CN111503634A - Ultra-low fire-tube-discharging boiler burner without high excess air and/or external flue gas recirculation - Google Patents

Abstract

Ultra low exhaust tube boiler burners without high excess air and/or external flue gas recirculation. According to an embodiment, the open flame heater comprises a fuel and combustion air source outputting fuel and combustion air to a combustion volume comprising a combustion volume wall, the wall defining a lateral extent separated from an external volume. According to an embodiment, the open flame heater comprises a boiler heater, the combustion volume wall comprising combustion conduits defining a lateral extent of the combustion volume, which separates the combustion volume from the water and steam volume. The open flame heater includes a mixing tube aligned to receive fuel and combustion air from a fuel and combustion air source. The mixing tube may be separated from the combustion volume wall by a separation volume. The open flame heater includes a bluff body flame holder aligned to receive a fuel and combustion air mixture from the mixing tube outlet end. The bluff body flame holder may be configured to hold a combustion reaction to heat a combustion volume wall. The combustion volume wall may comprise a combustion conduit. The combustion conduit may be configured to heat water in the water and steam volume.

Description

Ultra-low fire-tube-discharging boiler burner without high excess air and/or external flue gas recirculation

Cross Reference to Related Applications

This application claims priority from U.S. provisional patent application No. 62/798,913 entitled "U L TRA L OW emissons fire BOI L ERBURNER" filed on 30.1.2019 (docket No. 2651-338-02) and from U.S. provisional patent application No. 62/844,669 entitled "PI L OT STABI L IZED BURNER" filed on 7.5.2019 (docket No. 2651-348-02). each of the foregoing applications is incorporated herein by reference to the extent not inconsistent with the disclosure herein.

SUMMARY

According to one embodiment, a fired heater (fired heater) includes a fuel and combustion air source configured to output fuel and combustion air into a combustion volume wall defining a lateral extent of a combustion volume. The combustion volume wall may include a combustion conduit disposed to separate the combustion volume from the water and steam volumes. The open flame heater includes a mixing tube aligned to receive fuel and combustion air from a fuel and combustion air source. The mixing tube may be spaced from the combustion volume wall by a volume. The open flame heater includes a bluff body flame holder aligned to receive a mixture of fuel and combustion air from an outlet end of a mixing tube. The bluff body flame holder may be configured to hold a combustion reaction for heating the combustion volume wall. The combustion volume wall may be configured to heat the volumetric heat load.

According to one embodiment, the open flame heater comprises a fuel and combustion air source configured to output fuel and combustion air into a combustion volume wall defining a lateral extent of the combustion volume. The combustion volume wall may comprise a combustion conduit arranged to separate the combustion volume from the water and steam volume. The open flame heater includes a mixing tube aligned to receive fuel and combustion air from a fuel and combustion air source. The mixing tube may be spaced from the combustion volume wall by a volume. The open flame heater includes a bluff body flame holder aligned to receive a mixture of fuel and combustion air from an outlet end of a mixing tube. The bluff body flame holder may be configured to hold a combustion reaction for heating the combustion volume wall. The combustion volume wall may be configured to heat a volumetric heat load.

According to one embodiment, a combustion system includes a frame configured to be mounted on an inner surface of a combustion volume wall and one or more bluff bodies supported by the frame. The combustion system includes a pilot burner (pilot burner) configured to selectively support a pilot flame for heating the one or more bluff bodies and a secondary fuel source configured to supply a secondary fuel to a combustion reaction held by the one or more bluff bodies.

According to one embodiment, a fuel and air source for a burner may include a fuel riser tube (fuel riser) extending to a tip, a wall of a main combustion air plenum disposed about the fuel riser tube and defining a main combustion air plenum chamber (primary combustion air plenum), and a variable swirler (variable swirler) disposed to controllably swirl primary combustion air at any of two or more different rotational velocities at least at a location corresponding to the tip of the fuel riser tube.

According to one embodiment, a method of operating an open flame heater includes outputting fuel and combustion air from a fuel and combustion air source into a combustion volume wall defining a lateral extent of a combustion volume. In one embodiment, the open flame heater is a boiler heater. The combustion volume wall may comprise a combustion conduit arranged to separate the combustion volume from the water and steam volume. The method may include receiving fuel and combustion air from a fuel and combustion air source in a mixing tube aligned to receive fuel and combustion air from the fuel and combustion air source. The mixing tube may be spaced from the combustion volume wall by a spacing volume. The method may include receiving a mixture of fuel and combustion air from an outlet end of a mixing tube at a bluff body flame holder, holding a combustion reaction of the fuel and combustion air with the bluff body flame holder, heating a combustion conduit with the combustion reaction, heating water in a volume of water and steam with the combustion conduit.

According to one embodiment, a method comprises: suspending the frame from an inner surface of the combustion volume wall; supporting one or more refractory bluff bodies with a frame; selectively supporting a pilot flame with a pilot; heating one or more refractory bluff bodies with a pilot flame when present; supplying a secondary fuel to the one or more refractory bluff bodies using a secondary fuel source; and maintaining a combustion reaction of the auxiliary fuel with the combustion air with the one or more refractory bluff bodies.

According to one embodiment, a method of operating a fuel and air source for a combustor includes: outputting a primary fuel from a fuel riser tube extending to a tip; providing main combustion air to a main combustion air plenum chamber defined by walls of a main combustion air plenum disposed about the fuel riser and defining the main combustion air plenum chamber; and swirling the primary combustion air at any one of two or more different rotational speeds, at least at a location corresponding to a tip of the fuel riser, using the variable swirler.

Brief Description of Drawings

FIG. 1 is a cross-sectional view of a low emission open fire heater configured as a boiler heater, according to one embodiment.

FIG. 2 is a close-up cross-sectional view of a portion of the low emission boiler heater of FIG. 1, according to one embodiment.

Fig. 3 is a side cross-sectional view of a portion of the combined fuel and combustion air source and pilot of fig. 1 and 2, according to an embodiment.

FIG. 4 is a schematic view of a flame holding portion of the combustion system of FIG. 1, according to an embodiment.

FIG. 5A is a schematic view of a frame portion of the bluff body flame holder of FIGS. 1 and 4, according to an embodiment.

FIG. 5B is a detailed view of a frame portion of the bluff body flame holder of FIGS. 4 and 5A, according to one embodiment.

FIG. 6 is a simplified diagram of a burner system including a perforated flame holder configured to hold a combustion reaction, according to an embodiment.

FIG. 7 is a side cross-sectional view of a portion of the perforated flame holder of FIG. 6, according to an embodiment.

FIG. 8 is a flow diagram illustrating a method for operating a combustor system including the perforated flame holder shown and described herein, according to one embodiment.

FIG. 9A is a simplified perspective view of a combustion system including another alternative perforated flame holder according to an embodiment.

FIG. 9B is a simplified side cross-sectional view of a portion of the reticulated ceramic perforated flame holder of FIG. 9A, according to an embodiment.

Figure 10 illustrates several variations of individually and in combination supported bluff bodies according to one embodiment.

FIG. 11 is a flow diagram illustrating a method of operating a boiler heater, according to an embodiment.

FIG. 12 is a flow chart illustrating a method of operating a combustion system, according to an embodiment.

FIG. 13 is a flow chart illustrating a method of operating a fuel and air source for a combustor, 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, like reference numerals generally identify like components, unless context dictates otherwise. Other embodiments may be utilized, and/or other changes may be made, without departing from the spirit or scope of the present disclosure.

FIG. 1 is a cross-sectional view of a low emission open flame heater configured as a boiler heater 100 according to one embodiment.

FIG. 2 is a close-up cross-sectional view 200 of a portion of the low emission open flame heater 100 of FIG. 1, according to an embodiment.

Referring to fig. 1 and 2, the open flame heater 100 may include a fuel and combustion air source 102, the fuel and combustion air source 102 configured to output fuel and combustion air into a combustion volume wall 104, the combustion volume wall 104 defining a lateral extent of a combustion volume 106. In one embodiment, the combustion volume wall may include combustion conduits 104, the combustion conduits 104 being configured to separate the combustion volume 106 and the water from the steam volume 108. According to one embodiment, the open flame heater 100 may include a mixing tube 110, the mixing tube 110 aligned to receive fuel and combustion air from the fuel and combustion air source 102. The mixing tube 110 may be spaced apart from the combustion volume wall 104 by a spacing volume 116. According to one embodiment, the open flame heater 100 may include a bluff body flame holder 112, the bluff body flame holder 112 aligned to receive a mixture of fuel and combustion air from an outlet end 114 of the mixing tube 110. The bluff body flame holder 112 may be configured to hold a combustion reaction for heating the combustion volume wall 104. In one embodiment, the combustion volume wall 104 may be configured to heat the heat load volume 108. The heat load volume 108 may include water and steam volumes.

According to one embodiment, the spacing volume 116 comprises an annular volume between the mixing tube 110 and the combustion volume wall 104. In one embodiment, the mixing tubes 110 and the combustion volume wall 104 are concentric. In another embodiment, the mixing tubes 110 and the combustion volume wall 104 are not concentric. According to one embodiment, the separation volume 116 defined by the mixing tube 110 and the combustion volume wall 104 is provided for carrying flue gas for recirculation.

According to one embodiment, the mixing tube 110 further includes an inlet end 202 spaced from the fuel and combustion air source 102. In one embodiment, the inlet end 202 of the mixing tube 110 may include a flare 204, the flare 204 tapering inwardly away from the fuel and combustion air source 102 toward a cylindrical region of the mixing tube 110. In another embodiment, the inlet end 202 of the mixing tube 110 may include a flare 204, the flare 204 arranged to direct the flue gas passing through the annular volume 116 from the outlet end 114 of the mixing tube 110 to the inlet end 202 of the mixing tube 110.

According to an embodiment, the inner surface 206 of the combustion volume wall 104 may comprise a refractory material configured to provide thermal insulation.

According to one embodiment, the combustion volume wall 104 may be configured to be kept cool by the heat load 108, e.g., by water with water in the steam volume 108, and the mixing tube 110 may be configured to be kept warm by the combustion reaction and flue gas. In one embodiment, the cooling temperature of the combustion volume wall 104 is configured to draw flue gas generated by the combustion reaction from the region proximate the bluff body flame holder 112 toward the inlet end 202 of the mixing tube 110. The flue gas may be introduced into the mixing tube 110 by a flow of fuel and combustion air output by the fuel and combustion air source 102. In one embodiment, the mixing tubes 110 are configured such that combustion air, fuel, and flue gas mix as they flow through the mixing tubes 110 to form a lean mixture of air and fuel for supporting the combustion reaction. According to one embodiment, the fuel and combustion air source 102 may be configured to selectively hold a pilot flame. Optionally, the open flame heater 100 may include a pilot flame device (not shown) configured to selectively hold a pilot flame.

