Rotary disc filter and module for constructing same

Field of the Invention

0001The present invention relates to a rotary disk filter comprising a drum having a central longitudinal axis and being rotatably arranged about the same and adapted to receive a liquid which is to be filtered, and at least one disk-shaped filter member which on the outside of the drum extends outwards in the transverse direction of the drum and which has a filter support and at least one filter portion supported thereby, a first liquid duct extending from the drum through the filter member and out through the filter portion, and the fifter portion being made of filter segments, which are detachably secured to the filter support. The invention also relates to a module for building a filter support for a rotary disk filter.

Background Art

0002Rotary disk filters are known from, for example, SE-C-224,131. In this filter, water is conducted through one end of a central rotatable drum and through openings in the circumference of the drum radially outwards to disk-shaped filter chambers. Each of the filter chambers is defined by a disk-shaped filter member having opposing filter portions which are supported by an annular filter support arranged between the same. The filter members are mounted in parallel along the longitudinal axis of the drum. When water flows out through the filter portions, particles are retained in the filter chambers. When cleaning the filter portions, the drum is rotated and water is flushed onto the filter portions from outside in the upper area of the rotary disk filter, particles and water flowing into the upper area of the drum and being collected in a trough extending through the drum. The filter portions comprise annular filter cloth portions arranged on the sides of the filter supports.

0003<patcit id="pcit0001" dnum="SE465857B"><text>SE-B-465,857</text></patcit> (<patcit id="pcit0002" dnum="WO9112067A"><text>WO 91/12067</text></patcit>) discloses a rotary disk filter of a similar kind, in which the disk-shaped filter members comprise a plurality of separate, disk-shaped filter sections, which together establish annular filter members. By the annular filter members being divided into a plurality of separate units, also the filtercloth is divided into smaller pieces, which means that in case of a local damage to the cloth a replacement of the cloth is necessary on only one of the filter sections, not on an entire annular disk.

0004In the two rotary disk filters described above, the filter cloth can be fastened in one of a plurality of ways. In a common solution, the filter cloth is glued directly to the filter support on opposing sides thereof. This is particularly common when the cloth consists of some textile or plastic material. The cloth can also be made of metal. In that case, it is often welded to the filter support, and if necessary reinforcement ribs are welded to the outside of the filter cloth for improved securing thereof. In a further way of fixing the cloth to the support, the cloth is designed as a "bag" which is slipped around a filter support and is shrunk on the same.

0005Rotary disk filter constructions of this kind suffer from several problems. The filter cloth has a limited life in normal use and must be replaced at regular intervals. Moreover the filter cloth is sensitive and can easily be damaged, necessitating a premature replacement thereof. If the cloth is damaged, an entire filter cloth portion must be replaced.

0006Rotary disk filters with detachably secured filter segments have therefore been developed. Such a rotary disk filter is disclosed in <patcit id="pcit0003" dnum="WO9930797A"><text>WO 99/30797</text></patcit>, which discloses a rotary disk filter which has a filter portion consisting of several filter segments. The filter segments are detachably secured to a filter support and comprises a frame and a filter cloth expanded by the frame. The frame and the filter support are made of metal. Using detachably secured filter segments makes it easier to replace parts of the filter. This rotary disk filter functions in asatisfactory manner, but it is desirable to improve it further by, for instance, making manufacture less expensive. It would also be desirable to make these rotary disk filters lighter and less bulky when dimensioned for large flows. Moreover it would be desirable for the filter disks to entrain a smaller amount of water in their rotary motion than has been possible so far. A smaller amount of water would then accompany the particles through the trough of the rotary disk filter for drawing off filtered-off particles, wh ich could thus increase the capacity of the rotary disk filter.

Summary of the Invention

0007An object of the present invention is to provide a rotary disk filter which, compared with prior-art rotary disk filters, is more compact and thus has a higher filtering capacity with the same space occupied.

0008Another object of the invention is to provide a rotary disk filter which is lighter than prior-art rotary disk filters.

0009A further object is to provide a rotary disk filter which compared with prior art can be manufactured at a lower cost.

0010A special object of the present invention is to provide a module that enables construction of a filter support for a more compact rotary disk filter.

