Ignition-stable burner

Abstract

The present application relates to a pilot stable burner, according to one embodiment, a burner system comprising: a pilot burner disposed in a furnace at a distal position along a main fuel and combustion air flow axis; and one or more primary fuel nozzles disposed at a proximal location along the primary fuel and combustion air flow axis. A pilot burner is configured to support a pilot flame, and one or more primary fuel nozzles are configured to support a primary flame in contact with the pilot flame. The pilot burner is arranged to cause the main fuel and the combustion air to be ignited by the pilot flame.

Description

[0001] This application is a divisional application of an application with an application date of May 7, 2020, application number 202080034369.8, and invention name “Ignition Stabilization Burner”.

[0002] Cross-references to related patent applications

[0003] This application claims the benefit of priority to co-pending U.S. Provisional Patent Application No. 62 / 844,669, entitled “PILOT STABILIZED BURNER,” filed on May 7, 2019. This application also claims the benefit of priority to co-pending U.S. Provisional Patent Application No. 16 / 782,861, entitled “LOW EMISSION MODULAR FLARE STACK,” filed on February 5, 2020. Each of the foregoing patent applications is incorporated by reference to the extent not inconsistent with the disclosure herein. Summary of the invention

[0004] According to one embodiment, the burner system includes: a pilot burner disposed at a distal position along the main fuel and combustion air flow axis in the furnace; and one or more main fuel nozzles disposed at a proximal position along the main fuel and combustion air flow axis. The pilot burner is configured to support a pilot flame, and the one or more main fuel nozzles are configured to support a main flame in contact with the pilot flame. The pilot burner is configured to cause the main fuel and combustion air to be ignited by the pilot flame.

[0005] According to one embodiment, a burner system includes: a main fuel source disposed at a proximal position along a flow axis of a furnace; a pilot burner disposed at an intermediate distance along the flow axis; and a distal flame holder disposed at a distal position along the flow axis; the pilot burner being configured to support a pilot flame to heat the distal flame holder. The main fuel source is configured to provide the main fuel to the distal flame holder after the distal flame holder is at least partially heated. The distal flame holder is configured to maintain at least a portion of a combustion reaction supported by the main fuel.

[0006] According to one embodiment, a method for operating a burner system includes providing heat from a pilot flame supported by a pilot burner to a distal flame holder, the pilot flame being fueled by a pilot fuel. The distal flame holder and the pilot burner are disposed in a furnace and are proximate to each other, the pilot burner being disposed between the distal flame holder and one or more main fuel nozzles, wherein a distance between the pilot burner and the distal flame holder is less than a distance between the pilot burner and the one or more main fuel nozzles. The method for operating a burner system includes: introducing a mixed main fuel and air into the distal flame holder; and maintaining at least a portion of a combustion reaction of the mixed main fuel and air by the distal flame holder while the pilot burner continues to support the pilot flame.

[0007] According to one embodiment, a method for operating a burner system includes: supporting a diffusion flame across a portion of the width of a furnace volume at a location remote from a furnace floor; providing combustion air to the furnace volume from a location near the furnace floor; outputting a high-pressure main fuel jet from each of one or more main fuel nozzles at one or more locations near the furnace floor; mixing the main fuel with the combustion air while the main fuel and combustion air travel from the location near the furnace floor to a distal location; combusting the main fuel by exposing the mixed main fuel and air to the diffusion flame to produce a main flame. According to one embodiment, the main flame is held by a distal flame holder, which is further away from the furnace floor than the diffusion flame.

[0008] According to one embodiment, a combustion system includes: an oxidant source configured to output oxidant into a furnace volume; a pilot burner configured to support a pilot flame by outputting a pilot fuel to support a pilot diffusion flame at least during a preheat state; and a main fuel nozzle configured to output the main fuel from a proximal position into the furnace volume during a standard operating state at least after the preheat state is completed. The combustion system includes a distal flame holder positioned in the furnace volume to be preheated by the pilot flame during the preheat state, and to maintain a combustion reaction of the main fuel and the oxidant near the distal flame holder during the standard operating state. The combustion system includes: a combustion sensor configured to sense a condition of the combustion system and generate a sensor signal indicative of the condition of the combustion system; and one or more actuators configured to adjust the flow of the main fuel from the main fuel nozzle, adjust the flow of the pilot fuel to the pilot burner, and adjust the flow of the oxidant from the oxidant source. The combustion system includes a controller that is communicatively coupled to the actuator and the combustion sensor, the controller being configured to receive sensor signals from the combustion sensor and to control the actuator to adjust the flow of the pilot fuel, the main fuel, and the oxidant in response to the sensor signals and according to software instructions stored in a non-transitory computer readable medium coupled to the controller.

[0009] According to one embodiment, a computing system implemented method for operating a combustion system includes: receiving a sensor signal from a pilot flame sensor during a preheat state of the combustion system indicating a condition of a pilot flame in a furnace volume supported by a flow of a pilot fuel and an oxidant; and receiving a sensor signal from a distal flame holder sensor during the preheat state, the sensor signal indicating a temperature of a distal flame holder positioned in the furnace volume so as to be preheated by the pilot flame to an operating temperature during the preheat state. The method includes: in response to the sensor signal from the pilot flame sensor and in accordance with software instructions stored on a non-transitory computer readable medium, outputting a control signal to control one or more actuators to adjust the flow of the pilot fuel, adjust the flow of the oxidant, or generate an arc to ignite the pilot flame; and if the sensor signal from the distal flame holder sensor indicates that the distal flame holder has reached the operating temperature, outputting a control signal to control one or more actuators to transition the combustion system from the preheat state to a standard operating state, the standard operating state corresponding to supporting a combustion reaction of a main fuel and an oxidant in the distal flame holder and in accordance with software instructions stored on the non-transitory computer readable medium. The method includes: receiving a sensor signal indicating a condition of a distal flame holder from a distal flame holder sensor during a standard operating state; and in response to the sensor signal from the distal flame holder sensor during the standard operating state and in accordance with software instructions stored on a non-transitory computer readable medium, outputting a control signal to control one or more actuators to adjust the flow of a main fuel or to adjust the flow of an oxidizer.

[0010] According to one embodiment, a low-emission modular burner system includes one or more burner modules. Each burner module includes: a main fuel source, which is valve-controlled separately from all other fuel sources, and the main fuel source is configured to selectively deliver a main fuel flow to be diluted by a flow of combustion air; a main fuel igniter, which is configured to cause the main fuel flow emitted from the main fuel source to ignite; a distal flame holder, which is separated from the main fuel source and the main fuel igniter by a corresponding non-zero distance, and the distal flame holder is configured to maintain a combustion reaction supported by the main fuel flow when the distal flame holder is at or above a predetermined temperature; and a preheating device, which is configured to preheat the distal flame holder to a predetermined temperature. The low-emission modular burner system includes: a common combustion air source, which is configured to provide combustion air to each of a plurality of burner modules; and a wall, which surrounds the entirety of one or more burner modules, and the wall is configured to laterally contain the combustion fluid corresponding to the one or more burner modules.

[0011] According to one embodiment, a burner includes: a housing having a combustion air inlet at a base; and a burner module positioned within the housing. The burner module includes: an inlet configured to be coupled to a primary fuel source and receive combustion air via the housing; a distal flame holder positioned within the housing; and a primary nozzle configured to receive a flow of primary fuel from the inlet and emit the primary fuel flow toward the distal flame holder.

[0012] According to one embodiment, a burner system includes: a distal flame holder, which is configured to maintain a combustion reaction of a fuel and an oxidant; an oxidant duct, which is configured to guide the oxidant toward the distal flame holder; a main fuel nozzle, which is oriented to guide the flow of the main fuel into the combustion volume for mixing with the oxidant in a dilution region between the main fuel nozzle and the distal flame holder when the temperature of the distal flame holder is higher than a predetermined temperature; and a mixing tube, which is arranged in the dilution region and extends from a mixing tube inlet to a mixing tube outlet between the main fuel nozzle and the distal flame holder, the mixing tube being formed so that the flow of the oxidant and the fuel discharges the flue gas into the mixing tube for mixing with the fuel and the oxidant. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1A is a block diagram of a burner system according to one embodiment.

[0014] Figure 1B is a block diagram of a burner system including a distal flame holder according to one embodiment.

[0015] Figure 2A is a diagram of a burner system according to one embodiment.

[0016] Figure 2B is an illustration of a burner system including a distal flame holder according to one embodiment.

[0017] Figure 3 is a perspective view of a combustion system according to one embodiment.

[0018] Figure 4 is an illustration of an H-shaped pilot burner according to one embodiment.

[0019] Figure 5 is an illustration of a pilot burner in a helical shape according to one embodiment.

[0020] Figure 6 is an illustration of a pilot burner having a hexagonal shape according to one embodiment.

[0021] Figure 7is a simplified diagram of a combustion system including a distal flame holder configured to hold a combustion reaction, wherein the distal flame holder includes a perforated flame holder, according to one embodiment.

[0022] Figure 8 According to an implementation scheme Figure 7 A side cross-sectional view of a portion of a perforated flame holder.

[0023] Fig. 9 is a flow chart illustrating a method for operating a burner system including the distal flame holder shown and described herein, according to one embodiment.

[0024] Fig. 10A is a simplified perspective view of a combustion system including a reticulated ceramic perforated flame holder configured to maintain a combustion reaction according to one embodiment.

[0025] Fig. 10B According to an implementation scheme Fig. 10A A simplified side cross-sectional view of a portion of a reticulated ceramic perforated flame holder.

[0026] Fig.11 is a flow chart illustrating a method for operating a burner system according to one embodiment.

[0027] Fig.12 is a flow chart illustrating a method for operating a burner system according to one embodiment.

[0028] Fig.13A is a diagram of a combustion system including a distal flame holder and a capacitive combustion sensor according to one embodiment.

[0029] Fig. 13B is a top view of a distal flame holder and capacitive combustion sensor according to one embodiment.

[0030] Fig.14 is a diagram of an arrangement for each of a plurality of burner modules according to one embodiment.

[0031] Fig.15 According to one embodiment, a Fig.14 Diagram of the control circuit used in the control system.

[0032] Fig.16 is a block diagram of a burner system according to one embodiment.

[0033] Fig.17 is a diagram of a burner system according to one embodiment.

[0034] Fig.18is a diagram showing a horizontally fired burner system including a remote pilot burner and a mixing tube, according to one embodiment. DETAILED DESCRIPTION

[0035] In the following detailed description, reference is made to the accompanying drawings which form a part of this document. Unless otherwise indicated in the context, similar symbols in the drawings generally represent similar components. Other embodiments may be adopted and / or other changes may be made without departing from the spirit or scope of the present invention.

[0036] Figure 1A 1 is a block diagram of a burner system 100 according to one embodiment. The burner system 100 includes a pilot burner 104 and one or more main fuel nozzles 106. The pilot burner 104 and the main fuel nozzles 106 are disposed in a furnace volume 101.

[0037] According to one embodiment, the pilot burner 104 is disposed in the furnace 101 at a distal position along the main fuel and combustion air flow axis A. The one or more main fuel nozzles 106 are disposed along the main fuel and combustion air flow axis A at a proximal position.

[0038] According to one embodiment, the pilot burner 104 is configured to support a pilot flame 108. As described in more detail below, the pilot flame 108 helps ignite and / or maintain the main combustion reaction 110.

[0039] In one embodiment, the pilot burner 104 supports the pilot flame 108 by outputting the pilot fuel 112. The pilot flame 108 is supported by the pilot fuel 112 and the combustion air introduced into the furnace volume 101. Thus, the pilot flame 108 is a combustion reaction of the pilot fuel 112 and the combustion air.

[0040] In one embodiment, the one or more primary fuel nozzles 106 are configured to support a primary flame 110 within the furnace volume 101. The primary flame 110 is supported downstream of the pilot flame 108.

[0041] In one embodiment, the primary fuel nozzle 106 supports the primary flame 110 by outputting the primary fuel 114 into the furnace volume 101. The primary flame 110 is supported by the primary fuel 114 and combustion air introduced into the furnace volume 101. Thus, the primary flame 110 is a combustion reaction of the primary fuel 114 and the combustion air.

[0042] In one embodiment, the pilot burner 104 and the one or more primary fuel nozzles 106 are configured to simultaneously support a main flame 110 in contact with a pilot flame 108. The pilot burner 104 is configured to cause the main fuel and combustion air to be ignited by the pilot flame 108.

[0043] In one embodiment, the main flame 110 may not be in contact with the pilot flame 108. Instead, the main flame 110 may be separated from the pilot flame 108 by a gap.

[0044] In one embodiment, the pilot burner 104 includes a plurality of tubes or arms extending transversely from the axis A. The tubes or arms include a plurality of orifices that output the pilot fuel. Thus, the pilot flame 108 is maintained above each of the tubes, arms, or segments of the pilot burner 104. The shape of the pilot burner 104 may be selected to cover a lateral area corresponding to the area above the main fuel nozzle 106, or the area through which the main fuel 114 passes.

[0045] In one embodiment, the main fuel 114 passes through gaps or open spaces between the laterally extending portions of the pilot burners 104. As the main fuel 114 passes adjacent to the pilot flame 108, the main fuel 114 may initially be ignited by the pilot flame 108. After the main fuel 114 has been ignited, thereby generating the main flame 110, the main flame 110 may be supported by the main fuel 114 in a stable state.

[0046] In one embodiment, the laterally extending arms of the pilot burner 104 form a star shape. Additionally or alternatively, the pilot burner 104 may form a spiral shape, a circular shape, an H-shape, a square shape, a hexagonal shape, or other shapes that cover the desired lateral distance while including gaps through which the main fuel 114 may pass. (See, e.g., Figures 2A to 6 . )

[0047] In one embodiment, the pilot burner 104 includes a pilot fuel manifold. The pilot fuel manifold includes transversely extending tubes, segments, arms, or portions. The pilot fuel 112 is output from orifices located in the transversely extending tubes, segments, arms, or portions of the pilot fuel manifold.

[0048] According to one embodiment, when the burner system 100 is operated at rated heat output, the main flame 110 comprises a flame having a heat output that is at least 10 times the heat output of the pilot flame 108. In one embodiment, operating at rated heat output corresponds to operating in a steady-state standard operating mode of the burner system 100. In another embodiment, when the burner system 100 is operated at rated heat output, the main flame 110 comprises a flame having a heat output that is at least 20 times the heat output of the pilot flame 108.

[0049] According to one embodiment, the burner system 100 has a NOx output of about twenty parts per million or less, adjusted to 3% excess O2 at a stack operably coupled to the burner system 100. In one embodiment, the burner system 100 has a NOx output of about twenty parts per million or less, adjusted to 3% excess O2 at an exhaust stack operably coupled to the burner system 100.

[0050] Figure 1B is a block diagram of a burner system 111 including a distal flame holder 102 according to one embodiment. Figure 1B The burner system 111 is substantially similar to Figure 1A The burner system 100 is different in that the burner system 111 includes a distal flame holder 102 .

[0051] According to one embodiment, the burner system 111 includes: a main fuel source 106 disposed at a proximal position along a flow axis A of the furnace volume 101; a pilot burner 104 disposed at an intermediate distance along the flow axis A; and a distal flame holder 102 disposed at a distal position along the flow axis A. The pilot burner 104 may be configured to support a pilot flame 108 to heat the distal flame holder 102. The main fuel source 106 may be configured to provide the main fuel 114 to the distal flame holder 102 after the distal flame holder 102 is at least partially heated. The distal flame holder 102 may be configured to maintain at least a portion of the main flame 110 supported by the main fuel 114.

[0052] In one embodiment, the distal flame holder 102 is a perforated flame holder. Figures 7 to 10B The operation and structure of the perforated flame holders are described in greater detail.In other embodiments, the distal flame holder 102 may include one or more solid bluff body flame holders, or may include a mixture of one or more perforated flame holders and one or more bluff body flame holders.

[0053] Figure 2A is a diagram of a burner system 200 according to one embodiment. The burner system 200 includes a pilot burner 104 and a main fuel nozzle 106. Figure 2A 1, the pilot burner 104 supports the pilot flame 108 by outputting the pilot fuel 112. Although not shown in FIG. Figure 2A , but the primary fuel nozzle 106 is configured to support the primary flame 110 by outputting a primary fuel 114 .

[0054] According to one embodiment, the pilot burner 104 is supported by and receives fuel via a fuel pipe 220. The fuel pipe 220 extends into the furnace volume 101 via an opening 240 in a floor 238 of the furnace. A reinforcement 222 may be positioned around the fuel pipe 220 to prevent the fuel pipe 220 from rocking. The main fuel nozzle 106 also extends through the opening 240 in the floor 238. The main fuel nozzle 106 may be supported by a fuel riser 224. In one embodiment, the main fuel nozzle 106 includes an orifice that outputs the main fuel 114 at a 2° spread.

[0055] According to one embodiment, the pilot burner 104 defines a plurality of fuel orifices 218 having a sufficiently large collection area to collectively support the low momentum pilot flame 108. In one embodiment, the main fuel 114 and the combustion air output by the main fuel nozzle 106 form a combustible mixture that expands in width as it flows from a proximal position of the main fuel nozzle 106 to a distal position of the pilot burner 104. The plurality of fuel orifices 218 may be sufficiently widely disposed on the furnace volume 101 to cause the pilot flame 108 to contact the main fuel 114 and the combustion air mixture over the width of the combustible mixture. In another embodiment, the main fuel nozzle 106 is configured to output fuel that co-flows with air.