According to one embodiment, the pilot flame device may be disposed distal to the fuel and combustion air source 102, proximate upstream of the bluff body flame holder 112. The pilot flame arrangement may comprise at least one pilot fuel nozzle. The pilot flame device may be configured to hold a pilot flame. In some embodiments, the pilot flame device may selectively receive fuel and combustion air from the fuel and combustion air source 102. In such embodiments, the fuel and combustion air source 102 may be configured to supply fuel and combustion air to the distal pilot flame device when the first fuel circuit 308 is open and the second fuel circuit 314 is closed. In other embodiments, the pilot flame device can include at least one of a pilot fuel source and a pilot oxidant source. The pilot flame may be configured to ignite the fuel and air flow from the fuel and combustion air source 102 to provide a combustion reaction for heating the combustion volume wall 104. When the open flame heater is operating at a rated heat output, the combustion reaction used to heat the walls of the combustion volume can provide a heat output at least 10 times the heat output of the pilot flame. In embodiments having a distal pilot flame device, an igniter 326 may be disposed proximate the pilot flame device to ignite the pilot flame. The distal pilot flame device may be structurally supported by at least one of the combustion volume wall 104, a bluff body flame holder support structure (e.g., the frame 402 described below), and/or the mixing tube 110. Alternatively, the distal pilot flame device may extend from and be supported by the fuel and combustion air source 102, extending from a location proximate to a wall defining the extent of the water and steam volume 108. According to one embodiment, a pilot fuel nozzle of a pilot flame apparatus may include a fuel manifold having a plurality of sections coupled together, each section having a plurality of fuel apertures configured to transfer fuel from an interior of the fuel manifold to a combustion volume (combustion volume) within a furnace. The plurality of segments may be formed as respective tubes configured to freely transfer fuel delivered from the fuel tubes into the fuel manifold. At least a portion of the tubes may be arranged as spokesThe spokes extend circumferentially from a center disposed substantially at the centerline (along the fuel and combustion air flow axis). At least a portion of the tubes may be arranged in an "X", a rectangle, "H", a wagon wheel, or a star. In one embodiment, the pilot fuel nozzle may include a manifold including a curvilinear tube. The curved tubes may be arranged in a spiral "

Shape'

Form "or" ∞ "form.

Fig. 3 is a side cross-sectional view 300 of a portion of the combined fuel and combustion air source and pilot 102 of fig. 1 and 2, according to an embodiment.

According to one embodiment, the fuel and combustion air source 102 includes a controllable swirler 302 configured to selectively impart a swirling motion to primary combustion air 303 flowing within a primary combustion air plenum chamber 304 defined by a primary combustion air plenum 306. The fuel and combustion air source 102 may be configured to selectively maintain a pilot flame when the controllable swirler 302 selectively imparts a swirling motion to the main combustion air 303.

According to one embodiment, the fuel and combustion air source 102 may include: a main combustion air plenum 306; a first fuel circuit 308 configured to selectively output a primary fuel to one or more locations 310, 312 (within the primary combustion air plenum 306); a second fuel circuit 314 configured to selectively output a secondary fuel through a plurality of fuel risers 316 disposed outside the main combustion air plenum 306. In one embodiment, the fuel and combustion air source 102 may be configured to supply fuel and combustion air to the bluff flame holder 112 when the first fuel circuit 308 is stopped and when the second fuel circuit 314 is open. The fuel and combustion air source 102 may be configured to support a pilot flame when the first fuel circuit 308 is open and the second fuel circuit 314 is closed.

In one embodiment, the pilot flame may be configured to heat the bluff body flame holder 112 to an operating temperature while the fuel and combustion air source 102 holds the pilot flame. In another embodiment, the fuel and combustion air source 102 may be configured to output fuel and combustion air through the mixing tube 110 to the bluff flame holder 112 when the fuel and combustion air source 102 is not holding a pilot flame

According to one embodiment, the fuel and combustion air source 102 includes a first combustion air damper 318, the first combustion air damper 318 configured to control the flow of the main combustion air 303 through the main combustion air plenum 306. In another embodiment, the source of fuel and combustion air 102 includes a second combustion air damper 320, the second combustion air damper 320 configured to control the auxiliary combustion air through the auxiliary combustion air plenum 322.

In embodiments employing a distal pilot flame device, the fuel and combustion air source 102 may include a main combustion air damper (not shown) configured to control the flow of main combustion air 303 through a dedicated pilot air plenum (not shown).

According to an embodiment, the open flame heater 100 further comprises a burner controller 324, the burner controller 324 being configured to control at least one selected from the group consisting of: an actuator 328 operably coupled to the variable swirler 302, the first fuel circuit 308, the second fuel circuit 314, the first combustion air damper 318, the second combustion air damper 320, and the igniter 326. In other embodiments, combustor controller 324 may be operably coupled to combustion sensor 330.

As discussed in more detail below with reference to fig. 6, the igniter 326 may include a discharge (e.g., spark) igniter, a hot surface igniter, or a pilot flame device. FIG. 4 is a diagram of a flame holding portion 400 of the combustion system of FIG. 1, according to an embodiment.

According to one embodiment, the open flame heater 100 further comprises a frame 402, the frame 402 being configured to be suspended on the inner surface 206 of the combustion volume wall 104. In one embodiment, the frame 402 is configured to support the bluff body flame holder 112 within the combustion volume wall 104. In one embodiment, the bluff body flame holder 112 includes one or more perforated flame holders. The one or more perforated flame holders may comprise a mesh ceramic perforated flame holder. In another embodiment, the bluff body flame holder 112 includes one or more bluff bodies 404. In one embodiment, the frame 402 and the one or more bluff bodies 404 supported by the frame 402 include a plurality of frames 402 supporting a respective plurality of bluff body tiles, each frame 402 disposed at a different respective distance from the fuel and combustion air source 102. In another embodiment, the frame 402 and the one or more bluff bodies 404 supported by the frame 402 comprise a single frame 402 supporting a plurality of bluff body tiles 404. In one embodiment, the bluff body flame holder 112 is a refractory material. According to one embodiment, the one or more bluff bodies comprise two or more bluff bodies.

According to one embodiment, the frame 402 and the one or more bluff bodies 404 supported by the frame 402 comprise a plurality of frames 402 supporting a respective plurality of bluff body bricks 404, each frame of the plurality of frames 402 being disposed at a different respective distance from the fuel and the pilot of the combustion air source 102.

Returning to FIG. 3, according to one embodiment, the fuel and combustion air source 102 includes a fuel riser tube 332 extending to a tip 334. The main combustion air plenum 306 includes a wall disposed about the fuel riser tube 332. The wall defines a main combustion air plenum chamber 304. The variable swirler 302 is configured to controllably swirl the primary combustion air 303 at any of two or more different rotational velocities, at least at a location corresponding to the tip 334 of the fuel riser 332.

According to one embodiment, the walls of the main combustion air plenum 306 form a tapered region at the outlet end of the main combustion air plenum 306 near the tip 334 of the fuel riser 332.

According to one embodiment, the fuel and combustion air source 102 includes a lobe mixer (e.g., 412) configured to increase radial mixing of fuel, air, and flue gas recirculated from the combustion reaction.

FIG. 5A is a schematic view 500 of a frame 402 portion of the bluff body flame holder 112 of FIGS. 1 and 4, according to an embodiment.

FIG. 5B is a detailed view 501 of a frame 402 portion of the bluff body flame holder 112 of FIGS. 4 and 5A, according to an embodiment.

Referring to fig. 1, 2, 3, 4, 5A and 5B, the combustion system may include: a frame 402 configured to be suspended from the inner surface 206 of the combustion volume wall 104; one or more bluff bodies 404 supported by the frame 402; a pilot configured to selectively support a pilot flame for heating the one or more bluff bodies 404; and a supplemental fuel source, such as a supplemental fuel riser 316, configured to supply supplemental fuel to the combustion reaction held by the one or more bluff bodies 404.

According to one embodiment, the auxiliary fuel source may be actuated to supply auxiliary fuel when the pilot burner is selected to not support a pilot flame.

According to one embodiment, at least a portion of one or more bluff bodies 404 may comprise one or more perforated flame holders. In one embodiment, the one or more perforated flame holders are configured to support a combustion reaction of a fuel and an oxidant upstream, downstream, and within the perforated flame holders.

Fig. 6 is a simplified diagram of a burner system 600 including a perforated flame holder 612 configured to hold a combustion reaction, according to an embodiment. The perforated flame holder 612 is an example of a bluff body flame holder 112 and, in some embodiments, may be implemented by the bluff body flame holder 112 of fig. 1, 4, and 10. As used herein, unless further definitions are provided, the terms perforated flame holder, perforated reaction holder, porous flame holder, porous reaction holder, duplex structure (duplex) and duplex brick shall be considered synonymous.

Experiments conducted by the inventors have shown that the perforated flame holder 612 described herein can support very clean combustion. In particular, in pilot scale to full scale experimental use of the combustor system 600, the output of nitrogen oxides (NOx) is measured as millions from as low as single digitThe fraction (ppm) drops to a concentration NOx at the flue that is undetectable (less than 1 ppm). At typical flue temperatures for industrial furnace applications (1400 ℃ F.), (1600 ℃ F.) in 3% (dry) oxygen (O)₂) These significant results were measured at concentrations and undetectable carbon monoxide (CO). Furthermore, these results do not require any special precautions, such as Selective Catalytic Reduction (SCR), selective non-catalytic reduction (SNCR), water/steam injection, external Flue Gas Recirculation (FGR), or even other extreme conditions that may be required for conventional combustors in order to approach such clean combustion.

According to an embodiment, the burner system 600 includes a fuel and oxidant source 102 configured to output a fuel and an oxidant into a combustion volume 604 forming a fuel and oxidant mixture 606. As used herein, the terms fuel and oxidant mixture and fuel stream are used interchangeably and are considered synonymous according to context, unless further definitions are provided. As used herein, the terms combustion volume, combustion chamber, furnace volume, and the like are to be considered synonymous unless further definitions are provided. A perforated flame holder 612 is disposed in the combustion volume 604 and positioned to receive the fuel and oxidant mixture 606.

FIG. 7 is a side cross-sectional view 700 of a portion of the perforated flame holder 612 of FIG. 6, according to an embodiment. Referring to fig. 6 and 7, the perforated flame holder 612 includes a perforated flame holder body 608 defining a plurality of perforations 610 aligned to receive the fuel and oxidant mixture 606 from the fuel and oxidant source 102. As used herein, unless further definition is provided, the terms perforation, aperture (pore), hole (aperture), elongated hole (elongated aperture), and the like, shall be considered synonymous in the context of the perforated flame holder 612. The perforations 610 are configured to collectively retain a combustion reaction 702 supported by the fuel and oxidant mixture 606.

The fuel may comprise hydrogen, a hydrocarbon gas, a vaporized hydrocarbon liquid, an atomized hydrocarbon liquid, or a powdered or pulverized solid. The fuel may be a single species or may comprise a mixture of gases, vapors, atomized liquids and/or pulverized solids. For example, in process heater applicationsThe fuel may comprise flue gas or by-products from the process, including carbon monoxide (CO), hydrogen (H)₂) And methane (CH)₄). In another application, the fuel may include natural gas (primarily CH)₄) Or propane (C)₃H₈). In another application, the fuel may include No. 2 fuel oil or No. 6 fuel oil. The inventors similarly contemplate dual fuel applications and flexible fuel applications. The oxidant may comprise oxygen carried by air, flue gas and/or may comprise another oxidant, pure or carried by a carrier gas. Herein, the terms oxidant (oxidant) and oxidizer (oxidazer) should be considered synonymous.

According to one embodiment, the perforated flame holder body 608 may be defined by: an input face 613 disposed to receive the fuel and oxidant mixture 606, an output face 614 facing away from the fuel and oxidant source 102, and a peripheral surface 616, the peripheral surface 616 defining a lateral extent of the perforated flame holder 612. A plurality of perforations 610 defined by the perforated flame holder body 608 extend from the input face 613 to the output face 614. The plurality of perforations 610 may receive the fuel and oxidant mixture 606 at the input face 613. The fuel and oxidant mixture 606 can then be combusted within or proximate to the plurality of perforations 610, and the combustion products can exit the plurality of perforations 610 at or proximate to the output face 614.

