DE9422355U1 - Apparatus for treating filler material such as recovered fibers - Google Patents

Description

APPARATUS for treatment of material containing fillers

LIKE RECOVERED FIBERS

The present invention relates to a device for processing secondary fibers and/or a fraction that leaves a centrifugal sorting plant as rejects. As is known, secondary fiber sources include both the so-called paper machine rejects, which can be recycled as raw material, and the actual post-consumer waste paper and cardboard. The present invention relates in particular to the processing of such secondary fibers in such a way that the fillers therein can be recovered as well as possible and returned to the process as efficiently and economically as possible.

In the short cycle of paper machines producing filler-containing paper grades and in particular coated paper grades, a large part of the mineral and pigment fraction is today discharged from the process as reject material from the centrifugal sorting plant, which could be used as raw material for paper in terms of its content, but is too coarse in terms of particle size.

In the short circuit of paper machines producing SC papers and other filler-containing paper grades, the mineral fraction leaving the centrifugal sorter as reject is the coarse part of the mineral fraction added during pulp dosing, the particle size of which is usually above 10 pm.

In the short circuit of paper machines producing coated paper grades, the mineral fraction leaving the process as rejects mainly contains a non-dispersible coating layer of coated waste paper. The coating pigment is not dispersed in the dispersion system to form sufficiently fine particles. The fraction of the coating pigment that is not dispersed and generally has a size of more than 10 pm becomes rejects in the centrifugal sorter of the short circuit.

The same applies to secondary pulp systems where coated newsprint or other heavily coated raw materials are used as raw materials for recycled paper. In the secondary pulp defibration system, the coating pigment of the coated paper separates from the actual fibre layer of the paper as more or less sheet-like fractions which are partially dispersed by the process. However, the dispersion is not complete and these non-dispersed coating pigment particles are rejected as centrifugal sorting rejects from the sorting stage of the process. However, the majority of the particles would be useful in papermaking as fillers due to their raw material content, which could possibly be added to the fibre suspension in the later stages of papermaking. The size of these particles is such that said particles cause problems in papermaking if they are not dispersed and thus qualified for use as fillers.

US-A-4 504 016 describes a process and a device for cleaning chemical pulp by sorting. The problem underlying the patent is to increase the yield of chemical pulp during its production. In the process, the pulp is sorted and a coarse fraction, i.e. knots and splinters, is treated in a refiner and further sorted. Since this is a production process for chemical pulp, no other substances, e.g. filler, are present in the process. The document also shows the removal of the rejects from the hydrocyclone from the system.

US-A-4 167 438 discloses a process and apparatus for the treatment and purification of fibrous material, e.g. mixed waste paper. The publication shows the combined recycling of both fibers and fillers back to use. There are no suggestions there for using the process to separate and treat the bare filler fraction of the waste paper pulp.
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In an arrangement according to the present invention, the loss of fillers/minerals leaving the centrifugal sorter as rejects is reduced by separating the fraction with a concentrated mineral content in the

Centrifugal sorting plant to disperse mineral fractions and return them to the process.

By using the device according to the present invention, the following advantages arise, for example:

Losses of filler/mineral, water, chemicals, heat and fiber are as low as possible. Only the unusable fraction and the fraction that cannot be converted into a recyclable form are discharged in a very concentrated form.
- The dispersion of mineral particles is based on internal shear forces

the suspension, i.e. mechanical wear is minimal.

The investment costs of the system are very low. The technical implementation is carried out using commercially available equipment and the payback period is short.

- The system is easy to build, i.e. it can be integrated into an existing

existing system by adding a sorting device that fractionates the mineral fraction and wood fraction separately and a new type of cleaner for the expulsion of rejects in a very concentrated form after the last cleaning stage as well as a treatment stage that subsequently disperses the mineral fractions.

For example, in the short cycle of a paper machine, the treatment is carried out individually for each machine, whereby the water circuits between the machines, for example, are not mixed.

The system is a continuously operating part of the short circuit of a paper machine or a sorting system. The process conditions are therefore constant and operation is problem-free.

The process is self-adjusting: for example, if the amount of coarse fraction increases, the system only returns the dispersed fraction to the process, while the rest is discharged from the system.
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The characteristic features of the device according to the present invention emerge from the appended claims.

