Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS AND DEVICE TO MANUFACTURE CELLULOSE PULP
FIELD OF THE INVENTION
The present invention refer to a fiber development process and a fiber
development device to treat wood fibers. One of the aims with the present
invention is to manufacture wood containing printing grades of paper, news-
print paper qualities and finer paper qualities (value added grades of paper)
such as SC/LWC, from preferably TMP (thermo mechanical pulp), CTMP or
CMP. This is performed with a significant energy saving, bleaching chemicals
saving and lower investment costs in washing and dewatering equipment,
Another aim with the invention is to manufacture TMP, CTMP, CMP or other
mechanical pulp with lower energy input, yet holding an acceptable quality of
the pulp. Another aim is to by using a modified process and a modified device
according to the invention to treat fiber from any pulping process for example
DIP, Kraft pulp or any other pulp and thereby saving energy and improving pulp
quality among other things. Another aim is to improve drainability and
dewatering of a cellulose pulp.
DESCRIPTION OF PRIOR ART
The technology that is used today to manufacture mechanical pulp such as
TMP, CTMP, CMP and improved qualities of these, is with help of one or multi-
stage refining in the main line where the energy consumption is a known
problem. Thereafter a separation is done with help of screening in multiple
stages where a long fiber fraction is separated. This fraction is treated with
simple or multi-stage HC (high consistency) refining followed by screening
stages or with screening stages in between. Possibly the refined rejects from
the HC-refining can be treated with LC (low consistency) refining.
An improved process according to the above, to upgrade TMP pulp from news-
print paper to SC/LWC pulp by using LC-refining, is previously known see US
6361650 B1. What is described there is a system where one LC-refines the
whole advancing pulp stream, and thereafter fractionates the stream and then
treats the fractions. The fractionation is based on length by means of slotted
screens.
It is from US 4731160 known to use hydrocyclones to separate out two fractions
that are bleached with hydrogen peroxide (claim 1 and claim 2).
It is from US 5133832 known to bleach a long fiber fraction with hydrogen
peroxide (H202) and a short fiber fraction with dithionite (Na2S204).
It is known from EP 1077281 A1 to use HC-refining to treat fibers (primarily
recycled fibers) to arrive at a wood containing paper of higher quality. HC-
refining is followed by slot and hydrocyclone fractionation.
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Other documents which can be mentioned as references are WO 03/000982
A1, WO 01 20074 A1 and WO 2004/003288 A1
PROBLEM IN PRIOR ART
The known art doesn't show how one should do to get a paper with good
surface properties, at the same time as one saves energy and still gets a
paper
with good strength properties. Mechanical pulp such as TMP, can untreated be
used for finer paper qualities, but the yield is lowered and a higher energy
input
is required. To make finer paper qualities today one can use more expensive
chemical pulp fiber, such as, sulfate pulp, sulfite pulp or similar, that is
mixed
with mechanical pulp to achieve desired properties. The reinforcement chemical
pulp has high strength and long fibers. In none of the above mentioned
documents is a system disclosed that considers both the specific surface
(fiber
wall thickness) and the use of LC-refining to treat an accept fraction, to
improve
a mechanical pulp of newsprint quality, different bleaching chemicals for
different fractions separated on specific surFace, alternatively to produce a
pulp
of news-print quality with a considerable reduction of energy, bleaching
chemicals, dewatering and washing equipment investments.
This can be concluded as that the prior art does not show clear separation by
fiber morphology allowing selective treatment of different fractions, in
conjunction with effective treatment of the fibers, or fiberfraction,
responsible for
paper surface stability (roughening).
General description of the invention
To solve the above mentioned problem a process and a device according to the
following is proposed.
Process to manufacture cellulose pulps in which defibered cellulose is
screened
to remove shives, fractionated into at least two fractions (10, 11, 12)
preferably
at least three, which fractions is treated each by itself and then are brought
together completely or partly, characterized by that the fractionation is done
according to specific surface, preferably with a device (1 ) comprising
hydrocylones, and that the process comprises process stages (6,7) that
fractionates out fibers with high specific surface, preferably thin walled
fibers,
and that the process comprises process stages (2) that fractionates out fibers
having lower specific surface, preferably fibers with thicker fiber wall, and
that
one or several fiber fractions (3, 3a) are treated, to be split, fibrillated
and
permanently collapsed preferably by a device that comprises some sort of
milling machine (5, 5a) such as a refiner, ball mill or similar.
This has the effect that only the fibers in need of treatment because of
surface
stability problems are treated. The additional effect of the collapsed fibers
of the
fibers in need of this is a better surface stability of the paper.
