Rotary Vacuum Drum Filter

Rotary vacuum drum filter (RVDF) is one of the earliest filters used in industrial liquid filtration requirements. The filter resembles a large drum on its side, half of which is submerged in the slurry, with the other half above it.


It is a continuous filter in which the solid constituent in a slurry or pulp is separated by a porous filter cloth or any other media, which is rotated through the pulp or slurry, with vacuum applied to the inner side of surface. It causes the solids to accumulate on the surface as a layer or coke through which the liquid is drawn.

The filter cloth wanders around the drum and as the drum rotates, the slurry is sucked into the cloth. Due to the rotation of drum out of the slurry, the cake is dried. This drying is caused due to the vacuum that is continuously being drawn through the cake in the disclosed section of the drum. At the end of the rotation cycle, at around a three o'clock position, the filter cake discharges and the process repeats itself. The filters may incorporate a drum cloth, which is caulked onto the drum itself, or they may make use of an endless belt that tracks off and discharges away from the drum.

How it works?
The process cycle of a rotary drum vacuum filter is continuous wherein each revolution consists of cake formation, cake washing, drying and the cake discharge.

As the drum rotates - partly submerged in the slurry - vacuum draws the liquid through the filter medium (cloth) on the drum surface that retains the solids. The vacuum pulls the gas (or air) through the cake and as the drum rotates, it continuously removes the liquid. If needed, the cake can be washed before the final drying and discharge. The air and the filtrate flows through the internal filtrate pipes, rotary valve and into a vacuum receiver wherein the liquid is separated from the stream of gas. Vacuum is generally formed by a liquid ring vacuum pump or a barometric leg.

Multiple receivers that are connected to the filter valve provide for the separation of mother liquor from the wash liquor, and the level of vacuum may vary at the cake forming and washing/drying zones.

Applications:
Some important applications of rotary vacuum drum filter include, uses in -

• Kaolin Clay
• Titanium Dioxide
• Alumina (Red mud)
• Pharmaceuticals
• Chemical Processing
• Food Processing (Starches)

It is very important to select a right cover media for the drum as it helps in maintaining the quality of filtration while taking care of the rigorous cleaning, which is done through scrapping. Polyester, nylon and polypropylene have proved to be good quality fabrics for filters.