CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit from U.S. Provisional Patent Application No. 62/128,478 entitled "BURNER WITH REDUCED NOx OUTPUT FROM A NITROGEN-CONTAINING FUEL," filed March 4, 2015 (docket number 2651 -275-02); which, to the extent not inconsistent with the disclosure herein, is incorporated by reference.

SUMMARY

According to an embodiment, a method includes providing a first fuel to a perforated reaction holder and generating a second fuel by holding a gasification reaction of the first fuel within the perforated reaction holder. The method further includes adding an oxidant to the second fuel, mixing the oxidant and the second fuel, and passing the second fuel and oxidant to a perforated flame holder. The method further includes holding a combustion reaction between the second fuel and the oxidant within the perforated flame holder and transferring heat from the perforated flame holder to the perforated reaction holder. Temperature, low oxygen concentration, and/or kinetics, may enable the arrangement to convert fuel-borne nitrogen carried by the first fuel to be reacted and output from the system preferentially as molecular nitrogen, rather than as oxides of nitrogen (NOx).

According to an embodiment, a combustion system includes a first fuel source configured to output a first fuel, a perforated reaction holder is configured to receive the first fuel and to hold a gasification reaction of the first fuel within the perforated reaction holder. The gasification reaction generates a second fuel. The combustion system includes an oxidant source configured to mix an oxidant with the second fuel. The combustion system further includes a perforated flame holder positioned to receive the second fuel and the oxidant and to hold a combustion reaction between the second fuel and the oxidant within the perforated flame holder. A physical heat supporting channel can be coupled between the perforated reaction holder and the second perforated reaction holder, the physical heat supporting channel being configured to transfer heat from the perforated flame holder to the perforated reaction holder.

In another embodiment, heat output from the combustion reaction in the perforated flame holder can be output at least primarily to a heat load. The perforated reaction holder can receive heat from another heat source to support the (endothermic) first fuel gasification reaction. For example, an electrical resistance heater can be operatively coupled to the perforated reaction holder and to a control circuit such as a thermostat, timer, or current controller to maintain a selected gasification reaction temperature in the perforated reaction holder.

According to an embodiment, a low oxides of nitrogen (NOx) burner includes a perforated reaction holder defining a plurality of perforations that collectively form a gasifier perforation volume configured to support a gasification reaction of a first fuel. The gasification reaction generates a second fuel. The burner includes a perforated flame holder defining a plurality of perforations that collectively form a flame holder perforation volume configured to support a combustion reaction of the second fuel. A heat supporting physical channel is configured to receive heat from the combustion reaction and to carry the heat for output to the gasifier perforation volume. A fuel channel is configured to carry fuel gas output by the gasification reaction to the combustion volume.

According to an embodiment, a method for generating heat energy from a nitrogen containing fuel includes receiving a first fuel including fuel-bound nitrogen into a plurality of first perforations of a perforated reaction holder, generating a second fuel by holding a gasification reaction of the first fuel in the first perforations, and outputting the first fuel from the gasifier perforation volume. The method also includes receiving the first fuel and combustion air into a plurality of second perforations of a perforated flame holder, collectively supporting a low NOx combustion reaction in the plurality of second perforations, outputting heat to a thermal load, outputting heat into the heat supporting physical channel, and transferring heat through the heat supporting physical channel to the plurality of first perforations of the perforated reaction holder. The gasification reaction conditions favor the output of previously fuel-bound nitrogen as molecular nitrogen and disfavor the output of the previously fuel-bound nitrogen as an oxide of nitrogen such as NO. Oxidant (e.g., combustion air) is mixed with the second fuel after the second fuel exits the gasifier perforation volume and before the mixed second fuel and oxidant enter the plurality of perforations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a combustion system, according to an embodiment.

FIG. 2 is a simplified perspective view of a burner system including a perforated reaction holder, according to an embodiment.

FIG. 3 is a side-sectional diagram of a portion of the perforated reaction holder of FIGS. 1 and 2, according to an embodiment.

FIG. 4 is a flow chart showing a method for operating a burner system including the perforated reaction holder of FIGS. 1, 2 and 3, according to an embodiment.

FIG. 5 is a side-sectional diagram of a combustion system, according to an embodiment.

FIG. 6 is a simplified perspective view of a combustion system including a burner body that defines both a flame holder perforation volume and a gasifier perforation volume, according to an embodiment. FIG. 7A is a simplified side view of a combustion system including a plurality of tubes, according to an embodiment.

FIG. 7B is a simplified top view of the combustion system of FIG. 7A, according to an embodiment.

FIG. 8 is a flow chart illustrating a method of using a low NOx burner, according to an embodiment.

FIG. 9 is a flow chart illustrating a method of using the low NOx burner, according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the

accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

FIG. 1 is a block diagram of a combustion system 100, according to an embodiment. The combustion system includes a perforated flame holder 102 that defines a flame holder perforation volume 103. The combustion system 100 also includes a perforated reaction holder 104 that defines a gasifier perforation volume 105. A heat supporting physical channel 106 is coupled to the perforated flame holder 102 and the perforated reaction holder 104. A fuel channel 108 extends between the perforated reaction holder 104 and the perforated flame holder 102. A fuel source 1 1 1 is positioned adjacent to the perforated reaction holder 104. An oxidant source 1 10 is positioned adjacent to the perforated flame holder 102. According to an embodiment, the combustion system 100 supports a low NOx combustion reaction within the perforated flame holder 102 in conjunction with a gasification reaction held in the perforated reaction holder 104. The fuel source 1 1 1 supplies a first fuel including fuel bound nitrogen to the perforated reaction holder 104. The perforated reaction holder 104 holds a gasification reaction of the first fuel. The gasification reaction generates fuel gas and molecular nitrogen (N ₂ ). The fuel gas generated by the gasification reaction is passed to the perforated flame holder 102 via the fuel channel 108. The oxidant source 1 10 outputs an oxidant that mixes with the fuel gas either before or after the fuel gas is received by the perforated flame holder 102. The perforated flame holder 102 holds a combustion reaction of the fuel gas and oxidant mixture within the flame holder perforation volume 103. The combustion reaction generates heat. Some of the heat generated by the combustion reaction is transferred to the perforated reaction holder 104 by the heat supporting physical channel 106. The heat that is transferred to the perforated reaction holder 104 supports the gasification reaction. In this way, the combustion system 100 supports a combustion reaction that generates low levels of NOx.

In conventional combustion systems, burning a fuel that includes fuel bound nitrogen can result in the generation of high levels of oxides of nitrogen (NOx). As the fuel is combusted, the fuel bound nitrogen bonds with oxygen to form NOx.

According to an embodiment, the combustion system 100 can reduce the amount of NOx by holding a gasification reaction of the first fuel within the perforated reaction holder 104 in a low oxygen environment. The gasification reaction generates a second fuel, fuel gas, for example, that is then combusted within the perforated flame holder 102. As described in greater detail below, low levels of oxygen in the gasifier perforation volume 105 can result in lower NOx formation.

Gasification may be described as a process of converting fuel into carbon monoxide, hydrogen and carbon dioxide, without combustion, with a controlled amount of oxygen and/or steam. The oxygen may, for example, be entrained in air and/or a recycled flue gas. An oxidant source that supplies oxidant for the gasification reaction can be augmented or replaced by a steam source, and/or the steam may be produced from the fuel.

