Drying section for producing kraft paper

Abstract

The invention relates to a drying section, in particular a post-drying section (20), for drying a fibrous web, for an installation for producing kraft paper, wherein the drying section comprises an impact drying region (71), which has at least one impact drying stage (83), in particular three impact drying stages (83), and each impact drying stage (83) is delimited upstream and downstream in the machine running direction (1) by a respective drying cylinder (72), which is paired with a drying screen (73) that follows the outer circumference of the drying cylinder (72) in a pressing region (74) and in particular presses a fibrous web passing through the drying section against the drying cylinder (72). The impact drying stage (83) is designed such that, between the outlet of the pressing region (74) located upstream in the machine running direction (1) and the inlet of the pressing region (74) located downstream in the machine running direction (1), a fibrous web passing through the drying section passes through a free shrinkage section of at least 15.0 m.

Description

[0001] Drying section for the production of kraft paper

[0002] The present invention relates to a dryer section for producing kraft paper as well as a kraft paper production plant, a method and a use according to the independent patent claims.

[0003] Processes for producing 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 stretchability or air permeability.

[0004] The properties of paper depend significantly on the conditions during its production. One object of the present invention can therefore be seen as providing a method and a device that can produce kraft paper with an improved property profile compared to the prior art.

[0005] 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 initial fiber suspension 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 here have a significant influence on the extensibility properties of the resulting paper.

[0006] Dewatering or drying takes place in various process steps and plant components. After initial dewatering of the fiber suspension in a wire section, the resulting fiber web is dried by thermally removing the water by heating the fiber web.

[0007] For this purpose, it is known that the fibrous web is subjected to a process known as impact drying. Impact drying is achieved by deflecting the fibrous web around heated cylindrical rollers and, during this process, being exposed to a stream of hot air 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 shrink freely within the impact drying section.

[0008] 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 outer circumference of a drying cylinder by drying screens or similar pressing devices.

[0009] 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.

[0010] Prior art plants exhibit certain disadvantages with regard to the production of stretchable papers. One object of the invention can therefore be seen as enabling the improved production of papers with high stretchability. Typically, a plant for producing kraft paper comprises several drying devices arranged one after the other (e.g., contact drying cylinders with or without impact drying hoods), with the entire drying device being referred to as the drying section.

[0011] The dryer section can be divided into several sections, with different sections in the machine direction usually being separated by another device for processing the fibrous web. A typical example in which several dryer section sections are provided is a plant used in particular for the production of sack kraft paper. According to the prior art, a first dryer section section, referred to as the pre-dryer section, is provided, followed by an edger for edgering the fibrous web. After passing through the edger, the fibrous web is led into a second dryer section section, referred to as the post-dryer section. If the edger is not used in such a plant, the fibrous web can be led past the edger through a bypass device in which essentially no treatment of the fibrous web takes place.Even then, there is a division into pre-drying section and post-drying section.

[0012] 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 section and an impact drying section, whereby the impact drying section usually follows directly after the contract drying section.

[0013] It is known that the impact drying area comprises several (e.g., three) impact drying sections through which the fibrous web is passed. The impact drying sections are typically arranged between two drying cylinders with an associated drying wire, with the drying wire pressing the fibrous web against the outer periphery of the drying cylinder in the contact area.

[0014] The inventors have now observed that dryer sections known in the prior art often do not allow for uniform shrinkage of the fibrous web 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 dryer section that enables the production of paper, in particular kraft paper, with high uniform extensibility.

[0015] The present invention therefore relates in particular to a dryer section, which preferably forms a post-dryer section of a plant for producing kraft paper, wherein the dryer 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 downstream of a contact drying area.

[0016] 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.

[0017] This enables improved free shrinkage of the fibrous web during the drying process, which ultimately allows improved control of the cross-direction stretch properties of the produced kraft paper.

[0018] The impact drying area is divided into several, for example three, impact drying sections. 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 fabric. Each drying roller with its associated drying fabric can be referred to as a contact drying section.

[0019] In a contact drying section, the drying fabric lies particularly partially against the outer circumference of the drying roller and thus forms a contact area in which the fibrous web is or can be pressed against the outer circumference of the drying roller.

[0020] The free shrinkage length is now in particular the length that a fibrous web travels 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.

[0021] Typically, no devices are provided in this area that press the fibrous web against the outer circumference of drying rollers or rollers.

[0022] Cylindrical rollers press, as is the case in the contact drying area.

[0023] An impact drying section, for example, comprises two or more impact drying units, each of which comprises a heatable cylindrical roller 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 enables the fibrous web to be heated from both sides.

[0024] The temperature of the heated cylinder roller is preferably above 100°C, 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 above the cylinder rollers, at least in sections, enabling particularly advantageous free paper web shrinkage.

