US20240401798A1

US20240401798A1 - HIGH PERFORMANCE LOW NOx BURNER AND SYSTEM AND METHOD OF OPERATION

Info

Publication number: US20240401798A1
Application number: US18/737,219
Authority: US
Inventors: Donald Kendrick; William A. Santana; Venkatesh Iyer
Original assignee: Clearsign Technologies Corp
Current assignee: Clearsign Technologies Corp
Priority date: 2021-05-19
Filing date: 2024-06-07
Publication date: 2024-12-05

Abstract

According to embodiments, burner systems include a first plurality of main fuel nozzles positioned in a flame tube or combustion chamber and configured to supply a flow of main fuel to a burner in the flame tube, and a second plurality of main fuel nozzles positioned outside the flame tube or combustion chamber and configured to introduce a flow of main fuel into a combustion air flow that is introduced to the burner.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. Continuation-in-Part application which claims priority benefit under 35 U.S.C 120 from co-pending U.S. patent application Ser. No. 18/513,131, filed Nov. 17, 2023, which is a U.S. Continuation-in-Part application claiming priority from International PCT Patent Application No. PCT/US2022/029325, entitled “HIGH PERFORMANCE LOW NOX BURNER AND SYSTEM”, filed May 13, 2022 (docket number 2651-355-04), which claims priority from U.S. Provisional Patent Application No. 63/190,606, entitled “HIGH PERFORMANCE BURNER AND SYSTEM,” filed May 19, 2021 (docket number 2651-356-02), now expired and from U.S. Provisional Patent Application No. 63/209,918, entitled “BOILER BURNER” filed Jun. 11, 2021 (docket number 2651-355-02), now expired, each of which, to the extent not inconsistent with the disclosure herein, is incorporated by reference.

SUMMARY

According to an embodiment, a burner system is provided that includes a first plurality of main fuel nozzles positioned in a flame tube or combustion chamber and configured to supply a flow of main fuel to a burner in the flame tube or combustion chamber. The system also includes a second plurality of main fuel nozzles positioned outside a body of the flame tube or combustion chamber and configured to introduce a flow of main fuel into a combustion air flow that is introduced into the burner through the flame tube.
According to an embodiment, a burner is provided that includes a flange configured to be mounted over an opening of a flame tube or combustion chamber and structured to support a burner that is mounted to the flange. The burner is configured to extend into the flame tube or combustion chamber. The burner includes a mixing tube that extends transverse to the flange and has a proximal inlet and a distal outlet. A first plurality of main fuel nozzles is positioned adjacent to the proximal inlet of the mixing tube and is configured to introduce main fuel into the mixing tube via the proximal inlet. A combustion air conduit is coupled at a first end to an opening in the flange on a side of the flange opposite the burner and is configured to supply a flow of combustion air through the flange to the proximal inlet of the mixing tube. A second plurality of main fuel nozzles is positioned within the combustion air conduit and is configured to introduce main fuel into the flow of combustion air upstream of the first plurality of main fuel nozzles and the proximal inlet of the mixing tube.
According to an embodiment, a pilot burner is positioned adjacent to the distal outlet of the mixing tube and is configured to ignite a mixture of combustion air and main fuel flowing from the distal outlet.
According to an embodiment, a first main fuel source is operatively coupled to and configured to supply main fuel to the first plurality of main fuel nozzles, while a second main fuel source is operatively coupled to and configured to supply main fuel to the second plurality of main fuel nozzles.
According to an embodiment, an annular fuel gallery is disposed around the combustion air conduit. A plurality of tubes extends radially into the combustion air conduit from the annular fuel gallery, and each of the plurality of tubes has at least one nozzle aperture formed therein, the nozzle apertures of each of the plurality of tubes together constituting the second plurality of main fuel nozzles. The second main fuel source is in fluid communication with the annular fuel gallery, which supplies main fuel to each of the second plurality of main fuel nozzles via the plurality of tubes. According to an embodiment, each of the plurality of tubes includes a plurality of nozzle apertures.
According to an embodiment, the proximal inlet of the mixing tube has a flared shape and the first plurality of main fuel nozzles is arranged in a radially symmetrical pattern concentric with the proximal inlet.
According to an embodiment, a blower is provided, with an output coupled to a second end of the combustion air conduit and configured to blow combustion air through the combustion air conduit to the burner.
According to an embodiment, a start-up method of a burner is provided, which includes introducing a flow of combustion air into a mixing tube of the burner positioned in a flame tube or combustion chamber, via a combustion air conduit and a proximal inlet of the mixing tube.
A first flow of main fuel is introduced into the proximal inlet of the mixing tube via a first plurality of main fuel nozzles positioned adjacent to the proximal inlet. Main fuel and combustion air mix within the mixing tube as they flow from the proximal inlet toward the distal outlet. A combustion reaction is ignited near the distal outlet of the mixing tube, and is supported by the mixture of fuel and air flowing in the tube. A second flow of main fuel is then introduced into the combustion air conduit via a second plurality of main fuel nozzles positioned upstream of the first plurality of main fuel nozzles and the proximal inlet. During or after the introduction of the second flow of main fuel, the volume of the first flow of main fuel is reduced.
According to an embodiment, the first flow of main fuel is completely stopped. According to another embodiment, the first flow of main fuel is reduced until a selected ratio of the first flow of main fuel, relative to the second flow, is reached. The selected ratio may be, for example, approximately 10:90, 30:70, 40:60, 50:50, 60:40, 70:30, etc.
According to various embodiment: introducing the second flow of main fuel and reducing the volume of the first flow of main fuel are done substantially simultaneously; introducing the second flow of main fuel and reducing the volume of the first flow of main fuel may be done while holding a total volume of main fuel substantially constant; or introducing the second flow of main fuel and the reducing the volume of the first flow of main fuel may be done in alternating incremental steps.
According to an embodiment, before introducing main fuel to the mixing tube, a pilot fuel supply is provided to a pilot burner positioned adjacent to the distal outlet of the mixing tube, and the pilot fuel is ignited. The main fuel and combustion air mixture is then ignited by the pilot flame.
According to an embodiment, the pilot burner is turned down or shut down after starting and stabilizing the main combustion reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partially side sectional view of a burner system, according to an embodiment.

FIG. 1B is a partially side sectional diagram of the embodiment of FIG. 1A.

FIG. 1C is a partially side sectional view of a flame holder and distal pilot burner shown in FIGS. 1A and 1B.

FIG. 2 is partially side-sectional view of a burner system, according to another embodiment.

FIG. 3A is a perspective view of a burner system, according to another embodiment.

FIG. 3B is a detailed view of the embodiment of FIG. 3A, from a different vantage point.

