EP2539504A1

EP2539504A1 - Dewatering press

Info

Publication number: EP2539504A1
Application number: EP11704981A
Authority: EP
Inventors: Fredrik NÄSLUND
Original assignee: Andritz Oy
Current assignee: Andritz Oy
Priority date: 2010-02-25
Filing date: 2011-02-22
Publication date: 2013-01-02
Also published as: CN102782212A; WO2011104209A1; SE534578C2; BR112012021235A2; SE1050177A1; CN102782212B

Abstract

A press for dewatering a liquid suspension of a solid biological material comprises a liquid-permeable dewatering drum, which is rotatably mounted in a frame, and a press trough which is adapted to press the liquid suspension against the liquid-permeable dewatering drum in such a manner that liquid is pressed into the dewatering drum, the press trough being adapted to be sealed against the frame by means of a trough seal (40) arranged in a trough seal retainer (42) which extends around at least part of the press trough, said trough seal retainer being adapted to retain, at least along one portion (50a-d) of its extension, the trough seal (40) with an inner radius of curvature between 20 and 800 mm.

Description

DEWATERING PRESS

Field of the Invention

The present invention relates to a press for dewatering a liquid suspension of a solid biological material. The invention further relates to a trough seal retainer and a trough seal ring for such a press as well as a method of manufacturing a trough seal ring.

Background Art

When dewatering a liquid suspension of a solid biological material, for example a suspension of cellulose fibres which are to be used for making paper pulp, use is often made of a press comprising a dewatering drum. Generally, the dewatering drum has a filter net or a screen plate on the outside thereof, against which the pulp is compressed in a gap formed between a press trough forming part of the press and the dewatering drum. The liquid that is pressed out of the suspension passes through the filter net or the screen plate, respectively, and into the drum. The liquid is then conducted out of the drum, while dewatered pulp is scraped off of the outside of the drum and conducted away for further treatment.

WO 2009/038529 discloses such a dewatering press.

The dewatering drum is rotatably mounted in a frame and the press trough is usually vertically adjustable relative to the drum and the frame. An object of said vertical adjustability is to facilitate cleaning, service and maintenance of the parts of the press that can only be accessed via the gap, since these parts are more easily accessible when the press trough is in its lowered position. Because the suspension is supplied to the dewatering press under pressure, it is important to ensure excellent tightness between the press trough and the frame. This is often solved by means of an inflatable, rectangular trough seal ring which is made of a hollow rubber profile. Owing to its inflatability it is capable of absorbing relatively large movements between the frame and the press trough. There is, however, a need for an improved trough seal. Summary of the Invention

An object of the present invention is to provide an improved trough seal.

This object is achieved by a press for dewatering a liquid suspension of a solid biological material, which press comprises a liquid-permeable dewatering drum, which is rotatably mounted in a frame, and a press trough which is adapted to press the liquid suspension against the liquid-permeable dewatering drum in such a manner that liquid is pressed into the dewatering drum, the press trough being adapted to be sealed against the frame by means of a trough seal arranged in a trough seal retainer which extends around at least part of the press trough, said trough seal retainer being adapted to retain, at least along one portion of its extension, the trough seal with an inner radius of curvature, as seen from above, between 20 and 800 mm. By using the trough seal retainer to create a bend on the trough seal having such a radius of cur- vature the trough seal can be made to change direction, and follow a desired path around the press trough, without requiring any jointing in the bend concerned. This facilitates the mounting of the trough seal, since fewer joints will be required to obtain a continuous trough seal. Preferably, said at least one portion of the trough seal retainer is arranged to retain the trough seal with an inner radius of curvature, as seen from above, between 30 and 200 mm, and more preferred between 60 and 100 mm.

Preferably, the trough seal retainer is arranged to retain the trough seal with an inner radius of curvature exceeding 20 mm along the whole length of the trough seal retainer. This facilitates the mounting of the trough seal con- siderably since no laborious corner jointing is required. More preferably, the trough seal retainer is arranged to retain a trough seal whose radius of curvature exceeds 30 mm, and even more preferred 60 mm, along the whole length of the trough seal retainer.

In one embodiment, the trough seal retainer comprises four substan- tially straight portions, which are interconnected by four curved portions so as to form a quadrangle with rounded corners, the curved portions having an inner radius of curvature exceeding 20 mm. Preferably, said four curved portions have an inner radius of curvature exceeding 30 mm, and more preferred 60 mm.

