EP1039021B1 - Method for wet screening fibrous suspensions in pressure screens and pressure screen - Google Patents

Abstract

The sieve, to sort a paper fiber suspension or separate it into fractions in a pressure sorting assembly, has an entry side which is structured so that the flow direction of the stripping eddy is reversed by the backflow. The backflow flushes the part of the sieve between the sieve opening and its adjacent downstream opening. A part of the fiber suspension flows through the sieve openings and the other part flows over them. The relative movements of the sieve cleaner generate pressure or suction bursts at the sieve openings to give flows forwards and backwards. The backflows are deflected on leaving the sieve openings to reverse the flow direction following the surface of the stripping eddy. The backflow wholly flushes the sieve openings between them and the neighboring downstream openings. The sieve openings are sorting slits (3), with their longitudinal extension across the direction (R) of cleaner movement. The axis of the developed stripping eddy is parallel to the sorting slit (3). The flushing of the sieve is at the side of it towards the cleaner. An Independent claim is included for a fiber suspension sorting sieve where the end surfaces (4) between the sorting slits (3) are extended (6) at the trailing ends (8), to cover the leading ends (7) of the neighboring end surfaces (4) by a length (b) of at least 0.5 mm or at least 1.0 mm. The leading end of the end surfaces and the under side of the extensions (6) over them are at an angle ( alpha ) of 3-45 degrees to each other, and pref. 5-25 degrees . The extensions (6) are at the end surfaces (4) at the entry side, where the suspension flows into the sorting slits when the pressure sorter is working. The trailing end is at the side of the end surface (4) which is downstream in relation to the fiber suspension flow (R) in operation. The end surfaces (4) are pitched against the sieve surface (5') at an angle ( beta ) of 5-50 degrees and pref. 10-30 degrees . The under side (9) of the end surface extension (6) is at an angle to the sieve surface (5') of 2-40 degrees and pref. 5-25 degrees . The end surface (4) has no edges which would form an additional build-up when the sieve is in operation. The sorting slits (3) are formed between profiled rods (2) mounted in reinforcements (1). The reinforcements (1) have recesses to hold the rods (2) by tension, as they are distorted on fitting the rods and reassert against them. The reinforcements (1) are rings, to give a cylindrical sieve structure, or the reinforcements (1) and rods (2) are on parallel planes to form a flat sieve. The under sides (9) of the end side extensions (6) have a number of spacer projections distributed over their length, supported by the neighboring end surfaces. The extensions (6) range generally over the whole length of the sorting slits (3). The extensions (6) can be divided a number of times along the sorting slits (3), and they can have an irregular shape along the slits (3). The sieve opening width (w) is 0.08-2.0 mm. The sorting slits (3) have a length which does not exceed 10 mm.

Description

The invention relates to a method according to the preamble of claims 1 and 2 and on a pressure sorter screen according to the preamble of claim 5.

An important application of such methods and devices is the sorting of Pulp suspensions. The fibers contained in the suspension should by Pass the sieve through while the unwanted solid components on the gap rejected and led out of the sieve again. By making the openings have an essentially elongated shape, i.e. are slits or gaps fibrous particles are more easily permeable than the flat ones, even if both types in should be of similar magnitude. With such sorting technology therefore a very good excretion effect from non-fibrous contaminants Fibrous suspensions possible. However, a high level of precision is a prerequisite Slit shape on the entire screen surface. Another important use is separation of different fibers, especially fractionation, e.g. due to the Fiber length or flexibility.

Strainers or strainer baskets are known from published patent application DE 33 27 422 A1, at which the sorting slots by essentially parallel, similar profiles with transverse retaining ribs are connected, are formed. The profiles are like this designed and arranged that the flow to the screen device during operation Surfaces of the profiles have an oblique contour and a tear-off edge behind them. This causes a deflection on the flowing suspension flow, which derives the suspension flow from the sorting slot so that vortices train, which the clearance of the sorting slots and the sieve passage of the fibers favor.