FIG. 3C is a perspective view of a structural component of the burner system of FIG. 3A, according to an embodiment

FIG. 3D is a perspective view of a flame holder portion of the burner system of FIG. 3A, according to an embodiment.

FIG. 4 is a schematic diagram of a burner system, according to an embodiment.

FIG. 5 is a perspective view a portion of the burner system of FIG. 4 , according to an embodiment.

FIG. 6 is a perspective view of a portion of the burner system of FIG. 4 , according to an embodiment.

FIG. 7 is a perspective view of a portion of the burner system of FIG. 4 , according to an embodiment.

FIG. 8A is a perspective view of a distal flame holder and distal pilot burner including shared structure for the burner system of FIG. 4 , according to an embodiment.

FIG. 8B is a cross-sectional view of the distal flame holder and distal pilot burner of FIG. 8A, according to an embodiment.

FIG. 8C is a cross-sectional view of the distal flame holder and distal pilot burner of FIG. 8A, according to an embodiment.

FIG. 8D is a partial view of an edge of a surface of the distal flame holder and distal pilot burner of FIG. 8A, according to an embodiment.

FIG. 9 is a perspective view of a portion of the burner system of FIG. 4 , according to an embodiment.

FIG. 10 illustrates a method relating to the operation of a burner system, according to an embodiment.

FIG. 11 is a process diagram illustrating a method for operating a burner apparatus, according to an embodiment.

FIG. 12 illustrates additional operations of the method of FIG. 11 , according to an embodiment.

FIG. 13A is a perspective view of a portion of a burner system, according to another embodiment.

FIG. 13B is a detailed view of the embodiment of FIG. 13A, from a different vantage point, according to an embodiment.

