HORIZONTALLY FIRED BURNER SYSTEM

Abstract

A horizontally-fired burner system includes, in a combustion volume, a distal flame holder, the distal flame holder including a plurality of columns each formed from a respective plurality of refractory tiles, and a fuel and combustion air source configured to output a flammable fuel and air mixture toward the distal flame holder. The distal flame holder is configured to hold a combustion reaction adjacent to each of the plurality of columns.

Claims

1. A horizontally-fired burner system, comprising: in a combustion volume, a distal flame holder, the distal flame holder including a plurality of columns each formed from a respective plurality of refractory tiles; and a fuel and combustion air source configured to output a flammable fuel and air mixture toward the distal flame holder via one or more main fuel nozzles; wherein the distal flame holder is configured to hold a combustion reaction adjacent to each of the plurality of columns.

2. The horizontally-fired burner system of claim 1, wherein the plurality of columns are disposed vertically in the combustion volume and in parallel to each other within the combustion volume.

3. The horizontally-fired burner system of claim 1, wherein at least one column of the plurality of columns has a greater cross-sectional area than another column of the plurality of columns.

4. The horizontally-fired burner system of claim 1, wherein the distal flame holder is configured to hold the combustion reaction upstream from, downstream from, and beside each of the plurality of columns.

5. The horizontally-fired burner system of claim 1, wherein at least a portion of the plurality of refractory tiles includes perforated refractory tiles.

6. The horizontally-fired burner system of claim 5, wherein the perforated refractory tiles are configured to hold at least a portion of the combustion reaction within perforations of each perforated refractory tile.

7. The horizontally-fired burner system of clam 6, wherein the perforated refractory tiles are formed from reticulated fibers.

8. The horizontally-fired burner system of claim 1, further comprising a plurality of water tubes arranged adjacent to at least one of a ceiling, a floor, and walls defining the combustion volume.

9. The horizontally-fired burner system of claim 8, further comprising: a plurality of steel tabs extending into the combustion volume between respective sets of mutually adjacent water tubes of the plurality of water tubes; wherein the distal flame holder further includes a mounting structure upon which each column of the plurality of columns is supported; and wherein the plurality of steel tabs are operatively coupled to the mounting structure to mechanically fix the location of the distal flame holder in the combustion volume.

10. The horizontally-fired burner system of claim 8, further comprising: a mortar bed formed over a bottom portion of a portion of the water tubes; wherein the plurality of columns are supported by the mortar bed.

11. The horizontally-fired burner system of claim 8, further comprising: one or more tabs extending downward into the combustion volume from the ceiling of the combustion volume; wherein the distal flame holder further includes a mounting structure that extends to a position near the ceiling of the combustion volume; and wherein the one or more tabs are operatively coupled to the mounting structure near the ceiling of the combustion volume to provide stability to the mounting structure and the plurality of columns.

12. The horizontally-fired burner system of claim 1, wherein the distal flame holder further comprises: a mounting structure upon which a plurality of columns are supported; and a plurality of ceramic tubes operatively coupled to the mounting structure and disposed adjacent to each respective column, the plurality of ceramic tubes being disposed to substantially prevent a plurality of refractory tiles from becoming dislodged from the respective columns.

13. The horizontally-fired burner system of claim 12, wherein the plurality of ceramic tubes are formed from at least one of sintered silicon carbide or yttrium-stabilized zirconia-alumina (YZA).

14. The horizontally-fired burner system of claim 1, wherein each refractory tile of the plurality of refractory tiles includes a keying feature configured to secure said each refractory tile to an adjacent refractory tile of the plurality of refractory tiles.

15. The horizontally-fired burner system of claim 1, wherein respective refractory tiles are formed from one or more materials selected from the group consisting of zirconium, silicon carbide, and yttrium-stabilized zirconia-alumina.

16. The horizontally-fired burner system of claim 1, further comprising: a mixing tube disposed in the combustion volume between the fuel and combustion air source and the distal flame holder to receive fuel and combustion air from the fuel and combustion air source, the mixing tube being configured to entrain flue gas with the fuel and the combustion air and to cause mixing of the fuel, the combustion air, and the flue gas prior to receipt of the mixture at the distal flame holder.

