WO1998011298A1

WO1998011298A1 - Sealing arrangement in fibre web drying apparatus

Info

Publication number: WO1998011298A1
Application number: PCT/FI1997/000539
Authority: WO
Inventors: Lasse SYRJÄ
Original assignee: Valmet Oy
Current assignee: Valmet Technologies Oy
Priority date: 1996-09-10
Filing date: 1997-09-09
Publication date: 1998-03-19
Anticipated expiration: 1999-03-10
Also published as: FI963563A0; FI963563A7; AU4303397A; FI101236B; FI101236B1

Abstract

A seal arrangement in a fibre web drying apparatus, in which a fibre web (5) is dried between two tight bands (1, 2) that move in the same direction around turning rolls (6a, 6b, 7a, 7b). The first band (1) is heated by a pressure chamber (9), and the second band (2) is cooled by a water chamber (10). The fibre web (5), with at least one wire (3, 4), is led through a drying zone formed by the bands (1, 2) so that the fibre web is in contact with the surface of the first band (1), and the wire (3, 4) is between the fibre web (5) and the second band (2). The drying apparatus comprises side chambers (11) in which pressure medium dripping from the chambers (9, 10) collects. The ends of the side chambers (11) are sealed with an end seal (13), which comprises elongated sealing elements (15) attached at at least their one end and having a length that is greater than the height of the area to be sealed.

Description

SEALING ARRANGEMENT IN FIBRE WEB DRYING APPARATUS

The invention relates to a sealing arrangement in a fibre web drying apparatus comprising two endless bands that are impermeable to air, first turning rolls, around which the first band is arranged to turn, and second turning rolls, around which the second band is arranged to turn; the first and second bands being arranged to run part of the way in parallel such that they define a drying zone between them; the first band being arranged to be heated by a chamber containing pressure medium, and the second band being arranged to be cooled by a chamber containing pressure medium; a fibre web and at least one felt or wire running between the bands such that the fibre web is in contact with the first, heated band, and the felt or wire is between the fibre web and the second, cooled band; and the drying apparatus comprising, on the side of these chambers, side chambers which enclose the edge of the bands and are separated from the chambers and from the ambient air, and in which the pressure medium dripping from the two chambers, from between the bands and the body portions of the chambers, collect.

It is previously known from many patent publications, such as Finnish Patent 92,735 and U.S. Patent 4,461,095, to dry a fibre web between two parallel metal bands moving in the same direction such that the fibre web is in contact with the heated metal band and that there is a felt between the fibre web and the second, cooled metal band, whereby the steam separated from the fibre web by heating condenses to the felt by the effect of the cold metal band. The basic idea is that two endless metal bands are arranged to run around turning rolls and that against the surface defined by the loops that the bands form are provided pressure chambers containing hot steam and water, respectively, such that the pressure produced presses the hot and cold bands, respectively, against the fibre web and the felt running between them. Together with seals, the bands, which are located between the pressure chambers, form one side of the pressure chambers such that the steam and water can directly affect the bands. The operation of the apparatus is fully known per se and has been disclosed e.g. in the above patent publications, which are incorporated herein by reference.

In Finnish Patent 92,735 a closed collecting chamber is arranged to enclose the edge of the bands, i.e. there is a 'side chamber' in which steam dripping from the steam chamber, from between the band and the seals, and, correspondingly, water dripping from the water chamber, from between the band and the seals, collect. From the side chamber the steam and the water can be removed without a risk of emitting them to ambient air. This, for example, helps to reduce noise problems caused by steam, and to collect the water and steam that have dripped from the chambers. However, it is very difficult to seal the ends of the side chambers because the wire and bands move laterally and to some extent also vertically, whereby a small amount of steam, water or condensate is uncontrollably emitted through the ends of the side chambers.

The object of the present invention is to provide an arrangement by which the quantity of steam, water and condensate uncontrollably emitted through the corners of the side chambers can be restricted.