FIG. 14 illustrates a process for operating a burner system, 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 burner system 100, according to an embodiment. The burner system 100 may be assembled as a unit and may be mountable to a boiler via its flange 102, which is drawn in partial cross section to show parts passing through the flange 102; these include a pilot fuel line 101, an igniter tube 108, and a combustion air tube 114, which passes air from a blower 113 through the flange 102 as shown in FIG. 1A. The combustion is conducted to a main burner assembly 116 and thence into a mixing tube 120. The inlet end of the mixing tube 120 may optionally include a bell section 126, which aids in reducing flue gasses into the inlet end of the mixing tube 120, when the burner system 100 is fixed in position inside a boiler flame tube. The boiler flame tube, which may be surrounded with water or other fluid, may be coaxial with and larger in diameter than the burner system 100, such that there is an annular space through which flue gases are able to pass, in a direction opposite to the flow inside the mixing tube 120, from the region adjacent to an outlet end of the mixing tube 120 toward the inlet end of the mixing tube, where they may be educed into the mixing tube.
A distal pilot burner 150 may be located downstream from the outlet end of the mixing tube 120. The distal pilot burner produces a pilot flame from pilot fuel arriving through the pilot fuel line 101 (or alternatively, a premixed pilot fuel and combustion airline 101) such that the pilot fuel is ignited by an ignition device at the distal end of igniter tube 108. The distal pilot burner 150 may further include a pilot-burner tube 152 and a ducted swirler 154; in an embodiment, these may both be coaxial with the mixing tube 120 and with one another. The ducted swirler 154 may be supported by support members 156 extending between the mixing tube 120 and the pilot-burner tube 152. In an embodiment, there may be three support members 156 radiating from an axis (which may be coincident with axes of the mixing tube 120 and/or the pilot-burner tube 152). Optionally, the pilot fuel line 101 may act as a support for the distal pilot burner 150, for the mixing tube 120, and/or for a distal flame holder, if separate from the distal pilot burner 150.
Although described primarily in relation to their use in boilers, embodiments disclosed and described herein may, according to other embodiments, also be employed to provide heat in other applications, such as, e.g., hot oil heaters, water bath heaters, glycol heaters, etc. Accordingly, unless explicitly recited therein, the claims are not limited to burner systems positioned or operating in boilers and/or flame tubes, but are to be read more broadly on burner systems in general.
The term pilot burner may, in some contexts, be considered to be limited to a burner that is always on. As used herein, the term pilot burner includes embodiments where the burner may be shut off, such as when a combustion reaction of main fuel is stable. In this form, structure associated with the pilot burner may provide flame holding, mixing, and/or other functionality even when fuel flow to the pilot burner is reduced or stopped. According to embodiments, a non-operating pilot burner (after fuel is turned off) continues to provide flame holding functions.
The pilot fuel line 101 may carry a fuel different from a main fuel for the main burner 116, or the pilot fuel and main fuel may be the same. When the pilot fuel line 101 carries a mixture of fuel and oxidant such as air, a premix flame results when the mixture is ignited; when the pilot fuel line 101 carries fuel only, the pilot burner supports a diffusion flame wherein combustion air is provided from the main combustion air source. The pilot fuel line 101 of FIG. 1 is intended to represent either alternative of a premixed pilot burner or a diffusion flame pilot burner. FIG. 1B is a side section view of an embodiment according to FIG. 1A. The burner diagram of FIG. 1B illustrates a center body 170. A vaned structure 172, which may be configured as a unitary insert, as a configuration of distinct inserts, or as an integral part of the burner system 100 may optionally be included.
The center body 170 may, in an embodiment, be of substantially constant cross-sectional area or diameter. In another embodiment, the center body 170 may be formed to have non-constant cross-sectional area or diameter. FIG. 1C shows the ducted swirler 154 in greater detail, and in cross section. A hollow swirler body 157 is shown in fluid communication with the pilot fuel line 101. Jet orifices 159 at the downstream tip of the swirler body 157 eject pilot fuel and/or fuel/air mixture into an outlet end of the pilot-burner tube 152. FIG. 1C shows two orifices 159 in side section and a third as a circle, behind the section plane; in the illustrated embodiment there may be a total of four orifices. Different numbers of orifices may be selected according to the designer's preference, system size, fuel characteristics, etc. Fuel jets emerging from the orifices 159 encounter swirling air to which rotation has been imparted by swirler vanes 158. The swirler vanes 158 may be fastened to one or both of the body 157 of the ducted swirler 154 and/or the interior of the pilot-burner tube 152.
As swirling air stabilizes a flame resulting from ignition of the fuel jets, the distal pilot burner 150 may operate as a flame holder. In an embodiment, the distal pilot burner 150 may be of all-metal construction and operate as an all-metal flame holder. The distal pilot burner 150 further may be of unitary construction, or, assembled into an integral whole. In an embodiment, the distal pilot burner may be integral with the mixing tube 120.
According to embodiments, main fuel may be introduced through a first plurality of main fuel nozzles 115 and common both to water tube and fire tube boiler burners.
According to embodiments, a plurality of second main fuel nozzles is provided outside the boiler/combustion chamber (upstream). FIGS. 13A and 13B are different perspective views of a burner system 1300, according to an embodiment, showing, in particular, a portion of the burner system positioned outside a boiler body or combustion chamber, which includes main fuel and combustion air supply elements. The flame tube 130 is partially cut away in FIG. 13A to show elements of a burner assembly, which, in the embodiment shown, are similar to elements described with reference to FIGS. 1A, 1B, 3A and 3B. An annular fuel gallery 1302 is disposed outside an air conduit 114 between a blower 113 and a flange 102. The blower 113 is configured to provide combustion air to the burner assembly positioned within the flame tube 130. Main fuel is supplied to the annular fuel gallery 1302 via a second main fuel pipe 1304. The annular fuel gallery 1302 is shown in phantom lines in FIG. 13B for clarity. A set of radial tubes 1306 extend into the air conduit 114 from the fuel gallery 1302 to points at or outside the centerline of the air conduit. In another embodiment, the tubes are connected across the centerline of the air conduit 114. Nozzle apertures 1308 are formed in each radial tube 1306 to form the second plurality of main fuel nozzles, upstream from the first plurality of main fuel nozzles, e.g., outside the boiler. The inner ends of the radial tubes may be closed.
In the embodiment of FIGS. 13A and 13B the annular gallery 1302 is shown positioned about midway between the blower 113 and the flange 102. According to another embodiment, the fuel gallery is positioned adjacent to or in contact with the flange 102, while in a further embodiment, the fuel gallery is close to or against the blower 113.
To achieve startup, with an igniter started, the first plurality of main fuel nozzles 115 are opened (or gradually opened) to flow main fuel into the mixing tube 120 while the second plurality of main fuel nozzles (described immediately above) do not flow fuel. For example, an igniter may include a spark or hot surface igniter, and starting the igniter may include providing current to the igniter. In an embodiment, the igniter includes a distal pilot burner 150 and starting the igniter includes maintaining a distal pilot flame. The inventors have found that combustion of fuel from the first plurality of main fuel nozzles 115 is most stable, which is important during start-up. After stable combustion of the main fuel is achieved, at least some main fuel flow may be shifted to the second plurality of main fuel nozzles 1308. According to embodiments, the fuel flow may ultimately be divided at a tuned ratio between the first and second pluralities of main fuel nozzles to achieve lowest NOx. For example, the fuel flow may be ultimately output at a 50:50 ratio of the first plurality of main fuel nozzle flow to the second plurality of main fuel nozzle flow. In another example, the fuel flow may be ultimately output at a 30:70 ratio of the first plurality of main fuel nozzle flow to the second plurality of main fuel nozzle flow. The second plurality of main fuel nozzles 1308 causes mixing of fuel and combustion air beginning near the second plurality of main fuel nozzles, further upstream from the first plurality of main fuel nozzles 115. The second plurality of main fuel nozzles 1308 may flow fuel to entrain flue gas into the preliminary mixture as it enters the mixing tube 120. A full mixture is output at the distal end of the mixing tube 120, near the pilot burner 150.
