AT527977A1 - Drying section for the production of kraft paper - Google Patents

Abstract

The invention relates to a drying section, in particular an after-drying section (20), for drying a fibrous web, for a plant for producing kraft paper, wherein the drying section comprises an impact drying area (71) which has at least one impact drying section (83), in particular three impact drying sections (83), wherein each impact drying section (83) is delimited upstream and downstream in the machine direction (1) by a drying cylinder (72) to which a drying fabric (73) is assigned, which follows the outer circumference of the drying cylinder (72) in a pressing area (74) and in particular presses a fibrous web passing through the drying section against the drying cylinder (72), wherein the impact drying section (83) is designed such that a fibrous web passing through the drying section is conveyed between the exit of the pressing area (74) arranged upstream in the machine direction (1) and the entrance the pressing area (74) arranged thereafter in the machine direction (1) passes through a free shrinkage distance of at least 15.0 m.

Description

Drying section for the production of kraft paper

The present invention relates to a dryer section for the production of kraft paper as well as a kraft paper production plant, a method and a

Use according to the independent patent claims.

Processes for the production of kraft paper are known in the art. Kraft paper is a special type of paper characterized, among other things, by its particularly high strength. Due to this property, it is used for various packaging applications, such as the production of paper bags. In addition to strength, other parameters are also important, depending on the specific application of the kraft paper, such as its extensibility or

the air permeability.

The properties of paper depend significantly on the conditions during its production. Therefore, one object of the present invention is to create a method and a device that provide a kraft paper with an improved property profile compared to the prior art.

can.

A critical step in the production of kraft paper is the drying of the fiber web, as a drastic increase in the dry content of the material must be achieved during the papermaking process. While the fiber suspension used initially usually has a dry content of less than 1%, the

Dry content of the finished paper web is typically at least 85%.

The drying processes that take place have a significant influence on the

Stretch properties of the resulting paper.

Dewatering or drying takes place in different process steps and plant sections. After initial dewatering of the fiber suspension in a wire section, the resulting fiber web is dried by thermal

Removal of water by heating the fibrous web.

For this purpose, it is known that the fibrous web is subjected to a so-called impact drying process. Impact drying is achieved by deflecting the fibrous web around heated cylinder rollers and, during this process, being exposed to a hot air stream to achieve drying. Advantageously, the temperature during cylinder drying is so high that the evaporating water creates a gas or vapor cushion, causing the fibrous web to glide over the cylinder surface. This allows the fibrous web to

an impact drying section can shrink freely.

Impact drying differs from contact drying, which is also known in the production of kraft paper, in that the fibrous web is not pressed against the surface by drying screens or similar pressing devices.

the outer circumference of a drying cylinder.

One important aspect of drying the fibrous web is the length of the area within which the fibrous web can shrink freely. This length, also known as the free shrink length, has a significant influence on the properties of the paper produced from the fibrous web, for example, its extensibility.

State-of-the-art systems have certain disadvantages with regard to the possibility of producing stretchable paper. Therefore, one object of the invention is to improve the production of paper with high stretchability.

make possible.

Usually, a plant for the production of kraft paper comprises several drying devices arranged one after the other (e.g. contact drying cylinders with or without impact drying hoods), whereby the entirety of the

Drying facilities are referred to as the drying section.

The dryer section can be divided into several sections, with different sections in the machine direction usually being separated by an additional device for processing the fibrous web. A typical example in which several dryer sections are provided is a plant that is used in particular for the production of sack kraft paper. According to the state of the art, a first dryer section, referred to as the pre-dryer section, is provided, which is followed by an upsetting device for upsetting the fibrous web. After passing through the upsetting device, the fibrous web is led into a second dryer section, referred to as the after-dryer section. If the upsetting device is not used in such a plant, the fibrous web can be led past the upsetting device via a bypass device, in which essentially no treatment of the fibrous web takes place. Even then, the division into

Pre-drying section and post-drying section.

Dryer section sections, which are used in particular as after-dryer sections, which are arranged in the machine direction after an upsetting device, can have a contact drying area and an impact drying area, whereby the impact drying area is usually directly connected to the contract drying area

follows.

It is known that the impact drying area comprises several (e.g. three) impact drying sections through which the fibrous web is guided. The impact drying sections are typically arranged between two drying cylinders with an associated drying wire, whereby the drying wire

Contact area presses against the outer circumference of the drying cylinder.

