WO1990007368A1

WO1990007368A1 - A device at rotating filters

Info

Publication number: WO1990007368A1
Application number: PCT/SE1988/000707
Authority: WO
Inventors: Bjarne Nilsson
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-06-12
Filing date: 1988-12-27
Publication date: 1990-07-12
Anticipated expiration: 1991-06-27
Also published as: SE8702468D0; SE8702468L; SE458174B

Abstract

A device for preventing re-wetting of thickened suspension in a filter of the type where a plurality of rotatable, axially spaced annular filter disks (3) are partially submerged in a container (1) for suspension, and where a collection trough (4) extends centrally through the filter disks (3) for collecting thickened suspension falling therefrom. Each filter disk comprises a plurality of filter sections (5) and each filter section is connected to a filtrate duct (7) situated at the circumference of the disk. At each filter disk (3) is arranged an arcuated channel (14) extending outside of the edges of the collection trough (4) such that filtrate flowing from a filter disk (3) is guided past the collection trough (4) and down into the suspension container (1).

Description

A DEVICE AT ROTATING FILTERS

The present invention relates to a device for preventing re-wetting of thickened suspension in a filter of the type where a plurality of rotatable, annular filter disks arranged axially one after the other are partially submerged in a container for the suspension, and where a collection trough centrally extends through the filter disks for collecting thickened suspension falling therefrom, each filter disk comprising a plurality of filter sections and each filter section being connected to a filtrate duct situated at the circumference of the disk.

In a filter of this type, a filtrate duct is connected to vacuum when the associated filter section moves under the suspension surface, as well as during a certain portion of its movement above the suspension surface, thereby to suck up excess liquid from the filter cake deposited on the filter section. In order that the. filter cake will loosen from the filter section this vacuum connection is inhibited when the section is in the area above the collection trough. An often prevailing problem occurs here, namely that filtrate, which has not yet had time to leave the filter section, runs out of the section and down into the collec- tion trough where it re-wets the relatively dry filter cake.

The object to the invention is to provide a device which simply and relyably removes the re-wetting problem described above. This has been achieved by the invention having been given the distinguishing features disclosed in the following claims .

The invention is described in the following with reference to the accompanying drawings, on which figure 1 is a schema- tic cross-section through a disk filter which is provided with a fixed device for preventing re-wetting according to the present invention, figure 2 is a section to a larger scale along the line II-II in figure 1, figure 3 is a cross- -section similar to the one in figure 1 through a disk filter which is provided with a device preventing re-wetting in accordance with the present invention, said device rota¬ ting with the disk filter, and figure 4 is a section to a larger scale along the line IV-IV in figure 3.

In figures 1 and 3 there is depicted a container 1 for suspension which is to be filtered, and the surface of the suspension is denoted by the numeral 2. A plurality of annular filter disks are partially submerged in the suspen- sion, these disks being mounted axially one after the other for rotation in the direction of the arrow A, one of the disks 3 being illustrated in the figures. A collection trough 4 extends through all the filter disks 3. The filter disk 3 comprises a plurality of filter sections 5, which are carried by an annular frame structure 6. Filtrate ducts 7 extend in an axial direction between all the filter disks 3 included in the filter. The ducts 7, which communicate with the interior of a filter section in each disk in a manner not more closely illustrated, are also in communication at one end of the filter with a means which establishes a subpressure in the filtrate ducts 7 according to a pre-de- termined program, when the associated filter sections are below the suspension surface 2, said means also maintaining the subpressure until the sections are in the area above the collection trough 4.

As will be seen from figures 2 and 4, the filter sections 5 in this example are of the type comprising two mutually spaced fluid tight layers 8 and 9 and a filter means spaced from these layers, e.g. in the form of a screening cloth 10. There are openings 11 in the fluid tight layers 8 and 9, so that liquid filtered through the screening cloth 10 can be sucked into the interior of the filter section, which is in communication with an axial filtrate duct 7. In the illu- ^♦ 5 strated example there is also an opening 12 in the radially inward end of the filter section 5.

Three filter sections are denoted by 5a, 5b and 5c in figures 1 and 3. In the rotational position assumed by the

10 section 5a there is still subpressure in the associated filtrate duct 7, and the filtrate can flow from the interior of the section 5a to the duct 7. Approximately in the posi¬ tion assumed by the section 5b, the subpressure ceases in the filtrate duct 7 and thereby in the interior of the

15 section 5b, whereafter, approximately in the position assu¬ med by section 5c the process of removing the filter cake deposited on the section is begun by spraying the filter cake with a water jet. As will be seen, the filtrate from the sections 5b and 5c can no longer reach the ducts 7, but

20 run radially inwardly in the respective section and leave the section to be received in the collection trough 4, where this filtrate undesirably causes re-wetting of the relative¬ ly dry product already there.