[0056] According to one embodiment, the pilot burner 104 includes a fuel manifold having a plurality of segments 219 joined together, each segment 219 having a plurality of fuel orifices 218 configured to allow fuel to pass from the interior of the fuel manifold to the furnace volume 101. The plurality of segments 219 may be formed as respective tubes configured to allow fuel delivered from a fuel tube 220 to freely enter the fuel manifold. In one embodiment, at least a portion of the tubes are arranged as spokes radiating from a center substantially disposed at a centerline along an axis. In other embodiments, at least a portion of the tubes may be arranged in an "X" shape, a rectangle, an "H" shape, a wagon wheel shape, or a star shape.

[0057] According to one embodiment, the pilot burner 104 includes a manifold that includes a curvilinear tube. In one embodiment, the curvilinear tube is arranged in a spiral, or “∞”.

[0058] According to one embodiment, the primary fuel nozzles 106 form a primary fuel dump plane at a proximal location that coincides with or is close to the floor 238 of the furnace.

[0059] According to one embodiment, the pilot burner 104 supports a diffusion flame at a distal location that is at least 100 main fuel nozzle 106 diameters away from the floor 238 of the furnace.

[0060] According to one embodiment, the pilot burner 104 includes at least one tube disposed transverse to the fuel and combustion air flow axis A. The at least one tube may include opposing vertical tabs extending upwardly from the at least one tube to form a "U" shaped channel.

[0061] According to one embodiment, the burner system 200 includes a pilot fuel source 230. The pilot fuel source 230 supplies the pilot fuel 112 into the fuel pipe 220. The pilot fuel 112 is output from the pilot burner 104 via the fuel orifice 218. The pilot fuel control valve 234 can be manually or electronically controlled to enable or close the flow of the pilot fuel 112 from the pilot fuel source 230 to the pilot burner 104.

[0062] According to one embodiment, the burner system 200 includes a main fuel source 232. The main fuel source 232 supplies the main fuel 114 to the main fuel nozzles 106. The main fuel 114 may be supplied to the main fuel nozzles 106 via the fuel riser 224. The main fuel control valve 236 may be manually or electronically controlled to enable or shut off the flow of the main fuel 114 from the main fuel source 232 to the main fuel nozzles 106.

[0063] According to one embodiment, the main fuel source 232 and the pilot fuel source 230 may be a single fuel source or reservoir whose fuel may be directed to the pilot burner 104 and the main fuel nozzle 106 , respectively, and may be individually controlled via, for example, the pilot fuel control valve 234 and the main fuel control valve 236 .

[0064] In one embodiment, combustion air is provided to the furnace volume 101 as a natural draft flow through openings 240 in the floor 238 of the furnace. Additionally or alternatively, combustion air can be provided to the furnace volume 101 in a manner other than through openings 240 in the floor 238. For example, the combustion air can include recycled flue gas, as discussed in more detail below. In another example, the combustion air can include forced draft from a blower (not shown).

[0065] Figure 2B is a diagram of a burner system 211 including a distal flame holder 102 according to one embodiment. The burner system 211 is substantially similar to Figure 2A The burner system 200 is different in that the burner system 211 includes a distal flame holder 102 positioned above the pilot burner 104, that is, disposed at a position farther away from the main fuel nozzle 106 than the pilot burner 104. Although the pilot burner supports the pilot flame 108 (see Figure 1A and Figure 1B ), but the distal flame holder 102 holds the main flame 110 (see Figure 1B ). The pilot flame 108 may ignite and stabilize the main flame 110 .

[0066] According to one embodiment, the distal flame holder 102 may include a perforated flame holder configured to hold the secondary flame 110 and control the length of the secondary flame 110. Such a perforated flame holder 102 may hold at least a portion of the secondary flame 110 within the perforated flame holder 102.

[0067] Figure 3 is a perspective view of a combustion system 300 according to one embodiment. The burner system 300 includes a pilot burner 104 and a main fuel nozzle 106. Although Figure 3 Although not shown, the pilot burner 104 is configured to support the pilot diffusion flame 108 by outputting the pilot fuel 112 through the low velocity orifice. Figure 3 , but the primary fuel nozzle 106 is configured to support the primary flame 110 by outputting the primary fuel 114 as one or more high velocity streams or “jets”.

[0068] According to one embodiment, the pilot burner 104 is supported by a fuel tube 220 and receives the pilot fuel 112 via the fuel tube. The fuel tube 220 extends into the furnace volume 101 via an opening 240 in a floor 238 of the furnace. A reinforcement 222 may be positioned around the fuel tube 220 to prevent the fuel tube 220 from rocking. The main fuel nozzle 106 also extends through the opening 240 in the floor 238. The main fuel nozzle 106 may be supported by a fuel riser 224. In one embodiment, the main fuel nozzle 106 includes an orifice that outputs the main fuel at a spread of about 2°.

[0069] According to one embodiment, the pilot burner 104 includes a fuel manifold having a plurality of segments 219 joined together, each segment 219 having a plurality of fuel orifices (e.g., Figure 2A , Figure 2B The plurality of segments 219 may be formed to be configured to allow fuel delivered from the fuel tube 220 to freely enter the corresponding tube of the fuel manifold. In one embodiment, at least a portion of the tubes are arranged as spokes radiating from a center substantially disposed at a centerline along the axis. Figure 3 In an embodiment, the plurality of segments 219 are arranged in an "X" shape.

[0070] In one embodiment, each segment 219 includes one or more sections 226 of reticulated ceramic disposed in and supported by a "U" shaped channel in the segment 219. The pilot fuel 112 may flow from the fuel orifices 218 into the channel or passageway of the one or more sections 226 of reticulated ceramic. The pilot flame 108 may be at least partially maintained within the channel or passageway of the one or more sections 226 of reticulated ceramic.

[0071] In one embodiment, the one or more sections 226 of reticulated ceramic are disposed above at least one of the tubes forming the plurality of sections 219. The at least one tube may define a plurality of fuel flow holes disposed along the length of the at least one tube. In one embodiment, the at least one tube defines a plurality of fuel flow holes configured to allow the gaseous pilot fuel 112 to flow upwardly into a "U" shaped channel formed above the at least one tube.

[0072] In one embodiment, the burner system 300 includes legs 252. The legs 252 may support the distal flame holder 102 (at Figure 3 ), including a solid bluff body and / or a perforated flame holder. The distal flame holder can hold a portion of the main flame 110.

[0073] Figure 4 is an illustration of an H-shaped pilot burner 104 according to one embodiment. The pilot burner 104 includes a plurality of fuel orifices 218 that may output the pilot fuel 112. The pilot burner 104 may be comprised of a plurality of tube sections joined together to form an "H" shape.

[0074] Figure 5 is an illustration of a pilot burner 104 having a spiral shape according to one embodiment. The pilot burner 104 includes a plurality of fuel orifices 218 that may output the pilot fuel 112. The pilot burner 104 may be comprised of a plurality of tube segments joined together to form a spiral shape.

[0075] Figure 6 is an illustration of a pilot burner 104 having a hexagonal shape attached to the sides of a central hub according to one embodiment. The pilot burner 104 includes a plurality of fuel orifices 218 that can output the pilot fuel 112. The pilot burner 104 can be made of Figure 6 The shape shown is composed of multiple pipe segments.

[0076] Figure 7is a simplified diagram of a combustion system 700 including a distal flame holder 102 configured to hold a combustion reaction, wherein the distal flame holder 102 comprises a perforated flame holder, according to one embodiment. According to various embodiments, the distal flame holder 102 can be implemented in the burner systems 111, 200, and 300. As used herein, the terms distal flame holder, blunt body flame holder, perforated flame holder, perforated reaction holder, porous flame holder, porous reaction holder, dual, and dual tile should be considered synonymous or interchangeable unless the context dictates otherwise or further definition is provided. Figures 7 to 10B A burner system that employs a perforated flame holder as a type of distal flame holder 102 is specifically described.

[0077] Experiments performed by the inventors show that the distal flame holder 102 described herein can support very clean combustion. Specifically, in pilot to full-scale experimental use of the burner system 700, the output of nitrogen oxides (NOx) was measured to drop from low single-digit parts per million (ppm) to undetectable (less than 1 ppm) concentrations of NOx at the stack. These remarkable results were measured at 3% (dry) oxygen (O2) concentration and undetectable carbon monoxide (CO) at typical stack temperatures (1400-1600°F) for industrial furnace applications. In addition, these results do not require any special measures, such as selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), water / steam injection, external flue gas recirculation (FGR), or other extreme conditions that conventional burners may even require in order to approach such clean combustion.

[0078] According to an embodiment, the burner system 700 includes a fuel and oxidant source 702 configured to output a primary fuel and an oxidant into a combustion volume 704 to form a primary fuel and oxidant mixture 706. The fuel and oxidant source may include a primary fuel nozzle 106. As used herein, unless further definition is provided, the terms fuel and oxidant mixture and fuel stream are used interchangeably and are considered synonymous according to the context. As used herein, unless further definition is provided, the terms combustion volume, combustion chamber, furnace volume, etc. should be considered synonymous. A perforated flame holder 102 is disposed in the combustion volume 704 and is positioned to receive the primary fuel and oxidant mixture 706.

[0079] Figure 8 According to one embodiment, Figure 7 A side cross-sectional view 800 of a portion of a perforated flame holder of a distal flame holder 102. Figure 7 and Figure 8, the perforated flame holder 102 includes a perforated flame holder body 708 defining a plurality of perforations 710 aligned to receive a primary fuel and oxidant mixture 706 from a fuel and oxidant source 702. As used herein, unless further definition is provided, the terms perforation, pore, aperture, elongated aperture, etc. should be considered synonymous in the context of the perforated flame holder 102. The perforations 710 are configured to collectively hold a combustion reaction supported by the primary fuel and oxidant mixture 706.

[0080] The fuel may include hydrogen, hydrocarbon gas, vaporized hydrocarbon liquid, atomized hydrocarbon liquid or powdered or pulverized solid. The fuel may be a single species or may include a mixture of gas, steam, atomized liquid and / or pulverized solid. For example, in process heater applications, the fuel may include fuel gas or a byproduct from the process, the byproduct including carbon monoxide (CO), hydrogen (H2) and methane (CH4). In another application, the fuel may include natural gas (mainly CH4) or propane (C3H8). In another application, the fuel may include No. 2 fuel oil or No. 6 fuel oil. The inventors similarly envision dual fuel applications and flexible fuel applications. The oxidant may include oxygen carried by air, flue gas and / or may include another oxidant, which is pure or carried by a carrier gas. In this article, the terms oxidant and oxidizer should be considered synonymous.

[0081] According to one embodiment, the perforated flame holder body 708 may be defined by an input face 712 configured to receive the primary fuel and oxidant mixture 706, an output face 714 facing away from the fuel and oxidant source 702, and an outer peripheral surface 716 defining a lateral extent of the perforated flame holder 102. The plurality of perforations 710 defined by the perforated flame holder body 708 extend from the input face 712 to the output face 714. The plurality of perforations 710 may receive the primary fuel and oxidant mixture 706 at the input face 712. The primary fuel and oxidant mixture 706 may then combust within or near the plurality of perforations 710, and combustion products may exit the plurality of perforations 710 at or near the output face 714.

[0082] According to one embodiment, the perforated flame holder 102 is configured to keep most of the combustion reaction 802 in the perforation 710. For example, on a steady-state basis, more than half of the fuel molecules output to the combustion volume 704 by the fuel and oxidant source 702 can be converted into combustion products between the input face 712 and the output face 714 of the perforated flame holder 102. According to an alternative explanation, more than half of the heat or thermal energy output by the combustion reaction 802 can be output between the input face 712 and the output face 714 of the perforated flame holder 102. As used herein, unless further definition is provided, the terms heat, thermal energy and thermal energy should be considered synonymous. As used above, thermal energy and thermal energy generally refer to the release chemical energy initially maintained by reactants during the combustion reaction 802. As used herein elsewhere, heat, thermal energy and thermal energy correspond to the detectable temperature rise experienced by a real subject characterized by heat capacity. Under nominal operating conditions, the perforations 710 may be configured to collectively maintain at least 80% of the combustion reaction 802 between the input face 712 and the output face 714 of the perforated flame holder 102. In some experiments, the inventors generated a combustion reaction 802 that was apparently entirely contained in the perforations 710 between the input face 712 and the output face 714 of the perforated flame holder 102. According to an alternative explanation, when the combustion is "time-averaged," the perforated flame holder 102 may support the combustion between the input face 712 and the output face 714. For example, during transients, such as before the perforated flame holder 102 is sufficiently heated, or if an excessively high (cold) load is placed on the system, the combustion may proceed slightly downstream from the output face 714 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 proceed slightly upstream of the input face 712 of the perforated flame holder 102.

[0083] Although "flame" is described in a manner to facilitate description, it should be understood that in some cases, there is no visible flame. Combustion occurs primarily within the perforations 710, but the "glow" of the combustion heat is primarily the visible glow of the perforated flame holder 102 itself. In other cases, the inventors have noticed transient "blows" or "flashbacks" in which the flame is visible in the region between the input face 712 of the perforated flame holder 102 and the primary fuel nozzle 718, in the dilution region D DSuch transient blow-backs or flashbacks are typically short-lived, such that on a time-averaged basis, the majority of the burning occurs in the perforations 710 of the perforated flame holder 102, between the input face 712 and the output face 714. In other cases, the inventors have noted significant burning occurring downstream from the output face 714 of the perforated flame holder 102, but the majority of the burning still occurs in the perforated flame holder 102, as evidenced by an observed persistent visible glow from the perforated flame holder 102.

[0084] The perforated flame holder 102 can be configured to receive heat from the combustion reaction 802 and output a portion of the received heat as thermal radiation 804 to a heat receiving structure (e.g., furnace wall and / or radiant section working fluid tube) in or near the combustion volume 704. As used herein, unless further definition is provided, the terms radiation, thermal radiation, radiant heat, thermal radiation, etc. should be understood to be substantially synonymous. In particular, such terms refer to blackbody radiation of electromagnetic energy primarily at infrared wavelengths, and also at visible wavelengths due to the high temperature of the perforated flame holder body 708.

[0085] See Figure 8 , the perforated flame holder 102 outputs another portion of the received heat to the main fuel and oxidant mixture 706 received at the input face 712 of the perforated flame holder 102. The perforated flame holder body 708 may receive heat from the combustion reaction 802 at least in the heat receiving region 806 of the perforated wall 808. Experimental evidence has shown the inventors that the location of the heat receiving region 806, or at least the location corresponding to the maximum rate of heat reception, may vary along the length of the perforated wall 808. In some experiments, the location of the maximum heat reception was significantly between 1 / 3 and 1 / 2 of the distance from the input face 712 to the output face 714 (i.e., a location slightly closer to the input face 712 than the output face 714). The inventors contemplate the following: Under other conditions, the heat receiving region 806 may be located closer to the output face 714 of the perforated flame holder 102. Most likely, the heat receiving region 806 (or for that matter, the heat output region 810 described below) does not have a clearly defined edge. For ease of understanding, the heat receiving area 806 and the heat output area 810 will be described as specific areas 806 , 810 .

[0086] The perforated flame holder body 708 can be characterized by a heat capacity. The perforated flame holder body 708 can hold an amount of heat energy from the combustion reaction 802 corresponding to the heat capacity multiplied by the temperature rise, and transfer the heat energy from the heat receiving area 806 to the heat output area 810 of the perforated wall 808. Typically, the heat output area 810 is closer to the input face 712 than the heat receiving area 806. According to one interpretation, the perforated flame holder body 708 can transfer heat from the heat receiving area 806 to the heat output area 810 via thermal radiation (shown as 804 in the figure). According to another interpretation, the perforated flame holder body 708 can transfer heat from the heat receiving area 806 to the heat output area 810 via thermal conduction along a thermal conduction path 812. The inventors contemplate that a variety of heat transfer mechanisms, including conduction, radiation, and possibly convection, can be used to transfer heat from the heat receiving area 806 to the heat output area 810. In this manner, the perforated flame holder 102 may act as a heat source to sustain the combustion reaction 802 even under conditions where the combustion reaction 802 would be unstable if supported by a conventional flame holder.

[0087] The inventors believe that the perforated flame holder 102 causes the combustion reaction 802 to begin within the thermal boundary layer 814 formed by the wall 808 adjacent to the perforation 710. With regard to combustion, which is generally understood to include a large number of individual reactions, and since most of the combustion energy is released within the perforated flame holder 102, it is apparent that at least most of the individual reactions occur within the perforated flame holder 102. As the relatively cool main fuel and oxidant mixture 706 approaches the input face 712, the mixture flow is divided into portions that flow through each perforation 710 separately. As more and more heat is transferred to the incoming main fuel and oxidant mixture 706, the hot perforated flame holder body 708 transfers heat to the fluid, particularly in the thermal boundary layer 814 of increasing thickness. After reaching the combustion temperature (e.g., the autoignition temperature of the fuel), the reactants continue to flow during the chemical ignition delay time, during which the combustion reaction 802 occurs. Therefore, the combustion reaction 802 is shown to occur within the thermal boundary layer 814. As the flow proceeds, the thermal boundary layer 814 merges at the merging point 816. Ideally, the merging point 816 is located between the input face 712 and the output face 714 that define the ends of the through-holes 710. At some location along the length of the through-holes 710, the combustion reaction 802 outputs more heat to the perforated flame holder body 708 than it receives from the perforated flame holder body 708. The heat is received at the heat receiving region 806, held by the perforated flame holder body 708, and transferred to the heat output region 810 closer to the input face 712, where it is transferred to the cold reactants (and any included diluent) to bring the reactants to an ignition temperature.

