recycled fiber pulp from a vortex cleaning plant (e.g. connected to the short circulation of a paper machine) effects the recovery and return of fillers in the recycled fiber pulp discharged from the vortex cleaning plant, in an efficient and economical manner. The loss of filler in the recycled fiber pulp discharged from the vortex cleaning plant is decreased by treating a concentrated fraction of the rejects from the vortex cleaning plant with a mixer/disperser for dispersing the filler in the recycled fiber pulp, and returning as much usable filler as possible back to the process.
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23. Apparatus for treating filler-containing material comprising:
a vortex cleaning plant including a first treatment stage and a last treatment stage, said last treatment stage comprising a fractionation stage producing a reject material; and further treatment apparatus connected to said vortex cleaning plant for treating the reject material therefrom, said treatment apparatus comprising at least one mixing/dispersing device, said further treatment apparatus comprising a first fractionation device connected between said vortex cleaning plant and said at least one mixing/dispersing device, and a second fractionating device disposed on the opposite side of said at least one mixing/dispersing device from said first fractionation device.
9. A method of treating recycled fiber pulp containing filler comprising the steps of:
(a) passing the recycled pulp containing filler to a vortex cleaning plant having a plurality of steps including first and last steps; (b) in the last step of the vortex cleaning plant dividing the pulp into a first finer fraction, and a second, coarser fraction; (c) returning the first fraction to the vortex cleaning plant; (d) screening the second fraction in a first screening stage to separate the recycled fiber pulp into a third fraction containing shives and other wood-based material, and a fourth fraction containing filler material; (e) passing the fourth fraction to a second screening stage in which the fourth fraction is divided into a fifth, fine material, fraction and a sixth, coarse material, fraction; and (f) dispersing the sixth fraction in a dispersion stage.
14. Apparatus for treating filler-containing material comprising:
a vortex cleaning plant including a first treatment stage and a last treatment stage, said last treatment stage comprising a fractionation stage producing a reject material including filler-containing material; further treatment apparatus connected to said vortex cleaning plant for treating the reject material therefrom, said treatment apparatus comprising at least one dispersing device for breaking the filler-containing material into smaller particles; a pump and a first fractionation device between said at least one dispersing device and said vortex cleaning plant; and a pump and a second fractionation device on the opposite side of said at least one dispersing device from said first fractionation device; and means for returning filler material broken into smaller particles to said vortex cleaning plant.
26. Apparatus for treating filler-containing material comprising:
a vortex cleaning plant including a first treatment stage and a last treatment stage, said last treatment stage comprising a fractionation stage producing a reject material including filler-containing material; further treatment apparatus connected to said vortex cleaning plant for treating the reject material therefrom, said treatment apparatus comprising first and second dispersing devices for breaking the filler-containing material into smaller particles; a pump and a first fractionation device connected between said vortex cleaning plant and said first and second dispersing devices; and a pump and a second fractionation device connected on the opposite side of said first and second dispersing devices from said first fractionation apparatus; and means for returning filler material broken into smaller particles to said vortex cleaning plant.
1. A method of treating filler-containing material utilizing a vortex cleaning plant having a plurality of steps including a last step, and utilizing a first fractionation stage and a last fractionation stage distinct from the vortex cleaning plant, said method comprising the steps of:
(a) passing filler-containing material to the vortex cleaning plant including the last step thereof in which the material is divided into a first, finer, fraction and a second, coarser, fraction; (b) passing the second fraction to the first fractionation stage to divide the second fraction into a third, fine, fraction, and a fourth, coarse, fraction; (c) returning the third fraction to the vortex cleaning plant; (d) dispersing the fourth fraction to produce dispersed material; (e) passing the dispersed material to the last fractionation stage; (f) in the last fractionation stage, dividing the dispersed material into a fifth, fine fraction and a sixth fraction; and (g) returning the fifth fraction to the vortex cleaning plant, or to be treated again in steps (b) or (e).
0. 27. A method of treating filler-containing material in a production process utilizing a vortex cleaning plant, the vortex cleaning plant having a plurality of steps including a predetermined step, and utilizing a first fractionation stage, a mixing/dispersion stage, and a second fractionation stage operatively associated with the vortex cleaning plant, said method comprising the steps of
(a) passing filler-containing material to the vortex cleaning plant including the predetermined step thereof in which predetermined step the material is divided into a first, finer, fraction and a second, coarser filler rich fraction containing filler material; (b) passing the second filler rich fraction to the first fractionation stage to divide the second fraction into a third, fine, fraction, and a fourth, coarse filler rich fraction; (c) returning the third, fine, fraction to an earlier point in the production process; (d) dispersing the fourth coarse filler rich fraction in the mixing/dispersion stage to produce dispersed filler rich material; (e) passing the dispersed filler rich material from the mixing/dispersion stage to the second fractionation stage; (f) in the second fractionation stage, dividing the dispersed filler rich material into a fifth, fine fraction and a sixth coarse fraction; and (g) returning the fifth fine fraction to an earlier point in the production process.
