Conventional Circular Thickener is simple but can be very large. The conventional thickener has a central feed well for introducing the feed slurry.
The top of the thickener acts as a clarifier and the clarified liquid overflows a peripheral weir at the top.
A rake in the bottom consolidates the thickened solids and moves them towards a central outlet where they are pumped out.
The floor usually has a shallow slope towards the outlet but some thickeners have flat bottom. Conventional thickeners may be operated with or without flocculants. Gravity thickener have a long residence time so take up large area.
However, the long residence time means that they can accept short term fluctuation in the feed slurry and the discharge of the underflow does not have to be continuous.
Feed suspensions to thickeners typically contains 5 to 20 % solids and the underflow may contain to 20 to 60 % solids.
Other design such as the high rate thickener, the tray thickener and the lamella thickener have been developed to reduce the size of the equipment.