EP0989232B1 - Drying section - Google Patents

Description

The invention relates to a dryer section of a machine for producing a material web, in particular paper or cardboard web, with at least one Pratlströmung drier for unilaterally applying a hot air and / or superheated steam impingement to the material web, the material web having its opposite side, in each case being acted upon by the Prali flow Side over an open, ie not smooth support surface is performed.

In the previously common multi-cylinder dryer sections, the paper web is guided for drying over several steam-heated cylinders or over an arrangement of several steam-heated cylinders and screen suction rolls. Especially at the beginning of drying, where the paper web still does not have sufficient strength, problems often arise with regard to the web guidance, which are in particular due to the fact that the still wet web sticks to the smooth contact surfaces, which are absolutely necessary for adequate heat transfer are. This often leads to web breaks and overstretching of the web edges. As a result, it is usually necessary to ensure that drying takes place more slowly, which means that the required drying section as a whole is longer. The problems mentioned above occur increasingly at higher web speeds.

In the solution described in WO 97/13031, hot air flow is applied to both sides of the fibrous web. Because of the forces acting on the fibrous web, it is supported on both sides by a band. This is relatively complex in relation to the drying result.

The aim of the invention is to create a dryer section of the type mentioned at the beginning, with which both an optimum drying rate and thus the smallest possible overall length of the dryer section are possible as well as a safe one Web guidance is guaranteed.

This object is achieved according to the invention; that the material web is guided over the support surface together with a deck seal lying between the material web and the impact flow dryer in question.

According to the essence of the invention, the material web is thus supported by the deck screen. This deck screen holds the material web on the support surface and also transports it in the event of a possible tear, so that no scrap can get caught in the respective impingement flow dryer.

At least one impingement flow dryer is expediently provided with a steam suction which serves for simultaneous evaporation. As a result, it is no longer necessary to switch between heating up and evaporation. With the elimination of the additional evaporation surface, the entire barrel length is further reduced.

An expedient practical embodiment of the dryer section according to the invention is characterized in that the material web is guided over an in particular larger support roller and the open support surface is formed either by the surface or a cover or covering of the support roller or by the surface of an endless belt guided over the support roller.

The relatively large back-up roller ensures safe and precise guidance with a constant radius of curvature. After the support roller no longer has to be designed as a pressure vessel, it can be relatively large in order to provide a correspondingly larger drying area.

The back-up roller can, for example, have an outer diameter in the range from approximately 2 to approximately 10 m.

If the open support surface is formed by the surface of an endless belt guided over the support roller, this endless belt can in particular be formed by an air-permeable screen. In principle, however, the use of an air-impermeable conveyor belt is also conceivable, for example. In addition, the open support surface can be formed, for example, by a shrink screen applied to the support roller.

According to an alternative advantageous embodiment of the dryer section according to the invention, the open support surface is formed by the surface of a support belt guided over a plurality of support rollers.

In particular with such a design, the open support surface can also be guided at least in sections, e.g. via a variety of support rollers. In addition, for example, an open support surface which is slightly curved at least in sections is also conceivable.

According to an expedient embodiment, the support rollers are arranged on an arc. The support band can in particular also be polygonal.

In order to facilitate the detachment of the material web from the respective support surface, compressed air can be applied to the material web at least in the removal area through the support surface.

If the material web is guided over a support roller, this can be provided or perforated with a grid structure, for example, and compressed air or the like can be applied to it on the inside at least in regions. Such a support roller can then be pressurized on the inside at least in the removal area in which the material web and possibly also a cover screen is removed from the support roller.

The temperature of the compressed air is expediently higher than about 20 ° C.

In a preferred practical embodiment, at least one impingement flow dryer is provided, which generates a hot air or superheated steam impingement flow with a temperature in the range from approximately 150 ° to approximately 450 ° C.

At least one impingement flow dryer with a plurality of high-performance nozzles is preferably used, these high-performance nozzles expediently being at the same constant distance from the material web during operation. This distance can be, for example, in the range from approximately 10 to approximately 50 mm.

At least one impingement flow dryer is preferably provided with at least one dryer hood, wherein such a dryer hood can advantageously be divided into zones in the web running direction and / or transversely to the web running direction. The paper quality can be influenced in the desired manner by zone-by-zone heating and drying. In particular, certain corrections to moisture cross profiles are possible.

At least one impingement flow dryer can be provided, for example, in an initial area of the dryer section. Additionally or alternatively, at least one such impingement flow dryer can also be provided in a main evaporation zone of the dryer section. Additionally or alternatively, at least one impingement flow dryer can also be provided in an end region of the drying section. This results in an even higher drying rate, which further shortens the drying section overall.

