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How does the diameter of the dust outlet affect the performance of a Cyclone Separator?

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 Introduction

A cyclone separator is also called a cyclone dust collector. The typical industrial cyclone is a centrifugal reverse-flow cyclone.

The dust outlet of a cyclone is called a material discharge outlet or cone-tip.

Sketch of a reverse-flow, cylinder-on-cone cyclone with a tangential inlet


I have been asked how the diameter of the dust outlet affects the performance of a cyclone a couple of times by colleagues and final users.

Normally, when engineers size and/or design a cyclone, they pick a standard one from manuals or handbooks. However, when dust loading is high, cyclone designers worry about whether the dust outlet is big enough. If the separated dust cannot be discharged immediately, a cyclone will not be functional.

In reality, after a cyclone was put into use, final users worried about the same thing. When there is blockage at the cone bottom, they have to hit the bottom part with a hammer to dislodge the plug, and this often leaves dents or deformation on the cyclone wall. Dents have an adverse effect on the collection efficiency of a cyclone.

Consequently, final users asked if the dust outlet was enlarged, will it help to solve the blockage problem and/or reduce the wear-out problem either? However, very few articles attempt to answer this question.

A cyclone performance calculation

To answer this question, Airvate engineers did a cyclone performance calculation. The result in the table below clearly shows that when the dust outlet becomes larger, both the pressure drop and collection efficiency of the cyclone decrease. However, it affects the collection efficiency of small particles more than that of big particles.

ID of dust outlet

(inches)

Pressure drop

(inchH2O)

Collection Efficiency

@ 2 micron

Collection Efficiency

@ 10 micron

2.0

7.83

43.35%

99.958%

3.0

7.68

40.17%

99.952%

4.0

7.55

37.16%

99.946%

5.0

7.29

31.62%

99.931%

Conditions for the calculation:

  • 170 ACFM of standard air;
  • Particle specific gravity: 2.73; dust loading: 2 grains/ft3;
  • 0.15mm absolute roughness of carbon steel construction assumed.
  • Diameter of Cyclone: 7 7/8”

So if you are using a cyclone to collect coarse dust particles, making the dust outlet a little bit bigger than that specified by standard cyclones will allow you to avoid blockage or even wear-out problems.

In reality, when the dust outlet is enlarged, the pressure drop will decrease for the cyclone itself only. However, for the whole dust collection system, when the total pressure drop of the whole system lowers, the fan will adjust its performance and move to a new operating point. At the new point, there will be more air volume in the system as a kind of compensation, and the cyclone will experience a higher inlet velocity. As a result, the collection efficiency and pressure drop of the cyclone will increase.  This is the reason why after the dust outlet of a cyclone is enlarged, a decrease of pressure drop and collection efficiency is not always obviously observed.

Cyclone services by Airvate that you can afford

Whether you are sizing a cyclone or using one now, if you need any services listed below, feel free to contact Airvate at info@airvate.com.

  • Have to change dimensions of inlet, gas outlet, and/or dust outlet, and want to know how the changes affect cyclone performance.
  • Need a new cyclone that has to meet the specified requirement.
  • Need a new cyclone with the best available performance in a limited space.
  • Want to avoid or reduce the wear-out or blockage that always happens to your cyclone.
  • Want to reuse an existing cyclone and know its performance in a new process.
  • Want to optimize the performance of an existing low-efficiency cyclone.
  • The existing cyclone collection efficiency is too high for the process and you want to lower it.
  • The existing cyclone has either too high or too low of a pressure drop.
  • Want to optimize the performance or solve any problems of the combo of an existing cyclone (as a pre-cleaner) and a baghouse.
  • Want to solve the uneven dust distribution problem in applications of dual-cyclone, quad-cyclone, or multi-barrel cyclone; with this issue, one or two cyclone barrels get more dust, and consequently it causes wear-out in the inlet section and cone bottom more quickly on it (them two) than on others.

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