U.S. patent application number 12/158222 was filed with the patent office on 2011-02-17 for method for manufacturing mechanical pulp.
This patent application is currently assigned to UPM-Kymmene Corporation. Invention is credited to Ernst-Martin Billing, Markku Gummerus, Esko Harkonen, Jean-Cristophe Hostachy, Serge Kocimski, Jouko H. Lehto, Folke Orsa, Mia Piirainen, Liisa Pirinen, Taisto Tienvieri.
Application Number | 20110036523 12/158222 |
Document ID | / |
Family ID | 37623877 |
Filed Date | 2011-02-17 |
United States Patent
Application |
20110036523 |
Kind Code |
A1 |
Harkonen; Esko ; et
al. |
February 17, 2011 |
METHOD FOR MANUFACTURING MECHANICAL PULP
Abstract
A method for manufacturing mechanical pulp. Raw material of the
mechanical pulp is introduced. The raw material is refined in a
first refining stage to form the mechanical pulp. The pH of the
mechanical pulp is adjusted to between 9 and 11 in a process step
in which a first process delay is arranged. The first process delay
is at least 0.5 hours. The mechanical pulp is sorted into a first
accepted stock and a first rejected stock. The first rejected stock
is ozonated. The pH of the first rejected stock is at the start of
the ozonation process is between 9 and 11. The ozonated first
rejected stock is refined in a second refining stage so that at
least a part of the ozonated first rejected stock will belong to a
second accepted stock. The first accepted stock and the second
accepted stock are combined. The mechanical pulp may be used.
Inventors: |
Harkonen; Esko; (Kajaani,
FI) ; Tienvieri; Taisto; (Valkeakoski, FI) ;
Lehto; Jouko H.; (Lappeenranta, FI) ; Gummerus;
Markku; (Tampere, FI) ; Orsa; Folke;
(Lappeenranta, FI) ; Pirinen; Liisa; (Valkeakoski,
FI) ; Piirainen; Mia; (Jormua, FI) ; Hostachy;
Jean-Cristophe; (Taluyers, FR) ; Kocimski; Serge;
(Orgeval, FR) ; Billing; Ernst-Martin; (Enger,
DE) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
|
Assignee: |
UPM-Kymmene Corporation
Helsinki
FI
|
Family ID: |
37623877 |
Appl. No.: |
12/158222 |
Filed: |
December 27, 2007 |
PCT Filed: |
December 27, 2007 |
PCT NO: |
PCT/FI2007/050721 |
371 Date: |
October 25, 2010 |
Current U.S.
Class: |
162/28 |
Current CPC
Class: |
D21B 1/16 20130101; D21C
9/153 20130101 |
Class at
Publication: |
162/28 |
International
Class: |
D21B 1/04 20060101
D21B001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2006 |
FI |
20065860 |
Claims
1. A method for manufacturing mechanical pulp, the method
comprising: introducing raw material of the mechanical pulp,
refining the raw material in a first refining stage to form the
mechanical pulp, adjusting a pH of the mechanical pulp between 9
and 11 in a process step in which a first process delay is
arranged, the first process delay being at least 0.5 hours, sorting
the mechanical pulp into a first accepted stock and a first
rejected stock, ozonating the first rejected stock whose pH at the
start of the ozonation process is between 9 and 11, refining the
ozonated first rejected stock in a second refining stage so that at
least a part of the ozonated first rejected stock will belong to a
second accepted stock, and combining the first accepted stock and
the second accepted stock.
2. The method according to claim 1, wherein the first rejected
stock is ozonated at a consistency which is higher that 30%.
3. The method according to claim 1, further comprising: sorting of
the ozonated and refined first rejected stock to the second
accepted stock and a second rejected stock.
4. The method according to claim 1, further comprising: ozonizing
the first accepted stock.
5. The method according to claim 4, wherein the first accepted
stock is ozonated at a consistency of from 0.5 to 1.5%.
6. The method according to claim 4, further comprising: adding
alkali to the ozonated first accepted stock in a process step in
which a second process delay is arranged, the second process delay
being at least 0.5 hours.
7. The method according to claim 1, further comprising: bleaching
the first accepted stock and the second accepted stock.
