EP0685325B1 - Device for separating the liquid portion from the solid portion in two-phase systems - Google Patents

Description

The invention relates to a device for separating the liquid portion of the solids content of finely dispersed mineral Slurries, in particular a ceramic slip, with a screw and with the screw surrounding the radial distance and cylindrical along the screw Filter means that with the screw a conveyor channel for the Limit slip, which is via a material feed on one End of the filter screw press fed and after promotion through the channels of the rotating snail at the other end than Solid discharge is discharged through a mouthpiece, the the liquid component flowing through the filter medium via a filtrate discharge is dissipated.

A device according to the preamble of claim 1 is already known (EP-B 0 138 920), in which the Filter medium surrounding the screw is arranged in a housing are. The filter medium surfaces facing the screw The filter media contained in the housing are to protect against Abrasion covered with an abrasion-resistant protective grille. In the mesh of this grid forms a stationary one Filter cake, which has a significant flow resistance for represents the filtrate drain. This resistance is all the more smaller, the smaller the thickness of the grid and the smaller the area covered by the bars Filter medium surface is. For reasons of strength and stability, but also to fulfill the protective function Thickness of the grid and the area covered by the grid not be reduced arbitrarily, so that one Reduction of the resistance for the filtrate drain set limits are. Apart from that caused by the protective grille disadvantageous flow resistance for the filtrate drain results from the use of the protective grille a structural effort of such a known filter screw press.

One similar to the device described above Filter screw press is in Japanese patent JP 55051000. Here, too, they are in one housing absorbed filter media to protect against abrasion on your side facing the snail through an inner tube protected. However, this inner tube is in one Low pressure and a high pressure area divided, the High pressure area more wear-resistant and overall higher Strength is designed. However, this does not change anything The fact that the disadvantages described above of a protective grille occur.

Another filter screw press, where the filter media protected by a metallic, perforated protective cover is the subject of French patent FR 596522.

The object of the invention is to overcome the disadvantage of the prior art Fix technology, especially a device for separation to create the liquid portion from the solid portion, which is structurally is simply constructed and without the need for additional Protective grille for the filter media gets along.

This object is achieved by the characterizing Features contained part of claim 1 solved, wherein expedient developments of the invention by the in the Characteristics contained subclaims are marked.

The invention is based on the knowledge that from the beginning to the two-phase system still over the middle of the screw channel is liquid to soft plastic, so that in the gap between Outside diameter of the screw and inside diameter of the filter cylinder a filter cake resting on the filter medium forms, the solids content higher than that of the medium is in the screw channel, so that due to the resting filter cake the filter media are protected against friction. For this The reason in this section is sufficient to use filter media, which are not designed for high abrasion resistance must or can additional protective measures of the filter medium by connecting protective grids and the like. The invention bears this through the two-stage structure the device bill, being in the first filter medium section Filter media with lower abrasion resistance are used can be, however, in the second subsequent Filter media section filter media can be used, which itself are characterized by a higher abrasion resistance. Suitable for this porous silicon carbide or silicon nitride cylinders. It is useful that the filter medium included in filter elements with limited axial length are, which are advantageously constructed identically. This offers the possibility of assembling the filter elements in a modular manner, by filter elements of the first filter medium section and filter elements of the second filter medium section arranged side by side along the screw axis become. The filter elements are against each other conventional seals sealed.

The filter means of the first filter section stand out through the finest pores close to the filter medium surface, the pore system expanding into the filter medium. As a result, fine particles are largely on the surface of the filter medium captured, whereas in the pore system fine particles penetrating the filter medium without further ado can happen. This will largely blockages avoided.

With finely disperse mineral sludges, especially with ceramic slip, adheres to the first filter section stationary filter cake layer on the surface of the filter medium so firm that it causes abrasion and primary constipation be kept away from the filter medium. In zone 2, so the second filter section, the two-phase system is already concentrated to a disperse plastic material. Here there is direct contact of the entire screw channel disperse solid particles with each other. The solid particles are apparently so firmly fixed in a solid framework, that penetration of the finest solid particles into the Filter medium does not occur even when the protective stationary cake layer no longer exists here. Because of this fact can be attributed to the originally according to EP-B 0 138 920 protective grille on the filter media be the resistance to the drainage of the filtrate increase very much and thereby lower the performance very much would. At the same time, the Construction. Relatively cheap filter elements sensitive to abrasion can be used for the first filter section , whereas only in the second filter section more abrasion-resistant abrasion elements are required.

