METHOD AND APPARATUS FOR A DUAL MODE BURNER YIELDING LOW NOX EMISSION

Abstract

A method of operating a burner includes providing supplying a combustible mixture containing a ratio of fuel and air that is incapable of maintaining a stable flame to a combustion chamber. The combustible mixture is ignited by an igniter, and presence of a flame is sensed. The igniter is maintained active to sustain combustion of the combustible mixture within the combustion chamber so that a space exterior to the combustion chamber is heated to a temperature at or above an auto-ignition temperature of the combustible mixture. The temperature of the space exterior is monitored and the combustible mixture is provided at a second flow rate, which is higher than the first flow rate, to extinguish the flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber. When combustion occurs in the space exterior to the combustion chamber, the igniter is deactivated.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional Patent Application No. 61/701,212, filed Sep. 14, 2013, which is incorporated herein in its entirety by this reference.

BACKGROUND

The use of high velocity gas burners is well known. In such burners, fuel gas and oxidant are mixed with one another and ignited in the interior of the burner. The resultant hot combustion gases then flow at high velocity through an outlet and into the furnace chamber for direct heating or into a radiant tube for indirect heating. The combustion of the fuel gas with an oxidant within the burner results in a greatly elevated temperature environment in the burner. To increase system efficiency, the oxidant can be pre-heated to result in higher temperatures. The preheating of the oxidant may be achieved by using a recuperative or regenerative system that uses the residual heat in the exhaust gas. This high temperature combustion environment provides two challenges. First, the burner internals and combustion chamber are exposed to the very high temperature environment. Second, when combustion is carried out at extremely high temperatures, thermal nitrogen oxides (NOx) formation is promoted. As combustion temperatures increase, the levels of NOx production also increase. In order to deal with higher combustion temperatures, burners may be constructed from high temperature grade materials, for example, the combustion chambers can be made of ceramic materials, which can withstand the high temperature environment. However, the difficulties associated with high NOx emissions still remain unaddressed.

SUMMARY

A method and apparatus for a burner adapted to heat a furnace, radiant tube, or other environment of use is described herein. In particular, a burner for providing a fuel gas in combination with an oxidant to effect controlled combustion (or oxidation) of the fuel gas in a manner to reduce NOx emissions is described. Combustion of the fuel gas is shifted from within the burner combustor to a location outside the burner once the temperature within the furnace/radiant tube has reached a sufficient level to complete combustion of the fuel gas.

The burner can provide oxidant and fuel at a ratio and/or velocity that does not permit the burner to maintain a stable flame. Accordingly, the burner can be provided with a stabilization device that is capable of maintaining a flame in the burner combustor notwithstanding the instability created by the oxidant and fuel ratio and/or velocity. The stabilization device can be turned on or off as desired.

More particularly, the fuel gas may be delivered through a fuel tube for discharge, such as axial and/or radial discharge, into a burner combustor for mixing with oxidant at a ratio and/or velocity that is not capable of maintaining a stable flame. During a start-up stage, the stabilization device is activated, and the fuel gas/oxidant mixture is ignited to combust within the burner combustor. The stabilization device maintains the flame in the burner combustor. During this period, the flame inside the burner combustor can be monitored with a flame sensor, such as a flame rod or UV scanner.

Once the temperature in the furnace/radiant tube reaches a pre-defined level at or above the auto-ignition temperature, the stabilization device can be turned off. When this occurs, flame will be destabilized and extinguished in the burner combustor such that all combustion will take place in the furnace chamber/radiant tube, and the flame sensor will detect a loss of flame inside the combustor. Due to the elevated temperature above auto ignition level in the furnace/radiant tube, this movement of the flame to the furnace/radiant tube space leads to combustion in the furnace/radiant tube in the absence of a flame in the burner. While the temperature levels within the furnace/radiant tube are sufficient to cause combustion of the fuel gas, these temperature levels nonetheless are low enough to avoid substantial NOx generation. Moreover, the high exit velocity of the air and fuel provides substantial blending and recirculation of the furnace/radiant tube atmosphere with the air/fuel mix, resulting in reduced temperature spikes formed in the core of the flame jet in the furnace/radiant tube, which are normally experienced during the standard operating mode of typical burners. After the flame ceases to exist in the burner combustor, the flow rate of the mixture of fuel gas and oxidant can be maintained, decreased, or increased, according to the needs of the furnace operator.