17. The horizontally-fired burner system of claim 16, further comprising: a mixing tube support structure configured to support the mixing tube, the mixing tube support structure configured to be supported by a surface defining the combustion volume.

18. The horizontally-fired burner system of claim 16, wherein the mixing tube is assembled inside the combustion volume from individual pieces sized to fit into the combustion volume through a man-way access hole having a diameter of less than about 20 inches.

19. The horizontally-fired burner system of claim 18, further comprising: a flame holder actuator operatively connected to the pre-heat burner; a sensor configured to detect a distal flame holder temperature; and a controller operatively coupled to the flame holder actuator, the controller configured to cause the pre-heat burner to, based on the detected distal flame holder temperature, hold a pre-heat flame when the distal flame holder needs to be pre-heated and to not hold the pre-heat flame when the distal flame holder is at an operating temperature.

20. The horizontally-fired burner system of claim 1, further comprising: a pre-heat burner disposed proximate the fuel and combustion air source, the pre-heat burner being operable to heat the distal flame holder to a temperature equal to or greater than an auto-ignition temperature of the fuel.

21. The horizontally-fired burner system of claim 20, wherein the pre-heat burner is operable to be extinguished just prior to providing main fuel from main fuel nozzles of the fuel and air source.

22. The horizontally-fired burner system of claim 1, further comprising: a distal pilot burner disposed adjacent to a plurality of columns; wherein the distal pilot burner is configured to maintain a pilot flame during combustion of main fuel in a combustion reaction held by the distal flame holder.

23. The horizontally-fired burner system of claim 1, further comprising: a distal pilot burner disposed adjacent to the plurality of columns in the combustion volume; wherein the distal pilot burner is configured to successively provide a pre-heating flame to raise a temperature of the distal flame holder to at least an auto-ignition temperature of main fuel prior to introduction of the main fuel, and to maintain a pilot flame during combustion of the main fuel in the combustion reaction held by the distal flame holder.

24. The horizontally-fired burner system of claim 23, wherein the distal pilot burner is configured to support a large combustion reaction during pre-heating of the distal flame holder and to support a smaller combustion reaction during subsequent combustion of the main fuel.

25. The horizontally-fired burner system of claim 24, wherein the distal pilot burner provides fuel for respective diffusion flames supported by each of the plurality of holes.

26. The horizontally-fired burner system of claim 23, wherein: the distal pilot burner includes a plurality of fuel runners, each having a plurality of holes and each fuel runner of the plurality of fuel runners disposed adjacent to a respective one of the plurality of vertical columns.

27. The horizontally-fired burner system of claim 1, further comprising: one or more sensors disposed at the distal flame holder and configured to detect at least one of a flame presence, a temperature, a flame characteristic, a pressure, a fuel/air proportion, a refractory tile condition, and a vibration amount; a fuel amount actuator disposed as part of the fuel and combustion air source and configured to change an amount of fuel supplied by the fuel and combustion air source; a controller operatively coupled to the one or more sensors and the fuel amount actuator, the controller configured to control the fuel amount actuator to change an amount of fuel supplied by the fuel and combustion air source based on one or more signals received from the one or more sensors.

28. The horizontally-fired burner system of claim 27, wherein the controller is further configured to store data based on the one or more signals received from the one or more sensors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] FIG. 1 is a depiction of a horizontally-fired burner system including a distal flame holder, according to an embodiment.

[0004] FIG. 2 is a depiction of an installed distal flame holder in a horizontally-fired burner system, according to an embodiment.

[0005] FIG. 3 is a depiction of an installed distal flame holder in a horizontally-fired burner system, according to another embodiment.

[0006] FIG. 4 is a depiction of an installed distal flame holder, according to another embodiment.

[0007] FIG. 5 is a simplified drawing showing a horizontally-fired burner system including a mixing tube, according to an embodiment.

[0008] FIG. 6 is a drawing showing a detailed cutaway view of a horizontally-fired burner system including a mixing tube, according to an embodiment.

[0009] FIG. 7 is a drawing showing a horizontally-fired burner system including a distal pilot burner, according to an embodiment.

[0010] FIGS. 8A and 8B are drawings showing detailed views of the distal pilot burner of FIG. 7, according to an embodiment.

