How a Decanter Centrifuge Works

A decanter centrifuge is a continuous sedimentation machine. It does the same job gravity does in a settling tank, but far faster. In a tank, denser solids drift slowly to the bottom because they weigh more than the surrounding liquid. A decanter replaces gravity with centrifugal force by spinning the mixture, so particles settle in seconds instead of hours.

The strength of that force is expressed in G-force, or multiples of gravity. It depends on how fast the bowl turns and its radius: G equals the angular velocity squared times the radius, divided by gravitational acceleration. Industrial decanters commonly develop several thousand times the force of gravity at the bowl wall, which lets them settle fine particles and separate liquids of only slightly different density.

A decanter has two main rotating parts that turn in the same direction: an outer solid-wall bowl and an inner helical screw called the scroll or conveyor. The bowl is cylindrical along most of its length and tapers to a cone (the beach) at one end. The scroll fits closely inside the bowl and carries a spiral flight along its full length.

The scroll turns at a slightly different speed than the bowl, a few revolutions per minute faster or slower. This difference is the differential speed, and it is set by a gearbox, typically a planetary or cycloidal unit, at the machine's end. The differential is what moves settled solids along the bowl; without it, solids would simply spin in place against the wall.

Feed slurry enters through a stationary pipe into the center of the rotating assembly and is accelerated up to bowl speed. As it flows through the bowl, the high G-force throws the denser solids outward against the wall while the clarified liquid, called the centrate, forms an inner layer.

Solids that collect on the bowl wall are caught by the rotating scroll flight and conveyed toward the conical beach. As the solids climb the beach, they rise above the liquid level and drain before dropping out through the solids discharge ports at the narrow end of the cone.

The clarified liquid flows the opposite direction along the bowl and overflows adjustable weirs (also called dam plates or a weir plate) at the cylindrical end. Changing the weir setting raises or lowers the depth of the liquid pool inside the bowl, which trades off between drier solids and clearer centrate. This is one of the main levers operators use to tune performance.

Because feed enters continuously and both solids and liquid discharge continuously, a decanter runs without stopping to unload. This makes it well suited to high-volume duties such as wastewater biosolids dewatering, drilling-mud solids control, and industrial process separation.

Decanters run at high speed against abrasive slurries, so wear is expected. The scroll flights and the bowl's inner surface erode over time, especially at the feed zone and the beach, which reduces conveying efficiency and separation quality. Tiles, tungsten carbide tips, and hardfacing are used to protect these surfaces and are replaced during a rebuild.

Bearings and the main gearbox carry heavy dynamic loads and are common wear points. Seals, the feed accelerator, and the drive belts also degrade. As parts wear unevenly, the rotating assembly can fall out of balance, which shows up as vibration and accelerates further damage. Restoring a decanter means inspecting these components, replacing worn parts, and rebalancing the assembly before a test run.