Title:
Process and Device to Manufacture Cellulose Pulp
Kind Code:
A1


Abstract:
Process and device to manufacture and dewater cellulose pulps in which defibered cellulose is screened to remove shives, fractionated in to at least three fractions (10, 3, 12), which fractions are treated each by itself and then are brought together completely or partly, and that the fractionation is done according to specific surface, preferably with hydrocyclones, 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 that have 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 with a refiner, ball mill or similar.



Inventors:
Wikdahl, Lennart Nils Anders (Djursholm, SE)
Bergstrom, Bernt-olof (Norrkoping, SE)
Shagaev, Oleg (Norrkoping, SE)
Nevander, Tore Rolf (Norrkoping, SE)
Application Number:
11/632572
Publication Date:
02/07/2008
Filing Date:
06/06/2005
Assignee:
Noss AB (Norrkoping, SE)
Primary Class:
Other Classes:
162/55, 162/234, 162/48
International Classes:
D21B1/12; D21D1/00; D21D1/20; D21D5/24; D21B
View Patent Images:



Primary Examiner:
CALANDRA, ANTHONY J
Attorney, Agent or Firm:
LEYDIG VOIT & MAYER, LTD (CHICAGO, IL, US)
Claims:
1. A process for manufacturing cellulose pulps, the process comprising: screening defibered cellulose to remove shives; fractionating the defibered cellulose, according to specific surface, with a device comprising hydrocylones, the step of fractionating comprising; fractionating out fibers with high specific surfaces; fractionating out fibers having lower specific surface, and fractionating the defibered cellulose into at least three fractions; treating the at least three fractions individually; bringing the at least three fractions together completely or partly, and using a device that comprises a comminution device, to split, fibrillate and permanently collapse at least one of the at least three fractions.

2. The process according to claim 1, wherein the fractions treated in the comminution device comprise fibers with a z-value between 0.3 and 0.8.

3. The process according to claim 1, wherein the comminution device permanently collapses the fibers of the fractions treated therein by inducing cracks in a fiber wall of the fibers.

4. The process according to claim 1, wherein the comminution device is configured to refine at a pulp consistency in the interval 0.8%-14%.

5. The process according to claim 1, wherein the comminution device comprises a refiner configured to run at an energy input of 10-800 kWh/t.

6. The process according to claim 1, wherein the fraction that comprises the fibers with high specific surface leaves from a base of a hydrocyclone stage.

7. The process according to claim 1, wherein the fraction with lower specific surface leaves from a base of a hydrocyclone stage.

8. The process according to claim 1, wherein the fraction enriched in a fines material and comprising the fibers with high specific surface is bleached by a bleaching agent in a non alkaline environment.

9. The process according to claim 8, wherein the pH at the bleaching is less than 9.

10. The process according to claim 8, wherein the bleaching agent is a reducing bleaching agent.

11. The process according to claim 8, wherein the bleaching agent comprises dithionite.

12. The process according to claim 1, wherein the fraction with fibers with lower specific surface is bleached with an oxidative bleaching agent.

13. The process according to claim 12, wherein the bleaching agent comprises hydrogen peroxide.

14. The process according to claim 12, wherein the bleaching agent comprises ozone.

15. The process according to claim 1, wherein a device for treatment comprising a comminution device is provided for peeling off fiber walls of fibers in the fraction that remains after previous process stages and which has the lowest specific surface.

16. The process according to claim 15, wherein the device for treatment comprises refining at greater than 14% consistency.

17. The process according to claim 1, wherein the fraction with fibers with lower specific surface, after treatment is mixed with the fraction with fibers with high specific surface to improve the dewatering properties.

18. The process according to claim 1, wherein the fraction with fibers with lower specific surface, is dewatered alone to a higher consistency than the finally wanted consistency of a mix of the fractions, so that the fraction with the fibers with high specific surface only needs to be dewatered partly or not at all.

19. The process according to claim 1, wherein the fractions comprising the fibers with high and lower specific surface, after treatment, are brought together to a pulp stream with a 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.

20. A device for improving properties of cellulose pulps, the improved properties concerning properties such as, light scattering, tensile index, tear index, surface roughness, bleaching chemicals consumption, energy consumption, the device comprising: a first hydrocyclone device for receiving the cellulose pull and dividing therefrom a first base fraction and a first apex fraction; a second hydrocyclone device for receiving the first apex fraction from the first hydrocyclone and dividing therefrom a second base fraction and a second apex fraction, and a refiner for receiving and treating the second base fraction at a consistency between 1-14%.

21. The device according to claim 20, wherein the device is configured to bleach the first base fraction with a non alkaline reducing bleaching agent.

22. The device according to claim 20, wherein the device is configured to bleach the second base fraction with an oxidizing bleaching agent.

23. The device according to claim 20, further comprising: a third hydrocylcone device for dividing the second apex fraction into a third base fraction and a third apex fraction; and a second refiner for treating the third base fraction after dewatering at a consistency between 1-14%.

24. The device according to claim 23, wherein the device is configured to bleach the third base fraction with an oxidizing bleaching agent.

25. The device according to claim 20, wherein the device is configured to bring together the first base fraction and the second base fraction to a common pulp stream with improved properties.

26. The device according to claim 20, wherein the device continues cleaning the third apex fraction with a fourth hydrocyclone that removes heavy impurities.