This is very essential for the economic and therefore practical success of the device.

Fine-pored sintered sieve mesh and porous silicon carbide are Examples of those required in the respective sections Filter media. Of course, others can suitable filter media are used.

The division according to the invention is particularly advantageous of the filtering screw cylinder into a number of self-supporting elements with a correspondingly smaller axial Extension of the filter elements in which the filter media in undivided steel cylinders are well attached, which makes the very high forces occurring during processing well absorbed can be. A closed housing that the Including filter elements is unnecessary, rather it is sufficient a frame that defines the position of the filter elements and the torques on the individual filter elements act, absorbs.

The filter elements are expediently designed to be self-supporting, the filter media either in a massive Steel cylinders are welded in or a steel cylinder over the filter medium is shrunk, which is particularly the case with Use of ceramic filter media is the case. As a result of This eliminates the self-supporting property of the filter elements Additional housing required. The filter elements are only connected by means of tie rods fixed and otherwise outside by a frame against rotation secured. This results in an overall very simple easy assembly of a filter screw press.

Finally, a special rinsing process is essential, around both the screw channel and the filter elements to be cleaned after long periods of operation. To do this in a first step the tap channels through tap water rinsed, whereas in a second work cycle the filter elements with changing flow direction, preferably individually under pressure Be rinsed with water. It is also possible without prior Rinsing the screw channels only the pore system Intermittent filter elements with rinsing water against the direction of flow of the filtrate.

Figur 1 eine schematische Schnittansicht der Vorrichtung durch die Längsachse,

Figuren 2 bis 5 Details eines Filterelements des ersten Abschnittes der Vorrichtung sowie

Figuren 6 bis 9 entsprechende Detaildarstellungen eines Filterelements des zweiten Abschnittes der Vorrichtung.

Figur 10 eine schematische Ansicht einer alternativen Ausführungsform der Vorrichtung.

A preferred embodiment of the invention is described below with reference to the drawing. Show in it

FIG. 1 shows a schematic sectional view of the device through the longitudinal axis,

Figures 2 to 5 details of a filter element of the first section of the device and

Figures 6 to 9 corresponding detailed representations of a filter element of the second section of the device.

Figure 10 is a schematic view of an alternative embodiment of the device.

The device of Figure 1 is through a filter screw press formed, which has a conventional screw 1, which within one by side by side filter elements 2 and 3 formed housing and arranged at 4 is rotatably mounted. By a drive, not shown rotated screw 1 serves to promote ceramic slip used for the purpose of separating the liquid portion of the solid content by the between the Screw 1 and the filter elements 2 and 3 formed screw channel is transported. The slip is at one end the filter screw press via the material feed 6 Screw channel 5 fed and leaves at the other end Press over the mouthpiece 7. At 8 there is a discharge opening shown, which serves as a bypass and in more detail below is explained. The filter elements 2 of the first filter medium section extend over at least half of the part of the screw that is effective for slurry extraction. in the illustrated embodiment are four filter elements 2, on which three filter elements of the Connect the second filter medium section. The along the Screw axis arranged cylindrically arranged side by side Filter elements 2 and 3 are next to each other Seals 9 of conventional design sealed. The filter elements 2 and 3 are self-supporting, so that an additional There is no housing for the filter screw press.

Finally, the filter screw press comprises a flushing water supply line 10, via which, via a water pump 11 and a control valve 12, flushing water can be supplied to the individual filter elements with the interposition of valves V ₁ to V _n . A further rinsing water circuit is formed by the water line 13 and the valve 14, which opens into the filter screw press at 15, and by the rinsing water line 15a and the control valve 16, the line 15a at the mouth end at 16a discharging the rinsing water from the screw channel. A sedimentation basin for the rinsing water is identified by 17, a line 18 also opening into the basin 17, which leads away from the bypass 8. Finally, in Figure 1 with 19 and 20 tie rods are shown schematically, which serve to fix the filter elements 2 and 3.

FIGS. 2 to 5 show the structure of the filter elements 2 of the first filter medium section. Figure 2 shows this Filter means 21 of the first filter means section, which preferably from several layers of one above the other Sieve fabrics is formed, which are sintered together. Thereby the porous system of the filter medium 21 results, which is otherwise circular cylindrical. Instead of one the filter medium can also be sintered together from a porous sintered metal cylinder, in particular sintered steel be educated.

