CN112090149A

CN112090149A - Filter unit and filtration system

Info

Publication number: CN112090149A
Application number: CN202010513392.7A
Authority: CN
Inventors: 康斯坦丁·格加诺夫
Original assignee: Grum Co ltd
Current assignee: Grum Co ltd
Priority date: 2019-06-17
Filing date: 2020-06-08
Publication date: 2020-12-18

Abstract

A filter unit (2) for filtering a liquid includes a holder (10) rotatably supported about a rotation axis (12) and including a plurality of holder portions (14) disposed around a circumference thereof. In each of the bracket portions (14), two first screen members (16) are provided to extend outwardly from the circumference of the bracket (10) and to approach each other with increasing distance from the circumference of the bracket (10) in the radial direction with respect to the rotational axis (12). Furthermore, in each carrier part (14), a second screen element (18) is provided, which extends substantially along the circumference of the carrier (10), so that the two first screen elements (16) and the second screen element (18) of the carrier part (14) are arranged substantially in the form of a triangle. The second screen member (18) has a mesh size greater than the mesh size of the first screen member (16).

Description

Filter unit and filtration system

Technical Field

The present invention relates to a filter unit for filtering liquids, and to a filtration system comprising such a filter unit.

Background

The filter unit or filter system filters out solids, particles and suspended solids from the liquid to be filtered. They are used, for example, in purification plants (especially as the third, usually last, purification stage), drinking water facilities, and industrial applications, for example, in applications for recovering materials from liquids or filtering cooling water. A filter unit or filtration system may also be used to remove algae from water or to treat potable water.

For example, a filter system with a filter unit, which is arranged in a basin and comprises a carrier, on the circumference of which a plurality of screen elements are arranged, is known from EP 3391949 a 1. The stand is rotatably supported around a feed pipe which supplies raw water to be purified. The raw water to be purified is fed to the filter unit radially inside the screen element and flows through the screen element into a basin surrounding the filter unit. To increase the surface area available for filtration, the screen elements of the filter unit are arranged in pairs such that two of the pair of screen elements extend outwardly from the circumference of the support and meet at an outwardly directed apex. Thus, the filter unit has a star-like shape.

However, if the screen element becomes fouled, the efficiency of the system is reduced and, in addition, the screen element is subjected to heavy loads, especially when the pressure difference between the feed and the sump or sump drain increases due to fouling. If the sieve element is torn, the not yet filtered contaminated liquid reaches the basin (clean water zone) surrounding the filter unit and contaminates the liquid there, i.e. the liquid that has been filtered.

Disclosure of Invention

It is an object of the present invention to provide an efficient and particularly reliable filter unit or filter system.

According to an aspect of the invention, a filter unit for filtering a liquid comprises: a bracket rotatably supported around a rotation axis, and a plurality of bracket portions disposed around a circumference of the bracket. Two first screen elements are arranged in each of the plurality of carrier parts in such a way that they extend outwardly from the circumference of the carrier and approach each other with increasing distance from the circumference of the carrier in a radial direction with respect to the axis of rotation. Additionally, a second screen element is disposed in each of the plurality of standoff portions. The second screen member extends substantially along the circumference of the carrier such that the two first screen members and the second screen member of the carrier portion are arranged substantially in the form of a triangle. The second screen member has a mesh size larger than the mesh size of the first screen member.

Thus, a filter unit is provided in which the second screen element, which first appears in radial direction with respect to the axis of rotation, is arranged to filter out larger solids, particles and suspended solids from the liquid before it reaches the first screen element. The load on the first screen elements is thus reduced, whereby their service life can be extended and the flow rate increased. The safety of the filter unit is also improved, since if one of the second screen elements breaks due to the action of large particles, the liquid will still be filtered by the first screen element. Thus, unfiltered liquid cannot enter the pool surrounding the filter. The first screen elements are arranged in a substantially star-shaped manner to increase the surface area available for filtration. The liquid to be purified can also enter the filter unit at a higher flow pressure.

The first and second screen members are configured and attached to the support such that when liquid flows from an inlet disposed radially inward of the first and second screen members relative to the axis of rotation into a pool disposed radially outward of the screen members, it passes through at least the second and first screen members. The filter unit is sealed in such a way that: the liquid flow cannot flow radially from the inside of the screen element to the radially outside of the screen element, except through the screen element.

