US20130260323A1

US20130260323A1 - METHOD AND APPARATUS FOR A DUAL MODE BURNER YIELDING LOW NOx EMISSION

Info

Publication number: US20130260323A1
Application number: US13/855,343
Authority: US
Inventors: Jianhui Hong; John William Wheeler
Original assignee: Eclipse Inc
Current assignee: Eclipse Inc
Priority date: 2012-04-03
Filing date: 2013-04-02
Publication date: 2013-10-03
Also published as: WO2013152012A1; RU2014144438A; IN2014DN09033A; CN104508373A

Abstract

A method and apparatus for a burner adapted to heat a furnace or other environment of use. In particular, a burner for providing a fuel gas in combination with an oxidant to effect controlled reaction of the fuel gas in a manner to reduce NOx emissions is described. Combustion of the fuel gas is shifted from 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.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims the benefit of U.S. Provisional Patent Application No. 61/619,771, filed Apr. 3, 2012, which is incorporated by reference in its entirety herein.

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 internal components and surfaces of the burner and combustion chamber are exposed to the very high temperature environment. Second, when combustion is carried out at extremely high temperatures, nitrogen oxide (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, difficulties associated with high NOx emissions still remain.

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.
One embodiment provides a burner with a nozzle having a movable fuel tube to shift combustion from within the burner into the furnace/radiant tube. More particularly, this embodiment provides a burner in which fuel gas may be delivered through the fuel tube for discharge, such as axial and/or radial discharge, into a burner combustor for mixing with oxidant at a ratio that provides a combustible mixture to sustain the flame in the burner combustor. During a start-up stage, the fuel tube is in a retracted position, and the fuel gas/oxidant mixture is ignited with a spark igniter to combust within the burner combustor. During that 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 above the auto-ignition temperature, the fuel tube can be moved toward the outlet of the burner to an extended position. During this time, the flame gradually moves with the fuel tube in the burner combustor towards the furnace chamber/radiant tube. As the fuel tube approaches a fully extended position near the outlet of the burner, the flame will be destabilized and extinguished 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 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. The high velocity of oxidant and fuel exiting the burner combustor contributes to destabilization and extinguishment of flame in the furnace/radiant tube. 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 spikes of temperatures 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 fuel gas and oxidant can be maintained, decreased, or increased, according to the needs of the furnace operator. The burner will begin to cool after the flame has ceased to exist in the burner combustor, and, thus, when the burner has cooled to a temperature below the auto-combustion temperature, the fuel tube may be retracted without the flame returning to the burner combustor. Alternatively, the fuel tube may stay in the extended position during the flameless mode operation. The latter creates a physical separation of the fuel and oxidant streams in the upstream portion of the burner combustor and may be advantageous when the auto-ignition temperature of the fuel/oxidant mixture is low, such as fuel gas mixture containing high percentage of hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 2 is a diagrammatic view illustrating a burner and control system of FIG. 1 with the fuel tube in an extended position;

FIG. 3 is a fragmentary sectional view of a nozzle assembly mounted within a combustor for the burner of FIG. 1, with the fuel tube retracted;

FIG. 4 is an end view of the nozzle assembly of FIG. 3;

FIG. 5 is a diagram showing the method of controlling the burner from the flame mode to the flameless mode;

FIG. 6 is a simplified view of the nozzle assembly mounted within a combustor for the burner of FIG. 1;

FIG. 7 is another simplified view of the nozzle assembly mounted within a combustor for the burner of FIG. 1;

FIG. 8 is a diagrammatic view illustrating another embodiment of a burner and control system for delivery of fuel gas and combustion air adapted to heat a furnace, radiant tube, or other chamber;

FIG. 9 is a diagrammatic view illustrating a burner and control system of FIG. 8 with the fuel tube in an extended position; and

FIG. 10 is an end view of the nozzle assembly for the burner and control system of FIG. 8.