The device according to the present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

Fig. 1a and 1b schematically show two filler treatment systems according to the prior art;

Fig. 2 schematically shows a filler treatment system according to a preferred embodiment of the present invention;

Fig. 3 schematically shows a filler treatment system according to a second embodiment of the present invention;
Fig. 4 schematically shows a filler treatment system according to a third embodiment of the present invention;

Fig. 5 schematically shows a filler treatment system according to a fourth embodiment of the present invention;

Fig. 6 schematically shows a filler treatment system according to a fifth embodiment of the present invention;

Fig. 7 schematically shows a filler treatment system according to a sixth embodiment of the present invention;

Fig. 8 schematically shows a filler treatment system according to a seventh embodiment of the present invention;
0 Fig. 9 shows schematically a version of the system shown in Fig. 8; and Figs. 10a-c are photographs, magnified 100 times, of the material fed to the apparatus of Fig. 8 and the two fractions obtained from the curved screen.

An example of the prior art arrangements for reducing filler/mineral losses is, for example, an arrangement according to Fig. 1a. There, mineral loss is reduced by fractionating all fine material, i.e. solids of a usable size, from the flow leaving the process back to the process. Said device works in such a way that the flow leaving the process is fed to a curved screen 10, a so-called Hydra screen, which divides the flow into two fractions. The coarser fraction is fed to an intermediate container 12 and the finer fraction to a filtrate container 14. The finer fraction is pumped from the filtrate container 14 by a pump 16 to a curved screen 18, a so-called Micra screen of the secondary stage, the coarser fraction of which is fed to the intermediate container 12 and the finer

Fraction, practically clear liquid, together with the fine filler to be reused, is passed, for example, to the dilutions required in the process. The fraction discharged from the intermediate container 12 as rejects from the curved screens 10 and 18 is pumped by a pump 20, for example, to a filter press 22 for thickening the coarse fraction to a more useful consistency. In addition to a curved screen 10, as in Fig. 1a, a finely perforated/slotted pressure screen or centrifugal sorter (Fig. 1b), such as the type generally used for sand separation, can also be used as a fractionating device.

According to Fig. 1b, the material to be treated comes as rejects from the third or fourth stage of a centrifugal sorting plant 32, where the fine fraction rejected by the centrifugal sorting plant 32 is returned for use. The material rejected by the centrifugal sorting plant is fed by a pump 34 to a curved screen 36, preferably a so-called Micra screen, and the liquid accepted by said curved screen 36, the so-called filtrate, is fed to the white water pit or, for example, for dilution in a secondary screening device. The rejects of the curved screen 36, in other words the thicker fraction, are in turn fed to the suction side of a pump 38, from where they are pumped on to a sorter 39, preferably a so-called eliminator-cleaner, which is shown, for example, in US patent 5,139,652. The accepts from the sorter 39 are fed to the suction side of a feed pump 30 of the third or fourth stage 32 of the centrifugal sorting system to be pumped back into recirculation.

However, it is characteristic of all the methods mentioned that they do not change/reduce the particle size/distribution of the solids to be treated, but separate the fine and usable fraction from the coarse fraction and return the fine fraction for reuse.

It is a characteristic feature of a dispersion process for mineral fractions that it is based on internal shear forces of the flow/suspension, which are generated mechanically. In order to reduce the shear forces in the suspension

In order for the suspension to have a dispersing effect, i.e. the shear forces would be strong enough, the concentration of the suspension must be high. In principle, the higher the concentration at which the treatment takes place, the more effective it is, i.e. the higher the shear forces to which the suspension can be exposed and the more efficiently the dispersion takes place.

The concentration of the mineral fraction is sufficiently increased by means of a new type of centrifugal sorter construction shown in US Patent 5,139,652, which sorter is extremely effective in classifying, but from which the coarse mineral fraction with a size of more than 10 pm is rejected as a very concentrated flow with a solids content of even more than 40%.

The concentration of the fractions to be treated can also be increased, for example, by filtering or precipitation, but it is characteristic of all these other methods that they require additional equipment and/or large volumes and are quite complicated to be carried out as a continuous, smooth process. The concentration of the mineral fraction in a new type of centrifugal sorter takes place in connection with the normal operation of the centrifugal sorter without any additional equipment.

After thickening, i.e. increasing the solids concentration, the mineral fraction is treated with mechanical mixing devices or grinding devices that create high internal shear forces in the suspension. As a result of the shear forces, the mineral particles rub against each other and are reduced to a particle size that allows them to be used as fillers in papermaking.

Fig. 2 and 3 show two process alternatives which differ from one another with regard to the step following the dispersing stage for mineral particles. In both embodiments, the material to be treated arrives as coarse rejects from the last stage of the centrifugal sorting system 32. The rejected coarse fraction is fed via a pump 44 to a sorter 46, preferably a so-called eliminator-cleaner, i.e. the first fractionation stage for rejects, whereby the separated fine material is fed to the inlet of pump 30.

