How are filter cakes washed and removed from a rotating vacuum drum?

In a rotary-drum vacuum filter, the process of handling the filter cake—the solid mass retained by the filter medium—is integrated into the continuous rotation of the drum.12

As the cylindrical drum rotates and is partially submerged in a trough of slurry, a partial vacuum inside the drum draws the filtrate through the filter medium, depositing the solids as a cake on the drum's surface. Once the cake has formed and emerged from the slurry, it can be sprayed with wash water to remove impurities. Finally, the washed cake is typically removed from the drum's surface using scrapers.1

In specific variations of this equipment, such as designs where the slurry is fed to the top of the drum, the cake may be dried by a hood supplied with hot air before being scraped off the bottom into a hopper. For particularly slimy or difficult solids, a precoat of filter aid may be used, where the filter cake and a thin layer of the precoat are continuously cut from the drum bed to maintain a clean surface.13