Multi-stage process for combusting fuels containing fixed-nitrogen species

Fuels containing fixed-nitrogen chemical species are combusted in a multi-stage process. The process which converts substantially all of the fixed-nitrogen into molecular nitrogen (and thus avoids the formation of significant amounts of nitrogen oxides from the fixed-nitrogen) comprises six steps: (a) mixing the fuel with at least one first oxidizing agent in amounts such that the equivalence ratio of said fuel to said oxidizing agent is at least about 1.4; (b) partially combusting the mixture resulting from step (a) in at least one first stage at a first temperature of about 1750 DEG to about 2150 DEG K., with a residence time of at least 0.03 second to less than 0.2 second; (c) injecting a free radical agent into the partially combusted mixture of said fuel and said first oxidizing agent; (d) reacting the mixture of said free radical agent and said partially combusted mixture of said fuel and said first oxidizing agent for at least about 0.05 second to about 0.2 second; (e) mixing the reaction products resulting from step (d) with at least one second oxidizing agent in an amount such that the equivalence ratio of reaction products to the total amount of oxidizing agents in the mixture will be about 1.0 or less, such mixing taking place under conditions such that the temperature of the mixture will not exceed about 1800 DEG K.; and (f) completely combusting the mixture resulting from step (e) in at least one second stage at a second temperature of less than about 1800 DEG K.