ARRANGEMENT WITH WHITE WATER CHANNEL

Abstract: An arrangement at a white water channel for handling of white water from a paper machine, which arrangement comprises a channel with an inlet end (1), which is arranged in connection to an outlet (2) for white water from a paper machine (3), an outlet end (4), which is provided with a main outlet (6), which runs to a container device (5), preferably a white water silo, wall portions (5A, 5B) which are provided between and at said channel ends (1, 4), and a channel bottom portion (8), said channel bottom portion (8) being arranged at a certain angle of inclination ( alpha 1) in relation to the horizontal plane, which angle ( alpha 1) must not be below a certain critical angle of inclination in order to avoid sedimentation on the bottom portion (8) of the channel, wherein at least one additional outlet (9) is provided between said main outlet (6) and said inlet end (1) in such a way that the bottom portion (8) of the channel is divided into first (8A) and second (8B) bottom portions, which are so arranged in relation to each other that the angle of inclination ( alpha 1, beta 2) for each one of said bottom portions (8A, 8B) exceeds said critical angle of inclination ( beta ).

Description: ARRANGEMENT WITH WHITE WATER CHANNEL The present invention relates to an arrangement with a white water channel, for the handling of white water from a paper machine, which arrangement comprises a channel with one inlet end which is provided in connection to an outlet for white water from a paper machine and an outlet end which is provided with an additional, main outlet, which additional outlet runs to a container device, preferably a white water silo; wall portions provided between and at said channel ends; and a channel bottom, said channel bottom being provided with a certain angle of inclination αl to the horizontal plane, which angle αl must not be below a certain critical angle of inclination in order to avoid sedimentation on the channel bottom. . KNOWN TECHNIQUE AND PROBLEMS In the wet end of a paper machine large amounts of water must be disposed of/drained from the pulp suspension/stock in order to cause formation of a fibre web. In very large machines it can be the question of about 1 m 3 /s, which is dewatered in the forming zone. This liquid, so called white water, must be handled in a rational and cost efficient manner. Almost the entire white water is collected (in a white water silo) and is therefore recirculated for use within other fields in the process, e.g. for dilution, washing of the pulp, etc. It is necessary that the air content is relatively low in order to be able to reuse the white water. Suitably, the removal of air is made in the simplest possible way, i.e. by giving the white water a sufficiently long stay for the air bubbles to rise to the surface and thus be removed from the water. For this purpose, a so called white water channel is provided at a paper machine. The channel has a certain length and width as well as a certain flow rate which are adopted to give the desired deaeration. Normally, the flow rate in the white water channel should not exceed 0.5 m/s to obtain good deaeration. Further, it is important to avoid turbulence, as there is otherwise a risk that the air bubbles will rotate down into the water again. In order not to disturb the flow mode, sedimentation on the bottom in the white water channel should be avoided. In order to avoid such sedimentation, the white water channel is provided with a certain, critical inclination in the flow direction, so that fibres and other particles can move safely against the outlet. Experience shows that said critical inclination should be at least 2°, suitably at least 3°, in order to create a safety "cleaning" of the bottom. In many installations there is, however, no possibility to provide the white water channel with a sufficiently great inclination, for instance depending on the fact that the mounting height of the bottom of the outlet from the paper machine is low in combination with a white water silo being place far from the paper machine. Known solutions of the above problems are that special cavities/recesses have been created in the floor of the plant on which the paper machine stands, so that sufficient inclination is obtained at the bottom of the channel which goes to the silo, which is placed on the bottom floor, i.e. a floor at a plane below the machine floor. In certain cases, essential portions of the machine floor must be removed in order to obtain sufficient inclination. It is realised that such a solution is not desirable, neither from a economic point of view nor from a safety point, on one hand it is expensive to cut away concrete material and to construct a suitable channel arrangement therein, and on the other hand it can imply that the stability/safety of the building can be difficult to maintain at a desirable level. An arrangement in connection with a white water channel is previously known through DE-29916787 Ul, the purpose of which is to prevent admixture of air because of, creation of whirls in the white water channel. The white water channel is divided into two entirely separate sections, which are located at different levels, the one above the other. The white water can flow down from the upper section to the lower one through a plurality of outlet pipes located at different levels. Through this arrangement, the ^ creation of whirls is thus prevented and hence admixture of air in the white water channel. There are, however, several drawbacks with such an