0011Yet another object is to provide a module that enables less expensive construction of a filter support for a rotary disk filter.

0012One more object is to provide a module for building a lighter rotary disk filter.

0013According to the invention, these objects are achieved by the rotary disk filter of the type stated by way of introduction being given the features that are evident from claim 1. Preferred embodiments are defined by the subclaims 2-8. The objects are also achieved by a module according to claim 9, preferred embodiments being defined in the subclaims 10-16.

0014The inventive rotary disk filter has at least one second liquid duct which extends between adjoining filter segments to provide liquid communication between the filter segments. In this way, liquid can move between the filter segments and is therefore not entrained in the rotary motion. As a result, the capacity of the rotary disk filter increases.

0015In one embodiment of the invention, the second liquid ducts comprise hollow spaces in the filter support. Liquid communication between the filter segments can thus be provided in an extremely simple way.

0016The filter support between the filter segments advantageously comprises a framework construction, whose hollow spaces constitute the second liquid ducts. In this manner, liquid communication can easily be provided, while at the same time the support can be made sufficiently strong with great economy in material.

0017According to a preferred embodiment of the invention, the filter body is made up of modules. A rational construction can thus be ensured.

0018Two modules preferably form a filter support round a filter segment, and the two modules are then interconnected at a distance from surrounding filter segments. This makes it possible to avoid joints between the filter segments, which makes it easier to provide a tight construction.

0019The filter segments can be secured to the filter support by means of grooves in the filter support which are extended in the plane of the filter segments. The filter segments can thus be safely secured to the filter support while at the same time it is easy to insert and remove the filtersegments. Moreovera certain self-sealing effect can be achieved.

0020According to one embodiment of the invention, the filter support forms at least a portion of a circumferential surface of the drum. This makes it possible to manufacture the drum with a reduced consumption of material.

0021The filter support is preferably made of plastic and can thus be manufactured at a relatively low cost. Further the filter support will be corrosion-resistant

0022The inventive module for building a filter support comprises two inner support portions and two outer support portions for at least partial enclosure of two adjoining filter segments, and an intermediate support portion adapted to be arranged between the two adjoining filter segments. Using such modules makes it possible to effectively build a filter support.

0023The intermediate support portion preferably comprises at least one liquid duct for providing liquid communication between adjoining elements. As a result, liquid can move between thefiltersegments and is therefore not entrained when the filter support rotates during operation of the rotary disk filter. This means that the capacity of the rotary disk filter can be increased.

0024The intermediate support portion advantageously comprises a framework construction, the hollow spaces of which constitute liquid ducts to provide liquid communication between adjoining filter segments. The framework construction gives good strength with a minimised consumption of material and further provides in a simple way ducts for the liquid to pass between the filter segments.

0025One end of the outer support portions and the inner support portions preferably has means for interconnecting two modules. The modules can thus easily be interconnected to form a filter support.

0026The inner support portions are advantageously arranged to form portions of a circumferential surface of the drum, which makes it possible to build the drum using a small amount of material.

0027The outer support portions and the inner support portions are preferably symmetrically arranged on the intermediate support portion. Only one type of module thus is required for building the filter support.

0028The inventive module may comprise grooves for securing of filter segments, which grooves extend in the plane of the filter segments. This makes it possible to safely secure the filter segments in a way that makes the segment easy to attach and detach.

0029According to a preferred embodiment, the inventive module is made of plastic. It can thus be manufactured relatively inexpensively and allows a light filter support to be built.

Brief Description of the Drawings

0030The invention will now be described in more detail with reference to the accompanying schematic drawings which by way of example illustrate currently preferred embodiments of the invention. <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a perspective view which schematically shows the principle of a rotary disk filter according to prior-art technique.</li><li><figref idref="f0002">Fig. 2</figref> is an end view of a rotary disk filter according to the invention with some concealed parts indicated by dashed lines.</li><li><figref idref="f0003">Fig. 3</figref> is a side view of the rotary disk filter in <figref idref="f0002">Fig. 2</figref> with some concealed parts indicated by dashed lines.</li><li><figref idref="f0004">Fig. 4</figref> is a perspective view of an inventive module for building a filter support.</li><li><figref idref="f0004">Fig. 5</figref> is a perspective view of a closing means for securing filter segments in the inventive rotary disk filter.</li><li><figref idref="f0004">Fig. 6</figref> is a top plan view of a filter segment.</li></ul>