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. FIG. 1 illustrates 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 as will be well known to those of skill in the art and which is 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 an air shroud 19 which, in turn, can surround a fixed fuel tube assembly 21 and a movable fuel tube 22 feeding a nozzle assembly 24 within a burner combustion chamber 26 (also referred to as a combustor) located adjacent to the open end of the burner. An annular air passageway 28 can be disposed between the outer walls of the air shroud 19 and the interior of the heat recuperator 18.
As shown, an oxidant 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 may adjust fuel feed in accordance with pre-established commands based on conditions in the furnace, radiant tube, and/or the burner.
A sensor 46, such as a flame sensor, or the like, may be present to continuously monitor the presence of a flame 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 movement of the fuel tube 22. It will be appreciated that the sensor 46 can be any suitable sensor and can be disposed in any suitable location.
Referring now to FIGS. 3 and 4, the nozzle assembly 24 can include 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 any suitable shape. In some embodiments, the radial disk portion can be planar. In other embodiments, the radial disk portion 52 can have a generally concave forward face projecting towards the outlet of the burner. The forward nipple portion 50 can form the end of the fuel tube 22, and the fuel tube 22 can be surrounded by the radial disk portion 52 such that the fuel tube 22 can move freely with respect to the radial disk portion 52.
The radial disk portion 52 can include a pattern of interior air passages 58. As will be described further herein, during operation, oxidant delivered from the oxidant supply 30 may flow through an annular gap 56 and the interior air passages 58 towards the burner outlet as shown by the arrows 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 through the axial gas passage opening 64 and the radial gas passage openings 66 and can mix with the oxidant. It will be appreciated, however, that the fuel gas and oxidant can pass the nozzle assembly in any suitable manner and at any suitable angle.
As mentioned, 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 80. 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 burner. The flame mode can provide the initial start-up of the furnace/radiant tube 16 using combustion of fuel gas and oxidant 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 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 oxidant control valve 32 and the fuel control valve 42 are set to an open condition. In this open condition, 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 axial gas passage opening 64 and the radial gas passage openings 66 to mix with the oxidant in the burner combustion chamber 26. An electric spark rod 69 or the like can be activated by the controller 34 to ignite the fuel/air mixture in the burner combustion chamber 26. This ignition results in combustion occurring in the burner, and a flame being present in the burner. This flame can be steadily maintained until the auto-ignition temperature in the furnace/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 46 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.
Referring to FIG. 1, 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 a device 90 to move the fuel tube 22 to an extended position as shown in FIG. 2. The device 90 can be any suitable mechanism for moving the fuel tube 22 between retracted and extended positions. For example, the device 90 can be an electric (such as a solenoid) or pneumatic system capable of moving the fuel tube 22. The movement of the fuel tube 22 toward the outlet 80 causes the flame in the burner combustor 26 to extinguish in order to reach the flameless mode 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), generally depicted as 46, which can be used as an indication that the flameless mode has been reached.
During the flameless mode, the fuel gas and oxidant are passed out of the burner 10 without undergoing combustion. Upon entering the high-temperature furnace/radiant tube environment, the fuel gas is raised to a temperature sufficient to activate combustion. 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, a substantial localized temperature spike does not occur. 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.
The movement of the fuel tube 22 toward the outlet 80 can cause a physical separation of the fuel gas and oxidant streams passing through the nozzle assembly 24, which results in a decrease in the effective residence time for reaction within the burner combustor 26. Combustion occurs at finite rates and therefore requires a certain residence time to finish. The decrease of residence time can extinguish combustion within the burner combustor. Flow recirculation helps stabilize the combustion within the burner combustor 26. Due to the converging shape of the burner combustor, the extension of the fuel tube 22 results in a reduction of flow recirculation within the burner combustor 26. Thus, the extension of the fuel tube 22 de-stabilizes and extinguishes the flame in burner combustor 26. Accordingly, available fuel gas and oxidant can be delivered into the furnace/radiant tube 16 prior to combustion. Due to the elevated temperature in the furnace/radiant tube 16, the fuel gas undergoes combustion downstream from the burner combustor 26. While the temperature levels within the furnace/radiant tube 16 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 oxidant and fuel provides substantial blending and recirculation of the flue gas with the oxidant/fuel mix, resulting in reduced combustion temperatures in the furnace/radiant tube 16. As noted above, after flame extinction and the initiation of flameless combustion, the flow rate of the mixture can be maintained, decreased, or increased according to the process needs.
