The basic decanter

Although a complicated piece of machinery, the decanter centrifuge embodies a simple principle, that of the screw conveyor. In basic terms, the decanter comprises a solid cylindrical bowl, rotating at high speed. Inside the bowl is a scroll (screw conveyor) rotating at a slightly different speed. The differential speed between bowl and scroll provides the conveying motion to collect and remove the solids, which accumulate at the bowl wall. 

A slurry of liquid and suspended solids is fed along the centre line, to some fixed position within the bowl, and is accelerated outwards to join the pond of liquid held on the bowl wall by the centrifugal force. This same force then causes the suspended solids to settle, and accumulate at the bowl wall. The clarified liquid then flows along the bowl, to leave at one end of it, over some kind of weir design, which sets the level of the liquid surface in the bowl. 

The other end of the bowl is sloped inwards, towards the centre, thus providing a beach, up which the solids are conveyed, to be discharged from the bowl, at the top of the beach. Whilst the solids are conveyed up the beach, some, hopefully most, of the entrained liquid drains back into the pond, to join the liquid flow towards the far end. 

The scroll usually is carried on a hollow axial hub, through which the slurry feed tube passes to the feed zone. The diameter, the number, and the pitch of the conveyor flights are chosen to match the needs of the slurry being treated — as are the depth of the pond, the length of the bowl, the conveyor differential speed, and the angle of slope of the beach. 

Most decanters operate with their axis horizontal, in which case they usually are mounted in substantial bearings at each end of the bowl. Vertical 

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The basic decanter is completed with a drive motor, usually electrical, and a gearbox, which controls the differential speed of the conveyor. 

The wastes produced in manufacturing processes vary in composition as widely as does the nature of the slurry-producing process. The range of modifications to the basic decanter structure enables it to cope with this wide variation in feed compositions. 

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