25 In order to prevent such re-wetting, according to the present invention there is provided a channel receiving filtrate flowing down from the sections 5, otherwise be collected in the collection trough 4, leading it past the collection trough and down into the container 1.

30

In figures 1 and 2" there is illustrated a first embodiment example of a device in accordance with the present inven¬ tion. In this embodiment an arcuate channel 14 is attached with the aid of struts between the edges of the collection 35 trough 4 and the inner circumference of the filter disk 3. The channel 14 suitably has a U-shaped cross-section with a bottom 15 and side walls 16 and 17. The side walls 16 and 17 preferably extend with a space between them and the filter cloth 10 upwards a distance along the sides of the sections 5, as illustrated in figure 2. The ends of the channel 14 terminate outside the edges of the collection trough 4, so that filtrate flowing in the channel is guided outside the trough 4 and down into the container 1.

In figures 3 and 4 there is illustrated an embodiment of the invention in which an annular channel 14' is arranged inside each filter disk 3 for rotation with the disk. The side walls 16' and 17' of the channel 14 have been bent inwards so that the channel engages against the section 5, as illu- strated in figure 4. The bending can be arranged such that the side walls keep the channel to the sections by spring action. Alternatively, non-illustrated struts can attach the channel 14' to the frame structure 6 and/or to the filtrate ducts 7.

As will be seen, both the arcuate channel 14 according to figure 1 and the annular channel 14' according to figure 3 are concentric with the filter disk 3. Although it is pre¬ ferred to permit the annular channel 14' to rotate with the filter disk 3, it can also be conceived as being ridgedly attached, similar to the arcuate channel 14. However, in the rotating case there is achieved the advantage that the channel is continuously flushed during passage through the suspension.

The annular channel 14' according to figure 3 can advan¬ tageously be made up from arcuate, mutually assemblable and separately removable sections, each including an angel of, for example, 180°, 120°, 90° or less. Hereby the exchange of individual filter sections 5 is facilitated. If the free edges of the side walls 16 and 17 or 16' and 17' are folded over, it is suitable that this folding is done inwardly according to figure 3, so that on the outside are no sharp edges on which fibres and the like can catch.

As will be clear from the above description the invention solves in a simple way the re-wetting problem mentioned in the introduction, by catching filtrate flowing from the sections of a filter disk and leading the filtrate outside the collection trough down into the suspension container.

Claims

C L I M S

1. A device for preventing re-wetting of thickened suspension in a filter of the type where a plurality of rotatably axially spaced annular filter disks (3) are partially submerged in a container (1) for the suspension, and where a collection trough <4) extends centrally through the filter disks (3) for collecting thickened suspension falling therefrom, each filter disk comprising a plurality of filter sections (5) and each filter section being connected to a filtrate duct C7> situated at the circum¬ ference of the disk, c h a r a c t e r i z e d i n that at each filter disk is arranged an arcuate channel 14;14'> substantially conforming to the inner circumference of the filter disk

(3), the chord of the channel being at least equal to the width of the collection trough (4).

2. A device as claimed in claim 1, c h a r a c t e r i z e d i n that the channel (14,14') has an arcuate shape and is concentric with a filter disk (3) .

3. A device as claimed in claim 1 or 2, c h a r a c t e r i z e d i n that the channel (14,14') has a width exceeding the thickness of a filter disk (3) at the inner circum erence thereof.

4. A device as claimed in claim 1, 2 or 3, c h a r a c t e r i z e d i n that the channel (14,14') has side walls (16,17) extending upwards along a portion of the sides of a filter disk (3) close to the inner circum¬ ference thereof.

5. A device as claimed in anyone of the preceding claims, c h a r a c t e r i z e d i n that the channel (14,14') is rigidly mounted on the carcass of the filter such as to be immovable relative to a filter disk (3).

6. A device as claimed in claim 5, c h a r a c t e r i z e d i n that the channel is fixed in the collection trough (4) .

7. A device as claimed in anyone of claims 1-4, the channel

(14') being annular, c h a r a c t e r i z e d i n that the channel (14') is rotatable with a filter disk (3) .

8. A device as claimed in claim 7, c h a r a c t e r i z e d i n that the side walls (16,17) of the channel (14') press against the sides of a filter disk (3) .

9. A device as claimed in claim 7, c h a r a c t e r i z e d i n that the channel (14') is mounted in a frame structure (6,7) or the like, carrying a filter disk (3) .

10. A device as claimed in claim 7, 8 or 9, c h a r a c t e r i z e d i n that the channel (14') is manufactured in assemblable arcuate sections.