Rotary drum vacuum filter is a very important tool for solid-liquid separation; it has various applications in the industrial field. The main advantage of this equipment is its relatively small space, low cost and easy to be maintained. All Rotary Vacuum Filters operate on a similar principle. A pressure differential between the surface and inside of the drum (or disc) is applied by means of vacuum.
This pressure differential cause’s transport of liquid through the filtration surface while the filter medium arrests solid particles and a cake is formed. As the drum rotates, the cake rises above the slurry level in the filter tank and air is drawn through the cake, forcing out liquid. The liquid (filtrate) exits the filter through the internal piping and the vacuum head.
It is consisting on a sheet metal drum. The diameter of drum ranges from 1 to 10 feet. This drum is carried on moving system. A vacuum system is also attached, so that, during filtration whole drum work under vacuum. The surface of the drum is the divided into different section by stripes.
i- Cake formation zone
ii- Washing zone
iii- Drying zone
iv- Cake removal zone
These steps are parallel to the axis of drum and welded to the shell. Filter medium is hold by metal strips on drum and covered by filter cloth.
In each section there are many pipes which open inside the cover plates. The side cover plate. There is also a stationary valve plate through which connection are made to the filtrate receiver. For compressed air and wash water connection vale are also given.
After washing, to remove the cake “Doctor knife” is provided. Doctor knife remove only the cake of from septum and does not damage the pre-coated layer of filter aid.
Before filtration rotary drum filter is dip in tank of filter aid for pre-coating purpose. Commonly is pre-coated up 3” to 5” by diatomaceous earth, perlite or purified wood cellulose.
After that drum is rotated in slurry tank at a speed of 1 to 2 rpm. 1/3 of drum is dip in slurry tank, vacuum is applied through a valve and filtration is started.
A layer solid builds in the form of cake on the surface of panel (filter cloth) in cake formation zone and filtrate pass through pipes and goes to vacuum receiver and collected in tank.
As, the panel leave the cake formation zone it enters to washing zone and in which water is sprayed on cake to extract all filtrate from cake and it sent to wash vacuum receiver. And panel enters to drying zone. In this section high vacuum is applied and all filtrate is sucked and cake is obtained in completely dried form.
Now this panel is moved to cake removal zone in which doctor knife remove dried cake from filter cloth without damaging the filter cloth. After that this panel again enter to cake formation zone for continuous filtration and cycle is repeated.
These filter are developed to overcome large problem of filter press and leaf filter. It is very versatile filter.
It is used generally for those operation in which the volume is very large, where process is continuous and where is labor cost must be kept downs. It is used where colloidal particles.
It is used for production of wallboard from gypsum.
It cannot be used for mixture of colloidal and coarse particles.