Low NOx indirect fire burner

An air-fuel burner comprising

• a heat-transfer tube formed to include an interior region,
• an air-fuel mixing chamber configured to establish a combustible air-fuel mixture therein, and
• an air-fuel nozzle coupled to the air-fuel mixing chamber and arranged to extend into the interior region of the heat-transfer tube, the air-fuel nozzle formed to include three nozzle exits communicating with a combustion chamber defined in the interior region between the air-fuel nozzle and the heat-transfer tube to move the combustible air-fuel mixture from the air-fuel nozzle into the combustion chamber through
• a first nozzle exit formed in the air-fuel nozzle to establish, when a portion of the combustible air-fuel mixture flowing through the first nozzle exit is ignited, a detached first flame extending in radially outward directions in the combustion chamber from the air-fuel nozzle toward the heat-transfer tube, and the detached first flame includes a root positioned to lie between the air-fuel nozzle and the heat-transfer tube and a tip arranged to stabilize on an interior surface of the heat-transfer tube,
• a second nozzle exit formed in the air-fuel nozzle and arranged to lie in spaced-apart relation to the first nozzle exit in a downstream direction away from the air-fuel mixing chamber to establish, when a portion of the combustible air-fuel mixture flowing the through the second nozzle exit is ignited, a detached second flame extending in radially outward directions in the combustion chamber from the air-fuel nozzle toward the interior surface of the heat-transfer tube, and the detached second flame includes a root positioned to lie between the air-fuel nozzle and the heat-transfer tube and a tip arranged to stabilize on the interior surface of the heat-transfer tube, and
• a third nozzle exit formed in the air-fuel nozzle and arranged to lie in spaced-apart relation to the second nozzle exit in the downstream direction to locate the second nozzle exit between the first and third nozzle exits and to establish, when a portion of the combustible air-fuel mixture flowing through the third nozzle exit is ignited, a attached third flame extending in the downstream direction away from the air-fuel nozzle and the detached first and second flames, and the attached third flame includes a root stabilized on the air-fuel nozzle and a tip extending in the downstream direction.

An air-fuel burner comprising

• a heat-transfer tube formed to include an interior region and adapted to discharge heat to an adjacent medium located outside the heat-transfer tube when exposed to heat from a flame generated in the interior region,
• an air-fuel mixing chamber adapted to mix air from an air supply and fuel from a fuel supply to establish a combustible air-fuel mixture therein, and
• an air-fuel nozzle coupled to the air-fuel mixing chamber and arranged to extend into the interior region of the heat-transfer tube in a downstream direction away from the air-fuel mixing chamber, the air-fuel nozzle including
• an air-fuel transfer conduit having an upstream end and a downstream end arranged to lie in spaced-apart relation opposite to the upstream end, the air-fuel transfer conduit being formed to include an air-fuel transfer passageway arranged to transport the combustible air-fuel mixture between the upstream end and the downstream end, and the air-fuel transfer conduit being coupled to the air-fuel mixing chamber at the upstream to cause the air-fuel transfer passageway to open into the air-fuel mixing chamber and the air-fuel transfer conduit is formed to include a first nozzle exit to establish, when a portion of the combustible air-fuel mixture is communicated from the air-fuel transfer passageway through the first nozzle exit is ignited, a detached first flame extending in radially outward directions from the air-fuel transfer conduit toward the heat-transfer tube, the detached first flame having a root positioned to lie in spaced-apart relation to the air-fuel transfer conduit between the air-fuel transfer conduit and the heat-transfer tube and a tip arranged to stabilize on an interior surface of the heat-transfer tube,
• an air-fuel discharge plate formed to include a third nozzle exit arranged to lie in spaced-apart relation to the first nozzle exit in the downstream direction to establish, when a portion of the combustible air-fuel mixture communicated from the air-fuel transfer passageway through the third nozzle exit is ignited, an attached third flame extending in the downstream direction away from the air-fuel transfer conduit and the detached first flame, and the attached third flame includes a root stabilized on the air-fuel discharge plate and a tip extending in the downstream direction, and
• a set of discharge-plate spacers arranged to interconnect the air-fuel discharge plate and the air-fuel transfer conduit, each pair of adjacent discharge-plate spacers cooperating with the air-fuel transfer conduit and the air-fuel discharge plate to define a second nozzle exit upstream of the third nozzle exit, the second nozzle exit is arranged to lie between the first nozzle exit and the third nozzle exit to establish, when a portion of the combustible air-fuel mixture communicated from the air-fuel transfer passageway through the second nozzle exit is ignited, a detached second flame extending in radially outward directions from the air-fuel nozzle toward the interior surface of the heat-transfer tube, and the set of discharge-plate spacers are arranged to partition the detached second flame produced from the second nozzle exit into a series of circumferentially spaced-apart second flame portions, each pair of adjacent second flame portions formed by each discharge-plate spacer cooperating to define therebetween a combustion-products corridor configured to provide means for communicating combustion products of the detached first and second flames away from the air-fuel mixing chamber in the downstream direction through an upstream region in the combustion chamber inhabited by the detached second flame and into a downstream region in the combustion chamber inhabited by the attached third flame.

An air-fuel burner comprising

• a heat-transfer tube formed to include an interior region and adapted to discharge heat to an adjacent medium located outside the heat-transfer tube when exposed to heat from a flame generated in the interior region and
• an air-fuel nozzle coupled to an upstream end of the heat-transfer tube and arranged to extend into the interior region of the heat-transfer tube, the air-fuel nozzle being configured to provide means for forming three nozzle exits communicating with a combustion chamber defined in the interior region and located between the air-fuel nozzle and the heat-transfer tube to cause a combustible air-fuel mixture to exit from the air-fuel nozzle into the combustion chamber through
• a first nozzle exit formed in the air-fuel nozzle to establish, when a portion of the combustible air-fuel mixture flowing through the first nozzle exit is ignited, a detached first flame extending in radially outward directions in the combustion chamber from the air-fuel nozzle toward the heat-transfer tube, and the detached first flame includes a root positioned to lie between the air-fuel nozzle and the heat-transfer tube and a tip arranged to stabilize on an interior surface of the heat-transfer tube,
• a second nozzle exit formed in the air-fuel nozzle and arranged to lie in spaced-apart relation to the first nozzle exit in a downstream direction away from the upstream end of the heat-transfer tube to establish, when a portion of the combustible air-fuel mixture flowing through the second nozzle exit is ignited, a detached second flame extending in radially outward directions in the combustion chamber from the air-fuel nozzle toward the interior surface of the heat-transfer tube, and the detached second flame includes a root positioned to lie between the air-fuel nozzle and the heat-transfer tube and a tip arranged to stabilize on the interior surface of the heat-transfer tube, and
• a third nozzle exit formed in the air-fuel nozzle and arranged to lie in spaced-apart relation to the second nozzle exit in the downstream direction to locate the second nozzle exit between the first and third nozzle exits and to establish, when a portion of the combustible air-fuel mixture flowing through the third nozzle exit is ignited, an attached third flame extending in the downstream direction away from the air-fuel nozzle and the detached first and second flames, and the attached third flame includes a root stabilized on the air-fuel nozzle and a tip extending in the downstream direction.