EP3966503B1 - Pilotstabilisierter brenner - Google Patents

Pilotstabilisierter brenner

Info

Publication number
EP3966503B1
EP3966503B1 EP20803052.8A EP20803052A EP3966503B1 EP 3966503 B1 EP3966503 B1 EP 3966503B1 EP 20803052 A EP20803052 A EP 20803052A EP 3966503 B1 EP3966503 B1 EP 3966503B1
Authority
EP
European Patent Office
Prior art keywords
burner
fuel
flame holder
pilot
main fuel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
EP20803052.8A
Other languages
English (en)
French (fr)
Other versions
EP3966503A4 (de
EP3966503A1 (de
Inventor
Colin James Deller
Donald Kendrick
Venkatesh Iyer
Douglas W. KARKOW
James K. DANSIE
Christopher A. Wiklof
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Clearsign Technologies Corp
Original Assignee
Clearsign Technologies Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US16/782,861 external-priority patent/US20210239317A1/en
Application filed by Clearsign Technologies Corp filed Critical Clearsign Technologies Corp
Priority to EP26157429.7A priority Critical patent/EP4717975A2/de
Publication of EP3966503A1 publication Critical patent/EP3966503A1/de
Publication of EP3966503A4 publication Critical patent/EP3966503A4/de
Application granted granted Critical
Publication of EP3966503B1 publication Critical patent/EP3966503B1/de
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N5/00—Systems for controlling combustion
    • F23N5/02—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium
    • F23N5/10—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using thermocouples
    • F23N5/105—Systems for controlling combustion using devices responsive to thermal changes or to thermal expansion of a medium using thermocouples using electrical or electromechanical means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/20—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone
    • F23D14/22—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone with separate air and gas feed ducts, e.g. with ducts running parallel or crossing each other
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D11/00—Burners using a direct spraying action of liquid droplets or vaporised liquid into the combustion space
    • F23D11/36—Details
    • F23D11/40—Mixing tubes; Burner heads
    • F23D11/406—Flame stabilising means, e.g. flame holders
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/02—Premix gas burners, i.e. in which gaseous fuel is mixed with combustion air upstream of the combustion zone
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/26—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid with provision for a retention flame
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/46—Details
    • F23D14/48—Nozzles
    • F23D14/58—Nozzles characterised by the shape or arrangement of the outlet or outlets from the nozzle, e.g. of annular configuration
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
    • F23D14/46—Details
    • F23D14/62—Mixing devices; Mixing tubes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N1/00—Regulating fuel supply
    • F23N1/002—Regulating fuel supply using electronic means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N3/00—Regulating air supply or draught
    • F23N3/005—Regulating air supply or draught using electrical or electromechanical means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23D—BURNERS
    • F23D2900/00—Special features of, or arrangements for burners using fluid fuels or solid fuels suspended in a carrier gas
    • F23D2900/00014—Pilot burners specially adapted for ignition of main burners in furnaces or gas turbines

Definitions

  • the document US 2017/0307212 A1 relates to a fuel nozzle assembly that includes one or more tapered fuel nozzles.
  • Each tapered fuel nozzle includes an acute trailing edge or tip at a top portion of the fuel nozzle.
  • One or more fuel orifices are arranged proximate the acute trailing edge or tip.
  • the present invention relates to a burner system according to independent claim 1, wherein further developments of the inventive burner system are provided in the sub-claims 2 to 9.
  • the present invention also relates to a method for operating a burner system according to independent claim 10, wherein further developments of the inventive method are provided in the sub-claims 11 to 13.
  • the present invention relates to a low emissions modular burner system according to claim 14, wherein further developments of the inventive low emissions modular burner system are provided in the sub-claims 15 to 16.
  • a burner system includes a pilot burner disposed in a furnace at a distal position along a main fuel and combustion air flow axis, 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 disposed to cause the main fuel and combustion air to be ignited by the pilot flame.
  • 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 is configured to support a pilot flame to heat the distal flame holder.
