Suction device for a disc filter and method for filtering liquids with a disc filter

Description

[0001] The invention relates to a disc filter with a suction device, wherein the suction device has at least one suction bar per disc-shaped filter body and a suction slot designed for suctioning the impurities of the filter cloth as well as a suction pump for suctioning the impurities, wherein the suction bar is movable radially to the axis of rotation of the disc filter and the distance of the suction bar from the filter cloth is adjustable.

[0002] Disc filters are used, for example, in wastewater treatment. They consist of one or more disc-shaped filter bodies, each with a supporting frame covered with filter cloth. Each disc-shaped filter body can be composed of several sections, each covered with a bag-like filter cloth.

[0003] The simplest type of filter cloth is a single-layer fabric that retains particles from the water through the sieving effect of its mesh. Filter cloths are typically multi-layered. They consist of a supporting fabric with a relatively large mesh size and a filter-active layer. This filter-active layer contains threads and filaments that are layered multiple times to form multiple curved flow channels. These channels retain even solid particles smaller than the free cross-section of the spaces between the threads, either mechanically or through absorption by the threads. Such a depth-filtration filter layer is usually made of needle-punched felt or random-fiber nonwoven fabric.

[0004] A more advantageous design is the filter cloth as a so-called pile fabric, i.e., as a tufted, plush, or velvet fabric consisting of a relatively large-mesh support fabric and a pile of threads woven, for example, in a W-weave. During filtration, the threads lie on the upstream side of the filter cloth, and their length, stiffness, and density are dimensioned such that the flowing liquid and the mechanical action of the suction lip during the cleaning process cause the threads to fold into a position approximately parallel to the support fabric. This results in multiple layers, forming a depth filter. Between these overlapping threads, numerous narrow, angled, and multiply curved flow channels are formed, in which even solid particles smaller than the clear width of the flow channels can be retained, partly mechanically and partly through absorption.

[0005] The flow resistance of the filter cloth is relatively high and increases rapidly as the flow channels become increasingly clogged. The filter cloth must therefore be cleaned at relatively short intervals. This is usually done by backwashing, i.e., by passing liquid, such as fresh water or filtrate, through the filter cloth in the opposite direction to the filtration direction. Backwashing can be carried out on the entire surface of the filter cloth simultaneously or only on a section of the filter cloth, which is moved across its surface gradually.

[0006] During backwashing of the pile fabric, the pile threads are exposed to a fluid flow directed away from the support fabric. This causes them to stand upright relative to the support fabric, becoming largely parallel to each other and to the flow direction. As a result, the volume of the pile layer increases significantly, and the flow channels between the pile threads are opened and straightened. This reduces the flow resistance for the backwash fluid, allowing it to flow between the pile threads at high speed. Simultaneously, it releases the solid particles that were previously mechanically blocked in the flow channels, enabling them to be detached and flushed away by the backwash fluid, overcoming the absorption forces.

[0007] Devices and methods for backwashing filter cloths are known.

[0008] EP 2 752 229 A1 relates to a suction device for factory filters. The suction device has a suction plate with a main suction slot and a parallel lower suction slot separated by a partition. As the filaments pass through the lower suction slot, they are aligned with a delay and fluctuate, before quickly aligning themselves in the main suction slot. This improves the backwashing effect.

[0009] WO 00 / 21638 describes a backwashing device for a drum filter. The backwashing device has a backwashing nozzle arranged radially outwards from the filter media to direct a flow of high-pressure fluid radially inwards against the outer surface of the filter media, thereby removing sediments that have accumulated on the radially inner surface thereof.

[0010] A cleaning device for the filter material of a rotary disc filter or a drum filter is known from AU 200021355 B2. The cleaning device comprises at least one spray nozzle suitable for spraying cleaning fluid onto a portion of the filter cloth in a direction opposite to the filter direction. Furthermore, the apparatus includes a drive device for generating a reciprocating motion of the spray nozzle. The drive device has a coupling that converts the rotary motion of the drum into the reciprocating motion of the spray nozzle in such a ratio that the rotary motion of the drum and the reciprocating motion of the spray nozzle are phase-shifted relative to each other.

