The present application is a national phase entry under 35 U.S.C. §371 of International Application No. PCT/SE2012/051350 filed Dec. 6, 2012, published in English, which claims priority from Swedish Patent Application No. 1100924-8 filed Dec. 15, 2011, the disclosures of which are incorporated herein by reference.
The invention relates to a mixing unit for use in a mixing apparatus for mixing treatment media into a fiber suspension, e.g. a lignocellulosic pulp suspension. The invention further relates to such a mixing apparatus.
Throughout the fiberline, i.e. the different process steps involved when converting wood chips or other fibrous raw material into pulp, there are several positions where mixing apparatuses are used to mix different kind of media into the pulp suspension. The treatment media added into the fiber suspension may for example be for heating, delignification or bleaching purposes. The treatment media may be in liquid or gaseous state.
When mixing treatment media into a fiber suspension, the issue of even and homogeneous distribution is of high importance for the mixing result achieved. A well-known mixer type is disclosed in international application WO2004/052517. The mixing device described in WO2004/052517 comprises a housing with a wall defining a mixing chamber into which pulp suspension is fed by a first feeder. The device further comprises a rotor shaft with a rotor body, arranged to produce turbulence in a turbulent flow zone. A second feeder is arranged to distribute a chemical medium into or in close vicinity to the turbulent flow zone.
Although the mixing efficiency is good in the mixer disclosed above, there is still a need for an improved device with a further enhanced mixing efficiency. As the production capacity for a fiberline increases, the flow rate through the mixing apparatuses in such fiberlines increases, which leads to shorter residence times in the mixing chamber.
Accordingly, there is a need for an improved mixing unit and a mixing apparatus
An object of the invention is to provide an improved unit for mixing for use in a mixing apparatus. A second object is to provide an improved mixing apparatus. These objects are achieved in accordance with the appended claims.
The invention provides a new unit for mixing for use in a mixing apparatus, the mixing unit comprising a rotor being arranged to be connected to a drive unit shaft for, in operation, simultaneous rotation with the shaft, the rotor comprising a rotor shaft and at least two rotor bodies arranged on the rotor shaft, each rotor body having a radial extension, the rotor bodies being arranged to be axially separated from each other along the rotor shaft. The rotor bodies are adapted to interact so as to form multiple mixing zones within the mixing chamber.
The mixing unit according to the current invention enables several turbulent flow zones, i.e. a prolonged mixing zone, in which the treatment media can be mixed into the fiber suspension. In that way a better mixing efficiency is achieved, ensuring that the treatment media is distributed homogeneously into the fiber suspension. The overall residence time in a mixing zone is thus increased by prolonging the mixing zone, i.e. a turbulent flow zone where mixing is achieved.
According to one embodiment, the formation of multiple mixing zones is achieved by the rotor bodies being arranged to counter-rotate. Such a counter-rotation of the rotor bodies will prevent solid body rotation of the fiber suspension and thereby enable good mixing.
In a preferred embodiment, the mixing unit comprises at least one stator body arranged to be placed between the rotor bodies in the axial direction along the rotor axis, the stator body having an extension in the radial direction, the rotor and stator bodies being adapted to interact to produce a turbulent flow in between them so as to form multiple mixing zones within the mixing chamber.
The function of the stator body placed in between the rotor bodies is to prevent the co-rotation of the fiber suspension with respect to the rotor and also to introduce a shear rate to the flow of fiber suspension and added treatment media. Such a shear rate gives rise to the turbulence and avoids a centrifugal effect, separating the normally lighter treatment media (especially when the treatment media is in the gaseous state) towards the center axis of the mixing apparatus and the fiber suspension in a radially outward direction towards the interior wall of the housing, which would occur if the stator body would be omitted. Such a centrifugal effect would result in inadequate mixing, since the treatment media in a gaseous state will separate from the fiber suspension. This effect may be more pronounced as the production volumes, and thus the flow rate of pulp suspension through a mixing apparatus, are increased.