  • the main fuel source is configured to provide main fuel to the distal flame holder after the distal flame holder is at least partially heated.
  • the distal flame holder is configured to hold at least a portion of a combustion reaction supported by the main fuel.
  • a method for operating a burner system includes providing heat to the 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 are disposed in a furnace and in proximity to one another, the pilot burner disposed between the distal flame holder and one or more main fuel nozzles with a distance between the pilot burner and the distal flame holder being smaller than a distance between the pilot burner and the one or more main fuel nozzles.
  • the method for operating a burner system includes introducing mixed fuel and air to the distal flame holder, and holding at least a portion of a combustion reaction of the mixed main fuel and air with the distal flame holder while the pilot burner continues to support the pilot flame.
  • a method for operating a burner system includes supporting a diffusion flame across a portion of a width of a furnace volume at a position distal 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 locations near the furnace floor to the distal position, combusting the main fuel to produce a main flame by exposing the mixed main fuel and air to the diffusion flame.
  • the main flame is held by a distal flame holder more distal from the furnace floor than the diffusion flame.
  • a combustion system includes an oxidant source configured to output an 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 preheating state, and a main fuel nozzle configured to output a main fuel into the furnace volume from a proximal position during a standard operating state at least after the preheating state is complete.
  • the combustion system includes a distal flame holder positioned in the furnace volume to be preheated by the pilot flame during the preheating state and to hold a combustion reaction of the main fuel and oxidant adjacent to 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 to generate a sensor signal indicative of the condition of the combustion system, and one or more actuators configured to adjust a flow of the main fuel from the main fuel nozzle, to adjust a flow of the pilot fuel to the pilot burner, and to adjust a flow of the oxidant from the oxidant source.
  • the method includes outputting control signals to control one or more actuators to adjust the flow of the pilot fuel, to adjust the flow of the oxidant, or to generate an arc to ignite the pilot flame responsive to the sensor signals from the pilot flame sensor and in accordance with software instructions stored on a non-transitory computer readable medium, and outputting control signals to control one or more actuators to transition the combustion system from the preheating state to a standard operating state if the sensor signals from the distal flame holder sensor indicate that the distal flame holder has reached the operating temperature, the standard operating state corresponding to supporting a combustion reaction of a main fuel and the oxidant in the distal flame holder and in accordance with the software instructions stored on the non-transitory computer readable medium.
  • the method includes receiving sensor signals from the distal flame holder sensor during the standard operating state indicating a condition of the distal flame holder, and outputting control signals to control one or more actuators to adjust a flow of the main fuel or to adjust the flow of the oxidant responsive to the sensor signals 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 low emissions modular burner system includes on or more burner modules.
  • Each burner module includes a main fuel source, separately valved from all other fuel sources, configured to selectively deliver a main fuel stream for dilution by a flow of combustion air, a main fuel igniter configured to cause ignition of the main fuel stream emitted from the main fuel source, a distal flame holder, separated from the main fuel source and the main fuel igniter by respective non-zero distances, the distal flame holder being configured to hold a combustion reaction supported by the main fuel stream when the distal flame holder is at or above a predetermined temperature, and a pre-heating apparatus configured to pre-heat the distal flame holder to the predetermined temperature.
  • the pilot burner 104 is configured to support a pilot flame 108.
  • the pilot flame 108 helps to ignite and/or sustain a main combustion reaction 110.
  • the pilot burner 104 supports the pilot flame 108 by outputting a pilot fuel 112.
  • the pilot flame 108 is supported by the pilot fuel 112 and combustion air introduced into the furnace volume 101. Accordingly, the pilot flame 108 is a combustion reaction of the pilot fuel 112 and combustion air.
  • the one or more main fuel nozzles 106 are configured to support the main flame 110 within the furnace volume 101.
  • the main flame 110 is supported downstream from the pilot flame 108.
  • the main fuel nozzles 106 support the main flame 110 by outputting main fuel 114 into the furnace volume 101.
