U.S. patent application number 12/734742 was filed with the patent office on 2011-07-07 for method and device for processing waste paper.
Invention is credited to Andreas Faul, Jens Winter.
Application Number | 20110162810 12/734742 |
Document ID | / |
Family ID | 40576857 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110162810 |
Kind Code |
A1 |
Faul; Andreas ; et
al. |
July 7, 2011 |
METHOD AND DEVICE FOR PROCESSING WASTE PAPER
Abstract
The invention relates to a method for processing waste paper
according to the following steps: a) the waste paper is decomposed
into fibres, b) the fibres are washed, c) the fibres are subjected
to a dispersion process, d) the fibres are subjected to a flotation
method, e) the fibres are processed for further treatment in a
paper machine. The liquid from the fibres obtained in step b) is
reintroduced into the fibre flow prior to step d). The invention
also relates to a device for carrying out said method.
Inventors: |
Faul; Andreas;
(Bietigheim-Bissingen, DE) ; Winter; Jens;
(Hemmingen, DE) |
Family ID: |
40576857 |
Appl. No.: |
12/734742 |
Filed: |
November 8, 2008 |
PCT Filed: |
November 8, 2008 |
PCT NO: |
PCT/EP2008/009447 |
371 Date: |
February 25, 2011 |
Current U.S.
Class: |
162/4 ;
162/233 |
Current CPC
Class: |
Y02W 30/64 20150501;
D21B 1/325 20130101; Y02W 30/646 20150501; D21B 1/32 20130101 |
Class at
Publication: |
162/4 ;
162/233 |
International
Class: |
D21B 1/12 20060101
D21B001/12; D21C 7/00 20060101 D21C007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 20, 2007 |
DE |
10 2007 055 557.3 |
Claims
1. A method for processing waste paper comprising the following
steps: a) the waste paper is decomposed into fibres, b) the fibres
are subjected to a washing process, c) the fibres are subjected to
a dispersion, d) the fibres are subjected to a flotation process,
e) the fibres are processed for further treatment in a paper
machine, wherein the liquid accumulating in step b) is supplied to
the fibre stream again before step d).
2. The method according to claim 1, characterised in that after
step b) and before step c), the fibres are subjected to at least
one thickening.
3. The method according to claim 2, characterised in that the
liquid accumulating during the at least one thickening is
removed.
4. The method according to claim 2, characterised in that the
liquid accumulating during the thickening is supplied to the fibres
again after step c).
5. The method according to claim 1, characterised in that the
fibres are subjected to at least one sorting before step b).
6. The method according to claim 5, characterised in that the
fibres are subjected to a coarse sorting and a fine sorting before
step b).
7. The method according to claim 1, characterised in that the
fibres are subjected to at least one thickening after step d).
8. The method according to claim 7, characterised in that the water
accumulating during the at least one thickening carried out after
step d) is supplied back to the fibre stream before step d).
9. The method according to claim 1, characterised in that at least
the liquid accumulating in step b) is subjected to a separate
thickening and the thickened material is supplied to the fibre
stream again before step d).
10. The method according to claim 9, characterised in that the
fibre stream accumulating after step c) is partially or completely
used as filter aid for the separate thickening.
11. The method according to claim 9, characterised in that the
water accumulating during the separate thickening is supplied to
the fibre stream again upstream of step b).
12. A device for processing waste paper having the following
features: a) a decomposition stage for decomposing the waste paper
into fibres, b) a washing stage for washing the fibres, c) a
dispersion stage for dispersing the fibres, d) a flotation device
for flotation of the fibres, e) at least one processing stage for
processing the fibres for further treatment in a paper machine,
wherein a line is provided for the liquid accumulating in the
washing stage, which branches off from the washing stage and opens
into the fibre stream again before the flotation device.
13. The device according to claim 8, characterised in that at least
one thickening stage is provided between the washing stage and the
dispersion stage.
14. The device according to claim 9, characterised in that a line
for the liquid accumulating in the thickening stage branches off
from the at least one thickening stage and opens into the fibre
stream again before the flotation device.
15. The device according to claim 8, characterised in that at least
one sorting stage is provided before the washing stage.
16. The device according to claim 11, characterised in that a
coarse sorting stage and a fine sorting stage are provided.
17. The device according to claim 8, characterised in that at least
one thickening stage is provided after the flotation device.
18. The device according to claim 17, characterised in that a line
for the extracted water branches off from the at least one
thickening stage and opens into the fibre stream before the
flotation stage.
