EP2516733A1

EP2516733A1 - Method and screening device for screening a fiber suspension

Info

Publication number: EP2516733A1
Application number: EP10798760A
Authority: EP
Inventors: Junichi Hashimoto
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2009-12-25
Filing date: 2010-12-16
Publication date: 2012-10-31
Also published as: JP2013515868A; WO2011076660A1; CN102782213A; KR20120099137A

Abstract

The invention relates to method for screening a fiber suspension (S) using a screening device, in particular a pressurized screen. Said device has at least one screen basket (1) inserted in a housing and enclosing a screen chamber (5). A part of the fiber suspension (S) fed into the screen chamber (5) passes through the screen openings and enters an accepted material chamber (3) as accepted material (A), while a different part of the fiber suspension (S) is deflected at the screen openings as rejected material. In a particularly effective embodiment, a part of the rejected material is thereby fed back into the screen chamber (5) as reject return flow (R'') and once again enters the region of the screen openings. As a further improvement, measures are proposed for homogenizing the flow rate, in particular with respect to the circumference.

Description

Method and screening device for sieving a pulp suspension

The invention relates to a method for screening a pulp suspension

with the help of a sieve device with at least one in a housing

provided, a screen chamber surrounding a screen basket is provided, the one

Variety of screen openings, through which a part of the screen room

led pulp suspension happens and passes as accepts in an accepts space is discharged from the screening device, while another part of the

Fibrous suspension rejected at the screen openings and at least partially discharged as a reject from the screening device.

The invention also relates to a screening device, in particular for carrying out the method with at least one inserted in a housing, a

Sieve room surrounding sieve basket, which with a variety of sieve openings

Is provided, pass through a part of the fed through an inlet into a feed space and then in the screen space pulp suspension and can reach into a radially outer Gutstoffraum, which is hydraulically connected to at least one Gutstoffauslass, while for the part of

Pulp suspension, which is rejected at the screen openings, at least one Rejektauslass is present, with at least one Siebräumer is in the screen space, which has a driven rotor body with clearing elements.

Processes of this type are used in the treatment of paper fiber suspensions to treat the pulp suspension in a wet sieving. A suitable screening device is called in the paper and pulp industry mostly "pressure sorter". It contains at least one screen basket, which is provided with a plurality of openings. The fibers contained in the suspension

should pass through the openings while the unwanted solid Components rejected and be led out of the sorter again. Preferably, a centrifugal procedure is used in which the suspension passes radially from the inside to the outside of the screen openings. When

Sorting holes are usually round holes or slots. Pressure graders of the type considered here are equipped with sieve scrapers, which are close to the

Sieve basket have past movable rake elements. As a result, clogging of the screen openings is prevented in a manner known per se. The Siebräumer is designed as a rotor, which is usually mounted concentrically to the screen basket.

The release effect of a pressure sorter is due to the fact that at least a portion of the impurities contained in the paper pulp suspension fed can not pass through the screen, so it is separated due to the size, shape or flexibility of the paper fibers. There are also pressure sorters are known in which additionally aimed at the density of the impurities separation is made by the different forces used in a centrifugal field of the impurities are used. Although a large part of the heavy parts would not pass through the screen openings usually used, so be rejected there, but there is a risk of damage or wear when they come into contact with the sieve.

Known methods of this type are relatively complex, especially because of the expensive screening devices that have to process a large amount of suspension and because of the energy demand. The latter is not the actual one

Fiber treatment but is due essentially to hydraulic losses in the device.

The invention is based on the object to reduce the cost of construction and operation of the screening device and / or to improve the efficiency of the process. In this case, a better efficiency can mean a higher acreage purity and / or a lower fiber loss due to residual fibers in the reject. This object is achieved by the features of independent claims 1, 6 or 7, wherein the dependent claims describe advantageous embodiments of the method. Claims 10 to 20 relate to advantageous screening devices for carrying out the method.

With the aid of the invention, a further optimization of the wet sieving process is possible. In particular, it is possible to divide the pulp suspension with a sieve more effective into usable fibers and non-interfering substances.

In specific embodiments, the physical conditions within the screening device are further uniformed. It is considered that unequal physical conditions, in particular

1.) unequal composition of matter (consistency, dirt load), at different points of the screen surface, viewed axially

2.) unequal flow velocities, viewed over the circumference,

3.) unequal composition of matter (consistency, dirt load), viewed over the circumference,

lead to a loss of efficiency and / or an unnecessary increase in energy demand.