Examples of suitable stabilization devices include a hot surface igniter, a continuous spark igniter, a plasma igniter, an arc igniter, a backflow fluid flow, a pilot flame, an electric field generator, a magnetic field generator, and an electromagnetic field generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic views illustrating a burner and control system for delivery of fuel gas and combustion air adapted to heat a furnace, radiant tube, or other chamber, in accordance with the disclosure;

FIG. 2 is a fragmentary sectional view of a fuel gas discharge nozzle mounted within a combustor for the burner of FIG. 1;

FIG. 3 is a fragmentary sectional view of the fuel gas discharge nozzle of FIG. 2 taken along line 3-3 in FIG. 4; and

FIG. 4 is a sectional view taken generally along line 4-4 of FIG, 2 showing the orientation of an air flow control disk surrounding the fuel gas discharge nozzle of FIG. 2;

FIG. 5 is a diagrammatic view illustrating a first embodiment of a stabilization device for the burner of FIG. 1;

FIG. 6 is a diagrammatic view illustrating a second embodiment of a stabilization device for the burner of FIG. 1;

FIG. 7 is a diagrammatic view illustrating a third embodiment of a stabilization device for the burner of FIG. 1;

FIG. 8 is a diagrammatic view illustrating a fourth embodiment of a stabilization device for the burner of FIG. 1;

FIG. 9 is a diagrammatic view illustrating a fifth embodiment of a stabilization device for the burner of FIG. 1;

FIG. 10 is a diagrammatic view illustrating a sixth embodiment of a stabilization device for the burner of FIG. 1; and

FIG. 11 is a diagrammatic view illustrating a seventh, eighth, and ninth embodiment of a stabilization device for the burner of FIG. 1.

FIG. 12 is a flowchart for a method of operating a burner in accordance with the disclosure.

Before the embodiments of the burner and method are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and/or the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for purposes of description only and should not be regarded as limiting. The use herein of “including,” “comprising,” and variations thereof is meant to encompass the items listed thereafter and equivalents, as well as additional items and equivalents thereof.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like elements are designated by like reference numbers in the various views. FIGS. 1-4 illustrate a burner 10 including a generally hollow tubular cover tube 12 having an open end 14 that projects into a furnace/radiant tube 16 or other environment to be heated. By way of example only, the burner 10 may project into an enclosed radiant heating tube, or the like, used for indirect heating of a furnace while avoiding substantial introduction of combustion products into the furnace. As another example, the burner 10 may project into a furnace for direct heating of a furnace with substantial introduction of combustion products into the furnace. In the illustrated embodiment, the cover tube 12 is disposed in surrounding relation to a hollow heat recuperator 18 of ceramic or the like having a convoluted surface extending outwardly from a housing 20. The recuperator 18 can surround fuel tube 22, which provides fuel to a nozzle assembly 24 disposed within a burner combustion chamber 26 (also referred to as a combustor) located adjacent to the open end 14 of the burner. An annular air passageway 28 can be disposed between the inner walls of the heat recuperator 18 and outer wall of the fuel tube 22.

As shown, an air supply 30 provides combustion air for delivery from a blower or other supply source (not shown) to the annular air passageway 28 for transmittal to the nozzle assembly 24. An oxidant control valve 32 is used to control the flow of oxidant. In this regard, the oxidant control valve 32 may be operatively connected to a controller 34 such as a PLC, computer, or the like which opens or closes the oxidant control valve 32 in accordance with pre-established commands based on conditions in the furnace/radiant tube and/or the burner. Likewise, a fuel supply 40 provides natural gas or other gaseous fuel for delivery to the fuel tubes 21 and 22 for transmittal to the nozzle assembly 24. A fuel control valve 42 is used to control the flow of fuel gas. In this regard, the fuel control valve 42 may be operatively connected to the controller 34, which adjusts fuel feed in accordance with pre-established commands based on conditions in the furnace, radiant tube, and/or the burner. It will be appreciated that the fuel gas, air and oxidant can pass into the nozzle assembly in any suitable manner.

