EP4653614A1

EP4653614A1 - Drying group and a drying section for a fiber web production line

Info

Publication number: EP4653614A1
Application number: EP25175908.0A
Authority: EP
Inventors: Paavo Sairanen; Juha Korhonen; Elina VILLIKARI; Juha Kaihovirta
Original assignee: Valmet Technologies Oy
Current assignee: Valmet Technologies Oy
Priority date: 2024-05-23
Filing date: 2025-05-13
Publication date: 2025-11-26
Also published as: CN121006720A; FI20245653A1

Abstract

The invention relates to a drying group for drying a fiber web, which drying group is a single tier drying group i.e. applies single wire draw and comprises at least two drying cylinders (12), at least one turning roll (11) and a drying wire (10) supporting the run of a fiber web, in which drying group the fiber web that is being dried is arranged to run on support of the drying wire (10) such that the drying wire (10) presses the fiber web on the drying cylinder (12) against heated cylinder surface, and the fiber web remains at the side of the outside curve of the turning roll (11) situated below and between the drying cylinders (12), and in which drying group a pocket space (T) is confined by two adjacent drying cylinders (12) and the turning roll (11) situated between and below the drying cylinders (12) and by the drying wire (10). Geometry of the drying group is fully compact such that distances in at least one of the pocket space (T) of the drying group between the two adjacent drying cylinders (12) and between the drying cylinder (12) and the turning roll (11) are 10-50 mm. The invention also relates to a drying section.

Description

Technical field

The invention relates generally to production of fiber webs and to drying sections of fiber web production lines. Especially, the invention relates to a drying group according to the preamble of the independent drying group claim. The invention also especially relates to a drying section for a fiber web production line according to the preamble of the independent drying section claim.