In almost all cases, processes of the type mentioned here are on one side of the screen a scraper moved close to it, which generates pressure and suction blows. Due to the brief pressure and suction surges, the direction of flow reverses Sorting opening around. The clearance of the sorting opening is ensured by the fact that Fiber accumulations or particles that cannot get through, contrary to normal flow direction are conveyed back again. Printing and Suction pulses can also be introduced directly into the suspension, e.g. about Membranes.

The devices mentioned have proven themselves in many applications. But it is however, it is not always possible to reliably keep the sorting slots free at the same time to lead the desired high throughput through the sieve slots.

In US 4,898,665 a screening device is described in which Inlet area to the sieve openings in each case step-like flow barriers ("obstacles") are attached, which accumulate the inflowing suspension. You cover that Screen openings also partially or completely cut off and produce in the flow Turbulence. The vortices thus generated at the end of the flow barrier are said to Direct the flow directly into the sieve openings. The flow barriers can also lead to stagnation points on the screen surface where there are annoying deposits fix.

The invention is based on the object of a method or a screening device to create specified type with which a better sieve clearance succeeds, at at the same time good cleaning effect and high sieve throughput.

This object is achieved in the characterizing part of claim 1, 2 and claim 5 measures mentioned.

The measures described in these claims will be in Inlet area of the flow openings advantageously formed. With help of the deflection generated, the backflow is not from the demolition vortex "captured", but flows against its direction directly at the downstream following face of the sieve over. This area of the sieve is designed so that the rinsing of the said face until the next following downstream Sieve opening takes place. It may also be the case that the direction of flow changes Micro vortices arise in the inlet area, the direction of rotation of which is opposite to that of the Demolition vortex is or that even the direction of rotation of the demolition vortex is reversed. With this measure according to the invention e.g. Fibers that may be attached to the Cling to the surface of the sieve, flow from another side, which detaches them from the Screen surface promotes. Such residues come from the pre-flow phase. The The same also applies to contaminants to be separated, especially if they are to be glued tend (stickies).

Slit-shaped sieve openings are particularly suitable for the process. With these is a possible advantage of the method can be achieved particularly effectively. Because it was found that the long fiber content in the sieve pass (accept) compared to conventional sieves is increased. Thus, a special problem of Slot sorting, namely the long fiber loss, easier to solve. But there are also other shapes, e.g. Round bores with deflection elements, one Can reverse vertebrae, conceivable.

The design, e.g. additional effort required on the profile bars can be found in keep narrow limits. As already mentioned and also known per se, the Possibility to manufacture such devices by using profile bars arranged side by side by fasteners, e.g. Rings are fixed. In the The selection of a different profile is then generally sufficient to carry out the invention. Standard profiles may have to be used, given the large number the sieves to be manufactured can be accepted. The new profiles can usually be used for screens of various sizes without modification.

Is used as a blank for the rods drawn profiles, such as steel or one Steel alloy, so special cross-sectional shapes are economical and precise produced.

Of course, you can also edit the surface afterwards seven produced the profile required for the invention are generated.

Cylindrical sieves of the type considered here are either centrifugal or flows through the centripetal region. The common terms mean centrifugal = radial Flow from the inside out, centripetal = radial from the outside in. Not this also always determines the position of the screen clearers. As is well known, Sieve clearing on the accept side and sieve clearing on the inlet side. The invention is used with advantage when there is a scraper on the inlet side.

Fig. 1

Strömungsverhältnisse am Einlauf des Drucksortierersiebes gemäß dem Stand der Technik;

Fig. 2

Strömungsverhältnisse bei der Durchführung des erfindungsgemäßen Verfahrens;

Fig. 3

Teil eines erfindungsgemäßen Drucksortierersiebes im Schnitt;

Fig. 4

einen zylindrischen Siebkorb;

Fig. 5

Variante, perspektivisch gezeichnet;

Fig. 6

eine weitere Variante im Schnitt;

Fig. 7

eine Variante mit runden Sieböffnungen;

Fig. 8

Details des Einlaufbereiches;

Fig. 9

eine Variation der Strömungsverhältnisse.

