LIFTED FLAME LOW NOx BURNER WITH FLAME POSITION CONTROL

Abstract

A low NOx burner includes a charging mechanism to charge a fuel stream or diluted fuel stream. A flame supported by the charged fuel stream can be held at a lifted location corresponding to high fuel dilution. If electrical power is lost or removed, the flame is shifted to a location corresponding to a lower fuel dilution.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit from U.S. Provisional Patent Application No. 61/717,371, entitled “LIFTED FLAME FAIL-SAFE LOW NOx BURNER”, filed Oct. 23, 2012; and U.S. Provisional Patent Application No. 61/725,095, entitled “FAIL-SAFE ELECTRODYNAMIC BURNER”, filed Nov. 12, 2012; and U.S. Provisional Patent Application No. 61/717,371, entitled “LIFTED FLAME FAIL-SAFE LOW NOx BURNER”, filed Oct. 23, 2012; and U.S. Provisional Patent Application No. 61/727,103, entitled “SYSTEM FOR SAFE POWER LOSS FOR AN ELECTRODYNAMIC BURNER”, filed Nov. 15, 2012; and U.S. Provisional Patent Application No. 61/765,022, entitled “PERFORATED FLAME HOLDER AND BURNER INCLUDING A PERFORATED FLAME HOLDER”, filed Feb. 14, 2013; and U.S. Provisional Patent Application No. 61/882,201, entitled “COMBUSTION SYSTEM AND METHOD FOR ELECTRICALLY ASSISTED START-UP”, filed May 10, 2013; each of which, to the extent not inconsistent with the disclosure herein, are incorporated by reference.

SUMMARY

According to an embodiment, a system for supporting a low oxides of nitrogen (NOx) flame includes a charging mechanism configured to apply a charge or voltage to a fuel or diluted fuel stream and a first flame support surface disposed adjacent to the fuel or diluted fuel stream and configured to support a flame when the charge or voltage is applied to the fuel or diluted fuel stream. An aerodynamic flame holder is disposed adjacent to the fuel or diluted fuel stream and configured to support the flame when the charge or voltage is not applied to the fuel or diluted fuel stream. The first flame support surface can be a perforated flame holder configured to support a low NOx flame in a plurality of gas passages formed to extend through the perforated flame holder.

According to an embodiment, a burner includes a means for at least intermittently applying a voltage or electric charge to a fuel or diluted fuel stream, a first means for holding a lean flame supported by the fuel stream or fuel and air stream at a first location when the voltage or electric charge is applied to the fuel or diluted fuel stream, and a second means for holding a rich flame supported by the fuel or diluted fuel stream at a second location when the voltage or electric charge is not applied to the fuel or diluted fuel stream. The first means for holding a lean flame include a perforated flame holder configured to support a low NOx flame in a plurality of gas passages formed to extend through the perforated flame holder.

According to an embodiment, a method for supporting a low NOx flame that is stable under changing conditions includes receiving a fuel or diluted fuel stream, applying a charge or voltage to the fuel or diluted fuel stream, and supporting a lean, low NOx flame at a first location with the fuel or diluted fuel stream. Upon receiving an interruption in electrical power, the method includes stopping application of the charge or voltage to the fuel or diluted fuel stream, shifting the flame from the first location to a second location, and supporting a rich, high stability flame at the second location. Upon again receiving electrical power, the method includes resuming the application of the charge or voltage to the fuel or diluted fuel stream and shifting the flame from the second location to the first location.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a lifted flame low NOx burner with flame position control, according to an embodiment.

FIG. 1B is a diagram of the lifted flame low NOx burner with flame position control of FIG. 1A, in a configuration following a loss of electrical power, according to an embodiment.

FIG. 2A is a diagram of a lifted flame low NOx burner with flame position control, according to another embodiment.

FIG. 2B is a diagram of the lifted flame low NOx burner with flame position control of FIG. 2A, in a configuration following a loss of electrical power, according to an embodiment.

FIG. 3A is a diagram of a lifted flame low NOx burner with flame position control, according to another embodiment.

FIG. 3B is a diagram of the lifted flame low NOx burner with flame position control of FIG. 3A, in a configuration following a loss of electrical power, according to an embodiment.

FIG. 4 is a diagram of a burner configured for supporting a low NOx flame in a fail-safe way, according to an embodiment.

FIG. 5 is a flow chart showing a method for supporting a low NOx flame that is stable under changing conditions, according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the disclosure.

FIG. 1A is a diagram of a system 100 for supporting low oxides of nitrogen (NOx) flame 102, according to an embodiment. A charging mechanism 104 is configured to apply a charge or voltage to a fuel or diluted fuel stream 106. A first flame support surface 108 is disposed adjacent to the fuel or diluted fuel stream 106 and configured to support the flame 102 when the charge or voltage is applied to the fuel or diluted fuel stream. An aerodynamic flame holder 110 is disposed adjacent to the fuel or diluted fuel stream 106 and configured to support the flame 102 when the charge or voltage is not applied to the fuel or diluted fuel stream 106.