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is returned to be fractionated again in the centrifugal sorting plant 32 and the coarse fraction is fed, with a consistency typical of the reject material from the EliminatoF Cleaner 46, into a mixing/dispersing device 48 where the rotor(s), propellers or the like mix it and create differences in the kinetic speed between the particles, i.e. shear forces, by the action of which the material is dispersed.

In the embodiment of Fig. 2, after dispersion in a mixing/dispersing device 48, the mixture is diluted, fed by a pump 50 to the sorter 52, preferably a so-called eliminator-cleaner, the last fractionation stage of the treatment process, and the dispersed mineral fractions are fractionated by a centrifugal sorter 52, from where the usable fractions are accepted so that they can be returned to the inlet of the pump 30 to be reused in the centrifugal sorting device 32, and the coarse fraction is discharged as rejects to be either reprocessed or totally rejected.

In the arrangement of Fig. 3, the separation of the usable and coarse fractions after dispersion and dilution is carried out with a sieve-like device 54, which is shown as a so-called micra sieve, where the openings of the sieve surface are selected so that the fraction flowing through is of a grain size such that it can be returned to the inlet of pump 30, and the coarse fraction on the sieve surface is discharged from the process or passed on for further treatment.

The recycling and dispersion process of the dispersed mineral fractions can of course also be carried out in two or more stages. The coarse fraction that is not dispersed in the first dispersion stage can of course be treated again and thus the mineral loss of the process can be reduced, see Fig. 4 to 7.

Fig. 4 illustrates an alternative to the embodiments of Figs. 2 and 3, namely for their final stages. That is, the reject from a sorter 46' is discharged at high consistency into a mixing/dispersing device 48', where the material

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after the dispersion stage, it is diluted and passed to the next sorter 46" by a pump 44'. The reject material from the sorter 46" is fed to a second mixing/dispersing device 48" and, after the dispersion stage and dilution by a pump 50, to a third sorter 46"', from where the reject material - as well as from the sorter 46" - is passed on for reuse or to one of the preceding sorting/fractionation stages (inlet of the separator 46' shown as an example).

Fig. 5 illustrates the connection of two sorters 56 and 56' in such a way that the reject material from the latter sorter 56' can not only be completely discharged from the system, but a part of it can also be fed back into a mixing/dispersion tank 58 for redispersion, whereby the material losses can in principle be completely avoided.

Fig. 6 illustrates an embodiment in which a sorting device 66 is followed by several mixing/dispersing devices 68, 68' and 68". Only after the three-stage dispersion described is the material fed by the pump 50 to a sorter 66', the accepted material from which is fed for reuse or back to the inlet of the preceding sorter 66 in front of the pump 44. The reject material, on the other hand, is either completely discharged or treated separately somewhere else. However, it is entirely possible that the reject material from the sorter 66' is also fed back to one of the preceding dispersion stages for further refining. It is also possible that only two or more refiner stages are provided - entirely dependent on requirements.

The dispersion treatment itself can also be carried out either as a single- or multi-stage process, and at least in theory a process could be possible where the coarse fraction is recirculated until any sand and similar impurities are ground and returned to the process, whereby the system could be completely closed.

Fig. 7 shows yet another embodiment, where the reject material from the sorter 76 is fed to a mixing/dispersing device 78, which comprises several superimposed mixing zones. The reject material dispersed in the device 78

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Material is fed by pump 50 into the final fractionation stage in a sorter 79. The purpose is to disperse material more effectively than in a single stage mixing vessel.

Fig. 8 illustrates an alternative to the embodiments of Fig. 2 and 3. In Fig. 8, the coarse reject material from the last centrifugal sorting stage 32, the ash content of which can be as high as 60 to 80%, is diluted with return water containing preferably as little solids as possible, for example clear filtrate S from the fines recovery, and is fed by a pump 80 to the inlet of a curved screen 82, a so-called Micra screen. A screen with a slot width of, for example, 100 pm is used as the screen surface of the curved screen 82. The inlet flow is separated by the curved screen 82 into thicker fraction and filtrate. All coarse fiber, splinter and impurity fractions are discharged with the thicker fraction. The filler particles that have passed through said 100 pm slots and most of the water reach the filtrate. The filtrate of the curved screen 82, which is preferably diluted with return water S containing as little solids as possible, is fed by a pump 84 to the inlet of the centrifugal sorter 86. The accepts of the centrifugal sorter 86, which contains most of the water and the fine filler fraction with a size of less than 10 pm, 0 is returned, for example, to the inlet of the last centrifugal sorting stage, to the pump 88 or reject thickener (dashed line B). The reject from the 86 centrifugal sorting stage contains the filler fraction with a particle size of more than 10 pm and a solids content of around 40 to 50%. Said reject is fed, for example, in free fall to a dispersing device 90, where the solid particles of the reject are exposed to high shear forces. The filler particles are split and the flow leaving the dispersing device 90 consists mainly of filler fraction with a usable, homogeneous particle size of less than 10 pm.

