Vibration-resistant low no.sub.x burner

Abstract

A low NO.sub.x burner includes a primary air and fuel discharge assembly which, in turn, includes a burner plate having a plurality of slots from which fuel gas jets and combustion air are discharged. The slots are arranged such that the width of the recirculation zones between adjacent slots substantially varies between the central region of the burner plate and its perimeter. With this construction, the local ignition patterns vary such that local oscillations of flame front occur at different frequencies so that vibrations are greatly dampened and resonance problems in the furnace minimized or eliminated. In applications where high excess air is not desirable, such as boiler applications, the burner is modified by providing a secondary fuel and flue gas injection assembly to form a two stage burner. In the preferred embodiment, the secondary injection assembly includes a plurality of discrete fuel and flue gas injection tubes arranged around the primary air and fuel gas discharge assembly. The secondary fuel and flue gases are directed radially inward and downstream from the burner plate so that they mix with the combustion air entering through the burner plate slots in a secondary combustion zone. The resulting delay in the combustion of the secondary fuel gas and the need for heating the flue gas lowers the overall combustion temperature, which in turn reduces the NO.sub.x formation in the second or downstream combustion zone.