In a gasifier, the fuel may undergo several different processes. In an embodiment, dehydration may occur. The resulting steam may be entrained into the gas flow and may be further involved with subsequent chemical reactions, e.g., a water-gas reaction.

The dehydration may be followed by pyrolysis, resulting in release of volatile compounds and production of char and/or tar, depending on an embodiment. In an embodiment, the char and/or tar is entrained, and consumed in the combustion reaction as an additional source of a relatively nitrogen-free fuel.

The gasification process may occur as the char and/or tar reacts with steam and/or oxygen to produce carbon monoxide and hydrogen. Concentrations of carbon monoxide, steam, carbon dioxide and hydrogen may be controlled through the reversible gas phase water-gas shift reaction.

In combustion systems, the rate limiting step in the thermal NOx formation mechanism is N ₂ + 0 = NO + 0, where NO is the predominant form of NOx (>90%) with NO ₂ being a minority (<10%). Because the N-N bond is a triple bond, this requires high energy (i.e., high temperature) and a relatively long period of time to progress. The thermal NOx formation mechanism also requires relatively close proximity to molecular O ₂ ~ the precursor for atomic oxygen (0).

In addition, combustion of a fuel carrying fuel-bound nitrogen provides an additional nitrogen source. The fuel-bound nitrogen can be reacted to primarily form molecular nitrogen or primarily form NO, depending on the reaction conditions.

Fuel-bound nitrogen can form NOx that avoids the high energy step of breaking the N-N triple bond. If the fuel molecule itself carries nitrogen (as CxHy , where C _x H _y N is a generic representation of a fuel molecule containing nitrogen in its molecular structure), then the nitrogen is often liberated responsive to a lower energy of activation. In fuels carrying nitrogen, such as heavy fuel oil, coal, etc., the fuel-born nitrogen is liberated very early, easily, and quickly, before the fuel even has a chance to contact oxygen. The overall (fast, low temp) reaction is C _x H _y N ~ HCN + .... Once the cyanide and its radical (HCN <r~> CM) are formed, a complicated pathway produces atomic nitrogen; for example:

CxHyN -» HCN CN -» NCO -» NH -» N

The formation of atomic nitrogen from fuel-bound nitrogen is relatively fast and can occur at low temperature.

Once N is created it can go to one of two pathways. 1 . N + NO - N ₂ + 0, or

2. N + O ₂ ^~ » NO + O

Reaction 1 consumes NO and produces N ₂ . Reaction 2 produces NO. If is noted that Reaction 2 requires oxygen. High excess air includes oxygen and thus favors reaction 2 and tends to create NO. Low excess air tends to be associated with low oxygen concentration, and tends to favor Reaction 1 .

Similarly, imperfect mixing (frequently encountered in conventional combustion systems) creates pockets of high O ₂ and favors Reaction 2.

In a combustion reaction, very good mixing of fuel and oxidant ahead of the combustion reaction (which occurs in the perforations of the perforated reaction holder 104, according to an embodiment) assures that oxygen is fairly low everywhere. The relatively low oxygen concentration, in combination with a short transit time through perforations, thus favors Reaction 1 . In a gasification reaction, low available oxygen reduces the chance of a free atomic nitrogen (or other reactive species), forming from the released nitrogen. By withholding some air from this zone, the (first) fuel is reacted (in a combination of reduction and oxidation reactions with energy exchange therebetween) to create H ₂ /H ₂ O, CO and tar or char (referred to herein as "second fuel"), but will generates low NOx. This step is referred to as "gasification" herein.

In an embodiment, the combustion system 100 uses a perforated flame holder 102, operable to hold a combustion reaction and downstream from the perforated reaction holder 104, which is operable to hold the gasification reaction. The second fuel (including any residual oxygen) is output from the perforated reaction holder 104. An oxidant source 1 10, such as a combustion air duct, provides oxidant, which mixes with the second fuel upstream from the perforated flame holder 102. The perforated flame holder 102 holds a

combustion reaction to covert the H ₂ and CO to H ₂ 0 and CO2, also without much NOx. The combustion releases a large amount of energy, available to cooperate with one or more heat loads to produce a desired effect, such as power generation, vehicle locomotion, chemical processing, etc.

According to an embodiment, the first fuel can include coal. The coal can be provided to the perforated reaction holder 104 as powdered coal. The powdered coal can contain fuel bound nitrogen. According to an alternate embodiment the first fuel can include heavy oil than can contain fuel bound nitrogen.

According to an embodiment, the oxidant source 1 10 outputs an oxidant to the perforated flame holder 102. The oxidant mixes with and entrains the fuel gas before or after the fuel gas enters the perforated flame holder 102. The oxidant dilutes the fuel gas, causing a fuel-lean mixture within the flame holder perforation volume 103. The oxidant source 1 10 can include a blower. The oxidant can include combustion air.

According to an embodiment, the combustion system 100 includes a gasification oxidant source 1 12. The gasification oxidant source 1 12 outputs an oxidant that mixes with and entrains the first fuel before or after the first fuel enters the perforated reaction holder 104.

According to an embodiment, the oxidant output by the oxidant source 1 12 can be flue gas generated from the combustion reaction and circulated by the oxidant source 1 12 to the perforated reaction holder 104. The flue gas can include a low oxygen concentration less than 6%. According to an embodiment the flue gas can include a low oxygen concentration of about 3% or less. The low oxygen concentration in flue gas, may, to the extent flue gas is recirculated to entrain the first fuel, contribute to the low oxygen environment within the gasifier perforation volume 105. Alternatively the gasification oxidant source 1 12 can output an oxidant other than flue gas. The oxidant can include low

concentrations of oxygen.

According to an embodiment, the combustion system 100 can include a preheating mechanism configured to preheat the perforated reaction holder 104 and/or the perforated flame holder 102 prior to initiating the gasification reaction and the combustion reaction. By preheating the perforated reaction holder 104 prior to supporting the combustion reaction, the preheating mechanism can heat the perforated reaction holder 104 so that the perforated reaction holder 104 can support the endothermic gasification reaction that generates the fuel gas. The preheating mechanism can also preheat the perforated flame holder 102 so that the perforated flame holder 102 to a threshold temperature at which the perforated flame holder 102 can sustain a stable combustion reaction of the fuel gas and oxidant within the perforated flame holder 102. Once the perforated flame holder 102 holds a stable combustion reaction, heat from the perforated flame holder 102 can be transferred to the perforated reaction holder 104 by the heat supporting physical channel 106. At this point the preheating mechanism is no longer needed to support the gasification reaction within the perforated reaction holder 104. The preheating mechanism can include one or more fuel nozzles configured to support one or more startup flames near the perforated reaction holder 104 and/or the perforated flame holder 102. Those of skill in the art will recognize, in light of the present disclosure, that many kinds of preheating mechanism can be used to preheat the perforated flame holders 104 and102.

The heat supporting physical channel 106 can include a heat conducting body configured to transfer heat from the perforated flame holder 102 to the perforated reaction holder 104. For example, the heat supporting physical channel 106 can include a heat pipe configured to transfer heat in a phase change fluid flow. The heat pipe can pass a phase change fluid that is heated by the combustion reaction and that in turn heats the perforated reaction holder 104. Additionally or alternatively, the heat supporting physical channel 106 can include a wall in thermal contact with both the perforated flame holder 102 and the perforated reaction holder 104. Those of skill in the art will recognize, in light of the present disclosure, that the heat supporting physical channel can include other types of bodies or channels configured to transfer heat from the perforated flame holder 102 to the perforated reaction holder 104.