According to another embodiment of the process is performed as follows
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Process to manufacture cellulose pulps in which defibered cellulose is
screened
to remove shives, and said pulp is then fractionated, and that the
fractionation is
done according to specific surface, preferably with a device (1 ) comprising
hydrocylones, characterized by that the process comprises process
stages(7) that fractionates out fibers with high specific surface, preferably
thin
walled fibers, and that the process comprises process stages (2) that
fractionates out fibers having lower specific surface, preferably fibers with
thicker fiber wall, and said pulp is fractionated into at least three
fractions (10,
3,(3a) 12), which fractions are treated each by itself and then are brought
together completely or partly, and that one or several fiber fractions (3, 3a)
are
treated, to be split, fibrillated and permanently collapsed preferably by a
device
that comprises a comminution device (5, 5a) such as a grinder, a refiner, a
ball
mill or similar.
According to an embodiment can this or those fractions (3,3a) that are treated
in
comminution device (5, 5a comprise fibers with a z-value between 0,3 and 0,8.
The effect of this is that as mentioned above only fibers in need of treatment
is
treated. This gives energy saving and/or a better product in the end.
According to an embodiment can the comminution device (5, 5a) be run so that
the fibers in the fraction at hand are collapsed permanently through cracks in
the fiber wall created by the comminution device.
The effect of this is that the fibers in need of treatment are less sensitive
to fiber
sprinback and the surface stability of the end product is improved, especially
when considering rewetting.
According to an embodiment can the comminution device (5, 5a) comprise
refining at a pulp consistency in the interval 0,8-14%, preferably in the
interval
1-5%.
According to an embodiment can the comminution device (5,5a) comprise
regfining at a pulp consistency of either of 0,8 %, 0,9 %, 1 %, 2%, 3%, 4%,
5%,
6%, 7%, 8%, 9%, 10%, 11 %, 12%, 13%, 14%.
According to an embodiment can the comminution device (5,5a) comprise
regfining at a pulp consistency of 3%-8%.
The effect of choosing the right interval of consistency is to get a fiber
development that gives permanently collapsed fibers yet not excessive fiber
cutting.
According to an embodiment can the comminution device (5, 5a) comprise a
refiner run at a energy input of 10-800 kWh/t preferably 100-600 kWh/t even
more preferred 200-500 kWh/t.
The effect of running at the right energy intervals is that the fiber
development
and collapses are adapted to the incoming fraction so that the splitting,
fibrillation gives the permanent collapse of the fibers needing treatment.
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According to an embodiment a fraction (10) that comprises fibers with high
specific surface leaves from the base of a hydrocyclone stage
The effect of using hydrocyclones is that the fibers are separated on specific
surface, and fibers of different lengths can be obtained in the same fraction.
According to an embodiment a fraction with lower specific surface (3, 3a) and
more thick walled fibers that have been treated leaves from the base of a
hydrocyclone stage.
According to an embodiment the fraction (10) enriched in fines material and
comprising fibers with high specific surface is bleached in non alkaline
environment.
The effect of this is that bleaching can be adapted to the fraction in
question.
Non alkaline bleaching environment is less sensitive to be affected by
impurities
in the fraction (10), said impurities can comprise metall ions for example.
Also
non-alkaline bleaching can be performed at a lower cost.
According to an embodiment the fraction (10) is bleached at a pH which is less
than 9.
According to an embodiment the fraction (10) is bleached with a reducing
bleaching agent.
According to an embodiment the fraction (10) is bleached with a bleaching
agent comprising dithionite.
The effect of using dithionite is that the bleaching is performed at a lower
cost
and that the dithionite is less sensitive to break down before it can bleach
the
fibers.
According to an embodiment the fraction (3,3a) with fibers with lower specific
surface is bleached with oxidative bleaching.
The effect of using oxidative bleaching on the fraction (3,3a) with lower
specific
surface is that, this or these fractions has much less of the impurities
discussed
above which tend to break down oxidative bleaching agents. Oxidative
bleaching agents are more effective and therefore the bleaching of this
fraction
(3,3a) with these types of bleaching agents are better with regard to
brightness,
of the pulp.
According to an embodiment the fraction (3, 3a) is bleached with a bleaching
agent comprising hydrogen peroxide.
According to an embodiment the fraction (3, 3a) is bleached with a bleaching
agent comprising ozone.
According to an embodiment the fraction (12) that remains after previous
process stages and which has the lowest specific surface is cleaned from sand,
bark and other heavy impurities and treated, preferably with a device (15), to
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peel of fiber wall of the fibers in this fraction (12) and that the device
comprises
some sort of comminution device such as a refiner, or similar and that the
fraction after treatment completely or partly is returned back to, preferably
back
ways, in the process.
According to an embodiment the device (15) refines at > 15 % more preferably
> 14 % consistency.
The effect of this is that cleaning of the pulp is performed, to remove
particles
and impurities that are unwanted in the final product. In this fraction fibers
remain that are after treatment possible to use in the final pulp. By
recovering
these fibers the fiber yield is improved.