19. The device according to claim 8, characterised in that a
separate thickening stage is provided at least for the liquid
accumulating in the washing stage.
20. The device according to claim 19, characterised in that a line
for at least some of the fibre stream accumulating after the
dispersion stage is provided after the dispersion stage and opens
into the thickening stage.
21. The device according to claim 19, characterised in that a line
branches off from the thickening stage and opens into the fibre
stream at least one point upstream of the washing stage.
Description
[0001] The present invention relates to a method and a device for
processing waste paper.
[0002] Nowadays, paper which meets high quality requirements can be
produced from waste paper. A particular problem here is the removal
of printing inks from the waste paper ("deinking"). Flotation
processes are used for this purpose in which hydrophobic ink
particles in a specific particle size range are separated from the
isolated paper fibres and discarded. In this case, all the fibres
should be retained as far as possible. Usually all those printing
inks used in the most important printing methods, i.e. intaglio and
offset printing, can be removed by this flotation process.
[0003] In addition, other printing processes are gaining in
importance which use printing inks which cannot be removed by the
commonly used flotation process because they are not released from
the fibre or because they form too-large or too-small or
hydrophilic ink particles. For example, UV-cross-linked inks and
vegetable-oil-based inks form too-large particles. For example,
toner or flexographic printing inks and ink jet printing inks form
too-small particles. In order to solve the problem of the
non-released or too-large ink particles, another process stage is
required in which the fibres tainted with these printing inks are
dispersed. In this case, the ink particles are released from the
fibres and at the same time comminuted. As a result, they can be
separated from the fibres in a subsequent step by a usual flotation
process. This additional process stage is associated with an
appreciable loss of fibres.
[0004] EP 1 731 662 A1 describes a process for processing waste
paper in which the isolated fibres are fractionated after the first
flotation step, i.e. divided into a short fibre fraction and a long
fibre fraction. The short fibre fraction substantially contains
short fibres and other fine substances and fillers. In addition to
the long fibres, the long fibre fraction contains substantially
larger impurities such as adhesive particles ("stickys"),
agglomerates and non-released printing inks still adhering to the
long fibres. Only the long fibre fraction undergoes dispersion. The
two fractions are combined again in the further course of the
process. In this case, the fibre losses are reduced and energy is
saved because the short fibre fraction is not co-dispersed. In
addition, the machine size for the dispersion can be reduced.
[0005] A further development of this process is also known in which
the fractionation takes place before the first flotation process.
After the long fibre fraction has been dispersed and possibly
purified by a sorting process, both fractions are each subjected to
a single flotation process separately. The hitherto necessary
second flotation process is omitted completely so that energy is
additionally saved and the two installations for the flotation
process can each be made smaller than hitherto.
[0006] However, this further development has the disadvantage that
during the fractionation the ink particles already released from
the fibres are still completely present since the hitherto usual
first flotation process is omitted. Consequently, the long fibre
fraction can contain ink particles which have already been released
and which are entrained in the course of the processing method.
These ink particles are then further comminuted during the
dispersion so that as a result of their then too-small particle
size, they can no longer be separated from the fibrous material or
the fibre suspension by means of the subsequent flotation process.
The dispersion has the disadvantageous effect on the particles
which have already been released that they are absorbed on the
fibres again. Another problem is that as a result of the separation
into a long-fibre fraction and a short fibre fraction, the quality
of the resulting paper can be unsatisfactory.
[0007] It is therefore the object of the present invention to
further develop a generic method or a generic device in such a
manner that all the ink particles are reliably removed and the
quality of the resulting paper is as far as possibly constantly
high.
[0008] The solution consists in a method having the features of
patent claim 1 and a device having the features of patent claim 12.
According to the invention, it is provided that the waste paper is
decomposed into fibres, the fibres are subjected to a washing
process, a dispersion process, and a flotation process, and are
then processed for further treatment in a paper machine, wherein
the liquid accumulating in step b) is supplied to the fibres again
before step d).
[0009] The term washing or washing process is defined as a
solid-solid separating process in which fine particles are
separated from the fibres. Suitable washing stages for this purpose
are known as such. A suitable known configuration of such a washing
stage comprises, for example, a central roller with a revolving
screen. The fibre stream is guided in a material distributor and
sprayed through a nozzle into the intermediate space between the
rotating central roller and the revolving screen. The fibre stream
is thickened by the screen tension and the resulting filtrate
containing the fine particles is hurled away as a result of the
centrifugal force and guided outwards. The washed and thickened
fibres are removed from the central roller and further
processed.
