How Cyclones Work

As mentioned in Chap. 1, cyclones work as a result of the centrifugal forces acting on the particles suspended in the swirling gas stream. This causes the particles, which are denser than the gas, to move outward to the cyclone wall, along which they are transported downward to the dust exit. The cleaned gas leaves near the centerline, in a reverse-flow cyclone through the roof. In a once-through or flow-through cyclone, the cleaned gas exits out the bottom.  

In this chapter we take a first look at the flow of gas and particles in cyclones. We also introduce the two key performance indicators for cyclones their separation efficiency and their pressure drop. 

---

With this discussion, we have introduced the basic working characteristics of gas cyclones. In Chaps. 4, 5 and 6 we shall consider the gas flow pattern and the separation in more detail, and also models for predicting them as reported in the research literature. In Chap. 10 we will discuss how cyclone performance can best be determined from laboratory and/or plant measurements. 

We will leave it to the reader to locate the point corresponding to Stk and Eu on the plot of Svarovsky, to see how well this cyclone works. Remember to change the scale velocity from Vin to (vz)- You will find the necessary information for this in Table 8.B.I. 

A full understanding of how the cyclone works and how individual particles behave within it has been slow in following these pioneering industrial devel-... 

A simple and reliable set of equations to predict cyclone performance from a known size distribution, cyclone geometry and flow rate does not exist. Laboratory testing must be used to ensure that a desired separation can be accon li ed. It is usefiil, therefore, to have some notion of how the important variables are related, in order to minimise the required amount of test work to optimise performance. The inqtortant design and process variables are cut size, cyclone diameter, flow rate and pressure drop. 

One naturally would like to re-use the media as long as it can be freed of the accumulated soot particles. In order to check how well it would work, a very simple de-duster set up was used in the tests at POSTEC, with contaminated sand simply being allowed to fall into the de-duster through a tube mounted over it. The other end of the tube led to a cyclone where the dust removed from the sand was collected. Figure 8, shows the separation achieved at loadings of I 1 and 1 3. 

---