The invention relates to a fluidized-bed device (F1, F2) provided with a hearth (1, 23) equipped with gas mixture feeds called primary feeds, said gas mixture being enriched with oxygen, and said hearth (1, 23) being provided with a network of two types of primary feed nozzle, a first type of nozzle (B1, B′1) injecting a first gas mixture at a first level close to the hearth (1, 23) and a second type of nozzle (B2, B′2) injecting a second oxygen-enriched gas mixture at a second level above the first level.According to the invention, said second type of nozzle (B2, B′2) consists of a device for mixing oxygen with a second gas component and connected by its lower end to an oxygen feed (11A, 11A′) and to a feed of second gas component, and of a device for injecting this mixture into the combustion chamber.