In one embodiment, the press trough is vertically adjustable relative to the frame between an operating position, in which the press trough is arranged to abut in a sealing manner against the frame by way of the trough seal, and a maintenance position, in which an air gap is formed adjacent to the trough seal between the frame and the press trough. This facilitates, for example, service and washing of the press gap that is formed between the dewatering drum and the press trough.

In one embodiment the trough seal retainer is fixedly attached to the frame.

In one embodiment the trough seal retainer is substantially U-shaped in cross-section for receiving the trough seal. Preferably, the trough seal retainer is arranged on the frame and its U-shaped cross-section is open downwards; furthermore the press trough is provided with a sealing collar against the upper surface of which the trough seal is adapted to abut in a sealing manner. In this way a substantially even sealing collar can be provided which is easy to wash. According to another aspect, an improved trough seal is achieved by means of a trough seal retainer for a press for dewatering a liquid suspension of a solid biological material, the trough seal retainer being adapted to retain a trough seal for sealing between a press trough and a frame for a dewatering drum, the trough seal retainer comprising at least one portion along its exten- sion that is adapted to retain the trough seal with an inner radius of curvature, as seen from above, between 20 and 800 mm. By using the trough seal retainer to create a bend on the trough seal having such a radius of curvature the trough seal can be made to change direction, and follow a desired path around the press trough, without requiring any jointing in the bend concerned. This facilitates the mounting of the trough seal, since fewer joints will be required to obtain a continuous trough seal. Preferably, said at least one portion of the trough seal retainer is arranged to retain the trough seal with an inner radius of curvature, as seen from above, between 30 and 200 mm, and more preferred between 60 and 100 mm.

Preferably, the trough seal retainer is adapted to retain the trough seal with an inner radius of curvature exceeding 20 mm along the whole length of the trough seal retainer. This facilitates the mounting of the trough seal considerably since no laborious corner jointing is required. More preferably, the trough seal retainer is arranged to retain a trough seal whose radius of curva- ture exceeds 30 mm, and even more preferred 60 mm, along the whole length of the trough seal retainer. In one embodiment, the trough seal retainer comprises four substantially straight portions, which are interconnected by four curved portions so as to form a quadrangle with rounded corners, the curved portions having an inner radius of curvature exceeding 20 mm. A trough seal retainer of this kind is particularly well suited for integration in currently commercially available dewatering presses which have a shape that makes them suitable for trough seal retainers adapted for jointed corners, whereby such presses too can benefit from the advantages of the present invention. Preferably, said four curved portions have an inner radius of curvature exceeding 30 mm, and more preferred 60 mm.

In one embodiment the trough seal retainer is substantially U-shaped in cross-section for receiving the trough seal.

According to a further aspect, an improved trough seal is achieved by a method of manufacturing a trough seal ring for a press for dewatering a liquid suspension of a solid biological material, comprising providing an elongate trough seal which is substantially straight at rest and has a first end and a second end, and joining said first end to said second end so as to form a trough sealing ring which along at least one portion of its extension has a ra- dius of curvature, as seen from above, between 20 and 800 mm. By creating in this way a bend on the trough seal having such a radius of curvature, the trough seal can be made to change direction, and follow a desired path around a press trough, without requiring any jointing in the bend concerned. This facilitates the mounting of the trough seal, since only one joint will be required to obtain a continuous trough seal. Preferably, the method comprises forming a trough seal ring which along said at least one portion of its extension has an inner radius of curvature, as seen from above, between 30 and 200 mm, and more preferred between 60 and 100 mm.

Preferably, the trough seal ring has a radius of curvature exceeding 35 mm along its whole extension. More preferably, the trough seal ring has a radius of curvature exceeding 30 mm, and even more preferred 60 mm, along its whole extension.

In a preferred embodiment, the method comprises positioning the trough seal in a trough seal retainer arranged on the press. This means that the trough seal retainer can be caused to retain the trough seal in such a manner that it maintains the desired radius of curvature.