arrangement. Firstly, because of the division into different levels, this design requires special conditions as to the plant building in order to make it possible to apply such an arrangement at all. It is not always desirable that such an adoption of the plant building should have to be made in order to eliminate air problems in the white water channel. Further, the design as such implies increased costs for outlets, etc., which is not desirable. Finally, it is uncertain if " such an arrangement according to the known construction is suitable for the removal of the small bubbles which are formed in connection with the formation and which follow the white water into the white water channel. As already mentioned, there is an advantage if the many small bubbles which are formed in connection with the formation are removed from the back water before it is re-circulated. DISCLOSURE OF THE INVENTION It is a purpose of the present invention to eliminate or at least minimise the problems mentioned above, which is achieved by an arrangement at a white water channel for handling white water from a paper machine, said arrangement comprising an inlet end which is arranged in connection to a white water outlet from the paper machine; an outlet end which is provided with a main outlet, said main outlet being connected to a container device, preferably a white water silo; wall portions provided between and at said ends of the channel; and a channel bottom, said channel bottom being arranged at a certain angle of inclination relative to the horizontal plane, which angle must not be below a certain critical angle of inclination in order to avoid sedimentation on the channel bottom, characterised therein that said additional outlet is provided between said main outlet and said inlet in such a way that the channel bottom is divided into a first and a second bottom portion, which are arranged in such a way relative each other that the angle of inclination for both of said bottom portions exceed said critical angle of inclination. Because of said arrangement you avoid the need to make changes of the existing floor surface on which the paper machine stands, while you save money as the construction in itself is very cost efficient. According to further aspects of the invention: - said critical angle of inclination is 2°, preferably 2,5°, and suitably 3°; - the start level H 3 of said second bottom portion is higher than the final level H 2 of said first bottom portion; - the start level H 3 of said second bottom portion essentially corresponds to the start level Hi of said first bottom portion; - a towards the flow of direction inclined bottom portion is provided between the start level H 3 of said second bottom portion and the rear edge of the additional outlet; - said bottom portion comprises a substantially linear portion, which is provided with an angle of inclination α3, wherein the angle α3 is larger than the angle αl and the angle α2, preferably the angle α3 is essentially larger than the angle αl and the angle α2; - an angle l and α2, respectively, is between 1 and 5°, preferably between 2,5 and 3 5°- - an angle of inclination αl is substantially as large as the angle α2, preferably the angles are quite similar; - an angle of inclination α3 is between 5 and 60°, preferably between 10 and 45°, suitably below 30°; - said additional outlet is connected to a pipe. BRIEF DESCRIPTION OF DRAWINGS The invention will be described more in detail below with reference to the enclosed drawings, of which Fig. 1 shows the principles for an arrangement according to a preferred embodiment of the invention; Fig. 2 shows an alternative embodiment according to the invention; and Fig. 3 shows a cross section through a white water channel according to the invention DETAILED DESCRIPTION In Fig. 1 a preferred embodiment of a water channel according to the invention is shown as well as the associated arrangement. An inlet end 1 of the channel is shown, which end is connected to an outlet 2 belonging to a paper machine 3. The paper machine 3 is arranged on a so called machine floor 11, which constitutes so to say a first floor level in the plant building. Below the machine floor 11 there is a bottom floor 12, on which a white water silo 5 is located. This silo is arranged at the outlet end 4 of the white water channel and receives white water through a main outlet 6. A pump 18 is provided to pump and/or to mix dilution water and the stock which is carried to the head box (not shown). In rear end of the white water channel there is an overflow 7 to guarantee that the white water level is kept substantially constant. Substantially vertical side walls 5 A, 5B are provided between the inlet end 1 and the outlet end 4. Further, the channel comprises a first 8A and a second 8B bottom portion, which portions are inclined in the flow direction. The second bottom portion 8B connects at its downstream end to said main outlet 6 at a level H 0 , which substantially coincides with the level of the machine floor 11. The start point for the second bottom portion H 3 lies at a level, which makes the bottom portion slope at a certain angle in relation to the horizontal plane. According to the preferred embodiment, this angle α2 is about 3°. Between the two bottom portions 8A and 8B there is an additional outlet 9 to which an outlet pipe 10 is connected. A pump 14 is provided at the end of the outlet pipe 10 to forward the white water. Suitably, said pump 14 is included in the reject circulation, wherein the drained liquid can be used for dilution of the reject