A sensor 46, such as a flame sensor, or the like, may be present to continuously monitor the presence of a flame within the burner combustion chamber 26, and to communicate such data to the controller 34. As will be described further herein, the controller 34 may utilize the data from the sensor 46 in combination with temperature data from the furnace/radiant tube to control the burner. It will be appreciated that the sensor 46 can be any suitable sensor and can be disposed in any suitable location. In one embodiment, the sensor 46 is embodied as an ultra-violet radiation or flame detector 69 that is disposed to sense for the presence of a flame directly within the combustor chamber 26, as shown in FIG. 5.

Referring now back to FIGS. 2-4, the nozzle assembly 24 can be in the form of a sleeve that is secured about the distal end of the fuel tube 22. In this regard, the illustrated nozzle assembly 24 includes a forward nipple portion 50 and a radial disk portion 52 disposed rearward (i.e. upstream) of the nipple portion 50. In this arrangement, the radial disk portion 52 can have a generally concave forward face projecting towards the outlet of the burner.

As best seen through joint reference to FIGS. 2 and 4, stand-offs 54 can be located at positions around the circumference of the radial disk portion 52 to provide centered spacing relative to the surrounding body. This can result in an annular gap 56 (FIG. 5) extending substantially around the perimeter of the radial disk portion 52. The radial disk portion 52 also includes a pattern of interior air passages 58. During operation, oxidant and/or air delivered from the supply 30 may flow through the annular gap 56 and the interior air passages 58 towards the burner outlet as shown by the arrows in FIG. 2.

As shown in FIG. 3, the forward nipple portion 50 can include an axial gas passage opening 64 and an arrangement of radial gas passage openings 66 aligned with corresponding openings in the fuel tube 22 for outward conveyance of the fuel gas. During operation, fuel gas can be passed outwardly from the axial gas passage opening 64 and the radial gas passage openings 66 and can mix with the oxidant.

The burner 10 may be operated in a flame mode with ignition within the burner combustor or in a flameless mode during which the oxidant and fuel gas combusts only downstream of the combustor outlet in an area 16 (FIG. 1), which is external to the combustor, The flameless mode may also be referred to as a volume combustion mode, i.e., when combustion is occurring in the volume of the furnace chamber or radiant tube in the absence of a flame in the combustion chamber 26 of the burner. The flame mode provides the initial start-up of the furnace/radiant tube 16 using combustion of fuel gas in the burner combustion chamber 26 to heat up the furnace/radiant tube. The flame mode can be followed by the flameless mode during which the fuel gas and oxidant are ejected from the burner 10 and is allowed to undergo combustion downstream of the combustor outlet. This dual mode operation results in substantially reduced NOx emissions.

Referring again to FIGS. 1-4, by way of example only, and not limitation, upon initiation of the flame mode, both the air control valve 32 and the fuel control valve 42 are set to an open condition that provides a flow of oxidant and fuel, which need not be capable of maintaining a stable flame within the burner. Unlike previously proposed burners, in which a combustible mixture capable of maintaining a stable flame after initial ignition was required within the burner, in the present embodiments, a mixture and/or flow rate of fuel, air and, optionally, the oxidant, may be insufficient to maintain a stable flame within the burner during operation in the flame mode. As used herein, oxidant is meant to describe any substance that contains oxygen, such as air, and/or other additives intended to make the combustion of fuel more efficient and/or to lower emissions.

When combusting in the open condition, air and/or another oxidant will pass along the annular air passageway 28 to the nozzle assembly 24 and fuel gas will pass along the fuel tube 22 to the nozzle assembly 24. At the nozzle assembly 24, a portion of the oxidant can flow through the annular gap 56 surrounding the radial disk portion 52, while the remainder of the oxidant can pass through the interior air passages 58. Concurrently, the fuel gas can be expelled from the nozzle assembly 24 to mix with the oxidant in the burner combustion chamber 26. As these materials mix, a flame stabilization device 90, as shown in FIG. 5, for stabilizing a flame in the burner combustor can be activated to initiate a flame, and remain active to perpetuate the flame as required.

