ROTATING FILTER WITH OUTER FILTRATE CONDUITS

Abstract: A disk filter including a plurality of rotatable, annular filter disks (3) arranged mutually spaced in an axial direction, and disposed for being partially immersed in a liquid or a suspension to be filtered. Each filter disk comprises a plurality of filter sections (4) which are in communication with axially directed filtrate conduits (2) arranged in the peripheries of the disks (3) for discharge of filtrate. The filtrate conduits (2) are provided with backwash barriers which are adapted to prevent liquid flow from the filtrate conduits radially inwards when the filter sections (4) rise above the liquid surface. The backwash barriers have been achieved by each filter section (4) being connected to an axial filtrate conduit in the form of a pipe (2), the main portion of the cross-section of the pipe at the place of attachment being located after each part of the filter section (4) as seen in the direction of rotation (A).

Description: ROTATING FILTER WITH OUTER FILTRATE CONDUITS The present invention relates to a disk filter including a plurality of rotatable, axially spaced annular filter disks adapted to partially immersed in a liquid or a suspension to be filtered, each disk comprising a plurality of filter sections being in communication with axially directed filtrate discharge conduits at the peripheries of the annular filter disks, said filtrate conduits being provided with backwash barriers adapted for preventing liquid flow from the filtrate conduits radially inwards when the fi1 ersections rise above the liquid surface. Λ filter of this kind is deπcribed, a . o . , in the Swediπh Pa ent Specif ca ion SE-C-8305Θ17-2 and the corresponding European and American Patent Specifications EP-B1-0160069 and US-A-4 634 529, respectively. According to this patent, the backwash barriers, i.e. barriers preventing re-wetting of a filter cake, such as dewatered fibres, deposited on the filter elements, extend from each filter element into associated axially directed conduits and comprise an extension of the trailing edge of the filter element as seen in the direction of rotation. It has been found that backwash barriers arranged in this way are relatively complicated to accomplish in practice. The object, of the present invention is consequently to provide a disk filter of the kind initially stated with backwash barriers which can be realized in a practically favourable fashion. This has been achieved by the invention having been given the distinguishing features disclosed in the following claims. The invention will now be described hereinafter with reference to the accompanying drawing, in which figure 1 is a partial cross-sec ion through a filter rotor, figure 2 is a detail to a larger scale of the filter rotor and figure 3 s a section along the line III-ITI in figure 1 to a further enlarged ncale. cross-section through a filter rotor, figure 2 is a detail to a larger scale of the filter rotor and figure 3 is a section along the line 11 I—1 I I in figure 1 to a further enlarged scale. A filter rotor for a rotating filter includes a plurality of axially spaced annular filter disk holders 1 and filtrate conduits 2 connecting them axially. Figure 1 is cross-section through such a filter rotor, which carries an annular filter disk 3 comprising a plurality of filter sections 4. All the filter sections of the filter are partially immersed in the liquid to be filtered which is received in a container 5. Extending through the central opening of the filter disks is a collecting trough 6 for solid material such as cellulose fibres, which are deposited on the filter sections during filtration and are caused to fall from the sections when the latter are above the trough. The illustrated filter sections are of the type including two mutually spaced carcass elements (not shown in detail) a d a filter cloth 7 kept spaced from the elements. The carcass elements are adapted for leading filtrate flowing through the filter cloth 7 to the space between the carcass elements. From this space the filtrate can flow through radial outlet openings 8 in the outer periphery of the filter section 4. The filter disk holder 1 has a substantially U-shaped cross-section with the opening 9 of the cross-section facing radially inwardly. In a manner not more closely illustrated, the filter sections 4 are mounted on the filter disk holder 1 so that their outlet openings 8 connect to the opening 9. The filtrate can thus flow from the interior of the filter sections 4 to the interior of the filter disk holders 1. The outlet openings 8 are preferably arranged only in the part of the periphery of the filter- sections 4 which is last ris.d above the liquid surface for rotation of the filter rotor in the direction indicated by the arrow A. The interior of the filter "• ■ disk holder 1 is suitably filled with a compound 10 in the portion which is located before the outlet openings 8 in the 5 direction of rotation. The filter holder 1 and the axially directed filtrate conduits 2 are connected to each other such that that the conduits 2, illustrated here as being circular pipes, extend uninterruptedly 10 for the whole of the axial direction through all the filter disk holders 1, while the latter, at least from the flow aspect, are interrupted at each axial filtrat conduit 2. More specifically, the arrangemen is such that the axial filtrate conduits 2 have openings 11 facing towards the direction of rotation A and are 15 formed to suit, the cross-sec ion of the filter disk holder 1 (figure 3) . The section of the filter holder 1 is tightly welded round these openings 11. The filter disk holder 1 is also welded to the opposite end of the filter conduits 2, where the tube wall is unbroken. Flow connection has thus been achieved by the 20 described arrangement from the interior of the filter sections 4 to the axial filtrate conduits 2. In accordance with the invention, and as will be clearly seen from the figures, the main part of the cross-section of the 25 filtrate conduits 2 is located after every other part of the associated filter section 4, reckoned in the direction of rotation A. This means that as long as the filtrate flows from a filter section, the. associated axial filtrate conduit 2 is located under the filter section and can receive and discharge 30 filtrate. Preferably, an imagined extension of the filtrate section trailing edge 12 in the direction of rotation A is a tangent to the associated axial filtrate conduit 2. This means, in 35 particular when the filter sections 4 have the illustrated oblige shape, that the openings 11 of the axial filtrate conduits 2 are above the bottoms of the conduits when the conduits 2 are in their uppermos position, i.e. the filtrate in the conduits 2 is effectively prevented from running back into the filter sections. For further improving the removal of filtrate through the conduits 2, a filter section 4 in one filter disk is displaced relative a filter section 4 in the next filter disk reckoned in the flow direction of the conduits 2, so that in the direction of rotation A the first mentioned filter section is in advance of the other filter section (not shown) . The filtrate conduit 2 to which these two filter elements are connected will thus slope downwards in the flow direction when the filter sections rise above the liquid level. In such a case it is also suitable that the radial filtrate conduits to which the axial filtrate conduits 2 are connected arid which lead to the filtrate discharge of the filter, slope downwards when the filter sections connected to the associated axial filtrate conduit 2 rise above the liquid surface (not shown) .