At least one drying group with at least one drying cylinder is expediently provided and at least one impingement flow dryer is preferably arranged upstream of this drying group in the web running direction, the material web preferably already having a dry content when it reaches the first drying cylinder, which is higher than approximately 55 to approximately 70%.

For example, after transfer from the press and drying on a back-up roll dryer, the material web can be dried from one side to the other along a straight line or slightly curved sections by impingement flow dryers located opposite one another to a dry content of, for example, about 55 to about 70%. For a respective drying on both sides, instead of two opposing impingement flow dryers, it is in principle also possible to provide a single dryer which engages around the web and acts on both sides. Until the desired degree of drying is reached, the material web is always supported by a non-smooth surface, so that the material web, which is still relatively moist, is not at any point must be removed from a smooth surface. A multi-cylinder dryer group can then follow, for example. It is also possible, for example, to pass a deck screen used both through a backup roll impingement dryer and through an adjoining rectilinear or slightly curved impingement dryer unit. The straight impingement dryer unit can, for example, be supplied with a second sieve as a supporting sieve. Instead, the paper web can also be transferred to two new screens, for example. In the area of the straight or slightly curved web guide, the material web can, for example, also be acted upon on both sides by a respective hot air or hot steam impingement flow. In this area of a straight or slightly curved web guide, for example, a corresponding impingement flow dryer can also be provided on only one side, while, for example, a plurality of support rollers can be arranged on the opposite side. In principle, it is also conceivable that the material web is subjected to a hot air or hot steam impingement flow from one side, on which a plurality of support rollers is arranged. In this case, the application takes place in particular through the area located between the support rollers.

In principle, the material web can be acted upon at different points from the same side or also from different sides with a respective hot air or hot steam impingement flow.

Further advantageous embodiments of the dryer section according to the invention are specified in the subclaims.

Figur 1

eine erste Ausführungsform einer Trockenpartie mit einem einer größeren Stützwalze gegenüberliegenden Prallströmungstrockner,

Figur 2

eine weitere Ausführungsform einer Trockenpartie mit zwei einer jeweiligen größeren Stützwalze gegenüberliegenden Prallströmungstrocknern, durch die die Materialbahn von unterschiedlichen Seiten her beaufschlagt wird,

Figur 3

eine weitere Ausführungsform einer Trockenpartie mit zwei einer jeweiligen größeren Stützwalze gegenüberliegenden Prallströmungstrocknern, wobei die beiden Stützwalzen einen unterschiedlichen Durchmesser aufweisen,

Figur 4

eine weitere Ausführungsform einer Trockenpartie mit zwei einer jeweiligen größeren Stützwalze gegenüberliegenden Prallströmungstrocknern, durch die die Materialbahn von der gleichen Seite her beaufschlagt wird,

Figur 5

eine weitere Ausführungsform einer Trockenpartie, in der die Materialbahn zwischen einem Decksieb und einem Stützband über eine Vielzahl von auf einem Kreisbogen angeordneten Stützrollen geführt ist,

Figur 6

eine weitere Ausführungsform einer Trockenpartie mit mehreren Prallströmungstrocknern, die einem über mehrere Stützrollen geführten Stützband gegenüberliegen,

Figur 7

eine weitere Ausführungsform einer Trockenpartie mit zwei einer jeweiligen größeren Stützwalze gegenüberliegenden Prallströmungstrocknern und zwei dazwischen angeordneten, einander gegenüberliegenden Prallströmungstrocknern für eine beidseitige Beaufschlagung der Materialbahn, wobei die Materialbahn gerade zwischen den beiden einander gegenüberliegenden Prallströmungstrocknern hindurchgeführt ist,

Figur 8

eine weitere Ausführungsform einer Trockenpartie mit zwei einer jeweiligen größeren Stützwalze gegenüberliegenden Prallströmungstrocknern und einem dazwischen angeordneten Prallströmungstrockner, an dem die Materialbahn entlang eines leicht gekrümmten Pfades vorbeigeführt ist, und

Figur 9

eine weitere Ausführungsform einer Trockenpartie mit einer einem größeren Stützwalze gegenüberliegenden Prallströmungstrockner und zwei dahinter angeordneten, einander gegenüberliegenden Prallströmungstrocknern für eine beidseitige Beaufschlagung der Materialbahn.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing; in this show:

Figure 1

a first embodiment of a dryer section with a baffle flow dryer opposite a larger back-up roll,

Figure 2

another embodiment of a drying section with two impact flow dryers opposite a respective larger support roller, through which the material web is acted on from different sides,