According to an embodiment the fiber stream with lower specific surface (3,
3a),
preferably with fibers with thicker fiber wall, after treatment is completely
or
partly mixed with the stream (10) of fibers and fines material with high
specific
surface to improve the dewatering properties.
The effect of mixing part of or completely the fraction (3, 3a) with the
fraction 10
is that it will be easier to extract water. The fraction 10 is enriched in
fibers and
fines with low specific surface, this fraction is difficult to dewater since
it tend to
plug filters and other dewatering equipment and even if not plugging equipment
dewatering is slow. By mixing in a fraction 10 comprising fibers with lower
specific surface, that are easier to dewater, the sum of fractions will also
have
improved dewatering properties.
According to an embodiment the fiber stream with lower specific surface (3,
3a),
preferably with fibers with thicker fiber wall, is dewatered alone to a higher
consistency than the finally wanted consistency of the mix of fractions, so
that
the fraction with fibers with high specific surface (10), preferably thin
walled
fibers and fines material only needs to be dewatered partly or not at all.
As mentioned above the fraction (3, 3a) is easier to dewater. This is due to
less
fines content in this fraction as well as different properties of the fibers
with
lower specific surface comprised in this fraction. By concentration dewatering
to
this fraction (3,3a) instead of trying to dewater the fines enriched fraction
(10), a
more optimized use of the dewatering equipment can be obtained, this is
among other things due to the lower tendency to plug the dewatering
equipment. This altogether makes it possible to lower investments in this type
of
equipment.
According to an embodiment fractions (10, 11, 11 a) comprising fibers with
high
and lower specific surface, after treatment is brought together to a pulp
stream
(32) with pulp that has been produced with lower input of energy and bleaching
agents than in a conventional factory for wood containing printing grades of
pulp, news-print pulp, SC, LWC, SC A++ pulp and other pulps.
By treating different pulp fractions in different ways a more optimized use of
the
fiber raw material is obtained.
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An effect of the treatment in the process above is that fiber development
performed makes the stream 32 easier to dewater on the paper machine.
To further describe, a device is disclosed to solve the discussed problem.
Device to treat cellulose pulps to give improved properties with regard to
properties such as, light scattering, tensile index, tear index, surface
roughness,
bleaching chemicals consumption, energy consumption, comprising a first
hydrocylone device (7), a second hydrocyclone device (2), a refiner (5) and
transfer devices between these, characterized by that cellulose pulp is led to
a
first hydrocyclone devise (7) dividing out a base fraction (10) and an apex
fraction (14) that via another hydrocyclone devise (2) dividing out a base
fraction (3) that after dewatering continues to further treatment with a
device (5)
comprising refiner and treatment is done at a consistency between 1-14%.
The effect of using hydrocyclones in the dividing in a device for treating
pulp is
that fibermorphology is the important factor determining what fibers will be
separated from others. This means that fiber length is not the factor on which
fractionation is based as when using screens. This means that the device can
divide out the fibers in need for treatment.
According to an embodiment of the device a base fraction (10) is bleached with
a non alkaline reducing bleaching agent.
The effect of this is that bleaching can be adapted to the fraction in
question.
Non alkaline bleaching environment is less sensitive to be affected by
impurities
in the fraction (10), said impurities can comprise metall ions for example.
Also
non-alkaline bleaching can be performed at a lower cost.
According to an embodiment of the device a second base fraction (11 ) is
bleached with an oxidizing bleaching agent.
The effect of using oxidative bleaching on a the fraction (3,3a) with lower
specific surface is that, this or these fractions has much less of the
impurities
discussed above which tend to break down oxidative bleaching agents,
oxidative bleaching agents are more effective and therefore the bleaching of
this fraction (3,3a) with these types of bleaching agents are better with
regard to
brightness.
According to an embodiment of the device an apex fraction (33) continues to a
hydrocyclone unit and is divided into a base fraction (3a) and an apex
fraction
(33a) in which said base fraction (3a) after dewatering is treated with a
refiner
(5a) at a consistency between 1-14%.
According to an embodiment of the device a base fraction (3a, 11a) is bleached
with an oxidizing bleaching agent.
According to an embodiment of the device treated base fractions (10, 11 and/or
11 a) are brought together to a common pulp stream (32) with improved
properties.
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An effect of the treatment in the device is that fiber development performed
makes the stream 32 easier to dewater on the paper machine.
According to an embodiment of the device an apex fraction (33, 33a) continues
to cleaning with hydrocyclones (8) that removes heavy impurities such as sand,
bark, and other heavy impurities which leaves in an apex fraction (12).
According to an embodiment of the invention a base fraction continues to
treatment comprising refining (15) at a consistency > 5% and this fraction is
then returned in an advancing pulp stream that are led to the inlet of the
device.
