Rotary Vacuum Drum Filter

RVDF and its purpose

Rotary Vacuum Drum Filter is a type of filtration device used for separating solids from liquids in various industrial processes. It functions on the principle of filtering the slurry through a sieve-like mechanism on a rotating drum surface, under the condition of vacuum. Normally, 30-50% portion of the drum is submerged in the slurry depending on the process. A pendulum type swinging agitator in the Vat keeps the slurry thoroughly mixed.

The main purpose of RVDF is to filter the slurry which may contain relatively high percentage of suspended solids (10-25%). Dischargeable cake may have thickness from to 5-30 mm depending on slurry characteristics. The sludge cake so formed may be a waste, by product or a recovered material from the process.

Types of RVDF

Scrapper Discharge – For Filters using Air Blow to loosen cake and use Rigid adjustable Scrapper blade to remove the cake. Normally, Scrapper has positive clearance setting between Drum and Scrapper tip. Also, there can be floating scrapper blade which is spring loaded to permit the blade to follow the contour of the inflated media.
Precoat Drum Filter – Used in conjunction with a precoat filter media, the precoat scrapper has knife edge sharpness that allows it to move against the precoat layer with micrometre accuracy. The scrapper is equipped with safety limit switch that actuates the alarm and stops the scrapper advancing mechanism when the precoat layer is reduced to predetermined level. Precoat layer of around 50-100 mm is quite common in the industries.
Belt Discharge Filter – Used when a dry cake is determined from materials having special discharge and cloth blinding problems, the Belt discharge consists of complete roller assembly i.e. Crowned discharge roll, return and guide rolls along with wash and scrapper mechanism for cleaning of belt.
String Discharge Drum Filter – The String Discharge consists of a number of uniformly spaced strings which are carried completely around the filter drum and over the discharge and return rollers. It is ideally suited for removal of filter cakes that are to be thermally dried. As the cake leaves the string it breaks into small pieces providing more surface area for contact with drier belt.
Wire Discharge – Consisting of a single or double strand of wire stretched across the face of the drum, the wire discharge is provided where cake is sticky and difficult to discharge. The cake is lifted from the drum, thus avoiding smearing.
Roller Discharge – Normally, where thin (1-5 mm) but highly adhesive cakes are formed, a Roller Discharge type filter may be used. Roll is driven floating type and has a smooth or serrated surface to promote adherence of cake. As the vacuum in the drum is released, the cake adheres to the roll and it is discharged by a scrapper blade resting against the roll.