The present invention generally relates to refining of fibrous material in a fiber refiner, and more particularly to feed variations during the refining process.
Refiners used for refining fibrous material, such as wood chips, into pulp typically comprise one or more refiner elements positioned oppositely and rotating relative to each other. One or both of the refiner elements can be rotatable. A fixed i.e. stationary refiner element is called the stator and the rotating or rotatable refiner element is called the rotor. In disc refiners, the refiner elements are disc-like and in cone refiners the refiner elements are conical. In addition to disc refiners and cone refiners, there are also so-called disc-cone refiners where the material to be defibrated is first refined by disc-like refiner elements and then further refined between conical refiner elements. Furthermore, there are also cylindrical refiners where both the stator and the rotor of the refiner are cylindrical refiner elements.
The refiner elements are positioned such that a refining space/gap is formed between the inner surfaces, i.e. the surfaces opposing one another, of the refiner segments. In disc refiners, which represent the most common refiner type, the material to be refined is usually fed through an opening in the middle of one of the refiner discs, usually the stator, to a central space between the discs. The material is then forced by the centrifugal force towards the circumference of the discs to emerge in the refining space/gap, where the refining/grinding of the fibrous material is carried out. The refined material is discharged from the refining space/gap, from the outer periphery of the refining surfaces of the refiner discs, to be fed onwards in the pulp manufacturing process.
The inner (refining) surfaces of the refiner elements are typically provided with one or more refiner segments, which are formed with a pattern of bars and intermediate grooves of different sizes and orientations, for improving the grinding action on the fibers. The refiner segments are typically positioned adjacently in such a way that each refiner segment forms part of a continuous refining surface. The pattern of bars and grooves may be divided into different zones located outside each other, e.g. a radially inner inlet zone where the fibrous material is fed into the refiner, and one or more radially outer refining zones where the refining of the material takes place. In the inlet zone there are usually fewer bars and grooves, and the pattern is coarser than in the refining zone(s).
Normally, the bars and grooves of the refiner segments extend substantially radially with respect to the rotational center of the refiner elements/discs. The bars may be inclined relative to a radial line passing through the refiner element to achieve a pumping effect, i.e. to enhance the travel of the material to be refined from the direction of the inner circumference towards the outer circumference of the segment, or an anti-pumping effect, i.e. to slow down the travel of the material to be refined towards the outer circumference of the segment. Thus, a pumping bar is a bar that produces, for the material to be refined, both a circular velocity component and a radial velocity component directed away from the center of the refining surface. The bar angle, or the feeding angle, between a pumping bar and the radius of the refiner element is thus directed opposite to the direction of rotation of the refiner element. The feeding effect/capability of a refiner segment may be controlled by the feeding angle. Large feeding angles increase the feeding effect, while smaller angles, and even negative angles, reduce the feeding effect. If the refiner segment comprises more than one refining zone, the feeding angle of the bars is usually the same within a refining zone, and decreases towards the periphery of the refiner segment for each refining zone.
When the fibrous material is refined in the refining space/gap between the refiner elements, some of the moisture in the material is turned into steam. The steam flow is usually very irregular, but some steam will flow towards the circumference of the refiner elements along with the material, and some of the steam will also flow “backwards” towards the center of the refiner elements. The steam flow will depend—among other things—on how the refiner segments are designed. The back-streaming steam will mainly flow in the grooves formed between the bars of the refiner segments towards the center of the refiner elements.
Usually, flow restrictions or dams are inserted in the grooves in the refiner segments in order to prevent unprocessed material to pass out through the refining gap. The dams guide the material to the space between opposite refiner bars, and thereby refining of the material can be promoted. However, the dams constitute an obstacle to the steam developed in the refining gap during the refining process. The steam is also forced upwards out of the grooves by the dams and disturbs the material flow through the refining gap. This in turn leads to blockage on the refining surface, which may affect the stability of the refining gap, rendering the material flow through the gap non-uniform. Variations in feed within the refining gap causes a decrease in the production capacity of the refiner, non-uniformity of the quality of the refined material and an increase in the energy consumed for the refining. Therefore, there is a need for improving the design of the refiner segments in order to overcome the above mentioned disadvantages.
