Method and apparatus for reducing nitrous oxide emissions from combustors

A method for operating a combustor of the type having a secondary fuel/air mixing tube and a plurality of primary fuel/air mixing tubes spaced radially outward therefrom, wherein the improvement comprises:

• flowing fuel and air into said primary mixing tubes at a ratio between approximately fifty to seventy-five percent (50-75%) of the stoichiometric ratio for the fuel employed;
• mixing said fuel and air in the primary mixing tubes;
• discharging said mixture from the primary mixing tubes circumferentially into the outer portion of the combustor;
• igniting said mixture from the primary mixing tubes;
• flowing fuel and air into said secondary mixing tube at a ratio not exceeding approximately seventy-five percent (75%) of the stoichiometric ratio for the fuel employed;
• mixing said fuel and air in the secondary mixing tube;
• imparting a circumferential swirl to the fuel and air mixture;
• discharging the swirling fuel and air mixture from the secondary tube to the central portion of the combustor, whereby the secondary fuel and air mixture is centrifuged radially outward into the ignited primary mixture.