According to an embodiment, the combustion system 100 can include a thermal load configured to receive heat from the combustion reaction directly or indirectly. The thermal load can include a chemical process, a liquefaction process, and/or an electricity generating process. Heat can be transferred to the thermal load by radiation from the perforated flame holder 102. The perforated flame holder 102 can be heated directly by the combustion reaction.

According to an embodiment, the low NOx burner 100 can further include a flame arrestor configured to prevent the combustion reaction from flashing back into the fuel gas channel 108.

In another embodiment, heat output from the combustion reaction in the perforated flame holder can be output at least primarily to a heat load. The perforated flame holder can receive heat from another heat source to support the (endothermic) first fuel gasification reaction. For example, an electrical resistance heater can be operatively coupled to the perforated reaction holder and to a control circuit such as a thermostat, timer, or current controller to maintain a selected gasification reaction temperature in the first perforated flame holder. Those of skill in the art will recognize, in light of the present disclosure, that heat can be added to the perforated reaction holder in many other way to support the gasification reaction. All such other ways fall within the scope of the present disclosure.

While FIG. 1 has disclosed that the gasifier perforation volume 105 is defined by a perforated reaction holder 104, other configurations are possible. For example, the gasifier perforation volume 105 can be defined by a single cavity burner instead of a perforated reaction holder. In this case, the fuel source 1 1 1 can output the first fuel into the single cavity burner defining the gasifier perforation volume 105. The single cavity burner holds a gasification reaction of the first fuel. The gasification reaction generates a fuel gas. The fuel gas is then passed to the perforated flame holder 102 as described previously. The perforated flame holder 102 holds a combustion reaction of the fuel gas and an oxidant within the flame holder perforation volume 103. The heat supporting physical channel 106 can transfer heat from the combustion reaction to the gasifier perforation volume 105. Alternatively another heat source can provide heat to the gasifier perforation volume 105.

FIG. 2 is a simplified diagram of a burner system 200 including a perforated flame holder 102 configured to hold a combustion reaction, according to an embodiment.

Experiments performed by the inventors have shown that perforated flame holders 102 described herein can support very clean combustion. Specifically, in experimental use of systems 200 ranging from pilot scale to full scale, output of oxides of nitrogen (NOx) was measured to range from low single digit parts per million (ppm) down to undetectable (less than 1 ppm) concentration of NOx at the stack. These remarkable results were measured at 3% (dry) oxygen (O2) concentration with undetectable carbon monoxide (CO) at stack temperatures typical of industrial furnace applications (1400 - 1600 °F). Moreover, these results did not require any extraordinary measures such as selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), water/steam injection, external flue gas recirculation (FGR), or other heroic extremes that may be required for conventional burners to even approach such clean combustion.

According to embodiments, the burner system 200 includes a fuel and oxidant source 202 disposed to output fuel and oxidant into a combustion volume 204 to form a fuel and oxidant mixture 206. As used herein, the terms fuel and oxidant mixture and fuel stream may be used interchangeably and considered synonymous depending on the context, unless further definition is provided. As used herein, the terms combustion volume, combustion chamber, furnace volume, and the like shall be considered synonymous unless further definition is provided. The perforated flame holder 102 is disposed in the combustion volume 204 and positioned to receive the fuel and oxidant mixture 206. FIG. 3 is a side sectional diagram 300 of a portion of the perforated flame holder 102 of FIGS. 1 and 2, according to an embodiment. Referring to FIGS. 2 and 3, the perforated flame holder 102 includes a perforated reaction holder body 208 defining a plurality of perforations 210 aligned to receive the fuel and oxidant mixture 206 from the fuel and oxidant source 202. As used herein, the terms perforation, pore, aperture, elongated aperture, and the like, in the context of the perforated flame holder 102, shall be considered synonymous unless further definition is provided. The perforations 210 are configured to collectively hold a combustion reaction 302 supported by the fuel and oxidant mixture 206.

The fuel can include hydrogen, a hydrocarbon gas, a vaporized

hydrocarbon liquid, an atomized hydrocarbon liquid, or a powdered or pulverized solid. The fuel can be a single species or can include a mixture of gas(es), vapor(s), atomized liquid(s), and/or pulverized solid(s). For example, in a process heater application the fuel can include fuel gas or byproducts from the process that include carbon monoxide (CO), hydrogen (H ₂ ), and methane (CH ₄ ). In another application the fuel can include natural gas (mostly CH ₄ ) or propane (C3H8). In another application, the fuel can include #2 fuel oil or #6 fuel oil. Dual fuel applications and flexible fuel applications are similarly contemplated by the inventors. The oxidant can include oxygen carried by air, flue gas, and/or can include another oxidant, either pure or carried by a carrier gas. The terms oxidant and oxidizer shall be considered synonymous herein.

According to an embodiment, the perforated flame holder body 208 can be bounded by an input face 212 disposed to receive the fuel and oxidant mixture 206, an output face 214 facing away from the fuel and oxidant source 202, and a peripheral surface 216 defining a lateral extent of the perforated flame holder 102. The plurality of perforations 210 which are defined by the perforated flame holder body 208 extend from the input face 212 to the output face 214. The plurality of perforations 210 can receive the fuel and oxidant mixture 206 at the input face 212. The fuel and oxidant mixture 206 can then combust in or near the plurality of perforations 210 and combustion products can exit the plurality of perforations 210 at or near the output face 214. According to an embodiment, the perforated flame holder 102 is

configured to hold a majority of the combustion reaction 302 within the

perforations 210. For example, on a steady-state basis, more than half the molecules of fuel output into the combustion volume 204 by the fuel and oxidant source 202 may be converted to combustion products between the input face 212 and the output face 214 of the perforated flame holder 102. According to an alternative interpretation, more than half of the heat or thermal energy output by the combustion reaction 302 may be output between the input face 212 and the output face 214 of the perforated flame holder 102. As used herein, the terms heat, heat energy, and thermal energy shall be considered synonymous unless further definition is provided. As used above, heat energy and thermal energy refer generally to the released chemical energy initially held by reactants during the combustion reaction 302. As used elsewhere herein, heat, heat energy and thermal energy correspond to a detectable temperature rise undergone by real bodies characterized by heat capacities. Under nominal operating conditions, the perforations 210 can be configured to collectively hold at least 80% of the combustion reaction 302 between the input face 212 and the output face 214 of the perforated flame holder 102. In some experiments, the inventors produced a combustion reaction 302 that was apparently wholly contained in the perforations 210 between the input face 212 and the output face 214 of the perforated flame holder 102. According to an alternative interpretation, the perforated flame holder 102 can support combustion between the input face 212 and output face 214 when combustion is "time-averaged." For example, during transients, such as before the perforated flame holder 102 is fully heated, or if too high a (cooling) load is placed on the system, the combustion may travel somewhat downstream from the output face 214 of the perforated flame holder 102. Alternatively, if the cooling load is relatively low and/or the furnace temperature reaches a high level, the combustion may travel somewhat upstream of the input face 212 of the perforated flame holder 102.

