The present application is a national phase entry under 35 U.S.C. § 371 of International Application No. PCT/SE2018/050636 filed Jun. 18, 2018, published in English, which claims priority from Swedish Application No. 1750776-5 filed Jun. 19, 2017, all of which are incorporated herein by reference.
The present invention generally relates to refining of fibrous material in a pulp or fiber refiner, and more particularly to evacuation of steam developed during the refining process.
A defibrator is a thermomechanical pulping refiner in which the pulp material, such as wood chips or other lignocellulose-containing fibrous material, is ground in an environment of steam between two refining discs, a rotating grinding disc (rotor) opposing a stationary disc (stator), or alternatively, two rotating discs opposing one another, to produce wood fibers. The refining discs are aligned along a pulp feeding axis and the rotating disc is arranged on a rotatable axis that can be rotated relative to the other disc by means of e.g. an electrical motor. The inner surfaces, i.e. the surfaces opposing one another, of the refining discs are typically provided with one or more refining segments having refining bars and grooves of different sizes and orientations, for improving the grinding action on the fibers. A refining space is defined between the inner (refining) surfaces of the refining segments, which are typically located near the circumference of the refining discs. Wood chips or similar fibrous material is fed via a feeding channel along the pulp feeding axis through a hole in one of the discs, usually the stator, and into a central space between the discs. Wood chips fed into the center of the refining discs are forced by the centrifugal force towards the circumference of the discs to emerge in the refining space between the refining surfaces of the refining segments, where the refining/grinding of the fibrous material is performed. The bars and grooves of the refining segments are usually finer nearer the circumference of the discs. The size of the refined fibers can to some extent be controlled by altering the distance between the discs and thus the refining surfaces where a closer distance produces finer fibers but also requires higher grinding force.
Generally, the lignocellulose-containing material contains water since the wood chips are usually steamed with hot water and/or steam before being introduced into the defibrator. Further, water may be supplied in connection with the refining. From this water, a great amount of steam is generated in the refining space during the refining operation of the fibrous material, since the grinding of the material requires a lot of energy due to the extensive friction and generates a lot of heat which evaporates the water. The generated steam may pass out of the refining space together with the refined material, and may also flow backwards towards the location where the incoming chips are fed into the defibrator. The steam flow through the refining space assumes a very high speed and can negatively affect the flow of fibrous material and also increase the energy consumption of the refiner. The steam may also flow in an irregular manner and thereby affect the stability of the refining gap, rendering the material flow through the gap non-uniform. This has a negative effect on the pulp quality. Therefore, it is important to minimize the disturbance from the steam developed during the refining process.
Previous efforts to alleviate the problems associated with the generation of steam between the refining discs have involved withdrawing steam from the central space between the refining discs. For example, U.S. Pat. No. 4,221,631 A shows a disc refiner comprising a pair of refining discs each of which has an inner refining surface. The refining surfaces are opposing each other during relative rotation of the discs and define a refining space between them. The refining segments are provided with passageways extending through the segments from the refining space to the rear surface of the segments for removing steam developed in the refining space and releasing it into the refining housing.
However, there is continued need in the art to further improve the evacuation of steam from the refining space of the refiner.
It is an object to provide a refining disc which further improves the evacuation of steam developed during the refining process.
This and other objects are met by embodiments of the proposed technology.
According to a first aspect, there is provided a first refining disc for a defibrator for refining fibrous material, where the first refining disc is adapted to receive a flow of incoming fibrous material from a feed screw. The first refining disc is provided with at least one steam evacuating channel comprising at least one steam inlet opening arranged on a side of the first refining disc adapted to face a second refining disc, and at least one steam outlet opening arranged on a side of the first refining disc adapted to face away from the second refining disc. The at least one steam outlet opening is arranged centrally of the at least one steam inlet opening with respect to the center of the first refining disc, and peripherally and/or centrally of a position where the flow of incoming material is to be received into the first refining disc from the feed screw, with respect to the center of the first refining disc.
According to a second aspect, there is provided a center ring arrangeable on a first refining disc for a defibrator for refining fibrous material, where the first refining disc is adapted to face a second refining disc and to receive a flow of incoming fibrous material from a feed screw. The center ring is provided with at least one steam evacuating channel comprising at least one steam inlet opening arranged on a side of the center ring adapted to face the second refining disc, and at least one steam outlet opening arranged on a side of the center ring adapted to face away from the second refining disc. The at least one steam outlet opening is arranged centrally of the at least one steam inlet opening with respect to the center of the center ring, and the at least one steam outlet opening is configured to be positioned peripherally and/or centrally of a position where the flow of incoming material is to be received into the first refining disc from the feed screw, with respect to the center of the first refining disc.
According to a third aspect, there is provided a defibrator for refining fibrous material, comprising a refining disc according to the above.
By introducing a steam evacuation channel according to the present invention, thereby facilitating evacuation of steam from the defibrator without disturbing the chip feed, at least the following advantages can be achieved:
In turn, the above leads to lower specific energy consumption (SEC), more uniform fiber quality and longer segment lifetimes.