  • the main flame 110 is supported by the main fuel 114 and combustion air introduced into the furnace volume 101. Accordingly, the main flame 110 is a combustion reaction of the main fuel 114 and the combustion air.
  • the pilot burner 104 and the one or more main fuel nozzles 106 are configured to simultaneously support the main flame 110 in contact with the pilot flame 108.
  • the pilot burner 104 is disposed to cause the main fuel and combustion air to be ignited by the pilot flame 108.
  • the main fuel 114 passes through gaps or open spaces between the laterally extending portions of the pilot burner 104.
  • the main fuel 114 may be initially ignited by the pilot flame 108 as the main fuel 114 passes adjacent to the pilot flame 108. After the main fuel 114 has been ignited, thereby generating the main flame 110, the main flame 110 can be supported in a steady state by the main fuel 114.
  • the laterally extending arms of the pilot burner 104 form a star shape. Additionally or alternatively, the pilot burner 104 can form a spiral shape, a circle shape, an H shape, a square shape, a hexagon shape, or other shapes that cover a desired lateral distance while including gaps through which the main fuel 114 can pass. (See, e.g., FIGS. 2A-6 .)
  • the perforated flame holder 102 can support combustion between the input face 712 and output face 714 when combustion is "time-averaged.” For example, during transients, such as before the perforated flame holder 102 is fully heated, or if too high a (cooling) load is placed on the system, the combustion may travel somewhat downstream from the output face 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 travel somewhat upstream of the input face 712 of the perforated flame holder 102.
  • Such transient huffing or flashback is generally short in duration such that, on a time-averaged basis, a majority of combustion occurs within the perforations 710 of the perforated flame holder 102, between the input face 712 and the output face 714.
  • the inventors have noted apparent combustion occurring downstream from the output face 714 of the perforated flame holder 102, but still a majority of combustion occurred within the perforated flame holder 102 as evidenced by continued visible glow from the perforated flame holder 102 that was observed.
  • the perforated flame holder 102 can be configured to receive heat from the combustion reaction 802 and output a portion of the received heat as thermal radiation 804 to heat-receiving structures (e.g., furnace walls and/or radiant section working fluid tubes) in or adjacent to the combustion volume 704.
  • heat-receiving structures e.g., furnace walls and/or radiant section working fluid tubes
  • terms such as radiation, thermal radiation, radiant heat, heat radiation, etc. are to be construed as being substantially synonymous, unless further definition is provided. Specifically, such terms refer to blackbody-type radiation of electromagnetic energy, primarily at infrared wavelengths, but also at visible wavelengths owing to elevated temperature of the perforated flame holder body 708.
  • the location of maximum receipt of heat was apparently between 1/3 and 1/2 of the distance from the input face 712 to the output face 714 (i.e., somewhat nearer to the input face 712 than to the output face 714).
  • the inventors contemplate that the heat receiving regions 806 may lie nearer to the output face 714 of the perforated flame holder 102 under other conditions. Most probably, there is no clearly defined edge of the heat receiving regions 806 (or for that matter, the heat output regions 810, described below). For ease of understanding, the heat receiving regions 806 and the heat output regions 810 will be described as particular regions 806, 810.
  • the perforated flame holder body 708 can be characterized by a heat capacity.
  • the perforated flame holder body 708 may hold thermal energy from the combustion reaction 802 in an amount corresponding to the heat capacity multiplied by temperature rise, and transfer the thermal energy from the heat receiving regions 806 to heat output regions 810 of the perforation walls 808.
  • the heat output regions 810 are nearer to the input face 712 than are the heat receiving regions 806.
  • the perforated flame holder body 708 can transfer heat from the heat receiving regions 806 to the heat output regions 810 via thermal radiation, depicted graphically as 804.
  • the perforated flame holder body 708 can transfer heat from the heat receiving regions 806 to the heat output regions 810 via heat conduction along heat conduction paths 812.