Detailed Description of a Preferred Embodiment

0031The fundamental function of a rotary disk filter according to the invention is largely the same as for prior-art rotary disk filters of the type as shown in <figref idref="f0001">Fig. 1</figref>. The function of the inventive rotary disk filter will therefore be explained with reference to <figref idref="f0001">Fig. 1</figref>. The rotary disk filter 1 has a slowly rotating drum 2 which supports a plurality of disk-shaped filter members 3, whose normal direction is parallel to and concentric with the longitudinal axis or rotary axis C of the drum 2 and whose lateral faces, which are axially directed and radially extended, support a filter cloth 4. The liquid A which is to be filtered is conducted through an inlet 5 to the interior of the drum 2. From the interior of the drum 2 the filtering liquid A is conducted out through openings in the circumferential surface 6 of the drum 2 to the interior of the disk-shaped filter members 3. From there the filtering liquid A is finally conducted in a filtering direction out through the filter cloth 4. Any particles in the filtering liquid A adhere to the inside of the filter cloth 4. The rotary disk filter 1 is provided with flushing nozzles 7 for cleaning of the filter cloth 4, which are mounted on a number of flush tubes 8 which extend between the disk-shaped filter members. The flush tubes 8 are adapted to conduct flush liquid to the flushing nozzles 7 and are connected to an elongate liquid-conducting tube 9 which extends parallel to the centre axis C of the drum. The flushing nozzles flush the filter cloth axially from outside, in a direction opposite to the filtering direction, and the flushed-out particles are collected in a discharge trough 10 which is placed in the drum 2 in the upper portion thereof.

0032As is evident from <figref idref="f0002">Fig. 2</figref>, the filter members 3 have according to a preferred embodiment of the invention a filter support 11 which extends radially outwards in the transverse direction of the drum 2 and is made up of a plurality of modules 12. The filter support 12 forms compartments in which filter segments 13 are arranged. As shown in <figref idref="f0004">Fig. 6</figref>, the filter segments 13 consist of a frame 14 which expands the filter cloth 4.

0033The modules 12 have, as shown in <figref idref="f0004">Fig. 4</figref>, an intermediate support portion 15, from one end of which extend two outer support portions 16 outwards. From the other end of the intermediate support portion 15 extend two inner support portions 17 outwards. The intermediate support portion 15 consists of a framework construction 18 with hollow spaces 19. The inner support portions 17 have openings 20 which allow the liquid which is to be filtered to pass from the interior of the drum 2. The inner and outer support portions 17,16 have at their ends holes 21 for insertion of screws for interconnecting two modules 12. On both sides of the intermediate support portion 15 there are two grooves 22 which extend parallel to the intermediate support portion 15 in the plane of the filter support 11. In each of the inner support portions 17 there are two parallel grooves 23 which are parallel to the inner support portion 17 and extend in the plane of the filter support 11.

0034<figref idref="f0004">Fig. 6</figref> shows a closing means in the form of a cover 24 for securing the filter segments 13 in the filter support 11.

0035In construction of the rotary disk filter 1, seven modules 12 are attached to each other by means of screws in the holes 21 in such a mannerthatthe modules form a semicircle. Two such semicircles are then mounted on the drum 2 and bolted together to form a filtersupport 11. By the joining of the modules 12 occurring essentially in the centre of the filter segments 13, tightness is improved compared with the case where the joining would occur between two filter segments 13.

0036In each of the compartments formed by the filter support 11 between two adjoining modules 12, a filter segment 13 is inserted into the grooves 22 and 23 on both sides of the modules 12. The cover 24 is slipped on to the outer support portions 16 of two adjoining modules 12 and the two parallel filter segments 13 which these modules 12 enclose together. The cover 24 is screwed to the outer support portions 16 of the modules 12. A number of thus constructed disk-shaped filter members 3 are mounted on the drum 2 to provide the rotary disk filter 1. In the embodiment illustrated, ten filter members 3 are mounted on the drum 2. However, as many as twenty-two filter members can be arranged on a drum 2 to provide a rotary disk filter 1 with greater capacity.

