EP3359734B1 - Method and machine for producing a fibrous web - Google Patents

Description

The subject of this invention is a process for producing a fibrous web, in particular for producing a tissue or tissue paper web. In this case, a pulp suspension is dehydrated to form a fibrous web in a Crescentformer and dried using a Yankee. In Crescentformer the pulp suspension is introduced via a headbox between a forming fabric and a felt and dewatered centrifugally in the region of a forming roll. The subject of this invention is also a device with which the method according to the invention can be carried out.

The production of high quality paper is traditionally done with TAD machines. These allow the production of very good product quality, but are very expensive to purchase and also the specific energy costs are far higher than in conventional drycrepe machines that have a Yankee.

In conventional tissue machines with crescent formers, ie with forming units in which the pulp suspension is introduced at a forming roll between a felt and a wire, the fibrous web is dewatered by the centrifugal forces occurring at the forming roll to about 10% dry content. Subsequently, the fibrous web is transported on the felt, dakuumentwässert to a dry content of about 20% to 23% vacuum and finally, after further dewatering of the wet felt by vacuum is no longer possible, mechanically pressed in a press section. The dry content increases about 40%. Thereafter, the thermal drying takes place on the Yankee.
The pressing of the fibrous web in a press section negatively affects the quality of the tissue web. By pressing the still wet paper web it loses bulk. However, the pressing is often necessary to achieve the required dry content before the web can be transferred to the Yankee.

The DE 10 2011 007 568 A1 describes a tissue machine in which the fibrous web is guided in front of the Yankee on a suction roll, which is wrapped by a permeable press belt. By the press belt, the fibrous web is less compressed than in conventional presses, but also occur thereby quality losses.

The US 3,224,928 discloses a paper machine with a crescent former having a forming roll, wherein directly after the forming roll a suction roll is arranged, over which the fibrous web is guided together with the felt and the wire.

The EP 1 837 439 A2 describes the ATMOS system from Voith. This is a system in which the fibrous web is dewatered using a permeable press belt. The EP 1 837 439 A2 specifically concerns the structure of the press belt.

The WO 01/00925 A1 describes a machine and a method for producing tissue in which a impingement dryer is arranged in front of the Yankee.

The WO 2009/063396 A1 discloses, inter alia, a tissue machine equipped with only two fabrics, a sieve and a felt.

The invention has for its object to provide a method for tissue production, can be produced in the highest possible tissue.

This object is achieved by a manufacturing method according to claim 1.

According to the invention, the fibrous web is passed together with the forming fabric and the felt immediately after the forming roll on a suction roll and further dehydrated there in the process.
In the area of the suction roll, no press belt is arranged, but the fibrous web is enclosed only by the forming fabric and the felt, thus a gentle drainage can take place. According to the invention, the felt is between the suction roll and the fibrous web and the forming fabric wraps around the fibrous web on the outside. Thus, a gentle pressure can be exerted on the fibrous web via the forming fabric, but in the region of the suction roll, the tensile stress of the forming fabric should be less than 15 kN / m, preferably less than 12 kN / m.

The fibrous web should preferably be flowed through by a hot fluid at the suction roll, for example, hot air at a temperature of about 150 ° C, in particular over 200 ° C, preferably above 250 ° C.

The humidity of the hot air supplied through the hood should preferably be above 150 gH ₂ O / kgAir, especially more than 300 gH ₂ O / kg air, preferably even more than 450 gH ₂ O / kg air. The supplied hot air should preferably be the exhaust air of the Yankee hood.

It is advantageous if the felt, the fibrous web and the forming fabric in the initial region of the suction roll, ie in the region in which the fibrous web comes into contact with the suction roll, are flowed through by steam. As a result, the temperature of the fibrous web is further increased, the viscosity of the water decreases and the vacuum dewatering is improved. The suction roll or the suction roll hood can also be divided into several zones, for example into two zones, viewed in the machine direction. This can be done in the first zone, a drainage with other operating parameters, for example, with a higher pressure, a higher temperature or with another medium.