[0010] Therefore, the released ink particles already present in the
fibre stream and any fillers which may be present are reliably
separated from the fibres. The fibres obtained in the course of the
process are particularly well suited for producing high-quality
papers because the degree of whiteness and cleanliness are
appreciably improved. In addition to the printing inks already
released, the filtrate obtained during the washing also contains
fine substances and short fibres which are important for the paper
quality. It is therefore provided according to the invention to
return this filtrate into the fibre stream before the flotation
stage. In this way, both the long fibres and the short fibres are
guided through the dispersion stage in a single fibre stream, where
the remaining printing inks are released from the fibres. The
printing ink particles which have already accumulated in the
filtrate of the washing stage after the washing are guided together
with the important fine substances and short fibres around the
dispersion stage and fed to the flotation stage. In this way it is
ensured that all the printing inks are removed during the flotation
whilst at the same time the loss of short fibres and fine
substances is minimised. In this way a substantially improved paper
quality is achieved and at the same time, the machine expenditure
for processing the waste paper is significantly reduced.
[0011] A further advantage of the method according to the invention
is that only one flotation stage is required which is situated
towards the rear, i.e. downstream in the process sequence compared
with the prior art. The material losses resulting from the second
flotation stage hitherto necessary in the prior art no longer occur
in the method according to the invention.
[0012] A further important aspect of the present invention consists
in that a fractionation of the fibres into a short fibre fraction
and a long fibre fraction hitherto deemed to be essential in the
prior art is omitted. For the person skilled in the art it was
surprisingly established that passing the combined short and long
fibres through a single washing stage, a single dispersion stage
and a single flotation device whilst simultaneously guiding the
filtrate obtained in the washing stage around the dispersion stage
is only associated with a low fibre loss. Almost the entire amount
of fibres obtained when decomposing the waste paper and a
significant fraction of the fine substances essential for the paper
quality ultimately reach the paper machine to produce new paper. As
a result, an appreciable improvement in the quality of the
resulting paper is achieved.
[0013] In addition, the method according to the invention is
substantially simplified compared with the prior art so that the
device according to the invention suitable for carrying out the
method has a substantially less complex structure than the
apparatus known in the prior art. This is therefore naturally
accompanied by considerable cost savings.
[0014] Advantageous further developments are obtained from the
dependent claims.
[0015] After the washing and before the dispersion, a further
thickening, for example, a high-consistency thickening, can take
place to further reduce the amount of the fibre stream guided
through the dispersion stage. This is particularly appropriate if
an optimal material density is to be set for the dispersion so that
the best possible shear effect can be achieved.
[0016] The liquid accumulating during the thickening can either be
removed or, in the same way as the filtrate obtained in the washing
stage, fed back into the fibre stream before the flotation
stage.
[0017] The fibres obtained during the decomposition of the waste
paper can be subjected to at least one usual sorting process before
the washing, for example, a coarse sorting or a fine sorting in
order to remove impurities which may still be present.
[0018] A feasible processing of the fibres for further treatment in
a paper machine can, for example, consist in at least one
thickening step in order to reduce the volume of the fibre
stream.
[0019] A further advantageous embodiment of the method according to
the invention consists in subjecting the filtrate accumulating in
the washing stage to a separate thickening and using the water
accumulating in this separate thickening to optimally adjust the
consistency of the fibre stream upstream of the washing stage in
order to further improve the fibre quality. The material
accumulating during the separate thickening is then fed back into
the fibre stream again before the flotation stage.
[0020] In a further development of this embodiment, the fibrous
material obtained after the dispersion can be used as filter aid
for the separate thickening. In this case, it is advantageous to
dilute the fibre stream again before flotation since the material
accumulating during the separate thickening in combination with the
fibrous material used as filter aid is possibly too viscous. The
water possibly accumulating during the additional thickening stages
provided before the actual paper manufacture is, for example,
suitable for this purpose. The combination of these advantageous
measures leads to the configuration of two water circuits by which
means not only the fibre quality can be optimised but also the
water loading of the method according to the invention and the
volume of the accumulating waste water can be reduced.
[0021] Exemplary embodiments of the present invention are described
in detail hereinafter with reference to the appended drawings. In
the figures:
[0022] FIG. 1 shows a block diagram of the first embodiment of a
method according to the invention;
[0023] FIG. 2 shows a block diagram of a second embodiment of a
method according to the invention.