The inventors have now observed that known prior art

Dryer section sections often do not shrink the fiber web evenly

between the edge and the center of the fibrous web, which has a detrimental effect on the properties of the paper obtained from the fibrous web. A specific object of the present invention can therefore be seen in creating a drying section which facilitates the production of paper, in particular

Kraft paper, with high uniform stretchability.

The present invention therefore relates in particular to a drying section, which preferably forms a post-drying section of a plant for producing kraft paper, wherein the drying section comprises an impact drying area with at least one, preferably several, impact drying devices. The impact drying area is arranged in the machine direction, in particular directly after a

Contact drying area arranged.

Completely unexpectedly and surprisingly, it was discovered that the problems described above can be overcome in particular by ensuring that the free shrink length in each of the impact drying sections is at least 15 m, for example at least 17 m or at least 25 m. The free shrink length can be between

15 m and 25 m.

This allows for improved free shrinkage of the fibrous web during the drying process, which ultimately leads to improved control of the

Stretchability properties in the transverse direction of the produced kraft paper are allowed.

The impact drying area is divided into several, for example three, impact drying sections, whereby the individual impact drying sections can be delimited on both sides in the machine direction, i.e. before and after or above and below, by a drying roller with an associated drying screen. Each drying roller with the associated drying screen can be

Contact drying section.

In a contact drying section, the drying screen is located in particular

sectionally on the outer circumference of the drying roller and thus forms a

Contact area in which the fibrous web is pressed against the outer circumference of the

Drying roller is pressed or can be pressed.

The free shrinkage length is now in particular the length that a fibrous web has to cover from the exit from the pressing area arranged upstream in the machine direction to the entry into the pressing area arranged downstream in the machine direction.

goes through.

Typically, no devices are provided in this area that press the fibrous web against the outer circumference of drying rollers or rollers.

Cylindrical rollers press, as is the case in the contact drying area.

An impact drying section comprises, for example, two or more impact drying devices, each of which comprises a heatable cylinder roll that heats the fibrous web from one side and a drying hood that blows hot air onto the other side of the fibrous web. This ensures double-sided

Temperature supply to the fibrous web is possible.

The temperature of the heated cylinder roller is particularly high, for example, between 110°C and 160°C, so that the moisture escaping from the fibrous web creates a vapor cushion. Due to this vapor cushion, the fibrous web floats, at least in sections, above the cylinder rollers.

which enables particularly advantageous free paper web shrinkage.

In the machine direction, between the two impact drying devices, i.e. cylindrical rollers with drying hoods, a further, also heated, drying roller can be provided, which is equipped with a drying hood or alternatively without one. This additional drying roller is particularly

nor is a dryer fabric or other pressing device assigned to it. Preferably, the dryer section has three impact drying sections

one behind the other, which are designed as described here, wherein the separation of the

Impact drying sections within the impact drying area by

Contact drying sections can be formed, which comprise a drying cylinder with an associated drying wire. In particular, the drying cylinders in the contact drying sections are also heated, but at a lower temperature than the rollers or cylinders in the impact drying section. If necessary, the drying cylinders in this area can also be unheated.

in order not to create any additional transverse shrinkage of the paper web.

In the machine direction upstream of the impact drying area, a contact drying area is provided, which comprises drying cylinders with associated drying wires and no impact drying devices. This drying area serves in particular to stabilize the fibrous web after treatment in, for example, an upsetting device (e.g., a Clupak device). This stabilizing function consists specifically in enabling crease-free travel and in centering the fibrous web in the system. In the subsequent impact drying area, the shrinkage of the fibrous web takes place through the drying process. The dry content of the fibrous web in the

Impact drying range is typically between 65% and 85%.

Each dryer fabric follows the outer circumference of the respective drying cylinder in a contact area, whereby the contact area constitutes a certain section of the outer circumference of the drying cylinder. The longer the length of the contact area, the longer the contact time of the fibrous web with each

individual drying cylinder and the stronger the drying effect.

In order to be able to vary the contact pressure with which the fibrous web is pressed against the drying cylinder via the dryer fabric, at least one of the guide rollers used to guide the dryer fabrics can be designed as a movable tension roller. This tension roller is arranged in such a way that

their displacement changes the tension exerted on the dryer fabric. Typically, each drying cylinder in the contact drying area has

a separately controllable drive. This allows the setting of different

Rotation speeds of the drying cylinders, which offers further advantages in terms of

For example, it is possible for the rotation speed of successive drying cylinders to increase steadily, which is not possible in dryer sections with only one dryer wire and without a separate

controllable drives is not possible.