Figure 3

1 a further embodiment of a drying section with two impingement flow dryers opposite a respective larger support roller, the two support rollers having a different diameter,

Figure 4

another embodiment of a dryer section with two impact flow dryers opposite a respective larger support roller, through which the material web is acted on from the same side,

Figure 5

another embodiment of a dryer section in which the material web is guided between a cover screen and a support belt over a plurality of support rollers arranged on a circular arc,

Figure 6

another embodiment of a dryer section with several impingement flow dryers, which are opposite a support belt guided over several support rollers,

Figure 7

a further embodiment of a drying section with two baffle flow dryers opposite a respective larger supporting roller and two baffle flow dryers arranged between them for a double-sided loading of the material web, the material web being passed straight between the two baffle flow dryers opposite one another,

Figure 8

a further embodiment of a dryer section with two impingement flow dryers opposite a respective larger supporting roller and an impingement flow dryer arranged between them, to which the material web is guided along a slightly curved path, and

Figure 9

a further embodiment of a dryer section with a baffle flow dryer located opposite a larger supporting roller and two baffle flow dryers arranged opposite one another behind it for loading the material web on both sides.

1 to 9 each show a section of a drying section 12 adjoining a press section 10, which, like the press section, belongs to a machine for producing a material web 14, here a paper or cardboard web.

In the embodiment according to FIG. 1, the dryer section 12 comprises an overhead impingement dryer 16, through which the material web 14 is subjected to a hot air and / or superheated steam impingement on one side. The material web 14 is with its side opposite the impingement dryer 16 over an open, i.e. not smooth support surface led. For this purpose, the material web 14 is guided together with a deck screen 18 over a larger support roller 20, which is wrapped in a bottom screen 20, which forms the open support surface in the present case. The subsequent removal of the material web 14 and the deck screen 18 is consequently facilitated by this endless belt or bottom screen 22.

In the removal area behind the large support roller 20, the material web 14 is guided together with the cover screen 18 around a suction roller 24, whereupon it is fed to a single-row drying group with a plurality of drying cylinders 26 and suction rollers 28 located in between. As can be seen from FIG. 1, the deck screen 18 is again separated from the material web 14 in the region of the first drying cylinder 26.

In the present case, the material web 14 is transferred in a closed train from the last press nip of the press section 10 to the impingement flow dryer 16. The material web 14 is supported by the deck screen 18 and led to the large support roller 20 on which the lower wire 22 runs. The large support roller 20 ensures safe and exact guidance of the two screens 18, 22 with the material web 14 in between, with a constant radius of curvature. As a result, and due to the low sieving tension required, damage to the material web 14 is excluded.

The support roller 20 no longer has to be designed as a pressure vessel and can therefore be significantly larger, as a result of which a larger drying area is made available. The deck screen 18 is expediently particularly open, thin and resistant to high temperatures in order to enable good impingement drying. It has the task of holding the material web 14 on the support roller 20 and of transporting it even if it breaks off, so that no scrap can get caught in the dryer hood of the impingement flow dryer 16 provided with several high-performance nozzles. The bottom wire 22 allows the material web 14 to be easily removed from the support roller 20. It does not have to be as open as the cover wire 18, but should nevertheless be impermeable to air. Both screens 18, 22 can be cleaned in the return.

The dryer hood of the impingement flow dryer 16 can be divided into longitudinal zones and have transverse zones for moisture profile correction. The dryer hood should be divided as possible so that it can be lifted off the support roller 20. In operation, the high-performance nozzles are at a constant distance from the surface of the material web 14, which distance can be, for example, in a range from approximately 10 to approximately 50 mm.

In the present case, the web of material 14 is supported by a press felt 30 of the press section 10 in a closed train through the top screen 18 supported by the support roller 20, the top screen 18 both in the area of the transfer of the web of material 14 from the press felt 30 and in the area of the transfer of the Material web 14 is guided onto the support roller 20 via a suction roller 32.

The material web 14 to be dried is consequently guided after the press section 10 between two open temperature-resistant screens 18, 22 around a large support roller 20 on which the drying hood of an impingement flow dryer 16 provided with high-performance nozzles is installed. The flow velocity of the hot air and / or hot steam impingement flow concerned can be, for example, in a range from approximately 60 to approximately 120 m / s. The temperature of this impingement flow can be, for example, in a range from approximately 150 to approximately 450 ° C. Basically, for example, the use of gas or steam heated hot air or superheated steam is possible. After a dry content of about 55 to about 70% has been reached, the material web 14 has sufficient strength and is now completely dried in a preferably single-row (possibly also two-row) cylinder dryer group. In order to avoid curl (drying from both sides) or to increase the drying capacity without extending the drying section, such a backup roll impingement dryer 16 can alternatively or additionally be installed, for example, in the closing part of the drying section 12 and / or in the main evaporation zone.