Another embodiment is disclosed as a process to produce and dewater
cellulose pulps in which defibered cellulose is screened to remove shives,
fractionated into at least three fractions (10, 3,(3a) 12), that the
fractionation is
done according to specific surface, preferably with a device (1 ) comprising
liydrocylones, characterized by that said pulp is fractionated into at least
three fractions (10, 3, 12), and that the process comprises process stages(7)
that fractionates out fibers with high specific surface, preferably thin
walled
fibers, and that the process comprises process stages (2) that fractionates
out
fibers having lower specific surface, preferably fibers with thicker fiber
wall that
the fraction having lower specific surface (3, 3a) is dewatered in a device
(5) to
a given consistency, and that this fraction (3, 3a) is then mixed at least
partly
with at least one other fraction (10) before the mixed stream are led to the
next
process step.
The effect of this is that fibers that are easiest to dewater can be dewatered
and
then they are mixed with a fraction which is more difficult to dewater, and
the
sum of fractions is a dewatered pulp.
Another embodiment of the process is disclosed with that defibering is done
through refining in one or several stages. The pulp is screened to remove
larger
particles. The advancing pulp stream is then led to fractionation based on
specific surface, which in the case of fibers means by fiber wall thickness.
The
particles that have the highest specific surface are sorted out first. In this
fraction there are thin walled fibers and fines particles, so called fines.
This
fraction doesn't need further treatment for fiber springback (surface
stability),
increased strength, better surface roughness properties (better smothness) and
so on, but can continue in the process. This fraction is bleached with a non
alkaline bleaching agent, such as dithionite. Remaining pulp stream is
fractionated once more on specific surface and here fibers with lower specific
surface are sorted out from fibers that have the thickest walls and having the
lowest specific surface. This fraction then continues to treatment with LC
(Low
Consistency) or MC (Medium Consistency) refining to create cracks in the fiber
wall, fibrillate the fiber and collapse the fiber without affecting the fiber
length to
much, i.e. there will be no significant reduction of the fiberlenght. This
prevents
among other things fiber springback in the final product. Then this fraction
is
bleached in an own bleaching stage with oxidative bleaching. The remaining
fraction with the lowest specific surface is cleaned, in hydrocyclones, for
example in a hydrocyclone cascade, to remove impurities such as sand, bark
and other heavy impurities. Remaining fibers with thick fiber walls continues
to
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treatment with for example HC refining and are returned back or backwards to
the process.
Definitions
There is a prevalent grouping of fibers into early wood, summer wood and late
wood. In this document according to figure 1 there are a grouping into four
different fibertypes. The difference between these fiber types are primarily
the
fiber wall thickness and the properties that are dependent from that, i. e.
surface
roughness, tensile index, moisture induced fiber springback etc. The four
fibertypes that are comprised in this application are characterized by a z-
value
according to table 1 and has been abbreviated to EEW, LEW, ELW and LLW,
which means, early early wood, late early wood, early late wood and late late
wood. These fibertypes differ by the specific surface and on a definition
basis
these can be described by the z-value, see table 1. The z-value is calculated
in
the following way.
4~cAw
Z- a
P
AW = Fiber wall cross-section area
P = Fiber circumference
Table 1
Fiber t pe EEW LEW ELW LLW
z-yalue 0<z<_0,3 0,3<z<_0,6 0,6<z<_0,8 0,8<z
In the paper industry fibers, problems are created when fibers, having a z-
value
between 0,3 and 0,8 when paper is rewetted, for example by printing, rise and
creates a rough surface even though the paper is calandered and has good
surface properties before the rewetting.
In the document refining at different consistencies is discussed. The
definition of
low, medium and high consistency at refining can be seen in the table below.
Table 2
Refining LC low) MC (medium) HC (high)
Consistency < 5 % 5-14 % >14
b wei ht
Further down in example 2 the Rm-value is mentioned, the definition of this is
the ratio between mass flow in the inlet to the apex flow (reject flow).
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Description of the drawingrs
Figure 1 Discloses the difFerent types of fibers which are fractionated out
and
treated in a process according to the invention.
Figure 2 Discloses the core of a system according to the invention
Figure 3 Discloses an embodiment of the core of a system according to the
invention
Figure 4 Discloses an embodiment of the core of a system according to the
invention
Figure 5 Discloses an embodiment of the core of a system according to the
invention
Figure 6 Discloses an embodiment of the core of a system according to the
invention
Figure 7 Discloses an embodiment of a complete process according to the
invention
Figure 8 Discloses the experimental disposition according to example 1
Figure 9 Discloses the experimental disposition according to example 2
Figure 10 Discloses results from example 2
Figure 11 Discloses results from example 2
Figure 12 Discloses results from example 2
Figure 13 Discloses results from example 2
Figure 14 Discloses results from example 2
Figure 15 Discloses results from example 2
Figure 16 Discloses an embodiment of the invention according to claim 28
Description of embodiments
According to an embodiment of the core of the invention, considered to be the
best mode for carrying out the invention, disclosed in figure 2 pulp follows
the
stream 13 to a hydrocyclone stage 7 with fractionating hydrocyclones, where
the incoming stream are divided up into two streams 10 and 14. The stream 10
comprises fibers with a z-value between 0 and 0,3 (EEW) and fines material.
