer tape

400

compact Press

401

suction press

402

press roll

403

Shoe press roll

404

central roll

405

bottom felt

406

central belt

407

Pick-up felt

500

forming fabric

Claims (15)

1. Drying apparatus (1) for drying a material web (100), in particular a paper, cardboard or tissue web, which has an upper side (101) and an underside (102), the drying apparatus (1) comprising at least a first drying section (2) and a second drying section (3), the first drying section (2) running substantially rectilinearly and having a first impingement flow hood (4) for loading the upper side (101) of the material web (100) with hot drying medium, the underside (102) of the material web (100) being assigned a first dryer fabric (20) for guiding the material web (100) through the first drying section (2), and the second drying section (3) having a second impingement flow hood (8) for direct loading of the underside (102) of the material web (100) with hot drying medium, the upper side (101) of the material web (100) being assigned a second dryer fabric (22) for guiding the material web (100) through the second drying section (3), and the second dryer fabric (22) being guided over at least one supporting face (103), characterized in that the upper side of the material web which is loaded directly with hot drying medium is free and is not covered by a further fabric belt, and the at least one supporting face (103) is of air-permeable and low-pulsation configuration.
2. Drying apparatus (1) according to Claim 1, characterized in that the supporting face (103) is evacuated.
3. Drying apparatus (1) according to Claim 1, characterized in that the supporting face (103) has perforations or holes or apertures.
4. Drying apparatus (1) according to at least one of the preceding claims, characterized in that the supporting face (103) is configured as a stationary plate which is flat and/or curved in the web running direction (14).
5. Drying apparatus (1) according to at least one of the preceding claims, characterized in that the supporting face (103) is formed by the shell of a supporting roller (10).
6. Drying apparatus (1) according to Claim 5, characterized in that the inner face of the shell of the supporting roller (10), at least a part region of the area wrapped around by the second dryer fabric (22), is assigned a suction box, the sealing strip at the beginning of the suction box being positioned in front of the run-on line of the material web (100).
7. Drying apparatus (1) according to Claim 1, characterized in that the second drying section (3) immediately follows the first drying section (2).
8. Drying apparatus (1) according to Claim 1, characterized in that the first impingement flow hood (4) and/or the second impingement flow hood (8) are/is formed in the web running direction (14) and/or in the transverse direction by a plurality of part hoods.
9. Drying apparatus (1) according to at least one of the preceding claims, characterized in that the drying performance of the first impingement flow hood (4) and/or the second impingement flow hood (8) can be set or regulated sectionally in the web running direction (14) and/or in the transverse direction.
10. Drying apparatus (1) according to Claim 1, characterized in that the first dryer fabric (2) is guided over at least one air-permeable and low-pulsation supporting face, in particular according to at least one of Claims 2, 3 and 4.
11. A papermaking machine for producing a material web (100), in particular a paper, cardboard or tissue web, comprising a pressing section (200) and a drying section, characterized in that the drying section comprises at least one drying apparatus (1) according to one of Claims 1 to 10, and the material web is transferred by a transfer belt (30) in the region of a suction roller (5) to the dryer fabric belt (20) of the first drying section (2).
12. Papermaking machine according to Claim 11, characterized in that a pressing section (200), consisting of at least one extended press nip (201, 202), is positioned in front of the drying apparatus (1).
13. Papermaking machine according to Claim 11, characterized in that a pressing section (200) having at least one extended press nip (203) and a calendering apparatus (300) arranged downstream of the latter is positioned in front of the drying apparatus (1).
14. Papermaking machine according to Claim 11, characterized in that a pressing section (200) having a compact press (400) and a calendering apparatus (300) which is arranged downstream of the latter is positioned in front of the drying apparatus (1).
15. Papermaking machine according to one of the preceding claims, characterized in that the material web (100) is guided in a closed draw through the pressing section (200) and through the drying apparatus (1).

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