Each first screen member and each second screen member may be configured as a one-piece unit or a multi-piece unit. The first screen element of the carrier part may also be formed by a single screen element with suitably arranged portions. Instead of providing a separate second screen member in each carrier part, a common second screen member may extend over several carrier parts arranged adjacent to each other in the circumferential direction. The first and second screen members may, if desired, comprise means for attachment to a support frame or a suitably designed frame structure.

Preferably, the diameter of the scaffold ranges between 0.5 and 2.5m, preferably between 1.0 and 2.0 m. The dimensions of the stent may be adapted to the respective application. It is contemplated that as the diameter of the carrier increases, the number of carrier sections and the number of screen elements may increase, thereby providing more surface area for filtration. In order to reduce the space occupied in the radial direction, it is also conceivable that the filter unit may be expanded in the axial direction. For example, a plurality of filter units may be arranged axially in a row, one behind the other, or the filter units may be equipped with a plurality of carriers oriented axially with respect to one another, or the carriers may have a plurality of screen elements arranged axially in a row, one behind the other.

The mesh size of the first and second screen elements is defined as the diameter of the largest sphere that just passes through the relevant screen element, i.e. through its mesh.

In order to achieve the most thorough filtration, in one embodiment the mesh size of the first screen element is preferably in the range of 3 μm to 150 μm, more preferably between 5 μm and 100 μm, even more preferably between 5 μm and 20 μm.

The mesh size of the second screen member is preferably in the range of 40 μm to 200 μm, more preferably between 80 μm to 150 μm, so that the second screen member can reliably retain the correspondingly larger particles and prevent them from reaching the first screen member. The mesh size of the second screen member may also be adapted to the requirements of a particular application or purpose of use and, in particular, may be a function of the mesh size of the first screen member.

It has been found to be particularly advantageous that the mesh size of the second screen element of the carrier section is 2-8 times, preferably 3-6 times, more preferably 3.5-4.5 times the mesh size of the first screen element of the carrier section.

In a preferred embodiment, the two first screen elements of the carrier section have the same mesh size. Thus, a uniform filtration of the liquid to be filtered is achieved. This also results in a particularly simple construction of the filter unit. By using a large number of individual first screen elements with the same screen aperture size, the cost of producing the filter unit can also be reduced.

In order to obtain a screen element with the most uniform possible configuration, and thus a reliable filtration of particles of a certain size, it is preferred that the screen apertures of the first screen element and the second screen element have a rectangular profile, in particular a square profile. The profile is viewed in a cross-section parallel to the plane of the associated screen element. For a mesh having a rectangular profile, the key characteristic of the mesh size is the length of the shorter side of the rectangle.

However, when the holes are viewed in this manner, it is also conceivable that one side of the rectangular outline of the holes may be much longer than the length of the side determining the size of the holes. It is therefore preferred that the lengths of the sides of the rectangular profile of the screen openings differ only slightly from each other and in particular that they should have the same length in order to avoid the passage of very narrow but long solid objects, particles and suspended solids. Thus, in a preferred embodiment, the apertures of the first and second screen members have a square profile.

The first and second screen elements preferably comprise fabric. The fabric can be produced relatively easily and with a particularly high degree of uniformity and at the same time the first and second screen elements are provided with screening holes having a rectangular profile. The fabric is preferably formed from round filaments (round filaments).

For possible application areas of the filter unit, it has been found to be advantageous if the fabric is made of stainless steel or plastic, preferably acid-resistant plastic, which is as tear-resistant as possible. Stainless steel is particularly strong, hygienic, easy to clean and easy to handle. Stainless steel such as AISI 316L may be considered. Plastic fabrics can be produced inexpensively, are light-weight and highly flexible and are therefore easy to integrate into a filter unit. Polyester fibers can be used, for example, as plastics. The skilled person can select alternative materials to suit the needs of a particular application.

In a particularly preferred embodiment, a screen frame is provided in each of the plurality of frame sections. The screen frame has a substantially triangular cross-section, the apex of which points radially outwards with respect to the axis of rotation and comprises two first screen elements of associated carrier parts.