The stabilization device or a suitable igniter, such as a spark rod, hot surface igniter, direct spark igniter, plasma igniter, electrical arc igniter, field igniter, pilot light igniter, and the like, can be activated by the controller 34 to ignite the fuel/air mixture in the burner combustion chamber 26 based on, or in response to, a signal provided by an ultra-violet detector, flame rod, or other type of flame sensor 69 disposed to sense the presence of a flame within the burner combustion chamber 26, as shown in FIG. 5. This on-demand ignition, which can be activated continuously, can provide stable combustion occurring in the burner while the flame mode operation is active. This flame can be maintained continuously or intermittently, as required, by the stabilization device until the auto-ignition temperature in the furnace or in an area outside of the radiant tube is achieved. Throughout the flame mode, thermocouples or other devices can continuously monitor the interior temperature of the furnace/radiant tube 16 and a flame sensor 69 can monitor the presence or absence of flame inside the burner combustor 26 to provide such data to the controller 34 by means of any suitable link.

Once the temperature within the furnace/radiant tube reaches a pre-established level (normally about 1550 degrees Fahrenheit or greater) the controller 34 can communicate with the stabilization device to deactivate the stabilization device. The deactivation of the stabilization device causes the flame in the burner combustor 26 to be extinguished when operation transitions to the flameless mode of operation of the burner 10. The absence of the flame in the burner can be detected using the flame sensor (e.g., a flame rod or UV sensor), which can be used as an indication that the flameless mode has been reached.

During the flameless mode, the fuel gas and oxidant can be passed out of the burner 10 without undergoing combustion. Upon entering the auto-ignition temperature furnace/radiant tube environment, the fuel gas and oxidant are raised to a temperature sufficient to activate combustion without requiring continuous or intermittent ignition. Alternatively, a sustained combustion within the furnace may not require a combustible mixture to be provided at all through the burner, Thus, the location of the onset of combustion is moved from the burner combustor 26 downstream to the furnace chamber/radiant tube 16. Due to the relatively disperse combustion zone outside of the burner 10 and the entrainment of the flue gas within the fuel/oxidant mixture, there is not a substantial localized temperature spike. NOx production is thereby substantially reduced. As will be appreciated, once the flameless combustion mode has been initiated, the flows of fuel gas and oxidant may thereafter be cycled on and off, or otherwise maintained, decreased, or increased, to adjust the temperature within the furnace/radiant tube as desired anywhere above an auto-ignition level.

The stabilization device can be any suitable device that is capable of maintaining a flame in the combustion chamber when the flow rate and/or flow mixture of oxidant and fuel gas would otherwise destabilize and either extinguish, blow out or not otherwise maintain a flame within the burner combustion chamber without the stabilization device. In one embodiment, shown in FIG. 5, the stabilization device can be a hot surface igniter 90. The hot surface igniter is a device that uses electrical power in the form of heat provided when an electric current passes through an electrical resistive element 92. The resistive element 92 is disposed at the end of a rod 94 that extends into the burner chamber 26 so that the resistive element 92 is adjacent the fuel flow orifices of the nozzle assembly 24. The rod 94 may be hollow to accommodate electrical conduits 96 that interconnect the resistive element 92 with appropriate connections to the controller 34. In this way, the controller 34 can control operation of the hot surface igniter 90.

During operation, the resistive element 92 is activated and heated to a temperature that is sufficient to ignite the oxidant/fuel mixture in the combustion chamber 26. The controller is connected to the hot surface igniter to turn it on and off. In operation, the hot surface igniter is turned on to reach a temperature sufficient to ignite the oxidant/fuel mixture, and is left in the on condition to maintain a flame in the burner combustor. Once the furnace/radiant tube has reached the desired temperature, the controller can turn off the hot surface igniter to destabilize the flame in the burner combustor and initiate the flameless mode in the burner combustor, It will be appreciated that the hot surface igniter can have any suitable shape and size. In addition, the hot surface igniter can be disposed in any suitable position. In one embodiment, more than one such igniter may be used in the same burner chamber.

In another embodiment, shown in FIG. 6, the stabilization device can be a direct spark igniter 98. The direct spark igniter 98 is a device that uses electrical power at a high voltage or that includes a voltage multiplier coil 100 associated with a spark-producing tip 102 that provide electrical arcing that serves to ignite a combustible mixture. The tip 102 is disposed at the end of a rod 104 that extends into the burner chamber 26 so that the tip 102 is generally adjacent the fuel flow orifices of the nozzle assembly 24. The rod 104 may be hollow to accommodate electrical conduits 105 that interconnect the tip 102 with appropriate connections to the controller 34. In this way, the controller 34 can control operation of the direct spark igniter 98.