The invention is explained with reference to drawings; show:

Fig. 1

Flow conditions at the inlet of the pressure sorter screen according to the prior art;

Fig. 2

Flow conditions when performing the method according to the invention;

Fig. 3

Part of a pressure sorter screen according to the invention in section;

Fig. 4

a cylindrical screen basket;

Fig. 5

Variant, drawn in perspective;

Fig. 6

another variant in section;

Fig. 7

a variant with round sieve openings;

Fig. 8

Details of the entry area;

Fig. 9

a variation of the flow conditions.

1 shows the prior art on the basis of a schematic sketch. The sieve has sorting slots 3 'which are formed between parallel bars 2' become. The flow lines are in two different flow situations represented by freehand arrows. The sorting slot shown on the right is used by the Suspension from the inlet side of the sieve opening to the outlet side in the Flows through slot flow direction S. With this flow direction met the sieve does the real thing, namely part of the suspension, which is fine enough is to be able to pass through the sorting slots 3 ', while in pass A another part is retained as an overflow. This is due to the Direction of flow and the profile shape of the sorting rods, right-handed demolition vortices 16 out. With this form of flow, it cannot be avoided that a stagnation point 13 between the vortex and the further outflow. This is symbolic characterized by a small deposit. The flow through the sieve opening is initially due to the constant overpressure. Become known also generated by the movement of a scraper 12 suction pulses. The ratios the suction pulse can be recognized by the sorting slot shown on the left. The Flow in the sorting slot itself is directed briefly upwards, i.e. against the actual production flow. The suction pulse turns the clockwise Demolition vortex 16 maintained.

The situation is different in the example shown in FIG according to the invention modified rods 2, the z. B. those shown in claim 4 Satisfy conditions. It can be seen that measures have been found and applied with which the right-hand rotating one is located at the sorting slot shown on the left Demolition vortex 16 can bypass. A left-handed vortex 17 can also form. The risk of deposits forming in the inlet area becomes significant reduced, i.e. significantly improves the clearing effect. The backflow can flow directly and unhindered along the end face 4 and also the Flush stagnation point 13 (the pre-flow phase).

In cases where the scraper 12 is on the flow side of the screen (not shown here) leads to a pressure pulse instead of a suction pulse Reversal of the flow direction in the sieve opening. The invention is also here applicable.

3 shows the part as an example of a pressure sorter screen according to the invention of such a sieve a little more detailed on average. This is again here around a bar screen in which the sorting slots 3 are formed between bars 2, which in a reinforcing element 1 are used. The profile of the bars is simplified drawn, e.g. without the usual rounding off. When the device is operating, the accepted part of the suspension as a sieve pass through the sorting 3 in the Slot flow direction S, in the example shown here from top to bottom. The screen surfaces 5 and 5 'are the fictitious connecting surfaces of the rods 2 on the Inlet and outlet side of the sieve. The bars 2 have end faces on the inlet side 4 and end faces 4 'on the outlet side. The end faces 4 of the inlet side are with a front end 7 and a rear end 8 limited. After this Pass the inlet-side end face 4 in the inflow direction R, that is to say on its rear end 8, the suspension forms a vortex with an axis approximately in Longitudinal direction of the sorting slots 3 is. As a result, the clearance effect in Operation of the pressure sorter improved.

According to the end faces 4 are at their rear end 8 Extensions 6 provided. These are designed in such a way that they are not just the only Cover sorting slot 3, but also the front end 7 of the the sorting slot 3 following rod 2. The cover of the end face 4 of the following rod, measured parallel to the end face, the length b. The extension 6 has an underside 9 facing the front end 7 of the adjacent rod on. This underside 9 and the front end 7 of the end face 4 are in an angle α to each other, which is between 3 and 45 °, preferably between Is 8 ° and 25 °. The choice of the angle a also ensures that the flow cross-section, seen in the direction of the upstream, expands. That is, in the In the opposite direction, i.e. the direction of the backflow, the suspension is accelerated, which is favorable for the dissolution and flushing of accumulations.

In cases where the sieve is not built up by rods, but e.g. by slitting of a previously closed sieve blank, the extensions 6 can e.g. by subsequent plastic deformation are formed so that they also the Cover sorting slot 3 and the adjacent area of the screen body.

