A process for at least one of a chemical and a physical treatment of fluidizable substances in a reactor. The process includes introducing a hot gas into an interior of the reactor through a gas supply tube and cooling at least one of the hot gas and the gas supply tube with a coolant. The cooling is performed by contacting the hot gas with the coolant so as to provide a temperature of a wall of the gas supply tube at least 50° C. lower than a temperature of the gas at an inlet of the gas supply tube facing away from the interior of the reactor.