Abstract: Device for injecting fluid in successive layers into a rotating fluidized bed and methods for catalytic polymerization, drying or other treatments of solid particles or for catalytic conversion of fluids, in which a succession of injectors (12), distributed around the fixed circular wall (2) of a circular reaction chamber, inject along this wall, in successive layers, one or more fluids (13), which entrain the solid particles (17), passing through this chamber, in a movement of rapid rotation whereof the centrifugal force concentrates these particles along this wall, thereby forming a fluidized bed rotating around a central duct (3), through which the fluids are removed.