TECHNICAL FIELD

The invention relates to an apparatus for washing and/or dewatering of cellulose pulp. BACKGROUND

Apparatuses for washing and/or dewatering of cellulose pulp are known in the art. Many different types of washing apparatuses are available, some of which are based on press washing and comprise means for pressing the pulp to remove liquid.

The twin-roll press is a well-known type of such a washing apparatus, which is provided with two counter-rotating rolls with perforated outer surfaces. A web of pulp is formed on the respective rolls and is transported in the direction of rotation in a vat partially surrounding the rolls, to the so-called press nip between the rolls. The liquid removed from the pulp, i.e. the filtrate, passes through the perforated roll surface in a radial inwards direction and is led to the ends of the press roll, where it is output. Washing liquid or other treatment liquid may be supplied to the pulp web through inlets in the vat. The twin-roll press uses displacement washing, where dirty liquid (liquor) in the pulp is replaced by cleaner wash liquid added to the vat, and pressing, and where the dirty liquid is pressed (squeezed) out from the pulp, in particular at the press nip.

Incoming pulp may be distributed lengthwise onto the respective rolls by means of a distribution device, for example as shown in EP1229164, which comprises a pressurized rotating screw.

Another type of distribution device is disclosed in WO2009131527, which distribution device comprises an inlet box with an inlet for incoming pulp and an outlet which opens towards the pulp web on the rotating roll, and wherein distribution means such as a feed screw is arranged inside the inlet box. SUMMARY

An object of the invention is to provide an apparatus for washing and/or dewatering of cellulose pulp having further improved capacity and/or performance and/or a simplified construction.

These and other objects are achieved by the present invention by means of an apparatus according to the independent claim. Preferred embodiments are defined in the dependent claims.

According to the invention, there is provided an apparatus for washing and/or dewatering of cellulose pulp, which apparatus comprises at least one rotatable press roll having a permeable outer surface, and at least one corresponding chamber wall at least partly enclosing the roll to define a pulp treatment chamber between the roll and the wall, at least one pulp distribution device extending along the length of the press roll and a discharge device arranged adjacent at least one of the pulp distribution device(s). The pulp distribution device comprises an inlet and an outlet, and is arranged to distribute pulp through its outlet onto the permeable outer surface. The discharge device extends along the length of the at least one press roll, and is arranged to remove pulp from the corresponding pulp treatment chamber. The apparatus furthermore comprises a sealing device being common for the discharge device and one of the at least one pulp distribution device, the sealing device comprising at least one sealing element bearing against the outer surface in order to seal against the press roll and to seal between the pulp distribution device and the discharge device.

In other words, the apparatus comprises a sealing device which provides the sealing function against the press roll for both the discharge device and one of the at least one pulp distribution devices, and furthermore seals between the discharge device and the pulp distribution device, i.e. separates the discharge device from one of the at least one pulp distribution devices at the outer surface of the press roll. The sealing device may be positioned between the discharge device and the pulp distribution device, or may form part of, such as a wall portion of, the discharge device and/or pulp distribution device. Consequently, a simple and effective configuration is achieved, which also allows the discharge device and the pulp distribution device to be positioned immediately adjacent, or even in abutment with, each other (as seen in the tangential direction of the drum), thereby resulting in use of a larger angular portion of the press roll(s). The sealing device may be called a sealing beam, since it is normally elongated and extends along the length of the press rolls.

The invention is thus based on the insight that a larger angular portion of the drum(s) may be used for dewatering/pressing by providing a common sealing device for the discharge device and a distribution device. The invention is furthermore based on the insight that such a sealing device results in a more economical apparatus with fewer parts.

It is understood that the sealing device, which is common for the discharge device and one of the at least one pulp distribution device, is a device formed as one unit, which may however comprise several parts. It is furthermore understood that the chamber wall which at least partly encloses the roll may be formed of a vat, or a vat together with one or more fixed or movable plates or wall portions. The vat itself may furthermore be formed of one or more parts.