The system 100 for supporting the low NOx flame 102 can include a fuel nozzle 112. The fuel nozzle 112 can include an electrically insulating body 114 configured to isolate the fuel or diluted fuel stream 106 from a voltage or ground other than a voltage corresponding to the charge or voltage applied to the fuel or diluted fuel stream by the charging mechanism 104. The fuel nozzle 112 can include an electrically conductive body 116 operatively coupled to the electrically insulating body 114. The electrically conductive body 116 can be configured to electrically float to a voltage corresponding to the charge or voltage applied to the fuel or diluted fuel stream by the charging mechanism 104.

The first flame support surface 108 can be disposed more distal from the fuel nozzle 112 than the aerodynamic flame holder 110. The first flame support surface 108 can be configured to support the flame 102 at a distance from the fuel nozzle 112 corresponding to a reduced fuel concentration compared to the fuel concentration proximate the aerodynamic flame holder 110. The reduced fuel concentration at the distance from the fuel nozzle 112 corresponding to the first flame support surface 108 can correspond to a reduced production of NOx compared to a higher fuel concentration flame 102 supported by the aerodynamic flame holder 110. Additionally and/or alternatively, the reduced fuel concentration at the distance from the fuel nozzle 112 corresponding to the first flame support surface 108 can correspond to a flame 102 that is unstable without the first flame support surface 108 being sufficiently hot, sufficiently intact, or without the charge or voltage being applied to the fuel or diluted fuel stream 106 by the charging mechanism 104.

The system 100 for supporting the low NOx flame 102 can include a voltage source 118 operatively coupled to the charging mechanism 104. Additionally and/or alternatively, the voltage source 118 can be configured to receive electrical power from an electrical power node 120 that is subject to loss of electrical power. The voltage source 118 may be subject to at least possible loss of operability for supplying electrical voltage to the charging mechanism 104.

The charging mechanism 104 may be subject to at least possible loss of operability for applying the charge or voltage to the fuel or diluted fuel stream responsive to a loss of voltage received from the voltage source 118. The at least possible loss of operability for applying the charge or voltage to the fuel or diluted fuel stream by the charging mechanism 104 can correspond to at least a possible loss of flame 102 stability when the flame 102 is supported by the flame support surface.

FIG. 1B is a diagram of the lifted flame low NOx burner with flame position control of FIG. 1A, in a configuration following a loss of electrical power, according to an embodiment. The aerodynamic flame holder 110 can be configured to cooperate with the fuel or diluted fuel stream 106 to cause the flame 102 to be supported by the aerodynamic flame holder 110 when the charging mechanism 104 loses operability for applying the charge or voltage to the fuel or diluted fuel stream 106.

Referring to FIGS. 1A and 1B, the aerodynamic flame holder 110 can be configured to support the flame 102 at a more stable fuel dilution than a flame 102 supported by the first flame support surface 108. Divergence of the fuel or diluted fuel stream 106 corresponds to dilution of the fuel by entrainment of air and/or flue gas peripheral to the fuel stream. At distances along the fuel or diluted fuel stream 106 near the fuel nozzle 112, little air or flue gas is entrained, and the fuel or diluted fuel stream 106 is “richer” and is less diluted. At distances along the fuel or diluted fuel stream 106 distal from the fuel nozzle 112, a greater amount of air or flue gas is entrained, causing the fuel or diluted fuel stream 106 to be “leaner” and more diluted. Less diluted flames can be relatively stable, but can suffer from high NOx production. More diluted flames can be characterized by low NOx production, but can suffer from being relatively unstable. According to embodiments described herein, a more dilute, lower NOx flame 102 can be stabilized by the application of electrical charge or voltage to a fuel or diluted fuel stream 106. Loss of electrical power by the fuel or diluted fuel stream 106 charging mechanism 104 may result in reduced flame 102 stability. According to embodiments, a fail-safe system causes the flame 102 to burn at a location along the fuel or diluted fuel stream 106 that is richer and more stable, albeit with higher NOx production.

In another embodiment, the first flame support surface 108 can include a flame support electrode 122 configured to attract the charge or voltage applied to the fuel or diluted fuel stream 106. The attraction of the charge or voltage applied to fuel or diluted fuel stream 106 to the flame support electrode 122 can cause the fuel or diluted fuel stream 106 to flow toward the flame support electrode 122. Additionally or alternatively, the flame support electrode 122 can be held at voltage ground.

A voltage source 118 can be operatively coupled to the flame support electrode 122. The voltage source 118 can be configured to drive the flame support electrode 122 to a voltage opposite in sign from the charge or voltage applied to the fuel or diluted fuel stream 106. The attraction of the charge or voltage applied to the fuel or diluted fuel stream 106 can cause the flame 102 to anchor to the flame support electrode 122.

The charging mechanism 104 can be disposed to apply a charge or voltage to the fuel or diluted fuel stream 106 between a fuel nozzle 112 and the aerodynamic flame holder 110. The charging mechanism 104 can be configured to impart a positive charge or voltage on the fuel or diluted fuel stream 106.