The arrangement of the invention is characterized by comprising an end seal at an end of the side chamber, the end seal comprising several elongated sealing elements which are attached at at least one end and which have a length that is greater than the height of the area to be sealed. The essential idea of the invention is to arrange at the end of the side chambers of the drying apparatus a seal that comprises several elongated elements which have a length that is greater than the height of the area to be sealed, whereby the elements bend in the flow direction during the use. This makes it possible to break the flow surface of the flowing steam, condensate or water in small parts, and to add flow resistance due to friction caused by wall flow. Further, the idea of a preferred embodiment is that the elongated elements are attached at their both ends.

The advantage of the invention is that the flow can be restricted by the arrangement according to the invention, and that the seal according to the invention adjusts to the varying area to be sealed. Consequently the quantity of steam, condensate and/or water emitted can be restricted and the rate of emission reduced, either so that no emission takes place, or so that any emission is primarily controlled. When the elongated elements of the seal are attached at their both ends, the elements are continuously evenly distributed, irrespective of e.g. variation in the flow direction.

In the following the invention will be described in greater detail with reference to the attached drawings, in which fig. 1 shows a schematic sectional side view of a drying apparatus of a paper machine, in which an arrangement according to the invention is used, fig. 2 shows a cross-sectional view of the edge of the drying apparatus shown in fig. 1 , seen from the travel direction of the web, fig. 3 shows a schematic sectional view of the arrangement according to the invention, seen from the travel direction of the web, fig. 4 shows a partly sectional side view of a seal used in the arrangement according to the invention, and fig. 5 shows a top view of the seal of fig. 4.

Fig. 1 shows a schematic sectional side view of a drying apparatus according to the invention seen from the travel direction of the web. The drying apparatus comprises a first band 1, or upper band, and a second band 2, or lower band, which are endless bands that are impermeable to air, have a good thermal conductivity, and are preferably made of metal; a fine wire or felt 3, a coarse wire 4 and a fibre web 5 passing between those surfaces of the bands which face each other. The fibre web 5 moves in the direction indicated by arrow A. The first band 1 is arranged to turn around first turning rolls 6a and 6b located at the ends of the drying apparatus. Correspondingly, the second band 2 is arranged to turn around second turning rolls 7a and 7b located below the first turning rolls 6a and 6b at the ends of the drying apparatus. The wires 3 and 4 are supported and guided by guide rolls 8. Since the pressure prevailing in the drying zone in the area between the bands 1 and 2 is usually different from the pressure prevailing outside or on the sides of the bands 1 and 2, seals are arranged on both sides of the apparatus between or at the edges of the bands 1 and 2, said seals preventing liquid or gas from dripping from the area between the bands 1 and 2 through the sides, or vice versa. To effect vapour heating required by the drying process, the drying apparatus comprises a pressure chamber 9, which is located above the first band 1. The first band 1 is sealed with seals 9a in respect of the body 9b of the pressure chamber 9 such that the steam in the pressure chamber 9 is maintained at a suitable pressure. Below the second band 2 there is a water chamber 10, which contains water that cools the second band 2. At the edges of the water chamber 10 there are seals 10a, with which the second band 2 is sealed in respect of the body 10b of the water chamber 10.

The operation of the drying apparatus is based on heating the first band 1 , which comes into contact with the web 5, with hot steam contained in the pressure chamber 9, whereby the water in the web 5 is vaporized and transferred through the wires 3 and 4 toward the second band 2 by the effect of the temperature of the first band 1. The second band 2, in turn, is continuously cooled with water located below it, whereby the steam produced on the surface thereof condenses into water and is removed with the band 2 and the wire 4.