Background

It is known that fiber webs, e.g., paper and board webs, are manufactured in devices and machines which together constitute a fiber web production line, which can be hundreds of meters long. As known from the prior art in fiber web production lines typically comprise an assembly formed by a number of the devices and the machines arranged consecutively in a process line. A typical production line for fiber web comprises a forming section comprising a head box and a wire section, a press section and a drying section and a reel-up. The production line can further comprise other sections and devices for treatment and/or finishing the fiber web, for example a sizer, a coating device, a calender. The production and treatment line also typically comprises at least one slitter-winder for forming customer rolls as well as a roll packaging apparatus.
As known from the prior art, drying groups of drying sections based on cylinder drying in a fiber web production line employ twin wire draw and/or single wire draw, i.e. twin or single tier drying groups. In single wire draw, i.e. in single tier drying groups, each group of drying cylinders comprises only one drying wire on whose support the fiber web runs through the entire group so that the drying wire presses the fiber web against the heated cylinder surfaces of the drying cylinders and the fiber web remains at the side of the outside curve of the turning rolls situated between the drying cylinders. Thus, in single wire draw in single tier drying groups, the drying cylinders are arranged outside the drying wire loop, and the turning rolls are arranged inside the loop. In the following description, by the term 'turning roll' is also meant a reversing roll or a reversing cylinder alternatively placed in a corresponding position, and these terms are to be understood as synonyms in this description and the claims. In the single tier drying groups of drying sections based on cylinder drying in fiber web production lines, a pocket space defined by a wire is formed between two adjacent drying cylinders and a turning roll situated between them in a lower row. In cross-direction the pocket space is typically limited by end seals located at respective ends of the pocket space. In connection with the pocket space, we speak of 'opening nips' and 'closing nips', i.e. 'opening gaps' and 'closing gaps', by which opening nip, or opening gap, is meant an area where the drying wire separates from the drying cylinder and, correspondingly, a closing nip, or a closing gap, is formed on the side of the pocket space when the drying wire runs to the turning roll. In a similar manner, when the drying wire leaves the turning roll, an opening nip, i.e. an opening gap, is formed on the outgoing side of the pocket space and, correspondingly, when the drying wire runs to the next drying cylinder, a closing nip, i.e. a closing gap, is formed between the drying wire and the drying cylinder.
As known from the prior art, by using different runnability components, such as blow and vacuum boxes, located in pocket spaces of drying groups runnablility of the drying section has been improved. These solutions comprise also drying groups of a drying section of a fiber web production line, in which in drying groups based on cylinder drying in the drying section, the run between a drying cylinder and a turning roll in the area of an opening gap has been arranged to be short. Traditional runnability components have seals in cross machine direction, against the drying wire and/or the cylinder for focusing the vacuum effect to at least some important fiber web wide parts of the pocket space for keeping the fiber web attached to the drying wire. The seals are prone to wear due moving surfaces, thermal elongation, changing underpressure and wire tension. This means that accurate and skilled assembly, control and maintenance of the seals is needed regularly. Sometimes, maintenance of the runnability component requires, it to be removed from its location in the pocket space.
In patent application publication EP1979534A1 is disclosed a drying section of a fiber web machine, in which drying section of the fiber web machine at least one drying group is a drying group which applies single wire draw and comprises at least two drying cylinders, at least one reversing cylinder and a wire supporting the run of a web, in which drying group the paper web that is being dried is arranged to run on support of the drying wire such that the drying wire presses the web on the drying cylinder against heated cylinder surfaces, and the web remains at the side of the outside curve of the reversing cylinders situated between the drying cylinders, and in which drying group a runnability component is placed in a pocket space confined by two adjacent drying cylinders and the reversing cylinder situated between them and by the drying wire, the drying cylinder and the reversing cylinder of the drying group are placed with respect to each other in such a way that the transfer of the web from the drying cylinder to the reversing cylinder is short, length of the transfer is 80 - 400 mm, and during said short transfer, a negative pressure effect is arranged to be applied by means of the runnability component to the web and to the drying wire supporting it, and for the purpose of confining an area of the negative pressure effect, seals of the runnability component are placed so as to be directed against the surface of the drying cylinder and against the surface of the reversing cylinder.
In patent application publication EP1979535A1 a drying section of a fiber web machine, in which dryer section of the fiber web machine at least one drying group is a drying group which applies single wire draw and comprises at least two drying cylinders, at least one reversing cylinder and a drying wire supporting the run of the web, in which drying group a paper web that is being dried is arranged to run on support of the drying wire such that the drying wire presses the web on a drying cylinder against heated cylinder surfaces, and the web remains at the side of the outside curve of the reversing cylinders situated between the drying cylinders, and in which drying group a pocket space is confined between two adjacent drying cylinders and the reversing cylinder situated between them, and the drying wire, and in which a negative pressure component is placed in at least one pocket space of the drying group to produce a negative pressure effect in the pocket space such that a pressure difference is effective over the drying wire and the web, and the drying cylinders and the reversing cylinder of the drying group are placed with respect to one another in such a way that the transfer of the web from the drying cylinder to the reversing cylinder and from the reversing cylinder to the next drying cylinder is short, whose length is 100 - 500 mm, and for the purpose of confining an area of the negative pressure effect, seals of the negative pressure component are placed so as to be directed against the surface of the drying cylinders, and the tension of the drying wire is at least 3 kN/m.
In the above examples known from the prior art the drying group has a so-called compact geometry, in which the wire draw limiting the pocket space has been made short by placing the respective drying cylinder close to the turning roll and a runnability component or a vacuum component has been located in the pocket space to confine an area of negative pressure effect. The runnability component or the vacuum component located in the pocket space increase the length of the drying section in machine direction. Even as the required space in the machine direction for one runnability or vacuum component is not big, the drying section typically has several drying groups, each typically provided with several runnability and/or vacuum components, and thus, the overall length requirement for these components in machine direction is signification. The runnability and vacuum components also require for example air systems and other equipment for operating, which also require space. It should also be noted that the runnability and vacuum components and their equipment also have a significant effect on overall manufacturing and operating costs of a drying section, as well as in investment and energy costs.
In patent publication FI102912B is disclosed in connection with an example of a drying group, that that distance between the drying cylinder and the turning roll can be 15 mm and that the distance between the drying cylinders is 205 mm, which in practise corresponds to a distance in a pocket space of a drying group provided with a traditional runnability component.
In patent publication US5539999A is disclosed that a single wire drying group can be done by a three-level geometry with staggered positioning of drying cylinder and turning rolls.
In patent publication US5068980A is disclosed a turnable partition wall located at a distance from a longitudinal end of a pocket space for creating an edge chamber at longitudinal edge area of the pocket space.
An object of the invention is to provide a drying group and a drying section of a fiber web production line to eliminate and/or minimize the above-noted problems and disadvantages associated with the drying groups known from prior art, in particular relating to problems and disadvantages of a runnability component placed in a pocket space of a drying group of a drying section.
A particular object of the invention is to provide an improved geometry of a drying group of a drying section, which is especially suitable for last drying groups of a drying section.
A particular object of the invention is to provide an improved geometry of a drying group of a drying section, by which cost savings, especially investment-wise, are achieved.
A particular object of the invention is to provide an improved geometry of a drying group of a drying section, by which energy savings are achieved.
A particular object of the invention is to decrease in production of runnability components and/or the systems amount, and number of materials needed.

