Section summary |
---|

1. Introduction |

2. Applications of
cyclones |

3. Cyclone
Standard Geometry |

4. Cyclone Step by Step design guide |

5. Cyclone design Excel calculation
tool |

There are different processes for collecting the dust in a gas
stream (see global overview
here), among them, cyclones are probably one of the most
widespread solution, in any industry. They are fairly simple from a
mechanical point of view and therefore generally provide a cost
effective solution. However, assessing the performance of a cyclone
and designing a new equipment for a particular application is not
always well understood and only partial literature is often found.
The objective of this page is to provide a step by step approach to
cyclone design. This can be sufficient to check quickly the
performance of an existing cyclone or during pre-design, *one
should however reckon that the methodology below is not suited for
detailed design which should be carried out with a reputable
supplier which will likely have refined the original calculation
codes provided in literature and made them more precise.* One
should also remark that the method given is only one among several
published models which may have different accuracy.

*Article in development, please stay tuned for updates*

Cyclones are particularly used in the following applications :

- Plastics : after transport of pellets, to catch plastic dust

- Wood industry : to collect dust from sawmills

- Chemicals : to collect dust from a process or at the end of a pneumatic conveying line to control emissions

- Agriculture : to dedust the air used to convey material to a silo

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...)

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

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

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

This design guide is based on the works published by Bohnet in 1997. The approach is valid for standard cyclones with squared tangential inlets and with a small dust load in the order of max 10 g/m3. For different types of inlet or higher dust loads, some corrections are necessary.

Validity of the model : as mentionned above it is a good model for estimating the performance of a cyclone in basic design or troubleshooting but gives errors up to 40% vs experiments, depending on the conditions, thus detail calculations should be done with the help of a company specializing in cyclone design and having improved the calculation code.

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

K ratios : K_{H}, K_{B}, K_{S}, K_{i},
K_{L}, K_{Z}, K_{D} from table 1 or actual
cyclone dimension

With :

A_{e} = product inlet section
area (m2)
_{B} = B_{C}/D_{c}

A_{i} = gas outlet section
area (m2)

R_{i} = radius of gas outlet
pipe (m)

Kr_{e} = average radius of
the fluid vein (m)

A_{f} = area of friction of
powder on the sides of the cyclone (m2)

K_{H} = H_{C}/Dc

K_{i} = D_{i}/D_{c}

K_{L} = L_{c}/D_{c}

K_{Z} = Z_{c}/D_{c}

K_{S} = S_{c}/D_{c}

D_{c} = diameter of the
cyclone (m)

With :

V_{c} = volumetric flow of
the continuous phase (gas) (m3/s)

u_{Ce} =inlet velocity (m/s)

u_{Ci} =outlet velocity (m/s)

K_{i} = D_{i}/Dc

K_{B} = B_{C}/Dc

K_{H} = H_{C}/Dc

Dc = diameter of the cyclone (m)
With :

C_{e} = coefficient of
contraction at inlet

K_{i} = D_{i}/Dc

K_{B} = B_{C}/Dc

K_{H} = H_{C}/Dc

u_{Ce} =inlet velocity (m/s)

u_{CC} =cyclone walls
velocity (m/s)

Re_{c} = Reynolds number

μ_{c} = viscosity of the
continuous phase (gas) (Pa.s)
_{c} = density of the continuous phase (kg/m3)

Dc = diameter of the cyclone (m)

ρC_{f} = friction coefficient

With :

u_{Cri} = gas velocity at the
radius Ri (m/s)

V_{c} = volumetric flow of
the continuous phase (gas) (m3/s)

K_{i} = D_{i}/D_{c}

K_{L} = L_{c}/D_{c}

K_{Z} = Z_{c}/D_{c}

K_{S} = S_{c}/D_{c}

D_{c} = diameter of the
cyclone (m)

u_{Cθi} = (m/s)

u_{Ci} =outlet velocity (m/s)

C_{e} = coefficient of
contraction at inlet

A_{e} = product inlet section
area (m2)

A_{i} = gas outlet section
area (m2)

R_{i} = radius of gas outlet
pipe (m)

r_{e} = average radius of the
fluid vein (m)

C_{f} = friction coefficient

A_{f} = area of friction of
powder on the sides of the cyclone (m2)

Particles having a diameter equal to the cut off diameter are captured with an efficiency of 50%. It means that the cyclone will capture 50% of the particles having this diameter in the gas stream and will let through the other 50%.

With :

u_{Cri} = gas velocity at the
radius R_{i} (m/s)

μ_{c} = viscosity of the
continuous phase (gas) (Pa.s)

K_{i} = D_{i}/D_{c}

Dc = diameter of the cyclone (m)

Δρ = difference in densities (kg/m3)

u_{Cθi} = (m/s)

The efficiencies are calculated relatively to the cut off diameter. Bigger particles will lead better efficiencies. Smaller particles to lower efficiencies. A factor Г is used in the calculation and is usually in the order of 3 (+/- 1).

d_{i} = particle of diameter i
for which the efficiency is calculated (m)

d_{c} = cut off diameter (m)

With :

ΔP_{c} = cyclone pressure drop
(Pa)

ξ_{c} = total pressure drop
coefficient of the cylone

ξ_{ce} = pressure drop
coefficient in the inlet and inside the cyclone

ξ_{ci} = pressure drop
coefficient in the outlet of the cyclone

C_{fi} = 0.70 to 0.75

A
simplified version of the calculation tool can be found here -
a more complete tool will be developped soon. 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

Bohnet 1997