Various embodiments are contemplated for the voltage source 118. The voltage source can, for example, include a linear power supply, a switching power supply, and/or a voltage multiplier. In an embodiment, the voltage source includes linear and/or switched mode power supply sections that output a chopped signal to a voltage multiplier. For example, the power supply sections can output a chopped DC waveform at 0 to +12 volts. The voltage source 118 can also include an 11-stage positive polarity voltage multiplier that receives the chopped DC waveform and multiplies it to about 24,000 volts for output to the charging mechanism 104. The voltage source 118 can also include one or more power supply sections that output a second chopped DC waveform at 0 to −12 volts. The voltage source 118 can include a second voltage multiplier, for example a 10 stage negative polarity voltage multiplier that receives the second chopped DC waveform and multiplies it to about −12,000 volts for output to the flame support electrode 122.

Referring to FIG. 1A, the charge or voltage applied to the fuel or diluted fuel stream 106 can be selected to cause the fuel or diluted fuel stream 106 to repel itself and to divert away from and/or around the aerodynamic flame holder 110. Additionally or alternatively, the aerodynamic flame holder 110 can be configured to allow the fuel or diluted fuel stream 106 to pass when the fuel or diluted fuel stream 106 carries the charge or voltage. A voltage can be at least intermittently applied to the aerodynamic flame holder 110, the voltage being selected to repel the charge or voltage carried by the fuel or diluted fuel stream 106.

FIG. 1B is a diagram of the lifted flame low NOx burner with flame position control of FIG. 1A, in a configuration following a removal of electrical power, according to an embodiment. In this configuration, the fuel stream and the aerodynamic flame holder 110 can be configured to cause the fuel or diluted fuel stream 106 to pass in close proximity to the aerodynamic flame holder 110 when no charge or voltage is applied to the fuel or diluted fuel stream 101.

The aerodynamic flame holder 110 can be configured to cause one or more vortices 124 to form in the fuel or diluted fuel stream 106 when the fuel or diluted fuel stream 106 passes in close proximity to the aerodynamic flame holder 110. The one or more vortices 124 can be selected to cause the flame 102 to maintain ignition adjacent to the aerodynamic flame holder 110 when no charge or voltage is applied to the fuel or diluted fuel stream 101 and the fuel or diluted fuel stream passes in close proximity to the aerodynamic flame holder 110

Referring to FIG. 1A, the charging mechanism 104 can be configured to cause the fuel or diluted fuel stream to separate from the aerodynamic flame holder 110 when the charging mechanism 104 begins to apply charge or voltage to the fuel or diluted fuel stream 106.

FIG. 2A is a diagram of a lifted flame low NOx burner with flame position control, according to another embodiment. The first flame support surface 108 can include a first aerodynamic flame support surface 202. The first aerodynamic flame support surface 202 can include a refractory material and/or an electrically insulating material. In an embodiment, the first flame support surface 108 can include a perforated flame holder configured to support a low NOx flame in a plurality of gas passages formed to extend through the perforated flame holder. The perforated flame holder can operate to maintain otherwise unstable (lean) combustion by acting as a heat sink and heat source for the flame 102, receiving heat output by the flame 102 and providing heat to preheat a lean fuel mixture entering the plurality of gas passages to maintain combustion.

FIG. 2B illustrates a configuration 201 of the system 200 illustrated in FIG. 2A when the voltage source 118 stops applying charge or voltage to the fuel or diluted fuel stream 106. The behavior of flame shifting can be similar to that of the embodiment of FIGS. 1A and 1B, described above FIG. 3A is a diagram of a lifted flame low NOx burner with flame position control, according to another embodiment. This embodiment can include a fuel or diluted fuel stream repulsion electrode 302 configured to push the fuel or diluted fuel stream 106 away from the aerodynamic flame holder 110 when the fuel or diluted fuel stream 106 carries the charge or voltage. The fuel or diluted fuel stream repulsion electrode 302 can be disposed between the aerodynamic flame holder 110 and a fuel nozzle 112. Additionally or alternatively, the fuel or diluted fuel stream repulsion electrode 302 can be disposed between the aerodynamic flame holder 110 and the charging mechanism 104. The fuel or diluted fuel stream repulsion electrode 302 can be substantially contained by or formed as a portion of the aerodynamic flame holder 110. Additionally or alternatively, the fuel or diluted fuel stream repulsion and/or attraction electrodes 302, 304 can be disposed between the first flame support surface 108 and the aerodynamic flame holder 110.

The fuel or diluted fuel stream repulsion electrode 302 can be configured as a dull, non charge ejecting electrode, as a sharp, charge ejecting electrode, as an ionic wind generator and/or can be configured as a serrated electrode.

The fuel or diluted fuel stream attraction electrode 304 can be configured to attract the fuel or diluted fuel stream 106 away from the aerodynamic flame holder 110 when the fuel or diluted fuel stream 106 carries the charge or voltage. Additionally or alternatively, the fuel or diluted fuel stream repulsion electrode 302 and a fuel or diluted fuel stream attraction electrode 304, the repulsion electrode 302 and attraction electrode 304 can be configured to cooperate to hold the fuel or diluted fuel stream 106 away from the aerodynamic flame holder 110 when the fuel or diluted fuel stream 106 carries the charge or voltage.