The filler fraction dispersed in the dispersing device 90 is fed by the pump 84 to the inlet of the centrifugal sorting stage 86, which functions in the manner described above. Thus, the unrefined filler fraction can be recirculated in the dispersing device 90 and the centrifugal sorters 86 until the filler particles are dispersed to a usable size.

Fig. 9 shows an alternative according to the embodiment of Fig. 8. The only significant difference from Fig. 8 is that instead of a curved screen a pressure screen 92 is used which, in the same way as the curved screen, divides the rejects coming from the centrifugal sorting stage 32 into a coarse fraction to be discharged from the process and into a fraction containing filler particles to be further treated, the treatment of which has already been shown in connection with Fig. 8. It must be noted, however, that when using the pressure screen 92 it may be possible to avoid the use of pump 84 of Fig. 8 because the fine fraction obtained from the pressure screen can be fed directly to the centrifugal sorters 86. Another difference in Fig. 9 from Fig. 8 is that the material refined in the disperser 90 is fed back to the inlet of the pressure screen 92 but not directly back to the centrifugal sorters as in Fig. 8.

Of course, in the embodiments of Figs. 8 and 9 it is also possible to connect more sorting and dispersing stages in series, as for example in Fig. 4. Furthermore, it is also possible to feed the dispersed material from the dispersing device 90 to, for example, a new sorting stage 94 (because of its alternative nature, the whole part of the process is shown by dashed lines), from where the usable fine material is returned for use and the coarse fraction is rejected and discharged from the system.

Fig. 10a to 10c show the feed (Fig. 10a), the filtrate (Fig. 10b) and the reject (Fig. 10c) of the curved screen in the process. From the drawings it can be seen how all the fibrous fraction and the large filler particles from the feed in Fig. 10a have been rejected in Fig. 10c and the filtrate, Fig. 10b, contains only filler fraction.

As can be seen from the embodiments shown above, which differ from each other to a certain extent, a new method and apparatus, hitherto unknown, have been developed for treating recycled fibrous material so that as much of the filler contained therein as possible could be recovered and reused. Firstly, it should be noted that all the apparatus shown in the drawings and in the description have

flow channels suitable for the respective application are connected to one another in a manner which is either shown in the drawings or described in the description or claims. It should also be noted that the embodiments described above are only examples of many different variations of the invention and are in no way intended to limit the inventive concept, but are given merely as examples. It is therefore clear that the mixing/dispersing device in the embodiments described above has been described as a container with at least one mixing/dispersing rotor; grinding devices or mill-like comminution devices known as such can also be used. It is also clear that the details described in connection with various embodiments are available for use in other embodiments without special note. The present invention is therefore defined solely by the appended claims.

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Claims (21)