During operation, the tip 102 is activated to produce an arc that is sufficient to ignite the oxidant/fuel mixture in the combustion chamber 26. The controller is connected to the direct spark igniter to turn it on and off. In operation, the direct spark igniter is turned on to produce a spark sufficient to ignite the oxidant/fuel mixture, and is left in the on condition to maintain a flame in the burner combustor. Once the furnace/radiant tube has reached the desired temperature, the controller can turn off the direct spark igniter to destabilize the flame in the burner combustor and initiate the flameless mode in the burner combustor. It will be appreciated that the direct spark igniter can have any suitable shape, size or configuration. For example, the tip 102 need only be disposed within the burner chamber, while the coil 100 may be located remotely from the tips at an external location relative to the burner 10. In addition, the tips can be disposed in any suitable position, or at multiple positions within the burner chamber. In one embodiment, more than one such igniter may be used in the same burner chamber.

In yet another embodiment, shown in FIG. 7, the stabilization device can be a plasma igniter 106. The plasma igniter 106 is a device that uses an electrical discharge to produce an arc in a gas disposed between two electrodes 108. The electrodes 108 are disposed at the end of a rod 110 that extends into the burner chamber 26 so that the electrodes 108 are adjacent the fuel flow orifices of the nozzle assembly 24. The rod 110 may be hollow to accommodate electrical conduits 112 that interconnect the electrodes 108 with appropriate connections to the controller 34. In this way, the controller 34 can control operation of the direct spark igniter 98.

During operation, the electrodes 108 are activated to produce an arc that is sufficient to ignite the oxidant/fuel mixture in the combustion chamber 26. The controller is connected to the plasma igniter to turn it on and off. In operation, the plasma igniter is turned on to produce an electrical arc sufficient to ignite the oxidant/fuel mixture, and is left in the on condition to maintain a flame in the burner combustor. Once the furnace/radiant tube has reached the desired temperature, the controller can turn off the plasma igniter to destabilize the flame in the burner combustor and initiate the flameless mode in the burner combustor. It will be appreciated that the plasma igniter can have any suitable shape, size or configuration. For example, the electrodes 108 need only be disposed within the burner chamber and controlled remotely by the controller 34 through an induction coil, capacitor, or other electrical device that is disposed within or outside of the burner 10. In addition, the electrodes can be disposed in any suitable position, or at multiple positions within the burner chamber. In one embodiment, more than one such igniter may be used in the same burner chamber.

In another embodiment, shown in FIG. 8, the stabilization device can be an arc igniter 114. The arc igniter 114 is a device that uses electrical power to provide electrical arcing that serves to ignite a combustible mixture. Tips 116, between which the arc is created, are disposed at the end of a rod 118 that extends into the burner chamber 26 so that the tips 116 are adjacent the fuel flow orifices of the nozzle assembly 24. The rod 118 may be hollow to accommodate electrical conduits 120 that interconnect the tips 116 with appropriate connections to the controller 34. In this way, the controller 34 can control operation of the arc igniter 114.

During operation, the tips 116 are activated to produce an arc that is sufficient to ignite the oxidant/fuel mixture in the combustion chamber 26. The controller is connected to the arc igniter to turn it on and off. In operation, the arc igniter is turned on to produce an electrical ark or spark sufficient to ignite the oxidant/fuel mixture, and is left in the on condition to maintain a flame in the burner combustor. Once the furnace/radiant tube has reached the desired temperature, the controller can turn off the arc igniter to destabilize the flame in the burner combustor and initiate the flameless mode in the burner combustor. It will be appreciated that the are igniter can have any suitable shape, size or configuration. For example, the tips 116 need only be disposed within the burner chamber. In addition, the tips can be disposed in any suitable position, or at multiple positions within the burner chamber. In one embodiment, more than one such igniter may be used in the same burner chamber.