[0088] In one embodiment, each perforation in the perforations 710 is characterized by a length L, which is defined as the length of the reactive fluid propagation path between the input face 712 and the output face 714 of the perforated flame holder 102. As used herein, the term reactive fluid refers to the substance that travels through the perforations 710. Near the input face 712, the reactive fluid includes a main fuel and oxidant mixture 706 (optionally including nitrogen, flue gas and / or other "non-reactive" substances). Within the combustion reaction 802 region, the reactive fluid may include plasma associated with the combustion reaction 802, molecules of reactants and their components, any non-reactive substances, reaction intermediates (including transition states), and reaction products. Near the output face 714, the reactive fluid may include reaction products and byproducts, non-reactive gases, and excess oxidant.

[0089] The plurality of perforations 710 may each be characterized by a transverse dimension D between the relative perforated walls 808. The inventors have found that if the length L of each perforation 710 is at least four times the transverse dimension D of the perforation, stable combustion can be maintained in the perforated flame holder 102. In other embodiments, the length L may be six times the transverse dimension D. For example, experiments have been conducted with L being at least eight times, at least twelve times, at least sixteen times, and at least twenty-four times the transverse dimension D. Preferably, the length L is long enough to allow a thermal boundary layer 814 to form adjacent to the perforated wall 808 in the reactive fluid flowing through the perforations 710 to converge at a merging point 816 within the perforations 710 between the input face 712 and the output face 714 of the perforated flame holder 102. In experiments, the inventors found that the L / D ratio worked well (i.e., produced low NOx, produced low CO, and maintained stable combustion) when it was between 12 and 48.

[0090] The perforated flame holder body 708 may be configured to transfer heat between adjacent perforations 710. The amount of heat transferred between adjacent perforations 710 may be selected such that heat output from the combustion reaction portion 802 in a first perforation 710 supplies heat to stabilize the combustion reaction portion 802 in an adjacent perforation 710.

[0091] See Figure 7 , the fuel and oxidant source 702 may also include a primary fuel nozzle 718 (e.g., corresponding to the primary fuel nozzle 106 described herein) configured to output the primary fuel 114, and an oxidant source 720 configured to output a fluid containing an oxidant. For example, the primary fuel nozzle 718 may be configured to output substantially pure fuel (rather than, for example, a fuel-air mixture). The oxidant source 720 may be configured to output combustion air carrying oxygen, and optionally, flue gas.

[0092] The perforated flame holder 102 may be held by a perforated flame holder support structure 722 configured to maintain the perforated flame holder 102 at a dilution distance D from the primary fuel nozzle 718. D The primary fuel nozzle 718 may be configured to emit a selected fuel jet to entrain the oxidant to dilute the fuel jet along a path through a dilution distance D between the primary fuel nozzle 718 and the perforated flame holder 102. D The fuel and oxidant travel to the perforated flame holder 102 to form the main fuel and oxidant mixture 706. In addition or alternatively, (particularly when a blower is used to deliver the oxidant contained in the combustion air), the oxidant or combustion air source 720 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 724 may be provided. Additionally or alternatively, the primary fuel nozzle 718 may be configured to emit a selected fuel jet to dilute the primary fuel nozzle 718 as the fuel jet travels through a dilution distance D between the primary fuel nozzle 718 and the input face 712 of the perforated flame holder 102. D And entrained oxidant and entrained flue gas.

[0093] The primary fuel nozzle 718 may be configured to emit fuel through one or more fuel orifices 726 having an inner diameter dimension referred to as a "nozzle diameter." The perforated flame holder support structure 722 may support the perforated flame holder 102 to be disposed at a distance D from the primary fuel nozzle 718 that is greater than 20 times the nozzle diameter. D The main fuel and oxidant mixture 706 is received at the perforated flame holder 102. In another embodiment, the perforated flame holder 102 is disposed at a distance D from the main fuel nozzle 718 that is 100 to 1100 times the nozzle diameter. D The primary fuel and oxidant mixture 706 is received at the combustion reaction 802. Preferably, the perforated flame holder support structure 722 is configured to hold the perforated flame holder 102 at a distance of about 200 times or more of the nozzle diameter from the primary fuel nozzle 718. When the distance traveled by the primary fuel and oxidant mixture 706 is about 200 times or more of the nozzle diameter, the mixture is sufficiently homogenized to allow the combustion reaction 802 to produce minimal NOx.

[0094] According to one embodiment, the fuel and oxidant source 702 may alternatively include a premixed fuel and oxidant source. The premixed fuel and oxidant source may include a premixing chamber (not shown), a fuel nozzle configured to output fuel into the premixing chamber, and an oxidant (e.g., combustion air) channel configured to output oxidant into the premixing chamber. A flame arrester may be disposed between the premixed fuel and oxidant source and the distal flame holder 102, and is configured to prevent flame flashback into the premixed fuel and oxidant source. Alternatively, as described herein, a pilot burner, a pilot flame holder, and / or a continuous pilot flame may be disposed between the fuel and oxidant source 702 and the distal flame holder 102 to ensure combustion of the main fuel and oxidant.

[0095] Whether configured for entrainment in the combustion volume 704 or for premixing, the oxidant source 720 may include a blower configured to propel the oxidant through the fuel and oxidant source 702 .

[0096] The perforated flame holder support structure 722 may be configured to support the perforated flame holder 102, for example, from a floor or wall (not shown) of the combustion volume 704. In another embodiment, the perforated flame holder support structure 722 supports the perforated flame holder 102 from the fuel and oxidant source 702. Alternatively, the perforated flame holder support structure 722 may suspend the perforated flame holder 102 from an overhead structure, such as a flue in the case of an upward firing system. The perforated flame holder support structure 722 may support the perforated flame holder 102 in various orientations and directions.

[0097] The perforated flame holder 102 may include a single perforated flame holder body 708. In another embodiment, the perforated flame holder 102 may include a plurality of adjacent perforated flame holder segments that collectively provide a tiled perforated flame holder 102.

[0098] The perforated flame holder support structure 722 may be configured to support the plurality of perforated flame holder segments. The perforated flame holder support structure 722 may include a metal superalloy, a cementatious material, and / or a ceramic refractory material. In one embodiment, the plurality of adjacent perforated flame holder segments may be connected by a fiber reinforced refractory cementitious material.

[0099] The perforated flame holder 102 may have a width dimension W between opposite sides of the peripheral surface 716 that is at least twice the thickness dimension T between the input face 712 and the output face 714. In another embodiment, the perforated flame holder 102 may have a width dimension W between opposite sides of the peripheral surface 716 that is at least three times, at least six times, or at least nine times the thickness dimension T between the input face 712 and the output face 714 of the perforated flame holder 102.

[0100] In one embodiment, the width dimension W of the perforated flame holder 102 may be less than the width of the combustion volume 704. This may allow a flue gas recirculation path 724 from above to below the perforated flame holder 102 to be located between the outer peripheral surface 716 of the perforated flame holder 102 and the combustion volume wall (not shown).

[0101] See again Figure 7 and Figure 8 , the perforations 710 may have various shapes. In one embodiment, the perforations 710 may include elongated squares, each having a transverse dimension D between opposite sides of the square. In another embodiment, the perforations 710 may include elongated hexagons, each having a transverse dimension D between opposite sides of the hexagon. In yet another embodiment, the perforations 710 may include hollow cylinders, each having a transverse dimension D corresponding to the diameter of the cylinder. In another embodiment, the perforations 710 may include truncated cones or truncated pyramids (e.g., frustums), each having a transverse dimension D that is radially symmetric relative to a length axis extending from the input face 712 to the output face 714. In some embodiments, the perforations 710 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 710 may have a transverse dimension D that is less than the standard reference quenching distance.

[0102] In one series of embodiments, each perforation of the plurality of perforations 710 has a transverse dimension D between 0.05 inches and 1.0 inches. Preferably, each perforation of the plurality of perforations 710 has a transverse dimension D between 0.1 inches and 0.5 inches. For example, the plurality of perforations 710 may each have a transverse dimension D of about 0.2 inches to 0.4 inches.

[0103] The porosity of the perforated flame holder 102 is defined as the total volume of all perforations 710 in the section of the perforated flame holder 102 divided by the total volume of the perforated flame holder 102 including the perforated flame holder body 708 and the perforations 710. The perforated flame holder 102 should have a porosity between 0.10 and 0.90. In one embodiment, the perforated flame holder 102 may have a porosity between 0.30 and 0.80. In another embodiment, the perforated flame holder 102 may have a porosity of about 0.70. It has been found that using a porosity of about 0.70 is particularly effective for producing very low NOx.

[0104] The perforated flame holder 102 may be formed of a fiber reinforced cast refractory material and / or a refractory material such as an aluminum silicate material. For example, the perforated flame holder 102 may be formed to include mullite or cordierite. In addition or alternatively, the perforated flame holder body 708 may include a metal superalloy such as Inconel or Hastelloy. The perforated flame holder body 708 may define a honeycomb structure. Honeycomb structures are an industrial term in the art that need not strictly refer to a hexagonal cross section and most commonly include cells of a square cross section. Honeycomb structures of other cross-sectional areas are also known.

[0105] The inventors have discovered that the perforated flame holder 102 can be made of a material that is available from Applied Ceramics, Inc. of Doraville, South Carolina. Ceramic honeycomb structure is formed.

[0106] The perforations 710 may be parallel to each other and perpendicular to the input face 712 and the output face 714. In another embodiment, the perforations 710 may be parallel to each other and formed at an angle relative to the input face 712 and the output face 714. In another embodiment, the perforations 710 may not be parallel to each other. In another embodiment, the perforations 710 may not be parallel to each other and do not intersect. In another embodiment, the perforations 710 may intersect. The perforated flame holder body 708 may be unitary or may be formed from multiple sections.

[0107] In another embodiment, which is not necessarily preferred, the perforated flame holder 102 can be formed of a reticulated ceramic material. The term "reticulated" refers to a mesh structure. Reticulated ceramic materials are typically made by dissolving a slurry in a sponge having a specific porosity, hardening the slurry, and burning off the sponge and curing the ceramic.

[0108] In another, less preferred embodiment, the perforated flame holder 102 may be formed from a ceramic material that is punched, drilled, or cast to form the channels.

[0109] In another embodiment, the perforated flame holder 102 may include a plurality of tubes or barrels bundled together. The plurality of perforations 710 may include a hollow cylinder and may optionally also include a void space between the bundled tubes. In one embodiment, the plurality of tubes may include a ceramic tube. A refractory adhesive material may be included between the tubes and configured to adhere the tubes together. In another embodiment, the plurality of tubes may include a metal (e.g., superalloy) tube. The plurality of tubes may be held together by a metal tensile member that is arranged to hold the plurality of tubes together and that is around the plurality of tubes. The metal tensile member may include stainless steel, superalloy wire and / or superalloy metal band.

[0110] Perforated flame holder body 708 may alternatively include stacked perforated material plates, each plate having an opening connected with the plate below and the opening of the plate pressed on it. Perforated plate may include perforated metal plate, ceramic plate and / or expansion plate. In another embodiment, perforated flame holder body 708 may include discontinuous filler body so that perforation 710 is formed in the void space between discontinuous filler body. In one example, discontinuous filler body includes regular filler shape. In another example, discontinuous filler body includes random filler shape. For example, discontinuous filler body may include ceramic Raschig ring, ceramic Bell saddle filler, ceramic square saddle filler, and / or metal ring or other shapes (for example super Raschig ring) that may be held together by metal retainer.

[0111] The inventors contemplate various explanations for why a burner system including the perforated flame holder 102 provides such clean combustion.

[0112] According to one embodiment, the perforated flame holder 102 can still act as a heat source to maintain the combustion reaction 802 even under conditions where the combustion reaction 802 would be unstable if supported by a conventional flame holder. This capability can be exploited to support combustion using a leaner fuel and oxidant mixture than would normally be feasible. Thus, according to one embodiment, at the point where the fuel stream 706 contacts the input face 712 of the perforated flame holder 102, the average fuel to oxidant ratio of the fuel stream 706 is below the (conventional) lower flammability limit of the fuel components of the fuel stream 706 - the lower flammability limit defines the lowest fuel concentration at which the main fuel and oxidant mixture 706 will burn when exposed to a transient ignition source at normal atmospheric pressure and an ambient temperature of 25°C (77°F).

[0113] It has been found that the perforated flame holder 102 described herein and the system including the perforated flame holder 102 and or the flame holder placed far side provide substantially complete combustion of CO (single digit ppm down to undetectable concentration, depending on experimental conditions) while supporting low NOx. According to one explanation, such performance can be achieved due to sufficient mixing (and other strategies) for reducing the peak flame temperature. The flame temperature tends to peak under slightly rich conditions, which can be obvious in any diffusion flame with insufficient mixing. By fully mixing, a homogeneous and slightly lean mixture can be achieved before combustion. This combination can lead to a reduction in flame temperature and thus reduce NOx formation. In one embodiment, "slightly lean" can refer to 3% O2, that is, an equivalence ratio of about 0.87. It is possible to use an even leaner mixture, but it may lead to an increase in O2 levels. In addition, the inventors believe that the perforated wall 808 can act as a radiator for the combustion fluid. This effect can alternatively or in addition reduce the combustion temperature and reduce NOx.

[0114] According to another explanation, if the combustion reaction 802 occurs in a very short duration, the generation of NOx can be reduced. Rapid combustion causes the reactants (including oxygen and entrained nitrogen) to be exposed to the NOx formation temperature for a short time that is not enough for the NOx formation kinetics to cause significant generation of NOx. Compared with conventional flames, the time required for the reactants to pass through the perforated flame holder 102 is very short. Therefore, the low NOx generation associated with perforated flame holder combustion can be related to the shorter duration required for the reactants (and entrained nitrogen) to pass through the perforated flame holder 102.

[0115] Fig. 9 is a flow chart illustrating a method 900 for operating a burner system including a distal flame holder 102 (e.g., a perforated flame holder) as shown and described herein, according to one embodiment. To operate a burner system including a distal flame holder, the distal flame holder is first heated to a temperature sufficient to maintain combustion of a fuel and oxidant mixture.

[0116] According to a simplified description, method 900 begins at step 902, where the distal flame holder is preheated to a start-up temperature T S After the distal flame holder is raised to the start-up temperature, the method proceeds to step 904 where fuel and oxidant are provided to the distal flame holder and combustion is maintained by the distal flame holder.

[0117] According to a more detailed description, step 902 begins with step 906, where startup energy is provided at the distal flame holder. Simultaneously with or after providing the startup energy, decision step 908 determines whether the temperature T of the distal flame holder is equal to or greater than the startup temperature T S As long as the temperature of the distal flame holder is below its activation temperature, the method loops between steps 906 and 908 in the preheating step 902. In decision step 908, if the temperature T of at least one predetermined portion of the distal flame holder is greater than or equal to the activation temperature, the method 900 proceeds to general step 904, where fuel and oxidant are provided to the distal flame holder and combustion is maintained by the distal flame holder.

[0118] Step 904 may be broken down into several discrete steps, at least some of which may occur simultaneously.

[0119] Beginning at decision step 908, a fuel and oxidant mixture is provided to the distal flame holder, as shown in step 910. For example, the fuel and oxidant may be provided by a fuel and oxidant source including a separate fuel nozzle and an oxidant (e.g., combustion air) source. In this method, 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 distal flame holder. The fuel may entrain the combustion air (or alternatively, the combustion air may dilute the fuel) to provide the fuel and oxidant mixture at the input face of the distal flame holder at a fuel dilution selected for a stable combustion reaction that may be maintained within the perforations of the distal flame holder.

[0120] Proceeding to step 912, the combustion reaction is maintained by a distal flame holder.

[0121] Heat may be output from the distal flame holder in step 914. The heat output from the distal flame holder may be used, for example, to power an industrial process, heat a working fluid, generate electricity, or provide power.

[0122] In optional step 916, the presence of combustion may be sensed. Various sensing methods have been used and contemplated by the inventors. Generally speaking, the combustion maintained by the distal flame holder is very stable and does not require unusual sensing of the system. Combustion sensing may be performed using infrared sensors, video sensors, ultraviolet sensors, charged material sensors, thermocouples, thermopiles, flame rods, and / or other combustion sensing devices. In additional or alternative variations of step 916, in the event that combustion is extinguished in the distal flame holder, a pilot flame or other ignition source may be provided to ignite the fuel and oxidant mixture.

[0123] Proceeding to decision step 918, if combustion instability is sensed, the method 900 may exit to step 924, where an error handling procedure is performed. For example, the error handling procedure may include shutting down the fuel flow, re-performing the preheating step 902, outputting an alarm signal, igniting a backup combustion system, or other steps. In decision step 918, if it is determined that the combustion in the distal flame holder is stable, the method 900 proceeds to decision step 920, where it is determined whether the combustion parameters should be changed. If no combustion parameters are to be changed, the method loops (within step 904) back to step 910 and continues the combustion process. If a change in the combustion parameters is indicated, the method 900 proceeds to step 922, where a combustion parameter change is performed. After the combustion parameters are changed, the method loops (within step 904) back to step 910 and continues combustion.

