Liquid purification or separation – Filter – Movable medium
Reexamination Certificate
2000-07-28
2001-09-04
Lithgow, Thomas M. (Department: 1724)
Liquid purification or separation
Filter
Movable medium
C210S331000, C210S334000
Reexamination Certificate
active
06283306
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application is the national phase under 35 U.S.C §371 of PCT International Application No. PCT/SE99/00081 which has an International filing date of Jan. 20, 1999, which designated the United States of America.
The present invention concerns a rotating filter, said filter including at least two annular filter disks each having a plurality of filter elements and each being carried by a shaft for rotation therewith about an axis perpendicular to a respective central plane of the filter disks, said filter disks being partly submerged in a vessel adapted to contain to a certain level a liquid to be filtered, and said filter further including discharge chute means extending into a space between adjacent filter disks for discharging solids deposited on and removed from facing filtering means of said filter elements.
2. Description of Background Art
WO 94/25140 (U.S. Pat. No. 5,656,162) describes a filter where the filter elements are arranged at a relatively large distance from the shaft and have a relatively small radial extension, thereby giving the filter disks an annular appearance Therefore, a filter of this kind is referred to as a ring filter. In this prior art ring filter, the filtering means of two adjacent filter rings have a common scraper arranged radially outside the filter rings. The tip end of the scraper introduced between the filter rings is axially and radially guided by sliding in a U-shaped guide ring provided between the filter rings and rotating therewith. The scraper also has a substantially U-shaped cross section thereby to serve also as a chute for filter cake removed from the filtering means.
This prior art filter has proved to perform extremely well. However, in certain cases it has been found that, when increasing the radial height of the filter elements, the amount or volume of filter cake material deposited on the filter elements becomes so large that, after its removed from the elements, the material may not be properly discharged by the chute-like scraper running in the rotating, channel-shaped guide ring between two adjacent filter rings. Thus, it may happen that a portion of a filter cake starts to rotate and twist between the scraper and the filtering means (normally a filter cloth) of the filter element and to build up its dimension such that it eventually damages the filter cloth.
SUMMARY OF THE INVENTION
The present invention has its primary object to provide a rotating filter as initially stated, which allows a largely increased radial height of the filter sectors in comparison to those according to the prior art referred to.
However, large radial heights of filter elements are well known in the art per se, see for instance U.S. Pat. No. 3,331,512. This patent discloses filter elements in the shape of sectors having a substantial radial extension from a shaft having axially extending filtrate discharge channels therein. To receive filter cake removed from two adjacent filter disks, a chute is introduced into the space between these disks. The chute extends from a position substantially straight above and close to the shaft to a position exteriorly of the filter disks. In a zone relatively close to the shaft, the chute is defined by low side walls which substantially increase in height as the bottom of the chute steeply slopes towards the exterior of the disks, while the top edges of the side walls extend in a substantially horizontal direction to the exterior of the disks. This filter is evidently intended for handling substantial amounts of filter cake. However, the same problem as referred to above will no doubt fall upon this filter, and that because of the obvious risk that portions of filter cake removed may get pinched between and edge of the chute and a surface of a filter sector, and there start rotating and building up a considerable thickness leading to damage of filter cloth, filter sectors and/or chute, and thereby to shutdown.
It is also an object of the present invention, thus, to provide a rotating filter as initially stated which allows removal of substantial amounts of filter cake without any risks of portions thereof getting trapped between the discharge means (the chute) and a filter means of a filter sector.
According to the present invention, this is achieved in that the axial spacing between radially outer edge portion of a discharge chute located radially inside radially inner edge portions of facing filtering means of adjacent filter disks is not less than the axial spacing between said inner edge portions, and that the axial spacing between the radially outer edge portions of the discharge chute located radially outside said radially inner edge portions is not more than said axial spacing between said inner edge portions.
The term “axial” and “radial”, as well as forms derived therefrom, used herein to define directions etc., refer to the rotational axis of the shaft of the filter and directions perpendicular to, or substantially perpendicular to, such axial directions.
Suitably, each filter element is radially spaced from said shaft by spacing means such that said radially inner edge portions of facing filtering means of adjacent filter elements are radially spaced from the shaft, said spacing means having less axial extension than said radially inner edge portions thereby providing space for said radially outer edge portions of said discharge chute to be located at a larger mutual axial spacing than said axial spacing between said radially inner edge portions.
Advantageously, the spacing means comprise conduit means for discharge of filtrate from the filter elements to said shaft.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 2655265 (1953-10-01), Little
patent: 3096278 (1963-07-01), Francom
patent: 3331512 (1967-07-01), Vore
patent: 3471026 (1969-10-01), Riker
patent: 3591009 (1971-07-01), Luthi
patent: 4056473 (1977-11-01), Nilsson
patent: 4220537 (1980-09-01), Takahashi et al.
patent: A979131 (1951-04-01), None
patent: A1-9425140 (1994-11-01), None
Birch & Stewart Kolasch & Birch, LLP
Lithgow Thomas M.
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