The Decanter centrifuge is the only sedimentation centrifuge designed from the start to handle significant solid concentration in the feed suspension. At the same time it can achieve quite good degrees of clarification of the liquid concentrate. Although a complicated piece of machinery it embodies a simple principle. They consist basically of a horizontal cylindrical bowl (1) rotating at a high speed, with a helical extraction screw (2) placed coaxially. The screw perfectly fits the internal contour of the bowl, only allowing clearance between the bowl and the scroll. The differential speed between screw and scroll provides the conveying motion to collect and remove the solids, which accumulate at the bowl wall.

The decanter operates mainly by sedimentation a process causing the separation of suspended solids by virtue of their higher density than the liquid in which they are suspended. If the density difference is high than gravity may provide sufficient driving force for the separation to occur in a reasonable time. If the density difference is small, or the particle size is very small, than gravity separation would take too long and the separation force must be increased by the imposition of centrifugal forces many times that of gravity alone.

1. Cylindroconical bowl
2. Helical extraction screw (scroll)
3. Feed
4. Distributor
5. Ring space
6. Settled product
7. Liquid level
8. Drying zone
9. Clarified liquid
10. Adjustable tresholds