In the flue gas cleaning process, cyclones are used for pre-separation of solid materials. This involves removal of coarse dust from the flue gas for the benefit of the downstream flue gas cleaning steps.

The centrifugal force is used to separate solids in a cyclone. This force is developed by rotation of the incoming flue gas, resulting in the dust particles getting hurled onto the outer walls. These then sink and fall into a receiving vessel.

The speed of rotation of the gas determines how effective the separation is - the faster the rotation the more efficient the separation.

100% separation efficiency is however not achieved with cyclones. The process is used to pre-clean the flue gases before the next purification steps.