Referring especially to FIGS. 1A, 1B, 2, 13A and 13B, according to embodiments, in the burner system 100, the proximal fuel source includes a first plurality of main fuel nozzles 115 disposed adjacent to the proximal inlet 126 to the mixing tube 120. A second plurality of main fuel nozzles 1308 is disposed within a combustion air duct 114 functionally upstream from the first plurality of fuel nozzles 115. The combustion air duct 114, together with the second plurality of main fuel nozzles 1308, may be positioned outside of the boiler or furnace body.
During a first phase of burner start-up, according to embodiments, main fuel is flowed through the first plurality of main fuel nozzles 115, and no fuel is flowed through the second plurality of main fuel nozzles. During the first phase of start-up, ignition of the fuel is (first) caused by a pilot flame produced by the distal pilot burner 150 from pilot fuel delivered to the distal pilot burner. During a second phase of burner start-up, the second phase occurring after the first phase of burner start-up, fuel flow is adjusted such that at least a portion of main fuel flows through the second plurality of main fuel nozzles 1308. Main fuel flow through the first and second pluralities of main fuel nozzles may be held between a 30:70 and a 70:30 flow ratio. This was found to minimize the output of NOx, measured at a flue (not shown). In one reproduceable set-up, fuel flow through the first and second pluralities of main fuel nozzles 115, 1308 was held at a 50:50 flow ratio while output of NOx was minimized at the flue.
According to an embodiment, the distal pilot burner 150 is configured to be shut off after achieving at least a portion of a start-up procedure of the boiler burner. It is believed that pilot fuel and combustion air delivered for combustion by the pilot burner was less well-mixed than main fuel delivered from the first 115 and/or second 1308 pluralities of main fuel nozzles, such that combustion produced by the distal pilot burner contributes a measurable amount of NOx. The distal pilot burner may be configured to be shut off to produce, at most, a de minimis flame from pilot fuel; after substantially completing the start-up procedure of the boiler burner.
After stable combustion of the main fuel from the first plurality of main fuel nozzles 115, and optionally from the second plurality of main fuel nozzles 1308, the flow of pilot fuel to the distal pilot burner 150 may be shut off. This was found to further decrease production of NOx.
FIG. 14 is a process diagram showing a start-up method 1400 of a burner system, according to an embodiment. In step 1402, combustion air is introduced into a proximal inlet of a mixing tube. A pilot fuel supply is provided to a pilot burner positioned at or adjacent to a distal outlet of the mixing tube, in step 1404. In step 1406, an igniter is activated to ignite the pilot burner. In step 1408, a main fuel is introduced to the proximal inlet of the mixing tube via a first plurality of main fuel nozzles, which are positioned adjacent to the proximal inlet. The main fuel and combustion air mix as they traverse the mixing tube, and are ignited by the pilot burner positioned at the outlet of the mixing tube. Once the burner is adequately warmed up by the combustion of the main fuel, main fuel is introduced, in step 1410, to the combustion air upstream from the proximal inlet of the mixing tube, via a second plurality of nozzles positioned in a combustion air tube configured to supply the combustion air to the burner. After main fuel is flowing from the second plurality of nozzles, the output of main fuel from the first plurality of nozzles may be reduced, in step 1412. According to another embodiment, step 1412 is omitted or delayed, such that the main fuel from the first plurality of nozzles is not reduced following step 1410 but is supplemented by the addition of the main fuel from the second plurality of nozzles. The flow of pilot fuel is terminated in step 1414.
According to various embodiments, step 1414 may be performed at any time after step 1408, i.e., before—or simultaneously with—performance of step 1410 or 1412, or after step 1412. According to another embodiment, the pilot burner is configured to remain in operation during operation of the boiler burner, in which case, step 1414 is only performed when the boiler burner is shut down. According to a further embodiment, the pilot burner is configured for continuous operation, in which case steps 1402 and 1414 are only rarely performed, with the pilot burner remaining in operation during periods in which no main fuel is provided.
According to one embodiment, the flow of main fuel from the first plurality of main fuel nozzles is reduced, in step 1412, until a selected ratio of fuel from the first and second pluralities of nozzles is achieved, e.g., 10:90, 40:60, 30:70, 50:50, 60:40, 70:30, etc. According to another embodiment, the flow of main fuel from the first plurality of main fuel nozzles is completely shut off during performance of step 1412, so that 100% of the main fuel is provided via the second plurality of nozzles.
According to an embodiment, steps 1410 and 1412 are performed simultaneously so that the flow of main fuel remains substantially constant while the flow from the first plurality of nozzles is reduced and the flow from the second plurality of nozzles is increased. Alternatively, steps 1410 and 1412 may be performed in alternating incremental steps.
FIG. 2 illustrates a burner system 200, according to an embodiment. The embodiment includes a transverse air duct 201 having an inclined plate 203 penetrated by a main fuel pipe 205 which delivers fuel to a center body 207, which may include fuel jets. The inclined plate 203 may be removable.
The embodiments described above illustrate and exemplify an all-metal flame holder. The embodiment(s) described below employ a flame holder which may not be all metal but may include refractory material.
According to embodiments, other alternative flame holding arrangements include a choke, a swirler, a plate, and/or a flare provided by features formed in the mixing tube or in an apparatus disposed inside the mixing tube. Such approaches and others may provide stream stabilization and/or a pressure differential selected to cause the combustion reaction to be stabilized at a position downstream from the outlet end of the mixing tube.
FIGS. 3A and 3B illustrate, in different perspectives, an embodiment of a burner system 300 which may include a distal flame holder including a refractory tile, such as a perforated tile 305. A flame tube 130, in an embodiment, may be an integral part of a boiler not illustrated in its entirety, and may be surrounded by water or liquid, or process structures. The flame tube 130 is shown in FIG. 3A in phantom view so as not to hide the other parts. The flame tube 130, or an analogous structure, may be included in other embodiments such as that of FIGS. 1A-1C, though not illustrated herein.
A mixing tube 120 may be disposed inside the flame tube 130 and may be coaxial with it. The mixing tube 120 may define an inlet and an outlet at respective ends thereof. The inlet end may be mounted onto a flange 102 and/or operatively coupled thereto. In an embodiment, a plane of the flange 102, or of some portion thereof, may be perpendicular to an axis of the mixing tube 120 and/or the flame tube 130. In an embodiment, the flange 102, the mixing tube 120, and at least some of the illustrated associated parts may constitute an integral structure which may be mounted, as a unit, to a boiler via flange bolt holes 302 (also shown in FIG. 3C) so as to extend into the flame tube with the inlet end nearer the flange 102 and the outlet end farther from the flange 102. In an embodiment, the mixing tube 120 has an outer diameter over a majority of the mixing tube length smaller than an inner diameter of the flame tube 130. The mixing tube 120 may be configured to convey combustion air, main fuel, and flue gas from the inlet to the outlet of the mixing tube 120.
In an embodiment, the mixing tube 120 and the flame tube 130 may be disposed generally or substantially horizontal for horizontal firing, or in other orientations, such as, e.g., vertically, according to the requirements of the particular application. The flange 102 may be mechanically configured to support the mixing tube 120 and other parts against the force of gravity, and other forces, when the flange 102 is affixed to the boiler.
FIG. 3C shows one embodiment of such a structure, which may be formed as a unitary whole, as by welding together of different pieces. The flange 102, with bolt holes 302 for attachment to the boiler, may be integral with a pipe section 324 which is adapted to accept therethrough a main burner assembly 315 (corresponding to main burner assembly 116 in FIGS. 1A and 1B) and also air from a blower 113 (shown in FIG. 3A), forming, in an embodiment, an air passage disposed to cause the combustion air to be blown into the mixing tube 120. The pipe section 324 may be fastened to both the flange 102 and to stays 322, which in turn are fastened to the mixing tube 120, forming a mechanically stiff structure the weight of which may be supported in a horizontal position by the flange 102 when bolted to the boiler (e.g., cantilevered). As is discussed further below, the mixing tube inlet may include a bell section 126, which in an embodiment may be a frustrum of a cone as illustrated in FIG. 3C. The mixing tube inlet may alternatively lack a bell structure, in an embodiment.