In an embodiment, the apparatus is a twin-roll press having two rotatable press rolls, and a corresponding chamber wall or vat for each roll, and two pulp distribution devices (one for each press roll), and a discharge device which is common for both press rolls. The discharge device is normally positioned above the nip. In this embodiment, two sealing devices are provided, wherein a first sealing device bears against the outer surface of a first press roll in order to seal against the first press roll and to seal between a first pulp distribution device and the common discharge device. In the same manner, a second sealing device bears against the outer surface of a second press roll in order to seal against the second press roll and to seal between a second pulp distribution device and the common discharge device.

In an alternative embodiment, the apparatus is a drum washer having one press roll, and consequently only one chamber wall or vat, one pulp distribution device and one discharge device.

In an embodiment, the common sealing device comprises two sealing elements arranged in parallel with a space there between. The common sealing device may be provided with at least one spray nozzle between the sealing elements, the at least one spray nozzle being arranged to clean the press roll. The sealing device may comprise two essentially parallel walls, each wall being provided with one of the sealing elements, wherein the sealing element is provided with an upper opening such that the press roll is visible from above between via a space formed between the walls.

In an alternative embodiment, the common sealing device comprises a single sealing element. In other words, one elongated sealing element or rib is provided along the length of the sealing device and press roll(s). Thus, the seal against the press roll and the seal between the pulp distribution device and the discharge device are both provided with one single sealing element which bears against the press roll along a single line of contact. Thus, the single sealing element separates the pulp distribution device from the discharge device at the outer surface of the press roll. Consequently, a compact and simple sealing device is achieved which occupies the shortest possible part of the circumference of the press roll. Although this embodiment does not have the possibility to visually inspect the press roll such as in the above described embodiment having two sealing elements, the inventors have realized that such visual inspection possibilities may not be necessary when the press is running, and that the roll may be monitored by other means, such as pressure measurements and/or measurements of fiber content in the filtrate. The sealing device may be provided with at least one spray nozzle arranged downstream the sealing element as seen in the direction of rotation. The at least one spray nozzle may be connected to a source of pressurized cleaning fluid in order to allow cleaning of the press roll.

In embodiments, the common sealing arrangement may be provided with a substantially tangentially extending surface portion facing the permeable surface of the press roll and being arranged at a distance therefrom. The surface portion extends from the vicinity of the sealing element and in the direction of rotation. This embodiment is advantageous since the pressure acting on the sealing element is decreased, resulting in reduced leakage and/or lower required pressure in the distribution device. This embodiment is preferably combined with the above described embodiment with a single sealing element, where the reduced pressure acting on the sealing element is particularly advantageous to reduce wear thereof. The distance may vary between 1 - 150mm depending on the application. The distance between the surface portion and the press roll may be non-constant, preferably the distance increases in the direction of rotation with the smallest distance closest to the sealing. This is advantageous since the risk of plugging in this area is decreased. The distances between the surface portion and the press roll varies depending on the application, but may be between 1 - 5 mm, preferably 1 -2 mm close to the sealing, whereas the distance at the opposite end of the surface portion may be up to 150 mm. At least one spray nozzle may be arranged through the tangentially extending surface portion. Thereby, injection of cleaning fluid is allowed into the space between the surface portion and the press roll to allow cleaning thereof.

In embodiments, the common sealing device is attached to, or forms part of, the pulp distribution device. This is advantageous since a further simplified apparatus is achieved, where the sealing device is mounted together with the pulp distribution device. The at least one pulp distribution device may be movably or rotatably arranged between an operating position and a service position, wherein access to the press roll is provided in the service position. Consequently, the sealing device is movable or rotatable together with the pulp distribution device, thus facilitating service of the apparatus. A side wall portion of the discharge device facing the pulp distribution device may be comprised in the common sealing device such that access to the interior of the discharge device is allowed when the at least one pulp distribution device is in the service position. In other words, the discharge device comprises an opening towards the pulp distribution device, and the sealing device comprises a side wall portion corresponding to the opening in the discharge device, thereby forming a side wall portion thereof.

