Dust-purification-techniques

Cyclones

Figure: Cyclone separator (source: http://www.meridianeng.com/cyclone.gif)

The air entrance speed of a cyclone lies between 10 and 20 m/s, the most usual speed is approx. 16 m/s. At fluctuations with these speeds (with lower speeds) the separation efficiency decreases very rapidly. To give an indication to the separation efficiency the formula of Lappleis used that is:
d₅₀ = √(9μb / 2πN Γ_iv_i)

In which:
d50 = particle sizes that with 50% outputs are broken away from (m)
b = inlet width of the cyclone supply (m)
N = number of turn cycles in the cyclone (≈ N=5, stipulated empirically)
vi = inlet speed (m/s)
Γi = specific mass of the dust particle (kg/m³)
µp = viscosity of the gas (kg/m).

Cyclones are most efficient at high air entrance speed, small cyclone diameter and large cylinder length (pencil cyclones).
The advantages of a cyclone as separator for substance are:

• Simple construction

• No moving components

• Little maintenance

• Low investment and functioning costs

• Constant pressure drop

• Saves room

• Dry relief during wet cyclone

The disadvantages are:

• High pressure drop (0.5 - 2.5 kPa), depending on of the construction version

• Low output for low particle diameter

• Bad performances at charge

• Emission of effluent at wet cyclone

• Erosion sensitive and constipation danger to the entrance

• Possibly noise nuisance

Usually a cyclone is used for its relatively high remaining emission because of its relatively small efficiency and used as a pre-separator to remove the largest dust load for second dust removal installation like for example a scrubber or cloth filter.
The pre-separator happen generally on particles > 5µm and are employed its in:

• The wood - and piece of furniture industry

• The construction sector

• The glass industry

• The transport sector with storage - and shipment

• The foods industry

• Detritus combustion installations

• The chemical industry

• Melting processes in metallurgy

• Coffee heathers
  

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