EP2898143A1

EP2898143A1 - Fractionation

Info

Publication number: EP2898143A1
Application number: EP13752884.0A
Authority: EP
Inventors: Wolfgang Mannes
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2012-09-21
Filing date: 2013-08-15
Publication date: 2015-07-29
Also published as: DE102012216950A1; CN104755672A; WO2014044475A1; CN104755672B

Abstract

The invention relates to a method for the fractionation of a fibre suspension (1) produced from used paper or from broke of a machine for the production of multi-layer fibre webs, wherein a long fibre fraction (11) with predominantly long fibres and a short fibre fraction (12) with predominantly short fibres are formed. The recycling efficiency is improved as a result of the Kappa number of the long fibre fraction (11) being lower than that of the fibre suspension (1).

Description

fractionation

The invention relates to a process for the fractionation of a pulp suspension produced from waste paper or scrap of a machine for the production of multilayer or multilayer fibrous webs, wherein a long fiber fraction with predominantly long fibers and a short fiber fraction with predominantly short fibers is formed. The recycling of waste paper is practiced for a long time. It is also common not only to clean the pulp suspension but also to fractionate. Fractionation is usually done mostly through sorters.

Fractionation allows the higher-grade long-fiber fraction to be used as needed.

However, the quality of the long fiber fraction limits, which restricts their reuse as a replacement of fresh fibers.

This is especially true in the reuse of printed waste paper, which must be freed from the inks prior to reuse in a known deinking process. The purified fibers are referred to as DIP and reused alone or together with pulp in the formation of fibrous webs.

In particular, in the production of high-quality papers, the use of DIP is often not possible because of the small average length-weighted fiber length of less than 1, 3 mm.

This also applies to multilayer or multi-layer fibrous webs in which individual layers or layers have a higher demand on the pulp quality.

The formation of a multilayer fibrous web via a multi-layer casserole, as described, for example, in DE-OS 40 29 545. Of the Headbox has this several nozzle chambers that are fed independently with different suspensions. Between the nozzle chambers slats are attached, which prevent premature mixing of the suspensions. Likewise, paper machines for forming multilayer fibrous webs by means of several independent headboxes are known. The individual layers are merged and vergautscht. This is described, for example, in DE 40 31 038. In both cases, it is a question of reducing the costs by using needs-based different pulp qualities. Most of the poorer qualities, ie the short fibers in the middle of the fibrous web or to form the back are used.

The reprocessing committee so far includes the dissolution and the exclusive reuse in a layer or layer with low demands on the pulp quality.

The object of the invention is therefore to allow the discharge of high-quality pulp to improve the efficiency of reuse.

According to the invention, this object is achieved in that the kappa number of the long fiber fraction is less than that of the pulp suspension to be fractionated. Since the fractionation is now not only based on the fiber length but also the kappa number of the long fiber fraction is taken into account, there is a significant increase in the quality of the long fiber fraction.

The reduced kappa number means over known fractionation processes that more flexible fibers with improved bondability are accumulated in the long fiber fraction. As a result, so can the strength of the fibrous web or layer or layer produced from this long fiber fraction be significantly improved, so that can be dispensed with the use of virgin fibers.

This also means that the kappa number of the long fiber fraction is below that of the short fiber fraction.

In order to enable the reduction of the kappa number from the starting suspension, it may be advantageous not to aim at the maximum possible length difference between the fractions. It is usually sufficient if the mean length-weighted fiber length of the long fiber fraction is at least 0.4 mm, preferably at least 0.5 mm larger than that of the short fiber fraction.

Nevertheless, in the interest of a high quality of the long fiber fraction, the aim should be that the mean length-weighted fiber length of the long fiber fraction is at least 1.4 mm and otherwise at least 1.6 mm for a pulp suspension formed at least partially from printed waste paper.

In order for the rotors to be able to develop a most extensive effect as a fractionating element, the pulp suspension should impinge on at least one rotor in the form of a free jet.

To ensure a high selectivity of the fractionation, it is advantageous if a beam of pulp suspension is directed to the rotor blades of a rotor for fractionation, wherein the jet direction with the rotation axis forms an angle of less than 45 ° and longer adhering to the rotor blades fibers due to Centrifugal force are thrown off the rotor blades and collected separately.