While a "flame" is described in a manner intended for ease of description, it should be understood that in some instances, no visible flame is present. Combustion occurs primarily within the perforations 210, but the "glow" of combustion heat is dominated by a visible glow of the perforated flame holder 102 itself. In other instances, the inventors have noted transient "huffing" or "flashback" wherein a visible flame momentarily ignites in a region lying between the input face 212 of the perforated flame holder 102 and the fuel nozzle 218, within the dilution region D _D . Such transient huffing or flashback is generally short in duration such that, on a time-averaged basis, a majority of combustion occurs within the perforations 210 of the perforated flame holder 102, between the input face 212 and the output face 214. In still other instances, the inventors have noted apparent combustion occurring downstream from the output face 214 of the perforated flame holder 102, but still a majority of combustion occurred within the perforated flame holder 102 as evidenced by continued visible glow from the perforated flame holder 102 that was observed.

The perforated flame holder 102 can be configured to receive heat from the combustion reaction 302 and output a portion of the received heat as thermal radiation 304 to heat-receiving structures (e.g., furnace walls and/or radiant section working fluid tubes) in or adjacent to the combustion volume 204. As used herein, terms such as radiation, thermal radiation, radiant heat, heat radiation, etc. are to be construed as being substantially synonymous, unless further definition is provided. Specifically, such terms refer to blackbody-type radiation of electromagnetic energy, primarily at infrared wavelengths, but also at visible wavelengths owing to elevated temperature of the perforated flame holder body 208.

Referring especially to FIG. 3, the perforated flame holder 102 outputs another portion of the received heat to the fuel and oxidant mixture 206 received at the input face 212 of the perforated flame holder 102. The perforated flame holder body 208 may receive heat from the combustion reaction 302 at least in heat receiving regions 306 of perforation walls 308. Experimental evidence has suggested to the inventors that the position of the heat receiving regions 306, or at least the position corresponding to a maximum rate of receipt of heat, can vary along the length of the perforation walls 308. In some experiments, the location of maximum receipt of heat was apparently between 1/3 and 1/2 of the distance from the input face 212 to the output face 214 (i.e., somewhat nearer to the input face 212 than to the output face 214). The inventors contemplate that the heat receiving regions 306 may lie nearer to the output face 214 of the perforated flame holder 102 under other conditions. Most probably, there is no clearly defined edge of the heat receiving regions 306 (or for that matter, the heat output regions 310, described below). For ease of understanding, the heat receiving regions 306 and the heat output regions 310 will be described as particular regions 306, 310.

The perforated flame holder body 208 can be characterized by a heat capacity. The perforated flame holder body 208 may hold thermal energy from the combustion reaction 302 in an amount corresponding to the heat capacity multiplied by temperature rise, and transfer the thermal energy from the heat receiving regions 306 to heat output regions 310 of the perforation walls 308. Generally, the heat output regions 310 are nearer to the input face 212 than are the heat receiving regions 306. According to one interpretation, the perforated flame holder body 208 can transfer heat from the heat receiving regions 306 to the heat output regions 310 via thermal radiation, depicted graphically as 304. According to another interpretation, the perforated flame holder body 208 can transfer heat from the heat receiving regions 306 to the heat output regions 310 via heat conduction along heat conduction paths 312. The inventors contemplate that multiple heat transfer mechanisms including conduction, radiation, and possibly convection may be operative in transferring heat from the heat receiving regions 306 to the heat output regions 310. In this way, the perforated flame holder 102 may act as a heat source to maintain the combustion reaction 302, even under conditions where a combustion reaction 302 would not be stable when supported from a conventional flame holder.

The inventors believe that the perforated flame holder 102 causes the combustion reaction 302 to begin within thermal boundary layers 314 formed adjacent to walls 308 of the perforations 210. Insofar as combustion is generally understood to include a large number of individual reactions, and since a large portion of combustion energy is released within the perforated flame holder 102, it is apparent that at least a majority of the individual reactions occur within the perforated flame holder 102. As the relatively cool fuel and oxidant mixture 206 approaches the input face 212, the flow is split into portions that respectively travel through individual perforations 210. The hot perforated flame holder body 208 transfers heat to the fluid, notably within thermal boundary layers 314 that progressively thicken as more and more heat is transferred to the incoming fuel and oxidant mixture 206. After reaching a combustion temperature (e.g., the auto-ignition temperature of the fuel), the reactants continue to flow while a chemical ignition delay time elapses, over which time the combustion reaction 302 occurs. Accordingly, the combustion reaction 302 is shown as occurring within the thermal boundary layers 314. As flow progresses, the thermal boundary layers 314 merge at a merger point 316. Ideally, the merger point 316 lies between the input face 212 and output face 214 that define the ends of the perforations 210. At some position along the length of a perforation 210, the combustion reaction 302 outputs more heat to the perforated flame holder body 208 than it receives from the perforated flame holder body 208. The heat is received at the heat receiving region 306, is held by the perforated flame holder body 208, and is transported to the heat output region 310 nearer to the input face 212, where the heat is transferred into the cool reactants (and any included diluent) to bring the reactants to the ignition temperature.

In an embodiment, each of the perforations 210 is characterized by a length L defined as a reaction fluid propagation path length between the input face 212 and the output face 214 of the perforated flame holder 102. As used herein, the term reaction fluid refers to matter that travels through a perforation 210. Near the input face 212, the reaction fluid includes the fuel and oxidant mixture 206 (optionally including nitrogen, flue gas, and/or other "non-reactive" species). Within the combustion reaction region, the reaction fluid may include plasma associated with the combustion reaction 302, molecules of reactants and their constituent parts, any non-reactive species, reaction intermediates

(including transition states), and reaction products. Near the output face 214, the reaction fluid may include reaction products and byproducts, non-reactive gas, and excess oxidant.

The plurality of perforations 210 can be each characterized by a

transverse dimension D between opposing perforation walls 308. The inventors have found that stable combustion can be maintained in the perforated flame holder 102 if the length L of each perforation 210 is at least four times the transverse dimension D of the perforation. In other embodiments, the length L can be greater than six times the transverse dimension D. For example, experiments have been run where L is at least eight, at least twelve, at least sixteen, and at least twenty-four times the transverse dimension D. Preferably, the length L is sufficiently long for thermal boundary layers 314 to form adjacent to the perforation walls 308 in a reaction fluid flowing through the perforations 210 to converge at merger points 316 within the perforations 210 between the input face 212 and the output face 214 of the perforated flame holder 102. In experiments, the inventors have found L/D ratios between 12 and 48 to work well (i.e., produce low NOx, produce low CO, and maintain stable combustion).

The perforated flame holder body 208 can be configured to convey heat between adjacent perforations 210. The heat conveyed between adjacent perforations 210 can be selected to cause heat output from the combustion reaction portion 302 in a first perforation 210 to supply heat to stabilize a combustion reaction portion 302 in an adjacent perforation 210.

Referring especially to FIG. 2, the fuel and oxidant source 202 can further include a fuel nozzle 218, configured to output fuel, and an oxidant source 220 configured to output a fluid including the oxidant. For example, the fuel nozzle 218 can be configured to output pure fuel. The oxidant source 220 can be configured to output combustion air carrying oxygen, and optionally, flue gas.