DETAILED DESCRIPTION

[0011] 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. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and/or other changes may be made, without departing from the spirit or scope of the disclosure.

[0012] Certain burner systems utilize a distal flame holder disposed downstream from a fuel and oxidant source. A mixture of fuel and oxidant in sufficiently flammable proportion enters perforations at an input side of the distal flame holder, is ignited and burned therein. Ideally the resulting combustion occurs at a speed and temperature that minimizes undesirable combustion products such as nitrogen oxides (NOx) while providing sufficient thermal energy to the distal flame holder to sustain combustion of the continuously received fuel and oxidant mixture and to provide heat for the relevant burner application.

[0013] FIG. 1 is a depiction of a horizontally-fired burner system including a distal flame holder, according to an embodiment. FIG. 2 is a depiction of an installed distal flame holder in a horizontally-fired burner system, according to an embodiment. FIG. 3 is a depiction of an installed distal flame holder, according to another embodiment. To the extent possible, similar numbering in each of the drawings is intended to reference similar features. For example, 100, 200, 300 each refer generally to a horizontally-fired burner system.

[0014] Referring to FIG. 1, a horizontally-fired burner system 100 may include, in a combustion volume 102, a distal flame holder 110 including a plurality of columns 112 each formed from a respective plurality of refractory tiles (202 in FIG. 2). At least one fuel and combustion air source 104 may be configured to output a flammable fuel and air mixture 108 toward the distal flame holder 110 via one or more fuel nozzles 106. The distal flame holder 110 may be configured to hold a combustion reaction adjacent to each of the plurality of columns 112 formed from the plurality of refractory tiles 202. In an embodiment, the plurality of columns 112 are disposed vertically in the combustion volume 102 and parallel to each other within the combustion volume. In another embodiment, at least one column of the plurality of columns 112 has a greater cross-sectional area than another column of the plurality of columns 112.

[0015] The distal flame holder 110 (210 IN FIG. 2) may be configured to hold the combustion reaction upstream from, downstream from, and/or beside each of the plurality of columns 112 of the plurality of refractory tiles 202 that constitute each column.

[0016] At least a portion of the plurality of refractory tiles 202 may include perforated refractory tiles. The perforated refractory tiles may be configured to hold at least a portion of the combustion reaction within perforations of each perforated refractory tile. According to an embodiment, the perforated refractory tiles 202 may include reticulated fibers.

[0017] The distal flame holder 110 including the plurality of columns 112, by virtue of the plurality of columns 112, may provide increased resistance to failure compared to a distal flame holder 110 having a continuous upstream face.

[0018] FIG. 2 depicts an installed distal flame holder 210, as viewed from upstream of the same, in a horizontally-fired burner system 200, according to an embodiment. A combustion volume 102 holding the distal flame holder 210 may have a roughly quadrilateral cross-section defined by a ceiling 203, a floor 205, and walls 207. The distal flame holder 210 may include a mounting structure 208 holding a plurality of columns 112, each column 112 comprising a respective plurality of refractory tiles 202. The mounting structure 208 may include metal or ceramic members at least at a top and bottom of the plurality of columns 112 and configured to secure the respective columns 112 against vibration, shaking, and the like. The combustion volume 102 may include tabs 206 affixed, e.g., by welding and/or fasteners, to one or more of the ceiling 203, the floor 205, and/or the walls 207 for securing the mounting structure 208. The mounting structure 208 may include features complementary to the tabs 206, for attachment thereto to provide stability to the mounting structure and the plurality of columns. In some embodiments the tabs 206 and mounting structure 208 may include one or more beams, e.g., steel beams, assembled to provide a stable base for the distal flame holder 210.

[0019] Although not shown in FIG. 2, the combustion volume 102 may accommodate a plurality of adjacent water tubes (not shown) at the ceiling 203, the floor 205, and the walls 207. In such instances, the tabs 206 may be affixed to and extend from the ceiling 203, the floor 205, and/or the walls 207 between the adjacent water tubes of the plurality of water tubes.