According to one embodiment, the perforated flame holder 612 is configured to hold a majority of the combustion reaction 702 within the perforations 610. For example, on a steady-state basis, more than half of the fuel molecules output by the fuel and oxidant source 102 into the combustion volume 604 can be converted into combustion products between the input face 613 and the output face 614 of the perforated flame holder 612. According to an alternative explanation, more than half of the heat or thermal energy output by the combustion reaction 702 may be output between the input face 613 and the output face 614 of the perforated flame holder 612. As used herein, the terms heat, heat energy and thermal energy should be considered synonymous unless further definitions are provided. As used above, heat and thermal energy generally refer to the released chemical energy initially held by the reactants during the combustion reaction 702. As used elsewhere herein, heat and thermal energy correspond to detectable temperature rises experienced by real bodies characterized by heat capacity. Under nominal operating conditions, perforations 610 may be configured to collectively hold at least 80% of combustion reaction 702 between input face 613 and output face 614 of perforated flame holder 612. In some experiments, the inventors generated a combustion reaction 702 that was apparently contained entirely in the perforations 610 between the input face 613 and the output face 614 of the perforated flame holder 612. According to an alternative explanation, the perforated flame holder 612 can support combustion between the input face 613 and the output face 614 when combustion is "time-averaged". For example, during transients, such as before the perforated flame holder 612 is sufficiently heated, or if excessive (cold) loads are placed on the system, combustion may travel somewhat downstream from the output face 614 of the perforated flame holder 612. Alternatively, if the cooling load is relatively low and/or the furnace temperature reaches a high level, the combustion may travel slightly upstream of the input face 613 of the perforated flame holder 612.

Although a "flame" is described in a manner that is convenient for description, it should be understood that in some cases, there is no visible flame. Burning occurs primarily in the perforations 610, but the "glow" of the heat of combustion is primarily the visible glow of the perforated flame holder 612 itself. In other instances, the inventors have noted transient "blowing" or "flashback" in which the dilution region D is in the region between the inlet face 613 of the perforated flame holder 612 and the fuel nozzle 618_DThe visible flame is ignited instantly. Such transient blowing or flashback is typically of a short duration such that, on a time-averaged basis, most of the combustion occurs between the input face 613 and the output face 614 within the perforations 610 of the perforated flame holder 612. In still other cases, the inventors have noted that significant combustion occurs downstream of the output faces 614 of the perforated flame holders 612, but most of the combustion still occurs within the perforated flame holders 612, as evidenced by the sustained visible heat light observed from the perforated flame holders 612.

The perforated flame holder 612 may be configured to receive heat from the combustion reaction 702 and output a portion of the received heat as thermal radiation 704 to a heat-receiving structure (e.g., a furnace wall and/or a radiant section working fluid tube) in or near the combustion volume 604. As used herein, the terms radiation, thermal radiation, radiant heat, thermal radiation, and the like are to be understood as being substantially synonymous unless further definitions are provided. In particular, such terms refer to black body radiation of electromagnetic energy primarily at infrared wavelengths, but also at visible wavelengths due to the high temperature of the perforated flame holder body 608.

Referring specifically to fig. 7, perforated flame holder 612 outputs another portion of the received heat to fuel and oxidant mixture 606 received at input face 613 of perforated flame holder 612. The perforated flame holder body 608 may receive heat from the combustion reaction 702 at least in the heat receiving region 706 of the perforated wall 708. Experimental evidence has shown to the inventors that the location of the heat receiving area 706, or at least the location corresponding to the maximum rate of heat reception, may vary along the length of the perforated wall 708. In some experiments, the location of maximum heat acceptance was evident between 1/3 and 1/2, which are distances from input face 613 to output face 614 (i.e., a location slightly closer to input face 613 than to output face 614). The inventors contemplate that, under other conditions, the heat receiving region 706 may be located closer to the output face 614 of the perforated flame holder 612. Most likely, the heat receiving area 706 (or for that matter, the heat output area 710 described below) has no clearly defined edges. For ease of understanding, the heat receiving area 706 and the heat output area 710 will be described as specific areas 706, 710.

The perforated flame holder body 608 can be characterized by a heat capacity. The perforated flame holder body 608 may hold thermal energy from the combustion reaction 702 in an amount corresponding to the heat capacity times the temperature rise and transfer the thermal energy from the heat receiving region 706 to the heat output region 710 of the perforated wall 708. Typically, the heat output region 710 is closer to the input face 613 than the heat receiving region 706. According to one explanation, the perforated flame holder body 608 may transfer heat from the heat receiving region 706 to a heat output region 710, shown in the figure as 704, by thermal radiation. According to another explanation, the perforated flame holder body 608 can transfer heat from the heat receiving region 706 to the heat output region 710 by thermal conduction along a thermal conduction path 712. The inventors contemplate that a variety of heat transfer mechanisms, including conduction, radiation, and possibly convection, may be used to transfer heat from the heat receiving area 706 to the heat output area 710. In this manner, the perforated flame holder 612 may act as a heat source to sustain the combustion reaction 702 even in cases where the combustion reaction 702 will no longer be stable when supported by a conventional flame holder.

The inventors believe that the perforated flame holder 612 causes the combustion reaction 702 to begin in a thermal boundary layer 714 formed adjacent to the wall 708 of the perforation 610. In the case of combustion, which is generally understood to include a large number of individual reactions, and since a large portion of the combustion energy is released within the perforated flame holder 612, it is apparent that at least a large portion of the individual reactions occur within the perforated flame holder 612. As the relatively cooler fuel and oxidant mixture 606 approaches the inlet face 613, the flow is divided into portions that flow through each of the perforations 610, respectively. As more and more heat is transferred to the incoming fuel and oxidant mixture 606, the hot perforated flame holder body 608 transfers heat to the fluid, particularly in the increasing thickness of the thermal boundary layer 714. Upon reaching the combustion temperature (e.g., the auto-ignition temperature of the fuel), the flow of reactants continues during the elapse of the chemical ignition delay time during which the combustion reaction 702 occurs. Thus, combustion reaction 702 is illustrated as occurring in thermal boundary layer 714. As the flow progresses, the thermal boundary layers 714 meet at a junction 716. Ideally, junction 716 is located between input face 613 and output face 614, which define the ends of perforations 610. At some point along the length of the perforations 610, the combustion reaction 702 outputs more heat to the perforated flame holder body 608 than it receives from the perforated flame holder body 608. Heat is received at the heat receiving region 706, held by the perforated flame holder body 608, and transferred to the heat output region 710 closer to the input face 613 where it is transferred to the cold reactant (and any included diluent) to bring the reactants to ignition temperature.

In one embodiment, each of the perforations 610 is characterized by a length L, which is defined as the reaction fluid propagation path length between the input face 613 and the output face 614 of the perforated flame holder 612. As used herein, the term reaction fluid refers to a substance that travels through the perforations 610. in the vicinity of the input face 613, the reaction fluid comprises a fuel and oxidant mixture 606 (optionally including nitrogen, flue gas, and/or other "non-reactive" substances.) in the combustion reaction 702 region, the reaction fluid can include a plasma associated with the combustion reaction 702, molecules of reactants and their constituent parts, any non-reactive substances, reaction intermediates (including transition states), and reaction products.

The plurality of perforations 610 may each be characterized by a transverse dimension D between opposing perforated walls 708 the inventors have found that stable combustion may be maintained in the perforated flame holder 612 if the length L of each perforation 610 is at least 4 times the transverse dimension D of the perforation, hi other embodiments, the length L may be greater than 6 times the transverse dimension D. for example, experiments have been conducted with L at least 8 times, at least 12 times, at least 16 times, and at least 24 times the transverse dimension D. preferably, the length L is long enough that the thermal boundary layer 714 forms adjacent to the perforated wall 708 in the reaction fluid flowing through the perforations 610 to converge at a convergence point 716 within the perforations 610 between the input face 613 and the output face 614 of the perforated flame holder 612. in experiments the inventors found that L/D works well (i.e., produces low NOx, produces low CO, and maintains stable combustion) when it is between 12 and 48.

The perforated flame holder body 608 may be configured to transfer heat between adjacent perforations 610. The amount of heat transferred between adjacent perforations 610 may be selected such that the heat output from the combustion reaction portion 702 in a first perforation 610 supplies heat to stabilize the combustion reaction portion 702 in the adjacent perforation 610.

Referring specifically to fig. 6, the fuel and oxidant source 102 may also include a fuel nozzle 618 configured to output a fuel and an oxidant source 620 configured to output a fluid including an oxidant. For example, the fuel nozzles 618 may be configured to output pure fuel. The oxidant source 620 may be configured to output oxygen-bearing combustion air and optionally flue gas.

The perforated flame holder 612 may be held by a flame holder support structure 622 configured to hold the perforated flame holder 612 at a dilution distance D from the fuel nozzles 618_D. The fuel nozzles 618 may be configured to emit selected fuel jets to entrain oxidant to pass through a dilution distance D between the fuel nozzles 618 and the perforated flame holder 612 as the fuel jets and oxidant follow a path_DTo the perforated flame holder 612 to form the fuel and oxidant mixture 606. Additionally or alternatively, (particularly when a blower is used to deliver oxidant contained in the combustion air), the oxidant or combustion air source 620 may be configured to entrain fuel and the fuel and oxidant mixture 606 travels through the dilution distance D_D. In some embodiments, a flue gas recirculation path 624 may be provided. Additionally or alternatively, the fuel nozzles 618 may be configured to emit selected fuel jets to travel through the dilution distance D between the fuel nozzles 618 and the input face 613 of the perforated flame holder 612 as the fuel jets travel_DAnd entrains oxidant and entrains flue gas.

The fuel nozzles 618 may be configured to emit fuel through one or more fuel orifices 626 having an inner diameter dimension referred to as a "nozzle diameter". The perforated flame holder support structure 622 may support the perforated flame holder 612 at a distance D from the fuel nozzle 618 that is greater than 20 nozzle diameters_DReceives a fuel and oxidant mixture 606. In another embodiment, the perforated flame holder 612 is disposed at a distance D from the fuel nozzle 618 that is 100 to 1100 times the nozzle diameter_DReceives a fuel and oxidant mixture 606. Preferably, the perforated flame holder support structure 622 is configured to hold the perforated flame holder 612 at a distance from the fuel nozzles 618 as a sprayAt a distance of about 200 or more times the diameter of the mouth. When the distance traveled by the fuel and oxidant mixture 606 is about 200 times the nozzle diameter or more, the fuel and oxidant mixture 606 is sufficiently homogenized so that the combustion reaction 702 produces minimal NOx.

According to one embodiment, the fuel and oxidant sources 102 may alternatively comprise premixed fuel and oxidant sources. The premix fuel and oxidant source may include a premix chamber (not shown), a fuel nozzle configured to output fuel into the premix chamber, and an oxidant (e.g., combustion air) passage configured to output oxidant into the premix chamber. A flame arrestor may be disposed between the premixed fuel and oxidant source and the perforated flame holder 612 and configured to prevent flame flashback into the premixed fuel and oxidant source.

Whether configured for entrainment in the combustion volume 604 or for premixing, the oxidant source 620 may include a blower configured to push oxidant through the fuel and oxidant sources 102.

The perforated flame holder support structure 622 may be configured to support the perforated flame holder 612, for example, from a bottom or wall (not shown) of the combustion volume 604. In another embodiment, the perforated flame holder support structure 622 supports the perforated flame holder 612 from the fuel and oxidant source 102. Alternatively, the perforated flame holder support structure 622 may suspend the perforated flame holder 612 on a top structure, such as a flame path (flow) in the case of an upward-firing system. The perforated flame holder support structure 622 can support the perforated flame holder 612 in various orientations and directions.

The perforated flame holder 612 can include a single perforated flame holder body 608. In another embodiment, the perforated flame holder 612 may include a plurality of adjacent perforated flame holder sections that collectively provide a tiled perforated flame holder 612.