At the beginning of the drying process, it is therefore no longer necessary to remove the moist material web 14 from smooth surfaces. In the way described safe web guidance is achieved in the critical range up to a dry content of, for example, 55 to about 70%. The heat supply (impingement nozzle flow) and the steam removal (suction openings) are preferably carried out simultaneously in such an impingement drying, so that no change between heating and evaporation is required. With the elimination of an additional evaporation surface, the run length is reduced. After the support roller 20 no longer has to be designed as a pressure vessel, it can be substantially larger, which entails a larger drying area. The drying performance at the beginning is only limited by influencing the paper quality when the drying speed is too high and no longer by the web guidance of the moist material web. The more flexible and faster controllable baffle nozzle hood, which is divided into longitudinal and transverse zones, enables the paper quality to be influenced. In particular, targeted heating and drying at the start and correction of moisture cross profiles are possible. The cross-shrinkage hindrance can be varied within limits due to the screen tension, since pressing on heating surfaces is no longer necessary.

The deck screen 18 can be made of plastic or metal, for example. The bottom wire 22 can be replaced by an impermeable conveyor belt. To form the non-smooth support surface, however, such a conveyor belt should also have a correspondingly open, ie not closed, surface. The transfer of the material web 14 from the press section 10 to the impingement flow dryer can be supported by a transfer foil in addition to the cover screen 18 or by an additional transfer felt 36, as indicated for example in FIG. 3. A drying hood can also use superheated steam operate. When using a solid jacket back-up roll, the roll jacket can be cooled via coolant channels or from the inside. The endless belt 22, for example formed by a bottom wire and provided with an open surface, can then be constructed in multiple layers with a coarser structure on the roller side in order to remove condensed water. In the present case, the lifting of the material web 14 from the deck screen 18 during transfer to and removal from the impingement flow dryer 16 is prevented by suction rollers 32 and 24, respectively. Grooved rollers or transfer foils can also be provided for this purpose.

FIG. 2 shows a further embodiment of a dryer section 14 with two impingement dryer 16 opposite a respective larger support roller 20, through which the material web is acted on from different sides. In the present case, the front impact flow dryer 16, viewed in the web running direction L, is arranged at the top and the rear impact flow dryer 16 is arranged at the bottom. Correspondingly, the support roller 20 assigned to the front impact flow dryer 16 lies below and the support roller 20 assigned to the rear impact flow dryer 16 lies above. Each of these two support rollers is wrapped around, for example, by a lower wire 22. The material web 14 is again guided together with a deck screen 18 over the large support roller 20 in question. The material web 14 is finally taken over by a dryer fabric 34 from the rear deck fabric 18. In contrast, in the exemplary embodiment according to FIG. 1, the single deck screen 18 provided there is separated from the material web 14 before it is brought together with the drying screen 34. Between the press section 10 and the front support roller 20, the material web 14 supported by the deck screen 18 is only guided over a single suction roller 32.

In the embodiment according to FIG. 3, the drying section 14, after the press section 10, again comprises two baffle flow dryers 16 which are assigned to a respective large support roller 20 and act on the material web 14 from different sides. In this case, the baffle flow dryer 16 viewed in the web running direction L is 16 arranged below and the rear impingement flow dryer 16 above. Correspondingly, the front large support roller 20 is at the top and the rear large support roller 20 is at the bottom. In addition, in the present case, the front support roller 20 has a smaller diameter than the rear support roller 20. The transfer of the material web 14 from the press section 10 to the front impingement flow dryer 16 or the large support roller 20 associated therewith takes place without free tension via an additional transfer felt 36 this transfer felt 36, the material web is finally taken over by the cover screen 18 guided over the front support roller 20, this cover screen 18 being guided in the take-over area over a suction roller 32. As in the exemplary embodiment according to FIG. 2, the material web 14 is also transferred in the present case from the cover screen guided over the front support roller 20 in the region of two suction rollers 24 to the cover screen 18 guided over the rear support roller 20. In the present case, too, the two large support rollers 20 are each wrapped, for example, by a lower wire 22. While in the exemplary embodiment according to FIG. 2, the transfer of the material web 14 from the top screen 18 guided over the rear support roller 20 in the area of two suction rollers 24 takes place directly to the screen belt 34, the transfer of the material web 14 to the single-row drying group of drying cylinders 26 with associated suction rollers 28 im the present case the FIG. 3 in the same way as in the exemplary embodiment according to FIG. 1.