In a preferred embodiment, said joining is achieved by vulcanization. In a preferred embodiment, the trough seal described above is inflatable. An inflatable trough seal profits much by the invention since its curved portion offers better inflatability and thus also a better sealing effect compared with the inflatability and sealing effect of an angled joint. This is due to the fact that the rubber material of an angled joint, which has a very small radius, will be thicker than the rubber material of a jointless portion with a greater radius of curvature; by way of example the rubber material of a 90 degree angle joint is 2 times thicker than the rubber material of a straight portion, since both joint ends of the rubber seal are cut at an angle of 45 degrees. Angled joints therefore result in impaired inflatability in the corners. Moreover, the actual hot vulcanization process that is normally used results in a thicker rubber material in the joint, which gives a slightly impaired inflatability also for a joint located in a substantially straight portion. Consequently, it is particularly desirable in the case of an inflatable trough seal to keep the number of joints at a minimum.

According to yet another aspect, an improved trough seal is achieved by means of an inflatable trough seal ring for sealing between a frame and a press trough in a press for dewatering a liquid suspension of a solid biological material, the trough seal ring having a minimum radius of curvature of at least 20 mm. A trough seal ring of this kind has no angled joints and is therefore easier to manufacture. It also allows a better seal between the trough and the frame. Preferably, said trough seal ring has a minimum radius of curvature of 30 mm, and more preferred 60 mm.

The press, the trough seal retainer, the trough seal ring and the method described above are suitable for dewatering paper pulp.

Brief Description of the Drawings

The invention will now be described in more detail, reference being made to the accompanying drawings.

Fig. 1 is a schematic cross-sectional view which illustrates a press for dewatering cellulose pulp.

Fig. 2 is a schematic perspective view along section ll-ll in Fig. 1 , with parts removed, and shows the press obliquely from below.

Fig. 3a is an enlarged cross-sectional view of the area III shown in

Fig. 2 with the press trough in its elevated position. Fig. 3b is an enlarged cross-sectional view of the area III shown in Fig. 2 with the press trough in its lowered position.

Fig. 4 is a schematic perspective view obliquely from below of a trough seal retainer and a trough seal.

Fig. 5 is an enlarged plan view of the area V shown in Fig. 4 with the trough seal mounted in the trough seal retainer.

Fig. 6 is an enlarged view of the cross-section VI-VI shown in Fig. 4, with the trough seal mounted in the trough seal retainer.

Fig. 7 is an enlarged plan view of an alternative embodiment of the area V shown in Fig. 4, with the trough seal mounted in the trough seal retainer.

Description of Preferred Embodiments

Fig. 1 illustrates, as seen from the side and in cross-section, a dewa- tering device in the form of a press 1 for dewatering a liquid suspension of a solid biological material, such as cellulose pulp. The press 1 has a first dewatering drum 2 and a second dewatering drum 4. The dewatering drum 2 is arranged to rotate counter-clockwise, as indicated by an arrow R in Fig. 1 . The dewatering drum 4 is arranged to rotate in the opposite direction, i.e. clockwise, but is, for the rest, similar in parts and function to the first dewatering drum 2, even though the second dewatering drum 4 is mirror-inverted relative to the first dewatering drum 2, and therefore the second dewatering drum 4 will not be described in more detail here.

The press 1 further comprises a press device in the form of a press trough 6 inside which the first dewatering drum 2 is arranged for rotation. The lower part of the drum 2 is surrounded by the press trough 6, and the upper part of the drum 2 is surrounded by a trough top 7. At one side the trough top 7 has an inlet 8 for a liquid suspension of cellulose pulp, i.e. wet cellulose pulp with a dry content typically in the range 3-15% by weight TS. The press trough 6 is provided with a number of liquid inlets 10 through which wash liquid may be supplied to the pulp.

When dewatering a liquid suspension the suspension is supplied to the press trough 6 via the inlet 8, as indicated by an arrow M, and is then compressed in the press gap 12 formed between the press trough 6 and the drum 2. The liquid contained in the suspension is pressed through the periphery of the drum 2 and into the interior of the drum 2, as indicated by an arrow W in Fig. 1 . Supplied washing liquid will also be compressed into the interior of the drum 2, as indicated by an arrow C. The liquid pressed inside will accumulate at the bottom of the drum 2 and flow out therefrom, in a manner that will be described below with reference to Fig. 2.

When the pulp has been sufficiently dewatered it is discharged from the press trough 6 at the point 14 shown in Fig. 1 and will then be pressed against the pulp that has been dewatered in a corresponding manner on the second dewatering drum 4. A scraper 16 is arranged to scrape off the dewatered cellulose pulp, which may typically have a dry content of 25-40% by weight TS, from the drum 2, whereby the dewatered pulp is pressed into a conveying pipe 18 and is discharged from the press 1 , as indicated by an arrow P.