  • the perforated flame holder 102 may act as a heat source to maintain the combustion reaction 802, even under conditions where a combustion reaction 802 would not be stable when supported from a conventional flame holder.
  • the hot perforated flame holder body 708 transfers heat to the fluid, notably within thermal boundary layers 814 that progressively thicken as more and more heat is transferred to the incoming main fuel and oxidant mixture 706.
  • a combustion temperature e.g., the auto-ignition temperature of the fuel
  • the reactants continue to flow while a chemical ignition delay time elapses, over which time the combustion reaction 802 occurs. Accordingly, the combustion reaction 802 is shown as occurring within the thermal boundary layers 814.
  • the thermal boundary layers 814 merge at a merger point 816.
  • the merger point 816 lies between the input face 712 and output face 714 that define the ends of the perforations 710.
  • the plurality of perforations 710 can be each characterized by a transverse dimension D between opposing perforation walls 808.
  • the inventors have found that stable combustion can be maintained in the perforated flame holder 102 if the length L of each perforation 710 is at least four times the transverse dimension D of the perforation. In other embodiments, the length L can be greater than six times the transverse dimension D. For example, experiments have been run where L is at least eight, at least twelve, at least sixteen, and at least twenty-four times the transverse dimension D.
  • the perforated flame holder body 708 can be configured to convey heat between adjacent perforations 710.
  • the heat conveyed between adjacent perforations 710 can be selected to cause heat output from the combustion reaction portion 802 in a first perforation 710 to supply heat to stabilize a combustion reaction portion 802 in an adjacent perforation 710.
  • the fuel and oxidant source 702 can further include a main fuel nozzle 718 (e.g., corresponding to main fuel nozzle(s) 106 described herein), configured to output main fuel 114, and an oxidant source 720 configured to output a fluid including the oxidant.
  • the main fuel nozzle 718 can be configured to output substantially pure fuel (as opposed to, e.g., a fuel-air mixture).
  • the oxidant source 720 can be configured to output combustion air carrying oxygen, and optionally, flue gas.
  • the oxidant source 720 can include a blower configured to force the oxidant through the fuel and oxidant source 702.
  • the perforated flame holder 102 can include a single perforated flame holder body 708. In another embodiment, the perforated flame holder 102 can include a plurality of adjacent perforated flame holder sections that collectively provide a tiled perforated flame holder 102.
  • the perforated flame holder support structure 722 can be configured to support the plurality of perforated flame holder sections.
  • the perforated flame holder support structure 722 can include a metal superalloy, a cementatious, and/or ceramic refractory material.
  • the plurality of adjacent perforated flame holder sections can be joined with a fiber reinforced refractory cement.
  • the perforated flame holder 102 can have a width dimension W less than a width of the combustion volume 704. This can allow the flue gas recirculation path 724 from above to below the perforated flame holder 102 to lie between the peripheral surface 716 of the perforated flame holder 102 and the combustion volume wall (not shown).
  • the perforations 710 can be of various shapes.
  • the perforations 710 can include elongated squares, each having a transverse dimension D between opposing sides of the squares.
  • the perforations 710 can include elongated hexagons, each having a transverse dimension D between opposing sides of the hexagons.
  • the perforations 710 can include hollow cylinders, each having a transverse dimension D corresponding to a diameter of the cylinder.
  • each of the plurality of perforations 710 has a lateral dimension D between 0.05 inch and 1.0 inch.
  • each of the plurality of perforations 710 has a lateral dimension D between 0.1 inch and 0.5 inch.
  • the plurality of perforations 710 can each have a lateral dimension D of about 0.2 to 0.4 inch.
  • the void fraction of a perforated flame holder 102 is defined as the total volume of all perforations 710 in a section of the perforated flame holder 102 divided by a total volume of the perforated flame holder 102 including perforated flame holder body 708 and perforations 710.
  • the perforated flame holder 102 should have a void fraction between 0.10 and 0.90.
  • the perforated flame holder 102 can have a void fraction between 0.30 and 0.80.