Advantageously, the fibrous web is then transported on the felt to the Yankee and transferred there via a press or preferably a shoe press on the Yankee surface. The entire machine then only needs two strings, the forming fabric and the felt.

It is favorable if the transfer of the fibrous web to the Yankee takes place with the aid of a shoe press roll, which is wrapped by the felt more than 60 °, preferably more than 90 °, ideally more than 120 °. As a result, the currently used deflection roller can be omitted below the shoe press roll.

Compared to conventional machines, the dry content after the forming unit is not only 10%, but more than 20%, in particular more than 25%, preferably more than 30%. Between forming unit and Yankee there is still enough space available for further units. Thus, there can be carried out a further drying step, for example with an impingement dryer or with a radiation dryer (eg infrared radiator). The dry content is then greater than 25%, in particular greater than 30%, preferably greater than 35%.

The advantage is that the fibrous web reaches the press at the Yankee with a dry content of more than 30%, instead of only 20% to 23% in conventional systems. With this higher dry content, the fibers are more resistant to mechanical pressing. This results in a gain in bulk after the press.

It is favorable if the felt has a fine-pored structure, wherein the average pore size of the fibrous web-facing surface of the felt is smaller than the average pore size of the side facing the suction roll. A fine and soft felt top to the fibrous web increases the contact area between felt and fibrous web, which promotes Kapillarentwässerung. By contrast, a coarser felt structure towards the suction roll favors the removal of water through the perforated suction roll surface into the interior of the roll. The fineness of the finer felt surface should be less than 6.7 dtex, preferably less than 3.3 dtex, the layer directly below it should have a fineness of less than 17 dtex, preferably less than 11 dtex, whereas the opposite felt side facing the suction roll would then be much more open is to drain the water through the To facilitate drilling of the suction roll. These dtex values refer to the basic fiber content of the felt.

The subject of this invention is also an apparatus for the production of tissue according to claim 11.

It is also conceivable that the forming fabric is lifted off the fibrous web after the forming roll, dried and then brought into contact again with the fibrous web in front of the suction roll.

In the following an embodiment of the invention with reference to FIG. 1 described.

In FIG. 1 the pulp suspension is introduced in a Crescentformer 10 via a headbox 1 in the region of the forming roller 2 between a felt 4 and a forming fabric 3.

The felt 4 and the forming fabric 3 wrap around a part of the outer periphery of the forming roll 2, thereby the water of the pulp suspension is thrown by centrifugal forces through the forming fabric 3 to the outside. The felt 4 is arranged on the inside. The fibrous web 9 after the forming roll 2 has a dry content of about 10%.

Following this centrifugal dewatering, the felt 4, the fibrous web 9 and the forming fabric 3 are guided over a suction roll 11, which is looped in regions. The suction roller 11 sucks through the felt 4, the moisture from the fibrous web 9, it takes place here a vacuum dewatering.

In order to improve the drainage, a steam blower box 12 is arranged in the initial wrap area of the suction roll 11, via which hot steam flows onto the fibrous web 9 and heats it. The fibrous web 9 after the suction roll 11 has a solids content of about 25% to 30%.

Since the fibrous web 9 is still very moist in the area of the suction roll 11, evaporation processes hardly occur here. Here, rather, the viscosity of the water in the fibrous web 9 is reduced by the supply of heat, whereby the water is sucked through the suction roller 11 from the fibrous web 9. The fine-pored felt 4 supports drainage by capillary drainage.

After the suction roll 11, the forming fabric 3 is lifted off the fibrous web 9. This is followed by impact drying in the present example. Drying by means of radiation (for example infrared radiation) would also be conceivable. The impingement dryer 8 is arranged on the side of the fibrous web 9. The fibrous web then has a solids content of about 30% to 35%. Finally, the fibrous web 9 is transferred by means of a shoe press roll 5 from the felt 4 onto a Yankee 6. In the present embodiment, the shoe press roll 5 is wrapped by the felt 4 with a wrap angle α of ~ 175 °. At Yankee 6, the fibrous web 9 is dried in a known manner with hot air supplied via the Yankee hood 7 and scraped off at the end. The dry content of the fibrous web 9 when transferring to the Yankee 6 is approximately 50%.