It is an object to provide a refiner disc which reduces the feed variations 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 refiner segment arrangeable on a refiner element in a refiner intended for refining fibrous material. The refiner segment has a radially inner edge and a radially outer edge and comprises refining zones where refining of the fibrous material takes place. The refiner segment is configured to travel in a first circumferential direction corresponding to an intended rotational direction of the refiner element when the refiner segment is arranged on the refiner element, and is provided with a pattern of bars arranged at a respective feeding angle within a respective refining zone, where the feeding angle is directed opposite to the first circumferential direction, and intermediate grooves between the bars, and dams extending between the bars and protruding above the surface of the grooves. The dams are arranged at least at the ends of at least some of the bars at the borders between the refining zones such that openings are formed at the borders between the refining zones, radially outside of the dams, with respect to the radially inner edge of the refiner segment. The openings are arranged such that a respective angle is formed between an imaginary line connecting the openings at a radially inner border of a respective refining zone and a line which is perpendicular to the radius of the refiner segment, where the angle is directed towards the inner edge of the refiner segment.
According to a second aspect, there is provided a refiner element for refining fibrous material, comprising at least one refiner segment according to the above.
According to a third aspect, there is provided a refiner for refining fibrous material, comprising at least one refiner segment according to the above.
By introducing refiner segments according to the present disclosure, at least the following advantages can be achieved:
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.
For further illustration of the prior art, a typical refiner 1 comprising refiner elements in the form of a coaxially arranged stator/rotor disc pair 2, 3 according to prior art is schematically illustrated in
As described in the background section there is continued need in the art to further reduce the feed variations during the refining process.
At least the following problems are associated with this design:
The present embodiments solve the above-mentioned problems by connecting the bars within a refining zone of the refiner segment with the dams in such a way that openings are formed in an anti-pumping direction, allowing steam to flow backwards without allowing the material to escape forwards without treatment. Furthermore, the present embodiments allow the angle of the bars and the width of the bars and grooves to be set individually for each refining zone, increasing the possibilities to improve the specific energy consumption, fiber quality and segment lifetime.
In the embodiments illustrated in
As illustrated in
In embodiments where the refiner segment 4 comprises more than one refining zone Z(x), e.g. Z1, Z2, Z3, . . . , Zn, where Zn represents the refining zone closest to the inner edge of the refiner segment 4, the angles β(x) and γ(x) increase towards the inner edge of the refiner segment 4 for each refining zone Z(x), i.e. β1≤β2≤β3≤βn and γ1≤γ2≤γ3≤γn.
According to a particular embodiment, 90°≤α(x)≤110°.
According to another particular embodiment, where the refiner segment 4 comprises more than one refining zone Z(x) as described above, 5°≤β1≤β2≤β3≤βn≤45°.
According to another particular embodiment, where the refiner segment 4 comprises more than one refining zone Z(x) as described above, 5°≤γ1≤γ2≤γ3≤γn≤45°.
In an example embodiment, the radially inner end of every other bar 10 is connected to a dam 12.
In a particular embodiment, at least some of the dams 12 have a smaller height than the bars 10.
As illustrated in
At least the following advantages are achieved with this design:
This is achieved without compromise in defibration/refining capability, i.e. wood/fiber flow restriction can still be the same.
All embodiments of the present disclosure can be fitted to a refiner arrangement well known in the art, for example refiners with a rotor-stator arrangement as well as refiners with two rotors instead of a rotor-stator arrangement, i.e. two rotors that can be rotated independently. In the current disclosure the main emphasis is on disc refiners, but the disclosure can be equally implemented in other refiner geometries as well.
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 |
---|---|---|---|
1751406-8 | Nov 2017 | SE | national |
Number | Name | Date | Kind |
---|---|---|---|
3910511 | Leider et al. | Oct 1975 | A |
5373995 | Johannson | Dec 1994 | A |
6032888 | Deuchars | Mar 2000 | A |
6311907 | Gingras | Nov 2001 | B1 |
20040149844 | Antensteiner | Aug 2004 | A1 |
20120012685 | Gingras | Jan 2012 | A1 |
20170275819 | Gingras | Sep 2017 | A1 |
Number | Date | Country |
---|---|---|
WO 2012115526 | Aug 2012 | WO |
Entry |
---|
Extended European Search Report, dated Apr. 10, 2019, 8 pages. |
Number | Date | Country | |
---|---|---|---|
20190145048 A1 | May 2019 | US |