The dryer screens typically do not have their own drives, but they

are driven by the drying cylinders.

The drying cylinders can be heated separately, with heating from the inside. For this purpose, the drying cylinders are equipped with a steam supply channel through which saturated steam (water) is fed.

can be introduced. The steam pressure can, for example, be up to 12 bar.

In the contact drying area, which is arranged upstream of the impact drying area, at least two, preferably three, drying cylinders and a corresponding number of drying screens are provided. The drying cylinders of the contact drying area are arranged directly one after the other, which means that no other drying devices, i.e. devices that have a significant drying effect, are located between them.

on the fibrous web.

The invention relates, where appropriate, to a drying section, in particular a post-drying section, for drying a fibrous web, for a plant for producing kraft paper, wherein the drying section comprises an impact drying area which has at least one impact drying section, in particular three impact drying sections, wherein each impact drying section is delimited in the machine direction before and after by a drying cylinder, to which a drying fabric is assigned, which follows the outer circumference of the drying cylinder in a contact area and in particular presses a fibrous web passing through the drying section against the drying cylinder

presses.

If appropriate, it is provided that the impact drying section is designed in such a way that a fibrous web passing through the drying section has a

free shrinkage distance of at least 15.0 m.

Optionally, it is provided that the impact drying section comprises at least one impact drying device, wherein an impact drying device comprises a cylinder roller around which the fibrous web is guided, and that a drying hood is associated with the cylinder roller, which directs hot air onto the surface of the

Fibrous web inflates.

Where appropriate, the impact drying section is provided free of

Dry sieving is.

If necessary, it is provided that the fibrous web in the impact drying section

rests freely on the outer circumference of the cylinder rollers.

Optionally, it is provided that the impact drying section comprises at least two, in particular three, impact drying devices, and that the impact drying section comprises a further drying cylinder, wherein the further drying cylinder is arranged in the machine direction between the two cylinder rollers

is arranged.

If necessary, it is provided that a drying hood is assigned to the additional drying cylinder, or that the additional drying cylinder is provided without

drying hood is designed.

Optionally, it is provided, characterized in that the impact drying area follows a contact drying area in the machine direction, wherein in the contact drying area at least two, in particular three, drying cylinders arranged one after the other in the machine direction are provided

and each drying cylinder is provided with an endlessly rotating drying screen

which is assigned to the outer circumference of the respective

Drying cylinder follows.

Optionally, the invention also relates to a plant for producing kraft paper comprising the following plant components:

- a wire section for forming a fibrous web by continuously applying a fibrous suspension along the machine direction through a headbox, - a shaking device for shaking the fibrous web transversely to the machine direction, i.e. in the transverse direction,

- a press section for pressing the fibrous web partially dewatered in the wire section,

- a drying section for drying the fibrous web,

- a winding station for winding up the paper web formed from the fibrous web.

Where appropriate, the drying section includes a drying section as shown here

described.

Where appropriate, it is provided that the drying section comprises a pre-drying section and an after-drying section, and that the after-drying section of the plant comprises a

Dryer section as described here.

If necessary, it is provided that an upsetting device, in particular a Clupak device, is installed between the pre-dryer section and the after-dryer section.

is arranged.

Optionally, the invention also relates to a process for producing kraft paper comprising the following steps:

- forming a fibrous web running along the machine direction by continuously applying a fibrous suspension to a wire section through a headbox,

- Shaking the fibrous web across the machine direction, i.e. in the transverse direction, by

a shaking device,

- Pressing the fibrous web, previously partially dewatered in the wire section, in a press section,

- further drying of the fibrous web in a drying section,

- Winding up the paper web formed from the fibrous web in a winding station, wherein the drying section comprises an impact drying area which has at least one impact drying section, in particular three impact drying sections, wherein each impact drying section is delimited in the machine direction before and after by a drying cylinder, to which a drying wire is assigned, which follows the outer circumference of the drying cylinder in a contact area and in particular presses a fibrous web passing through the drying section against

presses the drying cylinder.