The two large support rollers 20 are each wrapped around, for example, by a lower wire 22.

FIG. 4 shows an embodiment of a dryer section 14 with two upper impingement flow dryers 16 assigned to a respective lower large support roller 20, through which the material web 14 is acted on from the same side. As can be seen in FIG. 4, a common cover screen 18 is guided over the two lower support rollers 20. The two support rollers 20 are each looped around by a bottom wire 22 forming the open support surface.

FIG. 5 shows a further embodiment of a dryer section, in which the material web 14 is guided between the deck screen 18 and the bottom screen 22 via a plurality of support rollers 38 arranged on a circular arc. The open support surface, which facilitates the removal of the material web 14 and the deck screen 18, is again formed in this case by the bottom screen 22. In this case, too, the material web 14 is again guided between the two screens 18 and 22 past the impingement flow dryer 16 arranged above.

The so-called curl tendency is reduced by drying in succession from both sides in the embodiments according to FIGS. 2 and 3.

The bottom wire 22 can in principle also be omitted. Instead, the open support surface can be formed by the surface or a cover or covering of the relevant support roller 20. For example, a shrinking screen or the like can be applied to the support roller 20 in question, or the support roller 20 in question can be provided with a coated surface. The respective back-up roller can, for example, have a solid jacket or spoke / grid construction and can also be a polygon.

As can be seen, for example, from FIG. 5, the support can also be provided by a large number of small support rollers 38 which are arranged on an arc of a circle, so that the curvature of the material web 14 between the screens 18, 22 remains approximately constant. The illustrated embodiments can also be used for installation in the main evaporation zone or in the end part of the drying section 12 in question, which also applies to the remaining embodiments described below.

FIG. 6 shows an embodiment of a drying section 14, in which a plurality of impingement flow driers 16 lying at the top lie opposite a common support belt 40, over which the material web 14 is guided together with a cover screen 18 formed by a drying screen. A support roller 20 in question (see the previous exemplary embodiments) is replaced by the support belt 40 guided over a plurality of support rollers 38. The material web 14 is again taken over in a closed guide in the area of a suction roll 32 by a press felt 30 of the press section 10 and fed to the support belt 40 through the cover screen 18. In the present case, three impingement flow dryers 16 are provided, whereby the material web 14 in the region of these impingement flow dryers 16 is in each case guided in a straight line or slightly curved.

In this embodiment effecting one-sided impingement drying, the material web 14 has reached, for example, a drying content of about 60% following the last impingement dryer 16.

The open support surface, which enables easier removal, is in the present case provided by a correspondingly open, i.e. not closed surface of the support band 40 is formed. This support band 40 can be formed, for example, by a metal band, a foil or an air-impermeable fabric. Compared to a backup roller, the support belt 40 brings i.a. the advantage that it is easier to manufacture and easier to transport. This support band 40 should be so stable that it does not vibrate when it is subjected to the impingement flow dryer 16.

FIG. 7 shows an embodiment of the dryer section 14 with two impact flow dryers 16 located at the top, each of which is assigned to a large support roller 20 located at the bottom, and with two impact flow dryers 16 ′, 16 ″ arranged one above the other for acting on the material web 14 on both sides, the Material web 14 is passed straight between the two impingement flow dryers 16 ', 16 "one above the other.

The material web 14 is again in the area of a suction roller 32 by a porous cover band 18 made of metal or plastic from a press felt 30 Press section 10 taken over and fed in the area of a further suction roller 32 to the front large support roller 20, from which it is removed again together with the cover wire 18 in the area of a further suction roller 24, in order subsequently between the cover wire 18 and a further wire belt 42 made of metal or plastic to be passed along a straight path between the two impingement flow dryers 16 ', 16 "lying one above the other. Subsequently, the material web 14 and the cover screen 18 are again separated from the lower screen belt 42 in the area of a suction roller 24 and onto the rear support roller 20 located below , from which they are removed again in the area of a further suction roll 24 and are continued in a straight line to a subsequent suction roll 24. In the area of a further suction roll 24, the material web 14 is finally separated from the deck wire 18 and taken over by a drying wire 34 through which it again a single-row dry gr uppe from several drying cylinders 26 with associated suction rolls 28 is supplied.

As a result, the deck screen 18 is guided over both the front and the rear large support roller 20. In the area of these two large support rollers 20, the material web is dried from above by the two impingement flow dryers 16. On the other hand, the two impingement flow dryers 16 ', 16 "between them dry the material web 14 on both sides. The two support rollers 20 are each a grated support roller covered with a screen stocking. The diameter of these support rollers 20 can in particular be greater than approximately 2 m his.

