Nitrogen oxide control using internally recirculated flue gas

Claim 2

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in a floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone of said furnace by way of said inlet port; (b) discharging at least a first portion of said fuel into said combustion zone by way of said inlet port from a primary fuel nozzle whereby said first portion of said fuel mixes with air in said combustion zone and is combusted in said combustion flame; (c) collecting at least a part of said downdraft flue gas from adjacent said furnace wall; and (d) educting at least a portion of said collected downdraft flue gas into said combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein the driving fluid used for educting said portion of collected downdraft flue gas is pressurized fuel gas.

Claim 3

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in a floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone of said furnace by way of said inlet portion; (b) discharging at least a first portion of said fuel into said combustion zone by way of said inlet port from a primary fuel nozzle whereby said first portion of said fuel mixes with air in said combustion zone and is combusted in said combustion flame; (c) collecting at least a portion of said downdraft flue gas from adjacent said furnace wall; and (d) educting at least a portion of said collected downdraft flue gas into said combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein the driving fluid used for educting said portion of collected downdraft flue gas is steam.

Claim 4

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in a floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone of said furnace by way of said inlet portion; (b) discharging at least a first portion of said fuel into said combustion zone by way of said inlet port from a primary fuel nozzle whereby said first portion of said fuel mixes with air in said combustion zone and is combusted in said combustion flame; (c) collecting at least a portion of said downdraft flue gas from adjacent said furnace wall; and (d) educting at least a portion of said collected downdraft flue gas into said combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein the driving fluid used for educting said portion of collected downdraft flue gas is steam.

Claim 5

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in a floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone of said furnace by way of said inlet port; (b) discharging at least a first portion of said fuel into said combustion zone by way of said inlet port from a primary fuel nozzle whereby said first portion of said fuel mixes with air in said combustion zone and is combusted in said combustion flame; (c) collecting at least a part of said downdraft flue gas from adjacent said furnace wall; and (d) injecting said collected downdraft flue gas into said combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein: said furnace further includes an upwardly extending barrier member extending upwardly from said floor of said furnace and surrounding said fuel and air inlet port; said furnace also includes a horizontally extending barrier member spaced above said floor of said furnace and positioned between said tubes and said upwardly extending barrier member such that said horizontally extending barrier member and said floor of said furnace form a passageway wherein said downdraft flue gas is collected in accordance with step (c); at least one opening extend through said upwardly extending barrier member; an eductor extends into said opening; and at least a portion of said downward flue gas collected in said passageway is injected into said combustion flame in accordance with step (d) using said eductor and a pressurized driving fluid.

Claim 6

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in a floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone of said furnace by way of said inlet port; (b) discharging at least a first portion of said fuel into said combustion zone by way of said inlet port from a primary fuel nozzle whereby said first portion of said fuel mixes with air in said combustion zone and is combusted in said combustion flame; (c) collecting at least a part of said downdraft flue gas from adjacent said furnace wall; and (d) injecting said collected downdraft flue gas into said combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein: said furnace further includes an upwardly extending barrier member extending upwardly from said floor of said furnace and surrounding said fuel and air inlet port; said furnace also includes a horizontally extending barrier member spaced above said floor of said furnace and positioned between said tubes and said upwardly extending barrier member such that said horizontally extending barrier member and said floor of said furnace form a passageway wherein said downdraft flue gas is collected in accordance with step (c); at least one opening extend through said upwardly extending barrier member; an eductor extends into said opening; and at least a portion of said downward flue gas collected in said passageway is injected into said combustion flame in accordance with step (d) using said eductor and a pressurized driving fluid.

Claim 7

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet portion in the floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone by way of said inlet port; (b) discharging a first portion of said fuel into said combustion zone by way of said inlet port using a primary fuel nozzle such that said first portion of said fuel mixes with air in said combustion zone and is combusted in a primary zone within said combustion flame; (c) discharging a secondary portion of said fuel into said combustion zone from at least one secondary fuel nozzle such that said secondary portion of said fuel mixes with air in said combustion zone and is combusted in a secondary zone within said combustion flame; (d) collecting at least a part of said downdraft flue gas from adjacent said furnace wall; and (e) injecting said collected downdraft flue gas into said combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein at least a first portion of said collected downdraft flue gas is injected into said combustion flame by aspirating said first portion of said collected downdraft flue gas into said combustion flame using said secondary portion of said fuel.