In another alternative embodiment, a directional secondary airflow may be provided to the burner chamber 26 to provide a counter-flow of air and/or oxidant in a direction generally toward the nozzle assembly 24 and away from the outlet opening 14 of the combustion chamber, as shown in FIG. 9. In this figure, an igniter 90 is used, which can be any appropriate igniter type operating to ignite a self-sustaining flame within the combustion chamber 26 or, alternatively, maintain a continuous flame within the chamber 26 of an otherwise non-flame-sustaining mixture. In one embodiment, the secondary air flow 200 is provided through one or more openings 202 formed in the sidewall of the hollow heat recuperator 18 in a region overlapping with the combustion chamber 26. The air entering the combustion chamber 26 through each opening 202 is provided, in the illustrated embodiment, by a respective conduit 204 having a valve 206 associated therewith that is responsive to commands from the controller 34 and operable to selectively fluidly block the conduit 204. In this way, air and/or an oxidant can selectively be provided to the combustion chamber 26. The conduits 204 are associated with an air source 208 which can be at the same pressure as the air supply 30 or at a different pressure, for example, higher pressure, such that a stream of counter-direction air can be formed within the combustion chamber 26 when the valve(s) 206 is/are open.

While the secondary air flow 200 is provided to the combustion chamber, a flame region 210 may be formed in an area where air, oxidant and fuel provided by the nozzle assembly 24 meets the counter-flowing air from the conduits 204. In the illustrated embodiment, the region 210 overlaps with the igniter 90 such that the resulting flame can be sustained more efficiently within the combustion chamber 26. In operation, the controller 34 can open the valve(s) 206 to provide a counter-flow of oxidant to the oxidant and fuel passing the nozzle assembly. An ignition device, such as a spark, can ignite the oxidant/fuel mixture to create a flame in the combustion chamber. The counter-flow of oxidant can stabilize the flame in the combustion chamber. Once the furnace/radiant tube has reached the desired temperature, the controller can close the valve(s) supplying oxidant to the backward oxidant pathways, which will destabilize the flame in the burner combustor to initiate the flameless mode in the burner combustor. It will be appreciated that the flow pathways can have any suitable shape and size. In addition, the flow pathways can be disposed in any suitable position.

In another embodiment, shown in FIG. 10, the stabilization device can be a pilot flame igniter 122. The pilot flame igniter 122 is a device that maintains a relatively small flame lit by providing a predetermined and metered flow of fuel or a fuel/air mixture continuously. The relatively small flame, which is commonly referred to as a pilot flame, serves to ignite a larger fuel flow during operation. The pilot flame 124 is disposed at the end of a fuel conduit 126 that extends into the burner chamber 26 so that the pilot flame 124 is adjacent the fuel flow orifices of the nozzle assembly 24. Flow of pilot fuel in the conduit 126 may be controlled by a valve 128, and also ignition of the pilot flame 124 periodically may be accomplished by an igniter 129.

During operation, the pilot flame 124 is continuously kept lit to ignite the oxidant/fuel mixture in the combustion chamber 26. In operation, the pilot flame is turned on to produce a flame sufficient to ignite the oxidant/fuel mixture, and is left in the on condition to maintain a flame in the burner combustor. Once the furnace/radiant tube has reached the desired temperature, the controller can turn off the pilot flame or, alternatively, leave it on but otherwise increase the flow of fuel, air and oxidant to push the flame outside of the combustion chamber and initiate the flameless mode in the burner combustor. In other words, the increased velocity of the fuel and air may prevent the dwell of the flame within the combustion chamber, In such condition, the fuel for the pilot flame, which represents a very small portion of the fuel provided by the nozzle assembly 24, may be carried with the remaining fluids and combust outside of the combustion chamber 26. It will be appreciated that the pilot flame igniter can have any suitable shape, size or configuration. For example, the pilot flame 124 need only be disposed within the burner chamber. In addition, the pilot flame can be disposed in any suitable position, or at multiple positions within the burner chamber. In one embodiment, more than one pilot flame may be used in the same burner chamber.

In another embodiment, shown in FIG. 11, the stabilization device can be an electric, magnetic or electromagnetic field generator igniter 130 that produces an induction heating effect on a heater element, which can reach a temperature sufficient for ignition of a combustible mixture. The induction igniter 130 can be a device that uses a process for heating an electrically conductive material such as a metal by electromagnetic induction, where so-called eddy currents in alternating directions are generated within the material, whose electrical resistance causes heating of the material. Heat may also be generated by magnetic hysteresis losses in materials that have significant relative permeability. A heated tip 132 of the induction igniter is disposed at the end of a rod 134 that extends into the burner chamber 26 so that the tip 132 is adjacent the fuel flow orifices of the nozzle assembly 24. The rod 134 may be hollow to accommodate electrical conduits 136 that interconnect the tip 132 with appropriate connections to the controller 34. In this way, the controller 34 can control operation of the induction igniter 130.

