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Section summary |
---|

1. Introduction :
Leith & Licht method |

2. Domain of
validity |

3. Cyclone
Standard Geometry |

4. Leith & Licht model Step by Step
design guide |

5. Cyclone design Excel calculation
tool |

There are different methods published in the literature to design cyclones. The method presented in this page was developped by Leith & Licht in the 70s. The calculation principle is based on a force balance on the particles that need to be separated in the cyclone [Altmeyer]. From comparative of cyclone design methods that have been published in literature, the Leith & Licht method is not always the most precise [Altmeyer] [Dirgo]. However its quite simple calculation method makes it an interesting method for quick assessment.

*The method presented gives approximate results and should not be
used for detail design. It is presented to illustrate the
principles of designing a cyclone and for a rough estimation of
the design performance. A specialized company should always be
consulted for detail design prior to construction of a cyclone.*

Another
method is presented in this page, it can be interesting to
check different models.

The method of Leith & Licht was based on the following range of experimental data [Altmeyer] :

- Gas flowrate : 0.06 < V < 0.13 m3/s
- Temperature : 310 < T < 422 K
- Pressure : atmospheric
- Unspecified charge load

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Cyclones efficiency is directly related to their geometry, which
has been the object of various research. From these research papers,
a set of STANDARD dimensions have been defined. **Those
dimensions, or rather proportions, constitute the basis of most of
the design across the industry**. It is recommended to keep
those standard configurations, or some adaptation by reputable
suppliers, and not modify it. Specific design can still be developed
for specific high value applications (FCC for example) but it goes
beyond the methodology presented here, requiring modelization, pilot
trials...etc...

The table below is due to Koch and Licht (1977) and is summarizing the work of different authors (Lapple, Stairmand...)

Standard Geometries for cyclones with tangential inlet | |||||

Standard | High efficiency | ||||

Dimensions | Lapple | Swift | Peterson Whitby |
Stairmand | Swift |

a/D | 0.5 |
0.5 |
0.583 |
0.5 |
0.44 |

b/D | 0.25 |
0.25 |
0.208 |
0.2 |
0.21 |

S/D | 0.625 |
0.6 |
0.583 |
0.5 |
0.5 |

De/D | 0.5 |
0.5 |
0.5 |
0.5 |
0.4 |

h/D | 2 |
1.75 |
1.333 |
1.5 |
1.4 |

(H-h)/D | 2 |
2 |
1.84 |
2.5 |
2.5 |

B/D | 0.25 |
0.4 |
0.5 |
0.375 |
0.4 |

**Table 1 : Standard cyclone
geometries for a tangential inlet**

All the dimensions of the cyclones are related to the diameter D. A standard geometry is then selected and the diameter D is adjusted to get the desired performance.

**Figure 1 : Cyclone drawing and
nomenclature of characteristic geometry
**

The following data are required to be able to calculate a cyclone efficiency and cut off diameter with the model of Leith and Licht :

- Inlet gas flowrate
- Particle diameter
- Particle density
- Temperature
- Pressure
- Gas density
- Gas viscosity

The calculation method proposed is reported in [Dirgo]

If you design a new cyclone, **chose one of the standard geometry
in table 1 and assume a diameter D.** If you test an existing
cyclone, determine the different ratios for the actual equipment you
are evaluating.

All the individual length (a, b, S, de, B, h, H) must be determined.

The natural length l of a cyclone is farthest distance from the gas outlet that the gas goes while spinning.

With :

l = natural length of the cyclone (m)

De = diameter of gas outlet (m)

D = diameter of the cyclone (m)

a = vertical dimension of the gas
inlet (m)

b = horizontal dimension of the gas
inlet (m)

Note : if l > (H-S) then l is replaced by H-S in the equations.

With :

d_{c} = diameter of the
cyclone at the natural length l (m)

D = diameter of the cyclone (m)

B = diameter of the product outlet
(m)

S = cyclone gas outlet duct length
(m)

l = cyclone natural length (m) as
calculated in paragraph 4.2

H = cyclone height (m)

h = cyclone cylinder height (m)With :

n = vortex exponent (-)

D = cyclone diameter (m)

T = temperature (K)

With :

Ψ = cyclone inertia parameter (-)

ρ_{p} = particles density
(kg/m3)

d = particles diameter (m)

d = particles diameter (m)

v_{i} = gas inlet velocity
(m/s)

n = vortex exponent (-) as calculated
in paragraph 4.5

μ = gas viscosity (Pa.s)

D = cyclone diameter (m)

With :

C = Geometry parameter (-)

De = diameter of gas outlet (m)

D = diameter of the cyclone (m)
De = diameter of gas outlet (m)

B = diameter of the product outlet (m)

S = cyclone gas outlet duct length (m)

l = cyclone natural length (m) as
calculated in paragraph 4.2

H = cyclone height (m)

h = cyclone cylinder height (m)
The efficiency of the cyclone can then be calculated thanks to the parameters given above.

η = cyclone efficiency

n as calculated in paragraph 4.4

Ψ as calculated in paragraph 4.5

C as calculated in paragraph 4.6

n as calculated in paragraph 4.4

Ψ as calculated in paragraph 4.5

C as calculated in paragraph 4.6

The calculation of the cut off diameter in the model of Leith and Licht is given by the following equations [Altmeyer] :

With :

N_{t} = number of times the gas
turns around in the cyclone in between the inlet and outlet

V_{0} = gas inlet volumetric flowrate (m3/s)

a = vertical dimension of the gas inlet (m)

V

a = vertical dimension of the gas inlet (m)

b = horizontal dimension of the gas
inlet (m)

dpc = cut off diameter of the cyclone (m)

μ = gas viscosity (Pa.s)

dpc = cut off diameter of the cyclone (m)

μ = gas viscosity (Pa.s)

D = cyclone diameter (m)

ρ_{p} = particles density
(kg/m3)

ρ = gas density (kg/m3)

The pressure drop in the cyclone is
given, according to Leith and Licht by the following formula
[Altmeyer] :

With :

ΔP = cyclone pressure drop (Pa)

Va = vertical dimension of the gas inlet (m)

b = horizontal dimension of the gas
inlet (m)

De = diameter of gas outlet (m)

A simplified version of the
calculation tool can be found here. Note that this tool **cannot
be used for detail design** as stated in the file, always link
with a commercial company to confirm the design.

Sources

[Dirgo] Cyclone Collection Efficiency: Comparison of Experimental Results with Theoretical Predictions, Dirgo & Leith, Aerosol Science and Technology, 2007

[Altmeyer] Comparison of different models of cyclone prediction
performance for

various operating conditions using a general software, Altmeyer et
al, Chemical Engineering and Processing, 2004