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.
The speed of the screw conveyor may be automatically adjusted by use of the variable frequency drive (VFD) in order to adjust to variation in the solids load.
Types Of Decanters
There are several types of decanter centrifuges currently utilized in the industry, the most widely recognized are vertical, horizontal and conveyor centrifuges. The principle behind a decanter centrifuge is based on the theory of gravitational separation. For example, if you fill a vessel with a mixture of mud and water, over time the weight of the mud will cause it to settle down at the base of the vessel. With the mud congealed at the bottom, the water will be forced upwards, creating a clear separation between the two.
A decanter centrifuge employs the same principles of gravitational force. However, unlike the glass mixture, the process is expedited through the use of continuous rotation. In fact, rotation provides anywhere from 1000 to 4000 times the normal gravitational force, reducing the time required for separation from hours to seconds.
The concept of rotational separation is similar to rides found at amusement parks and county fairgrounds. In these rides, placing yourself at an angle allows you to overcome the gravitational forces induced by rotation. Similarly, a decanter centrifuge is essentially a bowl tube that rotates at an extremely high speed. The bowl tube is equipped with an internal conveyor which moves in the same direction but at a different velocity.
How the Decanter Process Works:
• 1: The slurry is brought into the centrifuge through an intake pipe and onto a conveyor.
• 2: Utilizing an internal feed compartment, the conveyor moves the slurry through a nozzle into the bowl.
• 3: The bowl rotates at high speeds to induce centrifugal forces.
• 4: High speed rotation separates the solid material from the liquid in a matter of seconds.
• 5: The conveyor delivers the solid material upwards where it is discharged through a nozzle.
• 6: The solid material removed, the purified liquid is released from a separate output.
The ability to purify a liquid makes decanter centrifuges ideal for waste water treatment facilities. However, there are variety of industries for which such centrifuges play an important role. Similar to other decanter equipment, centrifuges are simple to install and do not require a foundation to build upon. Their efficiency saves time and materials and is an essential component for many blue collar industries..