The stream 14 comprises fibers with a z-value larger than 0,3 (LEW, ELW,
LLW). This stream continues to a hydrocyclone stage 2 with fractionating
hydrocyclones that divides the stream 14 into two streams 3 and 33. The
stream 3 comprises fibers with a z-value between 0,3 and 0,8 (LEW, ELW).
The stream 3 continues to dewatering 4 and to treatment in a refiner 5 with LC
or alternatively MC-refining. In the stream 11 that leaves the refining 5
there are
fibrillated, splitted and collapsed fibers. The stream 33 comprises fibers
with a
z-value larger than 0,8 (LLW) and impurities of heavier kind, the stream 33
continues to cleaning in a cyclone cascade 8 optimized for cleaning away sand,
bark and other heavy impurities. The impurities leave the process and the
stream 12 continues to other treatment. The streams 10, and 11 continues to
suitable treatment such as dewatering, complex binding of metals, bleaching
etc. By refining the base fraction 3 from hydrocyclone stage 2 it is possible
to
process the fibers that gives the largest problem with the surface properties
in
the final paper product and by concentrating on the stream it is possible to
save
energy compared with refining of the complete incoming fiber stream 13.
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Furthermore the streams 10, 11 and 12 can be treated separately in a suitable
way so that an optimized final product can be obtained.
According to a second embodiment which can be seen in figure 3 the incoming
pulp 13 is divided into the streams 10, 11, 11 a and 12. In this case the
stream
comprises fibers with a z-value which is less than 0,3 (EEW) and fines
material. The stream 11 comprises fibers with a z-value between 0,3-0,6 (LEW)
that have been treated in a refiner (MC or LC consistency) and the stream 11 a
comprises fibers with a z-value between 0,6-0,8 (ELW) and which have been
treated in a refiner (MC or LC consistency). And the stream 12 comprises
fibers
with a z-value larger than 0,8 (LLW). In this case it's possible to adapt the
refining conditions in 5 and 5a even more precisely and one can for example
adapt consistency and refining energy so that the use of the energy is even
more optimized.
According to one embodiment for a complete process shown in figure 7,
preheated chips are washed and defibered in two refiner stages (each stage
can comprise several refiners in parallel and fewer or more than two stages).
The pulp is diluted with water to a consistency of 3-4 % and is led to latency
chest, where the fibers are allowed to rest to make them resume their shape
after the refining process. The pulp is then pumped through screens at a
consistency of 1-3%, these being of slot or hole type, this is done to remove
shives and larger impurities. The reject stream from the screens are fed to
the
reject refining system, for example via a transfer device (not shown) to
stream
12, or directly to a device (23, 24,15, 25, 26) in the reject refining system.
If
there are chemicals or other substances such as complex binders, that needs to
be washed out, the pulp is washed in a washer 22 and the pulp 13 that has
finished defibering continues to a process 1 according to the invention.
In a hydrocyclone stage 7 a stream 10 is separated out comprising fibers with
a
z-value less than 0,3 (EEW) according to figure 1, with help from
hydrocyclones
of conventional type, for example Noss AM 80F, or other hydrocyclones of
suitable type. It's possible to imagine some other type of equipment
separating
on specific surface. Fibers with a z-value less than 0,3 together with fines
material are comprised in the pulp stream 10. In this arrangement a two stage
cascade is shown (6 second stage in cascade) and recirculation, but here one
can imagine several variants. Fibers with a z-value less than 0,3 and fines
leaves in the base of the hydrocyclones 6,7. In the pulp stream 14 fibers are
comprised with a z-value larger than 0,3 (LEW, ELW, LLW). In the next
sequence the stream continues into a new hydrocyclone stage 2. The base
fraction 3 from this comprises fibers with a z-value between 0,3 and 0,8 (LEW,
WLW). These fiber types are the ones which particularly causes fiber
springback in the finished product, which in turn creates problems with for
example roughness. The stream 3 continues to treatment, preferably LC-
refining (1-5%), alternative ways of treatment can be ball-mill, other
refining MC
(5%-14%) or mills of different kind, the treatment is done to induce (create)
cracks in the fiber wall, fibrillate the fiber and collapse the fiber
permanently,
without affecting fiber length to much. The apex fraction from the
hydrocyclone
stage 2 continues to a hydrocyclone cascade 8 to clean it from heavy
impurities
such as sand, bark and other heavy impurities, these leaves in the apex of the
hydrocyclones and leaves the process. The stream 12 from the base of these
io
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hyrdocyclones comprises fibers with a z-value larger than 0,8 (LLW) with very