The perforated flame holder 102 can be held by a perforated flame holder support structure 222 configured to hold the perforated flame holder 102 at a dilution distance D _D away from the fuel nozzle 218. The fuel nozzle 218 can be configured to emit a fuel jet selected to entrain the oxidant to form the fuel and oxidant mixture 206 as the fuel jet and oxidant travel along a path to the perforated flame holder 102 through the dilution distance D _D between the fuel nozzle 218 and the perforated flame holder 102. Additionally or alternatively (particularly when a blower is used to deliver oxidant contained in combustion air), the oxidant or combustion air source can be configured to entrain the fuel and the fuel and oxidant travel through the dilution distance D _D . In some embodiments, a flue gas recirculation path 224 can be provided. Additionally or alternatively, the fuel nozzle 218 can be configured to emit a fuel jet selected to entrain the oxidant and to entrain flue gas as the fuel jet travels through the dilution distance D _D between the fuel nozzle 218 and the input face 212 of the perforated flame holder 102.

The fuel nozzle 218 can be configured to emit the fuel through one or more fuel orifices 226 having an inside diameter dimension that is referred to as "nozzle diameter." The perforated flame holder support structure 222 can support the perforated flame holder 102 to receive the fuel and oxidant mixture 206 at the distance D _D away from the fuel nozzle 218 greater than 20 times the nozzle diameter. In another embodiment, the perforated flame holder 102 is disposed to receive the fuel and oxidant mixture 206 at the distance D _D away from the fuel nozzle 218 between 100 times and 1 100 times the nozzle diameter. Preferably, the perforated flame holder support structure 222 is configured to hold the perforated flame holder 102 at a distance about 200 times or more of the nozzle diameter away from the fuel nozzle 218. When the fuel and oxidant mixture 206 travels about 200 times the nozzle diameter or more, the mixture is sufficiently homogenized to cause the combustion reaction 302 to produce minimal NOx.

The fuel and oxidant source 202 can alternatively include a premix fuel and oxidant source, according to an embodiment. A premix fuel and oxidant source can include a premix chamber (not shown), a fuel nozzle configured to output fuel into the premix chamber, and an oxidant (e.g., combustion air) channel configured to output the oxidant into the premix chamber. A flame arrestor can be disposed between the premix fuel and oxidant source and the perforated flame holder 102 and be configured to prevent flame flashback into the premix fuel and oxidant source.

The oxidant source 220, whether configured for entrainment in the combustion volume 204 or for premixing, can include a blower configured to force the oxidant through the fuel and oxidant source 202.

The support structure 222 can be configured to support the perforated flame holder 102 from a floor or wall (not shown) of the combustion volume 204, for example. In another embodiment, the support structure 222 supports the perforated flame holder 102 from the fuel and oxidant source 202. Alternatively, the support structure 222 can suspend the perforated flame holder 102 from an overhead structure (such as a flue, in the case of an up-fired system). The support structure 222 can support the perforated flame holder 102 in various orientations and directions.

The perforated flame holder 102 can include a single perforated flame holder body 208. In another embodiment, the perforated flame holder 102 can include a plurality of adjacent perforated flame holder sections that collectively provide a tiled perforated flame holder 102.

The perforated flame holder support structure 222 can be configured to support the plurality of perforated flame holder sections. The perforated flame holder support structure 222 can include a metal superalloy, a cementatious, and/or ceramic refractory material. In an embodiment, the plurality of adjacent perforated flame holder sections can be joined with a fiber reinforced refractory cement.

The perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 216 at least twice a thickness dimension T between the input face 212 and the output face 214. In another embodiment, the perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 216 at least three times, at least six times, or at least nine times the thickness dimension T between the input face 212 and the output face 214 of the perforated flame holder 102. In an embodiment, the perforated flame holder 102 can have a width dimension W less than a width of the combustion volume 204. This can allow the flue gas circulation path 224 from above to below the perforated flame holder 102 to lie between the peripheral surface 216 of the perforated flame holder 102 and the combustion volume wall (not shown).

Referring again to both FIGS. 2 and 3, the perforations 210 can be of various shapes. In an embodiment, the perforations 210 can include elongated squares, each having a transverse dimension D between opposing sides of the squares. In another embodiment, the perforations 210 can include elongated hexagons, each having a transverse dimension D between opposing sides of the hexagons. In yet another embodiment, the perforations 210 can include hollow cylinders, each having a transverse dimension D corresponding to a diameter of the cylinder. In another embodiment, the perforations 210 can include truncated cones or truncated pyramids (e.g., frustums), each having a transverse dimension D radially symmetric relative to a length axis that extends from the input face 212 to the output face 214. In some embodiments, the perforations 210 can each have a lateral dimension D equal to or greater than a quenching distance of the flame based on standard reference conditions. Alternatively, the perforations 210 may have lateral dimension D less then than a standard reference quenching distance.

In one range of embodiments, each of the plurality of perforations 210 has a lateral dimension D between 0.05 inch and 1 .0 inch. Preferably, each of the plurality of perforations 210 has a lateral dimension D between 0.1 inch and 0.5 inch. For example the plurality of perforations 210 can each have a lateral dimension D of about 0.2 to 0.4 inch.

The void fraction of a perforated flame holder 102 is defined as the total volume of all perforations 210 in a section of the perforated flame holder 102 divided by a total volume of the perforated flame holder 102 including body 208 and perforations 210. The perforated flame holder 102 should have a void fraction between 0.10 and 0.90. In an embodiment, the perforated flame holder 102 can have a void fraction between 0.30 and 0.80. In another embodiment, the perforated flame holder 102 can have a void fraction of about 0.70. Using a void fraction of about 0.70 was found to be especially effective for producing very low NOx.

The perforated flame holder 102 can 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 102 can be formed to include mullite or cordierite. Additionally or alternatively, the perforated flame holder body 208 can include a metal superalloy such as Inconel or Hastelloy. The perforated flame holder body 208 can define a honeycomb. Honeycomb is an industrial term of art that need not strictly refer to a hexagonal cross section and most usually includes cells of square cross section. Honeycombs of other cross sectional areas are also known.

The inventors have found that the perforated flame holder 102 can be formed from VERSAGRID ® ceramic honeycomb, available from Applied

Ceramics, Inc. of Doraville, South Carolina.

The perforations 210 can be parallel to one another and normal to the input and output faces 212, 214. In another embodiment, the perforations 210 can be parallel to one another and formed at an angle relative to the input and output faces 212, 214. In another embodiment, the perforations 210 can be non- parallel to one another. In another embodiment, the perforations 210 can be non-parallel to one another and non-intersecting. In another embodiment, the perforations 210 can be intersecting. The body 308 can be one piece or can be formed from a plurality of sections.

In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from reticulated ceramic material. The term "reticulated" refers to a netlike structure. Reticulated ceramic material is often made by dissolving a slurry into a sponge of specified porosity, allowing the slurry to harden, and burning away the sponge and curing the ceramic.

In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from a ceramic material that has been punched, bored or cast to create channels. In another embodiment, the perforated flame holder 102 can include a plurality of tubes or pipes bundled together. The plurality of perforations 210 can include hollow cylinders and can optionally also include interstitial spaces between the bundled tubes. In an embodiment, the plurality of tubes can include ceramic tubes. Refractory cement can be included between the tubes and configured to adhere the tubes together. In another embodiment, the plurality of tubes can include metal (e.g., superalloy) tubes. The plurality of tubes can be held together by a metal tension member circumferential to the plurality of tubes and arranged to hold the plurality of tubes together. The metal tension member can include stainless steel, a superalloy metal wire, and/or a superalloy metal band.