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This application is the U.S. National Phase of International Application No. PCT/FI94/00086 filed Mar. 10, 1994.
The present invention relates to a method and apparatus for treating recycled fibers and/or fraction exiting from the vortex cleaning as mill reject. As is known, sources of recycled fibers include both the so called broke of a paper machine, which may be rerecycled as raw material, and the actual post-consumer waste paper and board. The present invention especially relates to the treatment of such recycled fiber materials so that the fillers therein may be recovered as well as possible and returned back to the process as efficiently and economically as possible.
In the short circulation of paper machines manufacturing filler-containing paper grades and especially coated paper grades a lot of mineral and pigment fraction is discharged nowadays from the process as mill reject of a vortex cleaning plant, which of its content might be utilized as raw material for paper, but is of its particle size too coarse.
In the short circulation of paper machines manufacturing SC grades and grades containing other fillers, the mineral fraction exiting the vortex cleaning as mill reject is the coarse portion of the mineral fraction added in the pulp dosing, the particle size being generally more than 10 μm.
In the short circulation of paper machines manufacturing coated paper grades the mineral fraction exiting the process as mill reject mainly contains non-dispersable coating layer of coated waste paper. The coating pigment has not dispersed in the dispersion system to particles fine enough. The fraction of the coating pigment, which has not been dispersed and is of its size generally more than 10 μm, is rejected in the vortex cleaning of the short circulation.
The same applies to systems for recycled pulp, in which coated newspaper or like heavily coated raw material for recycled paper is used as raw material. In the defiberizing system for recycled pulp the coating pigment of the coated paper is released from the actual fiber layer of the paper more or less in sheet-like fractions, which are partially dispersed due to the process. The dispersion is, however, not complete and that is why these coating pigment particles which have remained non-dispersed are discharged from the screening stage of the process as reject of the vortex cleaning. However, the majority of the particles would be of their raw material content filler material usable in the paper manufacture, which may possibly be added to the fiber suspension in the later stages of the paper manufacture. The size of these particles is such that said particles cause problems in the paper manufacture if they are not dispersed and thus made qualified to be used as fillers.
U.S. Pat. No. 4,504,016 discloses a process and apparatus for cleaning chemical cellulose by screening. The problem underlying the patent is to increase the yield of chemical pulp in the production thereof. In the process the cellulose is sorted and a coarse fraction, i.e. knots and shives, is treated in a refiber and further sorted. Since it is a question of a chemical pulp manufacture process there are no further substances e.g. filler material involved in the process. Also, the document teaches the removal of the rejects of the hydrocyclone out of the system.
U.S. Pat. No. 4,167,438 discloses a process and apparatus for preparing and cleaning fibrous material, e.g. mixed waste paper. The publication teaches the combined recycle of both fibers and fillers back to use. There is no suggestion that the process could be used for separating and treating the mere filler fraction of the waste paper pulp.
In an arrangement in accordance with the present invention the loss in fillers/minerals exiting the vortex cleaning as mill reject is diminished by treating fraction having a concentrated mineral content in the vortex cleaning plant for dispersing mineral fractions and returning them back to the process.
Advantages obtained by utilizing the method and apparatus in accordance with the present invention are, for example, following:
Filler/mineral, water, chemical, heat and fiber losses are as low as possible. Only useless fraction and fraction that cannot be changed into a form that can be re-used are discharged in a very concentrated form.
Dispersion of mineral particles is based on internal shear forces of the suspension, in other words mechanical wear is minimal.
Investment costs of the system are very low. Technical realization is carried out with commercial apparatuses, repayment period is short.
System is easy to build, i.e. it may be mounted to the already existing systems by adding a screening apparatus fractionating the mineral fraction and wood fraction separate and a new kind of cleaner for the discharge of reject in a very concentrated form after the last cleaner step and by adding a treatment stage dispersing the mineral fractions thereafter.
Treatment is carried out, for example, in the short circulation of a paper machine for each machine individually, whereby, for example, the water circulations between the machines are not mixed.