Optionally, the system 300 of FIG. 3A can include one or more first flame support surface(s) 108 formed as first aerodynamic flame support surface(s) 202 in lieu of or in addition to the flame support electrode(s) 122, similar to the embodiment depicted in FIG. 2A. FIG. 3B is a diagram of the lifted flame low NOx burner with flame position control of FIG. 3A, in a configuration following a removal or loss of electrical power, according to an embodiment. This embodiment can include at least a fuel or diluted fuel stream repulsion electrode 302 and a voltage source 118 configured to apply a voltage to the fuel or diluted fuel stream 106 charging mechanism 104 and the fuel and diluted fuel stream repulsion electrode 302. Wherein a loss of voltage applied by the voltage source 118 can cause the fuel or diluted fuel stream 106 to not be held away from the aerodynamic flame holder 110, and can cause the flame 102 to be supported by a vortex formed adjacent to the aerodynamic flame holder 110.

Referring to FIGS. 1A, 2A, 3A, the combustion reaction represented by the flame 102 can be enhanced by one or more field electrodes 126. According to an embodiment, the one or more field electrodes 126 can be disposed to apply an electric field or second charges to the flame 102, the electric field or second charges which can be selected to enhance combustion of the flame 102. Additionally and or alternatively, the one or more field electrodes 126 can be configured to cause enhanced mixing of the fuel and an oxidizer to increase the stability of the flame supported by diluted fuel. According to an embodiment, a voltage source 118 can be operatively coupled to the one or more field electrodes 126. The voltage source 118 can be configured to drive the one or more field electrodes 126 with a time-varying voltage. The one or more field electrodes 126 can be disposed more distal from the fuel nozzle 112 than the first flame support surface 108.

The one or more field electrodes 126 can include one or more ion-ejecting electrodes. The one or more field electrodes 126 can include one or more dull electrodes configured to apply an electric field to the flame 102 and not eject ions. Additionally or alternatively, the one or more field electrodes 126 can include a toric electrode. The one or more field electrodes 126 can be configured to flatten the flame 102.

Interaction of the electric field or second charges generated by the one or more field electrodes 126 with the flame 102 can enhance combustion. It was found that a flame 102 burned more vigorously responsive to the application of a voltage to the field electrode(s) than without a voltage applied to the field electrode(s). Loss of voltage applied to the field electrode(s) can result in a reduced combustion reaction rate, and hence a reduced flame 102 stability. By causing the flame 102 to be anchored to the first flame support surface 108 (e.g., either in the form of a flame support electrode 122 (FIGS. 1A, 3A) or a first aerodynamic flame support surface 202 (FIG. 2A). When the field electrode(s) are energized, the flame can output reduced NOx because of relatively greater fuel dilution at and above the first flame support surface 108. By causing the flame 102 to “fall” to the aerodynamic flame holder 110 if voltage fails to reach the field electrodes (see FIGS. 1B, 2B, 3B), the flame 102 can continue to burn stably (albeit with higher NOx output) than continuing to support the flame 102 under the leaner conditions at the first flame support surface 108.

In an embodiment, the voltage source 118 can be operatively coupled to a control mechanism such as a microcontroller- or microprocessor-based circuit to cause voltage to be applied to or to be removed from the electrical power node 120. The controller can alternatively include a human interface configured to receive commands from a human operator. For example, the control mechanism can be configured to output commands corresponding to a start-up method wherein the flame 102 is supported at the second location to pre-heat the first flame support surface. In another example, the controller can include a sensor configured to sense an operating condition of the first flame support surface, and the controller can be configured to cause a removal of voltage from the electrical power node 120 if the operating condition of the first flame support surface indicates a movement of the flame 102 to the aerodynamic flame holder 110 (e.g., if the first flame support surface 108 becomes too cool or suffers a mechanical failure). In another example, the controller can be configured to cause a removal of voltage from the electrical power node 120 upon receipt of a shut-down or idle command (e.g., responsive to a reduction in heat demand).

Various forms of charging mechanisms 104 are contemplated. According to an embodiment, the charging mechanism 104 can include at least one sharp electrode configured to operate as a charge ejecting corona electrode. The charging mechanism 104 can include at least one serrated electrode (as shown in the illustrative embodiments of FIGS. 1A, 1B, 2A, 2B, 3A, 3B. Additionally or alternatively, the charging mechanism 104 can include a conductive fuel nozzle 112.

The charging mechanism 104 can include an ionizer configured to supply ions to the fuel or diluted fuel stream 106 after exit of the fuel or diluted fuel stream 106 from the fuel nozzle 112. The ionizer can be configured to ionize the fuel prior to exit of the fuel stream 106 from the fuel nozzle 112. Additionally or alternatively, the ionizer can be configured to ionize flue gas or air upstream from or peripheral to the fuel or diluted fuel stream 106.

FIG. 4 is a diagram of a burner 400 configured for supporting a low NOx flame with flame position control, according to an embodiment. The burner 400 includes a means 104 for at least intermittently applying a voltage or electric charge to a fuel or diluted fuel stream 106. The burner 400 includes a first means 108 for holding a lean flame 102a supported by the fuel stream or fuel and air stream 106 at a first location 402 when the voltage or electric charge is applied to the fuel or diluted fuel stream 106. The burner 400 includes a second means 110 for holding a rich flame 102b supported by the fuel or diluted fuel stream 106 at a second location 404 when the voltage or electric charge is not applied to the fuel or diluted fuel stream 106.