0037In operation of the rotary disk filter 1, the liquid A, preferably polluted water, which is to be filtered is supplied through the inlet 5 at one end of the drum 2 and is passed through a first liquid duct which extends from the interior of the drum 2 through the openings 20 in the inner support portions 17 of the modules 12 and out through the filter cloth 4 of the filtermembers3. The drum 2 rotates slowly and the filter segments 13 which are positioned in the lower part of their course are passed by the liquid A. Pollutants then adhere to the inside of the filter cloth 4. When the filter segments 13 are positioned in the upper part of their course, they are cleaned by means of the above-described flushing equipment 7, 8, 9. The flushed-out pollutants are then removed by means of the discharge trough 10.

0038The hollow spaces 19 in the framework construction 18 of the intermediate support portions 15 form a second liquid duct through which the liquid A can move between the filter segments 13. In contrast to the prior-art rotary disk filters, the liquid A will therefore not be entrained in the rotary motion of the filter members 3. The amount of liquid accompanying the pollutants out through the discharge trough 10 will thus be reduced. Thespeed of rotation of the drum 2 can thus be increased, which means that the capacity of the rotary disk filter 1 is increased. Therefore the rotary disk filter 1 can be made more compact than prior-art rotary disk filters. Also the load exerted on the suspension and driving device of the drum is reduced.

0039The rotary disk filter 1 can be mounted at the factory and be delivered ready for use, but the module construction also makes it possible to deliver modules 12 for mounting the rotary disk 1 at the site where it is to be used. The module construction also makes it easy to enlarge an existing rotary disk filter 1 in order to increase its capacity. Modules 12, filter segments 13 and covers 24 for one or more new filter members 3 can then be delivered and mounted in the existing rotary disk filter 1.

0040In the example described, the modules 12 are made by injection moulding of ABS plastic. Also other plastic materials can be used, and a suitable manufacturing process is then selected with regard to the type of plastic. Plastic is advantageous since it is a relatively inexpensive material that is easy to work and furthermore is corrosion resistant. Other materials may also be selected, but it should be taken into consideration that it is convenient to use a material which has a low weight in relation to its strength, thus minimising the weight of the completed rotary disk filter.

0041The frame 14 of the filter segments 13 is advantageously made of pretensioned glass fibre, which makes the frame 14 strong, light and corrosion resistant. Alternatively, the frame 14 can be made of metal, preferably stainless steel. For sealing of the filter segment 13 against the filter support 4, the frame 14 is enclosed by a rubber strip, for instance of EPDM rubber. In order to facilitate insertion and removal of the filter segments 13 in the grooves 22, the outside of the rubber strip is flocked, which reduces friction against the filter support 11. The seal is to some extent also promoted by the filter segments 13, as the liquid A passes out through the filter cloth 4, being pressed outwards by the liquid pressure, so that the frame 14 is pressed against the outer boundary walls of the grooves 22, 23.

0042In the shown embodiment the filter cloth 4 which is expanded by the frame 14 is a microfilter cloth with filter holes in the range 10-100 µm. The filter cloth 4 is selected according to the filtering capacity that is required.

0043The inventive rotary disk filter can suitably be cleaned by means of a cleaning device of the type described in <patcit id="pcit0004" dnum="SE515001C"><text>SE-C-515,001</text></patcit> (<patcit id="pcit0005" dnum="WO0037159A"><text>WO 00/37159</text></patcit>).

0044It will be appreciated that many modifications of the embodiments of the invention described above are feasible within the scope of the invention, which is defined in the appended claims.

0045In the example shown, the modules 12 are mounted on a drum 2, the circumferential surface 6 of which has openings for the liquid to pass from the interior of the drum 2 to the filter segments 11. The light-weight modules 12 make it possible to select instead to make a skeleton for a drum and let the inner support portions 17 form the circumferential surface of the drum on the outside of the skeleton.

0046Instead of making the intermediate support portions 12 with a framework construction 18, they can be given a flat web in which holes are bored to provide liquid communication between the filter segments.