pulp. From the rear side of said additional outlet 9 there is a bottom portion 8D, which is inclined at a rather large angle α3 in relation to the horizontal plane. According to said preferred embodiment, the start point Hi for the first bottom portion 8A is located at about the same level as the start point H 3 for the second bottom portion, but as can be seen from what is shown in the figure, said levels can vary somewhat and still maintain their functionality according to the invention. It should be observed that the level of the start point H 3 for the second bottom portion is not placed too high in relation to the liquid level in the white water channel, so that no detrimental turbulence can occur at said position. Normally, this risk does, however, not exist, as the inclination is very small, which implies a low height of the construction. As can be seen from the figure, a wall portion 2A is provided at the bottom end H m of the outlet of the paper machine, which wall portion is inclined at a large angle, about 45°, downwards against the start point HI of the first bottom portion 8A. The purpose of said first heavy inclined wall portion 2A is to reduce the flow rate in the white water channel as rapidly as possible. The reason is that one wants a sufficiently low rate to avoid turbulence. Normally it is prescribed that the flow rate in the white water channel shall not exceed 0.5 m/s. The inclined bottom portions 8A, 8B have the same purpose, i.e. they slope to avoid or eliminate the establishment of turbulence in the white water channel. By using certain angles of inclination, αl, α2, in the flow direction one can avoid that sediment is deposited and built up on the bottom portions 8A_ 8B. With an angle αl, α2 = about 3° one can normally make sure that sediment is not deposited but follows the white water flow towards the outlet/s 6, 9, 13. Because of the division of the bottom portion 8 into two sub-portions 8A, 8B, the problem has been solved if the level difference between the bottom end H m of the outlet 2 of the machine and the lowest possible level HQ of the main outlet 6 is too small in relation to the distance L therebetween. The larger the distance is, the smaller angle can be established for the inclination of the bottom. Normally, the angle must at least exceed 2° in order to eliminate that sediment is deposited at the bottom. If the height difference and the distance between said points allows the establishment of an angle of inclination of at least 2° in relation to a bottom plane, a well functioning and cost efficient solution can still be obtained with the invention. Normally, in such cases a cutting of the existing machine floor 11 is made in order to obtain sufficient inclination downwards towards the silo. It has proved that this is a non-desirable solution, not the least from an economic point of view. An alternative embodiment of the invention is shown in Fig. 2. As can be seen, the bottom portion 8 is divided into three different bottom portions 8A, 8B, 8C. The reason is that the height difference between the bottom end H m of the outlet of the machine 3 is located at an insufficient height in relation to the machine floor 11 and the distance L to the silo 5. Thus, a sufficient angle of inclination α can only be obtained when the bottom portions use a division into more than two sub-portions. In other respects the solution is in principle the same as described above. A further modification, which is shown in Fig. 2, is that the two additional outlets 9, 13 are connected to one tube 10, 16 each, which tubes are connected to each other through a connection tube 15, which is suitably also arranged at a certain angle of inclination. Thus, one and the same pump 14 In Fig. 3 a cross section of a white water channel according to the invention is shown. As can be seen, the walls 5 A, 5B are suitably vertically arranged and the bottom in the transverse direction has a N-shape. Thanks to the N-shape, sediment will not only move towards the outlets in the flow direction but also inwardly towards the centre line of the channel , which makes it possible to use a rather limited size of the outlet and still manage to remove sediment. Due to this design it is quite possible to use a conventional tube 10 at the additional outlet 9 (the same principle is also applicable at the outlet 13). The invention is not limited to what has been described above but can be varied within the scope of the appending patent claims. It should thus be understood that in principle a various number of bottom portions can be used to achieve the purpose of the invention. Further, it should be understood, that other containers than a silo 5 can be used to collect the white water. Further, it is realised that the sub-flows which are taken from the additional outlets, preferably can be carried directly to other devices than a pump, for instance direct to a chest. It is realised that a pump need not always be used to transport the liquid which has been drained through the outlet pipe (e.g. the tube 10) but that a natural flow can advantageously be utilised in this connection. The man skilled in the art realizes also that the advantages of the invention can be utilized even if the levels Hi and H 3 are not equal. In the same way, he realizes that the angles αl and α2 need not be equal but that such an arrangement in certain connections is preferred. Further, it is realised that the white water channel can be made of many different materials and combinations of different materials, such as concrete, plastics, metals, etc.

