EP1096063B1 - Method and device for fractionating a paper fibre suspension - Google Patents

Abstract

To divide a suspension (S) of paper fibers into fractions, especially a suspension of used paper fibers, a sieve (1) separates it into two fractions, such as according to fiber length. A parallel flow (4) is generated by a sweeper (5) with a rough surface, so that the suspension (S) is dragged through by the sweeper (5) with virtually no slip. In a contact zone of up to 1 mm from the sweeper (5), the suspension is moved at a speed of at least 90% of the sweeper (5) speed. The sweeper (5) is moved along the line of the sieve (1), with a gap (A) between the sweeper (5) and the flow side of the sieve (1) of max. 20 mm. The sweeper (5) movement speed is at least 10 m/sec. in relation to the sieve or 20 m/sec. The sweeper (5) exerts little or no pressure or suction pulses towards the surface of the sieve (1). The surface (8) of the sweeper (5) carries a number of longitudinal recesses and pref. grooves (7), or it has a felt covering over the surface (8) which has high absorbency. The openings (6) in the sieve (1) are longitudinal, to separate a fiber fraction, set at an angle of 70-110 degrees to the direction of sweeper (5) movement. Spaced eddies are formed through projections or recesses at the sieve (1), working with the parallel flow (4). An Independent claim is included for an appts. to separate a paper fiber suspension into fractions, where the sweeper (5) has a roughened surface (8). Preferred Features: The grooves (7) at the surface (8) of the sweeper (5) have a height of max. 3 mm, at intervals of max. 3 mm. The projections or recesses at the sieve (1) have a max. height/depth of 2 mm. The sieve (1) is a cylinder, with an inner rotor as the sweeper (5), concentric to each other.

Description

The invention relates to a method according to the preamble of claim 1 and a fractionation device according to the preamble of claim 8.

It is known that aqueous paper fiber suspensions by wet sieving can be fractionated. Different procedural goals can be pursued firstly, the so-called sorting, i.e. the removal of unwanted components from the paper fiber suspension or secondly the Fiber fractionation, i.e. division of the paper fibers themselves into several fractions. Possible during the sorting process for many contaminants with a very good separation effect is, there are considerable stickies with the soft, sticky contaminants Separation problems. In fiber fractionation, certain Properties of paper fibers, e.g. Length, thickness or flexibility as Separation characteristic used. Such a process enables extraction of fiber materials with special properties from fiber mixtures such as Waste paper. But native raw materials can also be fractionated according to their fiber properties become. As a rule, a concentration of the Long fibers in the overflow of the sieve and a concentration of the short fibers in the Pass of the sieve reached. So far there have been processes for fiber fractionation Selectivity and / or throughput are inadequate in many cases.

The devices used for sorting on the one hand and for fiber fractionation on the other hand, are very similar in structure. As is known, almost always a screen clearer moves close to the screen to clear the blockage to prevent the sieve and thereby enable a large sieve throughput.

A sorting device, i.e. Separate unwanted components a fiber suspension is described in EP-A-0 299 258. Throughput To be able to increase, it is proposed that the surface of the screen clearer with webs provided due to their size and shape, e.g. inclined side surfaces, suction and Generate pressure pulses. These are intended in particular in cooperation with grooved Seven improve their freedom.

Another document, DE-A-198 36 318, also shows a pressure sorter with a rotor, the effect of which on the relative speed to the surrounding Suspension is based. It contains a large number of depressions in the form e.g. of Ball sections. The device shown in US 3,411,721 combines the Function of grinding with that of sieving. The rotor comes with a variety of Provide surveys that are intended to impart shock impulses to the pulp, e.g. to shred contained fragments.

The invention is based on the object of creating a method with which it succeeds in achieving a greater separation effect when fractionating - even from problematic ones Components such as Long fibers and stickies - to achieve.

This object is achieved by the features mentioned in the characterizing part of claim 1 solved.

Favorable fractionation devices are described in claims 8 to 11.

While in the known methods the reamer is used by changing Pressure and suction impulses or by creating turbulence the sieve of To keep blockages free, the inventive method leads to a Drag flow at the scraper, which is essentially parallel to the screen surface Moves circumferentially. The fibers in the suspension are therefore evenly oriented and the separation based on their length and / or their Flexibility is possible with a better effect. This is especially true for across Sorting columns aligned in parallel flow. Keeping the sieve openings clear is due to the surface structure of the sieve in cooperation with the Drag flow caused micro vortices and / or small-scale turbulence reached. Even when sorting out sensitive, easy-to-shred Contaminants such as stickies, the gentle sieve clearance according to the invention is cheaper. To generate the drag flow, the scraper can be roughened, e.g. with a Be provided with a plurality of grooves. Even a felt placed on the surface can Develop a drag effect.

