Vacuum Filters

As the drum rotates - partially submerged in the slurry - vacuum draws the liquid through the filter medium (cloth) on the drum surface which retains the solids. The vacuum pulls air (or gas) through the cake and continues to remove liquid as the drum rotates. If required, the cake can be washed prior to final drying...and discharge.  The filtrate and air flow through the internal filtrate pipes, through the rotary valve and into a vacuum receiver where the liquid is separated from the gas stream. Vacuum is normally developed by a liquid ring vacuum pump or barometric leg.  Multiple receivers connected to the filter valve allow for the separation of mother liquor from the wash liquor, and vacuum levels can be varied at the cake forming and washing/drying zones.  The units also are available as vapor retaining or vapor tight unit.  Here is a vapor tight unit:

As the drum rotates - partially submerged in the slurry - vacuum draws the liquid through the filter medium (cloth) on the drum surface which retains the solids. The vacuum pulls air (or gas) through the cake and continues to remove liquid as the drum rotates. If required, the cake can be washed prior to final drying...and discharge.  The filtrate and air flow through the internal filtrate pipes, through the rotary valve and into a vacuum receiver where the liquid is separated from the gas stream. Vacuum is normally developed by a liquid ring vacuum pump or barometric leg.  Multiple receivers connected to the filter valve allow for the separation of mother liquor from the wash liquor, and vacuum levels can be varied at the cake forming and washing/drying zones.  The units also are available as vapor retaining or vapor tight unit.  Here is a vapor tight unit:

The process cycle of the RDVF is continuous. Each revolution consists of:
 
1.  Cake Formation - during the time period the drum is submerged in the vat
2.  Cake Filtration - during the time period right after the drum exits the liquid
3.  Cake Washing (if required) - typically near the top of the drum
4.  Cake Dewatering/Drying - right after cake filtration (or washing, if required)
5.  Cake Discharge - right before the drum enters the liquid again

A rotary drum vacuum filter (RDVF) is a continuous filter.  The solids to be collected, whether in a pulp or slurry, are separated by a porous filter cloth or other media rotated through the pulp or slurry, with vacuum applied to the inner surface to cause the solids to accumulate on the surface as a cake or layer, through which the liquid is drawn.

CESCO offers a few different vacuum filter designs.  In general, vacuum filters are suitable for use with fast-filtering materials.  In addition, with the use of precoat filter aid, the precoat rotary drum vacuum filter is often used for sticky/oily hard to filter waste streams where it is important to have a fresh filter surface for each drum rotation.