In contrast to the usual use of a sieve there is hardly the risk of constipation. In addition, fractionation is very efficient, as mainly only the long, flexible fibers adhere to the rotor blades, collect, slide radially outward on the rotor blades and are thrown off from there.

To make this around the rotation axis as uniform as possible, the beam direction of the pulp suspension jet should be approximately parallel to the axis of rotation of the rotor.

It is advantageous if the jet of pulp suspension is accelerated before striking the rotor blades. This acceleration causes alignment of the fibers in the flow direction, which assists in capturing the long fibers by the rotor blades.

Furthermore, it has proved to be advantageous if the speed of the pulp suspension jet when hitting the rotor blades is between 3 and 20 m / s and / or the peripheral speed of the rotor blades is between 10 and 70, preferably between 20 and 40 m / s. In this way it is ensured that if possible only the long, flexible fibers adhere to the rotor blades, whereby the proportion of removed long fibers can be increased by increasing the peripheral speed.

So that the radial sliding out and centrifuging of the long fibers is not impaired, the pulp suspension jet should extend at least predominantly, preferably exclusively only over a radially inner region of the rotor blades.

A comprehensive use of the rotor blades can be achieved, in particular, if the pulp suspension jet has an annular cross-section enclosing the axis of rotation of the rotor. It is advantageous if the annular pulp suspension jet has a ring thickness between 1 and 5 mm. If the pulp suspension is formed from scrap of a machine, in particular a machine for producing multilayer or multilayer fibrous webs, then this pulp suspension should be led to fractionation at a pulp density between 1, 0 and 5.0%. This high consistency leads due to the lower thickening to a much higher efficiency.

Furthermore, in order to justify the fractionation effort, the long fiber fraction should comprise at least 10% of the fiber content of the reject pulp suspension.

The fractionation enables the separation of a better pulp quality in the form of the long fiber fraction, which can then be reused in a layer or layer with higher demands. The use with other paper machines is possible. This also means that both fractions are used to form different layers or layers of the fibrous web.

This optimizes the utility of the committee and justifies the extra effort for fractionation. In contrast, if the pulp suspension formed from waste paper, it should take place in the interest of high quality, the fractionation of the pulp suspension only after all cleaning stages and before the constant part of a machine for producing a paper, cardboard, tissue or other fibrous web.

In addition, the effort for the ejection of high-quality pulp can be significantly reduced if the pulp suspension prepared from waste paper before the actual fractionation an additional, known fractionation for pre-fractionation goes through, which long fiber fraction with increased length Fibers and a short fiber fraction with increasingly short fibers forms, with only the long fiber fraction is continued to fractionation.

The restriction to the long fiber fraction leads to a substantial reduction of the throughput of the pulp suspension to be treated in the following fractionation according to the invention.

Additionally or alternatively, it is furthermore advantageous if the pulp suspension produced from waste paper flows along the rotor with a pulp density of between 0.5 and 4.0%.

This optimizes the use of the waste paper and justifies the extra effort.

The invention will be explained in more detail below with reference to several exemplary embodiments. In the attached drawing shows:

FIG. 1 shows a schematic cross section through a fractionating device 5 according to the invention;

Figure 2: a plant scheme for the treatment of waste and

Figure 3: a plant scheme for waste paper processing.

As a fractionating device 5 for forming a long fiber fraction 1 1 with predominantly long fibers and a short fiber fraction 12 with predominantly short fibers is particularly suitable because of the high separating sharpness shown in Figure 1 device.

In this case, an annular pulp suspension jet is formed from the pulp suspension 1 via a centrally arranged shaped body 8 and directed onto the rotor blades 2 of a rotor.

In the event of a fault or a standstill, the gap between the nozzle housing 13 bounding the outside of the jet and the shaped body 8 is increased. This is in the example shown simply by a displacement of the nozzle housing thirteenth possible contrary to the flow direction.

This is to prevent clogging of the gap with fibers.

The molded body 8 causes an increase in the flow velocity of the pulp suspension 1 and thereby an increased orientation of the fibers in the flow direction, which supports the detection of long fibers by the rotor blades 2.

The rotor is driven here by a motor 9 arranged below.

The jet direction of the pulp suspension jet coincides with the rotor axis 3 of the rotor, wherein the velocity of the pulp suspension jet when hitting the rotor blades 2 is between 3 and 15 m / s and the peripheral speed of the rotor blades 2 is between 20 and 30 m / s.