Summary

To achieve the above-mentioned objects and those which come out later, the drying group according to the invention is mainly characterized by what is presented in the characterizing part of the independent drying group claim. The drying section according to the invention, in turn, is mainly characterized by what is presented in the characterizing part of the independent drying section claim. Advantageous features and embodiments of the invention are defined in dependent claims.
In this description and the claims by the term machine direction is meant the general process direction i.e., main running direction of the fiber web in the fiber web production line, as generally used in connection with fiber web production technology. By the term cross direction is meant the horizontal direction perpendicular to the machine direction. Further, it should be noted that by distances mentioned are meant the shortest distance between the mentioned objects, i.e. it is question of the distance measured between the closest points of the mentioned objects.
According to the invention the drying group for drying a fiber web is a single tier drying group i.e. applies single wire draw and comprises at least two drying cylinders, at least one turning roll and a drying wire supporting the run of a fiber web, in which drying group the fiber web that is being dried is arranged to run on support of the drying wire such that the drying wire presses the fiber web on the drying cylinder against heated cylinder surface, and the fiber web remains at the side of the outside curve of the turning roll situated below and between the drying cylinders, and in which drying group a pocket space is confined by two adjacent drying cylinders and the turning roll situated between and below the drying cylinders and by the drying wire, wherein geometry of the drying group is fully compact such that distances in at least one of the pocket space of the drying group between the two adjacent drying cylinders and between the drying cylinder and the turning roll are 10-50 mm.
According to an advantageous feature of the invention distances between the two adjacent drying cylinders and between the drying cylinder and the turning roll are 10-25 mm.
According to an advantageous feature of the invention distance between the two adjacent drying cylinders is 15-25 mm.
According to the invention the pocket space is closed at its longitudinal ends by end sealing and an end seal for the end sealing substantially covers cross-sectional area of the pocket space.
According to an advantageous feature of the invention the end seal is independently adjustable.
According to an advantageous feature of the invention the end seal comprises three curved concave end seals formed in a seal body.
According to an advantageous feature of the invention pocket space is free of runnability or vacuum components between the end seals.
According to an advantageous feature of the invention no air is supplied into the pocket space to effect the runnablility of the center areas of the fiber web.
According to an advantageous feature of the invention the turning roll is a vacuum turning roll.
According to an advantageous feature of the invention the vacuum turning roll is a perforated vacuum turning roll comprising vacuum connections.
According to an advantageous feature of the invention the vacuum turning roll comprises circumferential grooves.
According to an advantageous feature of the invention gap between the two adjacent drying cylinders is sealed by opposite directional boundary layer air flows of the circumferential surfaces of the two adjacent rotating drying cylinder.
According to an advantageous feature of the invention in connection with the drying cylinder a doctor beam is located.
According to an advantageous feature of the invention in connection with the doctor beam doctor ventilator is provided.
According to the invention the drying section for a fiber web production line comprises at least one single tier drying group, wherein at least one of the drying groups of the drying section is a single tier drying group according to the invention.
According to an advantageous aspect of the invention in the drying group applying the single tier drying, geometry is fully compact such that in at least one pocket space of the drying group distances between the two adjacent drying cylinders and the turning roll, which together limit the pocket space, are short 10-50 mm, advantageously 10-25 mm. Preferably the distance between the two adjacent drying cylinders is 15-25 mm and the distance between the drying cylinder and the turning roll is 10-25 mm. Thus, the cross-sectional area of the pocket space in view of the prior art drying groups is significantly decreased and thus, a more compact, fully compact, geometry of the single tier drying group is achieved. The pocket geometry of the single tier drying group is now in a surprising way compacted by dimensioning the drying cylinders and the turning roll diameter relations and/or distances between the drying cylinders and/or the turning roll, and thus, an improved drying group geometry, a fully compact geometry, is achieved. The fully compact geometry is thus formed by locating the drying cylinders close to each other and locating the turning roll in vertical direction close to both of the drying cylinders. Said fully compact geometry also provides that the fiber web wrap on the drying cylinder surface is 240-290 degrees, advantageously 260-280 degrees, and further it provides for savings in length of the drying section. The fully compact geometry fits to various dimensioning of drying and turning rolls.