Fig. 2 is a cross-sectional view along the section ll-ll in Fig. 1 and illustrates the first dewatering drum 2, and additional portions of the press 1 , obliquely from below. For the purpose of clarity the press 1 is illustrated with certain parts removed. The drum 2 has two end plates 20, only one of which is shown. The end plates 20 are arranged at either end of the drum 2 and have each a shaft journal 24 (only one is shown) so that the drum 2 is jour- nalled in a frame 27. The frame 27 stands on a solid base, e.g. a floor.

The dewatering drum 2 has a support pipe 28, which has the shape of a cylindrical sleeve attached to the two end plates 20. The support pipe 28 is provided with a number of openings 30, which are substantially evenly distributed across the support pipe 28, as is also indicated in Fig. 1 . Through these openings 30, liquid is able to pass into the interior of the drum 2 as liq- uid is being pressed out of the pulp by the press trough 8 and by the second drum 4 (Fig, 1 ). A liquid-permeable screen plate 48 surrounds the support pipe 28, and is separated from the support pipe 28 by means of lamellar rings 35,

The support pipe 28 has a length that is greater than the length of the portion of the support pipe 28 whose lower end is surrounded by the press trough 6. Thus, the press trough 6 extends only along the lower portion of the support pipe 28 along part of the whole length of the support pipe 28. A drainage arrangement in the form of a group 32 of drainage openings 33 are provided in the support pipe 28 outside the area that is surrounded by the press trough 6. Accordingly, the group 32 of openings 33 is provided in the outermost portion of the support pipe 28, as seen in the axial direction. The liquid that is pressed into the drum 2 in the portion that is surrounded by the press trough 6 will flow in the axial direction towards this group 32 of openings 33, and will be discharged from the drum 2 by way of the openings 33 of the group 32 as a liquid flow F, the liquid being thus drained from the drum 2. The liquid flow F passes out of the drum 2 via an outlet 34.

Sealing devices 36 are arranged at either end of the drum 2 for preventing liquid from leaking out from the drum 2 into the surrounding environment and also for collecting the liquid that passes out of the drum 2 through the openings 33 of the group 32.

When the drum 2 is being used for dewatering a liquid suspension of cellulose pulp, liquid that has been pressed out of the pulp in the gap 12 shown in Fig. 1 , will penetrate into the interior of the drum 2 by way of the openings 30 formed in the support pipe 28, as indicated by an arrow W in Fig. 1 . The support pipe 28 is without inner structures by which the liquid tends to be conveyed during rotation of the drum 2, and therefore the liquid will rapidly flow to the bottom of the drum 2, as indicated in Fig. 1 . The liquid that has accumulated at the bottom of the drum 2 will flow rapidly in the axial direction along the drum 2, as shown in Fig. 2, towards the openings 33 of the group 32 and will flow out of the drum 2 through these openings 33 of the group 32, as indicated by the arrow F in Fig. 2.

In order to facilitate service and maintenance, for example washing of the gap 12 between the press trough 6 and the drum 2, the press trough 6 is vertically adjustable relative to the drum 2, the frame 27 and the trough top 7. The vertical adjustability is achieved in the example shown by the press trough 6 being arranged on hydraulic pistons 38 (Fig. 1 ), which can be caused to lower the trough 6 relative to the frame 27, thereby enabling access to the gap 12. During operation of the press it is desirable to minimize the amount of suspension that flows out of the trough 6; to this end the press 1 is provided with a trough seal 40, which during operation of the press 1 seals between a trough wall 9 and a frame wall 44. The trough wall 9 is fixedly connected to and forms part of the trough 6 and the frame wall 44 is fixedly connected to and forms part of the frame 27. The trough seal 40 runs in a horizontal plane around the whole press trough 6 and seals along its whole extension between the press trough 6 and the frame 27. In this way the press trough 6 and the frame 27 together form a substantially tight cover which encloses a lower part of the two drums 2, 4 (Fig. 1 ) and the press gap 12. The detail view of Fig. 3a illustrates more clearly how, during operation of the press, the press trough 6, the frame 27 and the trough seal 40 interact to form a seal between the press gap 12 and the surrounding environment around the press 1 . The trough seal 40 is located in a trough seal retainer 42 which is substantially U-shaped in cross-section and which is fixedly attached to the frame wall 44. The frame wall 44 is fixedly connected to and forms part of the frame 27. The frame wall 44, the trough seal retainer 42 and the trough seal 40 all extend around the trough 6.