[0124] For example, if a change in heat demand is encountered, a change in combustion parameters may be arranged. For example, if less heat is required (e.g., due to reduced power demand, reduced power demand, or reduced industrial process throughput), the fuel and oxidant flow rates may be reduced in step 922. 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 startup mode, the fuel and oxidant flow rates may be gradually increased to the distal flame holder in one or more iterations of the cycle in step 904.

[0125] See again Figure 7 , the burner system 700 includes a heater 728 operably coupled to the distal flame holder 102. Figure 8 and Fig. 9 As described, the distal flame holder 102 operates by outputting heat to the incoming main fuel and oxidant mixture 706. This heat is provided by the combustion reaction 802 after combustion is established; but before combustion is established, this heat is provided by the heater 728.

[0126] The inventors have used and contemplated various heating devices. In some embodiments, the heater 728 may include a flame holder configured to support a flame, the flame being configured to heat the distal flame holder 102. The fuel and oxidant source 702 may include a main fuel nozzle 718 configured to emit a fuel stream 706 and an oxidant source 720 configured to output an oxidant (e.g., combustion air) adjacent to the fuel stream 706. The main fuel nozzle 718 and the oxidant source 720 may be configured to output a fuel stream 706 to be progressively diluted by an oxidant (e.g., combustion air). The distal flame holder 102 may be configured to receive a diluted main fuel and oxidant mixture 706 that supports a combustion reaction 802 that is stabilized by the distal flame holder 102 when the distal flame holder 102 is at an operating temperature. In contrast, the startup flame holder may be configured to support a startup flame at a position corresponding to a relatively unmixed fuel and oxidant mixture that is stabilized without the need for stabilization provided by the heated distal flame holder 102.

[0127] The burner system 700 may further include a controller 730 operably coupled to the heater 728 and the data interface 732. For example, the controller 730 may be configured to control a startup flame holder actuator configured to cause the startup flame holder to maintain a startup flame when the distal flame holder 102 needs to be preheated and to maintain a startup flame when the distal flame holder 102 is at an operating temperature (e.g., when T ≥ T S The starting flame is not maintained during the next operation.

[0128] Various methods for actuating the start-up flame are contemplated. In one embodiment, the start-up flame holder includes a mechanically actuated distal end configured to be actuated to intercept the main fuel and oxidant mixture 706 to cause thermal regeneration and / or stabilize the vortex, thereby maintaining the start-up flame; or actuated not to intercept the main fuel and oxidant mixture 706 to allow the main fuel and oxidant mixture 706 to travel to the distal flame holder 102. In another embodiment, a fuel control valve, a blower, and / or a damper can be used to select a main fuel and oxidant mixture 706 flow rate that is low enough to stabilize the start-up flame spray; and after the distal flame holder 102 reaches the operating temperature, the flow rate can be increased to "spray" the start-up flame. In another embodiment, the heater 728 may include a power source operably connected to the controller 730 and configured to apply an electric charge or voltage to the main fuel and oxidant mixture 706. The conductive start-up flame holder may be selectively connected to a ground voltage or other voltage selected to attract the charge in the main fuel and oxidant mixture 706. The inventors have discovered that charge attraction causes the starting flame to be held by the electrically conductive starting flame holder.

[0129] In another embodiment, the heater 728 may include a resistive heater configured to output heat to the distal flame holder 102 and / or to the main fuel and oxidant mixture 706. The resistive heater 728 may be configured to heat the distal flame holder 102 to an operating temperature. The heater 728 may also include a power source and a switch operable under the control of the controller 730 to selectively couple the power source to the resistive heater 728.

[0130] The resistive heater 728 may be formed in a variety of ways. For example, the resistive heater 728 may be formed by Wire (available from Sandvik Materials Technology division of Sandvik AB of Hallstahammar, Sweden), the The wire passes through at least a portion of the throughbore 710 defined by the distal flame holder body 708. Alternatively, the heater 728 may include an induction heater, a high energy beam heater (eg, microwave or laser), a friction heater, a resistive ceramic coating, or other type of heating technology.

[0131] Other forms of starting devices are contemplated. For example, the heater 728 may include a discharge igniter or hot surface igniter configured to output pulsed ignition to the oxidant and fuel. Additionally or alternatively, as discussed in more detail herein, the starting device may include a pilot flame device configured to ignite the main fuel and oxidant mixture 706 that would otherwise enter the distal flame holder 102. The discharge igniter, hot surface igniter, and / or pilot flame device may be operably coupled to a controller 730 that may cause the discharge igniter or pilot flame device to maintain combustion of the main fuel and oxidant mixture 706 in or upstream of the distal flame holder 102 before the distal flame holder 102 is sufficiently heated to maintain combustion.

[0132] The burner system 700 may also include a sensor 734 operably coupled to the controller 730. The sensor 734 may include a thermal sensor configured to detect infrared radiation or a temperature of the distal flame holder 102. The control circuit 730 may be configured to control the heater 728 in response to input from the sensor 734. Optionally, a fuel control valve 736 may be operably coupled to the controller 730 and configured to control the flow of fuel to the fuel and oxidant source 702. Additionally or alternatively, an oxidant blower or damper 738 may be operably coupled to the controller 730 and configured to control the flow of oxidant (or combustion air).

[0133] The sensor 734 may also include a combustion sensor operably coupled to the control circuit 730, the combustion sensor being configured to detect a temperature, video image, and / or spectral signature of the combustion reaction 802 held by the distal flame holder 102. The fuel control valve 736 may be configured to control the flow of fuel from the fuel source to the fuel and oxidant source 702. The controller 730 may be configured to control the fuel control valve 736 in response to input from the combustion sensor 734. The controller 730 may be configured to control the fuel control valve 736 and / or the oxidant blower or damper 738 to control the preheat flame type of the heater 728, thereby heating the distal flame holder 102 to an operating temperature. The controller 730 may similarly control the fuel control valve 736 and / or the oxidant blower or damper 738 to change the flow of the main fuel and oxidant mixture 706 in response to a change in heat demand received as data via the data interface 732.

[0134] Fig. 10A is a simplified perspective view of a combustion system 1000 including another alternative distal flame holder 102 according to one embodiment. According to one embodiment, the distal flame holder 102 is a mesh-like ceramic perforated flame holder configured to hold a combustion reaction. Fig. 10B According to one embodiment Fig. 10AA simplified side cross-sectional view of a portion of a mesh ceramic perforated flame holder 102. According to one embodiment, it can be implemented in various combustion systems described herein. Fig. 10A , Fig. 10B The distal flame holder 102 is configured to support a combustion reaction (e.g., Figure 8 According to one embodiment, the distal flame holder 102 may be configured to support a combustion reaction of the primary fuel and oxidant mixture 706 upstream, downstream, within, and adjacent to the reticulated ceramic perforated flame holder 102.

[0135] According to one embodiment, the perforated flame holder body 708 may include mesh fibers 1039. The mesh fibers 1039 may define branching perforations 710 woven around and through the mesh fibers 1039. According to one embodiment, the perforations 710 are formed as passages between the mesh fibers 1039.

[0136] According to one embodiment, the mesh fibers 1039 are formed as a mesh ceramic foam. According to one embodiment, the mesh fibers 1039 are formed using a mesh polymer foam as a template. According to one embodiment, the mesh fibers 1039 may include aluminum silicate. According to one embodiment, the mesh fibers 1039 may be formed of extruded mullite or cordierite. According to one embodiment, the mesh fibers 1039 may include zirconium oxide. According to one embodiment, the mesh fibers 1039 may include silicon carbide.

[0137] As mentioned above, the term "reticular fiber" refers to a reticular structure. According to one embodiment, the reticular fiber 1039 is formed of an extruded ceramic material. In the reticular fiber 1039 embodiment, the interaction between the main fuel and oxidant mixture 706, the combustion reaction 802, and the heat transfer to and from the perforated flame holder body 708 can be similar to the above description of Figures 7 to 9 The illustrated and described embodiments function similarly. One difference in activity is the mixing between the perforations 710 due to the mesh fibers 1039 forming a discontinuous perforated flame holder body 708 that allows flow back and forth between adjacent perforations 710.

[0138] According to one embodiment, the network of mesh fibers 1039 is open enough for downstream mesh fibers 1039 to emit radiation for receipt by upstream mesh fibers 1039 for the purpose of sufficiently heating the upstream mesh fibers 1039 to maintain combustion of the primary fuel and oxidant mixture 706. Compared to a continuous perforated flame holder body 708, the heat conduction paths between the mesh fibers 1039 (such as Figure 8The heat conduction path 812 in the mesh is reduced due to the separation of the mesh fibers 1039. This can cause relatively more heat to be transferred via thermal radiation (in Figure 8 804) from a heat receiving area or region (such as Figure 8 The heat receiving area 806 in the heat receiving area is transferred to the heat output area or zone (such as Figure 8 heat output area 810).

[0139] According to one embodiment, each perforation 710 may extend between an input face 712 to an output face 714 of the perforated flame holder 102. The perforations 710 may have different lengths L. According to one embodiment, the individual perforations 710 are not clearly defined by the length L because the perforations 710 branch into and out of each other.

[0140] According to one embodiment, the perforated flame holder 102 is configured to support or maintain the combustion reaction (see Figure 8 802) or at least partially maintains a flame between the input face 712 and the output face 714. According to one embodiment, the input face 712 corresponds to a surface of the perforated flame holder 102 proximal to the main fuel nozzle 718, or to a surface that first receives fuel. According to one embodiment, the input face 712 corresponds to an extent of the mesh fibers 1039 proximal to the main fuel nozzle 718. According to one embodiment, the output face 714 corresponds to a surface distal to the main fuel nozzle 718 or opposite to the input face 712. According to one embodiment, the input face 712 corresponds to an extent of the mesh fibers 1039 distal to the main fuel nozzle 718 or opposite to the input face 712.

[0141] According to one embodiment, the formation of the thermal interface layer 814, the heat transfer between the perforated flame holder body 708 and the gas flowing through the perforations 710, the characteristic perforation width dimension D, and the length L can each be considered to be related to an average or total path through the perforated reaction holder 102. In other words, the dimension D can be measured as the root mean square of the individual Dn values ​​determined at each point along the flow path. Similarly, the length L can be a length that includes a length contributed by the tortuosity of the flow path, which can be compared to the straight-line distance T from the input face 712 through the perforated flame holder 102 to the output face 714. RH Slightly longer. According to one embodiment, the void fraction (expressed as (total perforated reaction holder 102 volume - mesh fiber 1039 volume) / total volume) is about 70%.

[0142] According to one embodiment, the reticulated ceramic perforated flame holder 102 is a brick that is approximately 1 inch by 4 inches by 4 inches. According to one embodiment, the reticulated ceramic perforated flame holder 102 includes approximately 100 holes per square inch of surface area. Other materials and sizes may also be used for the reticulated ceramic perforated flame holder 102 in accordance with the principles of the present disclosure.

[0143] According to one embodiment, the reticulated ceramic perforated flame holder 102 may include shapes and sizes other than those described herein. For example, the perforated flame holder 102 may include a reticulated ceramic tile that is larger or smaller than the above-described sizes. Additionally, the reticulated ceramic perforated flame holder 102 may include shapes other than a generally cubic shape.

[0144] According to one embodiment, the reticulated ceramic perforated flame holder 102 may include a plurality of reticulated ceramic tiles. The plurality of reticulated ceramic tiles may be joined together so that each tile is in direct contact with one or more adjacent reticulated ceramic tiles. The plurality of reticulated ceramic tiles may together form a single perforated flame holder 102. Alternatively, each reticulated ceramic tile may be considered a different perforated flame holder 102.

[0145] Fig.11 1 is a flow chart illustrating a method 1100 for operating a distal flame holder burner system according to one embodiment. According to one embodiment, the method 1100 includes, in operation 1102, providing heat to a distal flame holder (102) from a pilot flame supported by a pilot burner, the pilot flame being fueled by a pilot fuel, the distal flame holder and the pilot burner being disposed in a furnace and proximate to each other. The pilot burner may be disposed between the distal flame holder and one or more main fuel nozzles, and the distance between the pilot burner and the distal flame holder is less than the distance between the pilot burner and the one or more main fuel nozzles. Operation 1104 includes introducing a mixed main fuel and air into the distal flame holder. Operation 1106 includes maintaining at least a portion of a combustion reaction of the mixed main fuel and air within the distal flame holder while the pilot burner continues to support the pilot flame.

[0146] Operation 1102 may include providing a pilot fuel from a pilot fuel source to a pilot burner, controlling a pilot fuel flow rate, and supplying a pilot fuel from a plurality of orifices (e.g., Figure 2A , Figure 2B , Figures 4 to 6 The orifice may be arranged on the width of the mixed main fuel and air. The operation may also include igniting the mixed main fuel and air with a pilot flame at the pilot burner.

[0147] According to one embodiment, the method 1100 may further include measuring a temperature of the distal flame holder, and when the temperature of the distal flame holder is equal to or above a predetermined threshold, reducing the pilot fuel flow rate to reduce the size of the pilot flame. Reducing the size of the pilot flame relative to the size of the combustion reaction of the mixed main fuel and air may result in reduced emissions of nitrogen oxides.

[0148] In operation 1104, introducing the mixed main fuel and air into the distal flame holder may include introducing the main fuel via the one or more main fuel nozzles at the proximal end of the mixing tube and introducing the air. The proximal end of the mixing tube may be disposed proximal to the one or more main fuel nozzles, and the distal end of the mixing tube may be disposed proximal to the distal flame holder. The mixing tube may be open from its proximal end to its distal end.

[0149] According to one embodiment, the method 1100 may further include directing the flue gas into a proximal end of the mixing tube.

[0150] In one embodiment, the pilot burner may be disposed between the distal flame holder and the distal end of the mixing tube.

[0151] Fig.12 1 is a flow chart illustrating a method 1200 for operating a burner system according to one embodiment. According to one embodiment, the method 1200 includes, in operation 1202, supporting a diffusion flame across a portion of the width of a furnace volume at a location remote from a furnace floor. Operation 1204 includes providing combustion air to the furnace volume from a location near the furnace floor. Operation 1206 includes outputting a high pressure main fuel jet from each of one or more main fuel nozzles at one or more locations near the furnace floor. Operation 1208 includes mixing the main fuel with the combustion air while the main fuel and the combustion air travel from a location near the furnace floor to a distal location. Operation 1210 includes burning the main fuel by exposing the mixed main fuel and air to a diffusion flame.

[0152] According to one embodiment, the method 1200 may further include maintaining a primary flame generated by burning the primary fuel in a stable position, wherein the distal flame holder is disposed further from the furnace floor than the diffusion flame.

[0153] In one embodiment, in operation 1202, the support of the diffusion flame may include generating and maintaining a diffusion flame at a pilot burner, which is disposed in the furnace volume between the one or more main fuel nozzles and the distal flame holder. The pilot burner may be disposed closer to the distal flame holder than it is relative to the furnace floor. In another embodiment, maintaining the diffusion flame at the pilot burner may include supplying a pilot fuel to the pilot burner, emitting a pilot fuel from one or more pilot fuel orifices of the pilot burner, and maintaining a mixture of combustion air and the emitted pilot fuel at the pilot burner to support the diffusion flame. The one or more pilot fuel orifices may constitute a plurality of pilot fuel orifices disposed on a portion of the width of the furnace volume, the portion being wide enough to contact the diffusion flame with a mixture of the main fuel and the combustion air over the width of the mixed main fuel and the combustion air. In addition and / or alternatively, the one or more pilot fuel orifices may include a plurality of pilot fuel orifices having a sufficiently large collection area to support a diffusion flame at low momentum. Maintaining the diffusion flame at the pilot burner may include controlling a rate at which pilot fuel is supplied to the pilot burner.

[0154] According to one embodiment, method 1200 may further include detecting a temperature of a distal flame holder disposed above the diffusion flame and reducing a rate of supplying pilot fuel to a pilot burner supporting the diffusion flame when the distal flame holder reaches at least a predetermined threshold temperature.

[0155] According to one embodiment, the method 1200 may further include detecting combustion of the primary fuel at the distal flame holder using a capacitive sensor configured to output a sensor signal to the controller.

[0156] According to one embodiment, the combustion system may include an oxidant source configured to output an oxidant into a furnace volume. The pilot burner may be configured to support a pilot flame by outputting a pilot fuel to support a pilot diffusion flame at least during a preheat state, and the main fuel nozzle may be configured to output the main fuel from a proximal position into the furnace volume during a standard operating state at least after the preheat state is completed. The combustion system may include: a distal flame holder positioned in the furnace volume to be preheated by the pilot flame during the preheat state, and to maintain the combustion reaction of the main fuel and the oxidant near the distal flame holder during the standard operating state; and a combustion sensor configured to sense a condition of the distal flame holder and generate a sensor signal indicative of the condition of the distal flame holder. The combustion system also includes one or more actuators configured to adjust the flow of the main fuel from the main fuel nozzle, adjust the flow of the pilot fuel to the pilot burner, and adjust the flow of the oxidant from the oxidant source. A controller may be communicatively coupled to the actuator and the combustion sensor. The controller may be configured to receive the sensor signal from the combustion sensor and control the actuator to adjust the flow of the pilot fuel, the main fuel, and the oxidant in response to the sensor signal and according to software instructions stored in a non-transitory computer readable medium coupled to the controller.

