EP0427218B1 - Drying system - Google Patents

Description

The invention relates to a drying device for high-speed moving material, in particular paper or fibrous webs, which are expediently from a number of steam-heated cylinders, in particular essentially on the same horizontal plane, and expediently from a series of unheated cylinders, approximately in the spaces between these cylinders , in particular likewise in a deflecting roller mounted either below or above the aforementioned horizontal plane, the jacket of which is perforated and / or provided with grooves, suction of air from these deflecting rollers is provided and these cylinders and the deflecting rollers are covered with a screen belt are equipped and the web of material on the cylinders is between their jacket and the screen belt or the like, while on the deflection rollers the screen belt comes to rest on the jacket of the rollers and the web of material on the outside of the screen belt, w an air-blowing device is provided on the deflecting rollers with air flows directed against their jacket.

Such an air bubble device is known from WO-A-8300514.

In multi-cylinder dryer sections of high-speed paper machines, so-called single-wire or slalom clothing is usually used, with endless screen belts and thus the paper webs being guided over steam-heated upper cylinders and also heated lower cylinders. This applies in particular to the first dryer group (s), but in some cases to the entire dryer section of paper machines. On the cylinders arranged below, the paper web lies outside the screen belt and is therefore no longer in direct contact with the jacket of these cylinders themselves, so that the contribution of the lower cylinders to paper drying is reduced accordingly. In addition, the high machine speeds create strong air currents that cause the paper web to lift off the screen belt in several places, which leads to wrinkling and quality disadvantages.

Railway stabilizers bring an improvement here; with getting higher However, machine speeds increase the web guiding problems considerably. Due to these web guiding problems and the fact that the drying of the lower cylinders wrapped in the sieve belt is reduced, very fast-running dryer sections were designed in such a way that only one heated row of cylinders, e.g. the upper row of cylinders, was present, while the lower cylinders were replaced by unheated guide rollers of smaller diameter. These guide rollers are perforated and partially provided with grooves, so that a vacuum or a vacuum can be generated by suction of air from these rollers. This vacuum holds the paper web to the dryer fabric so that the dreaded web lift-off and the formation of folds cannot occur.

This known design has great advantages with regard to the web guidance, but it has decisive disadvantages with regard to the drying performance: by omitting the heating of the lower cylinders, there is an overall reduction in the drying performance and thus an increase in the drying section for a given one Production output, which leads to a higher investment and space requirement for drying.

DE-OS 38 28 743 shows, inter alia, a drying group of a paper machine multi-cylinder dryer of the type described in the introduction, in which both deflection rollers, which correspond to the aforementioned guide rollers, and combined blower suction boxes arranged above the deflection rollers are connected to a vacuum generator. These blow-suction boxes are also connected to a pressure generator and have side flanks with nozzle openings through which air is blown under pressure against the screen belt and paper web runs freely guided between the cylinders and the deflecting rollers. In this known design, somewhat improved drying is achieved through the drying wire because, in particular with regard to the negative pressure applied to the inside of the perforated jacket of the deflecting rollers, the moisture removal is improved. However, this improvement does not yet adequately meet practical requirements. The loss of drying performance due to the loss of an entire row of cylinders cannot be compensated for by far.

Accordingly, the invention is based on a new concept for a high-speed multi-cylinder dryer section, which on the one hand ensures the good and safe guidance of the material, in particular the paper web, and on the other hand avoids the disadvantage of the unsatisfactory drying performance.

The goals set are achieved according to the invention, which is based on the drying device slid at the outset, by the features of the characterizing part of claim 1. Movement play is understood to mean a small distance between the blow-out surface of the tidal bubble device facing the jacket of the deflecting roller, which just barely Safety allows the sieve belt and the material web in question to move through in the gap between the air bubble device and the deflecting roller moving with the sieve belt. The air bubble device is preferably provided with a lifting device so that there is no blockage of the intermediate space when the paper web is being fed or when it is torn off. The lifting device can lift the air bladder device on one or both sides completely or partially from the cylinder surface. There should therefore be a gap which is just sufficient to bring the blowing performance as unimpeded as possible to the material web moving past with the screen belt, in order to support the suction work through the openings or in the grooves of the deflecting roller accordingly. In addition, by blowing hot air directly onto the paper web, a strong drying effect is achieved, which can partially or completely compensate for the loss of a row of cylinders.