thick fiber wall. These fibers' wall can not be broken easily by LC-refining
5, so
they continues to have the fiber wall pealed off, preferably by HC-refining or
other pealing treatment and in that way the fiber wall is made thinner, then
these treated fibers are returned to the process to once again continue
through
a system 1 according to the invention. The stream 10 continues to a bleaching
stage 17 where one bleaches with a bleaching agent that tolerates fines
material and small particles, preferably a bleaching agent that is used at non
alkaline conditions (pH below 9), such as dithionite, for example sodium
dithionite, zinc dithionite, or similar. The stream 11 that comprises fibers
with a
z-value between 0,3-0,8 (LEW, ELW) continues after adding of complex
binders to washing 27 and bleaching 16 preferably with hydrogen peroxide,
ozone or other suitable oxidative bleaching agent. By bleaching different
fractions with different bleaching agents it is possible to save bleaching
chemicals and you don't need to wash as much. The oxidative bleaching agents
are sensitive to for example heavy metals (e.g. Mn, Cr, Fe) that comes with
the
fines material, but in a process according to the invention the mayor part of
the
fines material are comprised in the stream 10 and never continues in large
amounts into the bleaching stage where the oxidative bleaching agents are
used. After a further washing 28 and 29 the fibers continues to dewatering in
a
disc filter 30. After that these fibers are returned and mixed with the fibers
in the
stream 10. By letting the disc filter 30 dewater this fraction 11 to a higher
consistency than necessary, the fraction 10 can be more diluted and in doing
so
an easier dewatering of the pulp seen as a whole is obtained. The fraction 10
is
difFicult to dewater due to larger contents of fines material. One could also
imagine to mix a part of the fraction 11 in the fraction 10 and in doing that
obtaining a pulp that is easier to dewater if one wants to dewater 10 itself.
The
pulp continues for treatment and the paper machine to manufacture value
added paper grades such as SC, LWC, SC-A++ and variants of these.
The system according to the invention can on detail level be arranged in
several
ways. The core of the invention is the fractionating arrangement that
preferably
constitutes of hydrocyclones, but can be made from other equipment that can
fractionate on specific surface. In figure 2, 3, 4, 5 and 6 one can see
different
variants of arrangements. Figure 2 discloses a magnification of a system where
one can see that it's possible to have a cascade in both the first
hydrocyclone
stage and/or in the second. The dashed line shows that one can have a
cascade if that is desired. Figure 4-6 develops part what is comprised in
figure
2, for clarity. Figure 4 discloses a single stage in both first 7 and second
stage
2. Figure 5 discloses how one has a system with a single stage in first stage
7
and a cascade in the second stage 2. Figure 6 discloses how one has
hydrocyclone cascades in both first stage 7 and in second stage 2.
In another embodiment the refiner 5 is removed and the process with
hydrocyclone stages (7,2 (2a),8) remains the same, instead of treating the
fibers after second hydrocyclonstage with a refiner, the easy dewatering of
the
base fraction leaving this stage is the goal. A more efficient use of the
discfilter
(4,4a) is obtained, see figure 16. As mentioned above the dotted lines means
that cascades are optional.
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Example 1
Softwood TMP was sampled from a factory which produces paper of news-print
quality. The sample was taken at the second stage refiner. After that the pulp
was latency treated at 90 °C for 3 hours and was then processed in the
new
system. Mass flow and different fiber fractions can be seen in table 3 and
figure
8.
Table 3
Flow m1 m2 m3 m4 m5 m6 m7
Total mass flow100 22 78 30 48 34 14
%.
Mass flow, - - 100 39 61 43 18
fractionation
8100 mass flow - - 100 27 75 52 23
fractionation
(%
P100 mass flow 100 12 90 53 35 24 8
The reject rate of 22 % in the two stage slotted screen, with slot width of
0,15
mm, was chosen for the purpose to reduce Sommerville chives to below 0,1
in pulp that continued to fractionation. The pulp with low contents of
Sommerville shives was fractionated in two-stages by hydrocyclones (Noss AM
80F) comprising a first stage consisting of a two-stage cascade and second
stage (single stage hydrocyclones). This arrangement allowed producing three
pulp fractions with different pulp quality due to the fiber morphology (i.e:
fiber
cross-sectional dimensions, specific surface).
Base 1 (m4) - accept from first stage cascade enriched in fibers with a z-
value
less than 0,3 (EEW) and fines material.
Base 2 (m8) accept from second fractionation stage enriched in fibers with a z-
value between 0,3 and 0,8 (LEW and ELW).
Apex 3 (m7) reject from second fractionation stage comprising fibers with a z-
value larger than 0,8 (LLW) thick-walled fibers.