If the proportion of long fibers divided off via the rotor blades 2 is to be increased, then the peripheral speed of the rotor blades 2 is to be increased for this purpose.

When cutting through the pulp suspension jet, predominantly longer fibers remain hanging on the rotor blades 2. These can accumulate there and are due to the centrifugal force on the rotor blades 2 to move radially outward and then thrown off.

Thus, the centrifuging is not affected by the pulp suspension jet, the pulp suspension jet is directed only to the radially inner part of the rotor blades 2, wherein the ring thickness is between 1 and 5 mm and the rotor blades 2 have a length between 10 and 20 mm.

In addition, the rotor with the rotor blades 2 sweeps over a circular area with a diameter between 300 and 2000 mm, which also ensures a sufficient capacity for an annular pulp suspension jet in conjunction with the desired flow rate. Since the annular pulp suspension jet is arranged coaxially to the axis of rotation 3, results in an optimal and uniform effect.

To catch the long and flexible, centrifuged by the rotor blades 2 fibers (long fiber fraction 1 1) runs around the rotor in the corresponding spin area a collecting chamber 6. The rest of the pulp suspension 1 passes through the rotor blades 2 and is collected below in a drip pan 7 as a short fiber fraction 12 and dissipated.

To assist in trapping the long fibers when cutting through the pulp suspension jet, the rotor blades 2 have a wing edge having a width with respect to the jet direction between 1 and 5 mm.

To facilitate the sliding of the long fibers radially outward, the vane edge may be radially outwardly inclined in the beam direction of the pulp suspension jet.

With this fractionating device 5 1 1 not only long, but in particular also flexible fibers can be accumulated in the long fiber fraction. Accordingly, the kappa number of the long fiber fraction can be lowered to below the capping number of the pulp suspension 1 and the short fiber fraction 12.

The average length-weighted fiber length of the long fiber fraction 1 1 is at least 0.5 mm larger than that of the short fiber fraction 12.

To ensure a sufficient quality, especially with regard to the strength of the fibrous web, the mean length-weighted fiber length of the long-fiber fraction 11 is at least 1.6 mm.

In the plant scheme for reject treatment shown in FIG. 2, the fibrous web is intended, by way of example, to consist of three separate headboxes 10a, 10b, 10c Layers are produced.

The material flows supplied to the headboxes 10a, 10b, 10c may differ from one another with regard to their composition, in particular with regard to fiber content, fiber type, fiber properties, fine and filler content and consistency.

After the formation of the individual layers in the former these are vergautscht together.

The, in the production of multi-ply fibrous web resulting scrap is usually discharged into an area below the paper machine and there dissolved in a reject pulper 4 again. Subsequently, the pulp suspension 1 formed from the broke can then be conducted at a pulp density between 1, 0 and 5.0% to a fractionating device 5 according to the invention. In the fractionating 5 it comes, as already mentioned, for splitting a long fiber fraction 1 1 with a high proportion of long, flexible fibers and a less valuable short fiber fraction 12 with a high proportion of short fibers. The long fiber fraction 1 1 comprises at least 10% of the fiber content of the broke in order to ensure sufficient economy.

While the short fiber fraction 12 is guided to the headbox 10b for the less demanding middle layer, the long fiber fraction 11 is used to form the blanket layer by means of headbox 10a. In contrast thereto, FIG. 3 shows a system diagram for the treatment of a pulp suspension 1 produced at least partly from printed waste paper. The dissolution of the waste paper takes place in a pulper 14, wherein in addition to water and the replacement of printing inks supporting chemicals are added. Subsequently, the pulp suspension 1 passes through several cleaning and Sorting stages 15, in which impurities are removed. Between these or as here thereafter, the pulp suspension 1 also passes through at least one deinking stage 16 in which the printing inks are removed. The ink removal is usually done by flotation.

A stock preparation plant usually has several successively arranged water circuits, also called loops. In these loops, the pulp suspension 1 passes through at least one cleaning stage 15 in the form of a flotation, a sorter, or the like. In addition, the loops often also have drainage facilities, such as disc filters, screw press o, ä.

