The flue gas first enters the cyclone dust collector which acts as a primary dust collector to make the large dust particles in the flue gas settle down. The cyclone dust collector is a dust removal device which uses the centrifugal force generated by the cyclone flow to separate the dust particles from the air flow. Afterwards, the flue gas enters the wet scrubber dust collector which is a circular-type cylinder. The circulating water enters the dust collector from the upper overflow tank to form a uniform water film on the inner wall of the dust collector. The flue gas is induced tangentially or spirally from the lower part of the cylinder and rotates in the cylinder. Under the influence of the centrifugal force, the dust particles are separated from the flue gas and then the flue gas is also spirally led out from the top of the cylinder. The dust particles are thrown to the water film, transferred to the bottom and finally discharged from the dust port.