FILTER DEVICE

Abstract: A component member is provided in the form of a filter sector (1) which forms a part of a filter disc in a paper/pulp machine, which sector (1) comprises two perforated plates (2) arranged so as to have a space therebetween for forming a drainage channel for water/filtrate, the device being assembled with the aid of a framework, and where the plates (2) are made of an acid-proof material and fashioned as planar faces arranged substantially parallel to one another, and that between the plates (2) there is provided an inner plate (6) which is corrugated or ridged so that preferably parallel drainage channels (7) are formed between the plates (2) and the inner plate (6).

Description: FILTER DEVICE The present invention relates to a component member of the type disclosed in the preamble of patent claim 1 below. Filter discs are used in the manufacture of paper and/or wood pulp. These discs rotate so as to pass through a suspension of pulp. A mat that is deposited on the filter disc is formed under the effect of gravity, and cloudy filtrate is extracted. The main filtration then takes place under vacuum. As the filter sectors leave the suspension, the residual filtrate is quickly drained off from the filter sectors and air is sucked into the mat, which is thus dried. Once the drying is over, the vacuum is cut off and the pulp is removed from the discs, usually by flushing with water. SE Patent 465 658 discloses a filter sector for rotating filter discs of the type described above. The filter sector comprises two folded elements surrounded by an ordinary filter cloth of a plastic material as filter medium, so that filtrate conduits are formed. The filter sector consists of three sector portions through which filtrate flows in the filtrate conduits. The conduits are so arranged that they intersectingly overlap one another in the mid-sector portion, and between the overlapping conduits there is provided a flow connection for filtrate from both outer sector portions. WO 98/11972 discloses a similar filter sector, but in this case the filter medium is made of metal or plastic that is perforated. On the basis of a desire to increase the sector area, the medium is profiled so as to be ridged, and the filter medium itself forms the filtrate conduits. The known devices have a number of deficiencies and drawbacks. For example, their filtrate drainage capacity is relatively small, which reduces their efficiency. In the case of the SE device, the use of a filter cloth is a particularly weak point as regards wear. Generally, the presence of plastic in the paper or pulp manufacturing process is undesirable because of the need for frequent interruptions of operation in order to change the cloth. The formation of the filtrate conduits is relatively complex and it is questionable whether they serve their purpose optimally, as turbulent flow could occur. In the WO device the filter/filtrate plates are securely clamped in the framework of the sector element. During use, the filtration area will be exposed to great alternating forces and over time fatigue fractures may occur. The invention serves to provide a new and advantageous component member in the form of a filter sector which does away with the drawbacks of the known filter sectors, and this is achieved by the features that are disclosed in the characterising clause of patent claim 1. Further advantageous embodiments of the invention are set forth in the dependent patent claims. In the device according to the invention, the filter element/section is 100% acid- resistant, has no plastic sheeting as filter material, and interruptions of operation in order to change the cloth have been eliminated. The internally located corrugated or ridged plate which, together with the perforated external plates, forms internal liquid channels, provides complete support for these plates along their entire length. This gives a better distribution of the load during operation. Since the plates are not fixed in the framework, but are merely held in place thereby with the aid of suitable fastening means, the risk of fatigue fractures is obviated. The liquid channels form advantageous flow patterns which in most cases result in reduced turbulence in comparison with the known devices. In this way, the fast drainage of the filtrate between the perforated discs is enhanced as there are no obstacles in the direction of the liquid flow, the liquid channels are well-defined and the ridge section takes a large amount of the liquid. The filter sector may also be made in the form of a "cassette" with separate base and ridge. The design according to the invention permits extremely low internal volumes, which is an advantage with a view to emptying the sector prior to flushing away filtered-off material. The low internal volume, with little liquid in the sector, gives an optimum separation of the "cloudy" filtrate from the "clear" filtrate. The relatively large ridge section, which may be made having a cross-sectional profile for receiving a large liquid volume, forms a main channel for collecting and removing the liquid from the sector. In this way, water/filtrate is prevented from remaining in the sector and wetting the pulp that has been collected on the perforated plates. The flushing water used for removing filtered-off material is sprayed into the sector and thus does not rewet the filtered-off material. The flat perforated plates ensure an effective removal of filtered material, and the removal may also be carried out by means of scrapers as an alternative to spray nozzles. The internal corrugated or ridged plate may also be pierced or perforated in order to provide enhanced washing facilities under difficult operating conditions, such as scaling problems which are commonly occurring phenomena in return fibre applications in connection with hard water. The invention will now be described with reference to the drawing wherein: Fig. 1 is an elevation view of a component member according to the invention; Fig. 2 is a side view of the component member; and Fig, 3 shows a section taken along the line A-A in Fig. 1. The component member forms a filter sector, generally indicated by means of the reference numeral 1. When a plurality of such filter sectors 1 are assembled, e.g., as described below, a filter disc is obtained which can be incorporated in a paper or pulp making machine. This machine may be of a common type which involves, wter alia, the use of vacuum during production, and it will not be described in more detail. The filter sector 1 comprises two preferably parallel plates 2 made of a suitable acid- resistant material such as, e.g., stainless steel. An inner plate 6 is provided between these plates 2 and the sector is held together by suitable fasteners 11 , which may include drag bars, rivets, screws or the like, and the framework comprising a first and second ridge element, 3 and 4 respectively, and a peripheral element 10 and a sector base 8. The whole peripheral area is sealed in an appropriate manner, e.g., by means of preferably acid-resistant sections which may be bent and shaped to fit snugly on the outside of the perforated plates. The sector 1 may also in an appropriate manner be shaped as a "cassette" with a separate base and ridge. The plates 2 are made having perforations 5 in the form of holes or longitudinal slots or slits, or a combination of such perforations, having a suitable size and shape, so that the plates 2 act as filter elements, the pulp suspension being deposited on the plates in the form of a mat when the filter disc rotates so as to pass through the suspension. The inner plate 6 is corrugated or ridged in form, so that, together with the plates 2, it forms liquid channels 7. The channels 7 are preferably parallel and arranged at a suitable angle relative to a horizontal plane defined by the section line A-A in Fig. 1, so that most of the channels 7 flow into in the first ridge element 3. This element forms a drainage channel and is made having a cross-sectional profile which ensures necessary drainage capacity so that water does not remain in the sector and wet the material that has been collected on the plates 2. The plates 2 extend beyond the side wall of the sector 1 and are terminated a little below, for example, about 50 mm, the edge where the framework begins. This consists of acid-resistant plates and extends right down to the base for securing to a shaft 9. In this way, together with the ridge elements 3, 4 or extensions thereof, a "funnel" is formed which runs into a corresponding opening in the shaft 9. In addition to forming the liquid channels 7 and to separating the filtrate and water from spray nozzles in order to wet the pulp on the perforated plates 2, the plate 6 acts in such manner as to distribute and take up the forces acting on the plates 2. The plate 6, across parts of or the whole of its extent, may also be equipped with suitable perforations to provide enhanced washing facilities under difficult operating conditions, such as scaling problems. In order to produce a complete filter disc, the necessary number of filter sectors 1 (which will depend upon how great a part of the disc each sector covers) will be fastened together around the shaft 9 which has the same number of channels as the number of sectors. The sectors 1 are arranged ridge element 3 to ridge element 4, the elements 3, 4 being guided towards one another by means of suitable brackets and being fastened together with the aid of suitable fasteners such as, for example, bolts arranged in suitable positions, for example, at the outer periphery of the filter disc.