[0025] 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 may be equipped with a drying hood or alternatively without one. In particular, this additional drying roller is not assigned a drying screen or other pressing device.

[0026] Preferably, the dryer section comprises three impact drying sections arranged one behind the other, configured as described here. The separation of the impact drying sections within the impact drying area can be formed by contact drying sections comprising 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. Optionally, the drying cylinders in this area can also be unheated to avoid additional transverse shrinkage of the paper web.

[0027] In the machine direction, upstream of the impact drying section, a contact drying section is provided, comprising drying cylinders with associated drying wires and no impact drying equipment. This drying section 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 centering the fibrous web in the system. In the subsequent impact drying section, the fibrous web shrinks through the drying process. The dry content of the fibrous web in the impact drying section is typically between 65% and 85%.

[0028] Each dryer fabric follows the outer circumference of the respective drying cylinder in a contact zone, with the contact zone comprising a certain portion of the outer circumference of the drying cylinder. The longer the length of the contact zone, the longer the contact time of the fibrous web with each individual drying cylinder and the greater the drying effect.

[0029] In order to vary the contact pressure with which the fiber 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 its displacement changes the tension exerted on the dryer fabric.

[0030] Typically, each drying cylinder in the contact drying section has a separately controllable drive. This allows for different rotation speeds to be set for the drying cylinders, which can offer further advantages in terms of draft buildup. 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 separately controllable drives.

[0031] The drying screens typically do not have their own drives, but are driven via the drying cylinders.

[0032] 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) can be introduced. The steam pressure can be up to 12 bar, for example.

[0033] 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 wires are provided. The drying cylinders of the contact drying area are arranged directly one after the other, meaning that no other drying devices, i.e., devices that exert a significant drying effect on the fibrous web, are provided between them.

[0034] The invention relates, where appropriate, to a drying section, in particular an after-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 upstream and downstream in the machine direction by a drying cylinder to which a drying fabric is assigned, which follows the outer circumference of the drying cylinder in a pressing area and in particular presses a fibrous web passing through the drying section against the drying cylinder.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 passes through a free shrinkage distance of at least 15.0 m 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.

[0035] Optionally, it is provided that the impact drying section comprises at least one impact drying device, wherein an impact drying device comprises a cylindrical roller around which the fibrous web is guided, and that a drying hood is associated with the cylindrical roller, which blows hot air onto the surface of the fibrous web.

[0036] Where appropriate, the impact drying section is provided free of drying screens.

[0037] If necessary, it is provided that the fibrous web rests freely on the outer circumference of the cylinder rollers in the impact drying section.

[0038] 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.

[0039] If necessary, it is provided that a drying hood is assigned to the additional drying cylinder, or that the additional drying cylinder is designed without a drying hood.

[0040] Optionally, it is provided, characterized in that the impact drying area follows a contact drying area in the machine direction, wherein at least two, in particular three, drying cylinders arranged one after the other in the machine direction are provided in the contact drying area, and wherein each drying cylinder is assigned an endlessly rotating drying wire which follows the outer circumference of the respective drying cylinder in a contact pressure area.

[0041] Optionally, the invention also relates to a plant for producing kraft paper comprising the following plant components:

[0042] - a wire section for forming a fibrous web by continuously applying a fibrous suspension along the machine direction through a headbox,

[0043] - a shaking device for shaking the fibrous web transversely to the machine direction, i.e. in the transverse direction,

[0044] - a press section for pressing the fibrous web partially dewatered in the wire section,

[0045] - a drying section for drying the fibrous web,

[0046] - a winding station for winding up the paper web formed from the fibrous web.

[0047] Where appropriate, the drying section includes a drying section as described here.

[0048] Where appropriate, the drying section is intended to comprise a pre-drying section and an after-drying section, and the after-drying section of the plant is a drying section as described here.

[0049] If necessary, it is provided that an upsetting device, in particular a Clupak device, is arranged between the pre-drying section and the after-drying section.

[0050] Optionally, the invention also relates to a process for producing kraft paper comprising the following steps:

[0051] - Forming a fibrous web running along the machine direction by continuously applying a fibrous suspension to a wire section through a headbox,

[0052] - Shaking the fibrous web transversely to the machine direction, i.e. in the transverse direction, by means of a shaking device, - Pressing the fibrous web, previously partially dewatered in the wire section, in a press section,

[0053] - further drying of the fibrous web in a drying section,

[0054] - 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 fabric is assigned, which follows the outer circumference of the drying cylinder in a pressing area and in particular presses a fibrous web passing through the drying section against the drying cylinder.

[0055] Optionally, it is provided that the fibrous web passes through a free shrinking section in the impact drying 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.

[0056] Where appropriate, the running speed of the fibrous web shall be at least 600 m / min.

[0057] If necessary, it is provided that cylinder rollers in the impact drying section are heated to a temperature of at least 110°C.

