Filter cloth arrangement in a rotating filter

Details Filter cloth arrangement in a rotating filter Filter cloth arrangement in a rotating filter

1992-11-18

1994-04-19

Sever, Frank

Liquid purification or separation

Plural distinct separators

Filters

210486, B01D 3323

Patent

active

053043049

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns a filter cloth device for rotating filters, said filter cloth being arranged outside a filter sector skeleton adapted to be carried by a filter rotor, and said filter cloth being provided with at least one bending resistant element extending through a pocket arranged in or on the filter cloth to restrain bulging of the filter cloth due to forces perpendicular to the plane of the filter cloth.
For filtering or screening in process industry there exist different kinds of rotating filters to separate solid particles from liquids, such as cellulose suspensions within the paper industry, either to thicken a suspension or to clean a liquid from particles. In a common kind of such filters a plurality of filter discs are mounted on a filter rotor, each filter disc comprising a plurality of annularly arranged filter sectors. Each filter sector comprises a skeleton outside which is arranged a screen cloth. The filter rotor is arranged partly submerged in a vessel. Screening can take place either from the vessel, which then includes suspension or the like, to the inner of each filter sector, as is the case in the filter according to for instance SE-B-7406315 (corresponding to U.S. Pat. No. 4,056,473), or, if the vessel is adapted to receive filtrate, from the inner of the filter sectors to the vessel, as is the case in the filter according to SE-A-9000557-0. In the latter kind of filter, which is used particularly when screening so called fines, i.e., very small particles, it is a problem that the screen cloth is subjected to large stresses due to internal pressure when a filter sector raises above the filtrate surface in the vessel and a large amount of unfiltered liquid is still present within the filter sector. Then the filter cloth tends to bulge out from the filter sector skeleton and to be stretched. Supporting ribs on the outside of the filter cloth attached to the filter skeleton, as suggested in FR-A-1 108 828, is one possible but practically unuseful solution to this problem, since the filter cloth from time to time must be changed. Another problem in this kind of filter is that spraying with water under high pressure takes place from the outside in order to remove particles deposited on the inside of the filter cloth, which leads to inward bulging of the filter cloth, which thereby may rupture. To some extent this problem may be remedied by ribs on the inside of the filter cloth attached to the filter skeleton, but still it can not be avoided that the filter cloth slides against these ribs and is subject to wear. Thus, a filter cloth must be permanently kept so tight that it cannot bulge in any direction. However, too much convexly curved surfaces which could facilitate keeping the cloth tightened result in a filter sector taking up too much room.
U.S. Pat. No. 4,578,192 describes a device for supporting a filter cloth against bulging when compressed air is introduced into a filter sector to remove a filter cake deposited on the outside of the filter cloth. This known device, referred to in the preamble, includes a U-shaped hair pin like clip having two bending resistant elements in the shape of extended legs integrated in the filter cloth and connected by a spacing means, the length of which corresponds to the thickness of the filter sector. In one embodiment, the two legs are introduced radially from the outside into pockets in the filter cloth on both sides of the filter sector. With necessity this must be done with both legs at the same time and in parallel, which in turn necessitates that the radially outer openings of the pockets are located exactly opposite to each other and that the pockets have the same radial direction. Further, the known device ensures adequate support against outwardly directed pressure only in the end where the spacing means keep the two legs together.
The object of the present invention is to provide a solution to the problems stated such that the filter cloth is supported against pressure influence in both directions but still is simple to chan

REFERENCES:
patent: 4056473 (1977-11-01), Nilsson
patent: 4578192 (1986-03-01), Muller

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