The perforated flame holder support structure 622 may be configured to support a plurality of perforated flame holder sections. The perforated flame holder support structure 622 may include a metal superalloy, a cementitious material (cementations), and/or a ceramic refractory material. In one embodiment, a plurality of adjacent perforated flame holder sections may be joined by fiber reinforced refractory cement.

Perforated flame holder 612 can have a width dimension W between opposite sides of outer peripheral surface 616 that is at least 2 times a thickness dimension T between input face 613 and output face 614. In another embodiment, the perforated flame holder 612 can have a width dimension W between opposing sides of the outer peripheral surface 616 that is at least 3 times, at least 6 times, or at least 9 times a thickness dimension T between the input face 613 and the output face 614 of the perforated flame holder 612.

In one embodiment, the width dimension W of the perforated flame holder 612 may be less than the width of the combustion volume 604. This may allow the flue gas circulation path 624 from above to below the perforated flame holder 612 to be located between the outer circumferential surface 616 of the perforated flame holder 612 and the combustion volume wall (not shown).

Referring again to fig. 6 and 7, the perforations 610 may have various shapes. In one embodiment, perforations 610 may comprise elongated squares, each having a transverse dimension D between opposite sides of the square. In another embodiment, perforations 610 may comprise elongated hexagons, each having a transverse dimension D between opposite sides of the hexagon. In yet another embodiment, the perforations 610 may comprise hollow cylinders, each having a transverse dimension D corresponding to a diameter of the cylinder. In another embodiment, perforations 610 may comprise truncated cones or truncated pyramids (e.g., frustums) each having a radially symmetric transverse dimension D with respect to a length axis extending from input face 613 to output face 614. In some embodiments, the perforations 610 may each have a transverse dimension D that is equal to or greater than the quenching distance of the flame, based on standard reference conditions. Alternatively, the perforations 610 may have a transverse dimension D that is less than a standard reference quenching distance.

In one series of embodiments, each of the plurality of perforations 610 has a transverse dimension D of between 0.05 inches and 1.0 inches. Preferably, each of the plurality of perforations 610 has a transverse dimension D of between 0.1 inches and 0.5 inches. For example, the plurality of perforations 610 may each have a transverse dimension D of about 0.2 inches to 0.4 inches.

The void fraction of the perforated flame holder 612 is defined as the total volume of all perforations 610 in a section of the perforated flame holder 612 divided by the total volume of the perforated flame holder 612 including the perforated flame holder body 608 and the perforations 610. The perforated flame holder 612 should have a void fraction between 0.10 and 0.90. In one embodiment, the perforated flame holder 612 may have a void fraction of between 0.30 and 0.80. In another embodiment, the perforated flame holder 612 may have a void fraction of about 0.70. It has been found that the use of a void fraction of about 0.70 is particularly effective for producing very low NOx.

The perforated flame holder 612 may be formed from a fiber reinforced cast refractory material and/or a refractory material such as an aluminum silicate material. For example, the perforated flame holder 612 may be formed to include mullite or cordierite. Additionally or alternatively, the perforated flame holder body 608 may include a metal superalloy, such as inconel or hastelloy. The perforated flame holder body 608 can define a honeycomb structure. Honeycomb is an industry term in the art that does not necessarily refer strictly to a hexagonal cross-section and most often includes cells of square cross-section. Other cross-sectional area honeycombs are also known.

The inventors have found that the perforated flame holder 612 is commercially available from Applied Ceramics, Inc. of Dulavel, south Carolina

A ceramic honeycomb structure is formed.

Perforations 610 may be parallel to each other and perpendicular to input face 613 and output face 614. In another embodiment, perforations 610 may be formed parallel to each other and at an angle to input face 613 and output face 614. In another embodiment, perforations 610 may not be parallel to each other. In another embodiment, the perforations 610 may be non-parallel to and do not intersect with each other. In another embodiment, perforations 610 may intersect. The perforated flame holder body 608 may be unitary or may be formed from multiple sections.

In another, not necessarily preferred embodiment, the perforated flame holder 612 may be formed from a mesh ceramic material. The term "reticulated" refers to a network structure. Reticulated ceramic materials are generally made by: the slurry is dissolved in a sponge with a specific porosity, the slurry is hardened, and the sponge is burned off and the ceramic is cured.

In another, not necessarily preferred embodiment, the perforated flame holder 612 may be formed from a ceramic material that is punched, drilled, or cast to form the channels.

In another embodiment, the perforated flame holder 612 may include a plurality of tubes or pipes bundled together. The plurality of perforations 610 may comprise hollow cylinders and optionally may also comprise interstitial spaces between the bundled tubes. In one embodiment, the plurality of tubes may comprise ceramic tubes. Refractory cement may be included between the tubes and configured to bond the tubes together. In another embodiment, the plurality of tubes may comprise metal (e.g., superalloy) tubes. The plurality of tubes may be held together by a metal tensile member that surrounds the plurality of tubes and is arranged to hold the plurality of tubes together. The metallic tensile member may comprise stainless steel, superalloy wire, and/or superalloy metal strip.

The perforated flame holder body 608 may alternatively comprise a stack of sheets of perforated material, each sheet having openings that connect with the openings of the underlying sheet and the sheet that is pressed above. The perforated sheet material may comprise a perforated metal sheet material, a ceramic sheet material and/or an expanded sheet material. In another embodiment, the perforated flame holder body 608 may include discontinuous filler bodies such that perforations 610 are formed in interstitial spaces between the discontinuous filler bodies. In one example, the discontinuous filler body comprises a structured filler shape. In another example, the discontinuous filler bodies comprise random filler shapes. For example, the discontinuous packing bodies may include ceramic raschig rings, ceramic bell saddles, ceramic intalox saddles, and/or metal rings, or other shapes that may be held together by a metal cage (e.g., super raschig rings).

The inventors contemplate various explanations as to why the burner system 600 including the perforated flame holder 612 provides such clean combustion.

According to one embodiment, the perforated flame holder 612 may still act as a heat source to sustain the combustion reaction 702 even under conditions where the combustion reaction 702 would be unstable when supported by a conventional flame holder. This capability can be exploited to support combustion using leaner fuel and oxidant mixtures than are generally feasible. Thus, according to one embodiment, at the point where the fuel stream 606 contacts the input face 613 of the perforated flame holder 612, the average fuel to oxidant ratio of the fuel stream 606 is lower than the (conventional) lower combustion limit of the fuel component of the fuel stream 606-the lower combustion limit defines the lowest fuel concentration that the fuel and oxidant mixture 606 will combust when the mixture 606 is exposed to a transient ignition source at normal atmospheric pressure and at an ambient temperature of 25 ℃ (77 ° F).

It was found that the perforated flame holder 612 and the burner system 600 including the perforated flame holder 612 described herein provided substantially complete combustion of CO (from a one digit ppm down to undetectable according to experimental conditions) while supporting low NOx. According to one explanation, such performance may be achieved as thorough mixing (and other strategies) are used to reduce peak flame temperatures. The flame temperature tends to peak under slightly rich conditions, which may be evident in any diffusion flame that is not well mixed. With sufficient mixing, a homogeneous and slightly lean mixture can be achieved prior to combustion. This combination can result in a reduction in flame temperature and, therefore, a reduction in NOx formation. In one embodiment, "slightly lean" may refer to 3% O₂I.e., an equivalence ratio of about 0.87. It is possible to use even leaner mixtures, but this may lead to O₂The level increased. Further, the inventors believe that the perforated wall 708 may act as a heat sink for the combustion fluid. This effect may alternatively or additionally reduce combustion temperatures and reduce NOx.

According to another explanation, if the combustion reaction 702 occurs within a very short duration, the production of NOx may be reduced. The rapid combustion exposes the reactants (including oxygen and entrained nitrogen) to the NOx formation temperature for a time short enough that the NOx formation kinetics result in significant NOx generation. The time required for the reactants to pass through the perforated flame holder 612 is very short compared to conventional flames. Thus, the low NOx production associated with perforated flame holder combustion may be related to the shorter duration required for the reactants (and entrained nitrogen) to pass through the perforated flame holder 612.

FIG. 8 is a flow chart illustrating a method 800 for operating a combustor system including the perforated flame holder shown and described herein. To operate a burner system that includes a perforated flame holder, the perforated flame holder is first heated to a temperature sufficient to sustain combustion of the fuel and oxidant mixture.

According to a simplified description, the method 800 begins with step 802, in which a perforated flame holder is preheated to a start-up temperature T_S. After the perforated flame holder is raised to the start-up temperature, the method proceeds to step 804, where fuel and oxidant are provided to the perforated flame holder and combustion is maintained by the perforated flame holder.

According to a more detailed description, step 802 begins with step 806, wherein a start-up energy is provided to the perforated flame holder. Concurrently with or after providing the start-up energy, decision step 808 determines whether the temperature T of the perforated flame holder is equal to or greater than the start-up temperature T_S. As long as the temperature of the perforated flame holder is below its start-up temperature, the method cycles between steps 806 and 808 within the preheat step 802. In decision step 808, if the temperature T of at least one predetermined portion of the perforated flame holder is greater than or equal to the start-up temperature, the method 800 proceeds to general step 804 where fuel and oxidant are provided to the perforated flame holder and combustion is maintained by the perforated flame holder.

Step 804 may be broken down into several discrete steps, at least some of which may occur simultaneously.

Beginning at decision step 808, a fuel and oxidant mixture is provided to the perforated flame holder, as shown at step 810. For example, the fuel and oxidant may be provided by fuel and oxidant sources including separate fuel nozzles and oxidant (e.g., combustion air) sources. In this method, the fuel and oxidant are output in one or more directions selected such that the fuel and oxidant mixture is received by the input face of the perforated flame holder. The fuel may entrain combustion air (or alternatively, the combustion air may dilute the fuel) to provide a fuel and oxidant mixture at the input face of the perforated flame holder of a fuel dilution selected for a stable combustion reaction that may be maintained within the perforations of the perforated flame holder.

Proceeding to step 812, the combustion reaction is maintained by the perforated flame holder.

In step 814, heat may be output from the perforated flame holder. The heat output from the perforated flame holder can be used, for example, to power an industrial process, heat a working fluid, generate electricity, or power.

In optional step 816, the presence of combustion may be sensed. Various sensing methods have been used and are contemplated by the inventors. Generally, the combustion maintained by the perforated flame holder is very stable and there are no unusual sensing requirements for the system. Combustion sensing may be performed using infrared sensors, video sensors, ultraviolet sensors, charged species sensors, thermocouples, thermopiles, flame rods, and/or other combustion sensing devices. In an additional or alternative variation of step 816, if combustion is extinguished in the perforated flame holder, a pilot flame or other ignition source may be provided to ignite the fuel and oxidant mixture.

Proceeding to decision step 818, if combustion instability is sensed, the method 800 may exit to step 824 where an error handling routine is executed. For example, the error handling routine may include shutting off fuel flow, re-performing the preheating step 802, outputting an alarm signal, igniting a backup combustion system, or other steps. If it is determined in step 818 that combustion in the perforated flame holder is stable, the method 800 proceeds to decision step 820, where it is determined whether the combustion parameters should be changed. If there are no combustion parameters to change, the method loops (within step 804) back to step 810 and continues the combustion process. If a change in the combustion parameter is indicated, the method 800 proceeds to step 822, where a combustion parameter change is performed. After the combustion parameters are changed, the method loops (within step 804) back to step 810 and combustion continues.

For example, if a change in heat demand is encountered, the combustion parameters may be scheduled to change. For example, if less heat is required (e.g., due to reduced power requirements, or reduced industrial process throughput), the fuel and oxidant flow rates may be reduced in step 822. Conversely, if the heat demand increases, the fuel and oxidant flow rates may be increased. Additionally or alternatively, if the combustion system is in a start-up mode, the fuel and oxidant flow rates may be gradually increased to the perforated flame holder in one or more iterations of the cycle within step 804.