According to an advantageous embodiment, the rotor and stator bodies have configurations enabling at least one rotor body to be introduced into and/or removed from the mixing chamber past at least one stator body. For embodiments where more than two rotor bodies are included, a respective stator body is arranged to be placed in between all of the rotor bodies of the mixing unit. A configuration according to the invention may thus include for example a first rotor body followed by a first stator body, a second rotor body followed by a second stator body and then a third and last rotor body. By ensuring that the respective configurations of the rotor and stator bodies are adapted to be able to pass each other in a longitudinal direction, an easy pull-out of the rotor is enabled, making replacement and maintenance easy. The direction of removal may be both ways in the longitudinal direction, either towards the drive unit or towards the discharge outlet. Naturally, this implies that alternatively, the stator body or bodies may be removed past the rotor bodies. In summary, the respective configuration of the rotor and stator bodies in their radial extension should be adapted to enable insertion and/or removal of a rotor or stator body by the respective bodies being adapted to be able to pass each other.
According to one embodiment, the at least one stator body is adapted to be mounted through the discharge outlet of the mixing apparatus. Such an embodiment enables an easy removal of the stator body as well, not having to dismantle the housing of the mixing apparatus.
According to yet another embodiment, the mixing unit may end with a terminal stator body, seen in a flow direction F of the fiber suspension towards the discharge outlet. In such an embodiment, the mixing unit seen in an axial direction in the flow direction of pulp suspension may comprise a first rotor body followed by a first stator body, a second rotor body and finally a second terminal stator body. It is however also possible to have additional rotor and/or stator bodies arranged before the terminal stator body. In one embodiment, the mixing unit comprises rotor and stator bodies arranged in such a way that a rotor body is always followed by a stator body. It should be noted that the rotor and stator bodies are not arranged on a common shaft but should preferably be centered around the same longitudinal center axis.
According to another embodiment, each stator body is mounted on a separate flange. Such flanges will be mounted to and at the same time constitute a part of the housing surrounding the mixing chamber. The interior of the flanges will form part of a interior wall defining the mixing chamber. In such a configuration the design of the rotor body does not have to be adapted to be able to be introduced past a stator body. Neither do the stator bodies have to be adapted for such a passing.
According to another embodiment, the stator comprises the inlet for treatment media. In such an embodiment, the treatment media may be added to the fiber suspension in a direction countercurrent to the flow of the pulp suspension on its way towards the discharge outlet. For some applications, such a countercurrent addition may improve the mixing of treatment media and fiber suspension. Moreover, when the inlet for treatment media is comprised within the stator, several distribution outlets may be provided throughout the stator which enables addition of treatment media into each individual mixing zone. Such possibilities may improve the distribution of treatment media into the fiber suspension.
According to another aspect of the invention, a mixing apparatus for mixing treatment media with fiber suspension is provided, which comprises the unit for mixing. Such a mixing apparatus may be provided with distribution pipes for treatment media to be added at a position in front of a first rotor body.
The invention, together with further objects and advantages thereof, may best be understood by reference to the following description and appended drawings, in which:
In the drawings, similar or corresponding elements are denoted by the same reference numbers.
The embodiment of the invention in which two rotor bodies are arranged to be counter-rotated is not illustrated in a figure. In such an embodiment, the rotor bodies would be arranged to be able to rotate in counter-direction e.g. by means of a planetary gearing. By counter-rotating, a potential solid body rotation of the fiber suspension will be prevented. In a mixing unit where two rotor bodies are arranged on the same rotor shaft, both rotor bodies rotating in the same direction, there is a risk that the fiber suspension will experience solid body rotation, i.e. the fiber suspension rotating as a solid body. If no shear component is introduced, there will be no turbulence and thus no mixing. The counter-rotating rotor body will introduce such a shear component and thereby prevent the solid body rotation and thus enable good mixing in a prolonged mixing zone.
The mixing unit 10 comprises a number of parts, together as a kit forming the mixing unit. It should be noted that the word unit should not in this context be interpreted as a unit in which all parts are directly connected to each other. Nonetheless, the different parts comprised in the mixing unit are arranged to be able to cooperate with each other.