The porous cylindrical filter media 22 of the second filter media section (Figure 6) are made of ceramic material formed, in particular silicon carbide or silicon nitride.

The sintered sieve mesh or sintered steel cylinder for the first one and the silicon carbide or silicon nitride cylinders for the second filter medium sections are each in a solid Steel cylinders 23a and 23b added, which in FIGS and 7 is shown.

According to Figure 3 are inside the steel cylinder 23 at a distance channels 24 running in the circumferential direction of approximately 20 mm are arranged, through one or more axially extending channels 25 are connected to each other, which the filtrate to outlet holes 26 lead in the steel cylinder 23a. Accordingly, also in Steel cylinder 23b for receiving the filter medium 22 of the second Circulating channels 24 provided in the filter medium section, which are connected by longitudinal channels 25 to the Drain filtrate through the outlet bore 26.

The sintered sieve fabrics or sintered steel cylinders are in the Steel cylinder 23a welded, as shown in Figure 5. The silicon carbide or silicon nitride cylinders according to FIG. 6 are ground to exact dimensions to form the filter element, so that the steel cylinder 23b is shrunk thermally can be. The composite filter element is shown in Figure 9.

The filter element according to FIGS. 6 to 9 are the Select tolerances of dimensions so that after cooling of the steel cylinder and at a filtration pressure of 120 bar the cylindrical filter medium (silicon carbide or silicon nitride) in the circumferential direction on average is tension-free. If the pressure in the screw channel or in The filter element assumes the value zero, the cylindrical one Filter medium through the shrunk-on steel jacket under high Circumferential pressure. The wall thickness of the cylindrical The filter medium is selected so that the silicon carbide or silicon nitride material is not overstressed becomes. Because the materials mentioned have high compressive stresses, however can only absorb low tensile stresses, it only succeeds on the way shown, filter elements made of these materials to create that absorb high filtration pressures. In this case, the cylindrical design is particularly important the steel cylinder as a full jacket, because in use half shells do not have a sufficiently uniform pressure load on the circumference of the cylindrical filter element can be guaranteed. This could break it of the filter elements.

The filter elements 2 and 3, as shown in FIGS. 2 to 5 and 6 to 9 are shown, are self-supporting and do not need to be supported from the outside by a special housing to become. You will only be on an appropriate one Arranged frame, which in Figures 4 and 8 with 27th is marked. This frame 27 has a recess 28 in which an extension of the steel cylinder engages, whereby the frame 27 onto the filter medium surface torque applied by the rotating screw inside records.

The filter elements have a limited axial length, whereby in the preferred embodiment, the length of the filter elements is in the range of 100 to 200 mm. By dividing up of the filter medium into individual filter elements results not just a modular system but also the filter media made of screen mesh and sintered steel corresponding to the surrounding ones Steel jackets are welded tight. Furthermore, this is problem-free thermal shrinking of the steel jackets on the filter media made of silicon carbide and silicon nitride guaranteed. Even with the targeted ones described below Proportional rinsing of the filter elements has proven itself this construction of the screw cylinder from individual Filter elements 2 and 3.

From the entry of the slip at 6 into the screw channel 5 to over the middle of the screw channel (up to approx. 60 percent by weight Dry matter) is the two-phase system in Snail channel still fluid to soft plastic. In this area the filter elements 2 are arranged. The snail is not yet effective (slightly falling pressure in this Zone). In the gap between the outside diameter of the screw and The inside diameter of the filter cylinder forms on the Filter cylinder resting filter cake, which is a significantly higher one Solids content as the medium in the screw channel. This filter cake also has a significantly higher, mechanical one Strength than the material in the screw channel. This resting filter cake layer is very essential in the first section because it keeps the friction away from the filter medium. This applies if a certain layer thickness is not undershot is based on test results Is 0.5 to 1 mm. The resistance to the filtrate drain lies essentially in this first filter medium section in this resting filter cake layer, because in the snail channel exists for reasons not to be explained here in detail almost no direct contact between the solid particles (Solid framework pressure 0). The resistance for the Filtrate drain can not be reduced as much as one The minimum thickness of the resting filter cake layer was not less can be. But it is without the use of a Protective grille that superfluous in the first filter section is, in any case, smaller than with a protective grille. In this zone, a few layers of fine-mesh sieve fabrics are sufficient, that have been sintered together, or porous sintered steel cylinders as a filter medium, since there is a risk to the Filter media does not exist due to abrasion.