The screen frame is used to hold and attach two first screen elements to the support. The two first screen elements may be stretched onto the screen frame and, if desired, the screen frame may reinforce or support the screen elements to protect them from damage. To this end, the screen frame may comprise appropriately designed support elements.

The screen frame of the bracket portion preferably further comprises a second screen element of the bracket portion. Thus, all screen elements of the holder part are arranged on the screen frame, which makes assembly of the filter unit simple.

The first screen element and possibly the second screen element of the frame part can easily be removed or replaced if the screen frame of the frame part is fixed detachably on the frame in a preferred manner. For this purpose, the screen frame can be screwed or clipped onto the carrier. The skilled person is familiar with alternative connection possibilities, preferably focusing on those possibilities that are easy to disconnect.

The first screen element and optionally the second screen element of the bracket portion may be attached to the screen frame in various ways. Each screen element may for example comprise a frame element which is inserted into the screen frame and is detachably or non-detachably connected thereto as required. The screen element itself may also be permanently attached to the screen frame. For example, the screen elements may be bonded to the screen frame by an adhesive or molded as an integral part of the screen frame.

Alternatively, the second screen member may also include a frame member by which the second screen member is directly attached to the bracket. The second screen element may also be integrated into the carrier and form, for example, a part of the circumferential surface of the carrier.

Preferably a second screen element is provided in each carrier part. It is also possible to provide a common second screen element which extends over a plurality of carrier parts arranged adjacent to one another in the circumferential direction of the carrier. For example, the second screen element may extend over two or more standoff portions. It is also conceivable that a single second screen element may extend around the entire circumference of the carrier and thus over all carrier parts. In this way, the second screen element forms part of the circumferential surface of the support.

The screen frames disposed adjacent to each other in the circumferential direction of the support may abut each other. A seal may be provided between adjacent frames to prevent liquid from passing between the frames. However, each screen frame may also be sealed radially with respect to the frame by a seal between the screen frame and the frame.

According to another aspect of the invention, a filtration system for filtering a liquid comprises a filter unit as described above; a basin (bassin) for containing filtered liquid, the basin at least partially surrounding the filter unit; and an inlet for supplying liquid to be filtered to the filter unit, wherein the inlet is arranged radially inside the first and second screen elements with respect to the axis of rotation of the support of the filter unit.

In this way, a filter system is provided which benefits from the advantages of the above-described filter unit.

Since the inlet is arranged radially inside the screen element, it is ensured that liquid will flow from the inlet through the screen element and into the basin.

Obviously, for its purpose, the inlet does not necessarily have to project so far axially that it is located inside the support defining the cylinder. Alternatively, the inlet may also be attached to the filter unit at one of the axial ends of the bracket. For example, the inlet may be flanged to one end of the support and thus not extend into the interior of the support. However, when considered in the radial direction, the inlet is closer to the rotational axis of the carrier than the screen element and is therefore located radially inside the screen element.

The filtration system may be configured as a stand-alone unit, in particular as a stand-alone tank, or may for example be integrated into a purification plant, so that a pool is formed for example by a channel of the plant.

The filtered liquid may be removed from the cell in various ways. For example, the basin may include an outlet for draining filtered liquid from the filtration system. However, the basin itself may be configured as a conduit or channel for draining filtered liquid.

Preferably, the level of liquid in the sump, and thus the level of liquid in the filter unit, is automatically adjusted. For this purpose, the filtration system may comprise a control unit and a liquid level measuring device for detecting the liquid level or filling level in the basin or in a separate region of the raw water zone. The liquid level can be automatically adjusted, in particular by control of the inlet and, if present, by control of the outlet.

According to a particularly preferred embodiment, the filter system comprises a plurality of cleaning nozzles, preferably spray nozzles (spray nozzles), to clean the screen element and the drainage channel. At least one cleaning nozzle of the plurality of cleaning nozzles is configured to clean the second screen member. To this end, at least one cleaning nozzle is directed at least one second screen element. The at least one cleaning nozzle for cleaning the second screen element may be formed by a separate cleaning nozzle or by a cleaning nozzle which is also provided for cleaning the at least one first screen element. Preferably, the cleaning nozzle is firmly supported in the filter system and the screen element is moved into the working area of the cleaning nozzle, i.e. the area of said screen element at which the cleaning nozzle is directed, by the rotation of the carrier about the axis of rotation. However, the cleaning nozzle can also be movably, in particular pivotably, supported.