[0020] FIG. 3 depicts an installed distal flame holder 310 in a horizontally-fired burner system 300, according to another embodiment. A combustion volume 302 may be defined by a wall 304 and a plurality of water tubes 303 arranged adjacent to the wall 304. A plurality of refractory columns 312 may be held in place by a mounting structure 308, including a top mounting portion 308a and a bottom mounting portion 308b. In an embodiment, each refractory column 312 may be formed as a stack of discrete refractory tiles (e.g., 202).

[0021] The inventors have found that, in an installation, the entire furnace structure, including the plurality of water tubes 303, exhibits significant vibration during operation. To keep the plurality of columns 112, 312, including the plurality of refractory tiles (202), from shaking apart or toppling over, various approaches were developed and others are contemplated.

[0022] According to an embodiment, each refractory tile 202 of the plurality of refractory tiles (202) may include a keying feature (not shown) configured to secure said each refractory tile (202) to an adjacent refractory tile (202) of the plurality of refractory tiles (202) or, more specifically, to prevent lateral movement of a refractory tile (202) with respect to subjacent and superjacent refractory tiles (202). Respective refractory tiles (202) may be formed from one or more materials selected from the group consisting of zirconium, silicon carbide, and yttrium-stabilized zirconia-alumina.

[0023] Alternatively, or additionally, the columns 112, 312 including a plurality of refractory tiles (202) may be stabilized by securing the columns to the wall 304. For example, according to an embodiment, the horizontally-fired burner system 100, 200, 300 further includes a plurality of steel tabs 306 extending into the combustion volume 302 between respective sets of mutually adjacent water tubes 303 of the plurality of water tubes 303. The distal flame holder 310 may further include a mounting structure 308a, 308b upon which the plurality of columns 312 are supported. The plurality of steel tabs 306 may be operatively coupled to the mounting structure 308a, 308b to mechanically fix the location of the distal flame holder 310 in the combustion volume 302. It will be appreciated by those having skill in the art that this arrangement may be applicable to other embodiments. For example, the embodiments described herein with respect to any of FIGS. 1-8 may take advantage of the structures and methods described for securing refractory tiles 202 of the columns 112, 312, etc.

[0024] Returning to FIG. 2, according to another embodiment, the horizontally-fired burner system 200 further includes a mortar bed 215 formed over a portion of the floor 205 and/or, in an embodiment that includes water tubes, over a bottom portion of a portion of the water tubes. The plurality of columns may be supported by a mounting structure 208 secured via the mortar bed 215. In one embodiment, the horizontally-fired burner system 200 further includes one or more top tabs 206 extending downward into the combustion volume 102, 302, etc. from a ceiling 203 of the combustion volume 102, 302, etc. The distal flame holder 210 (110, 310) may further include a mounting structure 208 that extends to a position near the ceiling 203 of the combustion volume 102. The one or more top tabs 204 may be operatively coupled to the mounting structure 208 near the ceiling 203 of the combustion volume 102 to provide stability to the mounting structure 208 and the plurality of columns 112 (312).

[0025] FIG. 4 is a depiction of an installed distal flame holder 410, according to another embodiment. FIG. 4 shows a view from downstream of the distal flame holder 410. The distal flame holder 410 includes an alternative structure for securing refractory tiles (202) of columns 412. Similar to embodiments described above, the distal flame holder 410 may further include a mounting structure 408 upon which a plurality of the columns 412 are supported. A plurality of ceramic tubes 422 may be operatively coupled to the mounting structure 408 and disposed, top to bottom, adjacent to the refractive tiles 202 along a length of each respective column 412, the plurality of ceramic tubes 422 being disposed to substantially prevent the plurality of refractory tiles (202) from becoming dislodged from the respective columns 412. In an embodiment, the plurality of ceramic tubes 422 are formed from at least one of sintered silicon carbide or yttrium-stabilized zirconia-alumina (YZA), although not limited to such materials. As illustrated, the ceramic tubes 422 may be arranged at least on a downstream side and on lateral sides of the columns 412.

[0026] FIG. 5 is a simplified drawing showing a horizontally-fired burner system 500 including a mixing tube 520, according to an embodiment. The mixing tube 520 may be disposed in a combustion volume 502 between a fuel and combustion air source 504 and a distal flame holder 510 to receive fuel and combustion air from the fuel and combustion air source 504. The mixing tube 520 may be configured to entrain flue gas 530, recirculated from downstream of the distal flame holder 510, with the fuel and the combustion air and to cause mixing of the fuel, the combustion air, and the flue gas 530 prior to receipt of the mixture at the distal flame holder 510. The distal flame holder 510 may include a plurality of columns 512, each column 512 being formed of a plurality of refractory tiles (202).

