Abstract: During use of a contact apparatus to remove harmful components, such as sulfur and nitrogen oxides, from waste gas, dust particles are deposited on the interior of the gas-solid contact zone and reduce efficiency of the apparatus. The dust particles can be removed by passing through the contact apparatus a current of a carrier gas supporting solid particles of, for example, siliceous sand. The particles have a diameter of 50 to 2000 .mu.m and the actual linear velocity of the carrier gas in the gas-solid contact zone is from 2 to 15 m/sec. The carrier gas can be the waste gas itself so that dust removal can be carried out without interrupting use of the apparatus. The solid particles can be removed from the carrier gas and recycled for further dust removal.