8. The method according to claim 1, further comprising: utilizing
the mechanical pulp in a paper product manufacturing process.
Description
[0001] Publication F161926 and corresponding publication DE 2444475
disclose a process in which pulp is treated with ozone. It is
possible that the pH of the pulp is adjusted after the
ozonation.
[0002] Publication F167412 and corresponding publication CA 1083870
disclose a process in which pulp is fractionated and one fraction,
possibly the coarse fraction, is treated with ozone. During the
ozonation alkali is fed into the process.
[0003] A problem related to the ozonation process is that it
produces strong organic acids. The organic acids lower the pH of
the pulp, which causes problems in a bleaching process, e.g. by
precipitating ferrous substances from the process water. The
organic acids also deteriorate process devices by causing
corrosion.
[0004] The above-mentioned drawbacks can be overcome by the method
of the invention. The method comprises [0005] introducing raw
material of the mechanical pulp, [0006] refining the raw material
in a first refining stage in order to form the mechanical pulp,
[0007] adjusting the pH of the mechanical pulp between 9 and 11 in
a process step in which a first process delay is arranged, the
first process delay being at least 0.5 hours, [0008] sorting the
mechanical pulp into a first accepted stock and a first rejected
stock, [0009] treating with ozone the first rejected stock whose pH
at the start of the ozonation process is between 9 and 11, [0010]
refining the ozonated first rejected stock in a second refining
stage so that at least a part of it will belong to a second
accepted stock, and [0011] combining the accepted stocks.
[0012] Mechanical pulp is treated in such a manner that after the
ozonation process the pH of the pulp is at a constant level
throughout the pulp, thus making the pulp easier to bleach. When
compared to the ozonation processes of mechanical pulps of prior
art, the novel method provides the following advantages: [0013]
lower energy consumption to reach the targeted pulp freeness,
[0014] better strength properties, [0015] prevention of corrosion
of the process devices located after the ozonation process thanks
to the pH control at pH value higher than 4, and [0016] better
final bleachability of the pulp.
[0017] In the method of the invention, raw material of the
mechanical pulp is introduced in a process. The raw material can be
softwood species, such as pine (Pinus sylvestris), Southern pine
(genus Pinus, several different species), spruce (Picea abies), or
mixtures of pine and spruce. Hardwood species and their mixtures
with softwood species are also possible raw materials. The raw
material can be in form of wood chips. The starting raw material
can also be logs which are ground in a PGW (pressure groundwood)
process.
[0018] The raw material, such as wood chips, which are dewatered in
order to reach a consistency which is from 25% to 35%, typically
30%, is fed in a refiner in which it is refined in a first refining
stage. The refiner can be a disc refiner or a disc refiner with a
conical section. The raw material is refined at an elevated
temperature and under pressure in the refiner in order to form
mechanical pulp. The first refining stage can also be accomplished
by a hammer mill.
[0019] The preferred raw material is pine because the method of the
invention is the most advantageous compared to other processes when
the raw material is pine. It is commonly known that the refining
ability of pine is poor. However, by using ozone it can be
improved. Pulp treated with ozone contains less fines and shives
compared to pulp which is not treated with ozone. The ozone
treatment has also a beneficial effect on a pitch removal which is
important in connection with the pine raw material.
[0020] The first stage refining is rather mild; the pulp is refined
to a freeness of 600-700 ml CSF. The upper limit can be even higher
than 700 ml CSF.
[0021] After the first refining stage there are two main options:
1) All the mechanical pulp can be led to an alkali treatment
reactor, or 2) The pulp can be sorted to a first accepted stock and
a first rejected stock, and the rejected stock is led to the alkali
treatment reactor.
[0022] According to the first main option, the whole mechanical
pulp is led to the alkali treatment reactor in order to achieve a
certain pH level. The mechanical pulp is treated with alkali, such
as sodium hydroxide (NaOH), sodium bicarbonate (Na.sub.2CO.sub.3),
magnesium hydroxide (Mg(OH).sub.2), or calcium hydroxide
(Ca(OH).sub.2). The process in the alkali treatment reactor is
arranged so that there is a process delay, i.e. the pulp stays in
the reactor for at least 0.5 hours, typically from 1 to 2 hours.
