This is the device that separates and collects the particle in the gas with the centrifugal force that reacts on the particle by carrying out rotating movement in dirty gas. The most representative device is the CYCLONE. When amount of gas for treatment is considerable and when high dust collection efficiency is required, there is the MULTI CYCLONE that is used by connecting many cyclones in a row when it comes to the light caliber (mostly 100mm ~ 150mm cyclone). CYCLONE in flows the gas within the scope of 7~15m/sec, and 100H2O pressure loss results when the entrance fluid velocity is about 12m/sec. Treatment effect decreases when the gas viscosity that passes though the inside is smaller and when the Entrance gas speed and particle’s density level are greater.