Claims: PATENT CLAIMS 1. An arrangement at a white water channel for handling of white water from a paper machine, which arrangement comprises a channel with an inlet end (1), which is arranged in connection to an outlet (2) for white water from a paper machine (3), an outlet end (4), which is provided with a main outlet (6), which runs to a container device (5), preferably a white water silo, wall portions (5 A, 5B) which are provided between and at said channel ends (1, 4), and a channel bottom portion (8), said channel bottom portion (8) being arranged at a certain angle of inclination (αl) in relation to the horizontal plane, which angle (αl) must exceed a certain critical angle of inclination in order to avoid sedimentation on the bottom portion (8) of the channel, characteris e d therein that at least one additional outlet (9) is provided between said main outlet (7) and said inlet end (1) in such a way that the bottom portion (8) of the channel is divided into first (8A) and second (8B) bottom portions, which portions are so arranged in relation to each other that the angle of inclination (αl, α2) for each one of said bottom portions (8 A, 8B) exceeds said critical angle of inclination. 2. An arrangement according to claim 1, characterised therein that said critical angle of inclination is 2°, preferably 2.5°, and more preferred 3°. 3. An arrangement according to claim 1, characterised therein that the start level (H 3 ) of said second bottom portion (8B) is higher than the final level (H 2 ) of said first bottom portion (8A). 4. An arrangement according to claim 3, characterised therein that the start level (H 3 ) of said second bottom portion (8B) essentially corresponds to the start level (Hi) of said first bottom portion (8A). 5. An arrangement according to claim 4, characterised therein that one, against the flow directed, inclined bottom portion (8D) is provided between the start level (H3) of said second bottom portion (8B) and the rear edge of the additional outlet (9). 6. An arrangement according to claim 5, characterised therein that said bottom portion (8D) comprises essentially a linear portion, which is arranged at an angle of inclination (α3), wherein the angle (α3) is larger than the angle (αl) and the angle (α2), preferably the angle (α3) is essentially larger than the angle (αl) and the angle (α2). 7. An arrangement according to any of the preceding claims, characterised therein that the angle (αl) and the angle (α2), respectively, are between 1 and 5°, preferably 2.5-3.5°. 8. An arrangement according to claim 7, characterised therein that the angle of inclination (αl) is substantially as large as the angle (α2), preferably the angles are quite similar. 9. An arrangement according to claim 6, characterised therein that the angle of inclination (α3) is between 5 and 60°, preferably between 10 and 45°, and more preferred below 30°. 10. An arrangement according to claim 1, characterised therein that said additional outlet (9) is connected to a tube (10), preferably a tube of standard size. 11. An arrangement according to claim 1, characterised therein that said channel bottom portion is divided into at least three bottom portions (8A, 8B, 8C), and that at least two additional outlets (9, 13) are provided between said main outlet (6) and said inlet end (1).

Inventors: MALM JAN, MALM, JAN
Applicants: MALM JAN, METSO PAPER KARLSTAD AB, MALM, JAN, METSO PAPER KARLSTAD AKTIEBOLAG
Application year: 2001
Main classification: D21F1
IPC codes: D21F1