The process delay is necessary because the alkali should penetrate
from the surface of the fibers of the pulp to the inner parts of
the fibers (or fiber aggregates, depending on how coarse the pulp
is), i.e. also the inner parts of the fibers and/or fiber
aggregates shall be treated in order to achieve the benefits of the
invention. The process delay can be arranged as well to a batch
process as a continuous process.
[0023] After the pulp is treated in the alkali treatment reactor,
it is led to a sorter, such as a screen or a cyclone. The pulp is
sorted to a first accepted stock and a first rejected stock. The
sorting step takes place in a consistency of from 0.5 to 1.5
percent, typically about one percent, and the first accepted stock
remains in that consistency after sorting. Usually the ratio
accepted stock/rejected stock may be approximately 20/80. However,
the ratio accepted stock/rejected stock may also be 60/40 or 50/50.
Thus, the accepted stock may be between 20 and 60 percent of the
total amount of the pulp, or even between 15 and 65 percent of the
total amount of the pulp.
[0024] The first rejected stock is first dewatered so that the
consistency of the first rejected stock is preferably higher than
30%. The consistency is more preferably higher than 35%. Excess
liquid is circulated back to the process. The first rejected stock
is led in the above-mentioned consistency to an ozone reactor in
which the first rejected stock is fluffed and ozonated. Depending
on the energy saving and pulp quality requirement, the ozonation
process is arranged so that the amount of ozone is between 0.5 and
10% and preferably between 1 and 4% of the weight of the pulp. The
process temperature is between 20 and 90.degree. C. Strong organic
acids form in the ozonation process, but the alkali by which the
first rejected stock has been treated neutralizes those strong
organic acids. The strong organic acids and the alkali form a
buffer solution whose pH can be kept on a certain level for a long
time although the ozonation process constantly produces organic
acids. At the end of the ozonation process the pH of the rejected
stock is between 5 and 7, which is a beneficial range in regard to
the following process steps.
[0025] After the ozonation the first rejected stock is refined in a
main line refining which may comprise sequential refiners. It is
possible that that the first rejected stock is sorted to a second
accepted stock and a second rejected stock. The second rejected
stock can be conveyed for further refining, i.e. to a third
refining stage, but it is also possible that it is just removed
from the process. If there is the third refining stage it is
accomplished in the same manner as the preceding refining
stages.
[0026] The first accepted stock and the accepted amount of the
first rejected stock are combined after the above-mentioned process
stages. The accepted amount of the first rejected stock refers to
all accepted stocks which have been obtained after the pulp has
been sorted to the first accepted stock and the first rejected
stock.
[0027] It is possible that the first accepted stock is treated with
ozone and the ozone treated pulps are combined. It is also possible
that some alkali is added to the first accepted stock after it has
been treated with ozone. The alkali may be the same that is added
before the ozonation. Further, it is possible that the accepted
stock which has not been ozonated is treated with the alkali before
it is combined with the accepted amount of the first rejected
stock.
[0028] The freeness of the resulting stock may be between 90 and
150 ml CSF but it is also possible that the lower limit is 30 or 40
ml CSF. Naturally, the above-mentioned freeness depends on the
desired paper quality.
[0029] According to the second main option, after the first
refining stage the pulp is sorted in a sorter, such as a screen or
a cyclone, to a first accepted stock and a first rejected stock.
The consistency in the sorter is between 1 and 2%. Usually the
ratio accepted stock/rejected stock may be approximately 20/80.
However, the ratio accepted stock/rejected stock may also be 60/40
or 50/50. Thus, the accepted stock may be between 20 and 60 percent
of the total amount of the pulp, or even between 15 and 65 percent
of the total amount of the pulp.
[0030] The first rejected stock is treated with alkali, such as
sodium hydroxide (NaOH), sodium bicarbonate (Na.sub.2CO.sub.3),
magnesium hydroxide (Mg(OH).sub.2), or calcium hydroxide
(Ca(OH).sub.2), in an alkali treatment reactor. The pH of the first
rejected stock is elevated to a level which is between 9 and 11
depending on the ozone amount to be applied and the raw material to
be treated. After that liquid is removed from the first rejected
stock so that a consistency which is preferably higher than 30% is
achieved. The consistency is more preferably higher than 35%.