In many cases, the advantages of the invention are best with such rooms achievable, the surface of which faces the sieve is predominantly continuous, which is not e.g. have a number of foils, wings, or bumps. In other cases it may be useful to find a compromise between the Separation effect and throughput. For technical / physical reasons namely that are often accepted that when generating a pure Parallel flow throughput through the screen is reduced compared to one Prior art methods with high turbulence. It must then be weighed up between the parallel flow which is as rectified as possible or a limited one Generation of vortices. Weak vortices can be created by e.g. a sieve and / or a reamer with profile grooves or strips is used.

In the forms of the method described so far, a fixed Sieve and a moving scraper. The kinematic reversal, too moving sieve and fixed or counter-moving scraper are easily conceivable to carry out the inventive method.

Fig. 1

schematisch dargestellt: Vorgänge des erfindungsgemäßen Verfahrens am Siebeinlauf;

Fig. 2

Oberfläche eines erfindungsgemäßen Räumers;

Fig. 3

Beispiel mit einem variierten Sieb;

Fig. 4

Teil eines geeigneten Siebes in Aufsicht;

Fig. 5

Vorrichtung zur Durchführung des Verfahrens, Ansicht von oben;

Fig. 6 + 7

verschiedene als Räumer verwendbare Rotoren;

Fig. 8

Detail eines speziellen Räumers.

The invention and its advantages are explained with reference to drawings.

Fig. 1

shown schematically: processes of the inventive method at the sieve inlet;

Fig. 2

Surface of a scraper according to the invention;

Fig. 3

Example with a varied sieve;

Fig. 4

Part of a suitable sieve under supervision;

Fig. 5

Device for carrying out the method, top view;

Fig. 6 + 7

various rotors that can be used as scrapers;

Fig. 8

Detail of a special scraper.

In Fig. 1, the relationships are shown that occur when performing the method in the area of sieve 1, scraper 5 and the paper fiber-containing moving in between Play suspension S. As is known per se, the suspension S is passed through the sieve 1 fractionated by a fraction flowing through the sieve openings 6, while a other part is rejected and ultimately in a designated place the equipment used for the process is removed. The scraper 5 is in Distance A from and relative to sieve 1 in the direction shown by arrow Movement direction 3 moves. Since the surface 8 of the reamer 5 is rough, e.g. like here shown, provided with a number of grooves 7, the suspension is almost dragged along without slip, so that a parallel flow 4 arises. This Parallel flow 4 is not strictly parallel to that facing the suspension Surface of the sieve. It will e.g. near the inlet to the screen openings 6 in Redirected towards sieve 1. However, their direction is crucial Difference to the very restless eddy currents that are usually used for Sieve clearing are generated. In particular, the new type of flow is stationary, i.e. constant in time, while usual clearers to an unsteady flow with time fluctuating pressure pulse and turbulence intensity. The one on the right speed profile shown with curve 10 makes the towing effect of Clearer designed according to the invention clearly. The suspension has about in the vicinity same speed VR as the scraper 5 itself. Then falls towards the sieve curve 10, with a clear parallel component also on screen 1 preserved. This creates a flow in the long fibers, but also Impurities are oriented approximately parallel to the screen surface, so that they have a strong tendency have to be rejected at the sorting opening.

2 shows a detail view of a section through the surface of a reamer 5. In particular, the grooves 7 provided to form the rough surface are dimensioned. Their width B at the widest point is advantageously less than 3 mm and theirs Height H at a maximum of 2 mm. Depending on the application, other dimensions can also be useful his. To achieve a good effect with this scraper, as many as possible to accommodate such grooves, i.e. they have a small distance C at surface 8 from each other. They can be straight parallel, but it is also a diamond or Conceivable wave pattern.

The sieve 1 'used according to FIG. 3 has a profile structure on its inlet side: The tops of the sieve bars 12 are opposite to the direction of movement 3 Angle a slightly inclined so that it is spatially narrow at the inlet into the sieve openings can form limited micro-vortices. Due to the inclination, protrusions form the sieve columns with the height E. It is also possible to use groove-like depressions with a appropriate depth in the sieve.

