Patent Application
20160023216
The present invention relates to the field of pulp refiners. More specifically it relates to a center plate for a rotor and a pulp refiner comprising a rotor with such center plate.
To mechanically refine pulp in an effective way to e.g. produce paper is a non-trivial subject. A plethora of refiners and refiner elements have been designed in order to further improve the mechanical refining action on the pulp.
A commonly used pulp refiner comprises a rotor unit and a stator unit that are aligned along a pulp feeding axis facing each other. The refining of the pulp is performed in a bounded area between the rotor unit and the stator. unit. During use of the pulp refiner pulp is fed via a feeding channel through a hole in the stator unit to emerge in an area bounded by the stator unit and the rotor unit. The rotor unit facing the stator unit is arranged on a rotatable axis that can be rotated by means of an electrical motor. The purpose of the rotor unit, which in the following will be simply referred to as a rotor, is to grind the pulp between a surface of the stator unit and a surface of the rotor. Thus, when pulp leaves the feeding channel and enters the bounded area between the rotor and the stator through a hole provided in the stator it flows in on the rotor and due to the rotation of said rotor the pulp is directed outwards towards the boundaries of the rotor and stator. On the boundaries there are usually provided refining segments on the surfaces of the rotor and/or the stator. The purpose of these refining segments is to improve the grinding action on the pulp.
One problem with such designs is that the pulp will be directed towards the boundaries in an uneven fashion. Large chunks of pulp will be localized in a particular position on the rim of the rotor/stator arrangement while other positions will be more or less devoid of pulp. This will in turn lead to uneven grinding of the pulp. Thus efforts have to be made to improve the distribution of the pulp.
Another problem within the art is that part of the pulp initially can get stuck in the middle of the center plate. This might lead to pulp piling up in the middle of the center plate which can negatively affect the pulp distribution. It is therefore also a need for a center plate design that opposes that pulp gets piled up in the middle of the center plate.
A known measure to achieve such a pulp distribution is to provide the center plate of the rotor surface with a set of wings or wing profiles, whose purpose is to direct the pulp more evenly towards the rim of the stator/ rotor arrangement. These wings are protrusions provided on the surface of the rotor facing the incoming pulp. The wings are mostly curved to obtain an arc-shaped form. By means of such wings pulp will be directed into the open channels defined between adjacent wings to thereby give a more even distribution of the pulp in the refining area. The constraints regarding the design of the wings constitute a very delicate dynamic problem where such phenomena as flow turbulence of the pulp have to be taken into consideration. This makes mathematical modeling of the dynamics intractable and direct observation of the wings effect on the dynamics is also complicated, partly due to the smallness of the refining area.
Several attempts have been made to improve the distribution of pulp. In U.S. Pat. No. 3,902,673 there is disclosed a refining machine for fragmented beating material. The machine comprises a rotationally symmetric annular infeed channel formed between a central body and an outer part surrounding the central body. The infeed channel has an increasing inner and outer diameter in the material feeding direction. The infeed channel redirects the movement of the material essentially radially outwardly in relation to the center of the rotating means. In U.S. Pat. No. 6,206,309 B1 there is disclosed an apparatus for refining lignocellulosic material between two relatively rotating elements. The rotary element is provided with a central feeding means comprising an axial screw and wings. In U.S. Pat. No. 4,396,161 there is disclosed a disk refiner for cellulose, paper or equivalent pulp provided with guiding vanes. The vanes are provided on the stator side of the refiner.
None of these proposed technologies are however optimal, hence there is a continued need in the art to further improve the pulp distribution for a pulp refiner. There is also a need to improve the distribution of the pulp in a way that softens the problems related to pulp getting stuck and piled up in the middle of the center plate.
It is one object of the present invention to provide a center plate for a rotor. In particular it is desirable to improve the efficiency of pulp distribution in a pulp refiner.
In accordance with the present invention these and other objects have now been realized by the discovery of a center plate for a rotor and a pulp refiner, the center plate having a surface including a central portion and a periphery and provided with a plurality of first wings for directing pulp flowing onto the center portion of the center plate towards the periphery of the center plate, wherein each of the plurality of first wings comprises an arc-shaped protrusion extending between a corresponding first point and a corresponding second point on the surface of the center plate, the first point being displaced from the center portion of the center plate and the second point being disposed further from the center portion of the center plate then the first point, the plurality of first wings having an arc shape that yields a larger pulp feeding angle then a circular arc intersecting the center portion of the center plate and ending in the same corresponding second point, and wherein the second point of each of the plurality of first wings lies on the periphery of the center plate. Preferably, the surface comprises a flat surface or a surface with a central protuberance.
In accordance with one embodiment of the center plate of the present invention the arc shapes of each of the plurality first wings are defined by circular arc extending between a corresponding first point and a corresponding second point having a chord that is longer than the chord of a circular arc beginning in the center portion of the center plate and ending in the same corresponding second point.
In accordance with another embodiment in the center plate of the present invention the first points of the plurality of first wings are symmetrically distributed around the center portion of the center plate.