According to an advantageous aspect of the invention inside of the pocket space between the end seals is empty i.e. free of runnability components extending through the pocket space, i.e. in cross direction in view of the main running direction extending structures or like are not located in the pocket space. This provides that no runnability or vacuum components are needed to be mounted or aligned inside the pocket space between the end seals, as the in the pocket space extending runnability or vacuum components can be omitted due to the fully compact geometry of the single tier drying group providing the runnability and vacuum properties inside the pocket space between the end seals.
According to an advantageous aspect of the invention no air is supplied into the pocket space to effect the runnablility of the cross directional center areas of the fiber web.
According to an advantageous aspect of the invention the pocket space is underpressurized only using as the turning roll a plain vacuum turning roll with perforation or a grooved vacuum turning roll with perforation. Preferably, the vacuum turning roll is a perforated vacuum turning roll comprising vacuum connections, by which the underpressure of the pocket space is operated. Further, preferably the vacuum is provided around the circumference of the vacuum turning roll such, that in addition to the pocket space also underpressure at the circumferential surface of the vacuum turning roll is operated. Advantageously, in addition to the perforation the mantle of the vacuum turning roll comprises circumferential grooves, which assists in distribution of the underpressure at the circumferential surface of the vacuum turning roll.
It has been surprisingly noted that in the gap between the two adjacent drying cylinders the opposite directional boundary layer air flows of the circumferential surfaces of the two adjacent rotating drying cylinder provide a sealing effect in the gap and thus, underpressure generated by the vacuum turning roll provides desired underpressure in the pocket space, as the opposite directional boundary layer air flows prevent leakage of air to the pocket space.
According to an advantageous aspect of the invention the pocket space is closed at its longitudinal ends by end sealing, i.e. by the end seals, which substantially cover cross-sectional area of the pocket space and which are located at the edge area of the drying wire such, that air leakage from outside the fiber web area through the drying wire is prevented to the by the end seals closed pocket space. Preferably the end seals are each supported only at its own side and thus, the end seals are independently adjustable. Advantageously, the end seal comprises three curved concave end seals, formed in a seal body such, that they form three triangular-shaped curved concave gap end seals contouring the surface of the respective cylinder. The seal body has a substantially triangular form and the gap end seals extend on the sides of the triangular form to the gap areas of the pocket space.
According to an advantageous aspect of the invention in connection with the drying cylinder in the drying group a doctor beam is provided, in connection of which doctor beam preferably doctor ventilator is provided to blow replacement air in vicinity of the fiber web to enhance drying of the fiber web and to support the fiber web against the drying wire.
According to an advantageous aspect of the invention the fully compact geometry of the drying group comprises 240-290 degrees, advantageously 260-280 degrees, wrap over the drying cylinders of the drying group.
According to an advantageous aspect of the invention at least one pocket space of a drying group is provided with the fully compact geometry. For example, a pocket space in the drying section located in connection with the transfer from one drying group to the next drying group may have a different geometry than other pocket spaces in the drying group.
By the invention and its advantageous features several advantages are achieved: A significantly shorter drying section in machine direction is achieved as the drying groups shorten by the inventive fully compact geometry of the drying groups. Further, the investment costs and the energy consumption is decreased as no runnability or vacuum components are needed in the pocket space to provide the required underpressure, created in the inventive drying groups by the fully compact geometry and the vacuum turning roll. In production of runnability components and/or the systems amount and number of materials needed is significantly decreased and also energy, raw materials consumption is significantly decreased. Thus, the fully compact geometry is sustainable and environmentally friendly.