[0157] According to one embodiment, the combustion system further comprises a pilot flame sensor configured to sense a condition of the pilot flame and output a sensor signal indicating the condition of the pilot flame. The combustion sensor may comprise a pilot flame sensor. In one embodiment, the pilot flame sensor may comprise a capacitive sensor, a resistive sensor and / or a tomographic sensor (e.g., using electrical capacitance tomography (ECT)).

[0158] According to one embodiment, the combustion system also includes an igniter configured to generate an arc. The controller may be configured to control one or more of the actuators so that if the capacitive sensor indicates that the pilot flame is not present and all safety interlocks are met, the igniter is caused to generate an arc to ignite the pilot flame. In one embodiment, the controller is configured to adjust the size of the pilot flame by controlling one or more of the actuators to adjust the flow of the pilot fuel or the oxidant in response to the sensor signal from at least the combustion sensor. The combustion sensor may be configured to detect the combustion reaction at the distal flame holder and output a sensor signal to the controller in response to the detected state of the combustion reaction. In one embodiment, the combustion sensor is configured to operate as a flashback sensor, which is configured to detect flashback of the combustion reaction from the distal flame holder toward the main fuel nozzle. The combustion sensor may include a capacitive sensor.

[0159] Fig.13A is a diagram of a combustion system 1300 including a distal flame holder 102 and a capacitive (EC) sensor 1305 according to one embodiment. Fig. 13B is a top view of the distal flame holder 102 and capacitive sensor 1305 according to one embodiment.

[0160] In one embodiment, the EC sensor can be configured as a capacitance tomography (ECT) sensor. Alternatively, the combustion sensor can be configured as a resistive or conductive sensor by modifying the signal processing. As used herein, the term capacitance will be understood to also refer to a resistive sensor or a conductive sensor. The EC sensor is essentially a simplified ECT sensor in that it has fewer electrodes and can sense the presence of combustion, but not necessarily the specific location of the combustion. It should be understood that references to ECT sensors similarly refer to EC sensors.

[0161] As used herein, the term electrical capacitance tomography (ECT) should be understood as described. ECT sensing can be essentially capacitive, or can be performed in addition or alternatively to measure conductivity, resistance, impedance or other electrical parameters. ECT may include multiple sensor channels, such as can be produced by moving the sensor through different positions or by using a sensor array, such as can be seen in more common (e.g., medical) tomography systems. In addition or alternatively, the ECT system may include a series of sensor channels, which are as few as a single channel defined by two electrodes positioned relative to a sensing area (e.g., a flame holding area, a flame-out area, a flashback area, a flue gas area, a pilot flame area, etc.). Unless the context otherwise dictates, the disclosure and claims herein should be given this broad meaning.

[0162] In one embodiment, the combustion system 1300 may include a combustion sensor including an EC sensor or an ECT device such as Fig.13A and Fig. 13B Capacitive sensor 1305. Capacitive sensor 1305 may include a first set of electrodes 1320 positioned laterally around distal flame holder 102 to sense a parameter of distal flame holder 102, including multiple pairs of electrodes 1320. Capacitive sensor 1305 may also include a second set of electrodes positioned upstream of distal flame holder 102. First set of electrodes 1320 may sense capacitance or other parameters near distal flame holder 102. Second set of electrodes may sense capacitance or other parameters upstream of distal flame holder 102 (e.g., at pilot burner (e.g., Figure 3 104)) or capacitance or other parameters upstream of the pilot burner. The controller 730 may compare the capacitance or other parameters sensed by the first set of electrodes 1320 with the capacitance or other parameters sensed by the second set of electrodes to detect combustion reaction parameters, the presence of flashback, etc.

[0163] In one embodiment, the combustion system 1300 may include a distal flame holder sensor that includes a capacitive sensor 1305. The distal flame holder sensor may share the use of the first set of electrodes 1320 described with respect to the combustion sensor. In this case, the first set of electrodes 1320, including electrode pairs positioned laterally around the distal flame holder 102, may serve as both the capacitive sensor 1305 and at least a portion of the combustion sensor.

[0164] In one embodiment, the combustion system 1300 may include a pilot flame sensor (not shown) that includes a capacitive sensor 1305. The pilot flame sensor and the combustion sensor may share the use of an electrode positioned upstream of the distal flame holder 102 or laterally around the distal flame holder 102. Two or more of the pilot flame sensor, the combustion sensor, and the distal flame holder sensor may share an electrode 1320 of the capacitive sensor 1305.

[0165] The combustion system 1300 includes a fuel and oxidant source 702, a distal flame holder 102, a controller 730, a capacitance tomography device 1305, and a memory 1307. The fuel and oxidant source 702 may include a primary fuel nozzle (e.g., the primary fuel nozzle 106 described above) and an oxidant source 720. Additionally, the fuel and oxidant source 702 may include a pilot burner, such as the pilot burner 104 described above.

[0166] According to one embodiment, the fuel and oxidant source 702 includes, for example, a fuel nozzle configured to output primary fuel and oxidant onto the distal flame holder 102. The distal flame holder 102 primarily maintains a combustion reaction of the fuel and oxidant near and / or within the distal flame holder 102.

[0167] According to one embodiment, the capacitive sensor 1305 may be configured as an image capture device (e.g., using ECT) that includes a plurality of electrodes 1320 positioned at selected locations adjacent to the distal flame holder 102. The capacitive sensor 1305 is configured to make an image of the distal flame holder 102 based on the capacitance between the electrodes 1320. The image represents a slice of the distal flame holder 102 based on the capacitance between the electrodes 1320. The capacitance between the pair of electrodes 1320 depends in part on the dielectric constant of the material between the pair of electrodes 1320. Specifically, the dielectric constant within the perforation of the distal flame holder 102 may change based on the characteristics of the combustion reaction within the perforation. Therefore, the image generated by the capacitive sensor 1305 may give an indication of the temperature within the perforation, or the concentration or flow of the fuel, oxidant, and flue gas corresponding to each location of the distal flame holder 102 based on the dielectric constant at each location of the distal flame holder 102. The controller 730 may analyze the image and adjust the combustion reaction based on the image.

[0168] According to one embodiment, the controller 730 is configured to cause the capacitive sensor 1305 to capture one or more images of the combustion reaction. In one embodiment, the controller 730 is further configured to analyze the one or more images and adjust the characteristics of the combustion reaction based on the analysis of the one or more images.

[0169] Fig. 13B 1 is a top view of a distal flame holder 102 and a capacitive sensor 1305 according to one embodiment. The capacitive sensor 1305 includes a plurality of pairs of electrodes 1320 positioned laterally around the distal flame holder 102. Each pair of electrodes 1320 includes two electrodes 1320 facing each other, wherein the distal flame holder 102 is positioned between the pair of electrodes 1320 or in a fringe field therebetween. According to one embodiment, the controller 730 controls each pair of electrodes 1320 to form a plurality of images (or aggregated images) of the distal flame holder 102.

[0170] In one embodiment, electrodes 1320a and 1320a are a pair, electrodes 1320b and 1320b are a pair, electrodes 1320c and 1320c are a pair, electrodes 1320d and 1320d are a pair, electrodes 1320e and 1320e are a pair, and electrodes 1320f and 1320f are a pair. Capacitive sensor 1305 can generate a capacitive tomography image based on the capacitance between the pair of electrodes 1320.

[0171] In one embodiment, the plurality of electrodes 1320 includes one or more first pairs of electrodes 1320 separated from each other by the distal flame holder 102 and disposed relative to each other in a first orientation substantially perpendicular to a main direction of flow of the primary fuel toward the distal flame holder 102. In one example, the first pair of electrodes 1320 may include a pair of electrodes 1320a and a pair of electrodes 1320b. The first pair of electrodes 1320a and 1320b senses the capacitance of the distal flame holder 102 along an X direction substantially perpendicular to the main direction of flow of the primary fuel and oxidant toward the distal flame holder 102. The main direction of flow of the primary fuel and oxidant toward the distal flame holder 102 may correspond to the Z direction.

[0172] In one embodiment, the plurality of electrodes 1320 includes one or more second pairs of electrodes separated from each other by the distal flame holder 102 and disposed relative to each other in a second orientation substantially perpendicular to both the first orientation and the main direction of flow of the primary fuel. In one example, the second pair of electrodes 1320 may include a pair of electrodes 1320c and a pair of electrodes 1320d. The second pair of electrodes 1320c and 1320d senses the capacitance of the distal flame holder 102 along a Y direction substantially perpendicular to the main direction of flow of the primary fuel and oxidant and substantially perpendicular to the orientation of the first pair of electrodes 1320a and 1320b.

[0173] In one embodiment, the plurality of electrodes 1320 may include pairs of electrodes 1320 oriented transversely to both a first pair of electrodes 1320a and 1320b and a second pair of electrodes 1320c and 1320d. The transverse pairs of electrodes 1320 may include a pair of electrodes 1320e and a pair of electrodes 1320f.

[0174] although Fig.13A and Fig. 13BThe view of shows a capacitive sensor 1305 including electrodes 1320 positioned laterally around the distal flame holder 102, but a capacitive sensor in accordance with the principles of the present disclosure may include electrode pairs positioned in configurations other than laterally positioned around the distal flame holder 102. The capacitive sensor may include an electrode pair positioned upstream of the distal flame holder 102, downstream of the distal flame holder 102, or at other locations depending on the particular aspect of the combustion system that the capacitive sensor is intended to sense or monitor. Thus, where appropriate, other sensors described or contemplated with respect to the embodiments disclosed herein (e.g., sensors 734, 1414) may include a capacitive sensor.

[0175] Fig.14 1400 is a diagram of a low-emission modular burner system 1400 including one or more burner modules 1401 according to an embodiment. Each burner module 1401 may include a main fuel source that is valve-controlled separately from all other fuel sources, which is configured to selectively deliver a main fuel stream 1404 to be diluted by a combustion air stream. In certain embodiments, the main fuel source may correspond to one or more main fuel nozzles 1402 or be implemented to include the one or more main fuel nozzles. Each burner module 1401 may include a main fuel igniter 1406, which is configured to cause the ignition of the main fuel stream 1404 emitted from the main fuel nozzle 1402. Each burner module 1401 may include a distal flame holder 102, which is configured to maintain a combustion reaction supported by the main fuel stream 1404 when the distal flame holder 102 is at or above a predetermined temperature. In one embodiment, the predetermined temperature may be equal to or greater than the main fuel autoignition temperature. According to one embodiment, each burner module 1401 may include a pilot burner 1408 configured to preheat the distal flame holder 102 to a predetermined temperature. In one embodiment, the pilot burner 1408 of each burner module 1401 may include a continuous pilot burner that is also operable to ignite the main fuel. In some embodiments, the distal flame holder 102 may be separated from the main fuel nozzle 1402 and the pilot burner 1408 by a respective non-zero distance (D1, D2).

[0176] The low emission modular burner system 1400 may include a common combustion air source 1405 and a wall 1407, the common combustion air source being configured to provide combustion air to each of the one or more burner modules 1401, the wall surrounding the entirety of the one or more burner modules 1401, and the wall 1407 being configured to laterally contain the combustion fluid corresponding to the one or more burner modules 1401. In one embodiment, the distal flame holder 102 is configured to maintain a combustion reaction supported by the main fuel flow 1404 when the distal flame holder 102 is at or above the main fuel autoignition temperature. In one embodiment, each pilot burner 1408 comprises a continuous pilot burner. In one embodiment, the pilot burner 1408 is configured to selectively output heat at any one of a plurality of heating rates. At least one heating rate may be selected to cause the sensed temperature of the distal flame holder 102 to rise to a predetermined operating temperature, and at least one other heating rate may be selected to cause the pilot burner 1408 to maintain a pilot flame function while a majority of the total fuel consumed per unit time is provided by the main fuel source 1402. In one embodiment, the common combustion air source 1405 is configured to provide natural draft combustion air to each of the one or more burner modules 1401 (1401).

[0177] Fig.15 According to one embodiment, a Fig.14 Diagram of control circuit 1512 used in control system 1412.

[0178] According to one embodiment, see Fig.14 and Fig.15 The low emission modular burner system 1400 also includes one or more individual main fuel valves 1410 for each burner module 1401, each main fuel valve 1410 including an individual main fuel valve actuator configured to operate in response to receiving a control signal, and also includes a control system 1412 configured to output a corresponding control signal to each individual main fuel valve actuator. In one embodiment, the control system 1412 also includes an interface 1514 between the control system 1412 and the input channel (see Fig.15 ). The input channel may include a physical (e.g., conductive) connection or a wireless connection. Thus, the interface 1514 may include a network interface and / or a hardware interface, such as, but not limited to, a USB interface, a PID controller interface, a relay interface, a radio interface, a WiFi interface, a Bluetooth interface, etc. In one embodiment, the interface 1514 includes an interface to one or more sensors configured to sense physical parameters associated with each burner module 1401 and the surrounding environment. Sensors (e.g., Fig.141414 in) and its operation may include capacitively coupled (e.g., patch) electrodes (which may alternatively be referred to as antennas) that cooperate to transmit and receive radio frequency signals across an area intended to maintain a combustion reaction. Changes in capacitance correspond to changes in the concentration of charged species, which have been found to covariate with the presence or absence of combustion. According to one embodiment, the electrodes may be provided in sufficient number and positioned to provide a tomographic scan of the combustion area. The sensor 1414 may be connected to the control system 1412 via a communication channel 1415. In some embodiments, the communication channel may be wired (e.g., conductive). In the case where the sensor 1414 employs capacitance measurement and / or capacitance tomography, the communication channel 1415 may provide voltage and / or current to the electrodes of the sensor 1414.

[0179] The interface 1514 may be configured to receive a signal corresponding to a burner capacity request. The control system 1412 may also include one or more burner module sensor inputs 1515a, 1515b, each of which is configured to receive a signal corresponding to a burner module state, wherein the burner module state is provided by the sensor hardware 1414. The control system 1412 may also include a microcontroller or other logic processor 1516, a computer readable memory 1518, and a module sequencer 1520 (which may optionally be embodied as the logic processor 1516 and the computer readable memory 1518 or executed by the logic processor and the computer readable memory when performing a module sequencing function), the module sequencer being configured to select a subset of the one or more burner modules 1401 for ignition. The control system 1412 may also include one or more corresponding master fuel valve driver outputs, each of which may be operably connected to one of the individual master fuel valve actuators 1410. In one embodiment, the one or more burner module sensor inputs 1515a, 1515b are configured to receive input from one or more sensors, such as sensor hardware 1414, or from one or more sensors external to the burner module (1401). The one or more sensors may include a demand sensor including one or more of a condensate pressure sensor, a thermal energy demand sensor, and a condensate presence sensor.

[0180] In embodiments having more than one burner module 1401, the control circuit 1512 (see Fig.15) may include a module sequencer 1520. The module sequencer 1520 may include a state machine configured to variably sequence the actuation of the one or more burner modules 1401. For example, it may be desirable to periodically change the assignment of burner modules to different positions in the actuation sequence as needed. In one embodiment, the last module turned on in the previous module sequence may also operate as the first / only module turned on during the shutdown state. In another embodiment, the assignment of burner modules 1401 does not need to be identical with respect to capacity, age (e.g., cycle count), and design. The startup sequence may be at least partially identical with respect to each base demand / surge capacity cycle. The inventors contemplate that various arrangements, actuation sequences, and assignment selections of the burner modules 1401 may provide specific advantages to specific application characteristics.

[0181] According to one embodiment, the low emission modular burner system 1400 also includes an operation sequencer 1522. In one embodiment, the control circuit 1512 may include the operation sequencer 1522. For a given module in the activation queue serviced by the module sequencer 1520, the operation sequencer 1522 may include a state machine configured to sequence the steps in the burner module startup plan for one or more of the burner modules 1401. The startup plan may be stored in the memory 1518 and periodically updated via the interface 1514 including a network interface. Exemplary methods and aspects of startup sequencing are described with respect to several other figures included herein.

[0182] According to one embodiment, the low emission modular burner system 1400 ( Fig.14 The control circuit 1512 of the control system 1412 also includes an actuator driver module 1524. In one embodiment, the control circuit 1512 may include the actuator driver module 1524. The actuator driver module 1524 may be configured to provide a corresponding control signal to each of the individual valve actuators. The actuator driver module 1524 may include a state machine configured to load the driver shift register enable bit in response to data from the startup sequencer for amplification by the power module 1526. The signals to and from the power module 1526 may be respectively connected to the actuable main fuel valve 1410 via the connector 1411. Similarly, the actuable pilot fuel valve 1416 may be respectively connected to the power module 1526 via the connector 1417.

[0183] Sensor 1414 is described herein as performing sensing functions or as signal output. In the embodiment where it is necessary to output a signal at sensor / electrode 1414, power module 1526 can be used to amplify such signals, for example, for the aforementioned transmission and reception of radio frequency signals across the combustion zone. In an alternative embodiment, sensor 1414 can provide a signal for generating data (for example, flame tomogram). In such an embodiment, dedicated sensor input 1515a, 1515b can be utilized. In another alternative embodiment, sensor 1414 can provide a subset of many data signals communicated via interface 1514 of control circuit 1512. As described above, interface 1514 can use various communication protocols to provide wireless or wired connection, and these communication protocols can allow sensor 1414 to communicate via standard methods such as USB, WiFi, Ethernet, etc.