Referring again to fig. 6, the burner system 600 includes a heater 628 operatively coupled to the perforated flame holder 612. As described in connection with fig. 7 and 8, the perforated flame holder 612 operates by outputting heat to the incoming fuel and oxidant mixture 606. After combustion is established, the heat is provided by combustion reaction 702; but prior to combustion being established, the heat is provided by heater 628.

Various heating devices have been used and are contemplated by the inventors. In some embodiments, the heater 628 may include a flame holder configured to support a flame disposed to heat the perforated flame holder 612. The fuel and oxidant source 102 may include a fuel nozzle 618 configured to emit a fuel stream 606 and an oxidant source 620 configured to output an oxidant (e.g., combustion air) adjacent to the fuel stream 606. The fuel nozzles 618 and the oxidant source 620 may be configured to output a fuel stream 606 to be gradually diluted by an oxidant (e.g., combustion air). The perforated flame holder 612 may be configured to receive the diluted fuel and oxidant mixture 606, which supports a combustion reaction 702 that is held by the perforated flame holder 612 when the perforated flame holder 612 is at an operating temperature. In contrast, the start-up flame holder may be configured to support a start-up flame that is stable without stabilization provided by the heated perforated flame holder 612 at a location corresponding to a relatively unmixed fuel and oxidant mixture.

The burner system 600 may also include a controller 630 operatively coupled to the heater 628 and the data interface 632. For example, the controller 630 may be configured to control a start-up flame holder actuator configured to cause the start-up flame holder to hold a start-up flame when the perforated flame holder 612 needs to be preheated and to be at an operating temperature when the perforated flame holder 612 is at an operating temperature (e.g., when T ≧ T_STime) does not maintain a start-up flame.

Various methods for actuating the start-up flame are contemplated. In one embodiment, the start-up flame holder includes a mechanically actuated bluff body configured to be actuated to intercept the fuel and oxidant mixture 606 to cause thermal regeneration and/or stabilize a vortex flow, thereby holding the start-up flame; or actuated to not intercept the fuel and oxidant mixture 606 and thereby cause the fuel and oxidant mixture 606 to travel to the perforated flame holder 612. In another embodiment, a fuel control valve, blower, and/or damper may be used to select a fuel and oxidant mixture 606 flow rate that is low enough to stabilize the start-up flame injection; and after the perforated flame holder 612 reaches an operating temperature, the flow rate may be increased to "blow out" the start-up flame. In another embodiment, the heater 628 may include a power source operatively coupled to the controller 630 and configured to apply an electrical charge or voltage to the fuel and oxidant mixture 606. The conductive start-up flame holder may be selectively coupled to a ground voltage or other voltage selected to attract charge in the fuel and oxidant mixture 606. The inventors found that the charge attraction results in a start-up flame to be held by the electrically conductive start-up flame holder.

In another embodiment, the heater 628 may comprise a resistive heater configured to output heat to the perforated flame holder 612 and/or to the fuel and oxidant mixture 606. The resistive heater 628 may be configured to heat the perforated flame holder 612 to an operating temperature. The heater 628 may also include a power source and a switch operable under the control of the controller 630 to selectively couple the power source to the resistive heater 628.

The resistive heater 628 may be formed in various ways. For example, the resistive heater 628 may be comprised of

Wire (commercially available from Sandvik Materials Technology division of Sandvik AB of Hallstahammar, Sweden),

the wire passes through at least a portion of the perforations 610 defined by the perforated flame holder body 608. Alternatively, heater 628 may include an induction heater, a high energy beam heater (e.g., microwave or laser), a friction heater, a resistive ceramic coating, or other type of heating technique.

Other forms of activation means are envisaged. For example, the heater 628 may include an electric discharge (e.g., spark) igniter or a hot surface igniter configured to output a pulsed ignition to the oxidant and the fuel. Additionally or alternatively, the starting means may comprise a pilot flame device arranged to ignite the fuel and oxidant mixture 606 that would otherwise enter the perforated flame holder 612. The discharge igniter, hot surface igniter, and/or pilot flame device are operably coupled to a controller 630 that can cause the discharge igniter or pilot flame device to maintain combustion of the fuel and oxidant mixture 606 in or upstream of the perforated flame holder 612 before the perforated flame holder 612 is sufficiently heated to maintain combustion.

According to one embodiment, the pilot flame device may comprise at least one fuel nozzle disposed at or near a distal location along the fuel and combustion air flow axis. For example, at least one fuel nozzle of the start-up flame device may be disposed proximate (e.g., just upstream of) a flame holder (e.g., perforated flame holder 612) to support a pilot flame.

According to one embodiment, the pilot flame starting apparatus may include at least one main fuel nozzle disposed at a distal location along the fuel and combustion air flow axis. The main fuel nozzle may be configured to support a pilot flame. A secondary fuel nozzle disposed at a proximal location along the fuel and combustion air flow axis may be configured to simultaneously or subsequently support a secondary flame in contact with the pilot flame, which may be ignited by the pilot flame at least once.

According to one embodiment, the burner system 600 may include a secondary fuel source disposed at a proximal location along a flow axis of the furnace, a primary fuel nozzle disposed at an intermediate distance along the flow axis, and a perforated flame holder disposed at a distal location along the flow axis. The primary fuel nozzle may be configured to support a primary flame to heat a flame holder (e.g., perforated flame holder 612). The secondary fuel source may be configured to provide the secondary fuel to the flame holder after the perforated flame holder is at least partially heated. The flame holder may be configured to hold at least a portion of a combustion reaction supported by a secondary fuel.

The combustor system 600 may also include a sensor 634 operatively coupled to the controller 630. The sensors 634 may include thermal sensors configured to detect infrared radiation or temperature of the perforated flame holder 612. The control circuit 630 may be configured to control the heater 628 in response to input from a sensor 634. Optionally, a fuel control valve 636 may be operatively coupled to the controller 630 and configured to control the flow of fuel to the fuel and oxidant source 102. Additionally or alternatively, the oxidant blower or damper 638 may be operatively coupled to the controller 630 and configured to control the flow of oxidant (or combustion air).

The sensors 634 may also include a combustion sensor operatively coupled to the control circuitry 630, the combustion sensor 634 being configured to detect temperature, video images, and/or spectral characteristics of the combustion reaction 702 held by the perforated flame holder 612. The fuel control valve 636 may be configured to control the flow of fuel from the fuel source to the fuel and oxidant source 102. The controller 630 may be configured to control the fuel control valve 636 in response to input from the combustion sensor 634. The controller 630 may be configured to control the fuel control valve 636 and/or the oxidant blower or damper 638 to control the preheat flame type of the heater 628 to preheat the perforated flame holder 612 to an operating temperature. The controller 630 may similarly control the fuel control valve 636 and/or the oxidant blower or damper 638 to vary the flow of the fuel and oxidant mixture 606 in response to changes in heat demand received as data via the data interface 632.

FIG. 9A is a simplified perspective view of a combustion system 900 according to an embodiment, the combustion system 900 including another alternative perforated flame holder 612. According to one embodiment, the perforated flame holder 612 is a mesh ceramic perforated flame holder. FIG. 9B is a side cross-sectional view of a portion of the reticulated ceramic perforated flame holder 612 of FIG. 9A, according to an embodiment. According to one embodiment, the perforated flame holder 612 of fig. 9A, 9B may be implemented in various combustion systems described herein. The perforated flame holder 612 is configured to support a combustion reaction (e.g., the combustion reaction 702 of fig. 7) of the fuel and oxidant mixture 606 received from the fuel and oxidant source 102 at least partially within the perforated flame holder 612. According to one embodiment, the perforated flame holder 612 may be configured to support a combustion reaction of the fuel and oxidant mixture 606 upstream, downstream, inside, and near the mesh ceramic perforated flame holder 612.

According to one embodiment, the perforated flame holder body 608 may include mesh fibers 939. The mesh fibers 939 can define branched perforations 610, the branched perforations 610 being woven around and through the mesh fibers 939. According to one embodiment, the perforations 610 are formed as passages between the mesh fibers 939.

According to one embodiment, the reticulated fibers 939 are formed as a reticulated ceramic foam. According to one embodiment, the reticulated fibers 939 are formed using reticulated polymer foam as a template. According to one embodiment, the mesh fibers 939 can comprise aluminum silicate. According to one embodiment, the reticulated fibers 939 may be formed from extruded mullite or cordierite. According to one embodiment, the mesh fibers 939 can comprise zirconia. According to one embodiment, the mesh fibers 939 can comprise silicon carbide.

The term "network fiber" refers to a network structure. According to one embodiment, the mesh fibers 939 are formed of an extruded ceramic material. In the reticulated fiber embodiment, the interaction between the fuel and oxidant mixture 606, the combustion reaction, and the heat transfer into and out of the perforated flame holder body 608 may function similar to the embodiments shown and described above with respect to fig. 6-8. One difference in action is the intermingling between the perforations 610 because the mesh fibers 939 form a discontinuous perforated flame holder body 608 that allows flow back and forth between adjacent perforations 610.

According to one embodiment, the network of mesh fibers 939 is sufficiently open to the downstream mesh fibers 939 to emit radiation for the upstream mesh fibers 939 to receive for the purpose of heating the upstream mesh fibers 939 sufficiently to maintain combustion of the fuel and oxidant mixture 606. The thermal conduction paths between the mesh fibers 939 (e.g., the thermal conduction paths 712 in fig. 7) are reduced due to the separation of the mesh fibers 939 as compared to the continuous perforated flame holder body 608. This may result in relatively more heat being transferred from the heat-receiving region or zone (e.g., heat-receiving region 706 in fig. 7) to the heat-output region or zone (e.g., heat-output region 710 in fig. 7) of the mesh fibers 939 by thermal radiation (as indicated by element 704 in fig. 7).

According to one embodiment, individual perforations 610 may extend between input face 613 and output face 614 of perforated flame holder 612 perforations 610 may have different lengths L according to one embodiment, individual perforations 610 are not clearly defined by length L because perforations 610 branch into and out of each other.

According to one embodiment, perforated flame holder 612 is configured to support or hold a combustion reaction (see element 702 of FIG. 7) or flame at least partially between input face 613 and output face 614. According to one embodiment, the input face 613 corresponds to a surface of the perforated flame holder 612 that is proximate to the fuel nozzles 618, or to a surface that first receives fuel. According to one embodiment, the input face 613 corresponds to the extent of the mesh fibers 939 proximate to the fuel nozzles 618. According to one embodiment, output face 614 corresponds to a surface remote from fuel nozzles 618, or to a surface opposite input face 613. According to one embodiment, the input face 613 corresponds to an extent of the mesh fibers 939 away from the fuel nozzles 618, or an extent of the mesh fibers 939 opposite the input face 613.

According to one embodiment, the formation of thermal boundary layer 714, heat transfer between perforated flame holder body 608 and the gas flowing through perforations 610, characteristic perforation width dimension D, and length L may all be considered to be related to an average or overall path through perforated reaction holder 612_RHSlightly longer. According to one embodiment, the void fraction (expressed as (total perforated reaction holder 612 volume-mesh fibers 939 volume)/total volume) is about 70%.

According to one embodiment, the mesh ceramic perforated flame holder 612 is approximately a 1 "× 4" × 4 "brick according to one embodiment, the mesh ceramic perforated flame holder 612 includes approximately 10 holes per square, meaning that a line across the surface of the mesh ceramic perforated flame holder 612 will pass through approximately 10 holes.

According to one embodiment, the reticulated ceramic perforated flame holder 612 may include shapes and dimensions other than those described herein. For example, the perforated flame holder 612 may comprise reticulated ceramic tiles of greater or lesser dimensions than those described above. Further, the mesh ceramic perforated flame holder 612 may include a shape other than a generally rectangular parallelepiped shape.