Excess liquid is circulated back to the process. The first rejected
stock is led in the above-mentioned consistency to an ozone reactor
in which the first rejected stock is fluffed and ozonated.
Depending on the energy saving and pulp quality requirement, the
ozonation process is arranged so that the amount ozone is between
0.5 and 10% and preferably between 1 and 4% of the weight of the
pulp. The process temperature is between 20 and 90.degree. C.
Strong organic acids form in the ozonation process, but the alkali
by which the first rejected stock has been treated neutralizes
those strong organic acids. The strong organic acids and the alkali
form a buffer solution whose pH can be kept on a certain level for
a long time although the ozonation process constantly produces
organic acids. At the end of the ozonation process the pH of the
rejected stock is between 5 and 7, which is a beneficial range in
regard to the following process steps.
[0031] After the ozonation the first rejected stock is led to a
refiner in order to accomplish a second refining stage. As the
first rejected stock has been treated with ozone, its properties
have been changed so that the second refining stage consumes much
less energy compared to stocks which are not treated with ozone.
The first rejected stock is conveyed from the refiner to a sorter
which sorts the first rejected stock to a second accepted stock and
a second rejected stock. The freeness of the accepted stocks, i.e.
the stock consisting of the first accepted stock and the second
accepted stock, may be between 90 and 150 ml CSF but it is also
possible that the lower limit is 30 or 40 ml CSF. Naturally, the
above-mentioned freeness depends on the desired paper quality.
[0032] The second rejected stock can be conveyed for further
refining, i.e. to the third refining stage, but it is also possible
that it is just removed from the process. If there is the third
refining stage, it is accomplished in the same manner as the
preceding refining stages.
[0033] The first accepted stock may be removed from the process and
used for other purposes, but it is also possible that the first
accepted stock and the second accepted stock are combined so that
they can be led as one stock to the following process step, which
is usually a bleaching step. The stock obtained from the second
refining stage has a pH that is between 5 and 7, and the first
accepted stock has about the same pH, so no further steps are
required to adjust the pH level.
[0034] The adjustment of the pH to a level which is between 9 and
11 before refining enhances the bleaching stage because the
peroxide consumption decreases. Harmful wood extractives are
soluble in the water in which the alkali is added.
[0035] The mechanical pulp obtained from the present method (the
above-mentioned first and second main options) is utilized in a
paper product manufacturing process. The paper product may be a
paper containing mechanical pulp, such as a printing paper
containing mechanical pulp, or it may be a cardboard.
[0036] In the following, the invention is explained through
examples and by referring to the figures in which
[0037] FIG. 1 shows a schematic view of a first process,
[0038] FIG. 2 shows a schematic view of a second process,
[0039] FIG. 3 shows schematic views of third and fourth
processes,
[0040] FIG. 4 shows tensile index as a function of SEC (specific
energy consumption), and
[0041] FIG. 5 shows tear index as a function of tensile index.
EXAMPLE 0
[0042] Methods which do not contain an alkali treatment before
ozonation were used in treating mechanical pulp made of pine.
[0043] Points 1 and 2 correspond to the results achieved from a
normal TMP refining in which pine is used as the raw material.
[0044] Point 5 in FIGS. 5 and 6 corresponds to the results achieved
from a process in which an ozonated pine reject is mixed with a
non-ozonated pine accept. No alkali is added.
[0045] Point 7 in FIGS. 5 and 6 corresponds to the results achieved
from a process in which an ozonated pine reject is mixed with an
ozonated pine accept. No alkali is added.
[0046] As one can see from FIGS. 5 and 6, .+-.20% energy saving and
better strength properties than in the normal pine process were
achieved by ozonating the pine reject.
EXAMPLE 1
[0047] In the following, the first process option is described by
referring to FIG. 1.