[0184] According to one embodiment, the low emission modular burner system 1400 may further include a demand module 1528. In one embodiment, demand for system capacity is received substantially in real time via a network interface included in the interface 1514. The demand module 1528 may be configured to selectively oversee automatic operation of the one or more burner modules 1401 based on at least one of a stored schedule and a received demand signal.

[0185] The demand module 1528 may consist essentially of data values ​​in registers of the memory 1518. In another embodiment, particularly in systems where real-time data access via the interface 1514 is not guaranteed, the demand module 1528 may include a real-time clock and planned system capacity as data. In one embodiment, the demand module 1528 may operate as a supervisory state that is configured to automatically operate the modular burner system 1400 based on seasonal and / or periodic demand dynamics. Similarly, in an environment with unordered dynamic demand, the operation of the interface 1514 may be more important. In systems characterized by unordered fluctuations in capacity demand, the inventors contemplate that interfaces with parallel or greater channel diversity and / or hardening may be desirable. Optionally, portions of the module sequencer 1520 may be virtualized and accessed by the cloud.

[0186] According to one embodiment, the logic processor 1516 is configured to read and execute computer executable instructions supported by the non-transitory computer readable memory 1518 to receive capacity input data corresponding to a burner capacity requirement signal, read module status sensor data from a sensor corresponding to at least one burner module to verify that a selected one or more of the burner modules 1401 are ready for ignition, select a subset of the one or more burner modules 1401 for ignition, and drive at least one of the individual main fuel valve (1410) actuators corresponding to the selected one or more burner modules to open so as to provide fuel to the combustion reaction supported by the one or more burner modules 1401.

[0187] According to one embodiment, the control system 1412 also includes a demand sensor. The demand sensor may include a thermal energy demand sensor.

[0188] According to one embodiment, each burner module 1401 also includes a pilot fuel source configured to provide a pilot fuel, a pilot fuel igniter (e.g., 1406) configured to ignite the pilot fuel flow, and a distal pilot or start-up burner (e.g., constituting a pilot burner 1408) configured to maintain a pilot flame supported by the pilot fuel, the pilot fuel source flow rate being selected to provide a pilot flame, the pilot flame being sized to raise the temperature of the distal flame holder 102 to a predetermined temperature. In one embodiment, the predetermined temperature is equal to or greater than the main fuel autoignition temperature. As used herein, the terms pilot, pilot burner, distal pilot and start-up burner, and preheating device should be considered synonymous unless the context dictates otherwise.

[0189] According to one embodiment, the main igniter 1406 includes a distal pilot. According to another embodiment, the main igniter 1406 includes the distal flame holder 102 when the distal flame holder 102 is heated to a predetermined temperature by the distal pilot 1408. That is, the fuel and combustion air can ignite when in contact with the preheated distal flame holder 102, rather than being ignited by a separate igniter. According to one embodiment, the predetermined temperature is the main fuel auto-ignition temperature.

[0190] According to one embodiment, the distal pilot burner 1408 is configured to be controlled to provide a pilot flame whose size is designed to raise the distal flame holder 102 to a predetermined temperature during the burner module startup cycle, and not provide a pilot flame whose size is designed to raise the distal flame holder 102 to a predetermined temperature at a time other than during the burner module startup cycle. In one embodiment, the distal pilot burner 1408 is configured to be reduced to a pilot flame capacity at a time other than during the burner module startup cycle. In another embodiment, the distal pilot burner 1408 is configured to stop supporting the combustion reaction at a time other than during the burner module startup cycle. In addition and / or alternatively, the distal pilot burner 1408 may be disposed adjacent to the distal flame holder 102, and the distal pilot burner 1408 is controlled to be reduced to a pilot flame capacity at a time other than during the burner module startup cycle. In another embodiment, the pilot burner 1408 is disposed adjacent to the distal flame holder 102, and the distal pilot output is selected to maintain a constant capacity at all times during operation. In one embodiment, the pilot burner 1408 is configured to ensure combustion of the main fuel, for example, when the distal flame holder 102 does not support a combustion reaction. The main fuel may be a hydrocarbon gas. The pilot fuel may be one or more of hydrogen, natural gas, or propane. According to an embodiment, the pilot fuel and the main fuel may be substantially composed of the same fuel.

[0191] According to one embodiment, the modular burner 1401 includes a housing 1403 having a combustion air inlet at a base. Each burner module 1401 may include an inlet configured to be coupled to a primary fuel supply source and receive combustion air via the housing 1403, a distal flame holder 102 positioned within the housing 1403, and a primary fuel nozzle 1402 configured to receive a primary fuel flow from the inlet and emit the primary fuel flow toward the distal flame holder 102.

[0192] According to one embodiment, each of the one or more burner modules 1401 is configured to be freestanding, supported only by couplings at the inlet.

[0193] In one embodiment, the burner module 1401 is configured to be coupled to and supported by a burner.

[0194] According to one embodiment, the primary fuel nozzle is one of a plurality of primary fuel nozzles 1402 , each of the primary fuel nozzles 1402 being configured to receive a primary fuel flow from an inlet and emit a primary fuel flow 1404 toward a respective portion of the distal flame holder 102 .

[0195] According to one embodiment, the modular combustor 1401 further includes a plurality of main fuel valves 1410 that are operably coupled between the common fuel line and respective ones of the plurality of main fuel nozzles 1402 and configured to independently control the operation of the respective main nozzles 1402. That is, although Fig.14 A main fuel valve 1410 is shown that is shared by each of the main fuel nozzles 1402 , but embodiments may include a separate and individually controllable main fuel valve 1410 for each main fuel nozzle 1402 .

[0196] According to one embodiment, the modular burner 1401 also includes a distal pilot burner 1408, which is positioned between the distal flame holder 102 and the main fuel nozzle 1402 for each burner module. The modular burner 1401 can be a modified burner positioned in a housing 1407, the modified burner including the distal flame holder 102 and the main fuel nozzle 1402. Each distal pilot burner 1408 can include a plurality of pilot nozzles arranged in an array. In another embodiment, the distal pilot burner 1408 is configured to support a pilot flame between the distal pilot burner 1408 and the distal flame holder 102.

[0197] The main fuel nozzle 1402 may include an orifice having a variable size. The main fuel nozzle 1402 may be configured to adjust the velocity of the main fuel flow. According to one embodiment, the modular combustor 1401 also includes an actuator operably coupled to the main fuel nozzle 1402 and configured to control the size of the orifice. The main fuel nozzles 1402 may each include a main nozzle outlet and a control element positioned to block a portion of the main nozzle outlet, and wherein movement of the control element changes the extent to which the main nozzle outlet is blocked by the control element.

[0198] In one embodiment, each burner module has a heating capacity of about 8 MBtu / Hr.

[0199] Fig.161 is a block diagram of a burner system 1600 according to one embodiment. The burner system 1600 includes a distal flame holder 1602 (corresponding to the distal flame holder 102 described herein), a fuel and oxidant source 1620, and a mixing tube 1610. The fuel and oxidant source 1620 may include an oxidant conduit 1604 for delivering an oxidant 1606a, and one or more primary fuel nozzles 1618 for primary delivery of the fuel 1606b. The fuel 1606b and the oxidant 1606a are mixed in the mixing tube 1610 on the way to the distal flame holder 1602, thereby producing a fuel and oxidant mixture 1607. The distal flame holder 1602 is configured and oriented to receive and (when at an operating temperature) ignite the fuel and oxidant mixture 1607. The oxidant conduit 1604 provides a passage for the oxidant 1606a (e.g., air) and directs the oxidant 1606a toward the distal flame holder 1602. The main fuel nozzle 1618 directs fuel 1606b toward the distal flame holder 1602. The main fuel nozzle 1618 can receive fuel 1606b from a fuel reservoir or pipeline (not shown, each or both are referred to as fuel supply herein) via a main fuel supply pipeline 1608. The burner system 1600 may include a single main fuel nozzle 1618 or a plurality of main fuel nozzles 1618, each of which is arranged and configured as described herein. The fuel 1606b emitted by the main fuel nozzle 1618 and the oxidant 1606a emitted by the oxidant conduit 1604 mix as they travel toward the distal flame holder 1602. The fuel 1606b and the oxidant 1606a achieve a sufficiently uniform fuel and oxidant mixture 1607 (see also Figure 7 element 706) to allow efficient and uniform combustion within the distal flame holder 1602 at operating temperatures.

[0200] The burner system 1600 can include a pilot burner 1612. The pilot burner 1612 is disposed proximate to the distal flame holder and provides a pilot flame that can maintain ignition of the fuel and oxidant mixture 1607. In some implementations, the pilot burner 1612 can receive fuel from a pilot fuel supply line 1614. Alternatively, the pilot burner 1612 can be fluidly connected to the main fuel supply line 1608.

[0201] According to one embodiment, the mixing tube may be positioned a predetermined distance from a floor of the burner system and may be configured to receive at least combustion air via the oxidant conduit 1604 .

[0202] As previously described in this disclosure, a source of flue gas diluent 1616 is contemplated. The inventors have observed that the introduction of a mixing tube facilitates the recirculation of flue gas from downstream of the distal flame holder 1602 as a large amount of flue gas diluent. Flue gas 1616 is discharged to the proximal end (i.e., the main nozzle end) of the mixing tube 1610 by the flow of the main fuel and combustion oxidant through the mixing tube 1610 between the main fuel nozzle 1618 and the distal flame holder 1602. The recirculated flue gas 1616 is mixed with the fuel and combustion air before reaching the distal flame holder 1602. The non-reactive elements of the resulting mixture minimize the possibility of flashback upstream of the distal flame holder 1602 while allowing additional combustion of the reactive elements of the flue gas, thereby reducing, for example, NOx and other potential pollutants.

[0203] Now go to Fig.17 , the burner system 1700 may include a distal flame holder 1602, a plurality of main fuel nozzles 1618, one or more distal pilot burners 1704 (e.g., corresponding to the pilot nozzles 1612), and a mixing tube 1710. The main fuel nozzles 1618 may be arranged to be fluidly connected to a main fuel source 1732. According to one embodiment, the flow of the main fuel from the main fuel source 1732 may be controlled via a main fuel control valve 1736. The one or more distal pilot burners 1704 may be arranged to be fluidly connected to the pilot fuel source 1730. According to one embodiment, the flow of the pilot fuel from the pilot fuel source 1730 may be controlled via a pilot fuel control valve 1734.

[0204] The remote pilot burner 1704 can be configured to support a pilot flame by outputting pilot fuel received from a pilot fuel source 1730 via a pilot fuel tube 1712. The pilot fuel tube 1712 can be disposed within the mixing tube 1710 or outside the mixing tube 1710 (advantageously for maintenance, temperature regulation, etc.). In some embodiments, the pilot fuel tube 1712 can form a portion of a support for the mixing tube 1710. According to one embodiment, the remote pilot burner 1704 can be supported by the pilot fuel tube 1712 and receive fuel via the pilot fuel tube. The pilot fuel tube 1712 extends into the furnace volume 1701 via an opening 1740 in the floor 1738 of the furnace. Each remote pilot burner 1704 (corresponding to the pilot burner 104 previously described) can include a pilot manifold formed in any of a number of shapes. For example, in Fig.17 In the embodiment, the ignition manifold is formed into a Y shape. See also the above corresponding to, for example Figures 3 to 6 A discussion of the pilot burner configuration is provided.

[0205] According to one embodiment, each distal pilot burner 1704 includes one or more manifolds defining a plurality of fuel orifices 1718 having a large collection area to co-support a low momentum pilot flame (not shown). In one embodiment, the main fuel and combustion air output by the main fuel nozzle 1618 form a combustible mixture that expands in width as it flows from a proximal position of the main fuel nozzle 1618 to a distal position of the distal pilot burner 1704. The plurality of fuel orifices 1718 may be disposed sufficiently widely over the furnace volume 1701 to cause the pilot flame to contact the main fuel and combustion air mixture over the width of the combustible mixture. In another embodiment, the main fuel nozzle 1618 may be configured to output fuel that co-flows with air.

[0206] According to one embodiment, the remote pilot burner 1704 includes a fuel manifold having a plurality of segments 1719 joined together, each segment 1719 having a plurality of fuel orifices 1718 configured to allow fuel to pass from the interior of the fuel manifold to the furnace volume 1701. The plurality of segments 1719 may be formed to be configured to allow fuel delivered from the pilot fuel tube 1712 to freely enter the corresponding tube of the fuel manifold. In one embodiment (e.g., as Fig.17 In one embodiment, at least a portion of the tubes are arranged as spokes radiating from a center substantially disposed at a centerline along the axis. In another embodiment, at least a portion of the tubes are arranged in an "X" shape, a rectangle, an "H" shape, a wagon wheel shape, or a star shape.

[0207] According to one embodiment, the distal pilot burner 1704 includes a manifold that includes a curvilinear tube. In one embodiment, the curvilinear tube is arranged in a spiral, or “∞”.

[0208] According to one embodiment, the mixing tube 1712 can be arranged about a longitudinal flow axis between the primary fuel nozzle 1618 and the distal flame holder 1602. According to one embodiment, the mixing tube 1710 can include a bell-shaped or flared portion 1714 at an end proximate the primary fuel nozzle 1618. The bell-shaped or flared portion 1714 can be disposed a predetermined distance from a floor 1738 of the burner system and can be configured to receive at least combustion air via an opening 1740 in the floor 1738.

[0209] As previously described in the present disclosure, a source of flue gas diluent is contemplated. The inventors have observed that the introduction of a mixing tube facilitates the recirculation of flue gas from downstream of the distal flame holder 1602 as a large amount of flue gas diluent and / or includes combustion products of the pilot flame maintained at the pilot burner 1704. Flue gas is discharged to the proximal end (i.e., the bottom plate end) of the mixing tube 1710 by the flow of the main fuel and combustion oxidant through the mixing tube 1710 between the bottom plate 1738 and the distal flame holder 1602. The recirculated flue gas is mixed with the fuel and combustion air before reaching the distal flame holder 1602. The non-reactive elements of the resulting mixture minimize the possibility of flashback upstream of the distal flame holder 1602 while allowing additional combustion of the reactive elements of the flue gas, thereby reducing, for example, NOx and other potential pollutants.

[0210] Those skilled in the art will recognize that one should not rely on Fig.17 1710 may have at least a majority of the input surface (e.g., Figure 7 The diameter of the mixture of fuel and oxidant (e.g., fuel and oxidant mixture 1607) provided by the input face 712 of the mixing tube 1710. The opening at the proximal end of the mixing tube 1710 closest to the primary fuel nozzle 1618 may have a maximum diameter that is sized to correspond to the opening 1740 in the bottom plate 1738 or sufficient to receive fuel input from each of the primary fuel nozzles 1618. For example, in an embodiment including a bell-shaped or trumpet-shaped portion 1714, the maximum diameter of the bell-shaped or trumpet-shaped portion 1714 may correspond to the opening 1740 in the bottom plate 1738 or may correspond to the farthest distance between at least the primary fuel nozzles 1618. The length of the mixing tube may be selected to allow sufficient time and / or distance for proper mixing of the fuel and oxidant before reaching the distal flame holder 1602.

[0211] According to one embodiment, a burner system includes a distal flame holder configured to maintain a combustion reaction of a fuel and an oxidant, and an oxidant conduit configured to direct the oxidant toward the distal flame holder. The burner system includes: a main fuel nozzle oriented to direct a flow of a main fuel into a combustion volume for mixing with the oxidant in a dilution region between the main fuel nozzle and the distal flame holder when the temperature of the distal flame holder is above a predetermined temperature; and a mixing tube disposed in the dilution region and extending from a mixing tube inlet to a mixing tube outlet between the main fuel nozzle and the distal flame holder, the mixing tube being formed to cause the flow of the oxidant and the fuel to discharge flue gas into the mixing tube for mixing with the fuel and the oxidant.

[0212] In one embodiment, the mixing tube is configured to cause the flow of oxidant and fuel to form a flue gas recirculation path.The flue gas recirculation path may be external to the combustion chamber.

[0213] According to one embodiment, the burner system further includes a pilot burner configured to support a pilot flame between an outlet of the mixing tube and a distal flame holder.

[0214] In one embodiment, the mixing tube includes a flared portion at the mixing tube inlet. The flue gas recirculation path may include at least an annular volume between the mixing tube and the wall of the combustion volume. The flue gas may be discharged into the fuel and oxidant streams at the mixing tube inlet for diluting the fuel and oxidant streams.

[0215] According to one embodiment, the burner system further comprises: a continuous pilot burner disposed adjacent to the distal flame holder, the continuous pilot burner being configured to heat the distal flame holder to the predetermined temperature; and a controller operably connected to the main fuel source, the controller being configured to receive an indication of the temperature of the distal flame holder and to control the flow rate of the main fuel in response to the indication of the temperature.

[0216] According to one embodiment, the burner system further comprises a mixing tube support structure configured to support the mixing tube, the mixing tube support structure configured to be supported by a surface defining the combustion volume.

[0217] Fig.18 is a diagram showing a horizontally fired burner system 1800 including a remote pilot burner 1804 and a mixing tube 1810, according to one embodiment. The inventors have observed that in various furnace applications, undesirable combustion oscillations occur between the remote flame holder 1802 and the fuel and oxidant (combustion air) source 1820. While not necessarily limited to closed furnace configurations - e.g., water heaters, boilers, or once-through steam generators (OTSGs) - such applications are representative environments that may allow for such combustion oscillations.