[0058] 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.

[0059] Optionally, it is provided 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.

[0060] 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, in particular in a process according to the invention.

[0061] Further features of the invention emerge from the patent claims, the figures and the description of the embodiment.

[0062] The present invention is explained in detail below using an exemplary embodiment.

[0063] They show:

[0064] Fig. 1a-c is a schematic overall view of a kraft paper manufacturing plant according to a first embodiment of the invention;

[0065] Fig. 2 is a schematic detailed view of a dryer section according to a second embodiment of the invention; and

[0066] Fig. 3 is a schematic detailed view of a dryer section according to the invention according to a third embodiment of the invention.

[0067] Unless otherwise indicated, the following features are shown in the figures: machine direction 1, wire section 2, headbox 3, shaking 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, pressing 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, impact drying section 83. Fig. 1 a c show a schematic overall view of a kraft paper production plant according to a first embodiment the invention.The system comprises, in the machine direction 1, a headbox 3, a wire section 2, a press section 5, a pre-drying section 19, an upsetting device 21, an after-drying section 20, a calendering device 22 and a winding station 7. The calendering device 22 can alternatively be designed as an embossing device.

[0068] The headbox 3 serves, in a known manner, to apply a fiber suspension to the continuously rotating dewatering wire 8 of the wire 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 can be transported away and / or fed to further processing steps.

[0069] The production speed of the system in this exemplary embodiment is approximately 1100 m / min. The resulting paper web has a paper width of approximately 6.4 m.

[0070] 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 inventive features of the plant relate in particular to the after-drying section 20.

[0071] 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 used in the plant shown in Fig. 1 to produce kraft paper.

[0072] The dryer section shown here comprises a contact drying area 70, followed by an impact drying area 71. Only the last part of the contact drying area 70 is shown in Fig. 2. The impact drying area 71 comprises three impact drying sections 83, also referred to as impact drying groups, each of which comprises two impact drying devices 77.

[0073] 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 by the cylindrical roller 79 and subjected to hot air blown by the drying hood 78, thereby undergoing a drying process. 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 is, at least in sections, not in direct contact with the outer surface of the cylindrical rollers 79.

[0074] 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.

[0075] 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.

[0076] The end of each impact drying section 83 is in turn 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.

[0077] The free shrink length is the length that the fibrous web 81 travels between its exit from the pressing area 74 located upstream (i.e., upstream) in machine direction 1 and its entry into the pressing area 74 located downstream (i.e., downstream) in machine direction 1. In other words, the free shrink length is the length over which the fibrous web 81 travels in machine direction 1 between two drying cylinders 72 with drying wires 73. Along the free shrink length, the fibrous web is given the opportunity to shrink.

[0078] 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 post-dryer section 20, is Fig. 1 b and c.

[0079] 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.

[0080] In terms of detailed structure and function, the dryer section shown in Fig. 1 is similar to that shown in Fig. 2.

[0081] 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.

[0082] In the impact drying devices 77, the cylindrical 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 cylindrical rollers 79. This allows for free shrinkage as the fibrous web 81 continues to dry.

[0083] The resulting kraft paper exhibits a variety of advantageous properties. The kraft paper produced according to the described embodiment has the following exemplary property profile:

[0084]

[0085] 'measured in an area ±5 cm from the geometric center of the paper web in its transverse direction

[0086] “measured in an area not exceeding 10 cm from the edge of the paper web in its transverse direction

[0087] 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 used in the plant shown in Fig. 1 to produce kraft paper.

[0088] In contrast to the embodiment shown in Fig. 2, the additional drying cylinders 80 are also equipped with a drying hood 78, which functions like the drying hoods 78 assigned to the cylindrical rollers 79. Consequently, in the embodiment according to Fig. 3, each impact drying section 83 has three impact drying devices 77, each of which in turn comprises a cylindrical roller 79 or a further drying cylinder 80, as well as a drying hood.

[0089] The remaining elements of the third embodiment are identical to those of the second embodiment, so reference is made to the relevant description.

Claims

1. A dryer section portion, in particular an after-dryer section (20), for drying a fibrous web, for a system for the production of kraft paper, wherein the dryer section portion comprises an impingement drying region (71), which has at least one impingement drying portion (83), in particular three impingement drying portions (83), and wherein, in the machine flow direction (1), each impingement drying portion (83) is delimited upstream and downstream by a respective drying cylinder (72), to which a drying wire (73) that follows the outer circumference of the drying cylinder (72) in a pressing region (74) and in particular presses a fibrous web passing through the dryer section portion against the drying cylinder (72) is assigned, characterised in that the impingement drying portion (83) is designed such that, between the outlet of the pressing region (74) arranged upstream in the machine flow direction (1) and the inlet of the pressing region (74) arranged downstream in the machine flow direction (1), a fibrous web passing the dryer section portion passes a free shrinkage segment of at least 15.0 m.