The outside of the trough wall 9 of the trough 6 is provided with a protruding sealing collar 46 in the form of an elongate L-shaped sectional ele- ment of metal whose one leg is welded tight against the trough wall 9. Naturally, the sealing collar 46 can be sealingly joined to the trough 6 in any other suitable manner. The trough seal 40 in Fig. 3a is inflated, i.e. it has been caused to expand by pressurisation of a gas in a cavity 54 in the trough seal 40. As is evident from Fig. 3a the trough seal 40 bulges slightly out of the trough seal retainer when inflated, so that the sealing collar 46 and the trough seal retainer 42 do not rub against each other. The U-shape of the trough seal retainer 42 helps to ensure, during inflation, that the trough seal 40 expands in the right direction, i.e. towards the sealing collar 46. Fig. 3b shows the same view when the press 1 is in a service position, i.e. when the press trough 6 is slightly lowered by means of the hydraulic pistons 38 (Fig. 1 ) as compared with the operating position shown in Fig. 3a. The service position allows better access to the press gap 12 for cleaning or other maintenance. In the embodiment shown the trough seal 40 is mounted on the frame 27 in such a manner that its surface for sealing against the vertically adjustable press trough 6 is oriented downwards. This means that the sealing surface of the press trough 6, which is formed of the upper side of the L-shaped sectional element, can be made substantially even. This makes it easier for rinsing water and pulp residue to drain away when cleaning the press gap 12.

Previously known trough seal rings are manufactured on site, during mounting of the trough seal in a rectangular trough seal retainer extending around the trough, by joining together four straight trough seal sections and four prefabricated, angled corner sections by means of hot vulcanization, so that the sections after vulcanization form a rectangular trough seal ring.

Sometimes four straight sections, whose ends are cut at an angle of 45°, are joined together by vulcanization, so that a rectangular, inflatable trough seal ring is obtained. However, this latter method of mounting the trough seal has been less preferred, since it requires a precision that can only be achieved in a workshop in order to obtain tight corners. It will be appreciated that the mounting of previously known trough seals is a relatively time-consuming and difficult operation, where parts of the frame need to be dismounted to enable easy access to the trough seal retainer.

Fig. 4 shows the trough seal retainer 42 according to one embodiment of the present invention obliquely from below. In the example shown, the trough seal retainer 42 consists of four straight U-beam sections 48a, 48b, 48c, 48d, which are interconnected by means of four curved U-beam profiles 50a, 50b, 50c, 50d. The U-beam profiles can for example be made of steel and joined together by welding joints. The trough seal retainer 42 is arranged to retain the inflatable rubber trough seal 40, which trough seal 40 will be de- scribed in further detail below with reference to Figs 5-7. As illustrated in Fig. 4 the trough seal 40 is provided with a compressed-air nipple 49 through which air can be supplied to the trough seal 40 for the purpose of inflating it. The nipple 49 is located adjacent an opening 51 in the trough seal retainer 42, which makes the nipple 49 accessible from the outside of the trough seal retainer 42.

The trough seal 40, which has a first end 41 and a second end 43, is arranged to form a closed trough seal ring 40' (dashed line) by joining the first end 41 to the second end 43. The trough seal ring 40' need not be circular; it may be for example substantially rectangular, as is evident from Fig. 4. Preferably the two ends 41 , 43 of the trough seal 40 are joined together by vulcanization. This makes the trough seal ring 40' essentially gas-tight, which is an advantage when inflating it. Preferably the ends are joined together at a straight segment of the trough seal retainer 42, as shown in Fig. 4, since this makes it easier to provide a durable joint. Moreover, it is preferred for the trough seal ring 40' to joined together at a straight angle, so that the trough seal ring thus formed is substantially straight at the joint and, consequently, has no angled portions along its length which have a radius of curvature r2 of less than 20 mm, according to the definition of the radius of curvature r2 of the trough seal that is illustrated in Fig. 5.

