Abstract: A diffuser or orifice plate is positioned across the bore of a feed pipe supplying a mixture of pressurized air and recycled flue gas to the combustion chamber of a gas burner associated with a boiler. The diffuser plate comprises inner and outer, radially spaced apart, annular baffles. The baffles define a central opening and an outer series of openings forming an annular array. Part of the gas mixture is accelerated as it passes through the restrictive outer openings and forms an annular stream. Part of the gas mixture passes through the central opening in the form of a lance-like stream. Fuel gas is injected into the annular stream immediately downstream of the diffuser plate. The resulting air/flue gas/fuel gas mixture mixes and adopts an elongated form in the combustion chamber. The burner feed assembly described contributes to maintaining the Ox content in the burner flue gas at a low level such as less than 15 ppm.