The present invention generally relates to disc refiners, and more particularly, to a double-disc pulp refiner comprising a disc center plate.
Double-disc pulp refiners have been utilized for many years to refine pulp and similar material by subjecting the pulp to the heat and stresses generated as the pulp passes radially through closely spaced, counter-rotating discs. As an example of prior art, the patent document U.S. Pat. No. 5,167,373 describes a double disc refiner in which two counter-rotating refiner discs which define a refining zone therebetween are counter-rotated at different speeds.
A problem in this type of refiner is that the incoming feedstock which enters non-centrally into the refiner may move not only towards the periphery of the refining discs as desired, but also towards the center of the refining discs, where the material may pile up which can negatively affect the distribution of material in the refiner. This may result in an uneven and turbulent material feed, leading to a higher specific energy consumption and lower production rate. Therefore, there is a need in the art to improve the material distribution in the refining area of a double disc refiner.
It is an object to provide a center plate which improves the distribution of lignocellulosic material in the refining area of a double disc pulp refiner.
This and other objects are met by embodiments of the proposed technology.
The invention relates to a double disc pulp refiner comprising a first refining disc and a second refining disc, the first refining disc being arranged at a feed end of the refiner where lignocellulosic material is fed into the refiner through inlet openings in the first refining disc and the second refining disc being arranged coaxially, spaced apart from and opposed to the first refining disc, said first refining disc being provided with at least one refining segment for refining the lignocellulosic material and a center plate having a cross-sectional profile adapted such that when the center plate is arranged on the first refining disc in the refiner, the center plate protrudes to a maximum height which is the same as, or higher than, a maximum height of the at least one refining segment provided on the first refining disc, said double disc pulp refiner, wherein said maximum height is such that the distance between the distal surface of said center plate and the surface of said second refining disc is as small as possible without having their surfaces touching each other.
Some advantages of the proposed technology are:
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:
The present invention generally relates to disc refiners, and more particularly, to a double-disc refiner comprising a center plate.
Throughout the drawings, the same reference designations are used for similar or corresponding elements.
As mentioned in the background section there is a need in the art to improve the material distribution in double disc pulp refiners. A problem in a typical double disc refiner is that the feeding of material into the refiner is not well controlled. The feedstock flows together with steam and dilution water through openings/channels in the refining disc on the feed side to end up between the refining discs. As described above, a problem in a typical double disc refiner is that the incoming feedstock which enters non-centrally into the refiner may move towards and pile up at the center of the refining discs, where it will not be refined since the refining of the material occurs between the refining segments which are located towards the periphery on the refining discs. The piling up of material in the middle results in an uneven and turbulent material feed, requiring a higher steam flow through the refiner and resulting in a higher specific energy consumption and lower production rate.
The center plate 20 has a cross-sectional profile which may vary in thickness and/or in height, i.e. how far away from the surface of the first refining disc 11 the profile of the center plate 20 protrudes. The center plate 20 should fill up at least part of the space between the refining discs 11, 12 at the middle of the discs, in order to prevent material from piling up there. Thus, at least part of the cross-sectional profile of the center plate 20 should extend from the surface of the first refining disc 11 towards the surface of the second refining disc 12 and preferably, it should extend from the surface of the first refining disc 11 equally far as, or further away than, any part of a cross-sectional profile of the refining segments 13 provided on the first refining disc 11. In other words, the center plate 20 has a cross-sectional profile adapted such that when the center plate 20 is arranged on the first refining disc 11 in the refiner 10, the center plate 20 protrudes to a maximum height which is the same as, or higher than, the maximum height of the refining segments 13 provided on the first refining disc 11. This means that the distal surface, i.e. the surface facing away from the first refining disc 11, of the center plate 20 is located at least as far away from the surface of the first refining disc 11 as the distal surface of the refining segments 13 on the first refining disc 11. In a particular embodiment, the center plate 20 has a cross-sectional profile adapted such that the distance between the distal surface of the center plate 20 and the surface of the opposed second refining disc 12 is as small as possible without the surfaces risking to touch each other during operation, i.e. the distance is approaching the predefined minimum safe value described above. More specifically, the distance between the distal surface of the center plate 20 and the surface of the opposed second refining disc 12 is chosen such that the expected or allowed wear of the segments during their life-time is taken into account. (Due to wear, the thickness of the segments is continuously reduced during operation of a double-disc refiner, and by keeping a constant refiner gap between the discs, the distance between the distal surface of the center plate and the surface of the opposed second refining disc is consequently continuously reduced during operation.) Normally some manufacturing tolerances are also allowed and also some wobbling of the disc during their rotation. With these effects considered, the distance between the distal surface of the center plate 20 and the surface of the opposed second refining disc 12 can, for example, be set to 5-15 mm, and more preferably to 8-12 mm.
In summary, the present embodiments of a center plate as shown in
All embodiments of a center plate according to the present disclosure can be fitted to the feed side disc of well-known double disc pulp refiners. One example of such a double disc refiner with annular discs is schematically described above with reference to
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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1950318-4 | Mar 2019 | SE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/SE2020/050172 | 2/17/2020 | WO | 00 |