According to one embodiment, the reticulated ceramic perforated flame holder 612 may comprise a plurality of reticulated ceramic tiles. A plurality of reticulated ceramic tiles may be joined together such that each tile is in direct contact with one or more adjacent reticulated ceramic tiles. A plurality of reticulated ceramic tiles may collectively form a single perforated flame holder 612. Alternatively, each reticulated ceramic tile may be considered a different perforated flame holder 612.

According to one embodiment, at least a portion of one or more bluff bodies 404 comprise one or more non-perforated flame holders 612.

Referring to fig. 5A and 5B, the frame 402 may include a latch 502, the latch 502 configured to press the frame 402 against the inner wall or surface 206 of the combustion volume wall 104. The frame 402 may be held by gravity (weight), pressure, and/or friction against the combustion volume wall 104. In one embodiment, the frame 402 is held in place by gravity (weight), positioning, pressing, and/or friction against the inner wall or surface of the combustion conduit.

According to one embodiment, the latch 502 may include: a moveable coupler 504 supported at a first end 506 of the frame 402; a bushing 507 coupled to the movable coupler 504; a lever 508 rotatably engaged with the bushing 507; and a boss 510 supported at a second end 512 of the frame 402 and rotatably engaged with the lever 508. When in the compressed state, the geometry of the latch 502 may provide an over-center (over-center) stable coupling to the ends 506, 512 of the frame 402. In one embodiment, the frame 402 is at least partially formed of high temperature steel. In another embodiment, the frame 402 is at least partially formed of stainless steel. Additionally and/or alternatively, the frame 402 is at least partially formed of ceramic. In another embodiment, the frame 402 is formed at least in part from silicon carbide. In yet another embodiment, the frame 402 is formed at least in part from zirconium.

Figure 10 illustrates several variations 1000 of the bluff body 404 of figure 4 supported individually and in combination, according to one embodiment.

According to one embodiment, the combustion conduit 104 is characterized by a cross-sectional area, and the frame 402 and the one or more bluff bodies 404 subtend less than the entire cross-sectional area. In one embodiment, the frame 402 and the one or more bluff bodies 404 supported by the frame 402 comprise a single frame 402 supporting a plurality of bluff body tiles 404. In another embodiment, the frame 402 and the one or more bluff bodies 404 supported by the frame 402 comprise a plurality of frames 402 supporting a respective plurality of bluff body bricks 404, each frame 402 disposed at a different respective distance from the fuel and the pilot of the combustion air source 102.

According to one embodiment, the fuel and combustion air source 102 includes an auxiliary fuel source and is configured to output auxiliary fuel and combustion air into the combustion conduit 104. In one embodiment, the combustion volume wall 104 defines a lateral extent of the combustion volume 106 and is disposed to separate the combustion volume 106 from the water and steam volume 108. According to one embodiment, the combustion system further includes a mixing tube 110, the mixing tube 110 aligned to receive the secondary fuel and combustion air from the fuel and combustion air source 102. The mixing tube 110 may be spaced apart from the combustion volume wall 104 by a spacing volume 116. In a boiler, the combustion volume walls 104 may comprise combustion tubes 104. According to one embodiment, the bluff body 404 is aligned to receive a mixture of the secondary fuel and combustion air from the outlet end 114 of the mixing tube 110. The bluff body 404 may be configured to maintain a combustion reaction to heat the combustion conduit 104. The combustion conduit 104 may be configured to heat water in the water and steam volume 108.

Referring again to fig. 1, 2 and 3, according to one embodiment, the fuel and combustion air source 102 includes: a fuel riser tube 332 extending to a tip 334; a main combustion air plenum 306 comprising walls disposed about the fuel risers 332 and defining a main combustion air plenum chamber 304; and a variable swirler 302 disposed to controllably swirl the primary combustion air at any of two or more different rotational velocities, at least at a location corresponding to the tip 334 of the fuel riser 332.

According to one embodiment, the fuel and combustion air source 102 is operable to support a pilot flame extending from an end of the main combustion air plenum 306 proximate the fuel riser tip 334 in the first mode or to supply combustion air to the blunt flame holder 112 without supporting a pilot flame in the second mode.

According to one embodiment, the secondary fuel source includes one or more secondary fuel nozzles 416 disposed remotely from the output end 414 of the main combustion air plenum 306.

According to one embodiment, the fuel riser tip 334 may form a fuel dump plane at a distal location that is at least 100 secondary fuel nozzle diameters away from the secondary fuel nozzles 416.

According to one embodiment, the fuel and combustion air source 102 includes a secondary combustion air plenum 322, the secondary combustion air plenum 322 configured to output secondary combustion air 305 independently of the output of the primary combustion air 303.

According to one embodiment, the walls of the main combustion air plenum 306 form a tapered region at the outlet end of the main combustion air plenum 306 near the tip 334 of the fuel riser 332.

Referring again to fig. 1, 2 and 3, the fuel and combustion air source 102 for the combustor may include: a fuel riser tube 332 extending to a tip 334; a wall of the main combustion air plenum 306 disposed about the fuel riser tube 332 and defining the main combustion air plenum chamber 304, and a variable swirler 302 disposed to controllably cause swirling of the main combustion air 303 at any of two or more different rotational velocities at least at a location corresponding to a tip 334 of the fuel riser tube 332. In one embodiment, the walls of the main combustion air plenum 306 form a tapered region 336 at the outlet end of the main combustion air plenum 306 near the tip 334 of the fuel riser 332. The tapered region may include a variable diameter region 336 and a constant diameter region 338. In one embodiment, the fuel risers 332 provide fuel orifices 310 at the tip 334. In another embodiment, the fuel risers 332 provide the fuel orifices 312 at a primary fuel output location disposed between the base 410 of the fuel risers 332 and the tip 334 of the fuel risers 332.

According to one embodiment, the fuel and air source for the burner may further include a lobe mixer 412 disposed near the tip 334 of the fuel riser 332. In one embodiment, a lobe mixer 412 is coupled to one end of the main combustion air plenum 306.

According to one embodiment, the variable swirler 302 may include a plurality of actuatable fixed position vanes that are collectively rotatable to at least two different angles. In another embodiment, the variable swirler 302 may include an air duct that forms a tangential main combustion air damper. In one embodiment, the variable swirler 302 is disposed within a wall of the main combustion air plenum 306, radially to the fuel riser 332.

According to one embodiment, the fuel and air source for the burner is operable to support a pilot flame extending from an end 414 of the main combustion air plenum 306 proximate to an end of the fuel riser tip 334 in the first mode or to supply combustion air to the bluff body flame holder 112 without supporting a pilot flame in the second mode.

According to one embodiment, the fuel and air source 102 for the combustor may also include one or more secondary fuel nozzles 416 disposed remotely from the output 414 of the main combustion air plenum 306.

According to one embodiment, the fuel and air source 102 for the burner may further include a secondary combustion air plenum 322, the secondary combustion air plenum 322 configured to output secondary combustion air independently of the output of the primary combustion air 303.

According to one embodiment, the fuel and air source 102 for the combustor may further include a flare 204 and a mixing tube 110, the flare 204 being configured to receive the air and fuel and the extracted flue gas stream from the air and fuel source 102, the mixing tube 110 being operably coupled to the flare 204. The mixing tube 110 may be operable to intermittently mix air and fuel and receive heat from the intermittently supported flame. The fuel and air source 102 for the burner may include a flame holder configured to intermittently receive heat from the flame, receive the fuel and air flow, and respectively raise the temperature and hold a second flame. In one embodiment, the flame holder is a bluff body flame holder 112. In one embodiment, the bluff body flame holder 112 may include one or more bluff bodies. In another embodiment, the bluff body flame holder 112 may be configured to output heat and conform to a second flame. The combustion volume wall 104 may include combustion conduits 104. The combustion conduit 104 may be configured to heat water in the water and steam volume 108. In another embodiment, the bluff body flame holder 112 may include a frame 402, the frame 402 configured to be held in the combustion volume 106 by gravity. Additionally or alternatively, the bluff body flame holder 112 may include one or more bluff bodies 404 supported by a frame 402.

According to one embodiment, the output 414 of the main combustion air plenum 306 is configured to hold the flame at a high rotational velocity of the air and fuel mixture and to allow the air and fuel to pass through without holding the flame at a low rotational velocity of the air and fuel mixture.

Fig. 11 is a flow diagram of a method 1100 of operating an open flame heater according to an embodiment.

According to one embodiment, a method 1100 of operating an open flame heater includes, in step 1102, outputting fuel and combustion air from a fuel and combustion air source into a combustion conduit, the combustion conduit defining a lateral extent of a combustion volume. The combustion conduit may be arranged to separate the combustion volume from the water and steam volume. Step 1104 includes receiving fuel and combustion air from a fuel and combustion air source in a mixing tube aligned to receive fuel and combustion air from the fuel and combustion air source. The mixing tube may be spaced apart from the combustion conduit by a spacing volume. Step 1106 includes receiving a mixture of fuel and combustion air from the mixing tube outlet end in the bluff body flame holder. Step 1108 includes maintaining a combustion reaction of the fuel and combustion air with the bluff body flame holder. Step 1110 includes heating the combustion conduit using a combustion reaction, and step 1112 includes heating the water in the water and steam volume using the combustion conduit.

FIG. 12 is a flow chart illustrating a method 1200 of operating a combustion system according to an embodiment.

According to one embodiment, the method 1200 includes, in step 1202, suspending a frame from an inner surface of a combustion conduit. Step 1204 includes supporting one or more refractory bluff bodies with a frame. Step 1206 includes selectively supporting a pilot flame with the pilot. Step 1208 includes, when a pilot flame is present, heating one or more refractory bluff bodies with the pilot flame. Step 1210 includes supplying a secondary fuel to the one or more refractory bluff bodies using a secondary fuel source, and step 1212 includes maintaining a combustion reaction of the secondary fuel with combustion air using the one or more refractory bluff bodies.

FIG. 13 is a flow chart illustrating a method 1300 of operating a fuel and air source for a combustor, according to an embodiment.

According to one embodiment, a method 1300 of operating a fuel and air source for a combustor includes, in step 1302, outputting primary fuel from a fuel riser tube extending to a tip. Step 1304 includes providing the main combustion air to a main combustion air plenum chamber defined by a wall of the main combustion air plenum disposed about the fuel riser and defining the main combustion air plenum chamber. Step 1306 includes swirling the primary combustion air with the variable swirler at any of two or more different rotational speeds, at least at a location corresponding to a tip of the fuel riser. In one embodiment, in step 1304, the walls of the main combustion air plenum form a tapered region at the outlet end of the main combustion air plenum proximate the tip of the fuel riser.

According to one embodiment, in one embodiment, the frame is configured to hold a flame holder. In one example, the frame may comprise a hexagon, wherein three or more sets of tracks are coupled to an inner surface of the frame. Each set of tracks comprises one track on a first plane of the hexagonal inner surface and a second track on a second plane directly opposite the first plane. Each set of tracks may accommodate one bluff body brick. Thus, the flame holder may be a bluff body flame holder.

According to one embodiment, the bluff body flame holder comprises one or more solid refractory bodies arranged at a distance from the mixing tube to receive the mixed fuel, air and flue gas.

According to one embodiment, the one or more refractory bluff bodies comprise solid ceramic tiles substantially impermeable to combustion air, the solid ceramic tiles configured to prevent combustion within the ceramic tiles.