The drainage channel is provided to collect deposits removed from the screen element by the plurality of cleaning nozzles and to conduct them away from the filter unit. The drainage channel is arranged radially inside the first and second screen elements with respect to the axis of rotation of the support of the filter unit. The plurality of cleaning nozzles are oriented in such a way that they are directed at the screen element arranged in the upper half of the filter unit. The drain channel is preferably located below the screen element at which the cleaning nozzle is directed. The deposits removed by the cleaning nozzles then fall down onto the drain troughs. From where they are carried away from the filter unit.

The at least one cleaning nozzle provided for cleaning the second screen element is preferably arranged radially inside the first screen element and the second screen element with respect to the rotational axis of the bracket of the filter unit and is attached to the drain trough. Thus, the at least one cleaning nozzle is directly aligned with the second screen member without the first screen member between the at least one cleaning nozzle and the second screen member. In addition, no additional fixing means are required inside the filter unit to hold and support the cleaning nozzle. Further cleaning nozzles of the plurality of cleaning nozzles, in particular those for cleaning the first screen element, may be arranged radially outside the first screen element and the second screen element with respect to the rotational axis of the carrier of the filter unit and aligned with the first screen element.

It is also preferred that the maximum liquid level allowed in the filtration system or pool is below the upper edge of the drainage channel. This prevents deposits removed by the plurality of cleaning nozzles from being washed back into the liquid to be filtered and from contaminating the screen element again. Furthermore, some of the plurality of rack sections may be disposed above the liquid level, and the screen elements of these rack sections will be cleaned by the plurality of cleaning nozzles.

So that a particularly high efficiency of the filter system or filter unit can be achieved and a sufficiently long preparation time for operation is provided, the carrier is rotated at intervals to move the soiled screen element into the working area of the cleaning nozzle and to move the clean screen element back into the liquid to be cleaned.

For example, the stent is rotated 1 to 20 times per hour, preferably 2 to 8 times. The carrier can be rotated stepwise (stepwise) so that in each step a certain number of screen elements are located in the working area of the cleaning nozzle. After a certain period of time, the carrier is rotated again and the screen element moving in the circumferential direction is moved into the working area of the cleaning nozzle. It is also conceivable that the carrier can be rotated continuously for a predetermined time, so that all screen elements can be cleaned by means of the cleaning nozzles. For example, the stent may be rotated for 1-2 minutes and then stopped. The rotation speed is relatively slow. The filter unit preferably requires a speed in the range of 1.5-2.5 minutes/revolution.

The rotation may occur at predetermined time intervals or may be automatically adjusted by the control unit in dependence on operating parameters such as the pressure difference between the inlet and the outlet. An increase in the pressure difference indicates that the screen element is full of dust and must be cleaned. When the pressure difference reaches a limit value, the control unit may initiate rotation of the cradle.

The plurality of cleaning nozzles are preferably formed by spray nozzles. The spray nozzle preferably discharges a water jet at a pressure in the range of 0.5 to 1.0 bar towards the screen element to be cleaned.

The jets discharged by each cleaning nozzle are preferably directed at the screen element to be cleaned at an angle in the range of 3-20 °. This ensures that deposits or dirt can be dislodged from the screen elements in the most reliable possible manner without forcing particles through the second screen element towards the first screen element.

Drawings

FIG. 1 shows a perspective view of the essential components of a filtration system according to an embodiment of the invention;

fig. 2 shows a detailed view of a part of a filter unit according to an embodiment of the invention in a perspective view;

FIG. 3 shows an exploded view of a portion of the filter unit shown in FIG. 2; and

fig. 4 shows a cross-sectional view of a portion of a fabric of a screen element of a filter unit according to an embodiment of the invention.

Detailed Description

The filtration system 1 comprises a filter unit 2, which is described in more detail below with additional reference to fig. 2-4. The filtration system 1 further comprises a sump 4 to contain the liquid filtered by the filter unit 2. The basin 4 at least partially surrounds the filter unit 2.

