Principle Microbiology

ROTARY VACUUM-FILTERS

Large rotary vacuum filters are commonly used by industries which produce large volumes of liquid which need continuous processing.
The filter consists of a rotating, hollow, segmented drum covered with a fabric or metal filter which is partially immersed in a trough containing the broth to be filtered.
The slurry is fed on to the outside of the revolving drum and vacuum pressure is applied internally so that the filtrate is drawn through the filter, into the drum and finally to a collecting vessel.
The interior of the drum is divided into a series of compartments, to which the vacuum pressure is normally applied for most of each revolution as the drum slowly revolves (~ 1 rpm).
How ever, just before discharge of the filter cake, air pressure may be applied internally to help ease the filter cake off the drum.
A number of spray jets may he carefully positioned so that water can be applied to rinse the cake. This washing is carefully controlled so that dilutions of the filtrate is minimal.
It should be noted that the driving force for filtration (pressure differential across the filter) is limited to one atmosphere (100 kN per meter square) and in practice it is significantly less than this.
In contrast, pressure filter can be operated at many atmospheres pressure. A number of rotary vacuum drum filters are manufactured.
Which differ in the mechanism of cake discharge from the drum.

(1)String discharge.
(2)Scraper discharge.
(3)Scraper discharge with precoating of the drum.