Base 2 (m8) was further refined in the LC-refiner (12" Andritz) at three
different
energy levels 215, 417, 504 kWh/t. The total energies for the different pulps
correspond to 73, 142, and 171 kWh/t for the pulp seen as a whole. The
obtained unrefined and refined pulps were tested separately. Also, pulp blends
were made from Base 1 and Base 2 according to the pulp mass flow split in the
system - 47:53% (b11, b12, bl3). Handsheets from different pulp fractions and
blends were made and tested. Dynamic de-watering tests, as well as surface
roughening tests were conducted on some pulp samples.
Base 1 (m4) and Base 2(m8) and their blends, were bleached using dithionite
and alkaline peroxide (lye and hydrogen peroxide) in different sequences.
Table 4
Flow m1 m2 m3 m4 m7 m8 m9a m9b m9c ~ b11 ~ bl2 ~ bl3
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WO 2006/033605 PCT/SE2005/000859
Freeness155 523 95 18 595 325 171 87 64 35. 25 86
Tensile 32,6 24,0 32,7 37,7 14,525,6 38,1 45,2 48,8 43,8 43,4 34,7
Index
kNm/k
Density 401 307 416 539 299 366 455 515 550 541 568 451
k /m3
Tear 7,6 9,0 6,8 5,4 4,2 6,8 6,3 5,3 4,8 5,1 4,8 6,8
Index
Nm~/k
Tensile 8,9 8,9 8,9 22,8 - 9,6 13,0 16,6 21,5 16,5 23,5 11,8
Index
P 16/R50
kNm/k
Surface 85 235 50 20 245 135 75 50 38 35 32 50
Roug-
ness,
ml/min
Specific51 40 59 79 39 45 45 45 47 62 61 62
Scat-
tering
Coefficie
nt m2/k
Opacity 94,5 89,0 96,1 98,8 93,193,8 94,1 94,6 95,0 97,4 97,1 97,3
ISO
SP 8,4 -- -- 545 - 1,9 5,1 24,1 52,2 45,9 - 34,9
Filtration
Resis-
tance
x 109
m/k
Stage - - - - - 215 417 504 - - -
Energy
kW h/t
Tot - - - - - - - - - 73 142 171
Energy
kW h/t
Table 5
m4+m8 =bl1
m4+m9b=bl2
m4 + m9c = bl 3
Physical pulp properties of different pulp fractions and their blends are
shown in
table 4 and table 5. As seen, the LC refining of the Base 2 fraction improves
the
pulp strength and sheet smoothness at a low total cost of refining energy.
Consequently, blends produced from blends between Base 1 (m4) and refined
Base 2 (m9 b-c) have better quality compared to blends made from blends
between Base 1 (m4) and unrefined Base 2(m8). This is accompanied by a
relatively moderate increase in the pulp's de-watering resistance. Compared to
what can be expected with HC-refining of this fraction to the same freeness.
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As measured by the relative change in sheet caliper and surface roughness, the
moisture induced fiber roughening change was 50 % lower in the sheets
produced from 8100 Bauer-McNett, obtained from blend 2, compared to that of
the sheets produced from fibers obtained from blend 1.
Also, the LC-refining improved the bonding ablility of the Base 2 long fibers
to
similar level as Base 1, as measured by tensile strength of the P16/R50 Bauer
McNett fraction. This resulted in relatively high long fiber bonding ability
of the
blend 2 and 3.
Bleaching of pulp according to Example 7
Before bleaching all pulps was treated in a Q-DTPA complex binding stage.
Base 2 was bleached with hydrogen peroxide and blended with unbleached
Base 1 and the blend was then bleached with dithionite.
The unbleached blend of Base 1 and Base 2 (blend 1 ) was bleached with
hydrogen peroxide in one stage.
Example 2
Latency treated second refiner stage pulp from a factory producing TMP of
news-print quality, was screened at a predetermined reject rate to remove
shives and was fractionated in a two stage cascade hydrocyclone system. The
reject rate was chosen so that 25% of the fibrous material, (25 % of the 8100
Bauer-McNett fiber fraction of the feed pulp), ended up in the base fraction,
Base 1 (s6).
The Apex 1 fraction (s4) was further fractionated in the hydrocyclone system
resulting in the Base 2 (s7) fraction containing 25 % of the fibrous material
(in
per cent of the initial hydrocyclone feed) and Apex 2 (s5). Similarly, Apex 2
(s5)
was fractionated, which resulted in Base 3 (s8) containing 25% of the fiber
material and Apex 3 (s9) containing at least 25 % of the fiber material
according
to the above.
The obtained fractions Bas 1, 2 and 3 were used for further experiments. Base
2 and 3 were refined at 300 kWh/t in a LC-refiner and the pulps where
processed in a similar way as the unrefined samples.
Base 2, 3 where split into two parts from which one part continued to LC-
refining at 300 kWhlt and one part which was not refined. The unrefined part
which comprised Base 1 and the unrefined part was decrilled (i.e. the P100
fines fraction was removed using a Bauer-McNett fractionator). The fiber
fraction was mixed with 40 % fines (by weight) obtained from the second stage
refiner at the TMP pulp factory. Two sets of handsheets at 60 g/m2 surface
weight were made. The first set of hand sheets where tested according to
SCAN standards.