In fig. 1, the level of the liquid in the basin 4 or filter unit 2 or feed basin is schematically shown (by the symbol▼Representation). The maximum level is preferably such that the filter unit 2 is not completely submerged in the liquid. Therefore, the extent to which the bath 4 surrounds the filter unit 2 is sufficient as long as the desired liquid level can be reached in the bath 4 or the filter unit 2. The basin 4 may for example be formed by a water tank (not shown here) with suitable side walls. However, the pool 4 may also be part of a channel or pool of a plant, such as a decontamination plant.

The filter system 1 may also include one or more cover plates 6 that cover the basin 4 and protect it from the spray water and mist. In that case, the filter unit 2 is substantially completely enclosed by the basin 4 and the at least one cover plate 6 and escape of spray water and contaminants during operation of the filter system 1 is avoided.

As can be seen particularly clearly in connection with fig. 1-3, the filter unit 2 comprises a holder 10, which holder 10 is rotatably supported about an axis of rotation 12. The stent 10 includes a plurality of stent sections 14 disposed about its circumference. The holder parts 14 do not have to be physically separated from each other by parts of the filter unit 2. In each frame portion 14 there are two first screen elements 16 arranged to extend outwardly from the circumference of the frame 10 and to approach each other with increasing distance from the circumference of the frame 10 in a radial direction relative to the axis of rotation 12. A second screen element 18 is also provided in each of the frame portions 14. The second screen member 14 extends substantially along the circumference of the support frame 10. The two first screen elements 16 and the second screen element 18 of the standoff portion 14 are arranged to form a substantially triangular shape. One side of the triangle, i.e., the side forming the edge of the second screen member 18, extends substantially along the circumference of the support frame 10, while the other two sides of the triangle, each forming the edge of the first screen member 16, extend outwardly from the circumference of the support frame 10 and form radially outwardly directed vertices.

As can be seen in fig. 1, the entire circumference of the carrier 10 is preferably divided into a carrier part 14 and equipped with first and

second screen elements

16, 18. Thus, a maximum filter surface area can be obtained relative to the diameter of the stent 10.

The filter system 1 further comprises an inlet 8 for supplying liquid to be filtered to the filter unit 2. The inlet 8 is arranged radially inside the substantially cylindrical filter unit 2. As can be taken from fig. 1, the inlet 8 for supplying the filter unit 2 with the liquid to be filtered is arranged radially inside the first and

second screen elements

16, 18 with respect to the axis of rotation 12. Liquid to be filtered enters the filter unit 2 through the inlet 8 and flows through at least one second screen member 18 and one first screen member 16 as the liquid to be filtered flows from the inlet 8 into the basin 4 surrounding the filter unit 2. Thus, the liquid to be filtered is filtered by the first and

second screen elements

16, 18.

The second screen member 18 has a mesh size greater than the mesh size of the first screen member 16 so that, as a first step, larger deposits are retained by the second screen member 18. The liquid that has been pre-filtered then passes through the first screen element 16 for further filtration. The first screen element 16 thus becomes fouled more slowly and is subjected to a lighter load than conventional filtration systems.

The inlet 8 may be flanged to the filter system 1 at one axial end of the filter unit 2, or, if the inlet 8 is in the form of an inlet pipe, it may extend into the filter unit 2 in the axial direction of the rotational axis 12, in particular into the holder 10, so that the filter unit 2 surrounds the inlet 8. Accordingly, the filter unit 2 is rotatably supported on this type of inlet pipe. However, it is preferred that the filter unit 2, i.e. the holder 10, is rotatably supported on the frame of the filter system 1.

In the embodiment shown here, the filter system 1 also comprises a plurality of cleaning

nozzles

20a, 20 b. Each cleaning

nozzle

20a, 20b is arranged to clean the first and/or

second screen member

16, 18. For this purpose, the

cleaning nozzles

20a, 20b are directed toward one or

more screen elements

16, 18 which are then arranged in the working region of the

cleaning nozzles

20a, 20 b.

Preferably, the at least one cleaning nozzle 20a for cleaning the second screen member 18 is arranged radially inside the second screen member 18 with respect to the rotational axis 12. The at least one cleaning nozzle 20a may be directly aligned with the second screen member 18 in question to be cleaned, without the first screen member 16 being present between the at least one cleaning nozzle 20a and the second screen member 18 in question. One or more cleaning nozzles 20b for cleaning the first screen member 16 may be disposed radially outward of the first screen member 16 relative to the rotational shaft 12. However, it is also possible to provide only the radially inner or radially outer side of the first and

second screen elements

16, 18 with

respective cleaning nozzles

20a or 20b, which are provided to clean the first and

second screen elements

16, 18. In order to ensure the most uniform cleaning of the first and

second screen elements

16, 18, a plurality of cleaning

nozzles

20a, 20b are preferably arranged in a row one behind the other parallel to the axis of rotation 12.