[0048] Raw material of mechanical pulp is first dewatered, for
example, in a thickener 1, such as a screw press, and after that
the raw material is fed into a refiner 2, in which the raw
material, such as pine chips, is refined in a first stage refining
at an elevated temperature and under pressure in order to form
mechanical pulp. The consistency during the refining is about 30%.
The preferred raw material is pine because the method of the
invention is the most advantageous compared to other processes when
the raw material is pine. The first stage refining is rather mild;
The pulp is refined to a freeness of 600-700 ml CSF. It is possible
that the freeness value is even higher than 700 ml CSF. The pulp is
treated with an alkali, such as sodium hydroxide, in an alkali
treatment reactor 3. The pH of the first rejected stock is elevated
to a level which is between 9 and 11. There is a delay in the
alkali treatment reactor 3 so that the pulp remains inside the
alkali treatment reactor for at least 0.5 hours, typically from 1
to 2 hours. The pulp is also diluted in the alkali treatment
reactor so that its consistency is between 0.5 and 1.5%.
[0049] The pulp is sorted in a sorter 4, such as a screen, to a
first accepted stock A1 and a first rejected stock R1. Usually the
ratio accepted stock/rejected stock is approximately 20/80, but
also other ratios, which are described in the general description,
are suitable.
[0050] After that the first rejected stock R1 is led to a thickener
5, such as a screw press, which removes liquid from the stock in
such a manner that a consistency which is higher than 35% has been
achieved. Excess liquid 9 is circulated back to the process. The
first rejected stock R1 is led in the above-mentioned consistency
to an ozone reactor 6 in which the first rejected R1 stock is
ozonated. Strong organic acids form in the ozonation process but
the alkali by which the first rejected stock has been treated
neutralizes those strong organic acids. The strong organic acids
and the alkali form a buffer solution whose pH can be kept on a
certain level for a long time although the ozonation process
constantly produces organic acids. At the end of the ozonation
process the pH of the rejected stock is between 5 and 7, which is a
beneficial range in regard to the following process steps.
[0051] After the ozonation the first rejected stock R1 is led to a
refiner 7. As the first rejected stock R1 has been treated with
ozone, its properties have been changed so that the refining stage
consumes much less energy compared to stocks which are not treated
with ozone. The first rejected stock R1 may be conveyed from the
refiner 7 to another refiner 8. It is also possible that the first
rejected stock is led to a sorter (not shown) which sorts the first
rejected stock to a second accepted stock and a second rejected
stock. The second rejected stock can be conveyed for further
refining but it is also possible that it is just removed from the
process.
[0052] The first accepted stock and the accepted amount of the
first rejected stock may be combined after the first rejected stock
has been treated in the above-mentioned manner so that they can be
led as one stock to the following process step, which is usually a
bleaching step. The obtained stock has the pH which is between 5
and 7.
[0053] Point 4 in FIGS. 4 and 5 corresponds to the result which is
achieved from the above-described process.
EXAMPLE 2
[0054] In the following, the second process is described by
referring to FIG. 2.
[0055] Raw material of mechanical pulp is first dewatered, for
example, in a thickener 1, such as a screw press, and after that
the raw material is fed into a refiner 2, in which the raw
material, such as pine chips, is refined in a first stage refining
at an elevated temperature and under pressure in order to form
mechanical pulp. The consistency of the pulp is about 30%. The
preferred raw material is pine because the method of the invention
is the most advantageous compared to other processes when the raw
material is pine. The first stage refining is rather mild; the pulp
is refined to a freeness of 600-700 ml CSF. The pulp is treated
with an alkali, such as sodium hydroxide, in an alkali treatment
reactor 3. The pH of the first rejected stock is elevated to a
level which is between 9 and 11. There is a delay in the alkali
treatment reactor 3 so that the pulp remains inside the alkali
treatment reactor for at least 0.5 hours, typically from 1 to 2
hours. At the same time the pulp is diluted to a consistency which
is between 0.5 and 1.5%.
[0056] The pulp is sorted in a sorter 4, such as a screen, to a
first accepted stock A1 and a first rejected stock R1. Usually the
ratio accepted stock/rejected stock is approximately 20/80, but
also other ratios are suitable.