The large support rollers 20 can be pressurized from the inside to cause the material web 14 to be blown off at the respective take-off point. The front support roller 20, viewed in the web running direction L, is pressurized on the inside as a whole, while in the rear large support roller 20 such an internal pressurization is only provided locally, specifically in the removal area.

As can be seen from FIG. 7, a cover 44 is provided in the lower region of the front support roller, which is not covered by the deck screen 18, by means of which the compressed air flow that supports the removal is concentrated on the removal area. The transfer zone is, for example, about 500 mm wide. For example, the compressed air temperature is greater than about 20 ° C. At least some of the impingement flow dryers 16, 16 ', 16 "can be designed to generate a respective hot air or superheated steam impingement flow whose flow speed is greater than or equal to approximately 100 m / s and whose temperature is approximately greater than or equal to 150 ° C.

In the embodiment shown in FIG. 8, the material web 14 is first dried on a large support roller 20, then on a slightly curved support surface and then again on a large support roller 20. To form the slightly curved support surface, a cover screen 18, which is also guided over the two large support rollers 20, is guided over a plurality of support rollers 38 lying in a correspondingly curved plane. The two impingement flow dryers 16 are each arranged below the relevant support roller 20. The material web 14 is thus dried from below by these two impingement flow dryers 16. Between these two impact flow dryers below 16, an impact flow dryer 16 '"is provided, which is arranged above the support rollers 38 and consequently ensures that the material web 14 is dried from above. As can be seen from FIG. 8, the material web 14 is between the deck sieve 18 and an overhead sieve belt 42 made of metal or plastic along a path curved slightly upward toward the impingement flow dryer 16 ″ ″ past this impingement flow dryer 16 ″ ″ for this purpose, a plurality of support rollers 38 located at the bottom and lying in a correspondingly curved plane are provided 7, there is no drying from the side of the support rollers 38 in the present case. In contrast, in the embodiment of FIG. 7, an impingement flow dryer 16 "is also provided on the side of the support rollers 38. In this exemplary embodiment according to FIG. 7, the support rollers 38 located below are also arranged in one plane.

In the embodiment according to FIG. 8, the support rollers 20 are again formed by latticed support rollers, each of which is covered with a sieve stocking and whose diameter can be greater than approximately 2 m. A respective internal blow box assigned to the support rollers 20 again serves to detach the web and clean the screen. In the present case, a local pressurization is provided for the front support roller 20, while the rear support roller 20 is pressurized overall on the inside. Correspondingly, in the present case, the rear support roller 20 is assigned a cover 44 in order to concentrate the compressed air flow accordingly on the removal area. The compressed air temperature can be greater than about 20 ° C, for example. Following the rear support roller 20 or the rear impingement dryer 16 the material web 14 is again removed from the deck screen 18 by a drying screen 34 and fed to a single-row drying group comprising a plurality of drying cylinders 26 with associated suction rolls 28.

As can be seen from the two FIGS. 7 and 8, the two large support rollers 20 are each supplied with compressed air via a common compressed air source 46 in the exemplary embodiments concerned.

Figure 9 shows a further embodiment of a dryer section 14, in which the material web 14 following the press section 10 first for one-sided drying by an overhead impingement dryer 16 over a large support roller 20 underneath which is wrapped by a lower wire 22 and then for drying on both sides is passed in a straight line between two impingement flow dryers 16 ', 16 "lying one above the other. Between the two impingement flow dryers 16', 16", which serve drying on both sides, the material web 14 is guided between the cover screen 18, which is also guided over the support roller 20, and a further screen belt 48.

After the transfer from the press section 10 and the drying on the large support roller 20 by the overhead flow dryer 16 located above, the material web 14 is thus in a straight line area, which for example can also be slightly curved, by two superimposed impact flow dryers 16 ', 16 " Dried on both sides at the same time, for example, up to a dry matter content of 55 to about 70% In principle, a single dryer covering the material web and correspondingly acting on both sides can also be provided for such drying on both sides supports at least one fabric so that it never has to be pulled off a smooth surface. Subsequently, the material web 14 is again fed to a dryer group comprising a plurality of drying cylinders 26 with associated suction rolls 28.

In the present case, the deck screen 18 is also passed through the area between the two impingement flow dryers 16 ', 16 "lying one above the other. The additional screen belt 48 is fed as a support screen. In principle, the material web 14 can also be transferred to two new screens A plurality of support rollers can also be provided again, in the present case a single-row drying group comprising a plurality of drying cylinders 26 with associated suction rollers 28 is also provided, but in principle, for example, a two-row drying group is also conceivable here.