This also results in a good and safe guidance of the material web in the area of the deflection roller. The latter is, according to the embodiment of the invention, by arranging a flow installation, in particular airflow and thus material web-guiding, in the intermediate spaces between the jackets of the cylinder (s) and the deflecting roller (s) on the part of the jacket of the deflecting roller which is not touched by the screen belt significantly improved. Guidance and drying performance can be additionally improved according to the invention if the flow installation has the completely closed side flanks facing the respectively adjacent sieve belt section and has an undivided interior which is connected to a vacuum generator. The guiding effect is additionally improved according to the invention if the distance of the side flanks of the flow installation from the respectively adjacent sieve belt strand increases, in particular continuously, seen in its direction of movement. The resulting diffuser-like expansion of the air flow in the area of the free material web or screen belt runs enables the air flows in the area of the freely moving runs or the free trains of the screen belt or material web to be controlled and good guidance of the material web in to ensure this area, in particular to avoid it being lifted off the screen belt as far as possible. A further improvement according to the invention can act in the same sense, which consists in the fact that the flow installation is at a smaller distance from the wire belt strand running onto the deflection roller than from the wire belt strand running off this roller.

According to the invention, it may be expedient to limit the air entrained by the sieve belt in order to avoid excess pressure and thus local lifting of the material web; This can be achieved in that in the region of the back facing away from the jacket of the associated deflecting roller, in particular the upper side, of the flow installation, an air separating device or seal extending into the gap between the flow installation and the up and / or down running belt section is provided.

The suction effect of the deflection rollers can be further increased according to the invention if the flow installation on the side facing the jacket of the associated deflection roller is sealed at its edges with respect to this jacket. Material web guidance or suction effect and drying effect can, according to the invention, also be made more favorable if the deflecting roller (s) is or are displaced from the plane of symmetry of the spaces between the cylinders to the screen belt run running onto the deflecting roller (s).

A further increase in the drying capacity can be achieved if (one) further air blower devices or (a) blow box are provided on the steam-heated cylinders, which also have the introduction of fresh air into the drying device and advantageously have (one) air injection opening (s) that is located in the space between adjacent cylinders on the side remote from the associated deflecting roller near one or both cylinders. In the direction of increasing the drying capacity, the steam-heated cylinders are designed as high-performance steel cylinders according to AT-PS 387 248 or the Austrian patent application A 1512/87.

In practice, a different way of guiding the air in the system can be favorable: According to the invention, it can be expedient if the air-blowing devices for the deflecting rollers are connected to an air-guiding circuit system which is separate from the rest of the ventilation system of the drying device. In other cases, it may also be better if, according to the invention, a common ventilation system is provided for the drying device, the interior space (s) of the flow installation (s) and the deflection roller (s) together on (a) vacuum generator are connected and if the air bubble device (s) and, if appropriate, the further air bubble device (s) are fed together via an air heating device.

In the present case, it is advantageous if, according to the invention, the diameter of the unheated deflection rollers connected to a vacuum generator is smaller than the diameter of the steam-heated cylinders, e.g. the diameter of the deflecting rollers is approximately 1000 - 1500 mm, the diameter of these cylinders is approximately 1800 mm.

Exemplary embodiments of the invention are described below with the aid of schematic drawings. Fig. 1 shows a dryer group with an air bubble device according to the invention and a flow installation according to the invention, wherein the steam-heated cylinders are arranged higher than the deflection rollers. Fig. 2 shows a similar drying device, but the arrangement of the cylinders and the deflecting rollers is reversed. Here is also a variant of the air cycle shown. 3 illustrates another embodiment variant with an additional air bladder device and a further variant of the air circuit.