During operation, the tip 132 is heated to a temperature sufficient to initiate combustion of the oxidant/fuel mixture in the combustion chamber 26. The controller is connected to the induction igniter to turn it on and off. In operation, the induction igniter is turned on to produce in the heated element a temperature sufficient to ignite the oxidant/fuel mixture, and is left in the on condition to maintain a flame in the burner combustor. Once the furnace/radiant tube has reached the desired temperature, the controller can turn off the induction igniter to destabilize the flame in the burner combustor and initiate the flameless mode in the burner combustor. It will be appreciated that the induction igniter can have any suitable shape, size or configuration. For example, the tip 132 need only be disposed within the burner chamber. In addition, the tips can be disposed in any suitable position, or at multiple positions within the burner chamber. In one embodiment, more than one such igniter may be used in the same burner chamber.

A flowchart for a method of operating a burner in accordance with the disclosure is shown in FIG. 12. When the burner is turned on, an igniter is activated at 301, and a combustible mixture is provided to an internal burner chamber at 302. In one embodiment, the combustible mixture forms within the burner chamber as streams of fuel, air and/or an oxidant are provided to the chamber and mix. Unlike past burner designs, the combustible mixture need not be capable of self-sustaining a flame within the burner chamber in the absence of a sustained ignition source, which operates to stabilize the flame within the combustion chamber. The presence of a flame is sensed at 304, and a determination of presence of a flame within the burner chamber is made at 306. At a positive flame determination, i.e., when a flame is detected in the combustion chamber, a temperature external to the burner is sensed at 308. The external temperature is compared to an auto-ignition temperature threshold at 310 and, when the auto-ignition temperature is reached or exceeded, the flow rates of fuel, air and/or oxidant may be altered to transition the flame outside of the burner chamber, or extinguish the flame altogether.

In one embodiment, the burner is configured to maintain flame within the burner chamber by continuously monitoring for presence of a flame while the external temperature is below the auto-ignition threshold, and to maintain an igniter in an active state as a form of flame stabilizer for an otherwise unstable flame. In the event no flame is detected at the determination 306, the system is shut-down and restarted by discontinuing the flow of combustible mixture at 314, ensuring the igniter is active at 301, and providing the combustible mixture at 302. The igniter is maintained in an active state continuously while the temperature is below the predetermined value for as long as a stable flame is desired. When the external temperature has been exceeded, the igniter is turned off at 316 to extinguish the flame or to transition the flame to an area external to the burner. Following the flame transition or extinction, the flame sensor is interrogated to ensure no flame is present or remains within the burner chamber at 317. When no flame is present, the process ends. However, when a flame is still present in the burner chamber after deactivation of the igniter, the flow rate of the combustible mixture may be incrementally increased or decreased at 318 to destabilize the flame present and to push the flame outside of the burner until the flame is no longer present. Alternatively, the system is shut-down and restarted, for example, as previously described, by restarting the igniter and restarting the combustible mixture supply.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein,

The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A method of operating a burner, comprising:

providing a combustion chamber in the burner, which is adapted to receive at least a fuel stream and an air stream;

activating an igniter within the combustion chamber;

supplying a combustible mixture containing a ratio of fuel and air to the combustion chamber at a first flow rate, the combustible mixture being incapable of maintaining a stable flame;

igniting a flame in the combustible mixture in the combustion chamber by activating an igniter;

sensing a flame presence within the combustion chamber;

maintaining the igniter active to stabilize the flame within the combustion chamber;

heating a space exterior to the combustion chamber to a temperature at or above an auto-ignition temperature of the combustible mixture;

monitoring the temperature of the space exterior; and

deactivating the igniter to destabilize the flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber when the temperature of the space exterior is at or above the auto-ignition temperature.

2. The method of claim 1, further comprising providing a secondary air stream, which represents at least a portion of the air stream, to the combustion chamber in a direction disposed at an angle relative to a flow direction of the fuel stream.