Claim 8

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet portion in the floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone by way of said inlet port; (b) discharging a first portion of said fuel into said combustion zone by way of said inlet port using a primary fuel nozzle such that said first portion of said fuel mixes with air in said combustion zone and is combusted in a primary zone within said combustion flame; (c) discharging a secondary portion of said fuel into said combustion zone from at least one secondary fuel nozzle such that said secondary portion of said fuel mixes with air in said combustion zone and is combusted in a secondary zone within said combustion flame; (d) collecting at least a part of said downdraft flue gas from adjacent said furnace wall; and (e) injecting said collected downdraft flue gas into said combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein at least a first portion of said collected downdraft flue gas is injected into said combustion flame by aspirating said first portion of said collected downdraft flue gas into said combustion flame using said secondary portion of said fuel.

Claim 9

A process as described in claim 4 wherein said secondary fuel nozzle is positioned peripherally to said inlet port.

Claim 10

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet part in the floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone by way of said inlet port; (b) discharging a first portion of said fuel into said combustion zone by way of said inlet port using a primary fuel nozzle such that said first portion of said fuel mixes with air in said combustion zone and is combusted in a primary zone within said combustion flame; (c) discharging a secondary portion of said fuel into said combustion zone from at least one secondary fuel nozzle such that said secondary portion of said fuel mixes with air in said combustion zone and is combusted in a secondary zone within said combustion flame; (d) collecting at least a part of said downdraft flue gas from adjacent said furnace wall; and (e) injecting said collected downdraft flue gas combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein: said furnace further includes an upwardly extending barrier member extending vertically from said floor of said furnace and surrounding said fuel and air inlet port; said furnace also includes a horizontally extending barrier member spaced above said floor of said furnace and positioned between said tubes and said upwardly extending barrier member such that said horizontally extending barrier member and said floor of said furnace form a passageway wherein said downdraft flue gas is collected in accordance with step (d); said horizontally extending barrier member has an inner edge; said inner edge is spaced apart from said upwardly extending barrier member such that a gap is defined between said inner edge and said upwardly extending barrier member; a plurality of secondary fuel nozzles are used in step (c) for discharging said secondary portion of said fuel into said combustion zone; and said secondary fuel nozzles are associated with said gap such that, in accordance with step (e), the flow of said secondary portion of said fuel from said secondary fuel nozzles aspirates at least a first portion of said downdraft flue gas collected in said passageway into said combustion flame.

Claim 11

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet part in the floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone by way of said inlet port; (b) discharging a first portion of said fuel into said combustion zone by way of said inlet port using a primary fuel nozzle such that said first portion of said fuel mixes with air in said combustion zone and is combusted in a primary zone within said combustion flame; (c) discharging a secondary portion of said fuel into said combustion zone from at least one secondary fuel nozzle such that said secondary portion of said fuel mixes with air in said combustion zone and is combusted in a secondary zone within said combustion flame; (d) collecting at least a part of said downdraft flue gas from adjacent said furnace wall; and (e) injecting said collected downdraft flue gas combustion flame to thereby lower the NO x content of the flue gas effluent from said furnace, wherein: said furnace further includes an upwardly extending barrier member extending vertically from said floor of said furnace and surrounding said fuel and air inlet port; said furnace also includes a horizontally extending barrier member spaced above said floor of said furnace and positioned between said tubes and said upwardly extending barrier member such that said horizontally extending barrier member and said floor of said furnace form a passageway wherein said downdraft flue gas is collected in accordance with step (d); said horizontally extending barrier member has an inner edge; said inner edge is spaced apart from said upwardly extending barrier member such that a gap is defined between said inner edge and said upwardly extending barrier member; a plurality of secondary fuel nozzles are used in step (c) for discharging said secondary portion of said fuel into said combustion zone; and said secondary fuel nozzles are associated with said gap such that, in accordance with step (e), the flow of said secondary portion of said fuel from said secondary fuel nozzles aspirates at least a first portion of said downdraft flue gas collected in said passageway into said combustion flame.

Claim 12

A process as described in claim 6 wherein at least one opening extends through said upwardly extending barrier member; an eductor extends into said opening; and a second portion of said downdraft flue gas collected in said passageway is injected into said combustion flame in accordance with step (e) using said eductor and a pressurized driving fluid.

Claim 13

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in a floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone of said furnace by way of said inlet port; (b) discharging at least a first portion of said fuel into said combustion zone by way of said inlet port from a primary fuel nozzle whereby said first portion of said fuel mixes with air in said combustion zone and is combusted in said combustion flame; (c) injecting at least a portion of said downdraft flue gas into said combustion flame using an injecting means, said injecting means being positioned above the top surface of said floor; and (d) allowing said portion of downdraft flue gas to flow from said furnace wall along the top surface of said floor until said portion of downdraft flue gas reaches said injecting means.

