Apparatus for cleaning a filter cloth in a filtering device

Details Apparatus for cleaning a filter cloth in a filtering device Apparatus for cleaning a filter cloth in a filtering device

2001-09-24

2003-07-22

Prince, Fred (Department: 1723)

Liquid purification or separation

Plural distinct separators

Filters

C210S327000, C210S330000, C210S333010, C210S391000, C210S403000

Reexamination Certificate

active

06596166

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an apparatus for cleaning a filter cloth in a filtering device.
BACKGROUND ART
Filtering devices of the type stated by way of introduction are used especially for filtering of particles from liquids.
Two variants of filtering devices of this type are predominant on the market.
The one variant is in technical language called rotary disc filter and is described, for example, in the brochure “Skivfilter” (in English: Rotary Disc Filter) issued by the Applicant (Hydrotech, 1996). The brochure, p. 2, shows in a perspective view the principle of such a rotary disc filter, see FIG.
1
. The rotary disc filter
10
comprises a horizontal, slowly rotating drum
11
, which supports a number of parallel, disc-shaped filter elements
12
which are successively arranged in spaced-apart relationship along the centre axis of the drum and which extend radially away from the drum
11
. The filter elements
12
have on their opposite lateral surfaces relatively large openings which are covered with a filter cloth
13
. The drum
11
has a number of openings through which the liquid A which is to be filtered can flow to the interior of the filter elements
12
. The filtering liquid A is conducted through an inlet into the drum
11
and then falls down to the interior of the disc-shaped elements
12
, from which the liquid A continues out through the filter cloth
13
so that the particles which are to be fiitered off adhere to the inside of the filter cloth
13
. For cleaning of the filter cloth
13
, the disc filter
10
is provided with spray nozzles
14
which are mounted on a number of fixed flush tubes
15
, which extend between the disc-shaped filter elements
12
. The flush tubes
15
are adapted to conduct flushing liquid to the spray nozzles
14
and are connected to an elongate liquid-conducting pipe
16
which extends parallel with the centre axis of the drum
11
. The spray nozzles
14
spray the filter cloth
13
axially from the outside, in a direction opposite to the filtering direction, and the flushed-away particles are collected in a discharge trough
17
which is placed inside the drum
11
in the upper portion thereof.
The other variant is in technical language called drum filter and described, for example, in the brochure “Trumfilter” (in English: Drum Filter) issued by the Applicant (Hydrotech, 1996). The brochure, p. 2, shows in a perspective view the principle of such a drum filter. See
FIG. 2
where the drum
21
has been cut open to be able to show the flushing equipment arranged outside the drum
21
. Thus the drum filter
20
comprises a horizontal, slowly rotating drum
21
, whose circumferential surface has relatively large openings which are covered with a filter cloth
22
. The liquid A that is to be filtered is passed into the drum
21
and is filtered as it falls downwards through the filter cloth
22
and out of the drum
21
. To avoid clogging of the filter cloth
22
on the rotating drum
21
, this is flushed clean with the aid of fixedly mounted spray nozzles
23
which are placed on the outside of the drum
21
and above the liquid level inside the drum
21
. The flushing is carried out radially inwards in a direction opposite to the filtering direction. The dirt which is flushed away from the cloth
22
inwards in the drum
21
reaches a discharge trough
24
which is placed inside the drum
21
just above its centre axis and which draws off the dirt.
The reverse flushing or cleaning can in both cases occur with a rotating or stationary drum, and the flushing may occur continuously or intermittently.
A problem which is common to these filtering devices is that the filter cloth has a tendency to clog in spite of the particular spray nozzles which flush the filter cloth in a direction opposite to the filtering direction. Clogging of the filter cloth deteriorates the efficiency or degree of efficiency of the filtering device.
Moreover the filter cloth of both variants has a tendency to be “striped” owing to irregular cleaning, which is a sign of the filter cloth not being sufficiently cleaned in certain portions.
The above drawbacks in turn result in the filter cloth needing be replaced too frequently.
For satisfactory cleaning of the filter cloth, a plurality of spray nozzles must according to the prior art solutions be arranged extremely close together, which means that the filtering device is rendered expensive.
SUMMARY OF THE INVENTION
An object of the present invention is suggest a solution to the above problems by providing an improved apparatus for cleaning a filter cloth in a filtering device.
The cleaning apparatus according to the invention comprises a driving device for providing a reciprocating motion of the spray nozzles. The reciprocating motion allows each spray nozzle to clean a larger portion of the filter cloth, which results in more efficient cleaning. Besides, the number of spray nozzles can be reduced.
The driving device has a coupling which is adapted to transform the rotary motion of the drum into the reciprocating motion of the spray nozzles. The coupling has such a gear ratio that the rotary motion of the drum and the reciprocating motion of the spray nozzles are out of phase with each other. By these two motions not occurring in step or phase with each other, it is avoided that a certain spray nozzle flushes the same parts of the filter cloth revolution after revolution. This means that each portion of the filter cloth is once now and then subjected to direct flushing by a spray nozzle. If the motions had occurred in phase, the above-described “striped” condition of the filter cloth would only have been converted into curved lines instead, thus causing incomplete cleaning.
The reciprocating motion of the spray nozzles preferably has a motion vector component, which is in a plane parallel to that portion of the filter cloth which in a certain rotational position is flushed and which is directed perpendicular to the direction of motion of said filter cloth portion. By the filter cloth moving in one direction and the spray nozzles at least partially moving in a direction perpendicular thereto, all portions of the filter cloth can be reached by a flushing jet from a spray nozzle.
The spray nozzles are advantageously arranged on a flush tube which is adapted to conduct the cleaning liquid to all spray nozzles. This solution makes the construction compact and robust.
According to a first aspect of the invention, the filtering device further comprises at least one disc-shaped filter element, whose normal direction is parallel and essentially concentric with the centre axis of the drum. The filter element extends radially away from and round the drum. The filter cloth is supported on at least one of the lateral surfaces of the disc-shaped filter element. The cleaning apparatus according to this first aspect advantageously comprises a flushing, ramp which is pivotable about a pivot axis, which is parallel with the centre axis of the drum. The pivotability of the flushing ramp gives the spray nozzles a reciprocating rocking motion, which results in more efficient cleaning of the filter cloth and, thus, an improved degree of efficiency of the filtering device.
According to a preferred embodiment of this aspect, the flushing ramp has flush tubes each supporting at least one spray nozzle. The flush tubes are intended to conduct the cleaning liquid to the spray nozzles. Thanks to the rocking motion of the flushing ramp, a spray nozzle supported on a flush tube is given a reciprocating motion on the one hand in the radial direction and, on the other hand, in the tangential direction, thus allowing all portions of the filter cloth to be reached by a spray nozzle.
For utilisation of the limited space between the disc-shaped elements, the flush tube is preferably arranged in a plane which is essentially parallel with the lateral surface of the filter element.
The flush tube has such a radial extent as to extend along essentially the entire portion of the lateral surface of the disc-shaped eleme

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