Fig. 2 shows a schematic cross-sectional view of the edge of a fibre web drying apparatus, seen in the travel direction of the fibre web. The reference numbers in fig. 2 correspond to those used in fig. 1. The edge of bands 1 and 2 is enclosed by a closed side chamber 11. In the side chamber 11 are collected steam and condensate dripping from between the seals 9a of the pressure chamber 9 and the first band 1 , and water dripping from between the seals 10a of the water chamber 10 and the second band 2. The steam, water and condensate are passed along one or more conduits 12 first to a collecting vessel and then for utilization. The side chamber 11 prevents the steam, condensate and water from being released into ambient air, which greatly reduces any problems of noise caused by the steam. The side chamber 11 also functions under pressure, whereby the seals 9a and 10a are not subjected to the entire pressure of the pressure chamber 9 or water chamber 10, and so their useful life is rather long. Fig. 2 also shows a schematic view of an end seal 13 at an end of the side chamber 11 at that point where the bands 1 and 2 and the wire 4 are outlet from the side chamber 11. At the inlet of the side chamber 11 , i.e. the end where the bands 1 and 2 and the wire 4 are inlet, it is also possible to arrange a similar end seal 13. For the sake of clarity, the felt 3 and the fibre web 5 are not shown in fig. 2.

Fig. 3 shows a schematic cross-sectional view of an arrangement according to the invention taken at the end seal 13 and seen in the travel direction of the web. The reference numbers in fig. 3 correspond to those used in figs. 1 and 2. The end seal 13 is located at the point where the pressure chamber 9, water chamber 10 and side chamber 11 end. Against the bands 1 and 2 are arranged static seals 14, which prevent most of the steam, condensate and water from being emitted from the pressure chamber 9 and the water chamber 10. Correspondingly, the static seals 14 also prevent the steam, water and condensate from being emitted from the side chamber 11. There is also a static seal 14 between the body 9b of the steam chamber and the body 10b of the water chamber. The bands 1 and 2 and the wire 4 move away from the viewing direction of fig. 3 at the same rate as the machine is driven. Further, in fig. 3, they move continuously sideways to the right and to the left, typically about ±5 mm. In connection with a change in the way of driving the drying apparatus, the bands and the wire transfer permanently typically about 20 mm sideways to the right or to the left. The bands 1 and 2 and the wire 4 can move freely sideways in respect of one another. Further, each one of the components also moves slightly in the vertical direction in the figure. Because of this, the end of the side chamber 11 cannot be sealed quite tightly with the static seals 14 at the edges of the bands 1 and 2 and the wire 4. Naturally, the most difficult situation in respect of sealing is when the bands 1 and 2 and the wire 4 are in the extreme left-hand position in fig. 3. In the arrangement of the invention this point is sealed with an end seal 13. The end seal 13 comprises several elongated elements. The length of the elements is greater than the height of the area to be sealed, whereby the elements bend in the flow direction. The elongated elements are able to move in the lateral and vertical directions, whereby they divide the flow area into small parts. The flow resistance is thereby increased due to friction caused by wall flow. As the bands 1 and 2 and the wire 4 move to the right in fig. 3, the elongated elements of the end seal 13 move closer to one another. As the bands 1 and 2 and the wire 4 move to the left in fig. 3, the area to be sealed is greater, but even here the elongated elements of the end seal 13 are distributed evenly over the area to be sealed, whereby the sealing effect is maintained good. One or more static seals 14 can be arranged in succession with the end seal 13, which further improves the sealing effect. Fig. 4 shows a cross-sectional side view of the end seal 13. The reference numbers in fig. 4 correspond to those used in figs. 1 to 3. Elongated sealing elements 15 are attached at their one end to a seal body 16. In the embodiment of fig. 4, the elongated sealing elements 15 are led through a hole in the seal body 16 to the other side, and also attached at their other end to the seal body 16. The other ends can be attached e.g. by means of a plate 18 so that the elongated sealing elements 15 are arranged between the plate 18 and the seal body 16, and so that the plate 18 is pressed against the seal body 16 e.g. by means of bolts 19. In addition, the ends of the elongated sealing elements 15 are most preferably attached after the plates 18 to one another e.g. by melting them together. The elongated sealing elements 15 can be made, for example, of yarn, such as wire yarn, band, thin flexible pipe or lamella, or some other essentially thin and flexible material. The essential feature is that the length of the elongated sealing element 15 has to be greater than the height of the area to be sealed, so that the element can bend in the flow direction and move horizontally and vertically, thereby filling essentially evenly the area to be sealed. Most preferably, the length of the elongated sealing elements 15 in the sealing direction, i.e. the distance that the elongated sealing elements 15 bend in the flow direction, is more than 50 times the diameter of the elements, whereby the flow resistance is good. When both ends of the elongated sealing elements 15 are attached e.g. in the manner shown in fig. 4, the position of the elongated elements 15 in the end seal 13 is continuously correct in respect of the flow direction, whether the direction of the flow is from right to left in fig. 4 or vice versa. Also, a change in the flow direction in the middle of the process does not affect the sealing effect of the end seal 13 in any way, which is significant for example in connection with the end seal 13 at the inlet end of the side chamber 11. For example, two end seals 13 as presented in fig. 4 can be placed at the point to be sealed so that the first seal 13 is placed in the position shown in fig. 4 and the second one is placed on top of the first one upside down, whereby the elongated sealing elements 15 of the end seals 13 coincide.