The filter system 1 further comprises a drain tank 22, the drain tank 22 being arranged to collect and guide out of the filter unit 2 deposits removed from the

screen elements

16, 18 by the plurality of cleaning

nozzles

20a, 20 b. Preferably, the drain channel 22 is arranged vertically below the

screen elements

16, 18, to which the

cleaning nozzles

20a, 20b are directed, so that it can collect the removed deposits.

In the embodiment shown here, at least one cleaning nozzle 20a for cleaning the second screen element 18 is attached to the drain channel 22. Therefore, there is no need to provide any additional fastening means inside the filter unit 2 to hold and support the at least one cleaning nozzle 20 a. Furthermore, the at least one cleaning nozzle 20a can thus be arranged as close as possible to the second screen element 18 to be cleaned.

A preferred construction of the filter unit 2 is described below with reference to fig. 2 and 3. In the preferred embodiment shown, the filter unit 2 includes a plurality of screen frames 24. Preferably, one screen frame 24 is provided in each frame portion 14. The screen frame 24 has a substantially triangular cross-section. Once the screen frame 24 is mounted on the frame 10, the plane of the cross-section is perpendicular to the axis of rotation 12 of the frame 10. In this state, the apex 26 of the substantially triangular cross-section of the screen frame 24 is also oriented radially outward relative to the axis of rotation 12. The screen frame 24 comprises at least two first screen elements 16 of the associated support frame portion 14. In particular, two first screen elements 16 are provided in both side faces of the screen frame 24 extending towards the apex 26 of the screen frame 24.

Each screen frame 24 preferably has the shape of a triangular prism, in particular a straight, regular prism. The length of the screen frame 24 is defined as its dimension parallel to the axis of rotation 12 and is preferably between 100 and 1500mm, more preferably between 200 and 800mm and even more preferably between 400 and 600 mm.

The end faces 28 of the screen frame 24 are preferably closed, but in an alternative embodiment each end face may be provided with a screen element.

The radially outwardly directed apexes 26 of the screen frame 24 may be rounded to flatten (rounded for flattened) and may optionally include screen elements 16a to further increase the available filtration area. In this case, the screen member 16a may also be cleaned by the

cleaning nozzles

20a, 20b, so that the deposit may be prevented from adhering to the apex 26 of the screen frame 24. The screen member 16a may be part of one of two adjacent first screen members 16 or may be formed from a single screen member 16 a.

Each of the two sides of the screen frame 24 oriented outwardly relative to the frame 10 includes a first screen element 16. Each first screen element 16 is preferably constructed as a one-piece unit and is connected to the screen frame 24. However, each first screen member 16 may also be formed from a multi-part unit, whereby several separate screen member parts are connected to the screen frame 24 in a manner to form the first screen member 16.

The first screen member 16 may be permanently or removably attached to the screen frame 24. For example, the first screen member 16 may be bonded to the screen frame 24 through the use of an adhesive, or may be integrally molded therewith. However, the first screen member 16 may also include a frame member over which the first screen member is stretched and then inserted into and attached to the screen frame 24.

The screen frame 24 may also include a support member 30 for supporting the first screen member 16. For example, the support element 30 is configured as a pillar starting from a portion of the screen frame 24 facing the support frame 10 and extending along an outwardly directed side of the screen frame 24 to the apex 26. The support member 30 is preferably disposed outside of the first screen member 16. Liquid flowing from the inside to the outside through the first screen member 16 urges the first screen member 16 toward the support member 30, which resists the pressure exerted on the first screen member 16 by the flow of liquid. The first screen member 16 may also be connected to an associated support member 30 adjacent thereto.

In a particularly preferred embodiment, the two first screen elements 16 and, if present, the screen element 16a at the apex 26 are formed by one and the same screen element, the respective parts of which are arranged accordingly. For example, the two first screen elements 16 and the screen element 16a at the apex 26 are formed from a continuous layer of fabric. However, the two first screen members 16 and the screen member 16a may also be formed of separate screen members.