The burner 400 can include a means 112 for supplying the fuel or diluted fuel stream 106 to the means for at least intermittently applying a voltage or electric charge to the fuel or diluted fuel stream 106. According to an embodiment, a means 118 for outputting a voltage can be operatively coupled to the means 104 for at least intermittently applying a voltage or electric charge to a fuel or diluted fuel stream 106.

The means 104 for at least intermittently applying a voltage or electric charge to the fuel or diluted fuel stream 106 and the first means 108 for holding the lean flame 102a can be supported by the fuel or diluted fuel stream 106 at the first location 402 when the voltage or electric charge is applied to the fuel or diluted fuel stream 106 are configured to cooperate to support a low NOx flame 102a.

Additionally or alternatively, the means 104 for at least intermittently applying a voltage or electric charge to the fuel or diluted fuel stream 106 and the second means 110 for holding the rich flame 102b can be supported by the fuel or diluted fuel stream 106 at the second location 404 when the voltage or electric charge is not applied to the fuel or diluted fuel stream 106 are configured to cooperate to support a high stability flame 102b.

The first means 108 for holding the lean flame 102 can be supported by the fuel or diluted fuel stream 106 at the first location 402 when the voltage or electric charge is applied to the fuel or diluted fuel stream 106. Additionally or alternatively the second means 110 for holding the rich flame 102 can be supported by the fuel or diluted fuel stream 106 at the second location 404 when the voltage or electric charge is not applied to the fuel or diluted fuel stream 106 can be configured to cooperate to shift the flame 102 from the first location 302 to the second location 404 when the means 104 for at least intermittently applying a voltage or electric charge to the fuel or diluted fuel stream 106 fails to apply the voltage or electric charge to the fuel or diluted fuel stream 106.

In an embodiment, the first means 108 can include a perforated flame holder configured to support a low NOx flame in a plurality of gas passages formed to extend through the perforated flame holder. The perforated flame holder can operate to maintain otherwise unstable (lean) combustion by acting as a heat sink and heat source for the flame, receiving heat output by the flame and providing heat to preheat a lean fuel mixture entering the plurality of gas passages to maintain combustion.

FIG. 5 is a flow chart showing a method for supporting a low NOx flame that is stable under changing conditions, according to an embodiment. In step 502, a fuel or diluted fuel stream is received. Receiving the fuel or diluted fuel stream can include receiving the fuel or diluted fuel stream from a fuel nozzle isolated from a voltage or ground other than a voltage corresponding to the charge or voltage applied to the fuel or diluted fuel stream. Step 502 can include receiving the fuel or diluted fuel stream from a fuel nozzle including an electrically conductive body that electrically floats to a voltage corresponding to the charge or voltage applied to the fuel or diluted fuel stream.

In step 504 a charge or voltage is applied to the fuel or diluted fuel stream. The charge or voltage can be applied to the fuel or diluted fuel stream between a fuel nozzle and an aerodynamic flame holder at the second location. The charge or voltage applied to the fuel or diluted fuel stream can include imparting a positive charge or voltage on the fuel or diluted fuel stream. Step 504 can include causing charge or voltage applied to the fuel or diluted fuel stream to repel itself and to divert away from or around an aerodynamic flame holder at the second location.

Applying the charge or voltage to the fuel or diluted fuel stream in step 504 can include ejecting charge from at least one sharp or corona electrode. Ejecting charge from at least one sharp or corona electrode can include ejecting charge from at least one serrated electrode. Additionally or alternatively, applying the charge or voltage to the fuel or diluted fuel stream can include applying a voltage to the fuel or diluted fuel stream with a conductive fuel nozzle. Additionally or alternatively, step 504 can include operating an ionizer to supply ions to the fuel or diluted fuel stream after exit of the fuel or diluted fuel stream from a fuel nozzle. The ionizer can be operated to ionize the fuel prior to exit of the fuel stream from a fuel nozzle. The ionizer can be operated to ionize flue gas or air upstream from or peripheral to the fuel or diluted fuel stream.

Proceeding to step 506, a lean, low NOx flame is supported at a first location with the diluted fuel stream. Step 506 can include supporting the flame with a first flame support surface at the first location disposed more distal from a fuel nozzle than the second location. In addition, Step 506 can include applying a voltage condition to a flame support electrode at the first location and/or can include attracting the charge or voltage applied to the fuel or diluted fuel stream with the voltage condition applied to the flame support electrode. The charge or voltage can be attracted to the fuel or diluted fuel stream with the voltage condition applied to the flame support electrode to cause the fuel or diluted fuel stream to flow toward the flame support electrode.

Applying the voltage condition to the flame support electrode can include holding the flame support electrode at voltage ground. Additionally or alternatively, applying the voltage condition to the flame support electrode can include applying a voltage opposite in sign from the charge or voltage applied to the fuel or diluted fuel stream. The voltage condition applied to the flame support electrode can cause the flame to anchor to the flame support electrode.

In step 506, supporting the lean, low NOx flame at the first location can include supporting the flame with a first aerodynamic flame support surface disposed at the first location. Supporting the lean, low NOx flame at the first location can include causing a vortex to form in the diluted fuel stream proximate a first aerodynamic flame support surface disposed at the first location. The first aerodynamic flame support surface can include an electrically insulating material, for example.