The perforated reaction holder body 208 can alternatively include stacked perforated sheets of material, each sheet having openings that connect with openings of subjacent and superjacent sheets. The perforated sheets can include perforated metal sheets, ceramic sheets and/or expanded sheets. In another embodiment, the perforated flame holder body 208 can include discontinuous packing bodies such that the perforations 210 are formed in the interstitial spaces between the discontinuous packing bodies. In one example, the discontinuous packing bodies include structured packing shapes. In another example, the discontinuous packing bodies include random packing shapes. For example, the discontinuous packing bodies can include ceramic Raschig ring, ceramic Berl saddles, ceramic Intalox saddles, and/or metal rings or other shapes (e.g. Super Raschig Rings) that may be held together by a metal cage.

The inventors contemplate various explanations for why burner systems including the perforated flame holder 102 provide such clean combustion.

According to an embodiment, the perforated flame holder 102 may act as a heat source to maintain a combustion reaction even under conditions where a combustion reaction would not be stable when supported by a conventional flame holder. This capability can be leveraged to support combustion using a leaner fuel-to-oxidant mixture than is typically feasible. Thus, according to an embodiment, at the point where the fuel stream 206 contacts the input face 212 of the perforated flame holder 102, an average fuel-to-oxidant ratio of the fuel stream 206 is below a (conventional) lower combustion limit of the fuel component of the fuel stream 206— lower combustion limit defines the lowest concentration of fuel at which a fuel and oxidant mixture 206 will burn when exposed to a momentary ignition source under normal atmospheric pressure and an ambient temperature of 25° C (77° F).

The perforated flame holder 102 and systems including the perforated flame holder 102 described herein were found to provide substantially complete combustion of CO (single digit ppm down to undetectable, depending on experimental conditions), while supporting low NOx. According to one

interpretation, such a performance can be achieved due to a sufficient mixing used to lower peak flame temperatures (among other strategies). Flame temperatures tend to peak under slightly rich conditions, which can be evident in any diffusion flame that is insufficiently mixed. By sufficiently mixing, a homogenous and slightly lean mixture can be achieved prior to combustion. This combination can result in reduced flame temperatures, and thus reduced NOx formation. In one embodiment, "slightly lean" may refer to 3% O2, i.e. an equivalence ratio of ~0.87. Use of even leaner mixtures is possible, but may result in elevated levels of O2. Moreover, the inventors believe perforation walls 308 may act as a heat sink for the combustion fluid. This effect may alternatively or additionally reduce combustion temperatures and lower NOx.

According to another interpretation, production of NOx can be reduced if the combustion reaction 302 occurs over a very short duration of time. Rapid combustion causes the reactants (including oxygen and entrained nitrogen) to be exposed to NOx-formation temperature for a time too short for NOx formation kinetics to cause significant production of NOx. The time required for the reactants to pass through the perforated flame holder 102 is very short compared to a conventional flame. The low NOx production associated with perforated flame holder combustion may thus be related to the short duration of time required for the reactants (and entrained nitrogen) to pass through the perforated flame holder 102. FIG. 4 is a flow chart showing a method 400 for operating a burner system including the perforated reaction holder shown and described herein. To operate a burner system including a perforated flame holder, the perforated flame holder is first heated to a temperature sufficient to maintain combustion of the fuel and oxidant mixture.

According to a simplified description, the method 400 begins with step 402, wherein the perforated flame holder is preheated to a start-up temperature, Ts. After the perforated flame holder is raised to the start-up temperature, the method proceeds to step 404, wherein the fuel and oxidant are provided to the perforated flame holder and combustion is held by the perforated flame holder.

According to a more detailed description, step 402 begins with step 406, wherein start-up energy is provided at the perforated flame holder.

Simultaneously or following providing start-up energy, a decision step 408 determines whether the temperature T of the perforated flame holder is at or above the start-up temperature, T _s . As long as the temperature of the perforated flame holder is below its start-up temperature, the method loops between steps 406 and 408 within the preheat step 402. In step 408, if the temperature T of at least a predetermined portion of the perforated flame holder is greater than or equal to the start-up temperature, the method 400 proceeds to overall step 404, wherein fuel and oxidant is supplied to and combustion is held by the perforated flame holder.

Step 404 may be broken down into several discrete steps, at least some of which may occur simultaneously.

Proceeding from step 408, a fuel and oxidant mixture is provided to the perforated flame holder, as shown in step 410. The fuel and oxidant may be provided by a fuel and oxidant source that includes a separate fuel nozzle and oxidant (e.g., combustion air) source, for example. In this approach, the fuel and oxidant are output in one or more directions selected to cause the fuel and oxidant mixture to be received by the input face of the perforated flame holder. The fuel may entrain the 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 at a fuel dilution selected for a stable combustion reaction that can be held within the perforations of the perforated flame holder.

Proceeding to step 412, the combustion reaction is held by the perforated flame holder.

In step 414, heat may be output from the perforated flame holder. The heat output from the perforated flame holder may be used to power an industrial process, heat a working fluid, generate electricity, or provide motive power, for example.

In optional step 416, the presence of combustion may be sensed. Various sensing approaches have been used and are contemplated by the inventors. Generally, combustion held by the perforated flame holder is very stable and no unusual sensing requirement is placed on the system. Combustion sensing may be performed using an infrared sensor, a video sensor, an ultraviolet sensor, a charged species sensor, thermocouple, thermopile, flame rod, and/or other combustion sensing apparatuses. In an additional or alternative variant of step 416, a pilot flame or other ignition source may be provided to cause ignition of the fuel and oxidant mixture in the event combustion is lost at the perforated flame holder.

Proceeding to decision step 418, if combustion is sensed not to be stable, the method 400 may exit to step 424, wherein an error procedure is executed. For example, the error procedure may include turning off fuel flow, re-executing the preheating step 402, outputting an alarm signal, igniting a stand-by combustion system, or other steps. If, in step 418, combustion in the perforated flame holder is determined to be stable, the method 400 proceeds to decision step 420, wherein it is determined if combustion parameters should be changed. If no combustion parameters are to be changed, the method loops (within step 404) back to step 410, and the combustion process continues. If a change in combustion parameters is indicated, the method 400 proceeds to step 422, wherein the combustion parameter change is executed. After changing the combustion parameter(s), the method loops (within step 404) back to step 410, and combustion continues. Combustion parameters may be scheduled to be changed, for example, if a change in heat demand is encountered. For example, if less heat is required (e.g., due to decreased electricity demand, decreased motive power requirement, or lower industrial process throughput), the fuel and oxidant flow rate may be decreased in step 422. Conversely, if heat demand is increased, then fuel and oxidant flow may be increased. Additionally or alternatively, if the combustion system is in a start-up mode, then fuel and oxidant flow may be gradually increased to the perforated flame holder over one or more iterations of the loop within step 404.

Referring again to FIG. 2, the burner system 200 includes a heater 228 operatively coupled to the perforated flame holder 102. As described in conjunction with FIGS. 3 and 4, the perforated flame holder 102 operates by outputting heat to the incoming fuel and oxidant mixture 206. After combustion is established, this heat is provided by the combustion reaction 302; but before combustion is established, the heat is provided by the heater 228.

Various heating apparatuses have been used and are contemplated by the inventors. In some embodiments, the heater 228 can include a flame holder configured to support a flame disposed to heat the perforated flame holder 102. The fuel and oxidant source 202 can include a fuel nozzle 218 configured to emit a fuel stream 206 and an oxidant source 220 configured to output oxidant (e.g., combustion air) adjacent to the fuel stream 206. The fuel nozzle 218 and oxidant source 220 can be configured to output the fuel stream 206 to be progressively diluted by the oxidant (e.g., combustion air). The perforated flame holder 102 can be disposed to receive a diluted fuel and oxidant mixture 206 that supports a combustion reaction 302 that is stabilized by the perforated flame holder 102 when the perforated flame holder 102 is at an operating temperature. A start-up flame holder, in contrast, can be configured to support a start-up flame at a location corresponding to a relatively unmixed fuel and oxidant mixture that is stable without stabilization provided by the heated perforated flame holder 102.