FIG. 5 shows an embodiment of a method of controlling the burner to move from the flame mode to the flameless mode. As described above, the fuel gas and oxidant mixture in the burner combustor can be ignited to create a flame in this region. At step 100, the burner can operate in the flame mode until a threshold temperature has been reached in the furnace/radiant tube. The threshold temperature is a temperature at or greater than the auto-combustion temperature for the fuel gas and oxidant mixture. At step 102, the temperature in the furnace/radiant tube is measured and compared to the threshold temperature. If the threshold temperature has not been reached, then the fuel tube remains retracted at step 110, and the burner continues to operate in the flame mode until another temperature measurement is taken and compared. If the threshold temperature has been reached or exceeded, then as represented in step 104, the fuel tube is extended; otherwise the fuel tube remains in the retracted position. As shown in step 106, a flame detection sensor can be used to monitor whether the flame is still present in the burner combustor. If the flame is no longer detected, then the flameless mode has been reached in step 108, and combustion is only occurring outside the burner in the furnace/radiant tube. The system can continue to monitor the temperature in the furnace/radiant tube against the threshold temperature. So long as the temperature remains at or above the threshold temperature and no flame is detected in the burner, the burner can continue to operate in the flameless mode. On the other hand, if the furnace/radiant tube temperature drops below the threshold temperature, or if a flame is detected in the burner after the fuel tube has been extended at step 104, the fuel tube can be retracted at step 110. At this point, the system can proceed again from step 100 as described above. Flame mode operation (step 100) may include interrupting fuel gas, purging with air and activating spark ignition when a flame is not detected, as are well known in the art. When a flame is detected in the burner after the fuel tube has been extended at step 104, an alarm signal may be issued to inform the operator that the flameless combustion mode was not achieved. The operator can then take appropriate actions.
As shown in FIG. 6, in some embodiments, fuel gas 82 may undesirably pass outside the movable fuel tube 22 before entering the burner combustor 26. For example, some of the fuel gas 82 may pass through a gap between the movable fuel tube 22 and the fixed fuel tube assembly 21 and/or a nozzle extension tube 23 such that fuel gas will enter the burner combustor 26 near the radial disk portion 52 instead of near the end of the movable fuel tube 22. This leakage of fuel gas 82 can increase the premixing of the fuel gas 82 and oxidant 84 in the burner combustor 26 and lead to higher NOx. The amount of leakage can be reduced by reducing the size of the gap between the exterior of the movable fuel tube 22 and the fixed fuel tube assembly 21 and/or a nozzle extension tube 23. The size of the gap can be reduced by machining the movable fuel tube 22 to fit closely within the fixed fuel tube assembly 21 and/or a nozzle extension tube 23. However, these components are subject to high temperatures near the burner combustor 26 that could cause them, in certain embodiments, to deform in a manner that could restrict or prevent the movement of the movable fuel tube 22.
Accordingly, the burner 10 may be provided with a suitable structure to reduce the amount of fuel gas leakage between the movable fuel tube 22 and the fixed fuel tube assembly 21 and/or a nozzle extension tube 23 without interfering with the movement of the movable fuel tube 22. As shown in FIG. 7, in certain embodiments a collar 86 may be closely fitted around the movable fuel tube 22 sufficiently upstream of the burner combustor 26 to avoid the high temperatures that can lead to deformation. The collar 86 can be attached to the fixed fuel assembly 21 in any suitable manner, such as by welding the collar 86 to the fixed fuel assembly 21. In some embodiments, as shown in FIG. 7, one or more holes can be drilled into the fixed fuel assembly 21. The holes can be filled with a welding material 88 to weld the collar 86 to the fixed fuel assembly 21. The close fit of the collar 86 around the movable fuel tube 22 can prevent, or restrict the amount of, fuel gas passing outside of the movable fuel tube 22. With the collar 86 in place, a suitably sized gap can be provided between the movable fuel tube 22 and the fixed fuel tube assembly 21 and/or a nozzle extension tube 23 to accommodate any deformation that may occur near the end of the movable fuel tube 22 without affecting the movability of the movable fuel tube 22. It will be appreciated that any suitable structure may be provided to restrict or prevent undesired premixing of the fuel gas with the oxidant.
As shown in FIGS. 8 and 9, in certain embodiments, the device for moving the fuel tube can be coupled at an alternative position on the movable fuel tube. The burner embodiment 200 of FIGS. 8 and 9 can be similar to the embodiments described above including features such as a cover tube open end 214, a recuperator 218, a fixed fuel tube assembly 221, a movable fuel tube 222, a nozzle assembly 224, a combustion chamber 226, an annular air passageway 228, an oxidant supply 230, an oxidant control valve 232, a controller 234, a fuel supply 240, a fuel control valve 242, an outlet 280, a fuel tube movement device 290, etc. More specifically, the fuel tube movement device 290 can be disposed adjacent to a portion of the fixed fuel tube assembly 221 and near where the oxidant supply 230 and fuel supply 240 enter the burner 200. The fuel tube movement device 290 can be connected to, and controlled by, the controller 234. The fuel tube movement device 290 can include a movement rod 292 extending from the device 290 that can be connected to the movable fuel tube 222 at any suitable position. As shown, the movement rod 292 can be connected near an end of the movable fuel tube 222 disposed near the combustion chamber 226. FIG. 10 shows the movable rod 294 passing through an opening 296 in the radial disk portion 252 of the nozzle assembly 224 in order for the movable rod 294 to attach to the movable fuel tube 222 near this location.
The movement rod 292 can be moved by the device 290 toward and way from the outlet 280 to push and pull the movable fuel tube 222 along the same direction. For example, FIG. 8 shows the moveable fuel tube 222 in its retracted position. In comparison, FIG. 9 shows the movement rod 292 and movable fuel tube 222 moved toward the outlet 280 in order to destabilize and extinguish the flame in the combustion chamber 226. It will be appreciated that, in some embodiments, the movement rod 292 can also move the nozzle assembly 224 toward and away from the outlet 280.
As noted, the fuel tube can be moved via any suitable mechanism. In addition, the fuel tube can be constructed and attached in any suitable way to permit the fuel gas exit to be moved from a position in the burner upstream and relatively far away from the burner outlet to a position at or near the burner outlet. It will also be appreciated that the nozzle assembly can be fixed, or can be moved with or moved independent from the fuel tube via any suitable mechanism.
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