Ad 1): The pulp suspension fed into the sieve device is constantly depleted of water and fibers along its way along the sieve, which means that consistency and dirt load increase. The result is a relatively high flow rate at the beginning of the wet sieving process with higher

Flow velocities in the screen openings, which are then significantly lower in the course. Different flow velocities in the screen openings but usually lead to a different

Separation characteristic ("separation limit") and thus to efficiency losses of

Overall process. The recirculation of a part of the reject takes place, specifically in the sieve area, where dirt load and consistency in front of the

Screen openings are still relatively small. Re 2.) For practical reasons, in the case of sieving devices, the inlet and outlet of the suspension must be through pipelines, which, whether radially or tangentially mounted, cause an asymmetrical flow in the sieve device, viewed over the circumference. This had previously been taken for granted, or the height of the device was increased to the terminals of the

Laying pipes differently (lower or higher). The invention, however, for the first time provides a solution to this problem by providing hydraulic means for uniform distribution over the circumference. This can be achieved by first passing the suspension through the inlet nozzle in an annular space and then through a constriction, in particular a throttle gap extending over the circumference (about 360 °) in which the flow is accelerated and thus advantageously is designed that in it the

Flow velocity is similar to the Siebdurchtrittsgeschwindigkeit. This is approximately achieved when the narrowest flow cross-section of the constriction is about as large as the entire open screen surface of the screen basket. In the annular space upstream of the constriction, therefore, a more even pressure distribution over the circumference can be established, regardless of where the inlet connection piece is positioned. The same principle can also be advantageous for the expiration of the accept from the

Sieve area are applied where the problem of imbalance by the

Gutstoffauslaufstutzen occurs. Particularly advantageous is the combination of both constrictions, ie both in the inlet and in the process.

So it can be a symmetric uniform distribution of and / or

flowing suspension can be achieved in which the suspension is not in

Circumference has to be guided around the screen basket, which is for the

optimal utilization of the screen surface and the screen characteristic is important.

That is, with relatively little effort, the size of the screen surface, which affects not only the screen costs but also the size of the screen device, can be reduced without loss of efficiency. This means savings in the cost of the screening device and energy consumption. If, however, an increase in Effective separation efficiency, this can be achieved with the same size of the screen surface. to 3.) If, as described in point 2.) described, to distribute the currents evenly over the circumference, then the composition of the

Suspension on the way along the sieve along the same, as under point 1.)

same increase in pollution and consistency is the same.

The invention and its advantages will be explained with reference to drawings. Showing:

Fig. 1 shown schematically in side view, a sorting device for carrying out the method according to the invention;

FIG. 2 shows a variant of the sorting device shown in FIG. 1; FIG.

Fig. 3 shows an advantageous dissolution zone for reject processing within the

Sorter;

4 shows a further possibility for the design of the dissolution zone;

Fig. 5 shows a special Rejektraum, shown cut in plan view;

6 shows another sorting device with axial conveyor for the reject return; FIG. 7 shows a special embodiment with a bottom reject outlet; FIG.

8 shows a special embodiment without reject circulation.

A typical embodiment of the method according to the invention with a corresponding sieve device is shown in FIG. 1. The sieve device contains in a housing a cylindrical strainer basket 1 which surrounds a sieve compartment 5.

The center line is vertical in position of use. One speaks then also of a vertical sorter. The method can also be carried out with non-perpendicular screening devices, for. B: in a horizontal sorter. The pulp suspension S to be screened is introduced laterally into the housing through an inlet 8, ie it flows in an asymmetrical manner. She first enters the annular inlet chamber 4, from which they radially inwardly through the throttle gap 6 in the Screening chamber 5 is pumped. The advantageous effect of this constriction (throttle gap 6) has already been described. The accepts coming from the screen room 5 the

Screen openings of the screen basket 1 has passed, enters the accepts space 3 and is guided out of this through a throttle gap 9 in an accepts collection chamber 7, to which the accepts outlet 10 is laterally connected, resulting in a

unbalanced outflow from the accepts 7. The position of Gutstoffauslasses 10 can be arbitrarily selected on the circumference, which z. B. facilitates the vote on the specific installation situation.

With heavy contamination of the pulp suspension S, is a

Heavy separation before reaching the screen basket 1 advantage. The larger heavy parts accumulate in the lower and radially outer part of the inlet chamber 4 and are derived here via the Schwerteilauslass 13 in the heavy section lock 14. This is favored when the inlet 8 is connected tangentially to the inlet space 4.