The filter media are expediently sintered together Screen fabrics or sintered steel in known pore structures realized, with the finest pores dense on the filter medium surface, where the filter cake is forms. From there, the pore system expands in the respective filter medium. This makes fine particles largely held onto the filter medium surface. Finest particles that penetrate the filter medium most likely the expanding channels pass the filter medium completely and leave with the filtrate. This significantly reduces the possibility of constipation.

In the second, immediately after the first filter medium section is the solids concentration in the screw channel with over 60 percent by weight so far that a clear distinction between medium in the screw channel and filter cake layer on the filter medium no longer is possible. The snail is clearly effective. The Drainage takes place here essentially by compression of the disperse plastic medium in the screw channel, the Solid particles are already touching directly. To avoid A filter medium made of very abrasion-resistant material must have abrasion Silicon carbide or silicon nitride can be used however a protective grille is not required. Through the very rough surface structure of the silicon carbide is partially still prevents wall sliding, but are at highest solids concentrations, wall gliding not more completely excluded.

Over a long period of operation, as is the case in practice occurs, the filtrate flow gradually decreases, indicating clogging is due. The fine pores of Filter medium and especially the stationary cake layer The filter medium will become used over a longer period of time of those also available in the two-phase system in the screw channel finest solid particles gradually added so that the flow resistance for the filtrate flow increases. This However, constipation can be reversed by flushing be made. The rinse runs in two steps from and at the end of a long stationary operation of the Filter screw press.

For the purpose of flushing, the mouthpiece 7 or the bypass 8 for the drainage of the plastic material on the mouthpiece side End of the screw channel opened to the flow resistance for the outflow of the plastic material from the screw channel greatly reduce. The snail continues to rotate and the slip flow via the material feed 6 is also maintained. The rotating screw is thus able the plastic material largely through its promotional effect to be removed from the screw channel, which takes place as long as to slip from material feed 6 to the outlet strikes at mouthpiece 7 or bypass 8. Then the Slip supply 6 shut off and water tap 14 opened so that water is fed into the filter screw press becomes. The water now flows through the snail channels and now leaves the housing of the filter screw press instead of slip via the mouthpiece 7 or the bypass 8. This effectively flushes the screw channel, largely cleaned of slip and plastic material becomes. The rotational movement of the snail supports the rinsing process. The rinsing process is finished when Slips and remains of plastic material from the snail channel have been washed out.

It then expediently rinses the filter elements on. For this, the connection to the water supply network at 14 and the outlets 7 and 8 are closed. Then rinse water is over at higher pressure Automatically controlled valves 12 and 16 in changing flow directions passed through the pore system of the filter medium. The change of direction is controlled in one predetermined timing by the solenoid valves 12 and 16. Der Flushing water flow for the filter media is one example hydraulically driven piston pump 11 promoted. The discharge pressure can then be hydraulic in a simple manner can be regulated (10 to 30 bar). The flushing water flow would be used for flushing with constant flow direction decrease after a short time because the fine particles that clog the pore system and through the flushing water flow first be detached from their positions, after short distance again in any corner of the pore system fix and lead to new constipation. This is avoided by a repeated reversal of the direction of the flushing water flow, the fine particles from very angled pore systems transported out, especially with filter media made of porous ceramics.

Expediently, only a limited section of the filtering screw cylinder is also always flushed in order to avoid that the flushing water flow flows over sections of the screw cylinder that have already been flushed out, while other sections which are still blocked remain unflushed. The individual filter elements 2 and 3 are therefore rinsed individually. This is accomplished in that only one of the valves V ₁ to V _{n is} opened one after the other.

This rinsing process of the filter elements is carried out a few times rinsing of the screw channel with tap water is interrupted, as previously described to remove residues of the dispers plastic material that is still from the surface of the Have loosened the filter medium to convey it out of the screw channel.

In special cases, a simplified one also works Flushing process, which during the ongoing operation of the Screw press without rinsing the screw channels beforehand can be applied. Rinse water is under a higher Pressure in the opposite direction as it is in the screw channel to the filtrate flow through the pore system of the filter elements. The rinse water flow must be repeated for each limited time interval can be switched on. Once the Flushing water flow switched off for the subsequent time interval due to the high pressure in the screw channel part of the flushing water entered in the screw channel through the pore system of the filter medium in the direction of the filtrate flow back, so that there is also a rinse alternating flow direction results. It also makes sense here rinse the filter elements one after the other.