The slot width w, which is decisive for the sieve characteristic, is formed as on the second and third sorting rod shown, between the bottom 9 of the extension 6 and End face 4 of the adjacent rod. The end faces 4 are in here Flow direction R increases with an angle of inclination β relative to the screen surface 5 inclined, causing the inflowing suspension against the slot flow direction S is distracted. As a result of this inclination, there is 8 at the rear end of an upstream rod, a difference h measured perpendicular to the screen surface 5 to the end face 4 of the adjacent rod. The one formed by this difference h Volume promotes the desired vortex.

As a rule, the extensions 6 run evenly over the entire length of the rods, so that the flow conditions are the same everywhere. But it is also conceivable instead of a continuous extension, a large number of small extensions to attach, e.g. to create advantageous cross vortex. One more way is to make the overhang of the extensions different. Because in operation of the pressure sorter along the rods different solids - in particular Contaminant concentrations occur, offers a change in the shape or size of the Extensions an additional opportunity for optimization.

4 according to the invention can be cylindrical Strainer basket designed by a plurality of annular reinforcing elements 1 is held together. The illustration shows only a part of the existing bars 2 and without the extensions being recognizable.

5, the part of a pressure sorter screen according to the invention is in perspective shown. One can again see one of the reinforcing elements 1, into which the rods 2 'are used. The profile of the rods points in the reinforcing elements 1 used side thickening. This particular shape depends on the manufacture together. The depressions 10 in the reinforcing elements 1 are Insert the bars 2 'so that they can be easily inserted. A subsequent plastic deformation of the reinforcing elements 1 the depressions narrowed and the rods clamped. The finished sieve is then with properly fixed rods.

6 are on the underside 9 of the extensions 6 with Spacers 11 provided. As a result, the gap width must be observed particularly precisely. In Seen longitudinally of the rods 2 ", the spacer lugs can be far apart, e.g. approx. 200 mm. In cases where, for screening technology reasons, relatively short Slots, e.g. 0.5 to 2 mm, if desired, this solution also offers correspondingly many spacers.

Fig. 7 shows an embodiment in which the pressure sorter screen 14 with round Screen openings 15 is provided. The direction of rotation of the vortex is reversed by the extensions 6 '.

In Fig. 8, the geometric conditions on the inflow side of the screen are somewhat presented in more detail. Similar to Fig. 6, the bottom 9 is here again Provide extensions 6 with an inclination angle y with respect to the screen surface 5, So not parallel to it, with the inclination between 2 ° and 40 °. Also the End face 4 itself is inclined with respect to screen surface 5. This angle of inclination β should be between 5 and 50 °. An obliquely directed channel is thus formed an inclined end face 4, which also the desired flushing of the end faces unfavorable conditions guaranteed.

9 shows a particularly strong effect of the measures according to the invention, namely that the right-handed demolition vortex 16 when flowing back into one left-turning vortex 17 is converted.

Claims (20)

1. A method for wet screening pulp suspensions in a pressure grader,

   in which said suspension is guided along a screen provided with screen openings, which causes breakaway eddies (16) to form on the inflow side into the screen,

   in which a portion of the pulp suspension passes through the screen openings as underflow (A) and the other portion is rejected as overflow, and

   in which with the aid of clearers (12) moving relative to the screen pressure or suction pulses are produced at the screen openings such that pre- and backflows are produced therein,

   characterised in that
   the inflow side of the screen is designed such that the direction of flow of the breakaway eddy (16) is reversed by the backflow,
   the backflow rinsing that portion of the screen which is located between the screen opening in question and the following one downstream.
2. A method for wet screening pulp suspensions in a pressure grader,

   in which said suspension is guided along a screen provided with screen openings, which causes breakaway eddies (16) to form on the inflow side into the screen,

   in which a portion of the pulp suspension passes through the screen openings as underflow (A) and the other portion is rejected as overflow, and

   in which with the aid of clearers (12) moving relative to the screen pressure or suction pulses are produced at the screen openings such that pre- and backflows are produced therein,