1. Device for treating filler-containing material, such as secondary fiber material consisting of paper, coated paper, cardboard and/or rejects, in conjunction with a multi-stage centrifugal sorting system ( 32 ) of the short circuit of the production machines producing the products in question, which system comprises devices arranged in conjunction with said centrifugal sorting system ( 32 ) for fractionating the material fed to said centrifugal sorting system ( 32 ) into a fiber-containing fraction and a mineral- and/or filler-containing fraction, as well as devices for further processing of said mineral-containing fraction, characterized in that the treatment devices for mineral material and/or filler consist of at least one mixing/dispersing device ( 48 , 48 ', 48 ", 58 , 68 , 68 ', 68 ", 78 ). 2. Device according to claim 1, characterized in that it further comprises a fractionating device ( 46 , 46 ', 46 ", 56 , 66 , 76 ) upstream of the mixing/dispersing device ( 48 , 48 ', 48 ", 58 , 68, 68 ', 68 ", 78 ) . 3. Device according to claim 1, characterized in that it further comprises a fractionating device ( 52 , 54 , 56 ', 46 ''', 66', 79) connected downstream of the mixing/dispersing device (48, 48', 48", 58 , 68 , 68 ' , 68 " , 78 ) in the process. 4. Device according to claim 2, characterized in that the fractionating device ( 46 , 46 ', 46 ", 56 , 66 , 76 ) is a centrifugal sorter. 5. Device according to claim 3, characterized in that the fractionating device ( 52 , 56 ', 46 ''', 66 ', 79 ) is a centrifugal sorter. 6. Device according to claim 3, characterized in that the fractionating device ( 54 ) is a sorter based on the application of a perforated or slotted plate, for example a curved screen or pressure screen. 7. Device according to claim 1, characterized in that the device consists of a pump ( 44 ), a fractionating device ( 46 ), a mixing/dispersing device ( 48 ), a pump ( 50 ) and a fractionating device ( 52 , 54 ). 8. Device according to claim 1, characterized in that the device consists of a pump ( 44 ), a fractionating device ( 46 '), a mixing/dispersing device ( 48 '), a pump ( 44 '), a fractionating device ( 46 "), a mixing/dispersing device ( 48 "), a pump ( 50 ) and a fractionating device ( 46 '''). 9. Device according to claim 1, characterized in that the device consists of a pump ( 44 ), a fractionating device ( 56 ), a mixing/dispersing device ( 58 ), a pump ( 50 ) and a fractionating device ( 56 '), the reject nozzle of which is connected to the mixing/dispersing device ( 58 ). 10. Device according to claim 1, characterized in that the device consists of a pump ( 44 ), a fractionating device ( 66 ), at least two mixing/dispersing devices ( 68 , 68 ', 68 '''), a pump ( 50 ) and a fractionating device ( 66 '). 11. Device according to claim 1, characterized in that the device consists of a pump ( 44 ), a fractionating device ( 76 ), an at least two-stage mixing/dispersing device ( 78 ), a pump ( 50 ) and a fractionating device ( 79 ). 12. Device according to claim 1, characterized in that the mixing/dispersing device ( 48 , 48 ', 48 ", 58 , 68 , 68 ', 68 ", 78 ) is a container which has at least one mixing element, preferably a rotor. 13. Device according to claim 1, characterized in that the mixing/dispersing device ( 48 , 48 ', 48 ", 58 , 68 , 68 ', 68 ", 78 ) is a disc, cone or mill refiner. 14. Device for treating filler-containing material, such as secondary fiber material consisting of paper, coated paper and/or cardboard, in connection with the sorting system of the secondary fiber material system, which device comprises a centrifugal sorting system ( 32 ) for fractionating the secondary fiber material into a fiber-containing accept fraction and a mineral-containing reject fraction, as well as devices for further processing of said mineral-containing reject fraction, characterized in that the treatment device for said reject fraction comprises at least one mixing/dispersing device ( 48 , 48 ', 48 ", 58 , 68 , 68 ', 68 ", 78 , 90 ). 15. Device according to claim 14, characterized in that said device comprises a fractionating device ( 46 , 46 ', 46 ", 56 , 66 , 76 , 86 ) which increases the concentration of the mineral-containing reject material and is arranged upstream of the mixing/dispersing device ( 48 , 48 ', 48 ", 58 , 68 , 68 ', 68 ", 78 , 90 ). 16. Device according to claim 14, characterized in that said devices also include a fractionation device ( 52 , 54 , 46 ''', 56 ', 66 ', 79 , 94 ) for carrying out the last fractionation step after the mixing/dispersing device ( 48 , 48 ', 48 ", 58 , 68 , 68 ', 68 ", 78 , 90 ). 17. Device according to claim 15, characterized in that the concentration-increasing fractionation device ( 46 , 46 ', 46 ", 56 , 66 , 76 , 86 ) in question is a centrifugal sorter. 18. Device according to claim 16, characterized in that the fractionating device ( 52 , 54 , 46 ''', 56 ', 66 ', 79 , 94 ) is a centrifugal sorter. 19. Device according to claim 14, characterized in that a sorter ( 82 , 92 ) based on the use of a perforated or slotted plate, for example a curved screen or pressure sorter, is arranged upstream of said fractionating device ( 86 ). 20. Device according to claim 14, characterized in that it comprises at least one pump ( 80 ), a first fractionation device ( 82 , 92 ), a second fractionation device ( 86 ), a mixing/dispersing device ( 90 ) and flow channels connecting these. 21. Device according to claim 14, characterized in that it further comprises a pump ( 84 ) arranged upstream of the fractionation device ( 86 ).