Method and apparatus for thickening lime mud with a disc filter

A method of thickening lime sludge utilizing a disc filter assembly comprising a plurality of disc filters, which disc filters rotate about a substantially horizontal axis into contact with lime sludge in a trough surrounding the disc filters, the disc filters each having wire surfaces extending substantially perpendicular to the axis of rotation, said method comprising the steps of:

• (a) rotating the disc filter assembly about the axis of rotation so that the wire surfaces of the disc filters come into contact with lime sludge in the trough and then move out of the trough so that a precoat filter layer is formed on the wire surfaces and a dried layer of lime sludge collects on the precoat layer;
• (b) scraping the dried layer of lime sludge from the precoat layers on the disc filter wire surfaces;
• and
• (c) without interrupting steps (a) and (b), at spaced points in time substantially removing the precoat layer from a wire surfaces by directing one or more high pressure jets of liquid at the precoat layer on the wire surface after scraping of the dried layer of lime sludge from the precoat layer.