Claims (14)

1. Method for production of a fibrous pulp web (9), especially for production of a tissue or sanitary paper web, in which a fibrous pulp suspension is dewatered in a Crescent former (10) to form a fibrous pulp web (9) and the fibrous pulp web (9) is dried with the aid of a Yankee (6), where the fibrous pulp suspension is fed through a headbox (1) in between a forming wire (3) and a felt (4) in the Crescent former (10) and is dewatered by centrifugal force in the area of a forming roll (2), where the fibrous pulp web (9) is guided over a suction roll (11) together with the forming wire (3) and the felt (4) directly after the forming roll (2), characterized in that the felt (4) is between the suction roll (11) and the fibrous pulp web (9) and in that the forming wire (3) is wrapped round the fibrous pulp web (9) on the outside in the area of the suction roll.
2. Method according to claim 1, characterized in that the fibrous pulp web (9) is wrapped round the suction roll (11) in places and a hot fluid flows through it there.
3. Method according to claim 2, characterized in that hot air at a temperature of more than 150°C, especially more than 200°C, preferably more than 250°C, flows through the fibrous pulp web (9) on the suction roll (11).
4. Method according to Claim 3, characterized in that damp, hot air flows through the fibrous pulp web (9) on the suction roll (11), where the moisture content is more than 150 g H₂O/kg air, especially more than 300 g H₂O/kg air, preferably even more than 450 g H₂O/kg air.
5. Method according to Claim 3 or 4, characterized in that the hot air applied is the exhaust air from a Yankee hood (7).
6. Method according to one of claims 2 to 5, characterized in that steam flows through the fibrous pulp web (9) in the initial section of the suction roll (11).
7. Method according to one of claims 1 to 6, characterized in that the fibrous pulp web (9) is conveyed to the Yankee (6) on the felt (4).
8. Method according to Claim 7, characterized in that the fibrous pulp web (9) is transferred to the Yankee (6) with the aid of a shoe press (5), where the felt is wrapped round the shoe press roll (5) at an angle of more than 60°, preferably more than 90°, and ideally more than 120°.
9. Method according to one of Claims 1 to 8, characterized in that the fineness of the felt surface facing the fibrous pulp web is less than 6.7 dtex, preferably less than 3.3 dtex, where the layer directly beneath it has a fineness of less than 17 dtex, preferably less than 11 dtex, and the fineness of the felt surface facing the suction roll is more than 17 dtex.
10. Method according to one of claims 1 to 9 characterized in that the fibrous pulp web (9) is pre-dried by an impingement dryer (8) before the Yankee (6) and after the suction roll (11).
11. Device for producing tissue with a Crescent former (10) and a Yankee (6), where the Crescent former (10) comprises a headbox (1), a forming roll (2), a felt (4), and a forming wire (3), where the felt (4) is located between forming roll (2) and fibrous pulp web (9), where a suction roll (11) is arranged immediately after the forming roll (2), where the felt (4), the fibrous pulp web (9), and the forming wire (3) are wrapped round the suction roll (11), characterized in that the felt (4) is between the suction roll (11) and the fibrous pulp web (9) and in that the forming wire (3) is wrapped around the outside of the fibrous pulp web (9) in the area of the suction roll.
12. Device according to Claim 11, characterized in that another thermal drying device (8), especially an impingement dryer, is provided after the suction roll (11) and before the Yankee (6).
13. Device according to one of Claims 11 or 12, characterized in that no other fabrics are provided in the tissue machine except the felt (4) and the forming wire (3) .
14. Device according to one of claims 11 or 13, characterized in that the fibrous pulp web (9) is transferred to the Yankee (6) with the aid of a shoe press roll (5) over which the felt (4) runs with an angle of wrap of more than 60°, preferably more than 90°, ideally more than 120°.

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