Further measures for improving the flow conditions, in particular for equalizing the flow velocities in the screening device are realized here. So it is favorable, if the cross-section of the between

Rotorköper 1 1 and strainer basket 1 lying cavity of the screening chamber 5 in the axial direction between inlet and outlet of the suspension reduced, while the accepts space 3 is larger in the same direction. As a result, the flow of the suspension from the screen space 5 into the accepts space 3 can be carried along the way along the strainer basket 1. This can be achieved by a conical shape of the corresponding walls in the same direction: they can e.g. be parallel to each other as shown here. Such a designed screening device can be smaller overall and thus cheaper and have lower hydraulic losses, so get along with less energy for the same technological result.

The rejected on the strainer basket 1 part of the suspension, in particular the contaminants, is collected in the above the screen basket 1 Rejektraum 15, in the a rotational flow is formed. They are partly removed via Rejektauslass 16 as reject R ^' from the housing 2 and partly recirculated as a reject return R ^" through the hollow interior of the open-topped rotor body 1 1 in the screen room 5. The overhead position of the Rejektraumes 15 facilitates the withdrawal of Air and light parts (eg Styrofoam) together with the reject R ^' In favorable cases, a venting line in the lid of the housing can be saved.The reject R ^' derived from the housing is, if necessary, resorted to avoid fiber losses ,

In the screen room 5 clearing elements 12 which are fixed to a rotor body 1 1, moved close to the inner surface of the screen basket 1. By

Relative to the surrounding liquid they produce pressure and suction surges, with which the screen openings are kept free. The rotor body 1 1 is driven for rotation. In addition to the shape shown here with rotor body 1 1 and freely flow around clearing elements 12, other rotors, for. B. with directly mounted on the rotor body clearing elements are used.

A mixture of contaminants and residual fibers is fed back to the screening process through the reject return R ^" , thereby giving the residual fibers a further possibility, as intended, to reach the accept, which is advantageously achieved by the position of the distribution openings 18, 19 in the rotor body 1 1 chosen so that the reject-return R ^" enters the sieve area, which treats the freshly added fiber suspension S. A decisive advantage of this type of internal reject return R ^" lies in the fact that a stream which is uniformly distributed over the entire circumference is formed and can then be guided in a targeted manner into a less loaded part of the screen basket 1.

The screen chamber 5 has at its uppermost part a central port 17 through which z. For example, dilution water W may be mixed into the reject return R ^" The dilution water flow may enhance the axial transport of the reject return R ^" , especially if the central port 17 is tight on the rotor body 1 1 or within the rotor body 1 1 opens. Another

Ability to add dilution water W provides a laterally in the

Substantially cylindrically shaped Rejektraum 15 attached, preferably tangentially attached nozzle 22, as shown in Fig. 2. This

Dilution water W is then targeted to the rejected reject R ^'

admixed, which offers the advantage that clogging by thickening

is prevented at the Rejektauslass 16.

Alternatively, the center port 17, if necessary, also be used to remove air and light parts that the screen basket 1 over

have flowed without having passed through the screen openings. Conveniently, the central socket 17 is then carried out flush with the lid of the device.

The recovery of residual fibers from reject reject R ^" can be significantly improved if the reject is further disintegrated or defibrated prior to re-screening, ie when fiber agglomerates and specks are comminuted, resulting in more fibers passing through the screen apertures Dissolution step is indicated in Fig. 2. For this purpose, at a point between the screen chamber 5 (here at the upper end of the screen basket 1) and the Rejektraum 15, a dissolving zone 20 is established, in which due to the relative movement between the rotor body 1 1 and housing breakup A favorable embodiment of the dissolving zone 20 is shown in somewhat greater detail in Fig. 3. A stator ring 25 connected to the housing and one connected to the rotor body 11 are shown Rotor ring 24, the distributed over the circumference for dissolution depressions, in particular s stage-like pockets 25 and 26 have. These have z. B. a depth T between 1 and 20 mm. Rotor ring 24 and stator ring 25 face each other at a distance, so that a gap forms between them, through which pass the substances rejected on the screen basket 1, wherein fiber agglomerates and specks are at least partially dissolved. With advantage are Rotor ring 24 and stator 25 detachable, for example, fastened with screws to easily replace them. This may be necessary because of wear, or serve to set a different resolution intensity. Such

Rejection is usually a compromise between desired

Fiber recovery and unwanted pulp shredding. Favorable is a processing by shear forces, in which no fiber damage occurs. The

Thinning intensity can also be affected by the number and geometry of the pockets. 4 shows another example of a dissolution zone. Rotor ring 24 ^' and

Stator ring 25 ^' are arranged here so that they intermesh and thereby transmit more pulses to the specks. They can be provided with pockets, grooves or a closed rough surface.