Optionally, it is provided that the fibrous web in the impact drying section passes through a free shrinking section which is arranged between the exit of the pressing area arranged upstream in the machine direction and the entrance of the pressing area arranged downstream in the machine direction, wherein the free shrinking section has a length of at least 15.0 m

has.

If necessary, it is provided that the running speed of the fibrous web

is at least 600 m/min.

If necessary, it is provided that cylinder rollers in the impact drying section are

heated to a temperature of at least 110°C.

If necessary, it is provided that drying hoods in the impact drying section are heated to a temperature of at least 160°C, if necessary up to 400°C.

If necessary, it is provided that the fibrous web enters the

Drying section has a dry content of at least 55 wt.%, in particular

of at least 65 wt.%, and/or that the fibrous web exits

from the drying section a dry matter content of not more than 95% by weight,

in particular of at most 85% by weight.

Optionally, the invention also relates to the use of a dryer section having one or more of the features described here, in particular a dryer section according to the invention, in a process for producing kraft paper, preferably in a process having one or more of the features described here

described features, in particular in a method according to the invention.

Further features of the invention emerge from the patent claims, the figures

and the description of the embodiment.

The present invention is explained in detail below using an exemplary embodiment.

They show:

Fig. 1a-c is a schematic overall view of a kraft paper manufacturing plant according to a first embodiment of the invention;

Fig. 2 is a schematic detailed view of a dryer section according to a second embodiment of the invention; and

Fig. 3 is a schematic detailed view of a drying section according to the invention.

Section according to a third embodiment of the invention.

Unless otherwise indicated, the following features are shown in the figures: Machine direction 1, wire section 2, headbox 3, jogging device 4, press section 5, dryer section 6, reeling station 7, dewatering wire 8, pre-dryer section 19, after-dryer section 20, upsetting device 21, calendering device 22, paper reel 25, contact drying area 70, impact drying area 71, drying cylinder 72, dryer wire 73, pressure area 74, guide roller 75, tensioning roller 76, impact drying device 77, drying hood 78, cylinder roller 79, further drying cylinder 80, fibrous web 81, displacement direction 82,

Pre-drying section 83.

Fig. 1a-c show a schematic overall view of a kraft paper production plant according to a first embodiment of the invention. The plant comprises, in the machine direction 1, a headbox 3, a wire section 2, a press section 5, a pre-dryer section 19, an upsetting device 21, an after-dryer section 20, a calendering device 22, and a winding station 7.

Calendering device 22 can alternatively be designed as an embossing device.

The headbox 3 serves, in a known manner, to apply a fiber suspension to the continuously rotating dewatering screen 8 of the screen section 2, thereby forming a fiber web. As the system progresses, the fiber web is continuously dewatered or dried, passing successively through the aforementioned system components. Finally, paper rolls 25 are formed, which are transported away and/or fed to further processing steps.

can.

The production speed of the system from this embodiment is

about 1100 m/min. The resulting paper web has a paper width of about 6.4 m.

The function of the individual plant components is sufficiently known to a specialist in the field of paper production and will not be explained in detail here. The features of the plant according to the invention relate in particular to the

Night drying section 20.

Fig. 2 shows an enlarged view of a dryer section according to a second embodiment of the invention in detail. The dryer section according to this embodiment can be

the plant shown in Fig. 1 to produce a kraft paper. The dryer section shown here comprises a contact drying area 70,

followed by an impact drying area 71. In Fig. 2 only the last part of the

Contact drying area 70 is shown.

The impact drying area 71 comprises three impact drying sections 83, also referred to as impact drying groups, each of which has two

Impact drying devices 77.

Each impact drying device 77 in turn comprises a drying hood 78 and a cylindrical roller 79 associated with this drying hood 78. The fibrous web 81, which passes through an impact drying device 77, is deflected via the cylindrical roller 79 and blown with hot air by the drying hood 78, thereby undergoing drying. Furthermore, the cylindrical roller 79 is heated, so that the moisture escaping from the fibrous web 81 creates a gas cushion, whereby the fibrous web 81, at least in sections, does not come into direct contact with the outer surface

the cylinder rollers 79 are in contact.

Between the two impact drying devices 77, there is an additional drying cylinder 80, which has a drive but no drying screen. The additional drying cylinder 80 is also heated.