Fig. 5 illustrates in greater detail the curved portion 50b of the trough seal retainer 42, and the corresponding portion of the trough seal 40. The curved portion 50b has a total curvature of approximately 90°, which gives the trough seal retainer 42 and the trough seal 40 a substantially rectangular shape with rounded corners (Fig. 4). The curved U-beam profile 50b of the trough seal retainer 42 has an inner radius of curvature r1 , defined as the radius of curvature of its radially inner surface abutting against the trough seal 40, of 75 mm. Further, the trough seal retainer 42 has an outer radius of cur- vature r3, defined as the radius of curvature of its radially outer surface abutting against the trough seal 40, of 1 10 mm. This gives the curved U-beam profile 50b an inner width D1 of 35 mm. The trough seal retainer 42 retains an inflatable, non-inflated trough seal 40 of a width D2, which in the example shown is approximately the same as D1 . Consequently, in the example shown the inner radius of curvature r2 of the trough seal 40, i.e. the radius of curvature of the radially inner surface of the trough seal 40 that abuts against the trough seal retainer 42, is approximately the same as the inner radius of curvature r1 of the U-beam profile 50b. Preferably D1≥D2≥(0.8^*D1 ), so that the trough seal 40 during inflation is allowed to expand mainly in the vertical direction, out through the opening in the U-beam profile. A preferred range for the width D2 of the trough seal 40 is between 10 mm and 70 mm.

The factors determining the choice of radius of curvature r1 of the curved portions 50a-d of the trough seal retainer 42 are on the one hand low mechanical stress on the curved portion of the trough seal 40 inside the curved portion 50b of the trough seal retainer 42 as well as excellent inflat- ability of the same and, on the other, a space-saving change of direction of the trough seal 40. In order to ensure the best possible inflatability, and thus the best possible sealing effect, while at the same time meeting the need for compact, rounded corners and the possibility of arranging the trough seal retainer 42 also on existing dewatering presses, it is preferred to design the trough seal retainer 42 such that at a curved portion 50b the trough seal 40 has an inner radius of curvature r2 of 20 to 800 mm, more preferred 30 to 200 mm, and even more preferred 60 to 100 mm. In this way an effective change of direction of the trough seal 40 is achieved without necessitating cutting of the trough seal 40 and jointing of its ends, which would require extra work and result in reduced sealing effect. Fig. 6 is a cross-sectional view of the trough seal retainer 42 and the trough seal 40. The trough seal 40, which in Fig. 6 is shown in a non-inflated state, comprises a wall 52, which encloses a cavity 54 extending along the trough seal 40. A segment of the circumference of the wall 52 forms a contact surface 56, which is adapted, during operation, to abut in a sealing manner against the sealing collar 46 (Fig. 3a). Another segment of the circumference of the wall 52 is provided with an attachment means for form-fitting engagement in the form of barbs 58 extending along the length of the trough seal 40. The barbs 58, which are arranged to cooperate with corresponding grooves 60 in the trough seal retainer 42 make it possible to mount the trough seal 40 in the trough seal retainer 42 by pressing the trough seal 40 into the U-profile of the trough seal retainer 42 until the barbs 58 lock in their respective grooves 60.

Moreover, the trough seal 40 is provided with a waist portion 62, which extends along the length of the trough seal 40 and which during inflation of the trough seal 40 allows the latter to expand generously towards the contact surface of the press trough 6, i.e. in the example shown towards the upper surface of the sealing collar 46 (Figs 3a-b). Fig. 7 illustrates an alternative embodiment 50b' of the curved portion 50b of the trough seal retainer 42, which embodiment differs from that which has been described above with reference to Fig. 5. Also in the embodiment shown in Fig. 7, the curved portion 50b' of the trough seal retainer 42 has a total curvature of approximately 90°. However, the curvature of the trough seal retainer 42 is not formed by a rounded portion with a well-defined radius of curvature r1 , but by a plurality of obtuse angles 64a, 64b, which each are significantly greater than 90°. The fact that the U-beam profile 50b' has an inner width D1 ' which is significantly greater than the width D2' of the trough seal 40 makes it possible to give the trough seal 40 a rounded bend with a radius of curvature r2 without being affected by the corners formed by the angles 64a, 64b. In the example shown in Fig. 7 the radius of curvature r2 of the trough seal 40 is the same as that in Fig. 5, i.e. 75 mm. As the trough seal 40 is designed to allow, during inflation, expansion mainly in the vertical direc- tion, out through the opening in the U-beam profile, the radius of curvature r2 of the trough seal 40 will remain, during inflation, within the desired range of 20-800 mm along the whole curved portion 50b' of the trough seal retainer 42. Different inner U-profile widths D1 ', D1 " can be selected for different portions of the trough seal retainer 42 to obtain the desired radius of curvature r2.