In one embodiment, the one or more refractory bluff bodies are configured to provide a vortex recirculation heat and a vortex recirculation mass flow of the combustion fluid to maintain the combustion reaction in one or more regions upstream, downstream, and/or surrounding the one or more refractory bluff bodies. Additionally or alternatively, the one or more refractory bluff bodies comprise a plurality of refractory bluff bodies configured to maintain a combustion reaction between the plurality of refractory bluff bodies.

In one embodiment, the bluff body flame holder comprises zirconium. In another embodiment, the blunt flame holder comprises aluminum silicate. Additionally or alternatively, the bluff body flame holder comprises silicon carbide. In one embodiment, the bluff body comprises mullite. In another embodiment, the bluff body comprises cordierite.

According to one embodiment, the one or more refractory bluff bodies comprise a plurality of refractory bricks having a thickness, a width, and a length, the thickness being no more than 40% of the lesser of the width and the length.

In one embodiment, the thickness of the plurality of refractory bricks is no more than 30% of the lesser of the width and the length. The thickness of the plurality of refractory bricks may be no more than 20% of the lesser of the width and the length.

According to one embodiment, at least one of the plurality of refractory bricks is a perforated refractory brick capable of supporting combustion within the brick perforations. The inventors have discovered that presenting a narrow thickness plane or combination of thickness planes (e.g., two planes, each at a 45 degree angle to the fluid flow) to the fluid flow may provide higher ignition capabilities than other orientations.

According to one embodiment, at least one of the plurality of refractory bricks is a solid refractory brick capable of inhibiting combustion within the brick. According to one embodiment, at least one of the refractory bricks is a perforated brick. The perforated tiles may comprise reticulated ceramic perforated tiles. The frame may house a combination of solid refractory bricks and perforated ceramic tiles. The inventors contemplate that the combination of solid and perforated bricks may provide the desired performance characteristics. Different numbers of bricks may similarly exhibit desired performance characteristics. For example, in one embodiment, the inventors omit the center tile and retain the other two tiles shown.

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

Claims (115)

1. An open flame heater comprising:

a fuel and combustion air source configured to output fuel and combustion air into a combustion volume, the combustion volume including a combustion volume wall defining a lateral extent separated from an external volume;

a mixing tube aligned to receive fuel and combustion air from the fuel and combustion air source, the mixing tube spaced from the combustion volume wall by a spacing volume; and

a bluff body flame holder aligned to receive a mixture of fuel and combustion air from the outlet end of the mixing tube, the bluff body flame holder configured to hold a combustion reaction to heat the combustion volume wall, wherein the combustion volume wall is configured to heat a thermal load of a volume of heat.

2. The open flame heater of claim 1, wherein the open flame heater comprises a boiler heater; and

wherein the combustion volume wall comprises a combustion conduit defining a lateral extent of the combustion volume, the combustion conduit being arranged to separate the combustion volume from a water and steam volume.

3. The boiler heater according to claim 2, wherein the combustion conduit is configured to be kept cool by water in the water and steam volume; and

wherein the mixing tube is configured to be kept warm by the combustion reaction and flue gas;

whereby the cooling temperature of the combustion conduit is configured to draw flue gas resulting from the combustion reaction from a region proximate the bluff body flame holder toward the inlet end of the mixing conduit; and

wherein the flue gas is introduced into the mixing tube by a flow of fuel and combustion air output by the fuel and combustion air source.

4. The open flame heater of claim 1, wherein the spacing volume comprises an annular volume between the mixing tube and the combustion volume wall.

5. The open flame heater of claim 1, wherein a separation volume defined by the mixing tube and the combustion volume wall is configured to carry flue gas for recirculation.

6. The open flame heater according to claim 1, wherein the mixing tube further comprises an inlet end spaced from the fuel and combustion air source.

7. The open flame heater according to claim 1, wherein the inlet end of the mixing tube comprises a flare that tapers inwardly away from the fuel and combustion air source toward a cylindrical region of the mixing tube.

8. The open flame heater according to claim 1, wherein the inlet end of the mixing tube comprises a bell mouth arranged to direct flue gas passing through the annular volume from an outlet end of the mixing tube to an inlet end of the mixing tube.

9. The open flame heater of claim 1, wherein an inner surface of the combustion volume wall comprises a refractory material.

10. The open flame heater of claim 1, wherein the mixing tube is configured such that combustion air, fuel and flue gas mix while flowing through the mixing tube to form a lean air and fuel mixture for supporting the combustion reaction.

11. The open flame heater of claim 1, wherein the fuel and combustion air source is configured to selectively hold a pilot flame.

12. The open flame heater of claim 1, further comprising a pilot flame arrangement disposed distal to the source of fuel and combustion air, the pilot flame arrangement being proximate upstream of the bluff flame holder, the pilot flame arrangement including at least a pilot fuel nozzle configured to selectively hold a pilot flame.

13. The open flame heater of claim 12, wherein the source of fuel and combustion air comprises the pilot flame device.

14. The open flame heater of claim 12, wherein the pilot flame device is configured to selectively receive fuel and air from the fuel and combustion air source.

15. The open flame heater of claim 12, wherein the pilot flame device comprises at least one of a pilot fuel source and a pilot oxidant source.

16. The open flame heater of claim 12, wherein the pilot flame is configured to ignite a flow of fuel and air from the fuel and combustion air source to provide a combustion reaction for heating the combustion volume wall.

17. The open flame heater of claim 16, wherein the combustion reaction for heating the combustion volume wall provides a heat output at least 10 times the heat output of the pilot flame when the open flame heater is operating at a rated heat output.

18. The open flame heater of claim 12, further comprising an igniter disposed proximate the pilot flame device and configured to ignite the pilot flame.

19. The open flame heater of claim 11, wherein the source of fuel and combustion air comprises a controllable swirler configured to selectively impart a swirling motion to primary combustion air flowing within a primary combustion air plenum; and

wherein the fuel and combustion air source is configured to selectively maintain the pilot flame when the controllable swirler selectively imparts a swirling motion to the main combustion air.

20. The open flame heater of claim 11, wherein the source of fuel and combustion air comprises:

a main combustion air plenum;

a first fuel circuit configured to selectively output a main fuel to one or more locations within the main combustion air plenum; and

a second fuel circuit configured to selectively output a secondary fuel through a plurality of fuel risers disposed outside the main combustion air plenum.

21. The open flame heater of claim 20, wherein the fuel and combustion air source is configured to supply fuel and combustion air to the bluff flame holder when the first fuel circuit is stopped and when the second fuel circuit is open; and

wherein the fuel and combustion air source is configured to support the pilot flame when the first fuel circuit is open and the second fuel circuit is closed.

22. The open flame heater of claim 11, wherein the pilot flame is configured to heat the bluff flame holder to an operating temperature while the fuel and combustion air source holds the pilot flame.

23. The open flame heater of claim 11, wherein the fuel and combustion air source is configured to output the fuel and combustion air through the mixing tube to the bluff flame holder when the fuel and combustion air source is not holding the pilot flame.

24. The open flame heater of claim 1, wherein the source of fuel and combustion air comprises a first combustion air damper configured to control the flow of main combustion air through the main combustion air plenum.

25. The open flame heater of claim 1, wherein the source of fuel and combustion air comprises a second combustion air damper configured to control auxiliary combustion air through an auxiliary combustion air plenum.

26. The open flame heater according to claim 1, further comprising:

a burner controller configured to control at least one selected from the group consisting of: an actuator operably coupled to the variable swirler, the first fuel circuit, the second fuel circuit, the first combustion air damper, the second combustion air damper, and an igniter.

27. The open flame heater of claim 26, wherein the burner controller is operably coupled to a combustion sensor.

28. The open flame heater of claim 1, further comprising a frame configured to hang from an inner surface of the combustion volume wall.

29. The open flame heater of claim 28, wherein the frame is configured to support the bluff flame holder within the combustion volume wall.

30. The open flame heater of claim 29, wherein the bluff body flame holder comprises one or more perforated flame holders.

31. The open flame heater of claim 30, wherein the one or more perforated flame holders comprise a mesh ceramic perforated flame holder.

32. The open flame heater of claim 29, wherein the bluff body flame holder comprises two or more bluff bodies.

33. The open flame heater of claim 32, wherein the frame and the two or more bluff bodies supported by the frame comprise a plurality of frames supporting a respective plurality of bluff body bricks, each frame disposed at a different respective distance from the fuel and combustion air sources.

34. The open flame heater of claim 33, wherein the frame and the two or more bluff bodies supported by the frame comprise a single frame supporting a plurality of bluff body bricks.

35. The open flame heater of claim 29, wherein the bluff body flame holder is a refractory material.

36. The open flame heater of claim 32, wherein the frame and the two or more bluff bodies supported by the frame comprise a plurality of frames supporting the respective plurality of bluff body bricks, each frame disposed at a different respective distance from a pilot of the fuel and combustion air source.

37. The open flame heater of claim 1, wherein the fuel and combustion air source comprises:

a fuel riser tube extending to a tip;

the main combustion air plenum including a wall disposed about the fuel riser and defining a main combustion air plenum chamber; and

the variable swirler being configured to controllably swirl the primary combustion air at any one of two or more different rotational velocities at least at a location corresponding to a tip of the fuel riser.

38. The open flame heater of claim 37, wherein the wall of the main combustion air plenum forms a tapered region at an outlet end of the main combustion air plenum proximate the tip of the fuel riser.

39. The open flame heater of claim 1, wherein the fuel and combustion air source comprises a lobe mixer arranged to increase radial mixing of fuel, air and flue gas recirculated from the combustion reaction.

40. The open flame heater of claim 1, wherein the bluff body flame holder comprises:

one or more solid refractory bodies disposed a distance from the mixing tube to receive the mixed fuel, air and flue gas.

41. A combustion system, comprising:

a frame configured to be mounted on an inner surface of a combustion volume wall;

one or more bluff bodies supported by the frame;

a pilot configured to selectively support a pilot flame for heating the one or more bluff bodies; and

a secondary fuel source configured to supply a secondary fuel to a combustion reaction held by the one or more bluff bodies.

42. The combustion system of claim 41, wherein the auxiliary fuel source is actuatable to supply auxiliary fuel when the pilot burner is selected to not support the pilot flame.

43. The combustion system of claim 41, wherein the one or more bluff bodies comprise solid ceramic tiles substantially impermeable to combustion air, the solid ceramic tiles configured to prevent combustion within the ceramic tiles.

44. The combustion system of claim 43, wherein the one or more bluff bodies are configured to provide a vortex recirculation heat and a vortex recirculation mass flow of a combustion fluid to maintain the combustion reaction in one or more regions upstream, downstream, and/or surrounding the one or more bluff bodies.

45. The combustion system of claim 44, wherein the one or more bluff bodies include a plurality of refractory bluff bodies configured to maintain a combustion reaction therebetween.

46. The combustion system of claim 43, wherein the bluff body flame holder comprises at least one of zirconium, aluminum silicate, silicon carbide, mullite, and cordierite.

47. The combustion system of claim 41, wherein at least a portion of the one or more bluff bodies includes one or more perforated flame holders.

48. The combustion system of claim 47, wherein the one or more perforated flame holders are configured to support combustion reactions of fuel and oxidant upstream, downstream, and within the perforated flame holders.

49. The combustion system of claim 47, wherein the perforated flame holder is a reticulated ceramic perforated flame holder.

50. The combustion system of claim 49, wherein the perforated flame holder includes a plurality of mesh fibers.

51. The combustion system of claim 50, wherein the perforated flame holder includes at least one of zirconium, aluminum silicate, silicon carbide, mullite, and cordierite.

52. The combustion system of claim 50, wherein the perforated flame holder includes about 10 holes per inch across the surface.

53. The combustion system of claim 50, wherein the reticulated fibers are formed as a reticulated ceramic foam.

54. The combustion system of claim 50, wherein the reticulated fibers are formed using reticulated polymer foam as a template.

