How Does a Decanter Centrifuge Work

What is a Decanter Centrifuge?

A decanter centrifuge is a cylindrical, rotating vessel that separates liquids and solids using centrifugal acceleration. It consists of a horizontal rotating bowl fitted with a screw conveyor. Feed slurry enters the bowl and centrifugal force causes solids to accumulate on the bowl wall while clarified liquid flows out through adjustable bowl outlets.

The conveyor rotates in the same direction but slightly slower, moving settled solids towards the conical end of the bowl. Solids are discharged continuously through the solids discharge ports. The differential speed allows separation efficiency to be optimized based on feed conditions.

Types of Decanters

There are several different types and configurations of decanter centrifuges:

Solid Bowl Decanters - The most common type, used for continuous separation and clarification of slurries

Tube Decanters - Used for extremely high feed solids up to 80-90%. only clarify liquid phase.

Disc-Stack Decanters - Utilize a stack of closely spaced metal discs. Very high G-force for fine separations.

Two-Phase Decanters - Designed to handle immiscible liquids with different densities, like oil-water separation.

Three-Phase Decanters - Used to simultaneously separate two immiscible liquid phases and one solid phase.

Conical Screen Bowl Decanters - Combine a screen section to enhance solids dewatering.

The selection depends on the specific separation duty and properties of the feed material.

How Do Decanter Centrifuges Actually Work?

 

A decanter centrifuge works by exploiting differences in density to achieve separation using centrifugal acceleration:

Feed slurry enters the rotating centrifuge bowl through a stationary inlet housing.

The extremely high G-forces, up to 4,000 Gs, cause immediate acceleration of the solids outward towards the bowl wall.

Lighter liquid phase remains towards the center and flows forward at a faster velocity than the solids bed.

Built-up solids are conveyed towards the conical end by the differential speed screw.

Clarified liquid flows over adjustable plate dams that control retention time and separation sharpness.

Solids discharge continuously out the conical end through the ports.

Clear liquid discharges through outlets at the other end.

This process allows efficient, continuous separation of solids and liquids in one uninterrupted operation. Separation sharpness is controlled by adjusting process variables.

What is the Mechanism of Decanter Centrifuges?

Decanter centrifuges achieve separation through two primary mechanisms:

Differential Centrifugal Acceleration

Due to density differences, heavier solids experience stronger centrifugal forces and accelerate faster towards the bowl wall, displacing the lighter liquid inwards. This allows clean separation without filters.

Differential Velocity

The conveyor screw rotates slightly slower than the bowl, creating a velocity difference that continuously moves settled solids towards discharge. This maintains the solids transport process and desired retention times.

Additionally, adjustable plate dams at the liquid outlets provide retention zones to enhance separation sharpness based on particle characteristics. The decanter mechanism provides very efficient separation across a range of applications.

What is the Difference Between a Decanter and Centrifuge?

While the terms are sometimes used interchangeably, there are some important differences:

Centrifuges separate through batch processing and need to be stopped periodically to discharge solids.

Decanter Centrifuges allow continuous, uninterrupted separation and discharge of solids. No need to stop runs.

Centrifuges build up high cake solids and then resuspend during discharge.

Decanters maintain steady-state operations for consistent results.

Centrifuge bowls are cylindrical with no internal conveying.

Decanters have a screw conveyor that transports solids.

Centrifuges require frequent manual cleaning of bowls.

Decanters have self-cleaning mechanisms.

For demanding industrial duties, decanter centrifuges offer significant advantages and better performance.

What is the Principle of 3 Phase Decanter Centrifuges?

Three-phase decanter centrifuges are designed to continuously separate three phases in one step:

Two immiscible liquid phases (typically oil and water)

One solid phase (sediments, sludge, etc.)

This is achieved by utilizing differences in phase densities and special inlet and outlet configurations:

Heavy solids settle on the bowl wall first and are conveyed towards discharge by the scroll.

The lighter liquid (oil) layers towards center of bowl.

Intermediate density liquid (water) concentrates in the middle zone.

Adjustable ports and dams allow separate discharge of all three phases.

With proper control of process variables, the three phases are discharged continuously with high purity separation. 3-phase decanters are ideal for cleanup of oily wastewaters and drilling fluids.

What is a Decanter Centrifuge Used For?

Decanter centrifuges have broad use across many industries due to their versatility and ability to handle challenging separations:

Wastewater Treatment - Sludge thickening and dewatering, biosolids concentration

Food Processing - Separation of oils, juices, beverages

Chemical - Catalyst and polymer recovery, lube oil purification

Pharmaceutical - Clarification of antibiotics and biopharmaceuticals

Mining - Tailings dewatering, minerals/metals separation

Oil Drilling - Recovery of drilling muds, solids control

Pulp & Paper - Separation of lignins, stickies, and coating colors

New applications continue to emerge as the technology improves. Decanter centrifuges provide continuous, hands-off separation of extremely fine solids from process liquids.

Conclusion

In summary, decanter centrifuges are versatile separation devices that provide continuous, automated solids removal across a broad array of industries. Their ability to handle challenging slurries with high solids loadings makes them uniquely suited to many separation duties. Understanding the centrifugal separation principles and mechanisms allows effective utilization of decanters to optimize process efficiency and improve sustainability through closed-loop recycling of water and chemicals. With their unmatched solids handling capabilities and minimal maintenance requirements, decanter centrifuges will continue growing as a separation technology of choice.

References

Leung, W.W. (1998). Industrial Centrifugation Technology. McGraw-Hill.

Ambler, C. (1959). The Fundamentals of Separation, Including Sharples Centrifuges. Sharples Corporation.

Hoffmann, T. (2021). Centrifugation in Density Gradients. Academic Press.

Svarovsky, L. (2000). Solid-Liquid Separation. Butterworth-Heinemann.

Dickin, F. (1995). Decanter Centrifuge Handbook. Gulf Publishing Company.

Heinzen, B. (2004). Handbook of Decanter Centrifuge Basics and Operation. Self-published.

Ward, A. (2018). Centrifugation: Basics, Common Problems, and Solutions. CreateSpace Independent Publishing.

Diessel, C. (2010). Solids Separation in Offshore Oil & Gas Production Systems. Gulf Publishing Company.