With the drying section according to the invention described with the aid of exemplary embodiments, a supported, draft-free web guide up to, for example, about 60% to about 70% dry content is thus possible, as a result of which the previous tear-off problems in this area are eliminated. Higher drying rates are possible, which results in a correspondingly shorter and more compact drying section. Negative effects on the paper properties are practically excluded. The impingement flow dryer can be used especially after pressing with subsequent single-tier dryer groups. If necessary, the variants described can be extended to the end of the dryer section. In principle, however, it is also conceivable to use the impingement flow dryer in a main evaporation zone of the dryer section. In principle, the use of impact flow dryers in connection with multi-row dryer groups is also conceivable.

LIST OF REFERENCE NUMBERS

10

press section

12

drying section

14

web

16

Impingement dryer

16 '

Impingement dryer

16 "

Impingement dryer

16 ''

Impingement dryer

18

a filter plate

20

larger backup roller

22

bottom wire

24

suction roll

26

drying cylinders

28

suction roll

30

press felt

32

suction roll

34

dryer

36

Transferfilz

38

support rollers

40

support band

42

screen belt

44

cover

46

Compressed air source

48

screen belt

L

Web direction

Claims (47)

1. Drying section (12) for a machine for producing a material web (14), in particular a paper or board web, comprising at least one impingement-flow dryer (16) for acting on one side of the material web (14) with a hot-air and and/or hot-steam impingement flow, the material web (14) being led with its side respectively opposite the side acted on by the impingement flow over an open, that is to say non-smooth, supporting surface, characterized in that the material web (14) is led over the supporting surface together with a top screen (18) located between the material web (14) and the relevant impingement-flow dryer (16).
2. Drying section according to Claim 1, characterized in that at least one impingement-flow dryer (16) is provided with a steam extraction system used for simultaneous evaporation.
3. Drying section according to one of the preceding claims, characterized in that the material web (14) is led over a supporting roll (20), in particular a relatively large supporting roll (20), and the open supporting surface is formed either by the surface or a cover or covering of the supporting surface (20) or by the surface of an endless belt (22) led over the supporting roll (20).
4. Drying section according to Claim 3, characterized in that the supporting roll (20) has an outer diameter in the range from about 2 to about 10 m.
5. Drying section according to Claim 3 or 4, characterized in that the open supporting surface is formed by the surface of an endless belt (22) led over the supporting roll (20), and this endless belt is formed by an air-permeable screen.
6. Drying section according to Claim 4 or 5, characterized in that the open supporting surface is formed by the surface of an endless belt (22) led over the supporting roll (20) and this endless belt (22) is formed by an air-impermeable transport belt.
7. Drying section according to Claim 4 or 5, characterized in that the open supporting surface is formed by a shrunk screen applied to the supporting roll (20).
8. Drying section according to one of the preceding Claims 3 to 7, characterized in that the supporting roll (20) has a solid-cover or spoke/lattice construction.
9. Drying section according to Claim 1 or 2, characterized in that the open supporting surface is formed by the surface of a supporting belt (40, 18, 22) led over a plurality of supporting rollers (38).
10. Drying section according to Claim 9, characterized in that the supporting rollers (38) are arranged on a circular arc.
11. Drying section according to Claim 9 or 10, characterized in that the supporting belt (22) is led in the manner of a polygon.
12. Drying section according to Claim 9, characterized in that the supporting rollers (38) lie in one plane or in a slightly curved surface.
13. Drying section according to one of the preceding claims, characterized in that the open supporting surface is flat, at least in some sections.
14. Drying section according to one of Claims 9-12, characterized in that the supporting belt (40, 18, 22) consists of metal or plastic.
15. Drying section according to one of Claims 9-12, characterized in that the supporting belt (40, 18, 22) is air-impermeable and preferably consists of an air-impermeable fabric.
16. Drying section according to one of the preceding claims, characterized in that the top screen (18) consists of plastic or metal.
17. Drying section according to one of the preceding claims, characterized in that, at least in a pick-up region in which it is picked up off the supporting surface, the material web (14) can be acted on with compressed air through the supporting surface.
18. Drying section according to one of the preceding claims, characterized in that the material web (14) is led over a supporting roll (20) provided with a lattice structure or perforated which, on the inner side, is acted on by compressed air or the like, at least in some regions.
19. Drying section according to Claim 18, characterized in that the supporting roll (20) is acted on with compressed air on the inner side, at least in the pick-up region in which the material web and possibly also the top screen (18) is picked up from the supporting roll.
20. Drying section according to Claim 19, characterized in that the temperature of the compressed air is higher than about 20°C.
21. Drying section according to one of the preceding claims, characterized in that, by means of at least one impingement-flow dryer (16), a hot-air or hot-steam impingement flow is produced whose temperature lies in the range from about 150 to about 450°C.
22. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) is provided with a plurality of high-power nozzles.
23. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) is provided with at least one dryer hood.
24. Drying section according to one of the preceding claims, characterized in that at least two supporting rolls (20) located one after another in the web running direction (L) and each assigned to an impingement-flow dryer (16) are provided, and in that the various supporting rolls (20) have, at least to some extent, a different diameter.
25. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) is provided with a dryer hood subdivided into zones in the web running direction (L) and/or transversely with respect to the web running direction (L).
26. Drying section according to Claim 22, characterized in that the high-power nozzles of a respective impingement-flow dryer (16) are at the same constant distance from the material web (14) during operation.
27. Drying section according to Claim 26, characterized in that the distance is in the range from about 10 to about 50 mm.
28. Drying section according to one of the preceding claims, characterized in that the flow velocity of a respective hot-air or hot-steam impingement flow is in the range from about 60 to about 120 m/s.
29. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) located above is assigned a supporting surface located below.
30. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) located below is assigned a supporting surface located above.
31. Drying section according to one of the preceding claims, characterized in that, in at least one region, the material web (14) can be acted on simultaneously on both sides with a respective hot-air and/or hot-steam impingement flow, preferably being led through this region in between two mesh belts (18, 42; 18, 48).
32. Drying section according to Claim 31, characterized in that the material web (14) is led in a straight line or along a slightly curved path through the region in which it is acted on on both sides.
33. Drying section according to Claim 31 or 32, characterized in that at least one mesh belt or supporting belt (18, 42, 44) is led over a plurality of supporting rollers (38).
34. Drying section according to Claim 33, characterized in that the supporting rollers (38) lie in one plane or in a slightly curved surface.
35. Drying section according to either of Claims 31 and 32, characterized in that at least one mesh belt (18, 42, 44) consists of metal or plastic.
36. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) is provided in an initial region of the drying section.
37. Drying section according to one of the preceding claims, characterized in that at least one drying group with at least one drying cylinder (26) is provided, and in that at least one impingement-flow dryer (16) is preferably arranged before this drying group in the web running direction, the material web, when it reaches the first drying cylinder (26), preferably already having a dryness content which is higher than about 55 to about 70%.
38. Drying section according to one of the preceding claims, characterized in that at least one single-row and/or at least one two-row drying group is provided.
39. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) is provided in an end region of the drying section (12).
40. Drying section according to one of the preceding claims, characterized in that at least one impingement-flow dryer (16) is provided in a main evaporation zone of the drying section (12).
41. Drying section according to one of the preceding claims, characterized in that at least two impingement-flow dryers (16) located one after another in the web running direction (L) are provided, by means of which the material web (14) can be acted on with a hot-air or hot-steam impingement flow from opposite sides.
42. Drying section according to one of the preceding claims, characterized in that at least two impingement-flow dryers (16) located one after another in the web running direction (L) are provided, by means of which the material web (14) can be acted on with a hot-air or hot-steam impingement flow from the same side.
43. Drying section according to one of the preceding claims, characterized in that, in addition to at least one impingement-flow dryer (16) which acts on one side of the material web, at least two impingement-flow dryers (16', 16") located opposite each other and acting on both sides of the material web (14) are provided.
44. Drying section according to one of the preceding claims, characterized in that, between two impingement-flow dryers (16) which are located one after another in the web running direction and act on the material web (14) with hot-air or hot-steam impingement flow from the same side, at least one further impingement-flow dryer (16', 16'', 16''') is provided in order to act on the material web (14) with hot-air or hot-steam impingement flow from the opposite side or from both sides.
45. Drying section according to one of the preceding claims, characterized in that, between two impingement-flow dryers (16) which are located one after another in the web running direction (L) and act on the material web (14) with hot-air or hot-steam impingement flow from opposite sides, at least one pair of mutually opposite impingement-flow dryers (16', 16") is provided in order to act on the material web (14) with hot-air or hot-steam impingement flow from both sides.
46. Drying section according to one of the preceding claims, characterized in that at least one group of three impingement-flow dryer units located one after another and each comprising one or two mutually opposite impingement-flow dryers (16; 16'''; 16', 16'') is provided, in the region of which the material web (14) is initially led along a circular arc, then in a plane or a slightly curved surface and then along a circular arc again.
47. Drying section according to one of the preceding claims, characterized in that a plurality of impingement-flow dryers (16) located one after another in the web running direction (L) are provided, and the material web (14) is acted on alternately from opposite sides by these impingement-flow dryers (16).