Medium-sized structures horizontal

Rotary Drum Filters The rotaiy drum filter is the most widely used of the continuous filters. There are many design variations, including operation as either a pressure filter or a vacuum filter. The major difference between designs is in the technique for cake discharge, to be discussed later. All the alternatives are characterized by a horizontal-axis drum covered on the cylindrical portion by filter medium over a grid support structure to allow drainage to manifolds. Basic materials of construc tion may be metals or plastics. Sizes (in terms of filter areas) range from 0.37 to 186 m (4 to 2000 ft ). 

The filter structure consists of a stack of plates attached to a hollow shaft which are mounted inside a pressure vessel with each plate covered with a suitable filter medium. The slurry is fed under pressure into the vessel and the cake, which is retained by the filter medium, forms on the top of each plate whilst the filtrate passes through the hollow shaft further to the process. Filter sizes may vary but generally the maximum is 60 m area and designed for a 6 bar operating pressure. Each circular plate in the stack is constructed with radial ribs that are welded to the bottom and support a horizontal coarse mesh screen which is covered with a finer woven metal screen or filter cloth to retain the cake. The bottom of the plate slopes towards the hollow central shaft which lets the filtrate flow freely through circumferential holes and further down the shaft to the filtrate outlet. The clearance between the plates is maintained by special spacers with "o" rings to positively seal between the slurry that surrounds the plates and the shaft that collects the filtrate. The height of the spacers determine the clearance for cake build-up and may be replaced to meet various process conditions. 

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