FIG. 4 shows part of a further sieve with which the method can be carried out. The intended direction of movement 3, with which a reamer (not shown) which interacts with this sieve 1, is also shown. The sieve is provided with a plurality of sieve openings 6, which are designed as narrow slots with a slot width D between 0.1 and 0.4 mm, preferably 0.15 to 0.25 mm. Their longitudinal extent has an angle of attack β of 100 ° with respect to the direction of movement 3 in the case shown. In general, however, it is 90 °.

Fig. 5 shows schematically a fractionation device in a view from above. It contains a housing 13 with a partially drawn cover 14. The sieve 1 is cylindrical Sieve basket, and the reamer 5 is designed as a cylindrical rotor. The rough one Surface 8 is indicated as a thick circular line. The suspension flows through the Inlet 15 between screen 1 and rotor. The sieve pass is through the Fine fraction outlet 16 and the sieve overflow through the coarse fraction outlet 17 dissipated. In special cases, more than these two fractions can be formed e.g. several fine fractions with the help of differently designed Screen openings. Sieve and rotor are arranged concentrically to each other, but they are other embodiments are also conceivable.

Fig. 6 shows a geometric representation of a circular cylindrical rotor trained reamer 5 with substantially axially parallel grooves 7. Such a shape, inserted concentrically in a circular cylindrical sieve, has a very gentle Effect, i.e. generates no significant pressure / suction impulses.

If, e.g. in order to increase the throughput at the sieve, at least weak with the scraper According to FIG. 7, pressure / suction pulses are to be generated with Profile strips 18 are provided. These can also generate the Support parallel flow, e.g. with the help of a steep leading edge.

In order not to impair the desired effect of the invention, the Profile strips 18 have only a small height F (Fig. 8). Your number can too be small, e.g. two to five spread over the circumference.

Claims (11)

1. Method for fractionating a paper fibre-containing suspension, in which the suspension (S) is divided by a wire (1, 1') into at least two fibre fractions, a clearer (5), which is movable relative to the latter, being used to keep the wire clear,
   characterised in that
   a parallel flow (4) is produced by means of a rough surface (8) of the clearer (5) on the inflow side (2) of the wire (1, 1'),
   a clearer (5) being used which is provided on its surface (8) with a multiplicity of oblong recesses, preferably grooves (7), or with a felt-like, readily wettable layer, and
   the suspension (S) being entrained by the clearer (5) virtually without slippage, said suspension being moved in the contact region extending up to one millimetre from the surface of the clearer (5) at at least 90% of the clearer speed.
2. Method according to claim 1,
   characterised in that
   the clearer (5) is moved along at a spacing (A) of at most 20 mm on the inflow side (2) of the wire (1, 1').
3. Method according to claim 1 or 2,
   characterised in that
   the clearer (5) is moved at a speed of at least 10 m/s relative to the wire (1, 1').
4. Method according to claim 3,
   characterised in that
   the clearer (5) is moved at a speed of at least 20 m/s relative to the wire (1, 1').
5. Method according to one of the preceding claims,
   characterised in that
   the clearer (5) produces no pressure or suction pulses towards the wire (1, 1').
6. Method according to one of the preceding claims,
   characterised in that
   fractionation takes place with a wire (1, 1'), the wire openings (6) of which are oblong, with a longitudinal extension which is at an angle of incidence (β) between 70° and 110° relative to the direction of movement (3) of the clearer (5).
7. Method according to one of the preceding claims,
   characterised in that
   fractionation takes place with a wire (1, 1') on which, by means of projections or recesses, spatially limited turbulences are produced in cooperation with the parallel flow (4).
8. Device for implementation of the method according to one of the preceding claims, having a housing (13), in which at least one wire (1, 1') is located, on which a clearer (5) can be moved along on the inflow side in order to prevent blockage of the wire openings (6) of the wire (1, 1'),
   characterised in that
   the clearer (5) has a closed, rough surface (8) which is formed by a layer of felt.
9. Device according to claim 8,
   characterised in that
   the wire (1') is provided with projections or recesses of at most 2 mm height or respectively depth.
10. Device according to claim 8 or 9,
    characterised in that
    the wire (1, 1') is a cylindrical wire in which a cylindrical rotor is disposed rotatably as clearer (5).
11. Device according to claim 10,
    characterised in that
    the wire basket and rotor are concentric.

Images