Claim 14

A process for combusting fuel and air to form a combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in a floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone of said furnace by way of said inlet port; (b) discharging at least a first portion of said fuel into said combustion zone by way of said inlet port from a primary fuel nozzle whereby said first portion of said fuel mixes with air in said combustion zone and is combusted in said combustion flame; (c) injecting at least a portion of said downdraft flue gas into said combustion flame using an injecting means, said injecting means being positioned above the top surface of said floor; and (d) allowing said portion of downdraft flue gas to flow from said furnace wall along the top surface of said floor until said portion of downdraft flue gas reaches said injecting means.

Claim 15

A process as described in claim 8 wherein said portion of downdraft flue gas is injected into said combustion flame in accordance with step (c) using a pressurized driving fluid.

Claim 16

A process as described in claim 9 wherein said pressurized driving fluid is steam.

Claim 17

A process as described in claim 9 wherein said pressurized driving fluid is fuel gas.

Claim 18

A process as described in claim 8 wherein: said furnace further includes an upwardly extending barrier member extending upwardly from said floor of said furnace and surrounding said fuel and air inlet port; at least one opening extends through said upwardly extending barrier member; said injecting means comprises an eductor which extends into said opening; and said portion of downdraft flue gas is injected into said combustion flame in step (c) being said eductor and a pressurized driving fluid.

Claim 19

A process as described in claim 12 wherein said pressurized driving fluid is steam.

Claim 20

A process for combusting fuel and air to form combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in the floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone by way of said inlet port; (b) discharging a first portion of said fuel into said combustion zone by way of said inlet port using a primary fuel nozzle such that said first portion of said fuel mixes with air in said combustion zone and is combusted in a primary zone within said combustion flame; (c) discharging a secondary portion of said fuel into said combustion zone from at least one secondary fuel nozzle such that said secondary portion of said fuel mixes with air in said combustion zone and is combusted in a secondary zone within said combustion flame, said secondary fuel nozzle being positioned above the top surface of said floor; (d) aspirating at least a first portion of said downdraft flue gas into said combustion flame using said secondary fuel nozzle and said secondary portion of said fuel; and (e) allowing said first portion of downdraft flue gas to flow from said furnace wall along the top surface of said floor until said first portion of downdraft flue gas reaches said secondary fuel nozzle.

Claim 21

A process for combusting fuel and air to form combustion flame in a combustion zone of a furnace such that the flue gas effluent from said furnace has a reduced NO x content, said furnace having a fuel and air inlet port in the floor thereof, a furnace wall extending upwardly from said floor, and a plurality of furnace tubes positioned adjacent said furnace wall such that a downward flow of downdraft flue gas occurs adjacent said furnace wall, said process comprising the steps of: (a) discharging said air into said combustion zone by way of said inlet port; (b) discharging a first portion of said fuel into said combustion zone by way of said inlet port using a primary fuel nozzle such that said first portion of said fuel mixes with air in said combustion zone and is combusted in a primary zone within said combustion flame; (c) discharging a secondary portion of said fuel into said combustion zone from at least one secondary fuel nozzle such that said secondary portion of said fuel mixes with air in said combustion zone and is combusted in a secondary zone within said combustion flame, said secondary fuel nozzle being positioned above the top surface of said floor; (d) aspirating at least a first portion of said downdraft flue gas into said combustion flame using said secondary fuel nozzle and said secondary portion of said fuel; and (e) allowing said first portion of downdraft flue gas to flow from said furnace wall along the top surface of said floor until said first portion of downdraft flue gas reaches said secondary fuel nozzle.

Claim 22

A process as described in claim 14 wherein said secondary fuel nozzle is positioned peripherally to said inlet port.

Claim 23

A process as described in claim 14 wherein: said furnace further includes an upwardly extending barrier member extending vertically from said floor of said furnace and surrounding said fuel and air inlet port; at least one opening extends through said upwardly extending barrier member; an eductor extends into said opening; a second portion of downdraft flue gas is injected into said combustion flame using said eductor and a pressurized driving fluid; and said second portion of downdraft flue gas is allowed to flow from said furnace wall along the top surface of said floor until said second portion of downdraft flue gas reaches said eductor.

Claim 24

A process as described in claim 16 wherein said pressurized driving fluid is steam.

Claim 25

A process as described in claim 14 wherein: a plurality of secondary fuel nozzles are used in step (c) and (d) for discharging said secondary portion of said fuel into said combustion zone and for aspirating said first portion of said downdraft flue gas into said combustion flame and said secondary fuel nozzles are positioned above the top surface of said floor and peripherally to said inlet port.