The beginning of each impact drying section 83 is defined by the point at which the fibrous web 81 exits the pressing area 74, which, viewed in the machine direction 1, is located directly above or in front of the

Impact drying section 83.

The end of each impact drying section 83 is again defined by the point at which the fibrous web 81 enters the pressing area 74, which, viewed in the machine direction 1, is located directly below or after the

Impact drying section 83.

The free shrinkage length is now the length that the fibrous web 81 travels between its exit from the pressing area 74 arranged upstream in the machine direction 1 (i.e. upstream) and its entry into the pressing area 74 arranged downstream in the machine direction 1 (i.e. downstream). In other words: The free shrinkage length is the length in which the fibrous web 81 in

Machine direction 1 between two drying cylinders 72 with drying screens 73

Along the free shrink length, the fibrous web is given the opportunity to

shrink.

In the present embodiment, the free shrink length is approximately 17.5 m. A representation showing a complete dryer section according to the invention,

also used as a night drying section 20, is shown in Fig. 1b and c.

Here it can be seen that the fibrous web is fed directly from the compression device 21 into the after-drying section 20, which begins with a sequence of three drying cylinders 72 with separate drying wires 73. These three drying cylinders 72 form

the contact drying area 70 of the after-drying section 20 according to the invention.

In terms of detailed structure and function, the one shown in Fig. 1 is similar to

Dryer section that of Fig. 2.

In one embodiment of a method according to the invention, the fibrous web emerging from the compression device 21 has a dry content of approximately 65%

and is introduced into a post-drying section 20 designed according to the invention.

In the impact drying devices 77, the cylinder rollers 79 are heated to a temperature of approximately 110-160°C, so that the fibrous web 81 is also heated and the moisture escaping from the fibrous web 81 creates a vapor cushion that forms between the fibrous web 81 and the outer surface of the cylinder rollers 79. As the drying process progresses,

Fibre web 81 allows free shrinkage. The resulting kraft paper has a number of advantageous properties.

Kraft paper produced according to the described embodiment has the

The following exemplary property profile:

determines machine direction (MD) /

Property according to cross direction (CD) Value Grammage ISO 536 — 80 g/m² nn MD 82 Nm/g

Tensile strength index ISO 1924-3

CD 70 Nm/g Tensile Energy Absorption Index | ISO 1924-3 | MD and CD 3.5 J/g

MD 8.0% elongation ISO 1924-3

CD 8.3% Center Elongation* ISO 1924-3 | CD 8.0% Edge Elongation** ISO 1924-3 | CD 8.7% Gurley Drag ISO 5636-5 | -- 5s Cobbeo ISO 535 — 32 g/m² Ambertec Formation — — 0.5 (g/m²)

*measured in an area +5 cm from the geometric center of the paper web in its transverse direction

*measured in an area of maximum 10 cm from the edge of the paper web in its transverse direction

Fig. 3 shows an enlarged view of a dryer section according to a third embodiment of the invention in detail. The dryer section according to this embodiment can also be

The plant shown in Fig. 1 can be used to produce a kraft paper.

In contrast to the embodiment shown in Fig. 2, the further drying cylinders 80 are also equipped with a drying hood 78, which functions like the drying hoods 78 assigned to the cylinder rollers 79. Consequently, in the embodiment according to Fig. 3, each impact drying section 83 has three impact drying devices 77, which in turn each comprise a cylinder roller 79 or a further drying cylinder 80 as well as a

The remaining elements of the third embodiment are identical to those of the

second embodiment, so that reference is made to the relevant description

becomes.

Claims (1)

