Methods and apparatus for burning fuel with low NO.sub.x formation

An improved burner apparatus for discharging a mixture of fuel and air into a furnace space wherein said mixture is burned and flue gases having low NO.sub.x content are formed therefrom comprising:

• a housing having an open end attached to said furnace space;
• means for introducing a controlled quantity of air into said housing and into said furnace space attached to said housing;
• primary mixer-nozzle means for mixing a mixture of fuel, air and flue gases and discharging said mixture into said furnace space attached centrally within said housing, said primary mixer-nozzle means including a pressurized fuel inlet for connection to a source of pressurized fuel, at least one air inlet and a plurality of flue gases inlet connections;
• a plurality of flue gases conduits connected at the ends thereof to said flue gases inlet connections and being positioned whereby the other ends thereof are located in spaced relationship around said primary mixer-nozzle means and connect to said furnace space whereby flue gases from within said furnace space are drawn into said flue gases conduits and are conducted to said primary mixer-nozzle means thereby;
• and
• a plurality of secondary fuel nozzle means attached to said housing and having pressurized fuel inlets for connection to a source of pressurized fuel for introducing additional fuel into said furnace space positioned in spaced relationship around the periphery of said housing whereby fuel introduced into said furnace space thereby mixes with air and flue gases contained within said furnace space.

A method of discharging an at least substantially stoichiometric mixture of fuel and air into a furnace space wherein said mixture is burned and flue gases having low NO.sub.x content are formed therefrom comprising the steps of:

• discharging said air into said furnace space;
• mixing a portion of said fuel with flue gases from said furnace space to form a first fuel mixture;
• discharging said first fuel mixture into said furnace space whereby said mixture combines with air and is burned in a primary reaction zone therein and flue gases having low NO.sub.x content are formed therefrom;
• and
• discharging the remaining portion of said fuel into a secondary reaction zone in said furnace space whereby said fuel mixes with flue gases and air contained in said furnace space to form a second fuel mixture which is burned in said secondary reaction zone and additional flue gases having low NO.sub.x content are formed therefrom.

A method of discharging an at least substantially stoichiometric mixture of fuel and air into a furnace space wherein said mixture is burned and flue gases having low NO.sub.x content are formed therefrom comprising the steps of:

• mixing a portion of said fuel with a portion of said air and flue gases from said furnace space to form a first fuel-air mixture diluted with flue gases;
• discharging the remaining portion of said air into said furnace space;
• discharging said diluted first fuel-air mixture into said furnace space whereby said mixture is burned in a primary reaction zone therein and flue gases having low NO.sub.x content are formed therefrom;
• discharging the remaining portion of said fuel into said secondary reaction zone wherein said remaining portion of fuel mixes with air remaining in said furnace space, with products of combustion from said primary reaction zone and with flue gases contained in said furnace space to form a second fuel-air mixture diluted with products of combustion and flue gases whereby said mixture is burned in said secondary reaction zone and additional flue gases having low NO.sub.x content are formed therefrom.