System is a continuously operating part of a short circulation of a paper machine, or of a screening system. In other words, the process conditions are constant and the operation trouble-free. Process adjusts itself, for example, if the amount of the coarse fraction increases, the system returns only the dispersed fraction to the process and the rest is discharged from the system.
The characteristics of the method and apparatus in accordance with the present invention become apparent in the enclosed patent claims.
The method and apparatus in accordance with the present invention are described more in detail below, by way of example, with reference to the accompanying drawings, in which
An example of the prior art arrangements for diminishing filler/mineral losses is, for example, an arrangement in accordance with FIG. 1a. There the mineral loss is diminished by fractionating all fine material, i.e. solid material of useful size, from the flow exiting the process back to the process. Said apparatus operates in such a way that the flow exiting from the process is brought to a curved screen 10, a so called Hydra-screen, which divides the flow into two fractions. The coarser fraction is led to an intermediate tank 12 and the finer fraction to a filtrate tank 14. The finer fraction is pumped from the filtrate tank 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 led to the intermediary tank 12 and the finer fraction, practically speaking clear liquid and the fine filler therewith to be reused, for example, for the dilutions necessary in the process. The fraction discharged from the intermediary tank 12 as reject of 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
According to
It is, however, characteristic of all said methods that they do not change/diminish the particle size/distri-bution of the solids to be treated, but only separate the fine and as such usable fraction and the coarse fraction and return the fine fraction to use.
It is a characteristic feature of a dispersion process of mineral fractions that it is based on internal shear forces of the flow/suspension which are mechanically generated. In order for the shear forces to have a dispersing effect in the suspension, in other words the shear forces to be effective enough, the concentration of the suspension must be high. Principally, the higher the concentration is, in which the treatment takes place, the more efficient it is, in other words the greater the shear forces are, which may be directed to the suspension and the more efficiently the dispersion takes place.
The concentration of the mineral fraction is sufficiently increased by means of a new kind of vortex cleaner construction disclosed in U.S. Pat. No. 5,139,652, said cleaner being extremely efficient in classifying, but from which the coarse mineral fraction, having the size of more than 10 μm, is rejected as a very concentrated flow having a solids content of even more than 40%.
The concentration of the fractions to be treated may be increased also, for example, by filtering or precipitating, but it is characteristic of all these other methods that they require additional apparatuses and/or great volumes and are rather complicated to be carried out as a continuous, trouble-free process. The concentration of the mineral fraction in a new kind of vortex cleaner takes place in connection with the normal operation of the vortex cleaner without any additional apparatuses.
After the thickening, i.e. the increase of the solids concentration, the mineral fraction is treated by mechanical mixing elements or grinding apparatuses generating great internal shear forces in the suspension. Due to the shear forces the mineral particles rub against each other and are comminuted to such a particle size, that they may be used as a filler in paper manufacture.
In the embodiment of
In the arrangement of
The recycling and dispersion process of the dispersed mineral fractions may, of course, also be carried out in two or more stages. The coarse fraction, which is not dispersed in the first dispersion stage, may, of course, be treated again and thus the mineral loss exiting from the process may be diminished, see
Also the refining treatment itself may be carried out either as one-stage or multistage process and at least in theory such a process might be possible, in which coarse fraction is recirculated for such a long time that also the possible sand, and like impurities are refined and returned to the process, whereby the system might be completely closed.
The filler fraction dispersed in the dispersion apparatus 90 is returned by the pump 84 to the feed of the vortex cleaning stage 86 operating in the above described manner. Thus the unrefined filler fraction may be recirculated in the dispersion apparatus 90 and vortex cleaners 86 until the filler particles are dispersed to a usable size.
Of course, it is possible also in the embodiments of
As may be seen from the above illustrated embodiments, which to some extent deviate from each other, new and previously unknown method and apparatus have been developed for treating recycled fibrous material so that as much of the filler therein as possible might be recovered and reused. Firstly, it must be noted that all the apparatuses illustrated in the drawings and in the description are connected to each other with flow channels suitable for the particular purpose, by a manner illustrated either in the drawings, or described in the description or claims. Further, it must be noted that the above described embodiments are only examples of many different variations of the invention and are by no means given to restrict the inventive concept, but are merely given as examples. Thus it is obvious that the mixing/dispersing apparatus in the above described embodiments is described as a tank, having at least one mixing/dispersing rotor, also grinders or mill-type comminuters known per se may be used. It is also obvious that the details described in connection with different embodiments are available to be used also in other embodiments without special notice. Thus the attached patent claims alone define the present invention.
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