Dolphin Centrifuge

5 Ways to Optimize Decanter Performance | Illustrated Guide

Table of Contents

30 Second Summary Takeaway

Decanter centrifuge performance optimization involves tuning or adjusting specific operating parameters to improve the separation efficiency of the decanter.

In this article, we discuss the 5 most effective and straightforward ways to achieve optimal decanter operation.

We will address the following typical questions related to the optimization process.

  • What is decanter optimization?
  • What parameters affect optimization?
  • How does pond-depth help optimize decanter performance?
  • How does bowl speed affect performance?
  • Isn't high speed always good for separation? Not Necessarily!
  • How does conveyor speed affect performance?

Pond Depth

The pond depth is the radial distance between the internal bowl wall and the inner surface of the concentric liquid layer. The high centrifugal force causes the liquid to form a concentric layer within the bowl.

Pond Depth Versus Cake Dryness Torque
Pond Depth Versus Cake Dryness Torque

Adjusting Pond Depth

It is easy to adjust the pond depth by changing the weir plates with different radii to the decanter bowl axis of rotation. The following is an image of a decanter weir plate.

Decanter Weir Plate
Decanter Weir Plate

The adjustment of the pond depth has the maximum effect on decanter centrifuge performance. In this section, we discuss these effects.

Deep Pond

Deep Pond Depth - Decanter Centrifuge
Deep Pond Depth - Decanter Centrifuge

Weir plates with shorter radii allow a deeper pond formation within the decanter bowl. This shorter radius increases the settling space available for sedimentation of sludge particles. Therefore, a deeper pond facilitates better sedimentation and sludge separation. Removal of more solids means clearer liquid.

However, the deeper pond depth also implies more liquid will cover the taper section (beach) of the bowl leading to reduced beach length, as shown in the diagram below. The reduced beach length impedes the liquid removal from the sludge as it travels up the beach towards the solids outlet ports. Therefore, a deeper pond causes wetter solids.

The decanter auger pushes the sedimented solids towards the solid ejection ports along the tapered section of the bowl (beach). A deeper pond exposes a shorter section of the beach and reduces the torque required to push the solids out.

In summary, a deeper pond leads to:

  • Removal of more solids from the liquid
  • Sludge with more liquid or wetter solids
  • Reduced torque on the solids auger

Shallow Pond

Shallow Pond Depth
Shallow Pond Depth

In contrast to a deeper pond, in this section, we discuss the effects of a shallow pond on decanter centrifuge performance.

Weir plates with longer radii cause the depth of the liquid layer to decrease, leading to a shallow pond depth. A liquid layer with reduced depth reduces the space available for solid settling, leading to reduced solids removal. Therefore, a shallower pond depth causes more solids in the liquid, leading to murkier liquid.

As shown in the diagram above, a shallow pond exposes more of the taper section of the decanter bowl, i.e., increased beach length. The more extended beach enhances the separation of solids from the liquid as the auger pushes the sludge up the beach under the high centrifugal force.

Therefore, a shallower pond causes drier solids.

A more extended beach also implies that the auger has to push the sludge over a longer distance, thereby increasing the torque on the auger.

In summary, a deeper pond leads to:

  • Removal of lesser solids from the liquid
  • Sludge with less liquid or drier solids
  • Increased torque on the solids auger

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Bowl Rotation or Bowl Speed

Decanter Energy Noise Wear versus Bowl Speed
Decanter Energy Noise Wear versus Bowl Speed

The rotational velocity of the bowl is known as the bowl speed or bowl RPM. This speed is directly proportional to the centrifugal force generated by the bowl. Therefore, a higher bowl speed indicates greater centrifugal force.

Adjusting Decanter Bowl Speed

The decanter bowl is directly connected to the drive motor. A slower motor speed reduces the bowl speed, and conversely, higher motor speed leads to higher bowl RPM.

Higher Bowl Speed

Performance Optimization Curves
Performance Optimization Curves

An increase in the bowl speed implies a higher g-force acting on the solids in the fluid. An increase in sedimentation is a direct consequence of higher centrifugal force. More sedimentation causes more solids to be separated from the liquid and pushed by the conveyor (auger), leading to higher torque on the auger.

Also, increased sedimentation means lesser solids in the existing fluid leading to clearer liquid and more solids removal.

A higher bowl RPM generates a higher centrifugal force acting on the solids being pushed up the tapered beach section of the bowl, which squeezes out more liquid from the solids causing drier solids.