[0027] The horizontally-fired burner system 500 may further include a pre-heat burner 508 disposed proximate the fuel and combustion air source 504. The pre-heat burner 508 may be operable to heat the distal flame holder 510 to a temperature equal to or greater than an auto-ignition temperature of the fuel. In an embodiment, the pre-heat burner 508 is operable to be extinguished just prior to provision of main fuel from main fuel nozzles 506 of the fuel and air source 504.

[0028] Further, the horizontally-fired burner system 500 (indeed any of the horizontally-fired burner systems described herein) may include a controller 505 operatively coupled to a data interface 507 and one or more sensors 509. The sensors 509 may be electrically connected to the controller 505 via a conduit 560 (including wires or other data signaling media) or may be wirelessly connected to the controller 505, e.g., by WiFi, Bluetooth, a proprietary communication protocol, or the like. The sensor(s) 509 may include, but are not limited to, transducers configured to measure a temperature and/or pressure, to determine a level of particulate in combustion products, to determine a fuel/oxidant proportion of a fuel and combustion air mixture, and/or the like. In an embodiment, the sensors 509 may include a refractory tile condition evaluation device. In an embodiment, the sensors 509 may include a sensor configured to measure vibration at the distal flame holder 510 or at any of the columns 512 thereof. The controller 505 may control an amount or rate of supply for the fuel and the combustion air supplied from the fuel and combustion air supply 504 by controlling actuators of the fuel and combustion air supply 504, based on one or more signals received from the one or more sensor(s) 509. The controller 505 may be configured to store data based on one or more signals received from the sensor(s) 509.

[0029] For example, in an embodiment the controller 505 may be configured to control a start-up sequence of the horizontally-fired burner system. For example, the controller 505 may control a flame holder actuator configured to cause the pre-heat burner 508 to hold the a pre-heat flame when the distal flame holder 510 needs to be pre-heated and to not hold the pre-heat flame when the distal flame holder 510 is at an operating temperature (e.g., when TT.sub.S).

[0030] FIG. 6 is a drawing showing a detailed cutaway view of a horizontally-fired burner system 600 including a mixing tube 620, according to an embodiment. As illustrated in FIG. 6, the mixing tube 620 may be assembled from multiple parts. For example, the mixing tube 620 may include pieces 622 permitting assembly inside a combustion volume 602 from the individual pieces 622. Each individual piece 622 may be sized to fit into the combustion volume 602 through a man-way access hole (not shown) having a diameter of less than about 20 inches. The mixing tube 620 may be supported within the combustion volume 602 by one or more mixing tube support structures 650. The combustion volume 602 may be defined by a plurality of water tubes 603 forming an interior perimeter of the combustion volume 602. The mixing tube support structure(s) 650 may rest on or be attached to one or more of the water tubes 603. Alternatively, or additionally, the mixing tube support structure(s) 650 may be disposed between adjacent water tubes 603. The mixing tube support structure(s) 650 may be formed from one or more heat tolerant materials, including, but not limited to, steel, ceramic, and the like. In operation, the mixing tube 620 is oriented to receive fuel and combustion air from a fuel and combustion air source 604 disposed at a proximal end of the mixing tube 620.

[0031] According to an embodiment, the mixing tube 620 may be arranged about a longitudinal axis of flow between the main fuel nozzles (506) and the distal flame holder 610. According to an embodiment, the mixing tube 620 may include a bell-shaped or flared portion 624 at an end proximate the main fuel nozzles (506) (also seen as flared portion 724 in FIG. 7). The bell-shaped or flared portion 624 may be disposed a predetermined distance from a fuel dump plane (i.e., a plane fuel emission from the main fuel nozzles 506) of the horizontally-fired burner system 600, and may be configured to receive at least the combustion air via an opening in the fuel and combustion air source 604. The flared portion 624 aids in limiting dispersion of fuel and combustion air, focusing flow thereof. In addition, the flared portion 624 may accelerate flow of recirculated flue gas (e.g., 530 in FIG. 5), aiding in mixture thereof with the fuel and combustion air.