In embodiments, the at least one pulp distribution device is of the type described in WO2009131527, i.e. comprises an inlet box having an inlet for incoming cellulose pulp to the inlet box and an outlet for transfer of the cellulose pulp onto the press roll, which outlet has a length that corresponds to the width of the press roll, and a rotating distribution means which is arranged to distribute the cellulose pulp along essentially the entire length of the outlet. The apparatus may be provided with a local throttle at or near the outlet of the pulp distribution device to facilitate initial dewatering through the outer surface of the press roll already in the pulp distribution device. In embodiments, the at least one corresponding chamber wall and pulp distribution device of the least one press roll together enclose more than 240°, and preferably at least 270°, and more preferably at least 290°, of the circumference of the outer surface of the press roll. Since initial dewatering may start already in the pulp distribution device, a long dewatering zone is thus provided.

The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail with reference to the appended drawings, which show presently preferred embodiments of the invention, wherein:

fig. 1 shows a schematic illustration of a prior art apparatus; fig. 2 shows parts of an embodiment of the invention provided with two parallel sealing elements attached to corresponding parallel walls;

fig. 3 shows parts of another embodiment of the invention provided with two parallel sealing elements; and

fig. 4 shows parts of yet another embodiment of the invention provided with a single sealing element.

DETAILED DESCRIPTION

Figure 1 shows a schematic illustration of a prior art apparatus for washing and/or dewatering cellulose pulp in the form of a twin-roll press. The apparatus comprises two press rolls 20 arranged to rotate in opposite directions, each roll having a permeable outer surface 21. The press rolls are partly enclosed by a vat (also referred to as a trough) having a vat wall 22 defining a vat chamber 25. The apparatus is provided with two pulp distribution devices 10, one for each press roll. The pulp distribution devices are arranged at upper portions of the press rolls for distribution of pulp onto the outer surface 21 of the press rolls.

Each pulp distribution device 10 comprises an inlet box or housing 18 which extends longitudinally along the respective press roll, and comprises an inlet 1 1 for incoming cellulose pulp to the inlet box and an outlet 12 for transfer of the cellulose pulp onto the press roll, which outlet has a length that corresponds to the width of the press roll and a rotatable distribution means 13, rotating in the direction of rotation D2, which distribution means is arranged to distribute the cellulose pulp along essentially the entire length of the outlet. The pulp distribution devices serve to form a pulp web on the outer surfaces 21 of the press rolls. Furthermore, depending on the configuration of the pulp distribution device, initial dewatering may take place already in the pulp distribution device. The pulp is thereafter transported along the vat chamber to the nip 23, where the distance between the press rolls is the smallest, and finally discharged from the apparatus by means of the discharge device 24 comprising a discharge screw. During the transportation, the pulp is dewatered by means of the permeable outer surfaces 21 , and optionally washed. The pulp distribution devices 10 and the discharge device 24 are each provided with sealing means bearing against the respective permeable outer surface 21 to provide sealing towards the upwardly open spaces between the pulp distribution devices and the discharge device 24.

In the apparatus shown in figure 1 , the vat wall 22 extends all the way from the pulp distribution device 10 to the nip 23, where the distance between the press rolls is smallest. The vat wall 22 and the pulp distribution device 10 of each press roll together enclose 230° of the circumference of the outer surface of the press roll.

In figure 1 , continuous vat walls 22 (partly) enclose the press rolls. In other embodiments, the vat wall is formed by two or more segments, which may be movable or rotatable to allow access to the press rolls. Furthermore, the vat walls may in other embodiments enclose a smaller portion of the circumference of the press rolls. The remaining portion of the circumference may be enclosed by one or more fixed or movable plates or wall portions which together with the vat form a pulp transportation chamber wall enclosing a pulp transportation or treatment chamber. In figure 1 , the pulp transportation chamber is the same as the vat chamber 25, and the chamber wall is the same as the vat wall 22. The pulp transportation chamber may furthermore be provided with means for supplying washing liquid thereto.