Supporting a lean, low NOx flame at a first location with the fuel or diluted fuel stream in step 506 can include supporting the flame at a distance from a fuel nozzle corresponding to a reduced fuel concentration compared to a fuel concentration proximate to the second location. The reduced fuel concentration at the first location can correspond to a reduced production of oxides of nitrogen by the flame compared to a higher fuel concentration flame supported at the second location.

The reduced fuel concentration at the first location can correspond to a flame that is unstable without the charge or voltage being applied to the fuel or diluted fuel stream.

In step 506, supporting a lean, low NOx flame at the first location with the diluted fuel can include allowing the fuel or diluted fuel stream to pass by an aerodynamic flame holder at the second location when the fuel or diluted fuel stream carries the charge or voltage. Allowing the fuel or diluted fuel stream to pass by an aerodynamic flame holder at the second location can include applying a voltage at least intermittently to an aerodynamic flame holder or a repelling electrode at the second location. The applied voltage can be selected to repel the charge or voltage carried by the fuel or diluted fuel stream.

While the lean, low NOx flame is supported at the first location, an electric field or second charges can be applied to the flame with one or more field electrodes. The electric field or second charges can be selected to enhance combustion in the flame. The electric field or second charges can cause enhanced mixing of the fuel and an oxidizer to increase the stability of the flame supported by diluted fuel stream. The electric field or second charges applied to the flame with one or more field electrodes can correspond to application of a time-varying voltage to the one or more field electrodes.

Applying an electric field or second charges to the flame with one or more field electrodes can include applying the electric field or second charges with one or more field electrodes disposed more distal from a fuel nozzle than the first location. The one or more field electrodes can include one or more ion-ejecting electrodes. The one or more field electrodes can include one or more dull electrodes. The one or more dull electrodes can be configured to apply an electric field to the flame and not eject ions. The one or more field electrodes can include a toric electrode. An electric field or second charges applied to the flame with one or more field electrodes can cause flattening of the flame with the electric field.

Proceeding to step 508, an interruption in electrical power is received. The interruption in electrical power can include receiving an interruption in electrical power delivered to and/or output by a voltage source that applies voltage to a charging mechanism that, in turn, applies the charge or voltage to the fuel or diluted fuel stream. Upon receiving the interruption in electrical power, the application of the charge or voltage to the fuel or diluted fuel stream is stopped, as shown by step 510.

Proceeding to step 512, the flame is shifted from the first location to a second location. Shifting the flame from the first location to a second location can occur spontaneously upon the loss of the charge or voltage applied to the fuel or diluted fuel stream.

Shifting the flame from the first location to a second location can include causing the fuel or diluted fuel stream to pass in close proximity to an aerodynamic flame holder at the second location when no charge or voltage is applied to the fuel or diluted fuel stream. Causing the fuel or diluted fuel stream to pass in close proximity to an aerodynamic flame holder can include causing one or more vortices to form in the fuel or diluted fuel stream. The one or more vortices can form when the fuel or diluted fuel stream passes in close proximity to the aerodynamic flame holder. The one or more vortices can be selected to cause the flame to maintain ignition adjacent to the aerodynamic flame holder when no charge or voltage is applied to the fuel or diluted fuel stream and the fuel or diluted fuel stream passes in close proximity to the aerodynamic flame holder.

After shifting the flame location, a rich, high stability flame is supported at the second location, as shown in step 514. The richness of the high stability flame can be relative. For example, the rich, high stability flame can be as lean as that typically burned by low NOx burners not using electrodynamic effects to stabilize the flame. Alternatively, the rich, high stability flame can be as rich as a typical burner not considered low NOx.

At some point, electrical power is again received, as shown in step 516. Upon restoration of electrical power, the application of the charge or voltage to the fuel or diluted fuel stream can be resumed, as indicated by a second instance of step 504.

In step 518, the flame is shifted from the second location to the first location. Shifting the flame from the second location to the first location can occur substantially simultaneously with resuming the application of the charge or voltage to the fuel or diluted fuel stream. Shifting the flame from the second location to the first location can occur at least partly responsive to like charges in the fuel or diluted fuel stream repelling one another. The mutual repulsion of the like charges at least partly can cause the fuel or diluted fuel stream to separate from an aerodynamic flame holder at the second location.

According to an embodiment, step 518 can include applying a voltage to an aerodynamic flame holder selected to repel the charges or voltage applied to the fuel or diluted fuel stream. The electrical repulsion between the aerodynamic flame holder and the charge or voltage applied to the fuel or diluted fuel stream can cause at least partly the fuel or diluted fuel stream to separate from the aerodynamic flame holder at the second location.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. A system for supporting a low oxides of nitrogen (NOx) flame, comprising:

a charging mechanism configured to apply a voltage to a fuel stream emitted from a fuel nozzle;

a first flame support surface disposed adjacent to the fuel nozzle and configured to support a flame when the voltage is applied to the fuel stream; and

an aerodynamic flame holder disposed adjacent to the fuel nozzle and configured to support the flame when the voltage is not applied to the fuel stream.

