Importance

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Abstract

A method and apparatus to clean a filter drum used for thickening lime mud. The drum is rotated about a horizontal axis in a first direction so that the circumferential surface of the drum moves into contact with lime mud in a vat and a precoat layer formed on the drum, as well as an external layer of lime mud which forms a thickened lime mud cake when a vacuum is applied to the drum withdrawing liquid from the lime mud. The thickened external layer of lime mud cake is scraped from the drum at a second side of the vat, and at a first opposite side of the vat a first jet of liquid is directed onto the drum surface (e.g. at a pressure of about 30-100 bar) to remove a strip of the precoat layer, a third jet of liquid cleans the drum after removal of the precoat layer, and a second jet of liquid is directed onto the drum with sufficient intensity (e.g. a pressure of about 2-20 bar) to remove, by spreading and partially detaching, a strip from the thickened lime mud cake. Typically the second jet is operated substantially continuously, except when the first and third jets are operated, the first and third jets being operated at spaced time intervals (e.g. periodically or intermittently). The invention results in partial removal of the precoat with a gentle liquid jet, easy removal of the entire precoat layer because the precoat is not yet hardened at its location of movement, intermittent use of high pressure jets which extends the life of the high pressure apparatus in the wire forming the drum, and optimum ease of installation and maintenance of the spray nozzles.

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First Claim