Fig. 5 shows a top view of an end seal according to fig. 4. The reference numbers in fig. 5 correspond to those used in figs. 1 to 4. For the sake of clarity, the elongated sealing elements 15 of the end seal 13 are not shown in fig. 5. The elongated sealing elements 15 are attached at their first end to holes 20 e.g. by tying them with non-corroding thread. When the elongated sealing element is e.g. 0.5 mm thick wire yarn, preferably more than 1000 wire yams are arranged in the end seal 13. There are then several wire yarns on top of one another and several next to one another, whereby their sealing effect is very good. The hole 17 extends almost along the entire width of the seal body 16, whereby the elongated sealing elements 15 can move widthwise of the end seal 13 as the size of the area to be sealed changes. The drawings and the description are only intended to illustrate the idea of the invention. The invention may vary in its details within the scope of the claims. It is thus not essential what pressure medium is used in the pressure chamber 9 and the water chamber 10. The pressure medium in the pressure chamber 9 can thus be, for example, steam, air, hot fuel combustion residue or water. In the water chamber 10 e.g. air, in addition to water, can be used as pressure medium.

Claims

1. A sealing arrangement in a fibre web drying apparatus comprising two endless bands (1, 2) that are impermeable to air, first turning rolls (6a, 6b), around which the first band (1) is arranged to turn, and second turning rolls (7a, 7b), around which the second band (2) is arranged to turn; the first (1) and second (2) bands being arranged to run part of the way in parallel such that they define a drying zone between them; the first band (1) being arranged to be heated by a chamber (9) containing pressure medium, and the second band (2) being arranged to be cooled by a chamber (10) containing pressure medium; a fibre web (5) and at least one felt or wire (3, 4) running between the bands (1 , 2) such that the fibre web (5) is in contact with the first, heated band, and the felt or wire (3, 4) is between the fibre web and the second, cooled band (2); and the drying apparatus comprising, on the side of these chambers (9, 10), side chambers (11) which enclose the edge of the bands (1, 2) and are separated from the chambers (9, 10) and from the ambient air, and in which the pressure medium dripping from the two chambers, from between the bands (1, 2) and the body portions (9b, 10b) of the chambers (9, 10), collect, characterized by comprising an end seal (13) at an end of the side chamber (11), the end seal (13) comprising several elongated sealing elements (15) which are attached at at least one end and which have a length that is greater than the height of the area to be sealed.

2. An arrangement according to claim 1, characterized in that the elongated sealing elements (15) are attached at their both ends.

3. An arrangement according to claim 2, characterized in that the end seal (13) comprises a body (16), attachment means for attaching the elongated sealing elements (15) at their both ends to the body (16), and a hole (17) in the body (16), the elongated sealing elements (15) being attached at their different ends to different sides of the body (16) and led through the hole (17).

4. An arrangement according to any one of the preceding claims, characterized in that the length of the elongated sealing elements (15) in the sealing direction is more than 50 times the diameter of the elements.

5. An arrangement according to any one of the preceding claims, characterized in that the elongated sealing elements (15) are wire yarns with a thickness of about 0.5 mm.