Brief description of the drawings

Aspects of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of some example embodiments when read in connection with the accompanying drawings and in the following the invention is described in more detail referring to the accompanying drawing, in which

In figure 1 is schematically shown an example of a drying group known from prior art.
In figure 2 is schematically shown an advantageous example of a drying group according to the invention.
In figure 3 is schematically shown an example of dimensioning of a drying group known from prior art.
In figures 4A-4C is schematically shown advantageous examples of dimensioning of a drying group according to the invention.

Detailed description

In the following description same reference signs designate for similar components unless otherwise mentioned and it should be understood that the examples are susceptible of modification in order to adapt to different usages and conditions within the frames of the invention. Repetition of some reference signs may have been omitted in figures for clarity reasons.
In figure 1 shown an example known from prior art of a single tier drying group applying single wire draw for a drying section of a fiber web production line, drying cylinders 12 are located in an upper row and turning rolls 11 are placed in a lower row. A fiber web to be dried is arranged to run on support of a drying wire 10 from the drying cylinders 12 to the turning rolls 11 in a manner of single wire draw. Runnability or vacuum components 14 are placed in a pocket space T remaining between two adjacent drying cylinders 12 and a turning roll 11 and the drying wire F, which runnability or vacuum component 14 produces a negative pressure that is used for enhancing the runnability of the fiber web W in cylinder drying, in particular in an area of a gap opening from the drying cylinder 12. The runnability component 14 produces a negative pressure area on the run of the web and the wire 10 from the drying cylinder 12 to the turning roll 11, Said negative pressure area is confined by seals 25, 26 sealing the operating area of the runnability component 14 to the run of the wire 10 in the area between the surface of the drying cylinder 12 and the surface of the turning roll 11. The runnability component 14 is typically provided with seals, for example mechanical or air flow seals. In drying groups according to prior art the cross-sectional (in view of the machine direction area of the pocket space T is typically about 0,25 m², as shown in figure 3.
In figure 2 shown advantageous example of a single tier drying group, i.e. applying single wire draw for a drying section of a fiber web production line, drying cylinders 12 are located in an upper row and turning rolls 11 are placed in a lower row. Rotating direction of the drying cylinders 12 is indicated by arrows R12 and rotating direction of the turning roll 11 is indicated by arrow R11. A fiber web to be dried is arranged to run on support of a drying wire 10 from the drying cylinders 12 to the turning rolls 11 in a manner of single wire draw. In the drying group applying the single tier drying, geometry is fully compact such that distances between the two adjacent drying cylinders 12 and the turning roll 11, which together limit the pocket space T, are short 10-50 mm, advantageously 10-25 mm. Preferably, the distance between the two adjacent drying cylinders 12 is 15-25 mm and the distance between the drying cylinder 12 and the turning roll 11 is 10-25 mm. Thus, the cross-sectional area of the pocket space T in view of the prior art drying groups is significantly decreased, to even only 0,12 m² and thus, a more compact, fully compact, geometry of the single tier drying group is achieved. The fully compact geometry of the single tier drying group can be formed by locating the drying cylinders 12 close to each other and locating the turning roll in vertical direction close to both of the drying cylinders 12. Said fully compact geometry also provides that the fiber web wrap on the drying cylinder surface is 240-290 degrees, advantageously 260-280 degrees, and further it provides for savings in length of the drying section. The fully compact geometry fits to various dimensioning of drying cylinders 12 and turning rolls 11. The inside of the pocket space T is free, i.e. empty of components, i.e. no cross-structures or like are located in the pocket space T. The pocket space T is underpressurized only using as the turning roll 11 a perforated vacuum turning roll comprising vacuum connections, by which the underpressure of the pocket space T is operated. Further, preferably the vacuum is provided around the circumference of the vacuum turning roll 11 such, that in addition to the pocket space T also underpressure at the circumferential surface of the vacuum turning roll 11 is operated. Advantageously, in addition to the perforation the mantle of the vacuum turning roll 11 comprises circumferential grooves, which assists in distribution of the underpressure at the circumferential surface of the vacuum turning roll. In the gap between the two adjacent drying cylinders 12 the opposite directional boundary layer air flows of the circumferential surfaces of the two adjacent rotating R12 drying cylinder 12 provide a sealing effect in the gap and thus, underpressure generated by the vacuum turning roll 11 provides desired underpressure in the pocket space T, as the opposite directional boundary layer air flows prevent leakage of air to the pocket space. The direction of the boundary layer air flow corresponds the rotating direction R12 of the respective drying cylinder 12. The pocket space T is closed at its longitudinal ends by end sealing 21 by end seals 21, which substantially cover cross-sectional area A of the pocket space T. Preferably the end seals 21 are each supported only at its own side and thus, the end seals 21 are independently adjustable. Advantageously, the end seal 21 comprises an end seal body 22 with three triangular gap end seals 23. The seal body 22 has a substantially triangular form and the end seals extend between respective gap end seals 23, i.e. on the sides of the triangular form. In the drying group in connection with the drying cylinder 12 a doctor beam15 is arranged and in connection of the doctor beam 15 preferably doctor ventilator 16 is provided to blow replacement air in vicinity of the fiber web to enhance drying of the fiber web and to support the fiber web against the drying wire 10.