For the dissolution of fiber agglomerates and specks z. As well as rotor and stator ring may be provided with teeth which are moved past each other at a distance.

For Fig. 3 is still to be noted that the screen openings 28 in the strainer 1 are shown as examples only as round holes, it can, for. B. slots with a width between 0.1 and 0.4 mm, preferably between 0.15 and 0.25 mm or round holes with a diameter between 1 to 2 mm. This choice depends heavily on the raw material.

As shown in Fig. 2, the method also offers the possibility of feeding rejects R ^''' coming from other separation processes to the screening process. Such rejects R ^''' may originate from other screening devices (reject discharge or venting) or hydrocyclones. So z. B. the reject of another, preferably downstream Drucksortierers flow through a direct line into the central socket 17. It is possible, the reservoir for these rejects R ^'"

save. They can also be introduced through a laterally mounted nozzle 22 in the substantially cylindrical or annular Rejektraum 15. They are then detected by the rotational flow and the reject return R ^" admixed.

The Rejektraum 15 is slightly higher in Fig. 2 than in Figure 1 and has a central Verdängerkörper 21 on. As a result, the rotational flow can be better maintained in this room, in particular dead spaces and unnecessary vortex are avoided.

The inlet space 4 ^' can be placed below the screen space 5 as shown in FIG. 2. In this example, the bearing housing 23 of the rotor body 1 1 is in the center of the inlet chamber 4 ^' , which avoids dead spaces and unnecessary vortex and also saves space. The throttle gap 6 ^' can then be a flat annular gap.

In Fig. 5 is a plan view of a sorting device according to the invention in section through the Rejektraum 15 is shown schematically and not completely. Advantageously, the rotational flow in the reject space 15 is braked by a barrier 29 and directed into the reject outlet 16. This too can reduce energy consumption. When the rotor body 1 1 in this Fig. 5, the cut is placed so that the stator ring 25 and the pockets 26 (only a few drawn) of the dissolving zone 20 are visible.

In order to guide the reject return R ^" better, an axial conveyor can be used, which is illustrated in an example in Fig. 6. A helical coil 30 is centrally located in the rotor body 11 Axialkraft generated

Schraubwendel 30, as shown here, co-rotate or fixed, z. B. attached to the lid. It is also advantageous to attach the axial conveyor with screws to replace it when z. B. another conveying effect is desired. The rotor change is easier.

The applications previously described in Figures 1 to 6 with a

Flow direction from bottom to top are in many cases optimal, but not mandatory. 7 shows a screening device in which the flow in the region of the screen basket 1 is guided from top to bottom. The reject R ^' leaves the housing through a downstream reject outlet 16, while the reject reflux R ^" rises upward through the rotor body 11 after being processed in the dissolving zone 20. It can then enter the sieve compartment 5 again Arrangement, the strainer 1 is easily accessible from above, which is an advantage when replacing.

FIG. 8 shows an example in which the principle of achieving equalization of the flow over the circumference by means of one or two constrictions is shown in FIG

Pressure sorter is applied without reject recirculation. Thus, known pressure sorters are substantially improved with this measure for the reasons already mentioned. The feed flow to the screen chamber 5 passes from the feed chamber 4 via a planar throttle gap 6 ^' in the screen chamber 5. The accept is guided from the accepts space 3 through the throttle gap 9 in the accepts collection space 7. The rejected on screen basket 1 shares come into the Rejektraum 15 and leave the device through the Rejektauslass 16. The combination of two constrictions is advantageous, but may also be sufficient. In this example, the pulp suspension S to be screened is fed up and the reject R is removed at the bottom. However, the flow guidance can also be reversed, that is, as in FIGS. 1 to 6.

Claims

claims:

1 . Process for sieving a pulp suspension (S) by means of a

Sieve device which is provided with at least one screen basket (1) surrounding a screen space (5) and having a plurality of screen openings through which a part of the pulp suspension (S) guided into the screen space (5) passes and as Acceptance material (A) is discharged into an accepts space (3) from the screening device,

while another part of the pulp suspension (S) is rejected at the screen openings and at least partially discharged as reject (R, R ^' ) from the screening device,

characterized,

that a part of the reject is returned as Rejektrrücklauf (R ^" ) in the screen space (5).

2. The method according to claim 1,

characterized,

that in the screen space (5) is at least one sieve clearer having a driven rotor body (1 1) with clearing elements (12), and that a part of the reject (R, R ^' , R ^" ) within the rotor body (1 1) and by means of a mechanical conveyor, in particular a connected to the rotor body (1 1) axial conveyor is returned to the screen space (5).