[0024] The block diagrams show two embodiments of the method
according to the invention in its entirety. The machines used for
this purpose and other devices as such are known to the person
skilled in the art so that their detailed description is
omitted.
[0025] FIG. 1 shows a first embodiment of the method according to
the invention. The waste paper is defibered, i.e. decomposed into
fibres in a decomposition stage 10 in a manner known per se. The
fibres obtained are present in a fibrous material mixture
containing short fibres and long fibres, wherein the short fibres
are already freed from printing inks whereas printing inks which
have not yet been released can adhere to the long fibres. The
fibrous material mixture therefore contains released ink particles
and in addition other fine materials and fillers as well as coarser
impurities such as adhesive particles ("stickys") and non-paper
components. In the exemplary embodiment the fibrous material
mixture is therefore subjected to a coarse sorting in a first
sorting stage 11 in a manner known per se and if necessary, a fine
sorting in a second sorting stage 16 in order to separate
impurities such as adhesive particles or non-paper components from
the fibres. According to the invention, the complete fibre stream
containing short fibres and long fibres is then supplied to a
washing stage 17 where it is subjected to washing. During the
washing fine solid particles such as fillers and printing inks
which have already been released but possibly also fine substances
and some short fibres are separated from the fibre stream. The long
fibres and some of the short fibres are retained in the fibre
stream.
[0026] After the washing, it is appropriate to subject the fibre
stream, for example, to a high-consistency thickening in a
thickening stage 19 in order to bring it to a suitable consistency
for the dispersion. The fibre stream is then dispersed in a
dispersion stage 21 in a manner known per se. At the same time, the
printing inks still adhering to the fibres, in particular the long
fibres, are released in the form of small ink particles. The ink
particles are now accessible to a flotation process whereby they
can be separated from the fibres. The fibres can, for example, be
oxidatively bleached at the same time as the dispersion.
[0027] Following the dispersion and optionally the bleaching, the
fibre stream is subjected to a flotation process in a flotation
device 23 in a manner known per se. In this case, it is provided
according to the invention that the filtrate accumulating during
the washing in the washing stage 17 is removed from the washing
stage 17 via a line 27 and is fed back into the fibre stream before
the flotation stage 23. The printing inks which have already been
released and are contained in the filtrate are in this way passed
around the dispersion stage 21 with the valuable fine substances.
Dispersion of the filtrate is not required and even undesirable
since the printing inks contained in the filtrate are already
present in dispersed form and no longer adhere to the fibres. In
this way, the qualitative result of the dispersion of the remaining
fibre stream in the dispersion stage 21 is improved. At the same
time, the dispersion stage 21 can be designed for a lower volume of
fibre stream than was hitherto necessary in the prior art.
[0028] It is possible to proceed in a comparable manner with the
water accumulating during the thickening in the thickening stage 19
in that in the exemplary embodiment, this is led off via the line
28 and fed back to the fibre stream together with the filtrate
accumulating in the washing stage 17 before the flotation stage
23.
[0029] During the flotation in the flotation stage 23, all the
hydrophobic solids having particles sizes lying approximately
between 5 .mu.m and 500 .mu.m in diameter are separated from the
fibres in a manner known per se. This includes in particular all
the printing inks which are present in dispersed form in the fibre
stream after the dispersion stage 21 or are fed back to the fibre
stream upstream of the flotation stage via the lines 27, 28.
[0030] The fibre stream thus purified can then be thickened in a
thickening device 24, for example, a disk filter and optionally
thereafter the fibres are bleached. In the exemplary embodiment
this is then followed by a high-consistency thickening in a further
thickening stage 25. The resulting fibre fleece can then be fed to
a paper machine. This paper machine can in particular be a sheet
forming unit which can produce single- or multi-ply paper products,
for example, two-ply corrugated board or four-ply cardboard.
[0031] In the embodiment shown as an example in FIG. 1, the method
according to the invention achieves the best results, i.e.
processed waste paper fibres of good to very good quality,
particularly when the consistency of the fibre stream before the
washing stage 17 and before the flotation stage 23 is approximately
the same. This means that when returning the filtrate from the
washing stage 17 or the liquid from the thickening stage 19, the
consistency of the fibre stream can be optimally adjusted before
the flotation stage 23.
[0032] For reasons of quality, the fibre stream can be present in a
particularly thin consistency before the washing stage 17 with the
result that the resulting filtrate is thinner than desired and on
account of quality considerations cannot be completely returned to
the fibre stream before the flotation stage 23. If such a water
excess exists, it can be appropriate to modify the method according
to the invention, as shown as an example in FIG. 1, in such a
manner that an embodiment of the method according to the invention
as shown as an example in FIG. 2 results.