4 and 5 show configurations in which only the air bubble device according to the invention or one with an additional air bubble device are provided in the upper region of the steam-heated cylinders.

6 and 7 show details in the area of the deflecting rollers on an enlarged scale compared to the aforementioned figures, namely FIG. 6 in front view, FIG. 7 as section A-A through FIG. 6.

In the present case, it is in particular a first dryer group of the dryer section of a paper machine, or a part of such a group. It is about single-belt guide groups. In front of it there is the press section of the paper machine for practical versions. The material or paper web is expediently conveyed from the press section to the dryer section in a closed guide. Behind it, if necessary, one or more single-wire conveyor guide groups - as shown below - can be provided in the dryer section, followed by one or more two-wire conveyor guide group (s) if necessary.

1, a drying group or drying device for material, in particular paper or fibrous webs moving at high speed is first described, specifically with an arrangement with drying cylinders 3 at the top and deflection rollers 2 at the bottom; in a corresponding form, however, it also applies to the reverse arrangement according to FIG. 2 with drying cylinders 3 arranged at the bottom, whereby it may be expedient to move a part of the drying groups with the cylinders on top according to FIG. 1 and a part with cylinders below within a drying section Fig. 2 execute.

The structure of the dryer section is shown using the example of a drying group in Fig. 1 or Fig. 2. From this you can see the overhead, steam-heated drying cylinder 3 made of cast iron or steel, which either as Drying cylinders of normal design or as high-performance cylinders are designed. Such high-performance drying cylinders are described in AT-PS 387 248 and in Austrian patent application A 1512/87. Here, a cylinder heated with a heat transfer medium, in particular steam, for paper machines has a metallic core cylinder provided on its surface with a number of grooves, preferably parallel to one another and optionally, in particular partly, parallel to its axis, and the cylinder is heated by Supply of the heat transfer medium, in particular steam, into the grooves. The grooves are, for example, machined into the surface of the core cylinder, and a metallic cylindrical outer jacket is drawn onto the core cylinder in a metal-contacting manner, in particular shrink-fit, with the formation of pressure spaces between it and the core cylinder, which can be welded to the core cylinder at its edges, and that Grooves have a continuously - preferably uniformly - changing cross-section over at least part of their length.

The lower deflections of the screen belt 15 or the material or paper web 14 are not formed by drying cylinders, as is usually the case, but deflection or guide rollers 2, the diameter of which is somewhat smaller than that of the drying cylinder 3. Typical dimensions are, for example, 1800 mm in diameter for the drying cylinder 3 and 1000 - 1500 mm in diameter for the deflection rollers 2 below. These deflection rollers are provided with a suction device 12 and have a perforated, preferably perforated jacket 13, so that inside the roller 2 A vacuum or negative pressure is created, and thus the material or paper web 14 is held in place by the negative pressure on the deflecting roller in its lower loop 14 '. The perforation of the deflecting rollers 2 can be distributed unevenly over their outer surface. In particular, a larger number of perforation openings or bores can be present in the region of the edge of the material web than in the central region of the web or of the roll shell. An air-blowing device 1 is arranged below these deflecting rollers, which causes intensive drying in this area by blowing hot air onto the material or paper web 14, 14 '. This makes it compared to a conventional dryer section - because of the missing Heating of the rollers 2 - reduced drying capacity compensated, or even increases compared to a conventional dryer section can be achieved. The material web 14 is guided in the entire area of the drying group through the endless, individual screen belt 15, which is guided in loops one after the other around the cylinders 3 and the deflection rollers 2.