[0057] After that the first rejected stock R1 is led to a thickener
5, such as a screw press, which removes liquid from the stock in
such a manner that a consistency which is higher than 35% has been
achieved. Excess liquid 9 is circulated back to the process. The
first rejected stock R1 is led in the above-mentioned consistency
to an ozone reactor 6 in which the first rejected R1 stock is
ozonated. The amount of ozone is between 0.5 and 10% and preferably
between 1 and 4% of the weight of the pulp. The temperature during
the ozonation is between 20.degree. C. and 90.degree. C.
[0058] Strong organic acids form in the ozonation process, but the
alkali by which the first rejected stock has been treated
neutralizes those strong organic acids. The strong organic acids
and the alkali form a buffer solution whose pH can be kept on a
certain level for a long time although the ozonation process
constantly produces organic acids. At the end of the ozonation
process the pH of the rejected stock is between 5 and 7, which is a
beneficial range in regard to the following process steps.
[0059] After the ozonation the first rejected stock R1 is led to a
refiner 7. As the first rejected stock R1 has been treated with
ozone, its properties have been changed so that the second refining
stage consumes much less energy compared to stocks which are not
treated with ozone. The first rejected stock R1 may be conveyed
from the refiner 7 to another refiner 8. It is also possible that
the first rejected stock is led to a sorter (not shown) which sorts
the first rejected stock to a second accepted stock and a second
rejected stock. The second rejected stock can be conveyed for
further refining, but it is also possible that it is just removed
from the process.
[0060] The first accepted stock A1 is led to an ozone reactor 11 at
a consistency which is between 0.5 and 1.5%. The first accepted
stock A1 is ozonated in the ozone reactor 11. Ozone may be injected
to the first accepted stock A1.
[0061] The first accepted stock A1 and the accepted amount of the
first rejected stock R1 are combined after the first stocks have
been treated in the above-mentioned manner so that they can be led
as one stock to the following process step, which is usually a
bleaching step. The obtained stock has a pH which is between 5 and
7.
[0062] Point 6 in FIGS. 4 and 5 corresponds to the result which is
achieved from the above-described process option.
[0063] As one can see from FIGS. 4 and 5, .+-.30% energy saving and
better strength properties than in the normal pine process were
achieved by treating the rejects by an alkali and ozonating the
pine reject (point 4 and point 6).
EXAMPLE 3
[0064] In the following, the third process is described by
referring to FIG. 3.
[0065] The third process is similar to that in example 2, except
that the first accepted stock is treated with alkali after the
ozonation in a mixing reactor 13. The amount of the alkali was 0.5
wt.-% of the total amount of the dry first accepted stock (for
example, 0.5 wt.-% of 100% NaOH). A process delay is arranged to
the mixing reactor 13. The pulp stays in the reactor 13 at least
for 0.5 hours.
[0066] Point 8 in FIGS. 4 and 5 corresponds to the result which is
achieved from the above-described process option.
EXAMPLE 4
[0067] In the following, the fourth process is described by
referring to FIG. 3.
[0068] The fourth process is similar to that in example 2, except
that the first accepted stock is treated with alkali after the
ozonation in a mixing reactor 13. The amount of the alkali was 2
wt.-% of the total amount of the dry first accepted stock (for
example, 2 wt.-% of 100% NaOH). A process delay is arranged to the
mixing reactor 13. The pulp stays in the reactor 13 at least for
0.5 hours.
[0069] Point 9 in FIGS. 4 and 5 corresponds to the result which is
achieved from the above-described process option.
[0070] As one can see from FIGS. 4 and 5, .+-.30% energy saving and
.+-.30% better strength properties than in the normal pine process
were achieved by treating the pine reject with an alkali, ozonating
the pine reject and adding an alkali into the accepted stock (point
8 and point 9).
[0071] A skilled person readily understands that the processes
described in the examples above can be combined differently. A
skilled person also understands what consistencies are required in
order to perform each process step. The mutual order of the first
process delay and the sorting step may be reversed; in that case, a
skilled person realizes that an adjustment of consistencies is
required and the first accepted stock and the first rejected stock
must be treated separately with the alkali if such treatment is
required for both stocks.
* * * * *