The screen frame 24 of the frame portion 14 may also include the second screen element 18 of the frame portion 14. As previously described with reference to the first screen member 16, the second screen member 18 may also be configured as a one-piece or multi-part unit and permanently or removably attached to the screen frame 24. The second screen element 18 is arranged on the side of the screen frame 24 facing the frame 10 and opposite the apex 26. The screen frame 24 may further comprise a support element for supporting the second screen element 18, which support element is arranged radially outside the second screen element 18 with respect to the rotational axis 12 in order to counteract the pressure of the liquid flow.

The second screen member 18 may include a frame member 32, with the screen member 18 stretched over the frame member 32. The frame member 32 may be inserted into and connected to the screen frame 24. However, the frame element 32 may also be mounted between the screen frame 24 and the frame 10 or directly connected to the frame 10 in the associated frame part 14. In particular, the second screen member 18 may be attached to the carrier 10 radially outward or radially inward of the carrier, whether it is attached to the frame member 32 or absent the frame member 32.

By arranging the screen frame 24 on top of the second screen member 18, placing them on the support frame 10, the second screen member 18 and the screen frame 24 can be mounted in a particularly simple manner and then fixed to the support frame 10 by suitable fixing means. In the embodiment shown, a bolt 34, for example, in particular a threaded bolt, is provided which is located at the boundary between circumferentially adjacent bracket parts 14 of the bracket 10. The second screen member 18, preferably having a frame member 32, and the screen frame 24 are disposed on the support frame 10 between bolts 34 circumferentially adjacent to each other on the support frame 10. Nuts 36 are screwed onto the bolts 34 whereby the screen frame 24 and the second screen member 18 are held in position on the support 10.

The screen frame 24 preferably comprises two flange portions 38 extending in a longitudinal direction parallel to the rotation axis 12, and this may firstly provide the support 10 with a flat contact surface and secondly may form a contact surface for the nut 36, so that the nut 36 may hold the screen frame 24 in place on the support by the flange portions 38. It is also preferred that the flange portions 38 of adjacent frames 24 are adjacent the same bolts 34, compressed by the same nuts 36. Thus reducing the number of mounting work and fastening means. Alternatively, the flange portion 38 may have an opening through which the bolt 34 passes. Those skilled in the art are familiar with a variety of fastening means suitable for this purpose.

A particularly robust support 10 is formed by two annular elements 40, one of which is arranged on each of the two end faces of the support 10. Between the ring elements 40, a plurality of rods 42 extend in the axial direction. Two adjacent rods 42 preferably form the boundary of the bracket portion 14. The bolts 34 may be provided on the ring element 40 and/or on the rods 42.

The screen frame 24, and in particular the flange portion 38 thereof, may be placed on the rod 42. The screen frame 24 is preferably placed completely over the ring element 40 and the bars 42 to create a sealing effect. Preferably, gaskets are provided on the side of the screen frame 24 facing the support 10 to ensure a leak-proof contact between the screen frame 24 and the support 10.

Obviously, in alternative embodiments, the second screen element 18 may be formed in such a way within the scope of the invention: the second screen element 18 extends over a plurality of standoff portions 14. To this end, the second screen member 18 (with or without the frame member 32) may be pre-formed according to the profile of the support 10, or it may be sufficiently flexible to conform to the profile of the support 10, or it may be integrated into the support 10.

Fig. 4 illustrates a portion of the

screen members

16, 18 on an enlarged scale to aid in describing the screening openings 44 of the first and

second screen members

16, 18. The screen apertures 44 of the

screen members

16, 18 have a rectangular profile. The rectangular profile of each screen aperture 44 is defined by a length L and a width B. Accordingly, the mesh size of the mesh 44 is defined as the diameter of the largest sphere that can just pass through the mesh 44. The largest sphere for the mesh 44 shown here is schematically represented by a circle having a diameter D. Therefore, in the case of a mesh 44 having a rectangular profile, a shorter one of the sides L or B is always the key factor. Thus, in the example shown here, this key factor is the width B.