Figure 2 shows parts of an apparatus according to an embodiment of the invention, which apparatus corresponds to the apparatus shown in figure 1 , with the difference being different discharge and pulp distribution devices. The apparatus comprises a sealing device 126 formed as an elongated beam extending in the lengthwise direction of the press roll 120. The sealing device 126 is common for the discharge device 124 and the pulp distribution device 1 10. The sealing device comprises two sealing elements 127a, 127b bearing against said outer surface 121 in order to seal against the press roll and to seal between the pulp distribution device and the discharge device. The sealing elements are arranged at a distance from each other, being attached to corresponding walls 128a, 128b, both extending along the length of the press roll and forming a space there between. A spray nozzle 130 is arranged between the walls 128a, 128b to allow cleaning of the outer surface of the press roll. The common sealing device is either attached to, or forms part of, the pulp distribution device. The attachment may be realized in the form of a bolted connection 131 . The walls 128a, 128b may extend all the way to the top of the apparatus or be connected to wall portions 129a-b of the pulp distribution device. An opening 132 is provided between the walls to allow visual inspection of the press roll from above. In this embodiment, the pulp distribution device is rotatably arranged (around a lower axis of rotation, not shown in the figure) between an operating position and a service position (rotated clockwise relative the shown position), wherein access to the press roll is provided in the service position. The wall 128a (and optionally 129a) forms a side wall portion of the discharge device facing said pulp distribution device such that access to the interior of the discharge device is allowed when the at least one pulp distribution device is in the service position. It is understood that the apparatus comprises a further sealing device on the left hand side of the discharge device 124 which is common for the discharge device and another pulp distribution device co-operating with a press roll being parallel to press roll 120. In other embodiments, the common sealing device may be attached to, or form part of, the discharge device 124, and the wall 128b (and optionally 129b) may form a side wall portion of the pulp distribution device facing said discharge device. In further embodiments, the pulp distribution device does not necessarily have to be rotatable, but may instead be fixed.

Figure 3 shows parts of an apparatus according to an embodiment of the invention, which embodiment corresponds to the embodiment in figure 2, with the main difference being that the sealing elements 227a, 227b are attached to a common wall portion 229 at a smaller distance from each other in order to occupy a smaller portion of the circumference of the press roll. Consequently, the pulp distribution device 210 encloses a larger portion of the circumference. Furthermore, the construction is simplified compared to the embodiment in figure 2 and may thus be cheaper to manufacture. This configuration however does not allow visual inspection of the press roll between the wall portions 229a-b of the pulp distribution device as in the embodiment in figure 2.

Figure 4 shows parts of an apparatus according to an embodiment of the invention, which embodiment corresponds to the embodiment in figure 3, with the main difference being that only a single sealing element 327 is provided, which consequently occupies an even smaller portion of the circumference of the press roll, such that the pulp distribution device 310 encloses an even larger portion of the circumference. In this embodiment, the chamber wall 322 and the pulp distribution device 310 of the press roll together enclose about 296° of the circumference of the outer surface of the press roll. The side wall 328 of the common sealing device 326 is provided with a portion 333 which extends from the vicinity of the sealing element and in the direction of rotation, and has a substantially tangentially extending surface portion facing the outer surface of the press roll and being arranged at a distance therefrom. The distance between the surface portion and the press roll increases in the direction of rotation with the smallest distance closest to the sealing element. A spray nozzle 330 is arranged through the wall portion 333 in a downstream position relative the sealing element 327 as seen in the direction of rotation in order to allow cleaning of the press roll and the space between the wall portion 333 and the press roll.

The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, the pulp distribution device may enclose a smaller portion of the circumference of the outer surface of the press roll (with the pulp transportation chamber wall thus enclosing a larger portion). The scope of protection is determined by the appended patent claims.