The loss of drying performance due to the elimination of the steam-heated lower cylinders that would otherwise be used could e.g. can be achieved by increasing the vapor pressure in the cylinders in the upper row. However, this is usually not possible because on the one hand the steam pressures are predefined from the steam supply and on the other hand the steam pressure is limited for safety reasons. A remedy here can be the use of a special high-performance cylinder according to AT-PS 387 248 or the Austrian patent application A 1512/87, which can achieve higher performance even at lower steam pressures. The combination of such a high-performance cylinder with the drying device according to the invention is therefore particularly advantageous.

By holding the material, in particular paper web 14 due to the vacuum or vacuum also on the lower deflection rollers 2, the shrinkage of the material web 14, including its part 14 ', is hindered and can only be in a small part, in the so-called free runs or Trains 14 '', 14 '' 'take place. This brings decisive advantages in terms of material and paper quality and their uniformity across the entire width of the machine.

The shrinkage of the material web, in particular paper web 14, takes place increasingly in the part in which the evaporation of the water takes place. This applies in particular to that free train 14 ″ which is then passed through a drying cylinder 3 until it hits the next deflecting roller 2. In order to reduce the shrinkage in this area, it is expedient to make this free pull 14 ″ particularly short, while the free pull 14 ″ ″ following the deflecting roller 3 can be somewhat longer.

This arrangement, which is advantageous for technological reasons, can be achieved insofar as the deflection roller 2 is not arranged symmetrically between the drying cylinders 3, but rather shifted somewhat, counter to the machine or material web direction (arrow 16!).

A flow installation 4 is provided above the perforated deflecting rollers 2, which essentially serves two purposes: on the one hand, this covers part of the circumference of the perforated deflecting roller 2 that is not in contact with the material web or paper, thus preventing the increased intake of air in this area. This has the advantage that the amount of air sucked in is greatly reduced and that the vacuum or negative pressure in the suction deflecting rollers 2 can be maintained with smaller amounts of air sucked out, which in particular brings energetic advantages.

In addition, seals 8, 8 ′ are arranged between the aforementioned flow installation 4 and the suction deflection rollers 2 in order to prevent air from penetrating. This can be done either by scraper-like sealing strips, by brushes or similar sealing devices.

The second purpose of this flow installation 4 according to the invention, on the other hand, relates to the control of the air flows in the area of the free material or paper runs 14 ″, 14 ″ ″ (trains) and thus the guidance of the material, in particular paper web 14 in this area . For this purpose, on the one hand, the distances between the flow installation 4, ie between its completely closed side flanks 4 ', 4''and the sieve belt 15 on the downward run and on the upward run free train or train 15', 15 '' differ chosen large. In addition, the flow installation 4 is not carried out parallel to the drying wire 15 or 15 'or 15'', but in an oblique arrangement, so that a diffuser-like expansion for the air flow occurs. For some applications, the arrangement of a seal 9 against the sieve belt 15 ', for example in the form of a brush belt or an elastic seal, is advantageously provided on the top surface 4''' of the flow installation 4. This arrangement makes it possible to limit the air entrained by the sieve belt 15, 15 ', so that in the part where the Screen belt and the material web run onto the lower deflection roller 2, no overpressure results; such an overpressure could otherwise lead to a local lifting of the material web 14. That favorable effect is further supported by the fact that a part of the air is sucked into the part of the deflecting roller 2 that remains free of the screen belt 15 or the material web 14, so that no disruptive excess pressure can build up.

For those cases in which the suction effect of the deflection roller 2 alone is not sufficient, suction from the interior of the flow installation 4 is also provided according to the invention. For this purpose, the flow installation has an undivided interior, which is connected to a vacuum generator, in particular a fan. The false air passing between the flow installation 4 and the deflecting roller 2 can thus also be removed, or a simpler design of the seals 8, 8 'is possible, since appropriate leakage air quantities can be permitted. In some cases, it will be possible to do without a seal at all. Here the entire flow installation 4 serves as a suction box.

By extracting the air, both from the deflection rollers 2 and from the entire, undivided flow installation 4, it is practically possible to remove all of the exhaust air to be removed from the dryer section, and there are therefore no additional suction devices on the extractor hood of the paper machine or Screen press or the like is required.

