Procedure for separating finely divided matter from a suspension by filtering

Claim 1

Improvement in a method of separating finely divided matter from a suspension by filtration in a periodically operated pressure filter unit including a filter tank having a roof, a filtrate collecting tank located above the filter tank, a plurality of filtering elements extending downwardly from the roof to the filter tank and the interior of the filtering elements communicating with the filtrate collecting tank, comprising the steps of introducing a lime sludge (or CaCO 3 ) into the filter tank, flowing the lime sludge under pressure through the filtering elements for depositing large-grain lime sludge on the exterior surface of the filtering elements within the filter tank while filtrate flows through the filtering elements into the filtrate collecting tank, flowing a green liquor containing sediment into the filter tank and passing the green liquor through the lime sludge layer on the exterior surface of the filtering elements and filtering the sediment in the green liquor on the lime sludge with the filtrate passing through the filtering elements into the filtrate collecting tank.