Patent claims 1. Drying section, in particular after-drying section (20), for drying a fibrous web, for a plant for producing kraft paper, wherein the drying section comprises an impact drying area (71) which has at least one impact drying section (83), in particular three impact drying sections (83), wherein each impact drying section (83) is delimited upstream and downstream in the machine direction (1) by a respective drying cylinder (72), to which a drying fabric (73) is assigned, which follows the outer circumference of the drying cylinder (72) in a pressing area (74) and in particular presses a fibrous web passing through the drying section against the drying cylinder (72), characterized in that the impact drying section (83) is designed such that a fibrous web passing through the drying section is conveyed between the outlet of the pressing area (74) arranged upstream in the machine direction (1) and the entrance of the pressing area (74) arranged downstream in the machine direction (1) passes through a free shrinkage distance of at least 15.0 m. 2. Drying section according to claim 1, characterized in that the impingement drying section (83) comprises at least one impingement drying device (77), wherein an impingement drying device (77) comprises a cylindrical roller (79) around which the fibrous web is guided, and that the cylindrical roller (79) is assigned a drying hood (78) which blows hot air onto the surface of the fibrous web. 3. Drying section according to claim 1 or 2, characterized in that - the impact drying section (83) is free of drying wires, and/or - that the fibrous web in the impact drying section (83) rests freely on the outer circumference of the cylinder rollers (79). 4. Drying section according to claim 2 or 3, characterized in that the impingement drying section (83) comprises at least two, in particular three, impingement drying devices (77), and that the impingement drying section (83) comprises a further drying cylinder (80), wherein the further Drying cylinder (80) is arranged in the machine direction (1) between the two cylinder rollers (79). Drying section according to claim 4, characterized in that a drying hood (78) is assigned to the further drying cylinder (80), or that the further drying cylinder (80) is designed without a drying hood (78). Drying section according to one of claims 1 to 5, characterized in that the impact drying area (71) follows a contact drying area (70) in the machine direction (1), wherein at least two, in particular three, drying cylinders (72) arranged one after the other in the machine direction (1) are provided in the contact drying area (70), and wherein each drying cylinder (72) is assigned an endlessly rotating drying wire (73) which follows the outer circumference of the respective drying cylinder (72) in a contact pressure area (74). Plant for the production of kraft paper comprising the following plant parts: - a wire section (2) for forming a fibrous web by continuously applying a fibrous suspension along the machine direction (1) through a headbox (3), - a shaking device (4) for shaking the fibrous web transversely to the machine running direction (1), i.e. in the transverse direction, - a press section (5) for pressing the fibrous web partially dewatered in the wire section (2), - a drying section (6) for drying the fibrous web, - a winding station (7) for winding the paper web formed from the fibrous web, characterized in that the drying section (6) comprises a drying section Section according to one of claims 1 to 6. Plant according to claim 7, characterized in that the drying section (6) comprises a pre-drying section (19) and a post-drying section (20), and that the 18 — 62956/MB/Mondi AG, Marxergasse 4A, 1030 Vienna (AT) The after-drying section (20) of the plant is a drying section according to one of claims 1 to 6. Plant according to claim 8, characterized in that a compression device (21), in particular a Clupak device, is arranged between the pre-drying section (19) and the after-drying section (20). Process for producing kraft paper comprising the following steps: - forming a fibrous web running along the machine direction (1) by continuously applying a fibrous suspension to a wire section (2) through a headbox (3), - shaking the fibrous web transversely to the machine direction, i.e. in the transverse direction, by a shaking device (4), - pressing the fibrous web previously partially dewatered in the wire section (2) in a press section (5), - further drying of the fibrous web in a drying section (6), - winding up the paper web formed from the fibrous web in a winding station (7), wherein the drying section (6) comprises an impact drying area (71) which has at least one impact drying section (83), in particular three impact drying sections (83), wherein each impact drying section (83) is delimited in the machine direction (1) before and after by a drying cylinder (72) to which a drying wire (73) is assigned, which follows the outer circumference of the drying cylinder (72) in a pressing area (74) and in particular presses a fibrous web passing through the drying section against the drying cylinder (72), characterized in that the fibrous web in the impact drying section (83) passes through a free shrinking section which is arranged between the exit of the pressing area (74) arranged upstream in the machine direction (1) and the entrance of the pressing area (74) arranged downstream in the machine direction (1), the free shrinking section having a length of at least 15.0 m. 11. Method according to claim 10, characterized in that the running speed of the fibrous web is at least 600 m/min. 12. Method according to claim 10 or 11, characterized in that cylindrical rollers (79) in the impact drying section (83) are heated to a temperature of at least 110°C, and/or that drying hoods (78) in the impact drying section (83) are heated to a temperature of at least 160°C, optionally up to 400°C. 13. Method according to one of claims 10 to 12, characterized in that the fibrous web has a dry content of at least 55 wt.%, in particular of at least 65 wt.%, upon entering the drying section and/or that the fibrous web has a dry content of at most 95 wt.%, in particular of at most 85 wt.%, upon leaving the drying section. 14. Use of a dryer section according to one of claims 1 to 6 in a process for producing kraft paper, in particular in a process according to one of claims 10 to 13.