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REMOVAL AND RENEWAL OF A PRECOAT ON A DISC FILTER

IP.com Disclosure Number: IPCOM000126186D
Publication Date: 2005-Jul-06
Document File: 5 page(s) / 39K

Publishing Venue

The IP.com Prior Art Database

Related People

Colin Beer: INVENTOR

Abstract

The present invention relates to disc-type filters having a layer of precoat thereon, and more particularly, to the washing and renewal of the precoat layer. The invention also relates to a method of cleaning the filter media or wire surfaces of such filters. The method and apparatus according to the invention are especially suitable for continuously renewing the precoat layer and/or washing the wire surfaces.

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REMOVAL AND RENEWAL OF A PRECOAT ON A DISC FILTER

The present invention relates to disc-type filters having a layer of precoat thereon, and more particularly, to the washing and renewal of the precoat layer. The invention also relates to a method of cleaning the filter media or wire surfaces of such filters. The method and apparatus according to the invention are especially suitable for continuously renewing the precoat layer and/or washing the wire surfaces.

In the precoat technique a suspension is filtered through a cake of material previously laid on the discs of the filter. If lime mud is being filtered and removed from a liquid, lime mud is typically also used as the precoat material. The surface layer of the precoat gets clogged while the filtering proceeds and must be removed from time to time. The techni­que normally used is to move the automatic scraper gradually inwards following a predetermined program, thus removing the clogged surface layer. After the scraper has moved in several steps closer to the disc or drum the rest of the precoat is removed and a new precoat is formed.

The arrangement disclosed in US patent no. 5,149,448 reduces the disadvan­ta­ges and problems of the known techniques described above by removing a strip at a time from the filtering layer by means of a liquid jet reciprocating continuously in the longitu­dinal direction of the drum. This has been effected by installing one nozzle or several nozzles under the scraper, continuously reciprocating in the longitu­dinal direction of the drum. The high-pressure nozzles, for example two in number, have been provided under the scraper so that the purpose of one of the nozzles is to break the precoat layer and to drop it to the filter vat after which the second nozzle is used to wash the filter cloth clean. The pressure of the water sprayed from the washing nozzles is approx. 50 - 100 bar which gives a very good cleaning result. The nozzle disperses the jets so that the precoat is removed and the wire washed from a strip of approx. 10 - 50 mm in width at a time.

Most usually, the filter discs rotate in atmospheric pressure, whereby the pressure difference needed for the filtering is formed by means of a suitable vacuum source, such as drop leg, vacuum pump or a centrifugal pump, inside the discs formed by sectors. Nevertheless, it is also possible to pressurize the whole filter, whereby the discs would be surrounded by elevated pressure. The partial vacuum, or more generally, the pressure difference causes a solid lime mud layer to begin to form on the wire-coated surfaces of the sectors. Scrapers have been arranged at a pre-determined distance from the surface of the wire on both sides of each of the filter discs so as to scrape the thickened lime mud layer from the precoat layer when the thickened layer has increased sufficiently in thickness.

As is known, the surface layer of the precoat becomes clogged while the filtering proceeds, and must be removed from ti...