The outlet of the mixing tube 120, located at a distal end the mixing tube 120, may incorporate a distal flame holder, which is shown in more detail in FIG. 3B. In an embodiment, the distal flame holder may include two flame holder tiles 305. The tiles 305 may be rectilinear (e.g., each shaped substantially as a parallelepiped with all faces rectangular) and may have parallel corresponding axes and/or alignments. As shown in FIG. 3B, two tiles 305 may be disposed in parallel and generally on either side of an axis of the mixing tube 120.
In an embodiment, a flame holder support structure 340 may extend from the outlet end of the mixing tube. The support structure 340 may be a distinct piece fastened to the outlet end of the mixing tube 120, or may be at least partially fabricated from the outlet end by cutting, bending, etc. FIG. 3A depicts an attachment 323; in this embodiment the support structure 340 may include a section of tubing sized and configured to be clamped onto an exterior of the mixing tube 120.
In an embodiment, the flame holder support structure 340 may include at least two mixing-tube extensions 344 formed integrally with the mixing tube 120, or with an extension fastened onto the mixing tube 120.
FIGS. 3A and 3B depict a burner system 300 in which a pilot fuel tube 101, in an embodiment, delivers pilot fuel to a distal pilot burner 350. The pilot fuel tube 101 may deliver fuel to at least one, preferably two or more, fuel runners 352 disposed transverse to the mixing tube 120 and downstream from the mixing tube outlet, as best seen in FIG. 3D, a view generally along the axis of the mixing tube 120.
FIG. 3D shows that the fuel runners 352 may include or define a plurality of fuel nozzles 353 along the lengths of respective fuel runners 352, which in an embodiment may be merely holes drilled through the upstream side of a fuel runner 352 (and/or in other places). Pilot fuel emerging from the nozzles 353 may be ignited by an igniter through an igniter (not shown) located in a distal end of an igniter tube 108, also visible in FIGS. 3A-3B.
In an embodiment, the two or more fuel runners 352 may be configured to create respective low-pressure areas opposite to the outlet of the mixing tube 120 and to support a pilot flame for igniting a main fuel from nozzles of the main burner assembly 315 (which main fuel optionally may be the same as or different from the pilot fuel). The two or more fuel runners 352 may be operatively coupled to the flame holder support structure 340. The respective low-pressure areas may be augmented by the draft produced by the blower 113, shown in FIG. 3A, which is configured to create a flow inside the mixing tube 120.
The distal pilot burner 350 may, in an embodiment, include respective metal aerodynamic structures 355 aligned with respective fuel runners 352 and disposed between the fuel runners 352 and the mixing tube outlet. These metal aerodynamic structures 355 may be configured to enlarge the respective low-pressure areas compared to a size of the low-pressure areas created by the two or more metal fuel runners 352 alone. The metal aerodynamic structures 355 may be perforated to change the scale of turbulence in the low-pressure areas, or otherwise be shaped to affect flow characteristics. The metal aerodynamic structures may be mechanically coupled to the flame holder support structure 340 and/or to the fuel runners 352.
The flame holder tiles 305 may include two or more porous refractory tiles each having at least one dimension smaller than at least one second dimension and may be supported by the flame holder support structure 340 in alignment with and downstream from the two or more fuel runners 352. FIG. 3D shows flame holder tiles 305 which are half as tall as the fuel runners 352, which allows them to be visible in this view. However, the flame holder tiles 305 may extend to a greater height and may be coextensive with the fuel runners 352 as best seen in FIG. 3B.
FIG. 3D depicts details of the flame holder support structure 340 less visible in the other figures, such as a cage assembly 303 and tile shelves 304, which support the weight of the flame holder tiles 305. In an embodiment, the flame holder tiles 305 include porous refractory material. The fuel runners 352 and aerodynamic structures 355 may extend through slots in the sides of the cage assembly 303, so that they are held in position. In an embodiment, the cage assembly 303 may be unitary with the support structure 340. The interior of the mixing tube 120 is visible in FIG. 3D.
In an embodiment, the two or more porous refractory tiles 305 each have at least one dimension smaller than at least one second dimension and are supported to have the at least one smaller dimension adjacent to the two or more fuel runners and the at least one second dimension disposed parallel to the mixing tube (into the plane of the paper in FIG. 3D). The at least one smaller dimension may include an edge defining an extent of first and second faces of the porous rectilinear refractory tiles.
In an embodiment, the mixing tube 120 and pipe section 324 may be separated as best shown in FIG. 3C, with a gap therebetween to allow flue gas to be educed into the inlet end of the mixing tube 120 by combustion air blown into the mixing tube, e.g., by the blower 113. In an embodiment, this eduction may be augmented by a bell section 126. The bell section 126 may be configured to form a low-pressure region circumferential to and closer to the flange 102 than a main portion of the mixing tube 120, such that the low-pressure region is configured to draw flue gas from a region near the outlet of the mixing tube and along a cooled wall of the boiler flame tube to be educed into the mixing tube by the blown combustion air. An annular gap between the mixing tube 120 and the boiler tube is seen in FIG. 3A, where the boiler tube is shown in dashed-line view.
The main burner assembly 315 may further include at least one main fuel nozzle 115 disposed to receive fuel via a first main fuel pipe 311 passing through the flange 102 and to output the main fuel into or adjacent to a stream of blown combustion air from the blower 113 between the flange and at least a portion of the mixing tube. In an embodiment, such a main fuel nozzle may be exemplified by the center body 207 shown in FIG. 2 . In an embodiment, the mixing tube 120 may be configured to provide a mixing volume for mixing the combustion air, main fuel, and flue gas prior to the combustion air, main fuel, and flue gas mixture being exposed to a pilot flame.
FIG. 4 is a schematic diagram of a combination distal flame holder and distal pilot 402 in place in a burner 400 according to an embodiment. The burner 400 may operate as a flare stack and/or as a burner in a boiler, and may operate intermittently or continuously. The burner 400 may burn a pure fuel or mixtures of combustible gas to prevent direct venting to the atmosphere. In an embodiment, a structure 406 of the burner 400 includes a mixing tube 404.
In an embodiment, the combination distal flame holder and distal pilot 402 is of essentially all-metal construction and may include a combination of a distal flame holder and a distal pilot burner. In various embodiments, this combination is unitary, or integral, or one-piece, or an assembly of parts adapted and configured for assembly into an integral whole. As shown in FIG. 4 , the distal pilot may be located above, or in, the distal end of the mixing tube 404, or, may be located above, or in, the distal end of the main structure 406, which may comprise a tube or pipe in which combustion occurs.
A main fuel source 412 and an air or oxidant source 410 may be located proximally (i.e., upstream from the distal flame holder and distal pilot burner 402), serving as a proximal fuel source and a proximal combustion air source, respectively, to provide for a main flame. The distal pilot portion of the combination distal flame holder and distal pilot 402 may, in an embodiment, use a different fuel, and/or include a separate fuel feed distinct from that of 412, and may receive fuel intermittently even during intervals in which the main fuel continuously burns; that is, the pilot burner may be turned off, or may operate continuously or intermittently, before, during, and/or after intervals of a main flame.
According to an embodiment, the distal pilot is natural gas- or propane-fired. The pilot fuel may, in an embodiment, be the same as the main fuel, or not. According to an embodiment, the main fuel may include light fractions or condensates from a hydrocarbon production or transport process, fuel gas from a refinery, or other combustible gas that might otherwise be vented to the atmosphere.
