Decanter centrifuge – Principle, Types, Parts, Uses

When it comes to separating solid/liquid mixes with a high solids content, decanter centrifuges are the way to go. These solid-shell scroll centrifuges or decanters, unlike chamber filter presses, run continuously. The finely distributed solid particles are separated from the suspension by strong centrifugal forces.

Decanters are useful in a wide variety of industries throughout the world. The centrifuges are optimally adapted for the specific application. Applications range from sludge dewatering to classification or wet classification to the sorting of solids.

To obtain optimum results, solid bowl decanter centrifuges must be custom designed to suit specific separation processes.

What is Decanter centrifuge?

• A decanter centrifuge is a type of centrifuge that is used to separate solids from liquids in a mixture. It is a continuous process that uses centrifugal force to separate the two components. 
• The mixture is fed into the centrifuge, and the solids are separated from the liquids by the centrifugal force generated by the spinning of the centrifuge. 
• The separated solids and liquids are then discharged from the centrifuge through separate outlets.
• Decanter centrifuges are used in a wide range of industries, including chemical, pharmaceutical, food processing, and environmental engineering. 
• They are particularly useful for separating solids that are too fine or too dense to be effectively separated by other methods, such as sedimentation or filtration. 
• Decanter centrifuges are also used to dewater sludge and to separate emulsions. 
• They are known for their high efficiency, low maintenance requirements, and ability to handle large volumes of material.

Working Principle of Decanter Centrifuges

A decanter centrifuge operates on the idea of separation via buoyancy. A component with a greater density would naturally sink to the bottom of a combination, while a less dense component would float on top. Continuous spinning enhances the velocity of settling in a decanter centrifuge, creating a g-force comparable to between 1000 and 4000 G’s. This drastically decreases the settling period of the components, so that mixtures that formerly required hours to settle can now be settled in a matter of seconds using a decanter centrifuge. This method of separation produces faster and more manageable outcomes.

A decanter is just a sedimentation tank wrapped around an axis. Solid particles that are heavier than liquid move to the bottom of the sedimentation tank by gravity and form a sediment (solid phase) at the bottom. A wine decanter, for example, can be thought of as a sediment vessel. The solid and liquid phases of a centrifuge are separated by centrifugal acceleration. The solid particles, which have a higher density and are hence heavier than the liquid, migrate outwards in the centrifuge’s revolving bowl due to centrifugal force. The sediment forms on the inside of the centrifuge bowl’s inner wall. The separation of solid particles from liquid is more faster and more efficient in a centrifuge because centrifugal forces of roughly 3000 g are applied instead of 1 g in a gravitational field.

Decanter-based separation of three phases

Using a 3 phase decanter centrifuge, it is feasible to separate three stages in a single operation. For instance, oil and water, which cannot be combined due to their differing densities, are separated from a solids phase. Between the layer of oil and the layer of solids, water gathers in the middle. Thus, the two liquids can be sucked from the decanter after being separated. As in 2-phase separation, the solids are conveyed via the scroll to the discharge holes.

Typical applications of three-phase separation include the manufacture of edible oils like olive oil, the processing of oil sludge, and the creation of biodiesel, among others.

Parts of Decanter Centrifuges

There are several key parts of a decanter centrifuge that work together to separate solids from liquids. These parts include:

1. The bowl: This is the main component of the centrifuge. It is a cylindrical container that spins on a horizontal axis. The mixture to be separated is fed into the bowl through a feed pipe, and the separated solids and liquids are discharged through separate outlets.
2. The scroll: The scroll is a helical screw that is mounted inside the bowl. It is driven by a motor, and it rotates at a slightly slower speed than the bowl. The scroll conveys the solids towards the outer wall of the bowl, where they are separated from the liquids by the centrifugal force.
3. The solids discharge port: This is an outlet located on the outer wall of the bowl that is used to discharge the separated solids.
4. The liquids discharge port: This is an outlet located on the bottom of the bowl that is used to discharge the separated liquids.
5. The drive system: This includes the motor and other components that are used to drive the bowl and scroll.
6. The control system: This includes the sensors and other components that are used to monitor and control the operation of the centrifuge.
7. The frame and support structure: This includes the frame and other structural components that support the bowl and other parts of the centrifuge.
8. The feed pipe: This is a pipe that is used to feed the mixture into the bowl of the centrifuge.
9. The feed pump: This is a pump that is used to feed the mixture into the feed pipe at a constant rate.
10. The feed control system: This includes the sensors and other components that are used to monitor and control the flow of the mixture into the centrifuge.

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.

Characteristics of Decanter centrifuges process

There are several characteristics of the decanter centrifuge process that make it an effective method for separating solids from liquids. These characteristics include:

1. Continuous operation: Decanter centrifuges can operate continuously, allowing for a continuous flow of material to be processed. This makes them suitable for high-volume applications.
2. High separation efficiency: Decanter centrifuges are able to separate solids and liquids with a high degree of efficiency, making them an effective method for separating fine or dense solids that are difficult to separate by other methods.
3. Adjustable separation parameters: The separation parameters of decanter centrifuges, such as the speed and angle of the bowl and scroll, can be adjusted to optimize the separation process for different types of materials.
4. Low maintenance requirements: Decanter centrifuges require relatively low maintenance, making them a cost-effective choice for many applications.
5. Versatility: Decanter centrifuges can be used to separate a wide range of materials, including liquids with different densities, suspensions, and emulsions.
6. Energy efficiency: Decanter centrifuges are generally more energy efficient than other methods of separation, such as filtration and sedimentation, as they require less energy to operate.
7. Compact design: Decanter centrifuges are relatively compact and can be easily integrated into existing process systems.

