In a cyclone separator used for separating solids from gases, we discovered placing at least one opening in a lateral surface of a gas outlet conduit on a side facing away from an inlet to the cyclone separator prevents coke deposits from forming thereon. A plurality of openings may be placed on the side of the lateral surface of the gas outlet conduit facing away from the inlet. In an embodiment, no openings are placed on a side of the lateral surface facing the inlet to the cyclone separator.