The burner system 200 can further include a controller 230 operatively coupled to the heater 228 and to a data interface 232. For example, the controller 230 can be configured to control a start-up flame holder actuator configured to cause the start-up flame holder to hold the start-up flame when the perforated flame holder 102 needs to be pre-heated and to not hold the start-up flame when the perforated flame holder 102 is at an operating temperature (e.g., when T > T _s ).

Various approaches for actuating a 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 206 to cause heat-recycling and/or stabilizing vortices and thereby hold a start-up flame; or to be actuated to not intercept the fuel and oxidant mixture 206 to cause the fuel and oxidant mixture 206 to proceed to the perforated flame holder 102. In another embodiment, a fuel control valve, blower, and/or damper may be used to select a fuel and oxidant mixture flow rate that is sufficiently low for a start-up flame to be jet-stabilized; and upon reaching a perforated flame holder 102 operating temperature, the flow rate may be increased to "blow out" the start-up flame. In another embodiment, the heater 228 may include an electrical power supply operatively coupled to the controller 230 and configured to apply an electrical charge or voltage to the fuel and oxidant mixture 206. An electrically conductive start-up flame holder may be selectively coupled to a voltage ground or other voltage selected to attract the electrical charge in the fuel and oxidant mixture 206. The attraction of the electrical charge was found by the inventors to cause a start-up flame to be held by the electrically conductive start-up flame holder.

In another embodiment, the heater 228 may include an electrical resistance heater configured to output heat to the perforated flame holder 102 and/or to the fuel and oxidant mixture 206. The electrical resistance heater can be configured to heat up the perforated flame holder 102 to an operating temperature. The heater 228 can further include a power supply and a switch operable, under control of the controller 230, to selectively couple the power supply to the electrical resistance heater. An electrical resistance heater 228 can be formed in various ways. For example, the electrical resistance heater 228 can be formed from KANTHAL® wire (available from Sandvik Materials Technology division of Sandvik AB of Hallstahammar, Sweden) threaded through at least a portion of the perforations 210 defined by the perforated flame holder body 208. Alternatively, the heater 228 can include an inductive heater, a high-energy beam heater (e.g. microwave or laser), a frictional heater, electro-resistive ceramic coatings, or other types of heating technologies.

Other forms of start-up apparatuses are contemplated. For example, the heater 228 can include an electrical discharge igniter or hot surface igniter configured to output a pulsed ignition to the oxidant and fuel. Additionally or alternatively, a start-up apparatus can include a pilot flame apparatus disposed to ignite the fuel and oxidant mixture 206 that would otherwise enter the perforated flame holder 102. The electrical discharge igniter, hot surface igniter, and/or pilot flame apparatus can be operatively coupled to the controller 230, which can cause the electrical discharge igniter or pilot flame apparatus to maintain combustion of the fuel and oxidant mixture 206 in or upstream from the

perforated flame holder 102 before the perforated flame holder 102 is heated sufficiently to maintain combustion.

The burner system 200 can further include a sensor 234 operatively coupled to the control circuit 230. The sensor 234 can include a heat sensor configured to detect infrared radiation or a temperature of the perforated flame holder 102. The control circuit 230 can be configured to control the heating apparatus 228 responsive to input from the sensor 234. Optionally, a fuel control valve 236 can be operatively coupled to the controller 230 and configured to control a flow of fuel to the fuel and oxidant source 202. Additionally or alternatively, an oxidant blower or damper 238 can be operatively coupled to the controller 230 and configured to control flow of the oxidant (or combustion air).

The sensor 234 can further include a combustion sensor operatively coupled to the control circuit 230, the combustion sensor being configured to detect a temperature, video image, and/or spectral characteristic of a combustion reaction held by the perforated flame holder 102. The fuel control valve 236 can be configured to control a flow of fuel from a fuel source to the fuel and oxidant source 202. The controller 230 can be configured to control the fuel control valve 236 responsive to input from the combustion sensor 234. The controller 230 can be configured to control the fuel control valve 236 and/or oxidant blower or damper to control a preheat flame type of heater 228 to heat the perforated flame holder 102 to an operating temperature. The controller 230 can similarly control the fuel control valve 236 and/or the oxidant blower or damper to change the fuel and oxidant mixture 206 flow responsive to a heat demand change received as data via the data interface 232.

FIG. 5 is a diagram of a low NOx burner 500, according to an

embodiment. The burner 500 includes a perforated flame holder 102 and a perforated reaction holder 104. The perforated flame holder 102 includes a plurality of perforations 210 extending between an input face of the perforated flame holder 102 and an output face of the perforated flame holder 102. The perforations 210 collectively define a flame holder perforation volume 103. The perforated reaction holder 104 includes perforations 518 extending between an input face of the perforated reaction holder 104 and an output face of the perforated reaction holder 104. The perforations 518 collectively define a gasifier perforation volume 105. Heat pipes 506 pass between the perforated flame holder 102 and the perforated reaction holder 104. A fuel source 1 1 1 is positioned adjacent to the perforated reaction holder 104.

According to an embodiment, the combustion system 500 supports a low NOx combustion reaction 304 within the perforated flame holder 102 in

conjunction with a gasification reaction 516 held in the perforated reaction holder 104. The fuel source 1 1 1 supplies a first fuel 51 1 including fuel bound nitrogen to the perforated reaction holder 104. The perforated reaction holder 104 holds the gasification reaction 516 of the first fuel 51 1 within the perforated reaction holder 104. The gasification reaction 516 generates second fuel 520 and molecular Nitrogen (N ₂ ). The second fuel 520 generated by the gasification reaction 516 is passed to the perforated flame holder 102 via the fuel channel 108, which corresponds to a path of travel between the second and first perforated flame holder 102 and the perforated flame holder 104. An oxidant source 1 10 outputs an oxidant 521 that mixes with the second fuel 520 either before or after the second fuel 520 is received by the perforated flame holder 102. The perforated flame holder 102 holds a combustion reaction 304 of the second fuel and oxidant mixture within the flame holder perforation volume 103. The combustion reaction 304 generates heat. Some of the heat generated by the combustion reaction 304 is transferred to the perforated reaction holder 104 by the heat supporting physical channel 106. The heat that is transferred to the perforated reaction holder 104 supports the gasification reaction 516. In this way, the combustion system 100 supports a combustion reaction 304 that generates low levels of NOx.

According to an embodiment, the second fuel 520 is a fuel gas.

According to an embodiment, the heat pipes 506 are physical heat carrying channels that pass a phase change fluid 514 therethrough. The phase change fluid 514 receives heat from the combustion reaction 304, flows toward the perforated reaction holder 104, and transfers heat to the perforated reaction holder 104. In this way, heat generated by the combustion reaction 304 is transferred to support the endothermic gasification reaction 516.

According to an embodiment, the perforated flame holder 102 radiates or otherwise heat 522 to a thermal load such as a working fluid, an electrical power generation system, and/or another type of heat load.