FIG. 5 is a perspective view of one embodiment of the combination distal flame holder and distal pilot 402 of FIG. 4 , in which a distal flame holder 510 and a distal pilot burner 520 comprise a single unit, optionally welded together from metal parts. Pilot fuel arrives at the unit via a pilot fuel pipe 502, which in the illustrated embodiment is pipe-threaded to assemble, gas-tight, to the unitary distal pilot above it. A collar or fuel header 524 accepts pilot fuel from the pilot fuel pipe 502, and the pilot fuel flows outwardly into arms 526, each arm 526 including a hollow metal tube optionally welded to the collar 524 and communicating with it, so that the pilot fuel flows into the several arms 526 and thence out from holes or orifices 528. There may be, for example, three holes 528 per arm 526. The released pilot fuel may be carried upward by a flow of main fuel and/or combustion air or oxidant for main combustion, and/or by convection, toward the flame holder 510.
The flame holder 510 may be welded to the collar 524 to form a unitary or one-piece whole, or it may be threaded to screw into an upper end of the collar 524 to form an integral assembly. The flame holder may include a cylindrical body 516 which may include a tapered end 518 as shown, to reduce flow resistance or for some other reason (one example of an aerodynamic structure).
Swirl vanes 512 are shown deployed around the body 516 and are, preferably, welded to it (although other attachments are within the scope of embodiments). The swirl vanes 512 act as a flame holder for the main-fuel combustion and, optionally, also for the pilot flame. (The arms 526 may act as auxiliary flame holders for the pilot flame, by diverting a flow of main fuel and air or oxidant.
In an embodiment, the pilot fuel pipe 502 may act as a mechanical support for the distal pilot 402.
FIG. 6 shows another embodiment, in which the swirl vanes 512 of FIG. 5 are shielded by an outer flow guide 612. As compared to the un-shielded swirl vanes 512 of FIG. 5 , the embodiment of FIG. 6 may generate different flow patterns and turbulence patterns due to the guide 612 and the less-pointed cap 618. The angled vanes 512 shown in FIG. 6 may be generally similar to those of FIG. 5 and may or may not extend the full axial length of the guide 612. In an embodiment, the guide 612 may have a diameter of 5 inches (13 cm).
In an alternate embodiment (not shown in FIG. 6 ), the guide 612 may have “V-gutters” or functionally similar flame holders welded (or otherwise fastened) to its outer surface to project in a radial pattern. Such V-gutters are shown in FIG. 8A and are explained below.
FIG. 7 illustrates the embodiment of the distal pilot 402, disposed above the distal-end opening of a mixing tube 404, and coupled to the pilot fuel pipe 502. In the illustrated embodiment, the pilot fuel pipe 502 rises through the mixing tube 404. In this embodiment, the main structure 406 includes a main combustion tube 706.
FIG. 8A shows an embodiment in which a pilot fuel pipe (not shown in FIG. 8A) couples to a side of the distal pilot 802 (corresponding to element 402 in earlier figures), specifically to at least one of four pilot-fuel distribution pipes 826. In a realized embodiment, each distribution pipe 826 is approximately 8 inches (20 cm) long and two of them, those on either side in FIG. 8A, terminates in a 1-inch NPT (National Pipe Thread) for screw-attachment to a not-illustrated pilot fuel pipe, while the other two distribution pipes 826 are sealed at their outer ends. In the illustrated realized embodiment, there are four distribution pipes 826, each the same length; their lengths appear different on the paper in FIG. 8A because it is a perspective view. In other embodiments, the number of distribution pipes 826 may vary—for example, in another realized embodiment not shown, there are five such pipes—and the distribution pipes 826 may be of non-uniform lengths and may not be angularly spaced at regular intervals, unlike the embodiment of FIG. 8A in which the angular spacing is 90 degrees between adjacent distribution pipes 826.
In an embodiment, pilot fuel pipes, which are sealingly screwed onto the ends of the distribution pipes 826, may act as a mechanical support for the distal pilot 802.
FIG. 8B shows, in cross section, a manifold header 810, which is hidden from view in FIG. 8A beneath element 850, that acts as a hub to join all the distribution pipes 826. In a unitary embodiment, the inboard ends of the distribution pipes 826 are fitted and welded into the four holes 812 (only three are seen in FIG. 8B); in an integral embodiment (not shown), the inboard ends of the distribution pipes 826 may be pipe-threaded into the four holes 812. The lower end of the manifold header 810 may be conically pointed as shown to embody an aerodynamic structure. The upper end includes a circular indentation into which a round disc (not illustrated) may be fitted and welded to close the interior of the manifold header 810; this disc may, however, optionally include holes to release pilot fuel upwardly for additional pilot flame. The illustrated manifold header 810 includes optional pilot-fuel release holes 814, which may be drilled through the sides of the manifold header 810, optionally at 45 degrees to the adjacent holes 812 as shown in FIG. 8B.
FIG. 8C is a cross section taken on plane C-C of FIG. 8A and shows one of several pilot-fuel release holes 528 (which are hidden in FIG. 8A) in the upper part of the distribution pipes 826. Each hole 528 may, for example, be drilled through the metal of the pipe 826.
A metal flame spreader 840 is disposed above each of the distribution pipes 826; as shown in FIG. 8A, an outer end of each flame spreader 840 may be held by a metal clip 832, and the inner end may be welded to the manifold header 810, making the structure unitary. The flame spreader 840 may, in an embodiment, act as a bluff-body flame holder for the pilot flame. The flame spreader 840 may be considered a local flame holder, for flames associated with the several pilot-fuel release holes 528.
FIGS. 8A and 8C illustrate a specific embodiment of a distal flame holder 510, namely, “V-gutters” 830, shown in perspective view in FIG. 8A and in cross-section in FIG. 8C. Such V-gutters 830 may act to stabilize the main fuel/air mix and/or flame. Although V-gutters are illustrated, other shapes are possible. For example, FIG. 8C shows, in dashed lines, an embodiment in which the outer portion of the “V” shape is bent up toward the vertical. Other concave-upward shapes may be used in place the concave-upward shapes shown in FIG. 8C.
FIG. 8D illustrates a pattern for edges of the V-gutters, in which the outer edges of the V-gutters 830 of FIG. 8A are crenellated. Other embodiments, not shown, could include other edge patterns, holes through the sides of the V-gutters, etc.
Considering FIG. 8A again, a central flame holder/pilot burner hub 850 may be added to the above-described structure below it. The central hub 850 can be fed pilot fuel through the above-mentioned disc which is fitted into the upper recess of the manifold header 810; this disc, as mentioned, might optionally include holes to release pilot fuel upwardly for additional pilot flame. Such disc holes may be positioned to inject pilot fuel into the annular gap 852 shown in FIG. 8A. In other embodiments, the central hub 850 be omitted. The central hub 850 may include an internal swirler. Such devices are often referred to as a “radial swirler flame holder”.
The parts described above may be considered a distal flame holder 510.
It is to be noted that, while some parts may be primarily in the nature of a distal flame holder or a distal pilot burner, this is not a sharp distinction. The distribution pipes 826 and arm tubes 526, for example, not only supply pilot fuel to a pilot flame but also act to some extent as flame holders for a main flame supported by main fuel and air. Thus, the unitary parts described above have a shared structure of pilot burner and pilot/main flame holder.
FIG. 9 illustrates an embodiment in which a tube, such as a mixing tube 404, has a combined distal pilot burner/distal flame holder beyond the distal end of the tube 404, supported by a pilot fuel pipe 502 which bifurcates and supports a drilled-tubing flame holder 826 with V-gutters 830, to which it also feeds pilot fuel. In this embodiment, unlike that of FIGS. 8A-8D, gutters and pipes are not radial, but more or less parallel. The two distribution pipes 826 may be formed as a single “U”-shaped tube that is fed a mixture of air and/or fuel from a common header pipe or tube. In FIG. 9 , two distribution pipes 826 are shown; in alternative embodiments (not illustrated), three or more distribution pipes may be fed from a common header (e.g., a “trident” configuration).
The embodiment of FIG. 9 has been used successfully in both flare and boiler applications.
In an embodiment, all of the parts illustrated in the above-described figures can be made of heat-resistant metal, such as for example 610 stainless steel, and the parts can be welded to one another to form a unitary whole; for example, the V-gutters 830 might be spot-welded to the distribution pipes 826. Thus, the distal flame holder 510 and the distal pilot burner 520 become one unit, which cannot be disassembled. In an embodiment, no ceramic is used in the construction.