Claims: P a t e n t c l a i m s 1. A component member in the form of a filter sector (1) which forms a part of a filter disc in a paper/pulp machine, which sector (1) comprises two perforated plates (2) arranged so as to have a space therebetween for forming a drainage channel for water/filtrate, the device being assembled with the aid of a framework, characterised in that the plates (2) are made of an acid-resistant material and fashioned as planar faces arranged substantially parallel to one another, and that between the plates (2) there is provided an inner plate (6) which is corrugated or ridged so that preferably parallel drainage channels (7) are formed between the plates (2) and the inner plate (6). 2. The member according to claim 1, characterised in that the plates (2, 6) are fastened together with the aid of a first and second ridge element (3, 4), the first ridge element (3) being made having a cross-sectional profile so that the element (3) forms a drainage channel. 3. The member according to claim 1 or 2, characterised in that the inner plate (6) is so arranged that the channels (7) run at an angle relative to the horizontal plane (A-A) transverse to the sector and towards the ridge element (3) so that most of the channels (7) flow into said element. 4. The member according to one of claims 1-3, characterised in that the inner plate (6) is provided with perforations. 5. The member according to claim 4, characterised in that the filter sector (1) is made in the form of a cassette having a separate ridge and base. 6. The member according to one of claims 1-4, characterised in that the plate (6) provides a support for the plates (2), and the fastening of the plates (2, 6) in the framework is provided by suitable fasteners (11) such as drag rods, rivets, screws or the like, so that the fastening exhibits a certain flexibility in order to thereby avoid fatigue fractures as a consequence of mechanical load on the plates. 7. The member according to one of claims 1-6, characterised in that the perforations (5) in the plates (2) are shaped as round, oblong or oval holes or as slits. 8. The member according to one of claims 1-7, characterised in that the first ridge element (3) is made having a U-shape, a square shape or an appropriate oval shape in order to increase the drainage capacity. 9. The member according to one of claims 1-8, characterised in that the whole of or parts of the member are made of stainless steel. 10. The member according to one of claims 1-9, characterised in that the filter sectors (1) are put together in that the ridge elements (3, 4) on the respective sectors (1) are fastened together with the aid of suitable means such as, for example, bolts arranged in suitable positions, for example, along the outer periphery, the elements being guided towards one another with the aid of suitable brackets, so that a complete filter disc is formed.

Inventors: HOERLYK LARS, HOERLYK, LARS
Applicants: BANDAK AS, HOERLYK LARS, HOERLYK, LARS
Application year: 2000
Main classification: B01D33
IPC codes: B01D33