In accordance with another embodiment in the center plate of the present invention the center plate comprises of plurality of second wings, wherein each of the plurality of second wings defines an arc shape profile protruding from the surface and each of the plurality of second wings is attached to a corresponding one of the plurality of first wings in a contact section and extends between the contact section and an end point. Preferably, each of the plurality of second wings further comprises a tongue portion contacting a first contact section of a corresponding one of the plurality of first wings, and an arc shaped portion attached to the tongue portion in a second contact section and having substantially the same arc shape as the corresponding one of the plurality of first wings. In another embodiment the height above the surface of the center plate of each of the plurality of second wings varies from a lowest height in the vicinity of the contact section to a highest height located between the contact section in the end point. Preferably, the highest height is located in the vicinity of the contact section. In another embodiment the arc shaped second sections of the plurality of second wings extend between the second contact section and the periphery of the center plate.
In accordance with the present invention a pulp refiner has also been discovered including a rotor and a stator, the rotor including a center plate having a surface including a central portion and a periphery and provided with a plurality of first wings for directing pulp flow onto the center portion of the center plate towards the periphery of the center plate, wherein each of the plurality of first wings comprises an arc shaped protrusion extending between a corresponding first point and a corresponding second point on the surface of the center plate, the first point being displaced from the center portion of the center plate and the second point being disposed further from the center portion of the center plate then the first point, the plurality of first wings having an arc shape that yields a larger pulp feeding angle than a circular arc intersecting the center section of the center plate and ending in the same corresponding second point, and wherein the second point of each of the plurality of first wings lies on the periphery of the center plate.
In further accordance with the present invention, the above and other objects are obtained by means of a center plate for a rotor in a pulp refiner. The center plate has a surface provided with a plurality of first wings for directing pulp flowing onto the center of the center plate towards the periphery of the plate. Wherein the surface is a flat surface or a surface with a central protuberance and where each of the first wings is an arc-shaped protrusion extending between a corresponding first point and a corresponding second point on the surface. The first point is displaced from the center point of the plate and the second point is arranged farther from the center point than the first point.
It is a further object of the present invention to provide a center plate where each of the first wings, which are extending between corresponding first and second points, are given an arc-shape that yields a larger distribution angle than a circular arc intersecting the center point of the center plate and ending in the same corresponding second point.
It is a still further object of the present invention to provide a pulp refiner with an efficient grinding performance; this is obtained by means of a pulp refiner equipped with a rotor having a center plate according to above.
Yet more objects and embodiments of the invention will be given in the detailed description.
The present 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 numbers are used for similar or corresponding elements.
To facilitate the understanding of the invention, there will first be given a general description of a pulp refiner and the functionality of such a refiner during use.
Reference is made to
During use pulp will be fed by means of a feeding mechanism, not shown, through the feeding channel 14. The pulp will pass through the hole 21 in the stator 20 and enter the refining zone 19. This refining zone 19 is defined by the gap between the rotor 10 and the stator 20 and can be quite small during operation. The pulp flowing into the refining zone 19 will be incident on the surface 1′ of the center plate 1 on the rotor 10. A number of first wing profiles or first wings 11 provided on the surface 1′ of the center plate 1 are used to steer the pulp out towards the outer parts or the rim of the refining area. On the outer part of the refining area the earlier mentioned refining segments will ensure an efficient grinding of the pulp.
As has been explained earlier, the choice of shapes for the wings to obtain a more efficient pulp distribution is a notoriously non-trivial subject since the motion of the pulp during the rotors rotation give rise to very complicated dynamics including turbulence. The inventor has found that a substantially more efficient pulp distribution can be obtained by providing a flat center plate 1 or a center plate 1 with a centrally located protuberance 110, with a number of arc-shaped first wings 11 that begin on first points 11a that are displaced from the center point 100 of the center plate 1. With such a center plate problems related to turbulence will be mitigated.
The center plate 1 according to the invention will also soften problems related to the fact that pulp can get stuck and pile up in the middle of a prior art center plate during an initial period of time. This problem depends at least partly on the fact that a substantial part of the pulp initially will flow in on the center plate at positions relatively far from the center point 100. Since prior art wings begin at the center point of a center plate 1 it will take some time before the wings get control of the pulp and can distribute it towards the rim. During the time it takes for the wings to control the pulp, the pulp will remain within the central area of the center plate 1. Since there is a continuous inflow of pulp onto the central area the pulp tends to pile up in the central area. This can in turn affect the pulp distribution negatively. By designing a center plate according to the present invention means are provided to quickly control the pulp that is flowing in on the center plate 1 at a distance from the center point 100. This is achieved by means of first wings 11 having first points 11a displaced from the center point 100 of the center plate 1. Since the inflowing pulp is controlled at a quicker rate it can be distributed towards the rim at a quicker rate. Therefore the present invention provides for a center plate 1 that yields an even distribution of pulp in a short period of time.