As explained above, a higher bowl speed requires the decanter motor to operate at a higher RPM leading to more energy consumption.

In summary, a higher bowl speed leads to:

  • Higher torque on the solids auger
  • Removal of more solids from the liquid & clearer liquid
  • Sludge with lesser liquid or drier solids
  • More power consumption

Lower Bowl Speed

Reduced bowl speed has the opposite effect on the decanter centrifuge performance due to increased bowl speed, as explained above.

A reduction in bowl speed leads to a reduction in the decanter bowl’s centrifugal force, leading to decreased sedimentation and, consequently, reduced solids removal.

The reduction in solids removal means lesser solids that need to be pushed out, leading to reduced load and torque on the conveyor.

Following the above, a lower bowl speed causes reduced solids removal and more solids in the separated liquid, leading to a murkier liquid.

Lower bowl RPM implies the motor is turning at a lower speed leading to reduced energy consumption.

In summary, lower decanter bowl speed leads to:

  • Lower torque on the solids auger
  • Removal of lesser solids from the liquid & murkier liquid
  • Sludge with more liquid or wetter solids
  • Reduced power consumption

Auger (Scroll) Speed

Decanter Bowl Auger Differential Speed
Decanter Bowl Auger Differential Speed

The auger speed refers to the differential speed between the decanter bowl and the auger. This speed is an indication of how quickly or slowly the auger is rotating inside the bowl.

Adjusting Auger Speed

The decanter bowl connects to the auger through the gearbox. The auger speed changes with the gearbox sun-wheel shaft speed. In other words, the user can adjust the auger speed by changing the sun-wheel shaft rotation speed.

Higher Auger Speed

If the auger is rotating faster, it can move more solids to the solids discharge ports per rotation, allowing the decanter higher solids handling capability. Therefore, it is desirable to have a higher auger speed for high solid applications.

A higher rotational speed of the auger also implies the solids are pushed out quickly before they accumulate and cause more resistance to the auger, thereby reducing the torque required.

Following the above considerations, a higher speed of the auger causes the solids not to have enough settling time and therefore retain more liquid. This quicker discharge leads to wetter solids.

Summarizing the effects of higher auger speed:

  • Higher solids handling capacity
  • Reduced torque on the auger (conveyor)
  • Wetter solids discharge

Lower Auger Speed

A slower auger RPM causes lesser solids movement reducing the solids handling capacity of the decanter. This reduced capacity means that a slower auger speed is better suited for low solid applications.

Also, a lower auger speed means the solids are pushed out slower, giving more time for the solids to settle and accumulate. Higher solids accumulation leads to higher torque on the conveyor.

Similarly, a lower auger speed allows more time for the solids to settle out, thereby removing more water from the solids and ejecting drier solids.

Summarizing the effects of lower auger speed:

  • Lesser solids handling capacity
  • Increased torque on the auger (conveyor)
  • Drier solids discharge

Auger Pitch

The auger pitch is the distance between the flights on the decanter auger. An auger with the flights closer to each other is known as a fine-pitch auger. On the other hand, if the flights are away from each other, it is known as a coarse pitch auger.

Adjusting the Auger Pitch

The pitch of the auger is a preset mechanical feature of the decanter. The user has the option to order the decanter with different auger pitches. However, once the decanter is manufactured, the only way to change the pitch is to replace the auger with a different pitch.

Fine Pitch Auger

A fine pitch of flights on the auger has similar performance effects as increasing the auger speed. So, a fine pitch leads to lower solids moving capacity.

The quick movement of solids also leads to higher auger torque.

Coarse Pitch Auger

As explained above, a coarse pitch auger has similar effects on the decanter performance as that of slow auger speed.

Therefore, a coarse flight pitch moves more solids per rotation which exerts lesser torque on the auger and gearbox. 

Effects of Auger Pitch on decanter performance are as follows:

Coarse PitchFine Pitch
Solids Handling CapacityHighLow
Torque On AugerLowHigh

Process Fluid Temperature

The fluid process temperature is significant when processing viscous fluid through a decanter centrifuge. Higher viscosity fluids such as crude oil resist the separation of solids. As the temperature of the fluid increases, the viscosity reduces, leading to better separation.

The fluid temperature does not affect the decanter performance in cases of low viscosity fluids such as water.

Summary

The 5 adjustments mentioned above help optimize decanter centrifuge performance. Needless to say, each application has a different set of parameters. However, following the guidelines above, the user can optimize the decanter centrifuge under set operating conditions.

Contact

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