[0032] According to an embodiment, the distal flame holder 612 may be secured in place at least in part by use of a mounting structure 608, which may include a base portion and/or top portions (see, e.g., FIGS. 2 and 3). A ceiling of the combustion volume 602 is not shown due to the cutaway nature of FIG. 6, and those of skill in the art will recognize that a top portion of the mounting structure 608 may engage a mounting tab or other securing mechanism affixed to the ceiling. Likewise, a bottom portion of the mounting structure 608 may be secured to a floor of the combustion volume and/or to the water tubes 603. As shown in FIG. 6, the bottom portion of the mounting structure 608 may include elements disposed between adjacent water tubes 603 to a more substantial portion beneath the water tubes 603. It will be appreciated that the mounting structure may, for longevity and stability, be formed from one or more heat tolerant materials, such as silicon carbide, mullite, cordierite, tempered steel, or the like.

[0033] The refractory tiles (202) forming the plurality of columns 612 (and other such columns described herein) may be formed from yttrium-stabilized zirconia-alumina or other elements having similar properties. In an embodiment, the refractory tiles (202) may be formed from reticulated fibers disposed to provide a plurality of perforations through the tile.

[0034] The horizontally-fired burner system of FIG. 6 further includes the above-described conduit 560 between the distal flame holder 610 and a controller (505). The conduit may include wires or other communication conveyance means for providing data from the distal flame holder 610 to the controller. For example, the distal flame holder 610 may include one or more sensors (509), such as a temperature sensor, pressure sensor, particular measuring sensor, emissions content sensor and/or the like. Additionally, the conduit 560 may carry an ignition signal to an igniter (not shown) configured to ignite a mixture of the fuel and combustion air from the fuel and combustion air source 604. In some embodiments the igniter may include a pilot flame or an electrical discharge (spark) actuator. In an embodiment the distal flame holder 610 itself may be heated to a temperature sufficient to ignite a mixture of fuel and combustion air on contact. Such temperature of the distal flame holder 610 may be reached by use of a distal pilot burner (740, described below), or an electric resistance heater incorporated into the distal flame holder 610.

[0035] One of skill in the art will recognize that the preceding paragraph describes features that are applicable to any of the embodiments disclosed herein.

[0036] FIG. 7 is a drawing showing a horizontally-fired burner system 700 including a distal pilot burner 740, according to an embodiment. The inventors have observed, in a variety of furnace applications, undesirable combustion oscillations occurring between a distal flame holder 710 and a fuel and oxidant (combustion air) source 704. Although not necessarily restricted to a confined furnace configuratione.g., a water heater, boiler, or once-through steam generator (OTSG)such applications are representative environments that can permit such combustion oscillations.

[0037] When fuel and oxidant are in sufficiently combustible proportion and exposed to sufficient heat for ignition, they can undesirably ignite upstream of the distal flame holder 710. This phenomenon tends to oscillate and is referred to herein as flashback, and is sometimes colloquially referred to as huffing. In some implementations, insufficiently and/or non-uniformly cooled oxidant, e.g., flue gas, can be recirculated from downstream of the distal flame holder 710, resulting in a fuel-oxidant mixture with a sufficiently high temperature that the mixture may ignite prior to reaching the distal flame holder 710. The flashback reduces the efficiency of the burner 700 at least in part because heat from this premature combustion is not (in a gas-fired burner) radiant heat, is not sufficiently absorbed by the distal flame holder 710 and/or boiler tubes, and is thus wasted. Combustion products from the flashback can dilute the mixture and thus temporarily snuff the flashback combustion. Hence the oscillating nature of flashback.

[0038] The distal pilot burner 740 may be configured for preheating of the distal flame holder 710 and/or to address undesirable flashback by providing a constant and/or controllable ignition source for the fuel and combustion air mixture at a position sufficiently near to the distal flame holder 710 to provide heat benefits from a pilot flame 742 to the distal flame holder 710.