Claims: C L A I M S -" 1. A diε;k filter, including a plurality of rotatablo, axially spaced annular filter disks (3) adapted to be partially immersed 5 in a liquid or a suspension to be filtered, each disk comprising a plurality of filter sections (4) being in communication with axial filtrate discharge conduits (2) at the peripheries of the annular filter disks (3) , said conduits (2) being provided with backwash barriers adapted to prevent liquid flow from the 10 filtrate conduits radially inwards when the filter sections (4) rise above the liquid surface, c h a r a c t e r i z e i n that each filter section (4) is connected to an axial filtrate conduit in the form of a pipe (2) , the main portion of the cross-section of the pipe at its position of attachment being 15 after every other part of the filter section (4), reckoned in the direction of rotation (A ) . 2. A disk filter as claimed in claim 1, c h a r a c t e r i z e d in that an imagined extension of the 20 trailing edge (12) of the filter section (4) in the direction of rotation (A) is substantially tangential to the axial filtrate conduit ( 2 ) . 3. A disk filter as claimed in claim 1 or 2, 25 c h a r a c t e r i z e d i n that the filter section (4) is connected to an annular channel (1) which is partially open radially inwardly, said channel in turn being connected to the axially directed filtrate conduit (2) . 30 4. A disk filter as claimed in any one of the preceding claims, c h r a c t e r i z e d i n that a filter section (4) in one filter disk (3) is displaced relative a filter section (4) in the next filter disk reckoned in the flow direction of the axially directed filtrate conduits (2) , so that the first 35 mentioned filter section is in advance of the other filter section in the direction of rotation (A) , and so that the axially directed filtrate conduit (2) to which these two filter sections are connected slopes downwards in the flow direction when the two filter sections rise above the liquid surface. 5. A disk filter as claimed in claim 4 , wherein each axial filtrate conduit (2) being connected to a substantially radial filtrate conduit in the outlet end of the filter, c h a r a c t e r i z e d i n that each radial filtrate conduit also slopes downwards in the flow direction when the filter sections (4) connected to the associated axially directed filtrate conduit (2) rise above the liquid surface.

Inventors: NILSSON BJARNE, NILSSON, BJARNE
Applicants: NILSSON BJARNE, NILSSON, BJARNE
Application year: 1988
Main classification: B01D33
IPC codes: B01D33