However, it is necessary to prevent narrow particles having a width less than the mesh size of the mesh 44 but a length greater than the mesh size from passing through the associated

screen member

16, 18. To this end, it is preferred that neither the length L nor the width B of the rectangular screen opening 44 be much greater than the selected and predetermined opening size of the

screen members

16, 18. Preferably, the length L of the mesh 44 is equal to the width B, which means that the mesh will have a square profile.

By forming the first screen member 16 and the second screen member 18 from a fabric, preferably a fabric made of round filaments 46, it is particularly easy to obtain screen openings 44 having a rectangular or square profile.

Alternative materials and filter fabrics are known to those skilled in the art and may be equally well used for the first and

second screen members

16, 18.

Claims

1. A filter unit (2) for filtering a liquid, comprising:

a bracket (10) that is rotatably supported around a rotation axis (12) and that includes a plurality of bracket portions (14) that are provided around the circumference of the bracket (10);

wherein in each of the plurality of bracket parts (14), two first screen elements (16) extend outwardly from the circumference of the bracket (10) and approach each other with increasing distance from the circumference of the bracket (10) in a radial direction relative to the rotational axis (12);

wherein a second screen element (18) is provided in each of the plurality of standoff portions (14), the second screen element (18) extending substantially along the circumference of the standoff (10), wherein the two first screen elements (16) and the second screen element (18) of each standoff portion (14) are arranged substantially in a triangle; and

wherein the second screen member (18) has a mesh size greater than the mesh size of the first screen member (16).

2. A filter unit (2) as claimed in claim 1, wherein the first screen element (16) has a mesh size between 3 μ ι η and 150 μ ι η.

3. A filter unit (2) as claimed in claim 2, wherein the second screen element (18) has a mesh size between 40 μ ι η and 200 μ ι η.

4. A filter unit (2) as claimed in claim 1, wherein the second screen member (18) of the holder portion (14) has a mesh size 2-8 times larger than the mesh size of the first screen member (16) of the holder portion (14).

5. A filter unit (2) as claimed in claim 1, wherein the two first screen elements (16) of the holder part (14) have the same mesh size.

6. A filter unit (2) as claimed in claim 1, wherein the screening apertures of the first (16) and second (18) screen elements have a rectangular profile.

7. A filter unit (2) as claimed in claim 1, wherein the first and second screen elements (16, 18) comprise a fabric.

8. A filter unit (2) as claimed in claim 7, wherein the fabric is formed of stainless steel or plastic.

9. A filter unit (2) as claimed in claim 8, wherein the fabric is formed from round filaments (46).

10. A filter unit (2) as claimed in claim 1, characterised in that a screen frame (24) is provided in each of the holder parts (14) of the plurality of holder parts (14), the screen frame (24) having a substantially triangular cross-section, the apex (26) of which is directed outwards with respect to the axis of rotation (12), and the screen frame (24) comprising two first screen elements (16) of the associated holder part (14).

11. A filter unit (2) as claimed in claim 10, wherein the screen frame (24) of the holder part (14) further comprises the second screen element (18) of the holder part (14).

12. A filter unit (2) as claimed in claim 10, wherein the screen frame (24) of the bracket part (14) is detachably fixed to the bracket (10).

13. A filter system (1) for filtering a liquid, comprising:

filter unit (2) comprising:

wherein the second screen element (18) has a mesh size greater than the mesh size of the first screen element (16);

an inlet (8) for supplying liquid to be filtered to the filter unit (2), wherein the inlet (8) is arranged radially inside the first screen element (16) and the second screen element (18) with respect to the rotational axis (12) of the support (10); and

a basin (4) for receiving filtered liquid, the basin at least partially surrounding the filter unit (2).

14. A filtration system (1) according to claim 13, further comprising a plurality of cleaning nozzles (20a, 20b) and a drain tank (22);

wherein at least one cleaning nozzle (20a) of the plurality of cleaning nozzles (20a, 20b) is arranged to clean the second screen element (18); and

wherein the drain channel (22) is arranged to collect the deposits removed by the plurality of cleaning nozzles (20a, 20b) and to guide the deposits out of the filter unit (2).

15. A filter system (1) according to claim 14, wherein the at least one cleaning nozzle (20a) of the second screen element (18) directed towards the holder part (14) is arranged radially inside the first screen element (16) and the second screen element (18) with respect to the rotational axis (12) of the holder (10) of the filter unit (2).