[0011] AU 2008217733 B2 relates to a device for cleaning the filter material of a rotary disc filter. The device has a rinsing ramp on which at least one spray nozzle is arranged. The spray nozzle is positioned to spray a cleaning fluid onto the filter cloth in a direction opposite to a filter direction. The rinsing ramp includes a drive device for moving the rinsing ramp along a longitudinal direction of the filter during cleaning. Two spray nozzles, rotatable in a plane substantially perpendicular to the axis of rotation of the rotary disc filter, are arranged on the rinsing ramp. The nozzles are arranged on both sides of a disc-shaped filter element and are aligned with each other and with the filter cloth on one side of the disc-shaped filter element.

[0012] CA 2813927 A1 describes a device for cleaning a filter cloth of a rotary disc filter. The device has a rinsing tube arranged between two adjacent parallel filter elements of the rotary disc filter. A plurality of spray nozzles are arranged in pairs around the rinsing tube, with their respective outlets located at a distance from the respective filter element that is greater than half the distance between two adjacent parallel filter elements.

[0013] US 2017 / 0165 597 A1 describes a device according to the preamble, which is used in particular for metallic filters.

[0014] DE 198 11 255 A1 describes a method and a device for backwashing a filter disc, wherein a volume flow of a liquid cleaning agent is guided through the filter element to be cleaned in the opposite direction to the flow direction of the filter disc.

[0015] EP 0 413 178 B1 relates to a disc filter for the mechanical treatment of biologically treated wastewater, comprising filter discs arranged on a rotatably mounted, driveable support tube, each disc having two suctionable filter surfaces. A suction device extends radially to the support tube.

[0016] EP 0 958 028 B1 discloses a method for filtering liquids with a filter cloth comprising a support fabric and, on the side exposed to the liquid flow, a pile of filaments. Backwashing is carried out by a suction bar. During backwashing, the filaments in the area of ​​the suction slot are raised to a position projecting away from the support fabric, whereby the filaments are subjected to a mechanical action by a surface of the suction bar facing them before reaching the suction slot, which prevents them from rising.

[0017] JP 6 158 581 B2 describes a filter device with disc-shaped filter materials. A cleaning device for backwashing is provided between the filter elements.

[0018] KR 101398838 B1 describes a disc filter with a suction device that has a suction bar with a suction slot which is movable relative to the disc filter.

[0019] WO 2026 / 030903 A1 describes a filter for filtering a liquid flow, comprising a filter arrangement with a number of filter discs arranged coaxially along a central flow path within a pressure vessel.

[0020] The present invention is based on the objective of optimizing extraction devices for disc filters.

[0021] The problem is solved in a suction device according to the preamble of claim 1 in that the filter cloth consists of a pole material and that the width of the suction bar is smaller than the radius of the disc-shaped filter bodies, wherein the suction bar is movable from a position corresponding to the smallest radius of the disc-shaped filter body to a position corresponding to the largest radius of the disc-shaped filter body.

[0022] The width of the suction bar is smaller than the radius of the disc-shaped filter media. Preferably, the width of the suction bar corresponds to one-third of the radius of the disc-shaped filter media. The suction bar can be moved from a position corresponding to the smallest radius of the disc-shaped filter media to a position corresponding to the largest radius of the disc-shaped filter media. In this way, the entire surface of the filter cloth of the disc-shaped filter media can be traversed and backwashed via the suction bar. The suction bar can be moved continuously from the position with the smallest radius to the position with the largest radius and back. Alternatively, the suction bar can be moved in steps. For example, the suction bar can be moved one step radially at time intervals or after each rotation of the disc filter.The suction bar can be immersed in the water in any position, which allows for particularly effective backwashing.

[0023] The radial design of the suction bar offers a particularly advantageous advantage: it allows for a narrower suction bar. This narrower design reduces the area of ​​the filter cloth that is suctioned by each suction bar, thus increasing suction capacity. Compared to arrangements of multiple suction bars in a row radial to the axis of rotation of the disc filter, this suction device has the advantage of eliminating the need for additional valves to control the individual suction bars via the suction pump, or for multiple suction pumps. This eliminates the need for failure-prone mechanical parts, thereby reducing the operating and maintenance costs of the suction device.

[0024] The design of the filter cloth as a pile material is particularly advantageous. During filtration, the pile threads form a depth filter with numerous narrow, angled, and multiply curved flow channels in which even solid particles smaller than the clear width of the flow channels can be retained, partly mechanically and partly through absorption.