2. (canceled)

3. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, further comprising a fuel nozzle, the fuel nozzle including an electrically insulating body configured to isolate the fuel stream from a voltage or ground other than a voltage corresponding to the voltage applied to the fuel stream by the charging mechanism.

4. The system for supporting a low oxides of nitrogen (NOx) flame of claim 3, wherein the fuel nozzle includes an electrically conductive body coupled to the electrically insulating body.

5. The system for supporting a low oxides of nitrogen (NOx) flame of claim 3, wherein the first flame support surface is disposed more distal from the fuel nozzle than the aerodynamic flame holder.

6. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the first flame support surface is configured to support the flame at a distance from the fuel nozzle corresponding to a reduced fuel concentration compared to the fuel concentration proximate the aerodynamic flame holder.

7-8. (canceled)

9. The system for supporting a low oxides of nitrogen (NOx) flame of claim 6, wherein the first flame support surface includes a perforated flame holder configured to support a low NOx flame in a plurality of passages extending through the perforated flame holder.

10. (canceled)

11. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, further comprising a voltage source operatively coupled to the charging mechanism.

12-15. (canceled)

16. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the aerodynamic flame holder is configured to cooperate with the fuel stream to support the flame when the charging mechanism loses operability for applying the voltage to the fuel stream.

17. (canceled)

18. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the first flame support surface includes a flame support electrode configured to attract a charge imparted by the voltage applied to the fuel stream.

19-20. (canceled)

21. The system for supporting a low oxides of nitrogen (NOx) flame of claim 18, further comprising a voltage source operatively coupled to the flame support electrode;

wherein the voltage source is configured to drive the flame support electrode to a voltage opposite in sign from the voltage applied to the fuel stream.

22. (canceled)

23. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the charging mechanism is disposed to apply the voltage to the fuel stream at a location between the fuel nozzle and the aerodynamic flame holder.

24. The system for supporting a low oxides of nitrogen (NOx) flame of claim 23, wherein the charging mechanism is configured to impart a charge of a selected polarity to the fuel stream by application of the voltage to the fuel stream.

25-26. (canceled)

27. The system for supporting a low oxides of nitrogen (NOx) flame of claim 24, wherein the charge mechanism is configured to apply a voltage to the aerodynamic flame holder selected to repel the charge imparted to the fuel stream.

28. (canceled)

29. The system for supporting a low oxides of nitrogen (NOx) flame of claim 27, wherein the aerodynamic flame holder is configured to cause one or more vortices to form in the fuel stream when the fuel stream passes in close proximity to the aerodynamic flame holder.

30-34. (canceled)

35. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, further comprising a fuel stream repulsion electrode configured to push the fuel stream away from the aerodynamic flame holder when the fuel stream carries a charge imparted by the applied voltage.

36-43. (canceled)

44. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, further comprising a fuel stream attraction electrode configured to attract the fuel stream away from the aerodynamic flame holder when the fuel stream carries a charge imparted by the applied voltage.

45. (canceled)

46. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, further comprising:

a fuel stream repulsion electrode; and

a voltage source configured to apply a voltage to the charging mechanism and the fuel stream repulsion electrode;

wherein a loss of voltage applied by the voltage source causes the fuel stream to not be held away from the aerodynamic flame holder, and causes the flame to be supported by a vortex formed adjacent to the aerodynamic flame holder.

47. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, further comprising one or more field electrodes disposed to apply an electric field to the flame, the electric field being selected to enhance combustion of the flame.

48. (canceled)

49. The system for supporting a low oxides of nitrogen (NOx) flame of claim 48, further comprising a voltage source operatively coupled to the one or more field electrodes, the voltage source being configured to drive the one or more field electrodes with a time-varying voltage.

50. The system for supporting a low oxides of nitrogen (NOx) flame of claim 48, wherein the one or more field electrodes are disposed more distal from a fuel nozzle than the first flame support surface.

51-54. (canceled)

55. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the charging mechanism includes a sharp electrode configured to operate as a charge ejecting corona electrode.

56. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the charging mechanism includes a serrated electrode.

57. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the charging mechanism includes an electrically conductive fuel nozzle.

58. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the charging mechanism includes an ionizer configured to supply ions to the fuel stream after exit of the fuel stream from the fuel nozzle.

59. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the charging mechanism includes an ionizer configured to supply ions to the fuel stream prior to exit of the fuel stream from the fuel nozzle.

60. The system for supporting a low oxides of nitrogen (NOx) flame of claim 1, wherein the charging mechanism includes an ionizer configured to ionize flue gas or air prior to a merging of the flue gas or air with the fuel stream.

61. A burner, comprising:

a means for applying a voltage to a fuel stream;

a first means for holding a flame supported by the fuel stream at a first location when the voltage is applied to the fuel stream; and

a second means for holding a flame supported by the fuel stream at a second location when the voltage is not applied to the fuel stream.

62. The burner of claim 61, further comprising a means for supplying the fuel stream to the means for applying a voltage to the fuel stream.

63. The burner of claim 61, further comprising a means for outputting a voltage operatively coupled to the means for applying a voltage to a fuel stream.

64. The burner of claim 61, wherein the means for applying a voltage and the first means for holding a flame are configured to cooperate to support a low NOx flame.