It is particularly advantageous that the cycle times for the rinsing processes in different directions for different lengths to get voted. As a result, a particle in the Direction of the longer cycle time on statistical average one covered a greater distance than in the opposite direction and so has a chance of being removed from inside the filter medium to become. With this procedure it is possible to a gradual constipation that occurs during longer periods of operation remove the filter elements with the finest particles.

The formation of individual filter elements together with the subdivision of the filtering screw cylinder into two sections come with different filter media in particular then to bear when it comes to the device for interpret greater power. The increase in the transport speed of the multiphase system in the screw channel and the flow rate of the liquid phase in the pore system, that is formed by the disperse solid phase set strict limits for fluidic reasons. A Increased performance of the device by extending the axial extension of the screw and by enlarging the Snail channel depth is therefore only to a very limited extent possible. In essence, performance can only be achieved through one Increase in diameter can be achieved. Filter elements with screen mesh for the first filter section can without major manufacturing problems and with reasonable Effort can be made with a larger diameter. Filter elements with porous ceramics, however, can only in diameter can be enlarged to a limited extent. There are already diameters from 400 mm hardly manageable manufacturing technology Problems with editing by grinding and accordingly high costs. To increase performance, the invention for this section the use of several filter screws proposed in parallel. Such an embodiment is shown in Fig. 10. Here, the first filter section 29 a filter screw with large Diameter. In contrast, the second filter section 30 is through several filter screws with a smaller one working in parallel Diameter formed with respect to the first filter section 29. In the embodiment according to FIG. 10 there are four working in parallel Filter screws 31 are provided. Here is the Diameter of the filter screws 31 of the second filter section 30 expediently a quarter of the diameter the filter screw 32 of the first filter section 29. Die Filter screws 31 feed the extrudate into a common one Mouthpiece 33, from which only one strand 34 is plastic Mass emerges. The opening cross section of the mouthpiece 33 is controlled in a known manner so that in front of the mouthpiece there is a constant predetermined pressure. The common Rotation frequency of the screws of the second filter section 30 is thus on the rotational frequency of the worm 32 of the first section voted that in the transition from section 29 to section 30 the concentration is established in the two-phase system, which makes it necessary to change the filter medium. Finally, in Fig. 10 with 35 drive units each Filter screws 31 designated.

Claims (18)