[0039] The distal pilot burner 740 may be disposed adjacent to the distal flame holder 710 in a combustion volume 702. The distal flame holder 710 may be formed of a plurality of columns 712 including refractory materials. In an embodiment, the distal pilot burner 740 is configured to maintain a pilot flame 742 during combustion of main fuel in a combustion reaction held by the distal flame holder 710. The main fuel and the combustion air may be supplied by the fuel and combustion air source 704 disposed a distance upstream from the distal pilot burner 740. Accordingly, in an embodiment, the distance between main fuel nozzles 706 of the fuel and combustion air source 704 and the distal pilot burner 740 may be at least 50 times a diameter of the main fuel nozzles 706, at least 100 times a diameter of the main fuel nozzles 706, or at least 200 times the diameter of the main fuel nozzles 706.

[0040] According to an embodiment, the horizontally-fired burner system 700 may include a mixing tube 720 disposed between the fuel and combustion air source 704 and the distal pilot burner 740. The mixing tube 720 may include a flared portion at an opening proximal to the fuel and combustion air source 704. The mixing tube 720 directs a flow of fuel and combustion air from the fuel and combustion air source 704 toward the distal pilot burner 740 and the distal flame holder 710. Flue gas 730 from downstream of the distal flame holder 710 may be recirculated outside the mixing tube 720 to enter the proximal end thereof for mixture with the fuel and the combustion air.

[0041] According to another embodiment, the horizontally-fired burner system 700 includes the distal pilot burner 740 disposed adjacent to the plurality of columns 712. The distal pilot burner 740 may be configured to successively provide a pre-heating flame to raise a temperature of the distal flame holder 710 to at least an auto-ignition temperature of main fuel prior to introduction of the main fuel, and to maintain the pilot flame 742 during combustion of the main fuel in the combustion reaction held by the distal flame holder 710. The distal pilot burner 740 may be configured to support a large combustion reaction during pre-heating of the distal flame holder 710 and to support a smaller combustion reaction during subsequent combustion of the main fuel.

[0042] As noted above with respect to FIG. 5, the horizontally-fired burner systems disclosed herein may include a controller 505 configured to receive sensor inputs and to control output of fuel and combustion air. In embodiments corresponding to FIG. 7, the controller 505 may additionally control use of the distal pilot burner 740. For example, the controller 505 may control an actuator (not shown) that controls rate and/or amount of fuel provided to the distal pilot burner 740 based on, e.g., sensor inputs showing temperature of the distal flame holder 710, presence or absence or quality of a flame at the distal flame holder 710 and/or at the distal pilot burner 740.

[0043] FIGS. 8A and 8B are drawings showing detailed views of the distal pilot burner 740 of FIG. 7, according to an embodiment. FIG. 8A is a front view of an embodiment of the distal pilot burner 740 looking upstream from the distal flame holder 710, while FIG. 8B is a top view looking down on a simplified cross-section of the distal pilot burner 740 and the distal flame holder 710. According to an embodiment, the distal pilot burner 740 includes a plurality of fuel runners 744, each having a plurality of holes 746. Each fuel runner 744 may be disposed adjacent to a respective one of the plurality of vertical columns 712. The distal pilot burner 740 may include fuel runners 744 disposed respectively in correspondence to each column 712 in the distal flame holder 710 (110, etc.). According to an embodiment, each of the fuel runners 744 may be supplied with fuel via a common fuel supply conduit 748 disposed adjacent to each of the plurality of vertical columns 712. One of skill in the art will recognize that other topologies for the distal pilot burner 740 may be applicable. For example, the distal pilot burner 740 may include a fuel manifold having a plurality of segments joined together, each segment having a plurality of fuel orifices configured to pass fuel from inside the fuel manifold to the furnace volume. The plurality of segments may be formed as respective tubes configured to freely pass the fuel delivered from a fuel pipe into the fuel manifold. In one embodiment, at least a portion of the tubes is arranged as spokes radiating from a center disposed substantially at a centerline along the axis. In another embodiment, at least a portion of the tubes is arranged as an X, a rectangle, an H, a wagon wheel, or a star. According to an embodiment, the distal pilot fuel includes a manifold including a curvilinear tube. In an embodiment, the curvilinear tube may be arranged as a spiral, , , or .. The distal pilot burner 740 may provide fuel for respective diffusion flames supported by each of the plurality of holes 746.

[0044] 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.