It will be appreciated that many variants of the embodiments described above are conceivable within the scope defined by the appended claims.

A press trough 6 has been described above which can be lowered for enabling cleaning, service and maintenance. It is sometimes also desirable to be able to adjust the width of the press gap 12 between the press trough 6 and the dewatering drum 2 depending on the character of the suspension and the desired degree of dewatering, for example by raising or lowering the press trough 6 until the desired gap width has been obtained. In order to compensate for large variations in the gap width while maintaining the sealing effect of the trough seal 40 the mounting of the sealing collar 46 to the press trough 6 can be designed such that it allows vertical adjustment, for example by the sealing collar 46 being adapted to be attached by means of screws at alternative positions on the press trough 6 instead of being welded to the trough 6.

A press trough 6 which is vertically adjustable relative to a frame 27 has been described above. Of course, as an alternative or complement, the frame 27 too can be vertically adjustable relative to the press trough 6. The press 1 described above is provided with liquid inlets 10 for washing liquid. A press of this kind can be referred to as a washing press. Naturally, the trough seal retainer 42 and the trough seal 40, respectively, described above can be used for other types of presses, including presses that are not provided with means for washing the material that is being dewatered.

It has been described above how the press 1 , with the trough seal 40 and the trough seal retainer 42, is used for dewatering a liquid suspension containing cellulose fibres. It will be appreciated that the press 1 can also be used for dewatering other types of suspensions of solid biological material. Examples of such materials are different types of biomasses that are to be dewatered, and possibly washed, before being used for the production of fuel, for instance through an ethanol production process, a biogas production process, or a fuel pellets production process, or before combustion of the biomass. Examples of biomass that can be dewatered in the press described above are straw, bagasse, other annual plants, grass, tops, leaves, needles, seaweed, moss, etc. The liquid in the suspension can be water, but also other liquids, for example various organic or inorganic solvents, can be present in the suspension that is to be dewatered. Similarly, the gas for inflating the inflatable trough seal can be air, but also other types of gases are conceivable.

A trough seal 40 made of rubber has been described above. A person skilled in the art may be faced with the choice between different kinds of natural and synthetic rubber, as well as other polymeric and non-polymeric materials; these all fall within the scope of the appended claims.

It has been described above how the trough seal 40 is inflatable. Al- though this is often preferred, a trough seal which is not inflatable is conceivable. Such a trough seal can be completely solid, or completely or partly hollow. Suitably, the trough seal has a relatively high elasticity for providing the desired seal against the sealing collar 46. Furthermore, a substantially rectangular trough seal retainer 42 with rounded corners has been described above. It will be appreciated that the trough seal retainer can be given other shapes, such as the shape of an oval or an irregular polygon with one or more rounded corners. It will also be ap- preciated that the trough seal retainer can be arranged to retain the trough seal with a radius of curvature according to the invention without the corners of the trough seal retainer being rounded; a specific example thereof is given with reference to Fig. 7. Moreover, the trough seal retainer 42 need not have the shape of a U-beam; the trough seal 40 can also be mounted on the frame 27 in other ways, for example by means of a screw joint, such that screws of the screw joint retain the trough seal with a radius of curvature according to the invention. In this case, the screw joint will serve as the trough seal retainer. In addition, it is not necessary for the trough seal retainer 42, and thus the trough seal 40, to be mounted on the frame 27; they may also be mounted on the press trough 6. According to a less preferred example of such a solution, because a satisfactory draining is often desirable in the service position, the trough seal 40 can be arranged on the L-section 46, where it is caused in suitable manner, e.g. by means of spigots, to assume a radius of curvature according to the invention. In this case, the L-section will serve as the trough seal retainer.