[0218] When the fuel and oxidant are in a sufficiently combustible ratio and are exposed to heat sufficient to ignite, they may ignite undesirably upstream of the distal flame holder 1802. This phenomenon tends to oscillate and is referred to herein as "flashback" and sometimes colloquially as "blowing". In some implementations, insufficiently and / or unevenly cooled oxidant (e.g., flue gas) may be recirculated from, for example, downstream of the distal flame holder 1802, thereby producing a fuel-oxidant mixture with a sufficiently high temperature so that the mixture may ignite before reaching the distal flame holder 1802. Flashback at least partially reduces the efficiency of the burner 1800 because the heat from this premature combustion is not radiated heat (in a gas burner), is not fully absorbed by the distal flame holder 1802 and / or the boiler tubes, and is therefore wasted. The combustion products from the flashback may dilute the mixture and thus temporarily extinguish the flashback combustion. Hence, the oscillatory nature of the flashback.

[0219] The distal pilot burner 1804 can be configured for preheating of the distal flame holder 1802 and / or to address undesirable flashback by providing a constant and / or controllable ignition source for the fuel and combustion air mixture at a location sufficiently close to the distal flame holder 1802, thereby providing a thermal benefit from the diffusion pilot flame 1808 to the distal flame holder 1802.

[0220] The distal pilot burner 1804 may be disposed in the combustion volume 1801 adjacent to the distal flame holder 1802. The distal flame holder 1802 may be formed of a plurality of columns comprising a refractory material. In one embodiment, the distal pilot burner 1804 is configured to maintain a diffusion pilot flame 1808 during combustion of the main fuel in the combustion reaction maintained by the distal flame holder 1802. The main fuel and combustion air may be supplied by a fuel and combustion air source 1820 disposed at a distance upstream of the distal pilot burner 1804. Thus, in one embodiment, the distance between the main fuel nozzle 1806 of the fuel and combustion air source 1820 and the distal pilot burner 1804 may be at least 50 times the diameter of the main fuel nozzle 1806, at least 100 times the diameter of the main fuel nozzle 1806, or at least 200 times the diameter of the main fuel nozzle 1806.

[0221] According to one embodiment, the horizontally fired burner system 1800 may include a mixing tube 1810 disposed between a fuel and combustion air source 1820 and a distal pilot burner 1804. The mixing tube 1810 may include a flared portion at an opening proximal to the fuel and combustion air source 1820. The mixing tube 1810 directs the flow of fuel and combustion air from the fuel and combustion air source 1820 toward the distal pilot burner 1804 and the distal flame holder 1802. Flue gas 1816 may be recirculated outside the mixing tube 1810 to enter its proximal end for mixing with the fuel and combustion air.

[0222] According to another embodiment, the horizontally fired burner system 1800 includes a remote pilot burner 1804 disposed adjacent to a plurality of columns. The remote pilot burner 1804 may be configured to sequentially provide a preheat flame to raise the temperature of the remote flame holder 1802 to at least the autoignition temperature of the main fuel prior to the introduction of the main fuel, and to maintain a diffusion pilot flame 1808 during combustion of the main fuel in a combustion reaction maintained by the remote flame holder 1802. The remote pilot burner 1804 may be configured to support a large combustion reaction during preheating of the remote flame holder 1802, and to support a smaller combustion reaction during subsequent combustion of the main fuel.

[0223] The disclosed horizontally fired burner system may include a controller 1812 (corresponding to, for example, the control system 1412 described herein) configured to receive sensor inputs, such as from a sensor 1815, and control the output of fuel and combustion air. Fig.18 In an embodiment of the present invention, the controller 1812 can control the use of the distal pilot burner 1804. For example, the controller 1812 can control an actuator (not shown) that controls the rate and / or amount of fuel provided to the distal pilot burner 1804 based on sensor inputs indicating, for example, the temperature of the distal flame holder 1802, the presence or absence or quality of a flame at the distal flame holder 1802 and / or the distal pilot burner 1804.

[0224] In view of this disclosure, those skilled in the art will recognize that a combustion system according to the principles of the present disclosure may include sensors and actuators other than those disclosed herein, other combinations of sensors and actuators, and controllers (e.g., Figure 7 730) other types of actions to be taken in response to the sensor signal. All such other sensors, actuators, combinations and actions fall within the scope of the present disclosure.

[0225] This application also involves the following aspects:

[0226] 1. A burner system, comprising:

[0227] a pilot burner disposed in the furnace at a distal position along the main fuel and combustion air flow axis; and

[0228] one or more primary fuel nozzles disposed at a proximal position along the primary fuel and combustion air flow axis;

[0229] wherein the pilot burner is configured to support a pilot flame; and

[0230] wherein the one or more primary fuel nozzles are configured to support a main flame in contact with the pilot flame;

[0231] Wherein the pilot burner is arranged such that the main fuel and combustion air are ignited by the pilot flame.

[0232] 2. The burner system of claim 1, wherein the main flame comprises a flame having a heat output at least 10 times that of the pilot flame when the burner system is operated at a rated heat output.

[0233] 3. The burner system of claim 2, wherein operating at the rated heat output corresponds to operating in a steady-state standard operating mode.

[0234] 4. The burner system of claim 2, wherein the main flame comprises a flame having a heat output at least 20 times that of the pilot flame when the burner system is operated at a rated heat output.

[0235] 5. The burner system of 1 further comprising a chimney operably coupled to the burner system, wherein the burner system has a NOx output of approximately twenty parts per million or less, adjusted to 3% excess O2 at the chimney.

[0236] 6. The burner system of claim 1, wherein the pilot burner outputs a pilot fuel, and the pilot fuel supports the pilot flame.

[0237] 7. The burner system according to 1, wherein the main fuel nozzle outputs a main fuel, and the main fuel supports the main flame.

[0238] 8. The burner system of claim 1, wherein the pilot burner defines a plurality of fuel orifices having a sufficiently large collecting area to collectively support a low momentum pilot flame.

[0239] 9. The burner system of claim 8, wherein the primary fuel nozzle and combustion air form a combustible mixture that expands in width as it flows from the proximal position to the distal position.

[0240] 10. The burner system of claim 9, wherein the plurality of fuel orifices are disposed sufficiently widely on the furnace to cause the pilot flame to contact the main fuel and air mixture across the width of the combustible mixture.

[0241] 11. The burner system of claim 8, wherein the primary fuel nozzle is configured to output fuel that co-flows with the air.

[0242] 12. The burner system of claim 1, wherein the pilot burner comprises a fuel manifold having a plurality of segments joined together, each segment having a plurality of fuel orifices configured to pass fuel from within the fuel manifold to a furnace combustion volume.

[0243] 13. The burner system of claim 12, wherein the plurality of segments are formed to be configured to allow the fuel delivered from a fuel pipe to freely enter a corresponding pipe of the fuel manifold.

[0244] 14. The burner system of claim 13, wherein at least a portion of the tubes are arranged as spokes radiating from a center disposed substantially at a centerline along the axis.

[0245] 15. The burner system according to 13, wherein at least a portion of the tubes are arranged in an "X"

[0246] Shaped like a 4-11, 4-23, 4-5, 6-7, 8-9, 10-11, 11-12, 12-13, 13-14, 15-16, 17-18, 19-20, 21-22, 22-23, 24-25, 26-27, 28-29, 30-40, 31-5

[0247] 16. The burner system of claim 13, further comprising the fuel tube configured to support the pilot burner at the distal location.

[0248] 17. The burner system of claim 1, wherein the pilot burner comprises a manifold comprising a curvilinear tube.

[0249] 18. The burner system according to 17, wherein the curved tube is arranged in a spiral shape,

[0250] or “∞”.

[0251] 19. The burner system according to claim 1, wherein the primary fuel nozzle forms a fuel dump plane at the proximal position coinciding with or close to the floor of the furnace.

[0252] 20. The burner system of claim 1, wherein the pilot burner supports a diffusion flame at the distal location that is at least 100 main fuel nozzle diameters from the floor of the furnace.

[0253] 21. The burner system of claim 20, further comprising an outer support configured to substantially prevent shaking of the fuel tube.

[0254] 22. The burner system of claim 1, wherein the pilot burner comprises at least one tube disposed transverse to the fuel and combustion air flow axis.

[0255] 23. The burner system according to 22, further comprising:

[0256] One or more sections of reticulated ceramic, the one or more sections of reticulated ceramic being disposed above the at least one tube.

[0257] 24. The burner system of claim 22, wherein the at least one tube defines a plurality of fuel flow holes disposed along a length of the at least one tube.

[0258] 25. The burner system of claim 22, wherein the at least one tube defines a plurality of fuel flow holes configured to allow gaseous fuel to flow upwardly into a "U" shaped channel formed above the at least one tube.

[0259] 26. The burner system according to 1, further comprising:

[0260] A distal flame holder is provided along the fuel and combustion air flow path.

[0261] The axis is disposed at a third position, further away from the main fuel nozzle than the pilot burner.

[0262] 27. The burner system of claim 26, wherein the distal flame holder comprises a perforated flame holder configured to control flame length.

[0263] 28. A burner system comprising:

[0264] a main fuel source disposed at a proximal position along a flow axis of the furnace;

[0265] a pilot burner disposed at an intermediate distance along the flow axis; and

[0266] a distal flame holder disposed at a distal position along the flow axis;

[0267] wherein the pilot burner is configured to support a pilot flame to heat the distal flame holder;

[0268] wherein the primary fuel source is configured to provide primary fuel to the distal flame holder after the distal flame holder is at least partially heated; and

[0269] Wherein the distal flame holder is configured to hold at least a portion of a combustion reaction supported by the primary fuel.

[0270] 29. The burner system of claim 28, further comprising support legs supporting the distal flame holder in the furnace.

[0271] 30. The burner system of claim 28, wherein the distal flame holder comprises a mesh ceramic.

[0272] 31. The burner system of claim 30, wherein the distal flame holder comprises a plurality of mesh fibers.

[0273] 32. The burner system of claim 31, wherein the distal flame holder is configured to support a combustion reaction of the fuel and the combustion air upstream, downstream, and within the distal flame holder.

[0274] 33. The burner system of claim 31, wherein the mesh fibers are formed into a mesh ceramic foam.

[0275] 34. The burner system of claim 31, wherein the distal flame holder comprises:

[0276] Input surface;

[0277] output surface; and

[0278] A plurality of perforations extend between the input face and the output face.

[0279] 35. The burner system of claim 34, wherein the perforations are formed as channels between the mesh fibers.

[0280] 36. A method for operating a burner system, comprising:

[0281] providing heat to a distal flame holder from a pilot flame supported by a pilot burner, the pilot flame being fueled by a pilot fuel, the distal flame holder and the pilot burner being disposed in the furnace in close proximity to one another, the pilot burner being disposed between the distal flame holder and one or more main fuel nozzles, the pilot burner being disposed at a distance from the distal flame holder that is less than a distance from the pilot burner to the one or more main fuel nozzles;

[0282] introducing a mixed main fuel and air into the distal flame holder; and

[0283] While the pilot burner continues to support the pilot flame, at least a portion of the combustion reaction of the mixed main fuel and air is maintained by the distal flame holder.

[0284] 37. The method of claim 36, wherein providing heat from the pilot flame supported by the pilot burner to the distal flame holder comprises:

[0285] providing the pilot fuel from a pilot fuel source to the pilot burner;

[0286] Controlling the pilot fuel flow rate;

[0287] emitting the pilot fuel from a plurality of orifices of the pilot burner, the orifices being disposed across the width of the mixed main fuel and air; and

[0288] The mixed main fuel and air is ignited at the pilot burner with the pilot flame.

[0289] 38. The method according to 36, further comprising:

[0290] measuring a temperature of the distal flame holder; and

[0291] reducing a pilot fuel flow rate to reduce a size of the pilot flame when the temperature of the distal flame holder is equal to or greater than a predetermined threshold;

[0292] Wherein reducing the size of the pilot flame relative to the size of the combustion reaction of the mixed main fuel and air results in reduced emissions of nitrogen oxides.

[0293] 39. The method of claim 36, wherein introducing the mixed main fuel and air into the distal flame holder comprises introducing the main fuel and introducing the air via the one or more main fuel nozzles at the proximal end of the mixing tube;

[0294] The proximal end of the mixing tube is disposed close to the one or more main fuel nozzles, and the distal end of the mixing tube is disposed close to the distal flame holder, the mixing tube leading from the proximal end to the distal end.

[0295] 40. The method according to 39, further comprising:

[0296] Flue gas is discharged into the proximal end of the mixing tube.

[0297] 41. The method of claim 39, wherein the pilot burner is disposed between the distal flame holder and the distal end of the mixing tube.

[0298] 42. A method for operating a burner system, comprising:

[0299] supporting a diffusion flame across a portion of the width of a furnace volume at a location remote from a furnace floor; providing combustion air to the furnace volume from a location near the furnace floor;

[0300] outputting a high pressure primary fuel jet from each of one or more primary fuel nozzles at one or more locations near the furnace floor;

[0301] mixing the primary fuel with the combustion air as the primary fuel and combustion air travel from the location proximate the furnace floor to the distal location; and

[0302] The main fuel is combusted by exposing the mixed main fuel and air to the diffusion flame to produce a main flame.

[0303] 43. The method of claim 42, further comprising maintaining the primary flame produced by the burning of the primary fuel in a stable position, wherein a distal flame holder is disposed further from the furnace floor than the diffusion flame.

[0304] 44. The method of claim 43, wherein supporting a diffusion flame comprises generating and maintaining the diffusion flame at a pilot burner disposed in the furnace volume between the one or more primary fuel nozzles and the distal flame holder.

[0305] 45. The method of claim 44, wherein the pilot burner is positioned closer to the distal flame holder than it is relative to the furnace floor.

[0306] 46. ​​The method of claim 44, wherein maintaining the diffusion flame at the pilot burner comprises:

[0307] supplying pilot fuel to the pilot burner;

[0308] emitting the pilot fuel from one or more pilot fuel orifices of the pilot burner; and

[0309] Ignition of the mixture of combustion air and the emitted pilot fuel at the pilot burner is maintained to support the diffusion flame.

[0310] 47. A method according to 46, wherein the one or more pilot fuel orifices constitute a plurality of pilot fuel orifices arranged on a portion of the width of the furnace volume, the portion being wide enough to allow the diffusion flame to contact the mixture of the main fuel and combustion air over the width of the mixed main fuel and combustion air.

[0311] 48. The method of claim 46, wherein the one or more pilot fuel orifices include a plurality of pilot fuel orifices having a sufficiently large collection area to support the diffusion flame at low momentum.

[0312] 49. The method of claim 44, wherein maintaining the diffusion flame at the pilot burner comprises controlling a rate at which pilot fuel is supplied to the pilot burner.

[0313] 50. The method according to 42, further comprising:

[0314] detecting a temperature of a distal flame holder disposed above the diffusion flame; and reducing a rate at which pilot fuel is supplied to a pilot burner supporting the diffusion flame when the distal flame holder reaches at least a predetermined threshold temperature.

[0315] 51. The method according to 50, further comprising:

[0316] The combustion of the primary fuel at the distal flame holder is detected using a capacitive sensor configured to output a sensor signal to a controller.

[0317] 52. A combustion system comprising:

[0318] an oxidant source configured to output an oxidant into the furnace volume;

[0319] a pilot burner configured to support a pilot flame by outputting a pilot fuel to support a pilot diffusion flame at least during a preheat state;

[0320] a main fuel nozzle configured to output a main fuel from a proximal position into the furnace volume during a standard operating state at least after the preheat state is completed; a distal flame holder positioned in the furnace volume to be preheated by the pilot flame during the preheat state and to maintain a combustion reaction of the main fuel and an oxidant proximate the distal flame holder during the standard operating state;

[0321] a combustion sensor configured to sense a condition of the distal flame holder and to generate a sensor signal indicative of the condition of the distal flame holder; one or more actuators configured to adjust the flow of the main fuel from the main fuel nozzle, adjust the flow of the pilot fuel to the pilot burner, and adjust the flow of the oxidant from the oxidant source; and

[0322] a controller communicatively coupled to the actuator and the combustion sensor, the controller being configured to receive the sensor signal from the combustion sensor and to control the actuator to adjust the flow rates of the pilot fuel, the main fuel, and the oxidant in response to the sensor signal and in accordance with software instructions stored in a non-transitory computer readable medium coupled to the controller.

[0323] 53. The combustion system according to 52, further comprising:

[0324] A pilot flame sensor is configured to sense a condition of the pilot flame and output a sensor signal indicative of the condition of the pilot flame.

[0325] 54. A combustion system according to 53, wherein the combustion sensor includes the pilot flame sensor.

[0326] 55. The combustion system of claim 53, wherein the pilot flame sensor comprises a capacitive sensor.

[0327] 56. The combustion system of claim 53, wherein the pilot flame sensor comprises a resistive sensor.

[0328] 57. The combustion system of 53, wherein the pilot flame sensor comprises a fault sensor.

[0329] 58. The combustion system of 55, further comprising an igniter configured to generate an electric arc.

[0330] 59. A combustion system according to claim 58, wherein the controller is configured to control one or more of the actuators to cause the igniter to generate an arc to ignite the pilot flame if the capacitive sensor indicates that the pilot flame is not present and all safety interlocks are met.