Referring again to FIG. 7 , the distal pilot 402 shown in that figure may be replaced by the distal pilot 802 of FIGS. 8A-8D. As in the case of FIG. 7 , the distal pilot 802 of FIGS. 8A-8D may be above the distal end of a mixing tube 404, or within a distal end of the mixing tube 404.
FIG. 10 illustrates a method 1000 that relates to operation of a burner system according to an embodiment. In operation 1002, providing a pilot burner and a metal flame holder. In operation 1004 a main flame of the main fuel is maintained by igniting the main fuel with a pilot flame of the pilot burner. In a further embodiment, the operation 1004 of maintaining the main flame may include one or more of igniting a pilot flame with a pilot fuel to reach a standby mode, holding the pilot flame in a standby mode, and adapting to variations in the main fuel, such as temperature, pressure, and/or fuel type or composition. In some embodiments, the pilot fuel may be different from the main fuel. The pilot fuel may be a more-energetic assist gas to be oxidized in a flare tube. That is, the assist gas may have a higher energy than the main fuel.
Any of the apparatus described above may be included in a “low NOx burner system,” i.e., a burner system that produces low oxides of nitrogen. For example, the burner system 100 of FIGS. 1A through 3D may constitute a low NOx burner, and the burner system 400 in FIG. 4 may constitute a low NOx burner, while the features described with respect to FIGS. 5 through 9 may be incorporated in a low NOx burner system. According to an embodiment, a low NOx burner system may include a main fuel nozzle disposed at a proximal position in a furnace and configured to output a main fuel into a combustion air stream. For example, the main burner assembly 315 in FIG. 3B may include one or more main fuel nozzles. A pilot burner may be disposed at a distal position. Optionally, the pilot burner may operate continuously. The pilot burner 150, 350, 520 may be configured to support a pilot flame to initiate combustion of the mixed main fuel and combustion air, such as from a main fuel source 412 and air source 410. A pilot burner 150, 350, 520 described above may be configured as a continuous pilot burner and may be arranged to maintain combustion of the mixed mail fuel and combustion air. Alternatively, the pilot burner 150, 350, 520 may be configured as non-continuous pilot burner, such that the pilot flame may be turned off. The inventors have observed that in some configurations turning off the pilot flamer can lower NOx when the man flame is sufficiently hot to support itself. A distal flame holder 305, 510, 850, 830 may be positioned to receive the mixed main fuel and combustion air, and may be configured to hold a combustion reaction of the mixed main fuel and combustion air.
According to an embodiment the continuous pilot burner 520 and the distal flame holder 510, 850, 830 may at least partially share the same structure (see combination pilot burner and distal flame holder 402 described in conjunction with FIG. 5 ). The distal flame holder (510, 850, 830) may include one or more bodies (e.g., distribution pipes 826 and arm tubes 526) defining one or more pilot fuel passages. The one or more bodies may define one or more apertures 528 operatively coupled to the one or more pilot fuel passages, the one or more apertures 528 being configured to operate as pilot fuel nozzles for outputting pilot fuel to support the pilot flame as a diffusion pilot flame. In an alternative embodiment, the pilot burner may be configured as a distal premix pilot burner supporting the pilot flame by combustion of a premixed mixture of pilot fuel and combustion air. The distal flame holder may be formed entirely or substantially (essentially) of metal parts. For example, the distal flame holder may be made of stainless steel. In some embodiments the distal flame holder may include a swirler 154, 512, 850. In some embodiments the distal flame holder may include a V-gutter 830, where in some embodiments the V-gutter 830 may define crenelated edges 830 in FIG. 8D.
In some embodiments the low NOx burner system may further include a combustion air source 410 configured to provide the combustion air stream. The low NOx burner system may further include a mixing tube 120, 404 disposed to receive the main fuel and combustion air stream into a proximal end of the mixing tube 120, 404 and to output mixed main fuel and combustion air at a distal end of the mixing tube 120, 404. The combustion air source may be configured to cause the stream of combustion air to educe flue gas into the proximal end of the mixing tube 120, 404. As a result, the mixed main fuel and combustion air that is output at the distal end of the mixing tube includes mixed main fuel, combustion air, and flue gas. The educing of the flue gas into the proximal end of the mixing tube 120, 404 may be performed by internal flue gas recirculation. In some instances, a natural draft combustion air source may be structured and/or arranged to provide the combustion air stream. In some embodiments the low NOx burner system may be configured as a flare.
In some embodiments, a forced draft combustion air source may be configured to provide the combustion air stream. The forced draft combustion air source may include a blower 113.
According to an embodiment, the low NOx burner system may be configured as a boiler burner. The low NOx burner may include a flame tube boiler structured and/or arranged to output heat from flame tubes (e.g., 130) carrying combustion products from the furnace, the output heat being directed or arranged to heat water in a shell surrounding the flame tubes. In some embodiments a water tube boiler may include water tubes (not shown) configured to transfer heat from the furnace to water flowing through the water tubes. Such embodiments may further include a superheater including steam tubes carrying steam. The superheater may be disposed in a flue disposed to receive hot combustion products from the combustion reaction.
According to an embodiment, the low NOx burner system configured as a boiler burner may include a mounting flange 102 configured to mount the low NOx burner system to the furnace. In embodiments that include a mixing tube 120, 404, one or more legs 322 may be structured and/or arranged to mechanically couple the mixing tube to the mounting flange 102. The mixing tube 120 mechanically supports the distal flame holder 305.
FIG. 11 is a process diagram illustrating a method 1100 for operating a burner apparatus, according to an embodiment. The method includes an operation 1102 of receiving main fuel and combustion air into a proximal end of a mixing tube. Another operation 1104 includes outputting mixed main fuel and combustion air from a distal end of the mixing tube. Operation 1106 includes receiving the mixed main fuel and combustion air at a distal flame holder. Operation 1108 includes causing ignition of the mixed main fuel and combustion air, at a location coincident with a distal flame holder, with a pilot flame supported by a continuous pilot burner. Each of the continuous pilot burner and the distal flame holder may at least partially include shared structure.
FIG. 12 illustrates additional operations 1200 of the method 1100 related to providing the structure and arrangement of elements of a low NOx burner. Operation 1202 includes providing a distal flame holder including a body defining at least one pilot fuel gallery inside the body. The body may be provided to include an external aerodynamic surface structured and/or arranged to cause one or more low pressure zones in flowing mixed fuel and combustion air and combustion gases reacted therefrom. In operation 1204 the method 1200 may include providing a continuous pilot burner by providing the body with a plurality of apertures providing for pilot fuel flow from the at least one pilot fuel gallery to a combustion volume outside the aerodynamic surface. According to an embodiment, the pilot fuel gallery may be configured as a pre-mixed pilot fuel and combustion air gallery, such that the plurality of apertures are premixed pilot nozzles. The pilot flame supported by the pilot fuel may ignite the mixed main fuel and combustion air in a region defined by the aerodynamic surface. According to an embodiment, the combustion volume outside the aerodynamic surface may include a volume adjacent to the aerodynamic surface. According to an embodiment, receiving the main fuel and combustion air may include receiving flue gas. For example, the receiving of mixed main fuel and combustion air at the distal flame holder may include receiving mixed main fuel, combustion air, and flue gas at the distal flame holder.
According to an embodiment, the method 1200 may include an operation 1206 of providing the main fuel and combustion air by providing respective main fuel nozzle(s) and a combustion air source. The combustion air source may include a blower such that providing the combustion air source may include pressurizing combustion air using a blower, according to an embodiment. Alternatively or additionally, providing the combustion air source may include admitting a metered rate of combustion air using a natural draft combustion air register.
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

