A decanter centrifuge separates solids from one or two liquid phases in one single continuous process. This is done using centrifugal forces that can be well beyond 3000 times greater than gravity. When subject to such forces, the denser solid particles are pressed outwards against the rotating bowl wall, while the less dense liquid phase forms a concentric inner layer. Different dam plates are used to vary the depth of the liquid – the so-called pond – as required.
The sediment formed by the solid particles is continuously removed by the screw conveyor, which rotates at a different speed than the bowl. As a result, the solids are gradually “ploughed” out of the pond and up the conical “beach”. The centrifugal force compacts the solids and expels the surplus liquid. The dried solids then discharge from the bowl. The clarified liquid phase or phases overflow the dam plates situated at the opposite end of the bowl. Baffles within the centrifuge casing direct the separated phases into the correct flow path and prevent any risk of cross-contamination.
3-Phase Decanter Centrifuges
A variation of the above design allows for the continuous separation of the solids (sludge) as well as the separation of 2 liquid phases (oil & water). A decanter centrifuge of this configuration is known as a 3-phase decanter centrifuge. Though they allow for a one-step separation of oil, water & sludge, they have some inherent limitations due to their sensitivity to feed variation and lower g-force as compared to a 3-phase, hi-speed vertical centrifuge.