EP1039021A1 - 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 Fibrous 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, that is to say slots or gaps fibrous particles are more easily let through 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 prerequisite is a high precision of the 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 that with transverse retaining ribs are connected, are formed. The profiles are like this designed and arranged so that the flow during operation of the screening device 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 eddies train which the clearing 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 Sort opening around. The clearance of the sorting opening is ensured by the fact that Fiber accumulations or particles that cannot get through, contrary to the 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 keep the sorting slots reliably free and 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 screen openings each have step-shaped 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 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 by the features of claim 1, 2 and claim 5 measures mentioned.

The measures described in these claims will be in Inflow area of the flow openings located 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 the end face of the sieve. 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 flow direction 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 in that profile bars arranged side by side by fasteners, e.g. Rings are fixed. In the The selection of a different profile is then usually 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 producible.

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 terms familiar per se mean centrifugal = radial Flows from the inside out, centripetal = radially from the outside in. Not this also always determines the position of the screen clearers. As is well known, there are 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 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 '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. In 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 takes place 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 upwards for a short time, 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. 2, which one 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 at the sorting slot shown on the left Demolishes vortex 16. A left-hand vortex 17 can also form. The risk of deposits forming in the inlet area becomes significant reduced, i.e. significantly improved 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. Here too is the invention 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 that is 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 Sort 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 8 ° and 25 °. The choice of the angle α also ensures that the flow cross-section, seen in the direction of the upstream, expanded. 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 screen 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 sieve 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. That 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 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 optimization possibility.

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 thickened side. 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 reasons of screening technology, 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 γ relative to the screen surface 5, So not parallel to it, with the inclination between 2 ° and 40 °. Also the The end face 4 itself is inclined with respect to the sieve face 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 (21)

Process for wet screening of fiber suspensions in a pressure sorter, in which it is guided along a sieve provided with sieve openings, resulting in tear-off vortices (16) on the inflow side into the sieve, in which a part of the fiber suspension passes through the sieve openings as a pass (A) and the other part is rejected as an overflow, and in which pressure or suction impacts are generated at the sieve openings with the aid of clearers (12) which are moved relative to the sieve in such a way that back and forth flows occur therein, characterized by that the inflow side of the sieve is designed in such a way that the flow direction of the tear-off vortex (16) is reversed by the backflow,
the backflow flushing the part of the sieve which lies between the relevant sieve opening and the downstream one. Process for wet screening of fiber suspensions in a pressure sorter, in which it is guided along a sieve provided with sieve openings, resulting in tear-off vortices (16) on the inflow side into the sieve, in which a part of the fiber suspension passes through the sieve openings as a pass (A) and the other part is rejected as an overflow, and in which pressure or suction impacts are generated at the sieve openings with the aid of clearers (12) which are moved relative to the sieve in such a way that back and forth flows occur therein, characterized by that the return flow is deflected when it emerges from the sieve opening in such a way that its direction of flow runs in the opposite direction to the circumferential flow of the demolition vortex (16), and that the back flow completely flushes the part of the sieve which lies between the relevant sieve opening and the downstream sieve opening. The method of claim 1 or 2,
characterized by that the sieve openings are designed as sorting slots (3), the longitudinal extension of which extends essentially transversely to the direction of movement (R) of the scraper (12) and that the axis of the tear-off vortices produced runs approximately parallel to the sorting slots (3). The method of claim 1, 2 or 3,
characterized by that the screen is rinsed on the side of the screen facing the scraper (12). Pressure sorter screen for wet screening of fiber suspensions with a plurality of essentially parallel sorting slots (3) through which the part of the fiber suspension accepted during wet screening, which has end faces (4, 4 ') between the sorting slots (3), each with a front end ( 7) and a rear end (8),
characterized by that the end faces (4, 4 ') at the rear end (8) are provided with extensions (6), which each cover an adjacent sorting slot (3) and also part of the front end (7) of the end face (4) adjacent to this sorting slot (3) to a length (b) of at least 0.5 mm,
the end face (4) at the front end (7) and the underside (9) of the extension (6) facing it at an angle (α) of between 3 ° and 45 °, preferably 5 ° to 25 ° to each other. Pressure sorter screen according to claim 5,
characterized by that the length (b) is at least 1 mm. Pressure sorter screen according to claim 5 or 6,
characterized by that the extensions (6) lie on the inlet-side end faces (4), on which the suspension flows into the sorting slot when the pressure sorter is in operation. Pressure sorter screen according to claim 5, 6 or 7,
characterized by that the rear end (8) is located on the side of the end face (4) which, when the pressure sorter is in operation, lies downstream with respect to the flow (R) of the fiber suspension to the sieve. Pressure sorter screen according to claim 5, 6, 7 or 8,
characterized by that the end faces (4) are inclined against the screen surface (5) with an angle of inclination (β) between 5 ° and 50 °, preferably 10 ° to 30 °. Pressure sorter screen according to one of claims 5 to 9,
characterized by that the end face (4) is free from edges that would create additional stagnation points during operation. Pressure sorter screen according to one of claims 5 to 10,
characterized by that the underside (9) of the extension (6) facing the sieve opening to the sieve surface (5) has an angle of inclination (γ) between 2 ° to 40 °, preferably 5 ° to 25 °. Pressure sorter screen according to one of claims 5 to 11,
characterized by that sorting slots (3) are formed between bars (2, 2 ', 2'') which consist of profiles and are fixed in reinforcing elements (1), the reinforcing elements (1) having recesses (10) for receiving the bars (2, 2 ', 2'') and connect several or all of the bars (2, 2', 2 '') on the sieve. Pressure sorter screen according to claim 12,
characterized by that the rods (2, 2 ', 2'') are fixed in the reinforcing elements (1) by stresses due to plastic deformation of the reinforcing elements (1). Pressure sorter screen according to claim 12 or 13,
characterized by that the undersides (9) of the extensions (6) have a plurality of spacer lugs (11) distributed over the longitudinal extent of the rods (2 ''), which are supported on the respectively adjacent end faces (4). Pressure sorter screen according to claim 12, 13 or 14,
characterized by that the reinforcing elements (1) are designed as rings, so that the sieve is a cylindrical sieve basket. Pressure sorter screen according to claim 15,
characterized by that reinforcing elements (1) and rods (2, 2 ', 2'') are arranged in mutually parallel planes, so that the screen is a flat screen. Pressure sorter screen according to one of claims 5 to 16,
characterized by that the sieve size (w) is between 0.08 and 2 mm. Pressure sorter screen according to one of claims 5 to 17,
characterized by that the extensions (6) extend substantially over the entire length of the sorting slots (3). Pressure sorter screen according to one of claims 5 to 17,
characterized by that the extensions (6) are often divided in the longitudinal direction of the sorting slots (3). Pressure sorter screen according to one of claims 5 to 19,
characterized by that the shape of the extensions (6) along the sorting slots (3) is inconsistent. Pressure sorter screen according to one of claims 5 to 20,
characterized by that the length of the sorting slots (3) is not greater than 10 mm.

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