According to an embodiment, the combustion system 500 includes a gasification oxidant source 1 12. The gasification oxidant source 1 12 can be a flue gas circulator that circulates a portion of a flue gas 524 generated by the combustion reaction 304 and output from the perforations 103 at the output surface of the perforated flame holder 102. The gasification oxidant source can circulate a portion of the flue gas 524 to entrain the first fuel 51 1 output from the fuel source 1 1 1 . The flue gas 524 has a relatively low oxygen concentration and therefore ensures a low oxygen environment within the gasifier perforation volume 105. According to an embodiment, the gasification oxidant source 1 12 can output a gas other than flue gas. The gas output by the gasification oxidant source 1 12 entrains the first fuel 51 1 .

FIG. 6 is a diagram of a combustion system 600, according to an embodiment. The burner 600 includes a burner body 623 that defines both a perforated flame holder and a perforated reaction holder. The burner body 623 includes a plurality of perforations 210 and 518. The perforations 210 collectively define a flame holder perforation volume 103. The perforations 518 collectively define the gasifier perforation volume 105. The perforations 210 extend vertically and have input apertures on a bottom face of the burner body and output apertures on a top face of the burner body 623. The perforations 518 extend laterally within the burner body 623 and have input apertures on a far lateral face of the burner body 623 and output apertures on a near lateral face of the burner body 623. Walls 106 separate the perforations 210 from the perforations 518. The walls 624 are physical heat supporting channels that support thermal conduction 626 therethrough. The burner 600 includes a fuel source 1 1 1 positioned adjacent to the burner body 623.

According to an embodiment, the combustion system 600 supports a low NOx combustion reaction 304 within the flame holder perforation volume 103 in conjunction with a gasification reaction 516 held in the gasifier perforation volume 105. The fuel source 1 1 1 supplies a first fuel 51 1 including fuel bound nitrogen to the perforations 518 via input apertures on a far lateral face of the burner body (not pictured in FIG. 6 because they are on the far side of the burner body 623 and are obscured in the view shown in FIG. 6). The burner body 623 holds the gasification reaction 516 of the first fuel 51 1 within the gasifier perforation volume 105 defined by the perforations 518. A second fuel 520 exit the perforations 518 via the output apertures on a near lateral face of the burner body. The second fuel 520 generated by the gasification reaction 516 is passed to the perforations 210 via the fuel channel 108. An oxidant source 1 10 outputs an oxidant 521 that mixes with the second fuel 520 either before or after the second fuel 520 is received by the perforated flame holder 102. The flame holder perforation volume 103 defined by the perforations 210 holds a combustion reaction 304 of the second fuel and oxidant mixture within the flame holder perforation volume 103. The combustion reaction 304 generates heat. Some of the heat generated by the combustion reaction 304 is transferred to the perforated reaction holder 104 through the walls 624. The heat that is transferred to the gasifier perforation volume 105 supports the gasification reaction 516. In this way, the combustion system 100 supports a combustion reaction 304 that generates low levels of NOx.

According to an embodiment, the second fuel 520 is a fuel gas.

FIG. 7A is a simplified side view of a combustion system 700, according to an embodiment. The combustion system 700 includes a plurality of tubes 702, 704. The tubes 702, 704 collectively define both a perforated flame holder and a perforated reaction holder. The tubes 702 extend into the face of the sheet in FIG. 7A. The tubes 704 extend vertically in FIG. 7A.The interiors of the tubes 702 define a flame holder perforation volume 103. The interiors of the tubes 704 define a gasifier perforation volume 105. The tube bodies themselves are physical heat channels that support thermal conduction therethrough. The combustion system 700 includes a fuel source 1 1 1 positioned adjacent to the tubes 704.

According to an embodiment, the combustion system 700 supports a low NOx combustion reaction 304 within the flame holder perforation volume 103 in conjunction with a gasification reaction 516 held in the gasifier perforation volume 105. The fuel source 1 1 1 supplies a first fuel 51 1 including fuel bound nitrogen to the perforations 518 via input apertures at a lower end of the tubes 704 as seen in the view of FIG. 7A. The burner body holds the gasification reaction 516 of the first fuel 51 1 within the gasifier perforation volume 105 defined by the interiors of the tube 704. A second fuel 520 exits the tube 704 at output apertures at a top end of the tubes as seen in FIG. 7A. The second fuel 520 generated by the gasification reaction 516 is passed to the tubes 702 via the fuel channel 108. An oxidant source 1 10 outputs an oxidant 521 that mixes with the second fuel 520 either before or after the second fuel 520 is received by the tubes 702. The flame holder perforation volume 103 defined by the interiors of the tubes 702 holds a combustion reaction 304 of the second fuel 520 and oxidant mixture within the flame holder perforation volume 103. The combustion reaction 304 generates heat. Some of the heat generated by the combustion reaction 304 is transferred to gasifier perforation volume 105 via the tube walls. The heat that is transferred to the gasifier perforation volume 105 supports the gasification reaction 516. In this way, the combustion system 100 supports a combustion reaction 304 that generates low levels of NOx.

FIG. 7B is a view of the combustion system 700 looking into the output apertures of the tubes 704, according to an embodiment. In FIG. 7B the input apertures of the tubes 702 are at the bottoms of the tubes 702. The output apertures of the tubes 702 are at the top of the tubes 702. The second fuel 520 output by the gasifier perforation volume 105 is provided to the input apertures of the tube 702. A combustion reaction 304 of the second fuel 520 and oxidant 521 is held within the flame holder perforation volume 103 defined by the tube 702. Flue gas 524 exits the tubes 702 at the output apertures.

FIG. 8 is a flow chart illustrating a method 800 of using a combustion system, according to an embodiment. According to an embodiment, the combustion system 100 of FIG. 1 can be configured to collectively execute method steps 800 shown in FIG. 8. The method starts at step 802, wherein the second fuel and combustion air in a lean mixture is received into a plurality of perforations in a perforated flame holder collectively defining a flame holder perforation volume. In step 804, a low NOx combustion reaction is collectively supported in the plurality of perforations. In step 806, heat is output to a thermal load 807. The thermal load 807 can include an electric power generation system, a chemical process, and/or a liquefaction process, for example. In step 808, heat is output into a physical heat channel. Proceeding to step 810, heat is transferred through the physical heat channel. In step 812 a first fuel, including fuel-bound nitrogen, is received into a perforated reaction holder. In step 814, the transferred heat is received into the perforated reaction holder. Continuing to step 816, a gasification reaction is supported in the perforated reaction holder with the received fuel and heat to output a second fuel 818. In step 820 the second fuel is diluted with the combustion air. The process 800 then loops to 802.

FIG. 9 is a flow chart of a method 900 for operating a combustion system, according to an embodiment. At 902 a first fuel is provided to a perforated reaction holder. At 904 a second fuel is generated by holding a gasification reaction of the first fuel within the perforated reaction holder. At 906 an oxidant is added to the second fuel. At 908 the oxidant and the second fuel are mixed. At 910 the second fuel and oxidant are passed to a perforated flame holder. At 912 a combustion reaction between the second fuel and the oxidant is held within the perforated flame holder. At 914 heat is transferred from the perforated flame holder to the perforated reaction holder.

According to an embodiment, each of the fuel particles may, during gasification, be reduced to a char or tar particle, referred to respectively as gasification residue. The gasification residue may be entrained in the second fuel and oxidant, travel into the perforations of the perforated flame holder, and be combusted.

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