Other advantages will be appreciated when reading the detailed description.
The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:
Throughout the drawings, the same reference designations are used for similar or corresponding elements.
As described in the background section there is continued need in the art to further improve the evacuation of steam from the refining area of the refiner.
However, in order to escape through the feed screw the steam formed between the rotor and the stator first has to find its way back towards the center of the rotor and stator, working against the flow of material being fed in the opposite direction, as illustrated in
Following the same reasoning as above, due to the weight of the material most of the material flow will be carried by the rotor, whereas the lighter steam flowing backwards will follow the stator side, as illustrated in
Therefore, the aim of the present invention is to provide a way for steam to be evacuated from the refining space without passing through the flow of incoming material, in order to avoid the feed conflict between the material flow and the back-streaming steam.
This is accomplished by providing a refining disc with at least one steam evacuating channel adapted to evacuate back-streaming steam from the refining space, transport it towards the center of the refining disc and release it outside of the refining space either peripherally or centrally of the flow of incoming material. In this way the steam is separated from the material flow and a feed conflict between the steam and the material can be avoided.
According to the present disclosure, this feed conflict can be avoided by evacuating the back-streaming steam out of the defibrator through one or more steam evacuating channels provided in one of the refining discs. Such a steam evacuating channel has at least one steam inlet opening arranged on the side of the refining disc facing the other refining disc, and at least one steam outlet opening arranged on the opposite side of the refining disc and centrally of the at least one steam inlet opening, and either peripherally or centrally of the flow of incoming material, with respect to the center of the refining disc.
The steam evacuating channel(s) 21 should preferably be provided in the refining disc 5 that the back-streaming steam 8b is travelling along, in order to “catch” more of the steam flowing along the surface of the refining disc 5. Usually the back-streaming steam will mainly be carried by the stator, as described above. Thus, in an embodiment the at least one steam evacuating channel 21 is provided in the stator 5.
As schematically illustrated in
In the embodiments of
Furthermore, in some embodiments at least a part of the steam evacuating channel(s) 21, preferably the first part as seen from the steam inlet opening 22, is arranged at an acute angle with respect to the inner surface of the refining disc 5, where the inner surface of the first refining disc (5) is facing the second refining disc (6). Thus, the back-streaming steam 8b is smoothly guided into the channel 21 and towards the center of the refining disc 5 without an abrupt change in direction, as illustrated in
In the embodiments illustrated in
In some embodiments the refining disc comprises a center ring and at least one steam channel may then be provided in the center ring. The segments of a refining disc are often replaceable and the purpose of a center ring is to hold the segments in place. Usually a center ring is arranged on the stator side of the defibrator. An example of a center ring according to prior art is shown in
Some examples of embodiments of center rings for a refining disc according to the present disclosure are shown in
In some embodiments, as illustrated in
Common for all of the embodiments of a center ring 20 illustrated in
In a particular embodiment, as schematically illustrated in
In some embodiments of a center ring 20 according to the present disclosure, at least a part of the steam evacuating channel(s) 21, preferably the first part as seen from the steam inlet opening 22, is arranged at an acute angle with respect to the flat side of the center ring 20, i.e. at an acute angle with respect to the inner surface of the refining disc 5, similarly to the above-described embodiments of a refining disc without a center ring. Also, a steam inlet opening 22 may have an edge or “lip” protruding towards the second refining disc 6, so that the edge or lip extends into the space between the refining discs 5, 6 in order to guide more of the steam into the channel 21.
All embodiments of the present disclosure can be fitted to a defibrator arrangement of well-known pulp/fiber refiners, for example refiners with a rotor-stator arrangement as described above, as well as refiners with two rotors instead of a rotor-stator arrangement, i.e. two rotors that can be rotated independently.
The embodiments described above are merely given as examples, and it should be understood that the proposed technology is not limited thereto. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the present scope as defined by the appended claims. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible.
Number | Date | Country | Kind |
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1750776-5 | Jun 2017 | SE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/SE2018/050636 | 6/18/2018 | WO |
Publishing Document | Publishing Date | Country | Kind |
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WO2018/236269 | 12/27/2018 | WO | A |
Number | Name | Date | Kind |
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4221631 | Hellerqvist et al. | Sep 1980 | A |
4725336 | Fisher | Feb 1988 | A |
5988538 | Bartels | Nov 1999 | A |
20070164143 | Sabourin et al. | Jul 2007 | A1 |
Number | Date | Country |
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0877117 | Nov 1998 | EP |
8803189 | May 1988 | WO |
9833594 | Aug 1998 | WO |
2017061936 | Apr 2017 | WO |
Entry |
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Extended European Search Report for Application EP18821128 dated Feb. 10, 2021, 3 pages. |
International Search Report from Application No. PCT/SE2018/050636 dated Sep. 10, 2018, 4 pages. |
Number | Date | Country | |
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20200149221 A1 | May 2020 | US |