[0033] FIG. 2 shows a second embodiment of the method according to
the invention which corresponds to the embodiment according to FIG.
1 in its essential steps. The process stages identical to the
exemplary embodiment shown in FIG. 1 are therefore provided with
the same reference numerals. The waste paper is likewise guided via
a decomposition stage 10, a first sorting stage 11 and optionally a
second sorting stage 16. The resulting fibre stream is further
processed in the same way as was described with reference to FIG.
1. The fibre stream is therefore supplied to a washing stage 17
where it undergoes washing. The fibre stream is then subjected to a
high-consistency thickening process in a thickening stage 19 and
then dispersed in a manner known per se in a dispersion stage 21.
At the same time as the dispersion, the fibres can, for example, be
oxidatively bleached. The fibre stream is then subjected to a
flotation process in a flotation device 23 in a manner known per
se. The purified fibre stream is thickened in a thickening device
24, for example, a disk filter. This is followed by a
high-consistency thickening in another thickening stage 25. The
resulting fibre fleece can now be supplied to a paper machine.
[0034] The modification of the method according to the invention
now consists in that the consistency of the fibre stream, i.e. the
degree of dilution, can be optimised in each phase of the method
according to the invention. The starting point for the modification
is the consideration that for reasons of quality, the fibre stream
can be present in a highly diluted form before the washing stage
17. The filtrate resulting from the washing stage 17 therefore
accumulates in a comparatively large quantity. Nevertheless, the
important short fibres and fine substances contained in this
filtrate, as described above, should not be lost. Consequently, the
filtrate extracted from the washing stage 17 by means of the line
18 is subjected to a separate thickening in a separate thickening
stage 31. By analogy to the embodiment of the method according to
the invention described in FIG. 1, the thickened filtrate is
returned to the fibre stream before the flotation stage 23. The
thickened filtrate contains the important short fibres and fine
substances and similarly to the method according to the invention
described in FIG. 1, the released printing inks which have already
accumulated during the defibering and sorting, which are finally
removed in the flotation stage 23. The water accumulating in the
thickening stage 31 can now be used to optimally adjust the
consistency of the fibre stream before the sorting stages 10 and/or
11 and/or before the washing stage 17 in order to ultimately obtain
a particularly good fibre quality.
[0035] The thickening devices known in the prior art operate with a
filter aid. A further modification of the method according to the
invention provides that the fibre stream resulting from the
dispersion stage 21 which has a suitable consistency is used for
this purpose. To this end the fibre stream is partially or
completely withdrawn after the dispersion stage and fed via a line
32 to the thickening stage 31 where the short and long fibres
contained in the fibre stream are used as filter aid, for example,
as supporting fibres in a vacuum disk filter known per se. The
person skilled in the art is naturally free to use a separate
filter aid instead of this.
[0036] If the fibre stream is used as filter aid, all the fibres
obtained in the thickening stage 31 such as fine substances,
fillers and dispersed printing inks, are fed back to the fibre
stream and subjected to a flotation in the flotation stage 23. For
this purpose the fibre stream must optionally be diluted again
before the flotation stage 23. In this case, a further modification
of the method according to the invention provides that the water
obtained in the thickening stages 24 and/or 25 is used for this
purpose and is returned into the fibre stream via the line 33
before the flotation stage 23.
[0037] The combination of all these modifications results in an
embodiment of the method according to the invention which comprises
two water circuits. A second, smaller, water circuit leads from the
last thickening stages 24 and/or 25 before the flotation stage 23
and back. The water contained therein is always cleaner than the
water contained in the first, larger, water circuit. This first
water circuit leads from the washing stage 17 or thickening stage
19 via the thickening stage 31 upstream of positions located before
the washing stage 17, for example, before the sorting stages 10
and/or 11 and/or before the washing stage 17. In this way, the
water loading of the method according to the invention is reduced.
In each stage of the method according to the invention, the
consistency of the fibre stream can be optimally adjusted. If it is
necessary to replace contaminated water by clean water in the
circuits, the comparatively clean water present in the second
smaller circuit can be discharged into the first larger circuit
whose contaminated water is fed to a clarification plant.
[0038] The water extracted from the second smaller circuit in this
way can be replaced by clean fresh water (not shown). Consequently,
not only the water loading of the method according to the invention
is reduced but the volume of waste water accumulating in a
clarification plant for purification is also reduced.
* * * * *