1. A device for separating the liquid portion from the solid portion of finely dispersed mineral sludge, more particularly of a ceramic slime, by means of a screw conveyor (1) with cylindrical filtering elements encompassing the screw conveyor and arranged along the length of the screw conveyor axis, said filtering elements together with the screw conveyor (1) delimiting a conveyor channel (5) for conveying the slime which is delivered into the screw conveyor (1) via a feeder (6) at one end of the device and which, after having been conveyed through the rotating screw conveyor, is discharged at the other end as a solid mass via a nose-piece (7), whereas the liquid portion flowing out through the filtering element is discharged via channels (24, 25) leading to a filtration conduit, characterised by a dual-phased structuring of the device, with an initial filtering element section on which is built up, directly upon the filtering element (21), a stationary filter cake layer having a distinctly higher proportion of solid matter than the slime which is conveyed within the screw conveyor channel (5) and which extends from the feeder (6) along the length of the screw conveyor axis, and with a second filtering element section connected immediately to it consisting of filtering elements (22) which have a higher degree of resistance to abrasion than the filtering elements (21) of the initial filtering element section and which, in the same way as the filtering elements of the initial filtering element section, are in direct contact with the sludge that is to be separated, whereby the two filtering element sections are constructed respectively of self-supporting filtering elements (2, 3) arranged adjacent to each other, of which each filtering element is in the form of a solid steel cylinder (23) with a cylindrical filtering element (21) or, as the case may be, (22) contained within it, so that, within each of the filtering elements (2, 3) and independently of the adjacent filtering elements (2, 3), channels are formed between the steel cylinder (23) and the filtering element (21, 22) contained within it.
2. A device according to claim 1, characterised in that the filtering elements, and specifically those pertaining preferably to the initial filtering element section (21), comprise very fine pores closely adjacent to the filtering element surface which faces towards the screw conveyor (1), from which point the channels of the pores extend inwards to the centre of the filtering element (21).
3. A device according to claim 1 or 2, characterised in that the filtering elements (21) of the initial filtering element section are constructed either of several layers of fine-meshed strainers that have been sintered together or of porous sintered-powder metal and the filtering elements (22) of the second filtering element section are constructed of a porous ceramic material, in particular of silicon carbide or silicon nitride.
4. A device according to one of the preceding claims, characterised in that the initial filtering element section extends from the slime inlet to at least the centre of the screw conveyor (1), preferably extending over a region in which the solid matter content of the slime is 42 to 60 per cent of weight, preferably to a maximum of 60 per cent weight, at which point the second filtering element section then adjoins.
5. A device according to one of the preceding claims, characterised in that the filtering elements (21) of the initial filtering element section are each welded on to the steel cylinder (23) and that the filtering elements (3) of the second filtering element section are constructed by means of thermal shrinkage of the corresponding steel cylinder (23) on to the filtering element (22).
6. A device according to claim 5, characterised in that the tolerances for the dimensions in the case of the filtering elements (3) of the second filtering element section are calculated in such a way that, subsequent to the cooling of the steel cylinder (23) and at a filtration pressure of approximately 120 bar in the screw conveyor channel (5), the cylindrical filtering element (22) is in an unstressed state in a circumferential direction within the element.
7. A device according to one of the preceding claims, characterised in that the filtering elements (2, 3) display axial extension in the region of 100 to 200 mm.
8. A device according to one of the preceding claims, characterised in that the channels of the filtering element (2, 3) are formed of channels (24) running in a circumferential direction preferably at a clearance distance of approximately 20 mm and connected by one or several axially aligned channels (25), which lead to one or several drilled outlet holes (26) in the steel cylinder (23).
9. A device according to one of the preceding claims, characterised in that the filtering elements (2, 3) are located and prevented from rotating on a frame (27) arranged along the length of the screw conveyor axis.
10. A device according to one of the preceding claims, characterised in that revolving seals (9) are arranged between adjacent cylindrical filtering elements (2, 3).
11. A device according to one of the preceding claims, characterised by a rinsing system in which the screw conveyor channels are rinsed during an initial operating cycle and the filtering elements (2, 3) during a second operating cycle.
12. A device according to claim 11, characterized in that the rinsing of the screw conveyor channels is effected by the nose-piece (7) or a bypass (8) located at the mouth-piece end of the screw conveyor (1) being opened, preferably with the screw conveyor (1) rotating and with the input of slime still continuing via the feeder (6), until such time as the slime has passed through from the inlet to the outlet by way of the nose-piece (7) or the bypass (8), and then the input of slime being stopped and water fed in at the feeder end of the device.
13. A device according to claim 11 or 12, characterized in that, subsequent to the rinsing of the screw conveyor channel and with the nose-piece (7), the bypass (8) and the slime feeder (6) closed, the rinsing of the filtering elements (2, 3) is effected by passing rinse water, which is under pressure and controlled by valves, through the pore system of the filtering elements (2, 3) in alternating directions of flow.
14. A device according to one of the claims 1 to 10 with a rinsing system, characterized in that, during the operation of the filter screw conveyor press without previous rinsing of the screw conveyor channel, rinse water which is under higher pressure than that presently existing in the screw conveyor channel is passed through the pore system of the filtering elements from the rinse water pump (11) via the valve (12) and in the opposite direction to the filtration flow, whereby the valve (12) is controlled in accordance with a pre-selectable timed cycle in such a way that, in the course of one rinsing process and in each case at frequent intervals, following a cyclic period during which the stream of rinse water is pumped through the filtering element in the opposite direction to the filtration flow, another timed Period ensues during which a free filtration discharge from the filtering elements is engaged, with the result that, because of the high internal pressure in the dual-phased system within the screw conveyor channel, a liquid flow is effected through the filtering elements in the same direction as the filtration flow.
15. A device according to one of the claims 11 to 14, characterised in that the rinsing process is maintained by the rotation of the screw conveyor (1).
16. A device according to one of the claims 11 to 15, characterised in that the individual filtering elements (2, 3) are rinsed in each case separately one after the other.
17. A device according to one of the claims 11 to 16, characterised in that the rinsing of the filtering elements (2, 3) is interrupted periodically by a rinsing of the screw conveyor channel.
18. A device according to one of the preceding claims, characterised in that several parallel operating filter screw conveyors (31) are provided in the second filtering section (30).

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