Abstract: A device enabling air-blast nozzles to be replaceably mounted in the walls of reaction chambers, or ovens used for processing materials, in order to remove material caked or accumulated on the inside surface of the walls (2). Fitted in the wall (2) is an exchangeable pipe (1) which extends from the outside through part of the wall towards the inside surface, a nozzle (5) being mounted at the oven end of the pipe.