3. The method according to claim 1 or 2,

characterized,

in that the rejected reject (R, R ^' , R ^" ) on the strainer basket (1) is at least partially further dissolved in the screening device. Method according to claim 1, 2 or 3,

characterized,

dilution water is added to at least part of the reject (R, R ^' , R ^" ).

Method according to claim 1, 2, 3 or 4,

characterized,

in that at least part of the reject (R ^' , R ^" ), in particular the part recirculated into the screen space (5), further reject (R ^'" ) is added from another separation process.

Process for sieving a pulp suspension (S) by means of a

while another part of the pulp suspension (S) is rejected at the screen openings and at least partially discharged as a reject (R, R ^' ) from the screening device, in particular according to one of the preceding claims, characterized

the pulp suspension (S) is distributed evenly over the circumference to the screen space (5).

Process for sieving a pulp suspension (S) by means of a

while another part of the pulp suspension (S) at the screen openings rejected and at least partially discharged as a reject (R, R ^' ) from the screening device, in particular according to one of the preceding claims, characterized

that the accepts (A) evenly distributed over the circumference from the

Gutstoffraum (3) is discharged.

8. The method according to claim 6 or 7,

characterized,

that the flow for uniform distribution by at least one circumferentially extending constriction, in particular at least one

Throttle gap (6, 6 ^' , 9) is guided, and that the flow velocity in the constriction is adjusted so that it the middle

Flow rate in the screen openings of the screen basket (1) corresponds to a tolerance of plus 50% to minus 50%.

9. Method according to one of the preceding claims,

characterized,

that a stationary pressure sorter is used, in which the

Fibrous suspension (S) from below and the reject (R, R ^' ) is discharged above.

10. Screening device in particular for carrying out the method according to one of the preceding claims with at least one in a housing

inserted, a screen space (5) surrounding strainer basket (1) which is provided with a plurality of screen openings,

through which a part of the pulp suspension (S) passed through an inlet (8) into an inflow space (4, 4 ^' ) and then into the sieve space (5) can pass and pass into an acouste space (3) located radially further outwards at least one accepts outlet (10) is hydraulically connected,

while at least one reject outlet (16) is present for the part of the pulp suspension (S) which is rejected at the screen openings, wherein in the screen space (5) is at least one sieve clearer, which has a driven rotor body (1 1) with clearing elements (12),

characterized,

in that the screening device has at least one hydraulic connection, by means of which part of the reject (R) rejected at the strainer basket (1) can be returned to the inlet space (4, 4 ^' ).

1 1. A screening device according to claim 10,

characterized,

the inflow space (4, 4 ^' ) is connected to a heavy-part outlet (13).

12. Screening device according to claim 10 or 1 1,

characterized,

in that the reject outlet (16) is arranged above the screen basket (1).

13. Screening device according to one of claims 10 to 12,

characterized,

that the accepts outlet (16) is arranged above the inlet (8).

14. Screening device according to one of claims 10 to 13,

characterized,

that between the screen space (5) and the Rejektraum (15) has a

Dissolution zone (20) with at least one rotor ring (24, 24 ^' ) and at least one stator ring (25, 25 ^' ) is located, between which the reject (R, R ^' , R ^" ) edited, in particular further resolved.

15. Screening device according to claim 14,

characterized,

the rotor ring (24, 24 ^' ) and stator ring (25, 25 ^' ) are provided with pockets (26, 27).

16. Screening device according to claim 14 or 15,

characterized,

in that the rotor ring (24, 24 ^' ) and stator ring (25, 25 ^' ) are detachably fastened, in particular with screws.

17. Screening device according to one of claims 10 to 16,

characterized,

that in the rotor body (1 1) an axial conveyor, in particular a

Helix (30) is located.

18. Screening device according to one of claims 10 to 17,

characterized,

in that the cross-section of the part of the screen space (5) lying between the rotor body (11) and strainer basket (1) decreases in the axial direction, while the accepts space (3) becomes larger in the same direction.

19. A screening device according to claim 18,

characterized,

that the change of the cross sections in the screen space (5) and in the accepts space (3) is generated by conical shapes of the corresponding walls in the same direction.

20. Screening device according to one of claims 10 to 19,

characterized,

that between the inlet space (4, 4 ^' ) and the screen space (5) and / or the accepts space (3) and a directly downstream of this

Acceptance space (7) each having at least one constriction, in particular at least one extending over the circumference throttle gap (6, 6 ^' , 9) whose narrowest flow cross-section is about as large as the entire open screen surface of the screen basket (1) and preferably between 50 and 200%, in particular between 50 and 150% of the open screen surface of the screen basket (1).