In summary, the following can be stated: A combination of the air blowing device 1 and the flow installation 4 on the suction deflecting roller 2 is preferred. The arrangement of the roller 2 is favorable not eccentric or shifted below the middle of the space between two drying cylinders 3. The arrangement of the flow installation 4 advantageously takes place at different distances from the 15 '' and 15 '' drying sieve 15 running up. The boundary walls 4 ', 4''of the flow installation 4 do not run parallel, but rather at a slight angle to the drying sieve 15', 15 '' therein Areas. The seal 8, 8 'between the flow installation 4 and the deflection roller 2 is recommended. The Air separation device 9 on the upper edge of the flow installation 4 favors the material web guidance. An additional suction 10 of air from the flow installation 4 (see also FIG. 7!) Favors the drying effect and the material guidance. The combination with an air blowing device 11 on the cylinders 3 is also recommended. The combination of high-performance steel cylinders with suction deflecting rollers 2 and ventilation systems (for example blow boxes 11 (FIG. 3) or blow boxes 18 (FIG. 5)) can also be favorable.

Fig. 2 shows schematically a drying group which is constructed essentially like the one shown in Fig. 1, but with an arrangement rotated by 180 °, i.e. with a row of cylinders 3, the level of which is below the level of the row of deflection rollers 2. The flow internals 4 and the bladder devices 1 are interchanged accordingly in their position. Gif. 2 also reveals the air circuit, for which reference is made to the lines ending with arrows, which indicates the air movements. 19 is an air heater, 20, 21, 23 and 24 are fans and 22 is a heat exchanger. As can be seen, the air bubble devices 1 for the deflecting rollers 2 are connected to an air-guiding circuit system which is separate from the rest of the ventilation system of the drying device.

FIG. 3 shows a further variant, in particular with regard to the air flow, the direction of which was again illustrated by arrows. An additional air bubble device 11 on a steam-heated cylinder 3 is provided here. Fans 20, 23 and 24 are again available, which are designed as suction or pressure blowers depending on their task. Here, a common ventilation system is provided for the drying device, the interior space (s) of the flow installation (s) 4 and the deflection roller (s) 2 being connected together to (a) vacuum generator 24 and the air blower device (s) ) 1 and optionally the further air bubble device (s) 11 are fed together via an air heating device 19.

4 and 5 show simplified arrangements, in particular the flow installation is missing. The air bubble devices 1 are, however, provided in both arrangements. The other existing parts of the plant were given the same reference numerals as the previous example illustrations. As shown in FIG. 5, additional drying devices 18 can be arranged in the area of the upper cylinders 3, such as special blow boxes, which reinforce the drying of the material or paper web by blowing hot air through the screen belt 15. These blow boxes at the top also serve to introduce the fresh air into the dry patient. At 26 here is also a suction fan, at 27 a pressure fan. Arrows again show the air movement.

Fig. 6 shows an enlarged section of the dryer section. One can see in particular the guidance of the paper web 14 and the drying wire 15 as well as the flow installation 4 or its boundary walls 4 ', 4' 'and 4' ''. In addition, the seal 9 against the screen belt and the seals 8, 8 'against the deflection roller 2 are shown by way of example.

FIG. 7 illustrates the section A-A according to FIG. 6. In addition to the deflection roller 2, the flow installation 4 with the suction 10 and the seals 8 ′ is shown schematically.