2. The dryer section portion according to claim 1, characterised in that the impingement drying portion (83) comprises at least one impingement drying apparatus (77), wherein an impingement drying apparatus (77) comprises a cylindrical roll (79) around which the fibrous web is guided, and in that a drying hood (78) blowing hot air onto the surface of the fibrous web is assigned to the cylindrical roll (79).

3. The dryer section portion according claim 1 or 2, characterised- in that the impingement drying portion (83) is free from drying wires, and / or- in that the fibrous web rests freely against the outer circumference of the cylindrical rolls (79) in the impingement drying portion (83).

4. The dryer section portion according claim 2 or 3, characterised in that the impingement drying portion (83) comprises at least two, in particular three, impingement drying apparatuses (77), and in that the impingement drying portion (83) comprises a further drying cylinder (80), wherein the additional drying cylinder(80) is arranged between the two cylindrical rolls (79) in the machine flow direction (1).

5. The dryer section portion according to claim 4, characterised in that a drying hood (78) is assigned to the further drying cylinder (80), or in that the further drying cylinder (80) is designed without a drying hood (78).

6. The dryer section portion according to any one of claims 1 to 5, characterised in that the impingement drying region (71) follows a contact drying portion (70) in the machine flow direction (1), wherein in the contact drying region (70) at least two, in particular three, drying cylinders (72) arranged one after the other in the machine flow direction (1) are provided in the contact drying region, and wherein a continuously circulating drying wire (73) is assigned to each drying cylinder (72), which follows the outer circumference of the respective drying cylinder (72) in a pressing region (74).

7. A system for producing kraft paper comprising the following system components: - a wire section (2) for forming a fibrous web by continuously applying a fibrous suspension along the machine flow direction (1) by a headbox (3),- a shaking apparatus (4) for shaking the fibrous web transversely to the machine flow direction (1), i.e. in the cross direction,- a press section (5) for pressing the fibrous web that has been partially dewatered in the wire section (2),- a dryer section (6) for drying the fibrous web,- a reeling station (7) for winding the paper web formed from the fibrous web, characterised in that the dryer section (6) comprises a dryer section portion as defined in any one of claims 1 to 6.

8. The system according to claim 7, characterised in that the dryer section (6) comprises a pre-dryer section (19) and an after-dryer section (20), and in that the after-dryer section (20) of the system is a dryer section portion as defined according to any one of claims 1 to 6.

9. The system according to claim 8, characterised in that a compacting apparatus (21), in particular a Clupak device, is arranged between the pre-dryer section (19) and the after-dryer section (20).

10. A method for producing kraft paper comprising the following steps:- forming a fibrous web extending in the machine direction (1) by continuously applying a fibrous suspension to a wire section (2) by a headbox (3),- shaking the fibrous web transversely to the machine direction, i.e., in the cross direction, using a shaking apparatus (4),- pressing the fibrous web, which has been partially dewatered in the wire section (2), in a press section (5),- further drying of the fibrous web in a dryer section (6),- winding the paper web formed from the fibrous web in a reeling station (7), wherein the dryer section (6) comprises an impingement drying region (71), which has at least one impingement drying portion (83), in particular three impingement drying portions (83), and wherein, in the machine flow direction (1), each impingement drying portion (83) is delimited upstream and downstream by a respective drying cylinder (72), to which a drying wire (73) that follows the outer circumference of the drying cylinder (72) in a pressing region (74) and in particular presses a fibrous web passing through the dryer section portion against the drying cylinder (72) is assigned,characterised in that the fibrous web passes through a free shrinkage segment in the impingement drying portion (83), which is arranged between the outlet of the pressing region (74) arranged upstream in the machine flow direction (1) and the inlet of the pressing region (74) arranged downstream in the machine flow direction (1), wherein the free shrinkage segment has a length of at least 15.0 m.

11. The method according to claim 10, characterised in that the travelling speed of the fibrous web is at least 600 m / min.

12. The method according to claim 10 or 11, characterised in that cylindrical rollers (79) in the impingement drying portion (83) are heated to a temperature of at least110°C, and / or in that drying hoods (78) in the impingement drying portion (83) are heated to a temperature of at least 160°C, and optionally up to 400°C.

13. The method according to any one of claims 10 to 12, characterised in that the fibrous web has a dry content of at least 55 wt%, in particular at least 65 wt%, when entering the dryer section portion and / or in that the fibrous web has a dry content of at most 95 wt%, in particular of at most 85 wt%, when leaving the dryer section portion.

14. Use of a dryer section portion according to any one of claims 1 to 6 in a method for the production of kraft paper, in particular in a method according to any one of claims 10 to 13.

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