27. The device according to claim 26, wherein the device is configured to refine a fourth base fraction from the fourth hydrocyclone at a consistency greater than 5%.

28. A process for producing and dewatering cellulose pulps, the process comprising: screening defibered cellulose to remove shives; fractionating the defibered cellulose into at least three fractions, according to specific surface, with a device comprising hydrocylones, the step of fractionating comprises: fractionating out fibers with high specific surface, and fractionating out fibers having lower specific surface; dewatering the fraction having lower specific surface to a given consistency, and mixing the fraction having lower specific surface with at least one of the other fractions.

Description:

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 U.S. Pat. No. 6,361,650 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 U.S. Pat. No. 4,731,160 known to use hydrocyclones to separate out two fractions that are bleached with hydrogen peroxide (claim 1 and claim 2).

It is from U.S. Pat. No. 5,133,832 known to bleach a long fiber fraction with hydrogen peroxide (H2O2) and a short fiber fraction with dithionite (Na2S2O4).

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.

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 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.

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 fraction/s 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 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, 11a) 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.

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 fraction/s 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 11a) are brought together to a common pulp stream (32) with improved properties.

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 hydrocylones, 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 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 FIG. 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. z=4π AwP2

AW=Fiber wall cross-section area

P=Fiber circumference

TABLE 1
Fiber typeEEWLEWELWLLW
z-value0 < z ≦ 0.30.3 < z ≦ 0.60.6 < z ≦ 0.80.8 < 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
RefiningLC (low)MC (medium)HC (high)
Consistency<5%5-14%>14%
(% by weight)

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).

DESCRIPTION OF THE DRAWINGS

FIG. 1 Discloses the different types of fibers which are fractionated out and treated in a process according to the invention.

FIG. 2 Discloses the core of a system according to the invention

FIG. 3 Discloses an embodiment of the core of a system according to the invention

FIG. 4 Discloses an embodiment of the core of a system according to the invention

FIG. 5 Discloses an embodiment of the core of a system according to the invention

FIG. 6 Discloses an embodiment of the core of a system according to the invention

FIG. 7 Discloses an embodiment of a complete process according to the invention

FIG. 8 Discloses the experimental disposition according to example 1

FIG. 9 Discloses the experimental disposition according to example 2

FIG. 10 Discloses results from example 2

FIG. 11 Discloses results from example 2

FIG. 12 Discloses results from example 2

FIG. 13 Discloses results from example 2

FIG. 14 Discloses results from example 2

FIG. 15 Discloses results from example 2

FIG. 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 FIG. 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.

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 FIG. 3 the incoming pulp 13 is divided into the streams 10, 11, 11a and 12. In this case the stream 10 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 FIG. 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 FIG. 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 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 FIGS. 2, 3, 4, 5 and 6 one can see different variants of arrangements. FIG. 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. FIGS. 4-6 develops part what is comprised in FIG. 2, for clarity. FIG. 4 discloses a single stage in both first 7 and second stage 2. FIG. 5 discloses how one has a system with a single stage in first stage 7 and a cascade in the second stage 2. FIG. 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 FIG. 16. As mentioned above the dotted lines means that cascades are optional.

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 FIG. 8.

TABLE 3
Flowm1m2m3m4m5m6m7
Total mass flow100227830483414
(%)
Mass flow,10039614318
fractionation (%)
R100 mass flow10027755223
fractionation (%)
P100 mass flow10012905335248
(%)

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 shives 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% (bl1, bl2, 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
Flowm1m2m3m4m7m8m9am9bm9cbl1bl2bl3
Freeness15552395185953251718764352586
Tensile32.624.032.737.714.525.638.145.248.843.843.434.7
Index
kNm/kg
Density401307416539299366455515550541568451
kg/m3
Tear7.69.06.85.44.26.86.35.34.85.14.86.8
Index
Nm2/kg
Tensile8.98.98.922.89.613.016.621.516.523.511.8
Index
P16/R50
kNm/kg
Surface852355020245135755038353250
Rougness,
ml/min
Specific514059793945454547626162
Scattering
Coefficient
m2/kg
Opacity94.589.096.198.893.193.894.194.695.097.497.197.3
% ISO
SP Filtration8.45451.95.124.152.245.934.9
Resistance ×109
m/kg
Stage215417504
Energy
kWh/t
Tot73142171
Energy
kWh/t

TABLE 5
m4 + m8 = bl 1
m4 + m9b = bl 2
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.

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 R100 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 1

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 R100 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 percent 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 kWh/t 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.

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 FIG. 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
Flows1s2s3s4s5s6s7s8s9r2r4r5r9
R10072%81%67%48%74%86%87%
P10028%19%33%52%26%14%13%
R10025%23%25%27%
total
Rm0.280.610.660.51

In FIG. 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 FIG. 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 FIG. 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 (FIG. 14). Sheets produced from Base 1 (s6) refined Base 2 (s7) and refined Base 3 (s8) which can be seen in FIGS. 12, 13 and 14 as Mix s6+raf s7+raf s8, mixed according to the total reject rate, see table 5, exhibited a 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 (FIGS. 14-15).

The propensity of the fibers to get increased surface roughness was significantly reduced after LC refining (FIGS. 14 and 15). After re-wetting, the caliper and the surface roughness changed of the calendered sheets produced from unrefined Base 2 R100 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% (FIG. 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.