Claims (14)

1. Drying system for material webs, in particular paper or fibrous webs (14), which are moved at a high speed, which system consists advantageously of one row of steam-heated cylinders (3), which are essentially disposed in the same horizontal plane, and advantageously of one row of unheated deflector rollers (2), which are disposed approximately in spaces between these cylinders (3), are in particular also mounted in a horizontal plane lying below or above the above-mentioned horizontal plane and the shell of which is perforated and/or provided with grooves, wherein air is sucked out of these deflector rollers (2), these cylinders (3) and the deflector rollers (2) are provided with a single-screen belt covering, the material web lies between the shell of the cylinders and the screen belt or similar at the cylinders, while the screen belt (15) comes to lie on the shell of the rollers and the material web on the outside of the screen belt (15) at the deflector rollers, and an air blast device (1) with air streams directed at the shell of the deflector rollers (2) is provided at the latter, characterised in that the air blast device (1) only partly embraces the shell, which is contacted by the screen belt or similar, of the deflector roller (2) in the portion lying at a distance from the cylinders (3) and entirely embraces the shell, which is contacted by the screen belt or similar, of the deflector roller (2) in the part conveying the screen belt and the material web to the following cylinder (3) with clearance of motion.
2. Drying system according to claim 1, characterised by the arrangement of an, in particular, air stream- and thus material web-conveying flow fitting (4) in the spaces between the shells of the cylinder(s) and the deflector roller(s) (2), which is/are largely embraced by the air blast device with clearance of motion in the region of its/their shell which is contacted by the screen belt or similar, at the part of the shell of the deflector roller (2) which is not contacted by the screen belt.
3. Drying system according to claim 2, characterised in that the flow fitting comprises completely closed lateral flanks, which face the respective adjacent screen belt section, and an undivided interior space, which advantageously communicates with an underpressure generator.
4. Drying system according to claim 2 or 3, characterised in that the distance of the lateral flanks of the flow fitting from the respective adjacent screen belt section increases, in particular steadily, viewed in the direction of movement of the latter.
5. Drying system according to one of claims 2 to 4, characterised in that the distance between the flow fitting and the screen belt section running onto the deflector roller is smaller than the distance of this flow fitting from the screen belt section running off this roller.
6. Drying system according to one of claims 2 to 5, characterised in that an air separating device (9) or a seal, which extends into the gap between the flow fitting and the screen belt section running on and/or off, is provided in the region of the back, in particular the upper side, of the flow fitting which is distant from the shell of the associated deflector roller.
7. Drying system according to one of claims 2 to 6, characterised in that the flow fitting is sealed off from the shell of the associated deflector roller at its edges on the side which faces this shell.
8. Drying system according to one of claims 1 to 7, characterised in that the deflector roller(s) is/are arranged off-centre from the plane of symmetry of the spaces between the cylinders towards the screen belt section running onto the deflector roller(s).
9. Drying system according to one of claims 1 to 8, characterised in that (a) further air blast device(s) (11) or (a) blast box(es) is/are provided at the steam-heated cylinders (3), this/these also serving to introduce fresh air into the drying system and advantageously comprising (an) air blast opening(s) which is/are disposed in the space between adjacent cylinders near one or both cylinder(s) on the side which is remote from the associated deflector roller.
10. Drying system according to one of claims 1 to 9, characterised in that the steam-heated cylinders (12) are constructed as high-power steel cylinders.
11. Drying system according to one of claims 1 to 10, characterised in that the air blast devices (1) for the deflector rollers (2) are connected to an air-conveying circulation system, which is separated from the rest of the ventilation system of the drying system (Figure 2).
12. Drying system according to one of claims 1 to 10, characterised in that a common ventilation system is provided for the drying system, the interior space(s) of the flow fitting(s) (4) and the deflector roller(s) (2) being jointly connected to (an) underpressure generator(s) (24), and that the air blast device(s) (1) and, if applicable, the additional air blast device(s) (11) are jointly supplied via an air heating device (19) (Figure 3).
13. Drying system according to one of claims 1 to 12, characterised in that the air blast device (1) can be raised entirely or partly from the cylinder surface on one or both side(s).
14. Drying system according to one of claims 1 to 13, characterised in that the diameter of the unheated deflector rollers (2), which are connected to an underpressure generator, is smaller than the diameter of the steam-heated cylinders (3), e.g. the diameter of the deflector rollers (2) is approximately 1000 - 1500 mm, while the diameter of these cylinders (3) is approximately 1800 mm.

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