An embodiment of a center plate 1 that contains a single first wing 11 is schematically disclosed in
In
To further clarify the shape of the arcs that defines the first wings 11 reference is made to
The above mentioned pulp feeding angle w for a first wing 11 can be determined through the following steps, where reference is made to
Approximate the central area where the pulp flows onto the surface 1′ of the center plate 1 with a circle 200;
Draw a line r from the center point 100 of the circle 200 in such a way that the line crosses the point where said circle 200 intersects with the arc-shaped first wing 11;
Draw the tangent for the arc-shaped first wing 11 in said point;
The pulp distribution angle w is then defined as the angle between the tangent of the arc-shaped first wing 11 in said point and the line extending from the center point and crossing the intersecting point between the circle 200 and the arc-shaped first wing 11.
According to the invention the first wings 11 should be designed to have an arc-shape that gives a pulp feeding angle w that is larger than the pulp feeding angle for a circular arc that begins in the center point 100 of the circle 200 and ends at the same second point 1 lb as the arc-shaped first wing 11. These are the particular values of the pulp feeding angle w mentioned above.
To design first wings 11 with arc-shapes that give efficient pulp feeding angles the first point 1 la for the first wing 11 should be provided within the area of the circle 200 that approximates the area of the center plate 1 onto which the pulp initially flows. In most cases this area corresponds more or less to the area of the centrally located through hole 21 in the stator 20. That is the area of the circle 200 should be more or less the same as the area of the through hole 21 in the stator 20 through which pulp from the pulp feeding channel 14 enters the area between the stator 20 and the rotor 10.
In
One preferred embodiment that yields the desired pulp feeding angle can be obtained by designing the first wing 11 so that it has the shape of a circular arc that extends between a first point 11a and a second point 11b. The first point 11a being displaced from the center point 100 of the center plate 1 in such a way that the chord of the arc-shaped first wing 11 is longer than the chord of a circular arc beginning in the center point 100 and ending at the second point 11b. With chord is here intended the straight line connecting the end points of the arc.
Another possible arc-shape for the first wings 11 is a more spiral shaped arc. That is, an arc whose end sections follows the shape of a circular arc but with a slightly flattened out mid-section. As long as the pulp feeding angle w is larger than the corresponding pulp feeding angle v for the circular arc 201 extending from the center point 100 one obtains an improvement in pulp distribution.
In
By designing a center plate 1 provided with such first wings 11 one surprisingly obtain a more efficient distribution of pulp to the area of the refining segments on the outer part of the rotor-stator arrangement. In the end a more efficient grinding of the pulp is obtained. Moreover the larger values of the pulp feeding angles w for the first wings 11 give a faster transportation of pulp to the rim of the center plate 1. This will in turn reduce the emergence of turbulence. A faster transportation of pulp to the rim is usually accomplished by means of increasing the rotation speed of the rotor. This is however an energy demanding operation so a center plate 1 with first wings 11 according to the invention provides for a less energy-consuming alternative for increasing the speed with which pulp is transported from the center area of the center plate 1 to the rim of the same.
Another exemplary embodiment of the center plate according to the invention is schematically depicted in
Another embodiment of center plate provided with first 11 and second 12 wings is shown in
An alternative embodiment to the one described in relation to
A further exemplary embodiment of the second wings 12 described above with regard to
In the embodiment described with regard to
For the embodiment described with regard to
All embodiments described earlier concerns first and second wings 11, 12 arranged on a surface 1′ of a center plate 1 for a rotor. The surface 1′ can in these embodiments be a flat surface or an essentially flat surface, one such embodiment is shown in a cross-sectional side view in
It is also possible to provide the surface 1′ with a central protuberance 110 or a bulge/bump. This is illustrated in a side view of the center plate 1 in
Preferably the protuberance 110 is a smooth protuberance without sharp ends, this to avoid possible irregularities in the flow which could lead to a turbulent motion of the pulp. The height of the protuberance above the surface 1′ of the central plate 1 should preferably not exceed the highest point of the height profile of the first wings 11. This is to ascertain that the inflowing pulp initially will be brought into contact with the first wings 11 and not with the protuberance 110. In this way the distribution of the pulp will begin as soon as the pulp falls onto the center plate 1.
Through the described designs, it is provided center plates 1 that display tremendous pulp distribution characteristics. The center plates 1 have an uncomplicated construction which makes them easier and less costly to produce. Since they are also robust they are less prone to be damaged. The fact that they contain no loose parts will make them easy to exchange if worn down.
All embodiments of a center plate 1 as described earlier can be fitted to a rotor arrangement of well-known pulp refiners. One example of such a pulp refiner 30 is schematically described above with reference to
Other refiners are however also possible. Such refiners include refiners equipped with two rotors instead of a rotor-stator arrangement. For example two rotors that can be rotated independently.
All the embodiments described above are to be understood as a few illustrative examples of the present invention. 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 scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1350290-1 | Mar 2013 | SE | national |
This application is a national phase entry under 35 U.S.C. §371 of International Application No. PCT/SE2014/050260, filed Mar. 4, 2014, which claims priority to Swedish Patent Application No. 1350290-1, filed on Mar. 12, 2013, the disclosures of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2014/050260 | 3/4/2014 | WO | 00 |
