Abstract: A method and apparatus for modulating the surface area of a radiant infrared burner over which combustion occurs as a function of burner heat output rate. This modulation serves to maintain the heat flux density on the surface of the burner at or near an optimum value over a range of heat output rates. The modulation is effected by means of a piston disposed in the internal cavity of a burner which blocks the passage of combustible gas to areas of the burner downstream of the piston from the gas inlet to the burner. The piston is displaced further downstream with increased gas flow rate resulting in combustion occuring over an increased area of the burner surface as burner heat output rate is increased. In its simplest embodiment, the invention comprises a burner oriented vertically with the combustible gas entering the bottom of the burner and a free piston which floats on the incoming gas stream at a level within the burner which is proportional to the gas flow rate.

Abstract: A method for burning a fuel, containing chemically bound nitrogen, in a two-stage, rich-lean combustion process, including; introducing the fuel and at least one stream of primary air into a primary combustion region at a fuel-air ratio above the stoichiometric ratio and in a manner to intimately mix the fuel and air and establish a stabilized flame adjacent the upstream end of the primary combustion region, maintaining the flame in the primary combustion region for a period of time sufficient to produce a combustion product mixture containing less than a predetermined amount of NO.sub.x pollutants and abruptly terminating the primary combustion region while introducing at least one stream of secondary air into the secondary region in an amount sufficient to reduce the overall fuel-air ratio below the stoichiometric ratio and in a manner to prevent backflow of the secondary air into the primary combustion region.