Description of Dissolved Air Flotation Unit
(Circular) Description Introduction
Paramount designs & manufacturers the circular DAF
systems in technical collaboration with M/s.Esmil Process Systems Limited,
Effluent dosed with Alum/Polyelectrolyte from flocculation tank is fed into
coagulation tube (feed well) situated at the centre of DAF unit. Coagulation
tube is a vertical cylinder suspended in the centre of the tank where the
flocculated effluent enters tangentially to ensure intimate mixing of the
flocculated solids with the micro bubbles which are generated due to depressurisation
of recycled effluent (which is also fed tangentially).
When the mixture of air & solid reach top of coagulation tube, the centrifugal
force tends to throw air/solids horizontally towards periphery of the tank & move
upwards & outwards to form a blanket of skimming (froth). This accumulated
skimming which floats on the top is continuously scraped from the surface
by the scraper arm into the scum box.
DAF separation principle is based on the fact that air is soluble is
liquid in direct proportion to the pressure applied. The treated effluent
to the saturation vessel by means of high pressure recycle pump where
plant air is injected which ensures saturation of this liquid with air.
saturated liquid is depressurised through a valve located on the discharge
the saturation vessel. Which is connected to the coagulation tube. When
the pressure is released the air dissolved under pressure comes out of
in the form of minute bubbles. These minute bubbles get attached to the
flocculated effluent & thus forming solids with combined specific
gravity less than the effluent, which finally floats to the surface.