Parameters and influencing factors of the separation

1. Feed, throughput, and dwell time

The to-be-processed separation medium can be fed into the centre of the infeed chamber of the scroll, where it is accelerated, via the feed. Residence time will be influenced by the throughput.

2. Acceleration

In the decanter bowl, the separating medium reaches its maximum speed, forcing solids to settle on the bowl’s inner circle. The bowl is characterised by its cylindrical or conical shape.

3. Differential velocity

A gear mechanism on industrial decanter centrifuges generates a speed differential between the decanter bowl and the scroll. The differential speed dictates the amount of solids in the outfeed.

4. Volumetric filling / Weir discs or overflow weir

Pond depth / Weir discs

In a decanter centrifuge, the clarified liquid flows to the cylindrical end of the bowl, where it exits through perforations in the bowl cover. These apertures contain precisely adjustable weir discs/plates that allow the bowl’s pond depth to be adjusted. The weir discs determine the bowl’s filling volume.

Applications of Decanter Centrifuges

Decanter centrifuges are used in a wide range of industries and applications, including:

1. Chemical industry: Decanter centrifuges are used to separate chemical products and by-products, such as acids, alkalis, and solvents. They are also used to purify and dewater chemical products, such as polymers and resins.
2. Pharmaceutical industry: Decanter centrifuges are used to separate pharmaceutical products and by-products, such as drugs, excipients, and intermediates. They are also used to purify and dewater pharmaceutical products, such as proteins and enzymes.
3. Food processing industry: Decanter centrifuges are used to separate food products and by-products, such as milk, juice, and fruit puree. They are also used to purify and dewater food products, such as cheese and yogurt.
4. Environmental engineering: Decanter centrifuges are used to treat and dewater sludge and other waste materials in wastewater treatment plants. They are also used to separate oil and water in oil spill cleanup operations.
5. Oil and gas industry: Decanter centrifuges are used to separate oil, water, and solids in drilling and production operations. They are also used to purify and dewater crude oil and other petroleum products.
6. Mining and mineral processing industry: Decanter centrifuges are used to separate minerals and other solids from water and other liquids in ore processing and beneficiation operations.
7. Power generation industry: Decanter centrifuges are used to dewater coal and other fuels in power generation operations.
8. Pulp and paper industry: Decanter centrifuges are used to dewater pulp and paper sludge in paper mills.
9. Other industries: Decanter centrifuges are also used in other industries, such as automotive, aviation, and aerospace, to separate and purify a variety of materials.

Advantages of Decanter Centrifuges

• Decanter centrifuges offer a tidy appearance and minimal to no odour issues.
• The device is not only simple to instal and quick to start up and shut down, but it also requires a little operating area compared to other competitive methods.
• The decanter centrifuge is adaptable due to the fact that the bowl portion and cone angle can be altered to accommodate various applications. In addition, the system can be pre-programmed with multiple design curves to predict the sludge type, but competing methods, such as a belt filter press, cannot adjust the belt type to accommodate different sludge types. [4] Its adaptability enables the machine to perform multiple activities, such as thickening and dewatering.
• The machine’s throughput capacity is more than that of smaller machines.
• This also reduces the required quantity of units.
• The gadget is straightforward to optimise and operate due to the small number of significant variables and dependable feedback data.
• In comparison to other processes, the decanter centrifuge has lower labour costs because it requires minimal constant maintenance and operator attention.
• In comparison to competing processes such as the belt filter process, the decanter centrifuge offers greater process flexibility and superior performance.

Disadvantages of Decanter Centrifuges

• The decanter centrifuge is unable to separate biological materials, such as cells and viruses, with very minor density changes. The tubular-bowl centrifuge is a competitive method capable of separating these difficult-to-separate solids.
• The machine can be extremely noisy and vibrational.
• Due to the device’s high G-forces, its energy consumption is significant.
• The centrifuge decanter has substantial equipment expenses. Hard surfacing and abrasion protection materials are required for the scroll in order to prevent wear and, consequently, maintenance.

What is the difference between centrifuge and decanter?

A centrifuge is a machine that uses centrifugal force to separate solids from liquids or to separate components of a mixture based on their densities. A decanter centrifuge is a type of centrifuge that is specifically designed to separate solids from liquids in a continuous process.

There are several key differences between a general centrifuge and a decanter centrifuge:

1. Continuous operation: Decanter centrifuges are designed for continuous operation, meaning that they can process a continuous flow of material. Other types of centrifuges, such as batch centrifuges, process material in batches.
2. Scroll: Decanter centrifuges have a scroll, which is a helical screw that is mounted inside the bowl and rotates at a slightly slower speed than the bowl. The scroll conveys the solids towards the outer wall of the bowl, where they are separated from the liquids by the centrifugal force. Other types of centrifuges may not have a scroll or may have a different type of conveyor system.
3. Solids discharge: Decanter centrifuges have a solids discharge port located on the outer wall of the bowl, which is used to discharge the separated solids. Other types of centrifuges may have a different method of discharging the solids.
4. Applications: Decanter centrifuges are primarily used to separate solids from liquids, while other types of centrifuges may be used for a wider range of applications, such as separating components of a mixture based on their densities or purifying liquids.

Overall, decanter centrifuges are a specialized type of centrifuge that is specifically designed for separating solids from liquids in a continuous process. Other types of centrifuges may have different design features and may be used for different purposes.

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