What is claimed is:

1. A method of operating a burner comprising:

providing a burner including a combustion chamber, a combustor outlet, a movable fuel tube, and a fuel tube movement device coupled to the movable fuel tube;

supplying the burner with fuel and oxidant, the fuel being supplied such that the fuel enters the movable fuel tube;

igniting the fuel and oxidant mixture in the combustion chamber;

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

activating the fuel tube movement device to move the movable fuel tube in a direction toward the combustor outlet to extinguish the flame in the combustion chamber such that combustion occurs in the space exterior to the combustion chamber in the absence of a flame in the combustion chamber.

2. The method of claim 1 wherein the movable fuel tube includes a first end and a second end, the first end being disposed near the combustion chamber.

3. The method of claim 2 wherein the fuel tube movement device is coupled to the movable fuel tube near the first end.

4. The method of claim 2 wherein the fuel tube movement device is coupled to the movable fuel tube near the second end.

5. The method of claim 1 further comprising a fixed fuel tube fixedly mounted within the burner, the movable fuel tube being at least partially disposed within the fixed fuel tube, the movable fuel tube being movable with respect to the fixed fuel tube.

6. The method of claim 5 further comprising a collar disposed between the fixed fuel tube and the movable fuel tube.

7. The method of claim 1 wherein the burner includes a nozzle assembly disposed near the combustion chamber.

8. The method of claim 7 wherein the nozzle assembly includes an opening for receiving a portion of the fuel tube movement device.

9. The method of claim 1 wherein the fuel tube movement device is an electrical device.

10. The method of claim 1 wherein the fuel tube movement device is a pneumatic device.

11. A burner comprising:

a combustion chamber terminating at a combustor outlet;

a movable fuel tube, the movable fuel tube including a first end disposed near the combustion chamber; and

a fuel tube movement device coupled to the movable fuel tube for moving the fuel tube toward and away from the combustor outlet.

12. The burner of claim 11 wherein the fuel tube movement device is coupled to the movable fuel tube near the first end.

13. The burner of claim 11 wherein the movable fuel tube includes a second end, and the fuel tube movement device is coupled to the movable fuel tube near the second end.

14. The burner of claim 11 further comprising a fixed fuel tube fixedly mounted within the burner, the movable fuel tube being at least partially disposed within the fixed fuel tube, the movable fuel tube being movable with respect to the fixed fuel tube.

15. The burner of claim 14 further comprising a collar disposed between the fixed fuel tube and the movable fuel tube.

16. The burner of claim 11 further comprising a nozzle assembly disposed near the combustion chamber.

17. The burner of claim 16 wherein the nozzle assembly includes an opening for receiving a portion of the fuel tube movement device.

18. The burner of claim 11 wherein the fuel tube movement device is an electrical device.

19. The burner of claim 11 wherein the fuel tube movement device is a pneumatic device.

20. The burner of claim 11 further comprising a sensor for detecting the presence of a flame in the combustion chamber.