In the dimensioning example known from prior art of figure 3 of a single tier drying group, in which distance between the drying cylinder 12 and the turning roll 11 are shorth. In this example diameter of the drying cylinders 12 is 1830 mm and diameter of the turning rolls 11 is 1500 mm. The distance G1 between the drying cylinder 12 and the turning roll 11 at closest point is 15 mm and distance G2 between two adjacent drying cylinders 12 at closest point is 270 mm and distance L3 between two adjacent turning rolls 11 at closest point is 600 mm. Distance L2 between center axis of two adjacent drying cylinders 12 is 2100 mm and distance L1 between center axis levels in vertical direction of the drying cylinders 12 and the turning rolls 11 is 1312 mm. The overlap length of the drying wire 10 on the drying cylinders 12 is 4298 mm and the overlap length of the drying wire 10 on the turning rolls 11 is 3524 mm. Thus, in this drying group according to prior art the cross-sectional area A in view of the machine direction area of the pocket space T is 0,25 m².
In the advantageous example of figure 4A of dimensioning of a single tier drying group according to the invention, in which diameter of the turning roll is small, and thus an advantageous diameter ratio in the drying group is achieved. The wrap, i.e. the circumferential contact of the fiber web on the surface of the drying cylinder, i.e. drying length on the drying cylinder is increased and the drying cylinders 12 are close to each other, in this geometry nine drying cylinders 12 can be located compared to prior art arrangement eight drying cylinders. In this example diameter of the drying cylinders 12 is 1830 mm and diameter of the turning rolls 11 is 1250 mm. The distance G1 between the drying cylinder 12 and the turning roll 11 at closest point is 15 mm and distance G2 between two adjacent drying cylinders 12 at closest point is 20 mm and distance L3 between two adjacent turning rolls 11 at closest point is 600 mm. Distance L2 between center axis of two adjacent drying cylinders 12 is 1850 mm and distance L1 between center axis levels in vertical direction of the drying cylinders 12 and the turning rolls 11 is 1250 mm. The wrap length of the fiber web and the drying wire 10 having common run on the drying cylinders 12 is 4364 mm and the wrap length of the fiber web and the drying wire 10 having common run on the turning rolls 11 is 2982 mm. Thus, the cross-sectional area A of the pocket space T is 0,12 m².
In the advantageous example of figure 4B of dimensioning of a single tier drying group according to the invention, the diameter of the drying cylinders 12 is large, and thus, an advantageous diameter ration in the drying group is achieved: drying length on the drying cylinder is increased and in this geometry eighteen drying cylinders 12 require length of nineteen drying cylinders 12 but drying length of which eighteen drying cylinders 12 provide drying length increase of four drying cylinders 12. In this example diameter of the drying cylinders 12 is 2200 mm and diameter of the turning rolls 11 is 1500 mm. The distance G1 between the drying cylinder 12 and the turning roll 11 at closest point is 15 mm and distance G2 between two adjacent drying cylinders 12 at closest point is 20 mm and distance L3 between two adjacent turning rolls 11 at closest point is 720 mm. Distance L2 between center axis of two adjacent drying cylinders 12 is 2220 mm and distance L1 between center axis levels in vertical direction of the drying cylinders 12 and the turning rolls 11 is 1500 mm. The wrap length of the fiber web and the drying wire 10 having common run on the drying cylinders 12 is 5257 mm and the wrap length of the fiber web and the drying wire 10 having common run on the turning rolls 11 is 3587 mm. Thus, the cross-sectional area A of the pocket space T is 0,17 m².
In the advantageous example of figure 4C of dimensioning of a single tier drying group according to the invention, in which drying length increase is achieved with more compact geometry in view of the example of figure 4A, also evaporation length on the turning roll 11 is increased. In this example diameter of the drying cylinders 12 is 1830 mm and diameter of the turning rolls 11 is 1500 mm. The distance G1 between the drying cylinder 12 and the turning roll 11 at closest point is 16 mm and distance G2 between two adjacent drying cylinders 12 at closest point is 20 mm and distance L3 between two adjacent turning rolls 11 at closest point is 350 mm. Distance L2 between center axis of two adjacent drying cylinders 12 is 1850 mm and distance L1 between center axis levels in vertical direction of the drying cylinders 12 and the turning rolls 11 is 1404 mm. The wrap length of the fiber web and the drying wire 10 having common run on the drying cylinders 12 is 4460 mm and the wrap length of the fiber web and the drying wire 10 on the turning rolls 11 is 3657 mm. Thus, the cross-sectional area A of the pocket space T is 0,13 m².
In the description in the foregoing, although some functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments or examples, those features may also be present in other embodiments or examples whether described or not. Above the invention has been described by referring to some advantageous examples only to which the invention is not to be narrowly limited. Many modifications and alterations are possible within the invention as defined in the following claims.

