Abstract: A duct having the shape of a pyramid frustum for the flow of powder in suspension in a carrier gas is of increasing width and decreasing height in the downstream direction. The duct has a solid end-wall and a wall provided with an opening between the open upstream base joined to a supply pipe and a solid portion joined to the open downstream base so as to form a spray-discharge nozzle. The device comprises a screen having holes for the discharge of carrier gas and a grid formed by flat partitions. Inclined deflectors extend transversely within the duct in the vicinity of the opening, the angle of inclination being of increasing value from the upstream end to the downstream end.