[0025] During backwashing, the flow channels are opened and straightened by the fluid flow directed away from the support fabric. This reduces the flow resistance for the backwash fluid, allowing it to flow at high speed between the pile fibers. Simultaneously, it releases solid particles that were previously mechanically blocked in the flow channels, enabling them to be dislodged and flushed away by the backwash fluid, overcoming the absorption forces. The wider suction bar and the associated higher suction capacity allow for a higher backwash velocity with the same pump output, thus enhancing the cleaning effect of the backwash.

[0026] By adjusting the distance between the suction bar and the filter cloth, backwashing can be optimized depending on the filter cloth being cleaned and the liquid being filtered. The liquid flow attracts the filter cloth to the suction bar, causing a certain deflection of the filter cloth. The distance between the suction bar and the filter cloth should be such that the filter cloth remains in contact with the entire surface of the suction slots of the suction bar.

[0027] A preferred embodiment of the invention provides that a suction bar is provided in the gap between each pair of disc-shaped filter bodies.

[0028] The suction bar features suction slots for vacuuming the two filter cloths of the disc-shaped filter bodies. This makes it particularly advantageous to vacuum two filter cloths simultaneously with a single suction bar.

[0029] One embodiment of the invention consists in the suction bar being linearly movable.

[0030] The suction bar can be moved linearly in a radial direction to the axis of rotation of the disc filter. The suction bar is moved from the position with the smallest radius of the disc-shaped filter elements to the position with the largest radius of the disc-shaped filter elements in order to suction the entire surface of the filter cloth of the disc-shaped filter elements.

[0031] Another embodiment of the invention consists in the suction bar being movable in a pendulum motion via a suction arm.

[0032] The suction arm can be made of a rigid material. The suction bar is located at one end of the suction arm and is moved by a pendulum motion from the position with the smallest radius of the disc-shaped filter body to the position with the largest radius of the disc-shaped filter body. Advantageously, the suction arm is long enough that the suction bar is below the water surface at every point of the pendulum motion.

[0033] It is advantageous for the suction device to have a collecting line at the pivot point of the suction beams, which is arranged parallel to the axis of rotation of the disc filter.

[0034] The water for backwashing the filter cloth is carried away from the suction bars via the collection pipe. Several suction bars can be connected to the collection pipe. The collection pipe can be made of a torsionally rigid material so that the pendulum motion is transferred to the suction bars via the collection pipe and the suction arm.

[0035] It is advantageous that the collection line is connected to the suction pump via a flexible hose connection.

[0036] In this way, even if the collecting pipe is rotated, it can still be connected to the suction pump.

[0037] One embodiment of the invention consists in the suction bar being movable via a positioning drive decoupled from the rotary motor of the disc filter.

[0038] The decoupling of the positioning drive from the rotary motor of the disc filter offers the advantage of preventing the suction bar from always traveling the same distance across the filter cloth. The decoupled rotary drive allows for flexible adjustment of the suction bar's movement to the operating condition of the disc filter. For example, the suction bar can be moved radially across the filter cloth continuously or in stages. Furthermore, the radial movement of the suction bar can be adjusted to the degree of contamination of the liquid being cleaned by the disc filter.

[0039] In a preferred embodiment of the invention, the positioning drive is hydraulically operated.

[0040] A further embodiment of the invention consists in the fact that the suction bar can be moved into a position outside the gap between the disc-shaped filter bodies.

[0041] Advantageously, the suction bars can be more easily inspected for damage, maintained, cleaned or replaced by using this method outside the gap between the disc-shaped filter bodies.

[0042] Finally, the invention comprises a method for filtering liquids with a disc filter with a suction device according to one of the preceding claims, wherein the liquid to be filtered is passed through a filter cloth and wherein the filter cloth is backwashed with the suction device at intervals.

[0043] The suction device according to the invention can be used both with new disc filters and can be retrofitted to existing disc filters.

[0044] An embodiment of the invention is described in more detail below with reference to a drawing.

[0045] It shows Fig. 1 a perspective view of a suction device according to the invention in the state mounted on a disc filter.