65. The burner of claim 61, wherein the means for at least applying a voltage and the second means for holding a flame are configured to cooperate to support a high stability flame.

66. The burner of claim 61, wherein the first means for holding a flame and the second means for holding a flame are configured to cooperate to shift a flame from the first location to the second location when the means for applying a voltage fails to apply a voltage to the fuel stream.

67. A method for supporting a flame that is stable under changing conditions, comprising:

applying a voltage to a fuel stream;

supporting a lean, low NOx flame at a first location with the fuel stream;

stopping application of the voltage to the fuel stream;

shifting the flame from the first location to a second location; and

supporting a rich, high stability flame at the second location.

68. The method for supporting a flame that is stable under changing conditions of claim 67, further comprising:

resuming the applying a voltage to the fuel stream; and

shifting the flame from the second location to the first location.

69. The method for supporting flame that is stable under changing conditions of claim 68, wherein the shifting the flame from the second location to the first location and the resuming the applying a voltage to the fuel stream include resuming the applying a voltage to the fuel stream and shifting the lame from the second location to the first location substantially simultaneously.

70-71. (canceled)

72. The method for supporting a flame that is stable under changing conditions of claim 68, further comprising applying a voltage to an aerodynamic flame holder selected to repel a charges imparted to the fuel stream by the voltage applied to the fuel stream.

73. (canceled)

74. The method for supporting a flame that is stable under changing conditions of claim 68, wherein shifting the flame from the second location to the first location includes causing a mutual repulsion between like charges in the fuel stream.

75-78. (canceled)

79. The method for supporting a flame that is stable under changing conditions of claim 67, wherein applying a voltage to the fuel stream includes applying the voltage to the fuel stream at a position between a fuel nozzle and an aerodynamic flame holder at the second location.

80. The method for supporting a flame that is stable under changing conditions of claim 67, wherein applying a voltage to the fuel stream includes imparting a charge having a selected polarity to the fuel stream.

81. (canceled)

82. The method for supporting a flame that is stable under changing conditions of claim 67, wherein applying a voltage to the fuel stream includes ejecting a charge from a sharp electrode.

83. (canceled)

84. The method for supporting a flame that is stable under changing conditions of claim 67, wherein applying a voltage to the fuel stream includes applying a voltage to the fuel stream via a conductive fuel nozzle.

85. The method for supporting a flame that is stable under changing conditions of claim 67, wherein applying the voltage to the fuel stream includes supplying ions to the fuel stream nozzle.

86-87. (canceled)

88. The method for supporting a flame that is stable under changing conditions of claim 67, wherein supporting a lean, low NOx flame at a first location with the fuel stream includes supporting the flame with a first flame support surface at the first location disposed more distal from a fuel nozzle than the second location.

89. The method for supporting a flame that is stable under changing conditions of claim 86, wherein supporting the flame with a first flame support surface at the first location includes supporting a perforated flame holder at the first location, the perforated flame holder being configured to support a flame in a plurality of gas passages formed to extend through the perforated flame holder.

90. The method for supporting a flame that is stable under changing conditions of claim 67, wherein:

applying a voltage to a fuel stream includes applying a voltage having a fi polarity to the fuel stream; and

supporting a lean, low NOx flame at a first location includes attracting the flame to the first location by applying, to a flame support electrode at the first location, a voltage having a second polarity, opposite the first polarity.

91-94. (canceled)

95. The method for supporting a flame that is stable under changing conditions of claim 67, wherein supporting a rich, high stability flame at a second location includes supporting the flame with a first aerodynamic flame support surface disposed at the second location.

96-97. (canceled)

98. The method for supporting a flame that is stable under changing conditions of claim 67, wherein supporting a lean, low NOx flame at a first location with the fuel stream includes supporting the flame at a distance from a fuel nozzle corresponding to a reduced fuel concentration compared to a fuel concentration proximate to the second location.

99-101. (canceled)

102. The method for supporting a flame that is stable under changing conditions of claim 101, further comprising applying a voltage to an aerodynamic flame holder or a repelling electrode at the second location, the voltage being selected to repel a charge carried by the fuel stream.

103-104. (canceled)

105. The method for supporting a flame that is stable under changing conditions of claim 67, wherein shifting the flame from the first location to a second location includes causing the fuel stream to pass in close proximity to an aerodynamic flame holder at the second location when no voltage is applied to the fuel stream.

106-107. (canceled)

108. The method for supporting a flame that is stable under changing conditions of claim 67, further comprising, while the lean, low NOx flame is supported at the first location, applying an electric field to the flame with one or more field electrodes, the electric field being selected to enhance combustion in the flame.

109. (canceled)

110. The method for supporting a flame that is stable under changing conditions of claim 108, wherein applying an electric field to the flame with one or more field electrodes includes applying a time-varying voltage to the one or more field electrodes.

111. The method for supporting a flame that is stable under changing conditions of claim 108, wherein applying an electric field to the flame with one or more field electrodes includes applying the electric field with one or more field electrodes disposed more distal from a fuel nozzle than the first location.

112-114. (canceled)

115. The method for supporting a flame that is stable under changing conditions of claim 108, wherein applying an electric field to the flame with one or more field electrodes includes flattening the flame with the electric field.