What is claimed is:

1. A horizontally-fired burner system, comprising:

a flange configured to be mounted to an opening of a flame tube or combustion chamber and structured to support a burner within the flame tube or combustion chamber;

a burner mounted to the flange and configured to extend into the flame tube or combustion chamber, the burner including:

a mixing tube extending transverse to the flange and having a proximal inlet and a distal outlet, and

a first plurality of main fuel nozzles positioned adjacent to the proximal inlet of the mixing tube and configured to introduce main fuel into the mixing tube via the proximal inlet;

a combustion air conduit coupled at a first end to an opening in the flange on a side of the flange opposite the burner and configured to supply combustion air through the flange to the proximal inlet of the mixing tube; and

a second plurality of main fuel nozzles positioned within the combustion air conduit and configured to introduce main fuel into a combustion air flow upstream of the first plurality of main fuel nozzles and the proximal inlet of the mixing tube.

2. The horizontally-fired burner system of claim 1, comprising a pilot burner positioned adjacent to the distal outlet of the mixing tube and configured to ignite a mixture of combustion air and main fuel flowing from the distal outlet.

3. The horizontally-fired burner system of claim 1, comprising a first main fuel source operatively coupled to and configured to supply main fuel to the first plurality of main fuel nozzles.

4. The horizontally-fired burner system of claim 3, comprising a second main fuel source operatively coupled to and configured to supply main fuel to the second plurality of main fuel nozzles.

5. The horizontally-fired burner system of claim 1, comprising an annular fuel gallery disposed around the combustion air conduit and configured to supply main fuel to the second plurality of main fuel nozzles.

6. The horizontally-fired burner system of claim 5, comprising a plurality of tubes extending radially into the combustion air conduit and in fluid communication with the annular fuel gallery, each of the plurality of tubes having at least one nozzle aperture formed therein, the nozzle apertures of each of the plurality of tubes together constituting the second plurality of main fuel nozzles.

7. The horizontally-fired burner system of claim 6, wherein each of the plurality of tubes includes a plurality of nozzle apertures.

8. The horizontally-fired burner system of claim 1, wherein the proximal inlet of the mixing tube has a flared shape and the first plurality of main fuel nozzles is arranged in a radially symmetrical pattern concentric with the proximal inlet.

9. The horizontally-fired burner system of claim 1, comprising a blower having an output coupled to a second end of the combustion air conduit and configured to blow combustion air through the combustion air conduit to the burner.

10. The horizontally-fired burner system of claim 1, comprising a main fuel pipe coupled to the annular fuel gallery and configured to supply main fuel to the annular gallery and the second plurality of main fuel nozzles.

11. The horizontally-fired burner system of claim 1, wherein the flange and burner are configured to be horizontally fired.

12. A start-up method for a horizontally-fired burner system, comprising:

introducing a flow of combustion air into a mixing tube of a horizontally-fired burner, positioned in a flame tube or combustion chamber, via a combustion air conduit and a proximal inlet of the mixing tube;

introducing a first flow of main fuel into the proximal inlet of the mixing tube via a first plurality of main fuel nozzles positioned adjacent to the proximal inlet;

igniting a combustion reaction near a distal outlet of the mixing tube, supported by a mixture of fuel and air; and

introducing a second flow of main fuel into the combustion air conduit via a second plurality of main fuel nozzles positioned upstream of the first plurality of main fuel nozzles and the proximal inlet.

13. The method of claim 12, comprising, during or after introducing the second flow of main fuel, reducing a volume of the first flow of main fuel into the mixing tube.

14. The method of claim 12, wherein the reducing the volume of the first flow of main fuel into the mixing tube includes completely stopping the first flow of main fuel into the mixing tube.

15. The method of claim 12, wherein the reducing the volume of the first flow of main fuel into the mixing tube includes reducing the first flow of main fuel until a ratio of the volumes of the first flow relative to the second flow is approximately 40:60.

16. The method of claim 12, wherein the reducing the volume of the first flow of main fuel into the mixing tube includes reducing the first flow of main fuel until a ratio of the volumes of the first flow relative to the second flow is approximately 50:50.

17. The method of claim 12, comprising performing the introducing the second flow of main fuel and the reducing the volume of the first flow of main fuel substantially simultaneously.

18. The method of claim 17, wherein the performing the introducing the second flow of main fuel and the reducing the volume of the first flow of main fuel substantially simultaneously includes holding a total volume of main fuel substantially constant while introducing the second flow of main fuel and reducing the volume of the first flow of main fuel.

19. The method of claim 13, comprising performing the introducing the second flow of main fuel and the reducing the volume of the first flow of main fuel in alternating incremental steps.

20. The method of claim 12, wherein the reducing the volume of the first flow of main fuel into the mixing tube includes reducing the first flow of main fuel until a ratio of the volumes of the first flow relative to the second flow is approximately 60:40.

21. The method of claim 12, further comprising, prior to performing the introducing the first flow of main fuel:

providing a pilot fuel supply to a pilot burner positioned adjacent to the distal outlet of the mixing tube; and

igniting the pilot fuel at the pilot burner.

22. The method of claim 21, comprising, after performing the igniting the combustion reaction:

reducing flow of the pilot fuel supply to the pilot burner.

23. The method of claim 21, comprising, after performing the igniting the combustion reaction:

stopping the pilot fuel supply to the pilot burner after the flame from the main fuel is stabilized.