After all cleaning stages 15, but still before a constant part of a paper machine, the discharge of long and flexible fibers to form a high quality pulp takes place in the form of long fiber fraction 1 1. In the constant part of paper machines, the highly consistent accepts of the stock preparation formed essentially of processed fibers and fillers are diluted with the white water collected in the paper machine, deaerated and fed to the headbox of the paper machine. In order to minimize the amount of pulp suspension 1 to be treated, the pulp suspension 1 for pre-fractionation is passed through an additional fractionating device 17 of known design. This additional fractionating device 17 forms a short fiber fraction with predominantly short fibers and a long fiber fraction with predominantly long fibers.

Subsequently, however, only the long-fiber fraction is fed as a pulp suspension 1 to be fractionated with a consistency between 0.5 and 4% of a fractionating device 5 according to the invention with rotor.

Claims

Claims 1. Process for the fractionation of a pulp suspension (1) made from waste paper or scrap of a machine for producing multilayer or multi-ply fibrous webs, wherein a long fiber fraction (11) with predominantly long fibers and a short fiber fraction (12) with predominantly short fibers is formed, characterized the kappa number of the long fiber fraction (11) is lower than that of the pulp suspension (1).

2. The method according to claim 1, characterized in that the mean length-weighted fiber length of the long fiber fraction (1 1) at least 0.4 mm, preferably at least 0.5 mm larger than that of the short fiber fraction (12).

3. The method according to claim 1 or 2, characterized in that the mean length-weighted fiber length of the long fiber fraction (1 1) at a, at least partially formed from printed waste paper pulp suspension (1) is at least 1, 4 mm.

4. The method according to any one of the preceding claims, characterized in that the mean length-weighted fiber length of the long fiber fraction (1 1) is at least 1, 6 mm.

5. The method according to any one of the preceding claims, characterized in that the pulp suspension (1) impinges in the form of a free jet on at least one rotor.

6. The method according to claim 5, characterized in that for fractionation a jet of the pulp suspension (1) is directed onto the rotor vanes (2) of a rotor, the jet direction forming an angle of less than 45 ° with the axis of rotation (3) and longer fibers adhering to the rotor vanes (2) due to the centrifugal force of the Rotor blades (2) are thrown off and collected separately.

7. The method according to claim 5 or 6, characterized in that the

Beam direction of the pulp suspension jet approximately parallel to the axis of rotation (3) of the rotor extends.

8. The method according to claim 6 or 7, characterized in that the jet of pulp suspension (1) is accelerated before impinging on the rotor blades (2).

9. The method according to any one of claims 6 to 8, characterized in that the

Speed of the pulp suspension jet when hitting the rotor blades (2) is between 3 and 20 m / s.

10. The method according to any one of claims 6 to 9, characterized in that the peripheral speed of the rotor blades (2) is between 10 and 70, preferably between 20 and 40 m / s.

1 1. Method according to one of claims 6 to 10, characterized in that the peripheral speed of the rotor blades (2) is increased to increase the proportion of removed long fibers.

12. The method according to any one of claims 6 to 1 1, characterized in that the pulp suspension jet extends at least predominantly, preferably exclusively over a radially inner region of the rotor blades (2).

13.Verfahren according to claim 12, characterized in that the

Pulp suspension jet has an annular, the axis of rotation (3) of the rotor enclosing cross-section.

14.A method according to claim 13, characterized in that the annular pulp suspension jet has a ring thickness between 1 and 5 mm.

15. The method according to any one of the preceding claims, characterized in that the pulp suspension (1) prepared from waste is conducted with a fiber density between 1, 0 and 5.0% for fractionation.

16. The method according to any one of the preceding claims, characterized in that the long fiber fraction (1 1) formed in the fractionation of scrap comprises at least 10% of the fiber amount of the Committee.

17. The method according to any one of the preceding claims, characterized in that the fractions formed from scrap are used in different layers or layers of a fibrous web.

18. The method according to any one of claims 1 to 14, characterized in that the fractionation of the pulp suspension produced from waste paper (1) after all cleaning stages (15) and before the constant part of a machine for producing a paper, cardboard, tissue or another fibrous web.

19. The method according to any one of claims 1 to 14 and 18, characterized

in that the pulp suspension (1) is produced from waste paper and passes through an additional fractionating device (17) before the fractionation, which forms a long fiber fraction with increasingly long fibers and a short fiber fraction with increasingly short fibers, with only the long fiber fraction for fractionation according to the invention being continued. Method according to one of Claims 5 to 14 and 18 and 19, characterized in that the pulp suspension (1) produced from waste paper flows along the rotor at a pulp density of between 0.5 and 4.0%.