[0331] 60. A combustion system according to claim 52, wherein the controller is configured to adjust the size of the pilot flame by controlling one or more of the actuators to adjust the flow of the pilot fuel or the oxidant in response to the sensor signal from at least the combustion sensor.

[0332] 61. The combustion system of claim 52, wherein the combustion sensor is further configured to detect the combustion reaction at the distal flame holder and output a sensor signal to the controller in response to the detected state of the combustion reaction.

[0333] 62. The combustion system of claim 61, wherein the combustion sensor is operable as a flashback sensor configured to detect flashback of the combustion reaction from the distal flame holder toward the primary fuel nozzle.

[0334] 63. A combustion system according to claim 61, wherein the combustion sensor comprises a capacitive sensor.

[0335] 64. The combustion system of claim 63, wherein the capacitive sensor comprises:

[0336] A first set of electrodes is positioned laterally around the distal flame holder and is configured to sense a parameter proximate the distal flame holder.

[0337] 65. The combustion system of claim 64, wherein the capacitive sensor comprises:

[0338] A second set of electrodes is positioned upstream of the distal flame holder and is configured to sense a parameter upstream of the distal flame holder.

[0339] 66. A combustion system according to claim 65, wherein the controller senses the combustion reaction by comparing the parameter sensed by the first set of electrodes with the parameter sensed by the second set of electrodes.

[0340] 67. A combustion system according to claim 66, wherein the first set of electrodes is part of the combustion sensor.

[0341] 68. The combustion system of claim 63, wherein the capacitive sensor comprises a set of electrodes positioned upstream of the distal flame holder and configured to detect flashback by sensing a parameter upstream of the distal flame holder.

[0342] 69. The combustion system of claim 63, wherein the capacitive sensor comprises a plurality of electrodes positioned laterally around the distal flame holder.

[0343] 70. The combustion system of claim 69, wherein the plurality of electrodes comprises one or more electrode pairs separated from one another by the distal flame holder.

[0344] 71. A combustion system according to claim 70, wherein the capacitive sensor generates a capacitive tomography image based on the capacitance between the one or more electrode pairs.

[0345] 72. A combustion system according to claim 69, wherein the plurality of electrodes include one or more first pairs of electrodes, the one or more first pairs being separated from each other by the distal flame holder and arranged relative to each other in a first orientation substantially perpendicular to a main direction of flow of the main fuel toward the distal flame holder.

[0346] 73. A combustion system according to 72, wherein the plurality of electrodes include one or more second pairs of electrodes, the one or more second pairs being separated from each other by the distal flame holder and arranged relative to each other in a second orientation substantially perpendicular to both the first orientation and the main direction of flow of the main fuel.

[0347] 74. A computing system implemented method for operating a combustion system, the method comprising:

[0348] receiving, during a preheat state of the combustion system, a sensor signal from a pilot flame sensor indicative of a condition of a pilot flame in a furnace volume supported by a flow of pilot fuel and oxidant; receiving, during said preheat state, a sensor signal from a distal flame holder sensor indicative of a temperature of a distal flame holder positioned in said furnace volume to be preheated by said pilot flame to an operating temperature during said preheat state;

[0349] in response to the sensor signal from the pilot flame sensor and according to software instructions stored on a non-transitory computer readable medium, output a control signal to control one or more actuators to adjust the flow of the pilot fuel, adjust the flow of the oxidant, or generate an arc to ignite the pilot flame;

[0350] outputting a control signal to control one or more actuators to transition the combustion system from the preheat state to a standard operating state corresponding to supporting a combustion reaction of a primary fuel and the oxidant in the distal flame holder and in accordance with the software instructions stored on the non-transitory computer readable medium if the sensor signal from the distal flame holder sensor indicates that the distal flame holder has reached the operating temperature;

[0351] receiving a sensor signal from the distal flame holder sensor during the standard operating state indicating a condition of the distal flame holder; and

[0352] In response to the sensor signal from the distal flame holder sensor during the standard operating state and in accordance with the software instructions stored on the non-transitory computer readable medium, a control signal is output to control one or more actuators to adjust the flow of the main fuel or to adjust the flow of the oxidant.

[0353] 75. The computing system implemented method of 74, wherein the receiving a sensor signal from the pilot flame sensor comprises receiving a capacitance tomography signal from the pilot flame sensor.

[0354] 76. The computing system implemented method of 74, wherein receiving a sensor signal from the distal flame holder sensor comprises receiving a capacitance tomography signal from the distal flame holder sensor.

[0355] 77. A low emission modular burner system comprising:

[0356] One or more burner modules, each burner module comprising:

[0357] a main fuel source, the main fuel source being valved separately from all other fuel sources, the main fuel source being configured to selectively deliver a main fuel flow for dilution by a flow of combustion air,

[0358] a main fuel igniter configured to cause ignition of the main fuel stream emitted from the main fuel source,

[0359] a distal flame holder separated from the primary fuel source and the primary fuel igniter by respective non-zero distances, the distal flame holder being configured to maintain a combustion reaction supported by the primary fuel flow when the distal flame holder is at or above a predetermined temperature, and

[0360] a preheating device configured to preheat the distal flame holder to the predetermined temperature;

[0361] a common combustion air source configured to provide combustion air to each of the plurality of burner modules; and

[0362] A wall surrounds the entirety of the one or more burner modules, the wall being configured to laterally contain a combustion fluid corresponding to the one or more burner modules.

[0363] 78. A low emission modular burner system according to 77, wherein the predetermined temperature is equal to or greater than the auto-ignition temperature of the main fuel.

[0364] 79. A low emission modular burner system according to 77, wherein the preheating device of each burner module includes a continuous pilot burner.

[0365] 80. A low emission modular burner system according to claim 79, wherein the continuous pilot burner is configured to selectively output heat at any one of a plurality of heating rates.

[0366] 81. A low emission modular burner system according to 80, wherein at least one heating rate is selected to cause the sensed temperature of the distal flame holder to increase to the predetermined operating temperature; and

[0367] At least one other heating rate is selected such that the preheating device maintains a pilot flame function while a majority of the total fuel consumed per unit time is provided by the main fuel source.

[0368] 82. A low emission modular burner system according to claim 77, wherein the common combustion air source is configured to provide natural draft combustion air to each burner module in the plurality of burner modules.

[0369] 83. The low emission modular burner system according to 77, further comprising:

[0370] one or more individual main fuel valves, the one or more individual main fuel valves each comprising an individual main fuel valve actuator configured to operate in response to receiving a control signal; and

[0371] Also includes:

[0372] a control system configured to output a respective control signal to each of the individual valve actuators;

[0373] The control system further comprises:

[0374] an interface between the control system and an input channel, wherein the interface is configured to receive a signal corresponding to a burner capacity request;

[0375] one or more burner module sensor inputs, each of the one or more burner module sensor inputs configured to receive a signal corresponding to a burner module status, wherein the burner module status is provided by sensor hardware;

[0376] a microcontroller, a computer readable memory, and a module sequencer configured to select a subset of the one or more burner modules for ignition; and

[0377] A respective one or more master fuel valve driver outputs are each operably coupled to one of the individual master fuel valve actuators.

[0378] 84. The low emission modular burner system of 83, wherein the control system further comprises:

[0379] An operation sequencer includes a state machine configured to sequence steps in a burner module startup plan for one or more of the burner modules.

[0380] 85. The low emission modular burner system of 83, wherein the control system further comprises:

[0381] An actuator driver module is configured to provide the respective control signal to each of the individual valve actuators.

[0382] 86. The low emission modular burner system of 83, wherein the control system further comprises:

[0383] A demand module is configured to selectively oversee automatic operation of the one or more burner modules based on at least one of a stored schedule and a received demand signal.

[0384] 87. The low emission modular burner system of 83, wherein the microcontroller is configured to read and execute computer executable instructions supported by the non-transitory computer readable memory to:

[0385] receiving capacity input data corresponding to the burner capacity request signal;

[0386] reading module status sensor data from one or more sensors corresponding to at least one burner module to verify that a selected one or more of the burner modules are ready to fire;

[0387] selecting the subset of the one or more burner modules for ignition; and driving at least one of the individual main fuel valve actuators corresponding to the selected subset of the one or more burner modules to open so as to provide fuel to the combustion reaction supported by the subset of the one or more burner modules.

[0388] 88. A low emission modular burner system according to 83, wherein the control system also includes a thermal energy demand sensor.

[0389] 89. The low emission modular burner system of claim 77, wherein the preheating device comprises:

[0390] a pilot fuel source configured to provide a pilot fuel,

[0391] a pilot fuel igniter configured to ignite the flow of pilot fuel, and

[0392] A distal pilot is configured to maintain a pilot flame supported by the pilot fuel, the pilot fuel source flow rate being selected to provide a pilot flame sized to raise the distal flame holder temperature to the predetermined temperature.

[0393] 90. A low emission modular burner system according to claim 89, wherein the predetermined temperature is equal to or greater than the auto-ignition temperature of the main fuel.

[0394] 91. A low emission modular burner system according to 89, wherein the main fuel igniter includes the distal pilot.

[0395] 92. A low emission modular burner system according to 89, wherein the main fuel igniter includes the distal flame holder when the distal flame holder is heated to the predetermined temperature by the distal pilot.

[0396] 93. A low emission modular burner system according to 89, wherein the distal pilot is configured to be controlled to provide the pilot flame sized to raise the distal flame holder to the predetermined temperature during the burner module startup cycle, and not to provide the pilot flame sized to raise the distal flame holder to the predetermined temperature at times other than during the burner module startup cycle.

[0397] 94. A low emissions modular burner system according to claim 93, wherein the remote pilot is configured to be reduced to a pilot flame capacity at times other than during a startup cycle of the burner module.

[0398] 95. A low emission modular burner system according to claim 93, wherein the remote pilot is configured to stop supporting the combustion reaction at times other than during the burner module startup cycle.

[0399] 96. A low emission burner system according to 89, wherein the distal pilot is disposed adjacent to the distal flame holder; and

[0400] Wherein the distal pilot output is selected to maintain a constant capacity at all times during operation.

[0401] 97. A low emission modular burner system according to 89, wherein the distal pilot is disposed adjacent to the distal flame holder; and

[0402] Wherein the remote pilot is controlled to be reduced to a pilot flame capacity at times other than during a startup cycle of the burner module.

[0403] 98. A low emission modular burner system according to 97, wherein the distal pilot is configured to ensure combustion of the main fuel.

[0404] 99. A low emission modular burner system according to 97, wherein the main fuel is hydrocarbon gas.

[0405] 100. A low emission modular burner system according to 97, wherein the pilot fuel is natural

[0406] gas or propane.

[0407] 101. A burner, comprising:

[0408] a housing having a combustion air inlet at a base; and

[0409] A burner module is positioned inside the housing.

[0410] The module includes:

[0411] an inlet configured to couple to a primary fuel source and receive combustion air via the housing;

[0412] a distal flame holder positioned within the housing; and

[0413] A primary nozzle is configured to receive a flow of a primary fuel from the inlet and emit the flow of the primary fuel toward the distal flame holder.

[0414] 102. The burner according to 101, wherein the burner module is configured to be a stand-alone

[0415] It is supported only by the connecting piece at the inlet.

[0416] 103. The burner according to 101, wherein the burner module is configured to be coupled to the

[0417] The burner is supported by the burner.

[0418] 104. The burner according to 101, wherein the main nozzle is one of a plurality of main nozzles,

[0419] Each of the primary nozzles is configured to receive a flow of the primary fuel from the inlet,

[0420] And emitting a primary fuel stream toward a corresponding portion of the distal flame holder.

[0421] 105. The burner according to 104 further comprises a plurality of main fuel valves, wherein the plurality of main fuel valves

[0422] The fuel injection nozzle is operably coupled between a common fuel line and a respective one of the plurality of primary nozzles and is configured to independently control operation of the respective primary nozzle.

[0423] 106. The burner according to 101, further comprising:

[0424] a distal pilot positioned between the distal flame holder and the primary nozzle; and

[0425] The burner module includes a modified burner positioned within the housing, the modified burner including the distal flame holder and the main nozzle.

[0426] 107. The burner according to 106, wherein the distal pilot comprises a plurality of

[0427] A pilot nozzle.

[0428] 108. A burner according to 106, wherein the distal pilot is configured to support the distal

[0429] A pilot flame between the side pilot burner and the distal flame holder.

[0430] 109. A burner according to 101, wherein the main nozzle includes a hole with variable size.

[0432] 110. The burner according to 109, wherein the main nozzle is configured to adjust the main fuel

[0433] The speed of the flow.

[0434] 111. The burner according to 109, further comprising an actuator, the actuator being operably connected

[0435] to the primary nozzle and is configured to control the size of the hole.

[0436] 112. The burner according to 109, wherein the main nozzle comprises a main nozzle outlet and a control element

[0437] The control element is positioned to block a portion of the main nozzle outlet, and

[0438] Movement of the control element varies the extent to which the primary nozzle outlet is blocked by the control element.

[0439] 113. A burner according to 101, wherein each burner module has a heating capacity of approximately 8 MBtu / Hr.

[0440] 114. A burner system comprising:

[0441] a distal flame holder configured to maintain a combustion reaction of a fuel and an oxidant;

[0442] an oxidant conduit configured to direct the oxidant toward the distal flame holder;

[0443] a primary fuel nozzle oriented to direct a flow of primary fuel into a combustion volume for mixing with the oxidant in a dilution region between the primary fuel nozzle and the distal flame holder when the temperature of the distal flame holder is above a predetermined temperature; and

[0444] a mixing tube disposed in the dilution zone and leading from a mixing tube inlet to a mixing tube outlet between the main fuel nozzle and the distal flame holder,

[0445] The mixing tube is formed such that the flow of the oxidant and fuel discharges flue gas into the mixing tube for mixing with the fuel and oxidant.

[0446] 115. The burner system according to 114, wherein the mixing tube is configured to cause the oxygen

[0447] The flow of catalytic agent and fuel forms a flue gas recirculation path.

[0448] 116. The burner system according to 115, wherein the flue gas recirculation path is

[0449] The outside of the combustion chamber.

[0450] 117. The burner system according to 114, further comprising:

[0451] A pilot burner is configured to support a pilot flame between the mixing tube outlet and the distal flame holder.

[0452] 118. The burner system according to 114, wherein the mixing tube includes a

[0453] The flared part at the mouth;

[0454] wherein the flue gas recirculation path comprises at least an annular volume between the mixing tube and a wall of the combustion volume, and

[0455] The flue gas is discharged into the fuel and oxidant streams at the mixing tube inlet to dilute the fuel and oxidant streams.

[0456] 119. The burner system according to 114, further comprising:

[0457] a sequential pilot disposed adjacent to the distal flame holder, the sequential pilot configured to heat the distal flame holder to the predetermined temperature; and

[0458] A controller is operably coupled to the primary fuel source, the controller being configured to receive an indication of a temperature of the distal flame holder and to control the flow of the primary fuel in response to the indication of the temperature.

[0459] 120. The burner system according to 114, further comprising:

[0460] A mixing tube support structure is configured to support the mixing tube, the mixing tube support structure being configured to be supported by a surface defining the combustion volume.

[0461] 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 purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. A burner system, comprising: a main fuel source disposed at a proximal position along a flow axis of the furnace; a pilot burner disposed at an intermediate distance along the flow axis; and a distal flame holder disposed at a distal position along the flow axis; wherein the pilot burner is configured to support a pilot flame to heat the distal flame holder; wherein the primary fuel source is configured to provide primary fuel to the distal flame holder after the distal flame holder is at least partially heated; and Wherein the distal flame holder is configured to hold at least a portion of a combustion reaction supported by the primary fuel. 2 . The burner system of claim 1 , further comprising support legs supporting the distal flame holder in the furnace. 3 . The burner system of claim 1 , wherein the distal flame holder comprises a reticulated ceramic. The burner system of claim 3 , wherein the distal flame holder comprises a plurality of mesh fibers. 5 . The burner system of claim 4 , wherein the distal flame holder is configured to support a combustion reaction of the primary fuel and combustion air upstream, downstream, and within the distal flame holder.

6. The burner system of claim 4, wherein the reticulated fibers are formed as a reticulated ceramic foam.

7. The burner system of claim 4, wherein the distal flame holder comprises: Input surface; Output surface; and A plurality of perforations extend between the input face and the output face.

8. The burner system of claim 7, wherein the perforations are formed as channels between the mesh fibers.

9. A method for operating a burner system, comprising: providing heat to a distal flame holder from a pilot flame supported by a pilot burner, the pilot flame being fueled by a pilot fuel, the distal flame holder and the pilot burner being disposed in the furnace in close proximity to one another, the pilot burner being disposed between the distal flame holder and one or more main fuel nozzles, the pilot burner being disposed at a distance from the distal flame holder that is less than a distance from the pilot burner to the one or more main fuel nozzles; introducing a mixed main fuel and air into the distal flame holder; as well as While the pilot burner continues to support the pilot flame, at least a portion of the combustion reaction of the mixed main fuel and air is maintained by the distal flame holder.

10. The method of claim 9, wherein providing heat from the pilot flame supported by the pilot burner to the distal flame holder comprises: providing the pilot fuel from a pilot fuel source to the pilot burner; Controlling the pilot fuel flow rate; emitting the pilot fuel from a plurality of orifices of the pilot burner, the orifices being disposed across the width of the mixed main fuel and air; as well as The mixed main fuel and air is ignited at the pilot burner with the pilot flame.

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