The mixing unit 10 comprises a rotor 11 and a stator 13. The rotor comprises a rotor shaft 11a, a first rotor body 11b and a second rotor body 11c. The extension of the first rotor body 11b in the radial direction is in the illustrated embodiment somewhat larger than the radial extension of the second rotor body 11c, the respective radial direction being defined with a starting point at the axial center of the rotor shaft and from there extending radially outwards towards the walls of the housing of the mixing apparatus 100. It should be noted that since the figure shows a cross-section of the mixing unit and apparatus according to the invention, the radial extension of the second rotor body may have an extension smaller than the one illustrated in the cross-section at other points of the circumference of the rotor body, which will be further explained in connection with
The stator 13 comprises a first stator body 13a and a terminal stator body 13b, according to the embodiment illustrated in
However, for an embodiment in which the first rotor body 11b is to be introduced into/removed from the mixing apparatus through the discharge outlet 107, the design and configuration of the protrusions 15 of the stator body 13a has to be chosen with the design of the first rotor body 11b in mind. In case of a terminal stator body, it may in one embodiment comprise flow restrictions in the form of a number of radially inwardly extending protrusions with their inwardly pointing ends connected to an inner ring. In an embodiment in which the rotor is to be introduced into/removed from the mixing apparatus in the opposite direction, it is primarily the configuration of the second rotor body 11c that needs to be adapted to be able to pass the first stator body 13a.
The design of a possible terminal stator body must also be chosen carefully to avoid separation of treatment media, since there will be no new shear introduced by a subsequent rotor body. A wake, i.e. a stagnation point, may thus occur in connection with the terminal stator body. Since the internal diffusivity of the treatment media and the fiber suspension will be different, especially when the treatment media is in gaseous state, such a stagnation point will lead to separation of the respective media and thus poor mixing
The mixing unit 10 according to the embodiment illustrated in
In an alternative embodiment, it is likewise possible that the rotor 13 of the mixing unit 10 can be inserted into and/or removed from the mixing apparatus in a direction opposite to the discharge outlet, i.e. in the direction towards the drive unit. The configuration of the rotor and stator bodies may then be adapted for the rotor to be able to be removed in both directions.
The mixing unit 10 and the mixing apparatus 100 according to the invention will now be described with reference to
It should be noted that, although the figure only shows one stator body, several stator bodies may be arranged in between rotor bodies of the rotor. Each stator body may then be attached via a separate flange. It is also possible to combine the embodiments illustrated in
According to one embodiment, illustrated in
For embodiments where several stator and rotor bodies are involved, the puzzle configuration must be such that the removal of all rotor or all stator bodies past all stator or rotor bodies, respectively, is enabled. This may for example be accomplished by after passing on rotor or stator body, turning the part to be removed (rotor/stator) to enable passing the next rotor/stator body.
Turning to the embodiment as illustrated in
Although the invention has been described with reference to specific illustrated embodiments, it is emphasized that it also covers equivalents to the disclosed features, as well as changes and variants obvious to a man skilled in the art, and the scope of the invention is only limited by the appended claims.
Number | Date | Country | Kind |
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1100924 | Dec 2011 | SE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/SE2012/051350 | 12/6/2012 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2013/089615 | 6/20/2013 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
15197 | Schlickeysen | Jun 1856 | A |
29397 | Park | Jul 1860 | A |
1585169 | Perkins | May 1926 | A |
1670593 | Miller | May 1928 | A |
2029691 | Robinson | Feb 1936 | A |
2179271 | Pick | Nov 1939 | A |
3940115 | Zipperer | Feb 1976 | A |
4826324 | Kunz | May 1989 | A |
4851571 | Sauer et al. | Jul 1989 | A |
4889431 | Liechti | Dec 1989 | A |
5823673 | Muntener | Oct 1998 | A |
5836689 | Wieland | Nov 1998 | A |
20060013064 | Bucher | Jan 2006 | A1 |
Number | Date | Country |
---|---|---|
29709060 | Jul 1997 | DE |
2004052517 | Jun 2004 | WO |
Entry |
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International Search Report for Application No. PCT/SE2012/051350 dated Mar. 21, 2013. |
Dence, Carlton W. and Reeve, Douglas W., Pulp Bleaching, Principles and Practice, Tappi Press, Atlanta, Georgia, 1996. |
Number | Date | Country | |
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20140369156 A1 | Dec 2014 | US |