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WO 2006/033605 PCT/SE2005/000859
The second set of hand sheets was cut into strips, calendered and used for
roughening experiments. After calendering, the strips were randomly split into
two groups. The first group was tested on tensile strength, density, porosity,
surface roughness and scattering. The second group of calendered strips was
subjected to 100 % humidity at 25 °C for 3 hours and after that was
subjected to
the same tests as the first group.
In Figure 9 on can se a representation of the set according to example 2. In
Table 5 the corresponding flow relationships can be studied. P 100 is added
fines fraction and how it's distributed. R 100 is the fiber fraction. It's
interesting
to note that Base 1 (s6) contains approximately 60 % of the P 100 fines
material
in the supplied pulp stream (s1 ).
Table 6
Flow s1 s2 s3 s4 s5 s6 s7 s8 s9 r2 r4 r5 r9
8100 72% 81 67% - - 48% 74% 86% 87% - - - -
%
P100 28% 19% 33% - - 52% 26% 14% 13% - - - -
R100 - - - - - 25% 23% 25% 27% - - - -
total
Rm - - - - - - - - - 0,28 0,61 0,66 0,51
~ ~ ~ ~
In Figure 10 there is disclosed how tensile index varies in the different
fractions.
The bonding ability descends significantly for the different hydrocyclone
stages
and in the last apex fraction Apex 3 (s9) the bonding ability of the fibers
are very
limited.
In Figure 11 freeness related to tensile strength can be seen. As seen, Base 1
(s6) has similar strength as the base fraction Base 2 (s7), but they have
different freeness. This can be explained by the significant difference in
fines
materials content between Base 1 (s6) and Base 2 (s7), see table 5.
LC refining of the base fraction Base 2 (s7) and the base fraction Base 3 (s8)
increases the strength of these. LC refining reduces freeness of the pulp to
some extent, but the amount of fines material that are produced do not
correspond to the slope of the regression of the freeness-fines material
relationship. The LC-refining has treated the fibers without a corresponding
fines material production.
Surface roughness in Base 3 (s8) long fiber fraction (P16/R50 ml/min) was
significantly reduced after LC-refining, while the bonding ability was
increased
to the same level as the long fiber fraction from Base 2 (s7) see Figure 12.
Long
fiber fraction of Base 2 (s7) increased the bonding ability to the same level
as
Base 1 (s6) after LC-refining without significantly changing roughness.
Similar trends of surface roughness and strength improvement has been
observed by producing hand sheets from a blend of Base 2 and Bas 3 whole
pulp (Figure 14). Sheets produced from Base 1 (s6) refined Base 2 (s7) and
refined Base 3 (s8) which can be seen in Figure 12, 13 and 14 as Mix s6 + raf
s7 + raf s8, mixed according to the total reject rate, see table 5, exhibited
a
is
CA 02559828 2006-09-13
WO 2006/033605 PCT/SE2005/000859
roughness value similar to the Base 1 (s6). The freeness of the blend was 55
ml
CSF.
Base 2 and Base 3 fractions exhibited higher tendency to get increased surface
roughness compared with Base 1, reflected in larger relative change of the
sheet caliper and surface roughness after re-wetting (Figure 14-15).
The propensity of the fibers to get increased surface roughness was
significantly reduced after LC refining (Figure 14 and 15). After re-wetting,
the
caliper and the surface roughness changed of the calendered sheets produced
from unrefined Base 2 8100 fiber fraction and TMP fines material with 7,5% and
75 % respectively. In contrast to this caliper and surface roughness of
calandered sheets made of refined Base 2 and TMP fines material changed
with 1,6 and 4,4 % respectively. The unrefined Base 3 gave 10 respectively 55
and for corresponding refined Base 3 the change was 1 respectively 11
(Figure 15). The relative change of the wetted sheets properties have been
calculated based on the caliper and roughness of the non-wetted sheets
containing unrefined base fraction.
From the above it shall be understood that cyclone stages according to the
invention are' modified according the fiber at hand to be treated. It should
for
example be understood that the person skilled in the art can put so called
broken or open cascades at all or places of choice in the system 1. Especially
it
should be noted that what's given in Figures only are variants of what the
thought of the invention is representing and the number of cyclones that are
used and their physical data are a question of adaptation of the construction
of
the system to the fibers it is constructed to treat. The same goes for the
concentration conditions that are at hand in the refiners according to the
invention and pressure drop over hydrocyclone stages.
Even if this document could be seen as presuming that fiber of the same kind
of
wood, the invention according to the claims shall not be interpreted as so.
Mixed fibers from different wood spices can also be treated according to a
system according to the invention, and a split up is performed according to
specific surface of the fiber respectively.
16