Claims

Drying group for drying a fiber web, which drying group is a single tier drying group i.e. applies single wire draw and comprises at least two drying cylinders (12), at least one turning roll (11) and a drying wire (10) supporting the run of a fiber web, in which drying group the fiber web that is being dried is arranged to run on support of the drying wire (10) such that the drying wire (10) presses the fiber web on the drying cylinder (12) against heated cylinder surface, and the fiber web remains at the side of the outside curve of the turning roll (11) situated below and between the drying cylinders (12), and in which drying group a pocket space (T) is confined by two adjacent drying cylinders (12) and the turning roll (11) situated between and below the drying cylinders (12) and by the drying wire (10), characterized in, that geometry of the drying group is fully compact such that distances in at least one of the pocket space (T) of the drying group between the two adjacent drying cylinders (12) and between the drying cylinder (12) and the turning roll (11) are 10-50 mm and that the pocket space (T) is closed at its longitudinal ends by end sealing and that end seal (21) for the end sealing substantially covers cross-sectional area (A) of the pocket space (T).
Drying group according to claim 1, characterized in, that distances between the two adjacent drying cylinders (12) and between the drying cylinder (12) and the turning roll (11) are 10-25 mm.
Drying group according to claim 1 or 2, characterized in, that distance between the two adjacent drying cylinders (12) is 15-25 mm.
Drying group according to claim 1, characterized in, that the end seal (21) is independently adjustable.
Drying group according to any of claims 1-4, characterized in, that the end seal (21) comprises three curved concave gap end seals (23) formed in a seal body (22).
Drying group according to any of claims 1-5, characterized in, that the pocket space (T) is free of runnability or vacuum components between the end seals (21).
Drying group according to any of claims 1-6, characterized in, that no air is supplied into the pocket space (T) to effect the runnablility of the center areas of the fiber web.
Drying group according to any of claims 1-7, characterized in, that the turning roll (11) is a vacuum turning roll.
Drying group according to claim 8, characterized in, that the vacuum turning roll (11) is a perforated vacuum turning roll comprising vacuum connections.
Drying group according to claim 8 or 9, characterized in, that the vacuum turning roll (11) comprises circumferential grooves.
Drying group according to any of claims 1-10, characterized in, that gap between the two adjacent drying cylinders (12) is sealed by opposite directional boundary layer air flows of the circumferential surfaces of the two adjacent rotating drying cylinder (12).
Drying group according to any of claims 1-11, characterized in, that in connection with the drying cylinder (12) a doctor beam (15) is located.
Drying group according to claim 12, characterized in, that in connection with the doctor beam (15) doctor ventilator (16) is provided.
Drying section for a fiber web production line, which drying section comprises at least one single tier drying group, characterized in, that at least one of the drying groups of the drying section is a single tier drying group according to any of the previous claims.