[0046] In Fig. 1 Figure 1 shows a suction device 1 according to the invention attached to a disc filter 2. The suction device 1 consists of several disc-shaped filter bodies 3, which have a support frame covered with filter cloth 10. During operation, the disc filter 2 rotates about its axis of rotation. The disc filter is immersed in a basin containing the liquid to be filtered. The liquid to be filtered passes through the filter cloth 10 from the outside to the inside, whereby solids are filtered out of the liquid. The filtered water can be extracted from the interior of the disc filter, for example, by means of a pump.

[0047] The suction device consists of a suction bar 4 for backwashing the filter cloth 10. During backwashing, the filter cloth 10 is rinsed with a liquid, such as fresh water or filtrate, in a direction opposite to the filtration direction. This allows solid particles trapped in the filter cloth 10 to be released.

[0048] The suction bar 4 is connected to a rigid suction arm 5. The suction arm 5 allows the suction bar 4 to move in a pendulum motion, and the liquid drawn in by the suction bar 4 can be discharged. This pendulum motion moves the suction bar 4 radially to the axis of rotation of the disc filter 2. The figure shows three exemplary positions of the suction bar: the position with the smallest radius of the disc-shaped filter body 3, a middle position, and the position with the largest radius. The suction bar 4 can be moved continuously or in steps. The pendulum motion of the suction bar 4 allows the entire surface of the filter cloth 10 of the disc-shaped filter body 3 to be backwashed. The length of the suction arm 5 is designed such that the suction bar 4 remains below the liquid surface in every position of the pendulum motion.

[0049] The suction bar 4, with the exception of the two outermost suction bars 4, is located in the gap between the disc-shaped filter bodies 3. The suction bars 4 located in the gap between the disc-shaped filter bodies 3 have suction slots for backwashing the respective filter cloths 10 of the two disc-shaped filter bodies 3.

[0050] The suction bars 4 are connected to the collection line 6 via the suction arm 5. The extracted liquid is discharged via the collection line 6. The collection line 6 is torsionally rigid and is rotated by the positioning drive 7. The rotation of the collection line 6 causes the suction bars 4 to move in a pendulum motion via the suction arms 5. The collection line is connected to the suction pump 9 via a flexible hose connection 8.

Claims

1. Disc filter (2) having a suction device (1), wherein the suction device (1) comprises at least one suction bar (4) per discoid filter body (3) and a suction slit designed for suctioning the impurities of the filter cloth (10), as well as a suction pump (9) for suctioning the impurities, wherein the suction bar (4) is movable radially to the axis of rotation of the disc filter (2) and the spacing of the suction bar (4) from the filter cloth (10) is adjustable, characterized in that the filter cloth (10) consists of a pile fabric and in that the width of the suction bar (4) is smaller than the radius of the disc-shaped filter body (3), wherein the suction bar can be displaced from a position that corresponds to the smallest radius of the disc-shaped filter body to a position that corresponds to the largest radius of the disc-shaped filter body.

2. Disc filter (2) having a suction device (1) according to claim 1, characterized in that a suction bar (4) is provided in the gap between two discoid filter bodies (3) in each case.

3. Disc filter (2) having a suction device (1) according to any of the preceding claims, characterized in that the suction bar (4) is linearly movable.

4. Disc filter (2) having a suction device (1) according to any one of claims 1 to 3, characterized in that the suction bar (4) is movable in a pendulum movement by means of a suction arm (5).

5. Disc filter (2) having a suction device (1) according to claim 4, characterized in that the suction device (1) comprises a manifold (6) in the pivot point of the suction bar (4), which manifold is arranged in parallel with the axis of rotation of the disc filter (2).

6. Disc filter (2) having a suction device (1) according to claim 5, characterized in that the manifold (6) is connected to the suction pump (9) via a flexible tube connection (8).

7. Disc filter (2) having a suction device (1) according to any of the preceding claims, characterized in that the suction bar (4) is movable by means of a positioning drive (7) which is decoupled from the rotary motor of the disc filter (2).

8. Disc filter (2) having a suction device (1) according to claim 7, characterized in that the positioning drive (7) is operated hydraulically.

9. Disc filter (2) having a suction device (1) according to any of the preceding claims, characterized in that the suction bar (4) is movable into a position outside of the gap between the discoid filter bodies (3).

10. Method for filtering fluids by means of a disc filter (2), in which the fluid to be filtered is conducted through a filter cloth (10), and in which the filter cloth (10) is backwashed at intervals by means of a suction device (1) according to any of the preceding claims.