The decanter centrifuge is the last line of mechanical defense in a solids-control train — the machine that catches the fine solids the shaker and hydrocyclones let through, down to a few microns. Under the covers it is simpler than its reputation: two parts rotating together, a big centrifugal field, and two adjustments that decide everything about how it performs.
The two rotating parts
A decanter has an outer solid-wall bowl and an inner helical screw called the scroll (or conveyor), and they rotate in the same direction. The bowl is cylindrical along most of its length and tapers to a cone — the ‘beach’ — at one end. Feed slurry enters through a stationary pipe into the centre of the assembly and is accelerated up to bowl speed, where centrifugal force well beyond 1,000 times gravity — drilling decanters run from over 1,000 G up to around 3,000 G — flings the denser solids out against the bowl wall while the lighter liquid forms concentric inner layers.
The scroll is what makes it a continuous machine. It turns at a slightly different speed than the bowl — a few revolutions per minute faster or slower, set by a gearbox — and that differential speed is what ploughs the settled solids along the wall toward the beach. Without the differential, solids would simply spin in place against the wall and never leave. Because feed, solids and liquid all move continuously, the machine runs without stopping to unload. Matching that G-force and differential to your specific solids is the kind of setup Rig IQ helps you get right before the bowl is even spinning.
Where the solids and the liquid go
Follow the two streams and the design makes sense. The scroll carries the settled solids up the beach; as they climb above the liquid level they drain, then drop out through the solids-discharge ports at the narrow end of the cone as a dewatered cake. Meanwhile the clarified liquid — the centrate — flows the opposite way along the bowl and overflows adjustable weirs (dam plates) at the cylindrical end. Two streams, two ends, continuously.
This is why the decanter sits at the end of the cascade: after the shaker removes the large cuttings and the desanders and desilters take the medium fractions, the centrifuge is the tool that pulls the ultrafine solids — roughly 2 to 7 microns — that everything upstream missed. It is also the machine used to recover barite from weighted mud. Deciding which of those two jobs a given centrifuge should be doing on your rig, and at what settings, is a decision Rig IQ is built to walk through.
The two levers that tune it
Almost everything an operator controls on a decanter comes down to two adjustments. The first is pool (pond) depth, set by the weir plates: raise the weir and the liquid pool inside the bowl gets deeper, giving finer clarification but a wetter cake; lower it and the beach exposes more, giving a drier cake but a less clear centrate. The second is differential speed: it sets how long the solids reside under the G-force before they are ploughed out — slower differential means longer residence and a drier cake, faster means quicker clearing but wetter solids.
Every duty is a balance between those two. Barite recovery wants one setting; polishing fine drilled solids to a clean discard wants another; dewatering wants a third. Push the pool deep and the differential slow for the driest cake, and you risk overloading the scroll; open them up for throughput and you sacrifice cut. There is no universal ‘correct’ setting — only the one that matches your fluid, your solids and your objective, which is exactly the trade Rig IQ models so you tune from numbers rather than by feel.
The machine, in four lines
Bowl + scroll rotate together; the differential speed (a few RPM apart, set by a gearbox) ploughs solids along the wall.
G-force >1,000 up to ~3,000 throws solids to the bowl wall; solids climb the cone (‘beach’) → discharge as cake. Liquid (centrate) overflows the weirs.
Removes ~2–7 µm — the final mechanical stage after shaker → desander → desilter.
Two levers: pool depth (weirs) · differential speed (scroll) — drier cake vs. clearer centrate.
A decanter is a bowl and a scroll turning together at a small differential, throwing fine solids to the wall at over 1,000 G. The scroll ploughs the cake up the cone to discharge; the clarified centrate overflows the weirs at the other end. It removes the 2–7 micron fines nothing upstream caught. Tune it with two levers — pool depth (weirs) and differential speed — balancing a drier cake against a clearer centrate for the job at hand.
Common questions
How does a decanter centrifuge work?
An outer bowl and an inner scroll rotate together at a slightly different speed. Feed enters the centre and is accelerated to bowl speed, where centrifugal force above 1,000 G throws the denser solids to the bowl wall. The scroll ploughs those solids up the conical 'beach' to the discharge ports as a cake, while the clarified liquid flows the other way and overflows adjustable weirs.
What is differential speed on a centrifuge?
It is the small difference in rotation speed between the bowl and the scroll — a few RPM, set by a gearbox. That difference is what conveys the settled solids along the bowl wall toward discharge; without it, solids would just spin in place. Slower differential means solids reside longer under G-force and leave drier; faster clears them quicker but wetter.
What does the pool (pond) depth do?
Pool depth is the liquid level inside the bowl, set by the weir plates. A deeper pool clarifies finer solids into the centrate but leaves a wetter cake; a shallower pool exposes more of the beach for a drier cake but a less clear centrate. It is one of the two main levers, alongside differential speed, for tuning a decanter.