3. The method of claim 2, wherein the secondary air stream is provided through at least one opening formed in a sidewall of a hollow body that defines the combustion chamber.

4. The method of claim 2, further comprising forming a flame region within the combustion chamber in an area where the secondary air stream and the fuel stream meet and overlap with the igniter.

5. The method of claim 2, wherein the secondary air stream and a remaining portion of the air stream are provided at different pressures.

6. The method of claim 2, further comprising selectively adjusting a flow rate of the secondary air stream.

7. The method of claim 1, wherein the igniter is one of a hot surface igniter, a direct spark igniter, a plasma igniter, an arc igniter, a pilot flame igniter, or an electric, magnetic or electromagnetic field generator igniter.

8. The method of claim 1, wherein the space exterior to the combustion chamber is a furnace chamber in a furnace, and wherein the space exterior to the combustion chamber is a radiant tube disposed in the furnace chamber.

9. The method of claim 1, wherein a controller automatically adjusts at least one of a flow rate of the fuel stream, a flow rate of the air stream, and a flow rate of an oxidant stream, which oxidant stream is included in the combustible mixture, based on signals provided to the controller that are indicative of the sensing of the flame presence and the monitoring of the temperature of the space exterior,

10. The method of claim 1, wherein the burner further comprises a nozzle for the fuel and air streams to pass through and intermix in the combustion chamber.

11. A method of operating a burner, comprising:

activating an igniter;

providing a fuel stream, a first air stream, and a secondary air stream to a combustion chamber of the burner;

intermixing the fuel, first and secondary air streams to form a combustible mixture at a first flow rate, said combustible mixture being incapable of maintaining a stable flame within the combustion chamber;

igniting the combustible mixture in the combustion chamber with the igniter;

sensing a flame presence within the combustion chamber;

maintaining the igniter active to sustain combustion of the combustible mixture within the combustion chamber;

heating a space exterior to the combustion chamber to a temperature at or above an auto-ignition temperature of the combustible mixture;

monitoring the temperature of the space exterior;

providing the combustible mixture at a second flow rate, which is higher than the first flow rate, to extinguish a flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber; and

when combustion occurs in the space exterior to the combustion chamber, deactivating the igniter and discontinuing the secondary air stream.

12. The method of claim 11, further comprising providing the secondary air stream to the combustion chamber in a direction disposed at an angle relative to a flow direction of the fuel stream.

13. The method of claim 12, wherein the secondary air stream is provided through at least one opening formed in a sidewall of a hollow body that defines the combustion chamber, wherein the burner further comprises a nozzle for the fuel and air streams to pass through and intermix in the combustion chamber, and wherein the at least one opening is different than nozzle openings provided for the fuel and first air streams.

14. The method of claim 11, further comprising forming a flame region within the combustion chamber in an area where the secondary air stream and the fuel stream meet and overlap with the igniter.

15. The method of claim 11, wherein the first and secondary air streams are provided at different pressures.

16. The method of claim 11, further comprising selectively adjusting a flow rate of the secondary air stream,

17. The method of claim 11, wherein the igniter is one of a hot surface igniter, a direct spark igniter, a plasma igniter, an arc igniter, a pilot flame igniter, or an electric, magnetic or electromagnetic field generator igniter.

18. The method of claim 11, wherein the space exterior to the combustion chamber is a furnace chamber in a furnace, and wherein the space exterior to the combustion chamber is a radiant tube disposed in the furnace chamber.

19. The method of claim 11, wherein a controller automatically adjusts at least one of a flow rate of the fuel stream, a flow rate of the first air stream, and a flow rate of an oxidant stream, which oxidant stream is included in the combustible mixture, based on signals provided to the controller that are indicative of the sensing of the flame presence and the monitoring of the temperature of the space exterior.

20. A method for operating a burner, comprising:

activating an igniter;

providing a combustible mixture to a combustion chamber;

sensing a flame presence in the combustion chamber;

maintaining activation of the igniter to stabilize a flame in the combustible mixture within the combustion chamber;

sensing an external temperature when a flame is sensed in the combustion chamber;

comparing the external temperature with an auto-ignition temperature of the combustible mixture; and, when the external temperature is greater or equal than the auto-ignition temperature,

transitioning the flame from the combustion chamber to an area external to the combustion chamber; and

deactivating the igniter.