   characterised in that
   the backflow upon emerging from the screen opening is deflected such that its direction of flow is reversed like the peripheral flow of the breakaway eddy (16), and that the backflow completely rinses that portion of the screen which lies between the screen opening in question and the following screen opening downstream.
3. A method according to Claim 1 or 2, characterised in that the screen openings are in the form of grading slots (3), the longitudinal extent of which is substantially transversely to the direction of movement (R) of the clearer (12) and that the axis of the breakaway eddies produced extends approximately parallel to the grading slots (3).
4. A method according to Claim 1, 2 or 3, characterised in that the rinsing of the screen takes place on the side of the screen facing the clearer (12).
5. A pressure grader screen for wet screening pulp suspensions, with a plurality of grading slots (3) oriented substantially parallel, through which the portion of the pulp suspension accepted during the wet screening passes, which has end faces (4, 4') between the grading slots (3) each with a front closure (7) and a rear closure (8), the end faces (4, 4') on the rear closure (8) being provided with extensions (6),
   which each cover an adjacent grading slot (3) and furthermore a portion of the front closure (7) of the end face (4) adjacent to this grading slot (3) over a length (b) of at least 0.5 mm,
   characterised in that
   the end face (4) on the front closure (7) and the underside (9) of the extension (6) which faces said closure are at an angle (α) of between 3° and 45°, preferably 5° to 25°, and
   that the end face is free of edges which would form additional stagnation points in operation.
6. A pressure grader screen according to Claim 5, characterised in that the length (b) is at least 1 mm.
7. A pressure grader screen according to Claim 5 or 6, characterised in that the extensions (6) are located on the inlet-side end faces (4), at which the suspension flows into the grading slot upon operation of the pressure grader.
8. A pressure grader screen according to Claim 5, 6 or 7, characterised in that the rear closure (8) is located on the side of the end face (4) which lies downstream upon operation of the pressure grader with respect to the approach flow (R) of the pulp suspension on to the screen.
9. A pressure grader screen according to Claim 5, 6, 7 or 8, characterised in that the end faces (4) are inclined towards the screen surface (5) at an angle of inclination (β) of between 5° and 50°, preferably 10° to 30°.
10. A pressure grader screen according to one of Claims 5 to 9, characterised in that the underside (9) of the extension (6) to the screen surface (5) which points towards the screen opening has an angle of inclination (γ) of between 2° and 40°, preferably 5° to 25°.
11. A pressure grader screen according to one of Claims 5 to 10, characterised in that grading slots (3) are formed between bars (2, 2', 2") which consist of profiles and are fastened in reinforcing elements (1), the reinforcing elements (1) having recesses (10) for receiving the bars (2, 2', 2") and connecting some or all of the bars (2, 2', 2") present on the screen.
12. A pressure grader screen according to Claim 11, characterised in that the bars (2, 2', 2") are fastened in the reinforcing elements (1) by stresses resulting from plastic deformation of the reinforcing elements (1).
13. A pressure grader screen according to Claim 11 or 12, characterised in that the undersides (9) of the extensions (6) have a plurality of spacer noses (11) distributed over the longitudinal extent of the bars (2"), which noses are supported on the respective adjacent end faces (4).
14. A pressure grader screen according to Claim 11, 12 or 13, characterised in that the reinforcing elements (1) are in the form of rings, so that the screen is a cylindrical screen basket.
15. A pressure grader screen according to Claim 14, characterised in that reinforcing elements (1) and bars (2, 2', 2") are arranged in planes parallel to one another, so that the screen is a flat screen.
16. A pressure grader screen according to one of Claims 5 to 15, characterised in that the screen width (w) is between 0.08 and 2 mm.
17. A pressure grader screen according to one of Claims 5 to 16, characterised in that the extensions (6) extend substantially across the entire length of the grading slots (3).
18. A pressure grader screen according to one of Claims 5 to 16, characterised in that the extensions (6) are subdivided many times in the longitudinal direction of the grading slots (3).
19. A pressure grader screen according to one of Claims 5 to 18, characterised in that the form of the extensions (6) along the grading slots (3) is non-uniform.
20. A pressure grader screen according to one of Claims 5 to 19, characterised in that the length of the grading slots (3) is no greater than 10 mm.

Images