55. The combustion system of claim 50, wherein the perforated flame holder includes:

an input face;

an output face; and

a plurality of perforations extending between the input face and the output face.

56. The combustion system of claim 55, wherein the perforations are formed as passages between the mesh fibers.

57. The combustion system of claim 56, wherein the perforations are branched perforations.

58. The combustion system of claim 56, wherein the perforations extend between the input face and the output face.

59. The combustion system of claim 55, wherein the input face corresponds to an extent of the reticulated fibers proximate to a fuel nozzle.

60. The combustion system of claim 59, wherein the output face corresponds to an extent of the mesh fibers away from the fuel nozzle.

61. The combustion system of claim 49, wherein the perforated flame holder is configured to support at least a portion of a combustion reaction within the perforated flame holder between the input face and the output face.

62. The combustion system of claim 41, wherein at least a portion of the one or more bluff bodies include one or more non-perforated flame holders.

63. The combustion system of claim 41, wherein the frame is held in place by at least one of weight, pressure, and friction against the combustion volume wall.

64. The combustion system of claim 63, wherein the frame includes a latch configured to press the frame against an inner wall or surface of the combustion volume wall;

wherein the latch comprises:

a movable coupling supported at a first end of the frame;

a bushing coupled to the movable coupler;

a lever rotatably engaged with the bushing; and

a boss supported at the second end of the frame and rotatably engaged with the lever.

65. The combustion system of claim 63, wherein the latch geometry provides an over-center stable coupling of the frame ends when in the compressed state.

66. The combustion system of claim 41, wherein the frame is formed at least in part from at least one of high temperature steel, stainless steel, ceramic, silicon carbide, or zirconium.

67. The combustion system of claim 41, wherein the combustion conduit is characterized by a cross-sectional area; and

wherein the frame and the one or more bluff bodies subtend less than an entire cross-sectional area.

68. The combustion system of claim 41, wherein the frame and one or more bluff bodies supported by the frame comprise a single frame supporting a plurality of bluff body bricks.

69. The combustion system of claim 41, wherein the frame and one or more bluff bodies supported by the frame comprise a plurality of frames supporting a respective plurality of bluff body bricks, each frame disposed at a different respective distance from a pilot of the fuel and combustion air source.

70. The combustion system of claim 41, wherein the one or more bluff bodies comprise a plurality of refractory bricks having a thickness, a width, and a length, the thickness not exceeding 40% of the lesser of the width and the length; and

wherein the plurality of refractory bricks are arranged to exhibit a thickness perpendicular to the fluid flow, and wherein the plane of the width × length is parallel to the fluid flow.

71. The combustion system of claim 70, wherein the thickness of the plurality of refractory bricks is no more than 30% of the lesser of the width and the length.

72. The combustion system of claim 71, wherein the thickness of the plurality of refractory bricks is no more than 20% of the lesser of the width and the length.

73. The combustion system of claim 70, wherein at least one of the plurality of refractory bricks is a perforated refractory brick capable of supporting combustion within a brick perforation.

74. The combustion system of claim 70, wherein at least one of the plurality of refractory bricks is a solid refractory brick capable of inhibiting combustion within the brick.

75. The combustion system of claim 41, further comprising a fuel and combustion air source, the fuel and combustion air source including the auxiliary fuel source, and the fuel and combustion air source configured to output the auxiliary fuel and combustion air into the combustion conduit.

76. The combustion system of claim 75, wherein the combustion volume wall defines a lateral extent of the combustion volume and is configured to separate the combustion volume from a water and steam volume.

77. The combustion system of claim 76, further comprising a mixing tube aligned to receive the auxiliary fuel and combustion air from the fuel and combustion air source, the mixing tube spaced from the combustion volume wall by the spacing volume.

78. The combustion system of claim 77, wherein the combustion volume wall includes a combustion conduit in a boiler;

wherein the bluff body is aligned to receive a mixture of a secondary fuel and combustion air from the outlet end of the mixing tube, the bluff body configured to maintain a combustion reaction to heat the combustion conduit, wherein the combustion conduit is configured to heat water in the water and steam volume.

79. The combustion system of claim 75, wherein the fuel and combustion air source comprises:

a fuel riser extending to a tip;

a main combustion air plenum configured to supply main combustion air and including a wall disposed about the fuel riser and defining a main combustion air plenum chamber; and

a variable swirler arranged to controllably swirl the primary combustion air at any of two or more different rotational speeds at least at a location corresponding to the tip of the fuel riser.

80. The combustion system of claim 79, wherein in a first mode the fuel and combustion air source is operable to support a pilot flame extending from an end of the main combustion air plenum proximate the tip of the fuel riser tube, or in a second mode combustion air is supplied to a bluff body flame holder without supporting the pilot flame.

81. The combustion system of claim 80, wherein the fuel and combustion air source comprises a secondary combustion air plenum configured to output secondary combustion air independently of the output of the primary combustion air.

82. The combustion system of claim 79, wherein a secondary fuel source includes one or more secondary fuel nozzles disposed remotely from an output end of the main combustion air plenum.

83. The combustion system of claim 79, further comprising a pilot flame device disposed distal to the source of fuel and combustion air proximate upstream of the bluff body flame holder, the pilot flame device including at least a pilot fuel nozzle configured to selectively hold a pilot flame.

84. The combustion system of claim 83, wherein the source of fuel and combustion air comprises the pilot flame device.

85. The combustion system of claim 83, wherein the pilot flame device is configured to selectively receive fuel and air from the fuel and combustion air source.

86. The combustion system of claim 83, wherein the pilot flame apparatus includes at least one of a pilot fuel source and a pilot oxidant source.

87. The combustion system of claim 83, wherein the pilot flame is configured to ignite a flow of fuel and air from the fuel and combustion air source to provide a combustion reaction for heating the combustion volume wall.

88. The combustion system of claim 83, wherein the combustion reaction for heating the combustion volume wall provides a heat output at least 10 times the heat output of the pilot flame when the open flame heater is operating at a rated heat output.

89. The combustion system of claim 83, further comprising an igniter disposed proximate the pilot flame device and configured to ignite the pilot flame.

90. The combustion system of claim 79, wherein a wall of the main combustion air plenum forms a tapered region at an outlet end of the main combustion air plenum proximate the tip of the fuel riser.

91. A fuel and air source for a combustor, comprising:

a fuel riser extending to a tip;

a main combustion air plenum comprising a wall disposed about the fuel riser and defining a main combustion air plenum chamber; and

a variable swirler arranged to controllably swirl primary combustion air at any one of two or more different rotational speeds at least at a location corresponding to the tip of the fuel riser.

92. The fuel and air source for a burner of claim 91, wherein the wall of the main combustion air plenum forms a tapered region at an outlet end of the main combustion air plenum proximate the tip of the fuel riser.

93. A fuel and air source for a burner as claimed in claim 92, wherein said tapered region includes a variable diameter region and a constant diameter region.

94. The fuel and air source for a burner of claim 91, wherein the fuel riser provides a fuel orifice at the tip.

95. The fuel and air source for a burner of claim 91, wherein said fuel riser tube provides a fuel orifice at a primary fuel output location disposed between a base of said fuel riser tube and said tip of said fuel riser tube.

96. The fuel and air source for a burner of claim 91, further comprising a lobe mixer disposed near the tip of the fuel riser.

97. The fuel and air source for a burner of claim 96, wherein the lobe mixer is coupled to one end of the main combustion air plenum.

98. A fuel and air source for a burner as claimed in claim 91, wherein said variable swirler comprises:

a plurality of actuatable fixed position vanes collectively rotatable to at least two different angles.

99. A fuel and air source for a burner as claimed in claim 91, wherein said variable swirler comprises an air duct forming a tangential main combustion air damper.

100. The fuel and air source for a burner of claim 91, wherein the variable swirler is disposed within a wall of the main combustion air plenum radially to the fuel riser.

101. The fuel and air source for a burner of claim 91, wherein in a first mode, the fuel and air source for the burner is operable to support a pilot flame extending from an end of the main combustion air plenum proximate to a tip of the fuel riser, or in a second mode, combustion air is supplied to a bluff body flame holder without supporting the pilot flame.

102. A fuel and air source for a burner as claimed in claim 91, further comprising:

one or more secondary fuel nozzles disposed remotely from an output end of the primary combustion air plenum.

103. A fuel and air source for a burner as claimed in claim 91, further comprising:

a secondary combustion air plenum configured to output secondary combustion air independently of the output of the primary combustion air.

104. A fuel and air source for a burner as claimed in claim 91, further comprising:

a flare configured to receive air and fuel from an air and fuel source and an extracted flue gas stream;

a mixing tube operatively coupled to the flare, the mixing tube operable to intermittently mix air and fuel and receive heat from an intermittently supported flame; and

a flame holder arranged to intermittently receive heat from the flame and receive the fuel and air flow, and to respectively raise the temperature and hold a second flame.

105. A fuel and air source for a burner as claimed in claim 104, wherein said flame holder is a bluff body flame holder.

106. A fuel and air source for a burner as claimed in claim 105, wherein said bluff body flame holder comprises one or more bluff bodies.

107. A fuel and air source for a burner as claimed in claim 105, wherein said bluff body flame holder is configured to output heat and convection with said second flame.

108. A fuel and air source for a burner as claimed in claim 107, wherein said combustion volume wall includes a combustion conduit; and

wherein the combustion conduit is configured to heat water in the water and steam volume.

109. A fuel and air source for a burner as claimed in claim 107, wherein said bluff body flame holder comprises a frame configured to be held in said combustion volume by gravity.

110. A fuel and air source for a burner as claimed in claim 107, wherein the bluff body flame holder comprises one or more refractory bluff bodies supported by the frame.

111. A fuel and air source for a burner according to claim 91, wherein an output end of the main combustion air plenum is configured to hold a flame at a high rotational velocity of the air and fuel mixture and to allow air and fuel to pass therethrough without holding the flame at a low rotational velocity of the air and fuel mixture.

112. A method of operating a boiler heater comprising:

outputting fuel and combustion air from a fuel and combustion air source into a combustion conduit defining a lateral extent of a combustion volume, the combustion conduit being arranged to separate the combustion volume from a water and steam volume;

receiving fuel and combustion air from the fuel and combustion air source in a mixing tube aligned to receive fuel and combustion air from the fuel and combustion air source, the mixing tube spaced apart from the combustion conduit by a spacing volume;

receiving a mixture of fuel and combustion air from an outlet end of the mixing tube in a bluff body flame holder;

maintaining a combustion reaction of fuel and combustion air with the bluff body flame holder;

heating the combustion conduit using the combustion reaction; and

heating water in the water and steam volume with the combustion conduit.

113. A method of operating a combustion system, comprising:

suspending the frame from the inner surface of the combustion conduit;

supporting one or more refractory bluff bodies with the frame;

selectively supporting a pilot flame with a pilot;

heating the one or more refractory bluff bodies with the pilot flame when the pilot flame is present;

supplying a secondary fuel to the one or more refractory bluff bodies using a secondary fuel source; and

maintaining a combustion reaction of the auxiliary fuel with combustion air with the one or more refractory bluff bodies.

114. A method of operating a fuel and air source for a combustor, comprising:

outputting a primary fuel from a fuel riser tube extending to a tip;

providing main combustion air to a main combustion air plenum defined by walls of the main combustion air plenum disposed about the fuel riser and defining a main combustion air plenum chamber; and

swirling primary combustion air with a variable swirler at any of two or more different rotational speeds, at least at a location corresponding to a tip of the fuel riser.

115. The method of claim 114, wherein the wall of the main combustion air plenum forms a tapered region at an outlet end of the main combustion air plenum proximate the tip of the fuel riser.

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