Claims

CLAIMS 1 . A press for dewatering a liquid suspension of a solid biological material, said press (1 ) comprising a liquid-permeable dewatering drum (2), which is rotatably mounted in a frame (27), and a press trough (6) which is adapted to press the liquid suspension against the liquid-permeable dewatering drum (2) in such a manner that liquid is pressed into the dewatering drum (2), the press trough (6) being adapted to be sealed against the frame (27) by means of a trough seal (40) arranged in a trough seal retainer (42) which extends around at least part of the press trough (6),

c h a r a c t e r i s e d i n that the trough seal retainer (42) is adapted to retain, at least along one portion (50a-d, 50b') of its extension, the trough seal (40) with an inner radius of curvature (r2) between 20 and 800 mm.

2. A press according to claim 1 , wherein the trough seal retainer (42) is adapted to retain the trough seal (40) with an inner radius of curvature (r2) exceeding 20 mm along the whole length of the trough seal retainer (42).

3. A press according to claim 1 or 2, wherein the trough seal retainer (42) comprises four substantially straight portions (48a-d), which are interconnected by four curved portions (50a-d) so as to form a quadrangle with rounded corners, the curved portions (50a-d) having an inner radius of curva- ture (r1 ) exceeding 20 mm.

4. A press according to any one of the preceding claims, wherein the press trough (6) is vertically adjustable relative to the frame (27) between an operating position, in which the press trough (6) is arranged to abut in a seal- ing manner against the frame (27) by way of the trough seal (40), and a maintenance position, in which an air gap is formed adjacent to the trough seal (40) between the frame (27) and the press trough (6).

5. A press according to any one of the preceding claims, wherein the trough seal retainer (42) is fixedly attached to the frame (27).

6. A press according to any one of the preceding claims, wherein the trough seal retainer (42) is substantially U-shaped in cross-section for receiving the trough seal (40).

7. A press according to claim 6, wherein the trough seal retainer (42) is arranged on the frame (27) and its U-shaped cross-section is open downwards and wherein the press trough (6) is provided with a sealing collar (46) against the upper surface of which the trough seal (40) is adapted to abut in a sealing manner.

8. A trough seal retainer for a press (1 ) for dewatering a liquid suspension of a solid biological material, the trough seal retainer (42) being adapted to retain a trough seal (40) for sealing between a press trough (6) and a frame (27) for a liquid-permeable dewatering drum (2), the trough seal retainer (42) being c h a r a c t e r i s e d b y at least one portion (50a-d, 50b') along its extension that is adapted to retain the trough seal (40) with an inner radius of curvature (r2) between 20 and 800 mm.

9. A trough seal retainer according to claim 8, wherein the trough seal retainer (42) is adapted to retain a trough seal (40) whose radius of curvature

(r2) exceeds 20 mm along the whole length of the trough seal retainer (42).

10. A trough seal retainer according to claim 8 or 9, which comprises four substantially straight portions (48a-d), which are interconnected by four curved portions (50a-d) so as to form a quadrangle with rounded corners, the curved portions (50a-d) having an inner radius of curvature (r1 ) exceeding 20 mm.

1 1 . A trough seal retainer according to any one claims 8-10, wherein the trough seal retainer (42) is substantially U-shaped in cross-section for receiving the trough seal (40).

12. A method of manufacturing a trough seal ring (40') for a press (1 ) for dewatering a liquid suspension of a solid biological material, comprising providing an elongate trough seal (40) which is substantially straight at rest and has a first end (41 ) and a second end (43), the method being characterised by joining said first end (41 ) to said second end (43) so as to form a trough seal ring (40') which, at rest and along at least one portion (50a-d) of its extension, has a radius of curvature (r2) between 20 and 800 mm.

13. A method according to claim 12, wherein the trough seal ring (40') has at rest a radius of curvature (r2) exceeding 20 mm along its whole extension.

14. A method according to claim 12 or 13, further comprising position- ing the trough seal (40) in a trough seal retainer (42) arranged on the press

(1 )-

15. A method according to any one of claims 12-14, wherein said joining is achieved by vulcanization.

16. A press, a trough seal retainer or a method according to any one of the preceding claims, wherein the trough seal (40) is inflatable.

17. An inflatable trough seal ring for sealing between a frame (27) and a press trough (6) of a press (1 ) for dewatering a liquid suspension of a solid biological material, the trough seal ring being characterised by a minimum inner radius of curvature (r2) of at least 20 mm.

18. A press, a trough seal retainer, a trough seal ring or a method according to any one of the preceding claims, wherein the press (1 ) is a dewatering press for paper pulp.