Apparatus for burning nitrogen-containing fuels

Claim 1

A combustor, for combustion of a fuel and production of a fuel-lean combustion effluent having a moving fuel-lean flame front, comprising: a first combustion chamber having a closed upstream end and an open downstream end, wherein said first combustion chamber has a volume sufficient to burn a substantial portion of said fuel under fuel-rich combustion conditions and without further addition of air to produce a fuel-rich combustion effluent comprising a moving fuel-rich flame front, unburned fuel, and partially burned fuel, wherein the length of said first combustion chamber is such that the minimum first combustion chamber retention time of said fuel is at least about 35 milliseconds when said fuel is flowing at a velocity ranging from about 1 foot/second to about 500 feet/second; a second combustion chamber having an open upstream end and an open downstream end, wherein said second combustion chamber has a volume sufficient to burn a portion of said fuel under fuel-lean combustion conditions to produce a fuel-lean combustion effluent comprising a moving fuel-lean flame front, wherein the length of said second combustion chamber is such that the minimum second combustion chamber retention time of said fuel is at least about 15 milliseconds when said fuel is flowing at a velocity ranging from about 1 foot/second to about 500 feet/second; a combustion mixture introduction means for introducing and intimately mixing said fuel and at least one stream of a first volume of primary air, in proportions sufficient to produce a fuel-rich combustible mixture, having a fuel/air ratio greater than the stoichiometric ratio, said combustible mixture introduction means, located adjacent said upstream end of said first combustion chamber, including: (1) a mixing chamber, a plurality of primary air introduction means spaced about the periphery of said mixing chamber and adapted to introduce a first stream of said first volume of primary air in a generally circular direction tangential to an inner wall of said mixing chamber, and (2) another plurality of primary air introduction means spaced about the periphery of said mixing chamber and adapted to introduce a second stream of said first volume of primary air in a generally circular direction tangential to the inner wall of said mixing chamber downstream from the introduction means adapted to introduce the said first stream of the first volume of primary air; wherein the second stream of said first volume of primary air will be introduced so as to swirl in a direction opposite the first stream of said first volume of primary air, such that as one of the plurality of means is introducing air in a clockwise direction, the other introduces air in a counterclockwise direction; and a fuel-rich combustion region termination means for abruptly terminating said fuel-rich combustion region at a location adjacent said downstream end of said first combustion chamber, wherein said fuel-rich combustion region termination means includes a means for reducing the cross-sectional area of fuel-rich combustion effluent leaving said first combustion chamber and introducing and intimately mixing at least one stream of a second volume of secondary air with said fuel-rich combustion effluent, immediately adjacent said downstream end of said first combustion chamber, in an amount sufficient to produce a fuel-lean combustible mixture having a fuel/air ratio less than the stoichiometric ratio, said second combustion chamber being in communication with said fuel-rich combustion termination means and being of an increased cross-sectional area so as to expand the combustion effluent and air leaving said fuel-rich combustion termination means.