  • the perforated flame holder 102 can have a void fraction of about 0.70. Using a void fraction of about 0.70 was found to be especially effective for producing very low NOx.
  • the perforated flame holder 102 can be formed from VERSAGRID ® ceramic honeycomb, available from Applied Ceramics, Inc. of Doraville, South Carolina.
  • the fuel may entrain the combustion air (or alternatively, the combustion air may dilute the fuel) to provide a fuel and oxidant mixture at the input face of the distal flame holder at a fuel dilution selected for a stable combustion reaction that can be held within the perforations of the distal flame holder.
  • step 916 the presence of combustion may be sensed.
  • Various sensing approaches have been used and are contemplated by the inventors.
  • combustion held by the distal flame holder is very stable and no unusual sensing requirement is placed on the system.
  • Combustion sensing may be performed using an infrared sensor, a video sensor, an ultraviolet sensor, a charged species sensor, thermocouple, thermopile, flame rod, and/or other combustion sensing apparatuses.
  • a pilot flame or other ignition source may be provided to cause ignition of the fuel and oxidant mixture in the event combustion is lost at the distal flame holder.
  • the burner system 700 can further include a controller 730 operatively coupled to the heater 728 and to a data interface 732.
  • the controller 730 can be configured to control a start-up flame holder actuator configured to cause the start-up flame holder to hold the start-up flame when the distal flame holder 102 needs to be pre-heated and to not hold the start-up flame when the distal flame holder 102 is at an operating temperature (e.g., when T ⁇ T S ).
  • the heater 728 can include an electrical discharge igniter or hot surface igniter configured to output a pulsed ignition to the oxidant and fuel.
  • a start-up apparatus can, as discussed in greater detail herein, include a pilot flame apparatus disposed to ignite the main fuel and oxidant mixture 706 that would otherwise enter the distal flame holder 102.
  • the electrical discharge igniter, hot surface igniter, and/or pilot flame apparatus can be operatively coupled to the controller 730, which can cause the electrical discharge igniter or pilot flame apparatus to maintain combustion of the main fuel and oxidant mixture 706 in or upstream from the distal flame holder 102 before the distal flame holder 102 is heated sufficiently to maintain combustion.
  • the distal flame holder 102 can be configured to support a combustion reaction of the main fuel and oxidant mixture 706 upstream, downstream, within, and adjacent to the reticulated ceramic perforated flame holder 102.
  • the perforated flame holder body 708 can include reticulated fibers 1039.
  • the reticulated fibers 1039 can define branching perforations 710 that weave around and through the reticulated fibers 1039.
  • the perforations 710 are formed as passages between the reticulated fibers 1039.
  • the reticulated fibers 1039 are formed as a reticulated ceramic foam. According to an embodiment, the reticulated fibers 1039 are formed using a reticulated polymer foam as a template. According to an embodiment, the reticulated fibers 1039 can include alumina silicate. According to an embodiment, the reticulated fibers 1039 can be formed from extruded mullite or cordierite. According to an embodiment, the reticulated fibers 1039 can include Zirconia. According to an embodiment, the reticulated fibers 1039 can include silicon carbide.
  • the term "reticulated fibers” refers to a netlike structure.
  • the reticulated fibers 1039 are formed from an extruded ceramic material.
  • the interaction between the main fuel and oxidant mixture 706, the combustion reaction 802, and heat transfer to and from the perforated flame holder body 708 can function similarly to the embodiment shown and described above with respect to FIGS. 7-9 .
  • One difference in activity is a mixing between perforations 710, because the reticulated fibers 1039 form a discontinuous perforated flame holder body 708 that allows flow back and forth between neighboring perforations 710.
  • the network of reticulated fibers 1039 is sufficiently open for downstream reticulated fibers 1039 to emit radiation for receipt by upstream reticulated fibers 1039 for the purpose of heating the upstream reticulated fibers 1039 sufficiently to maintain combustion of a main fuel and oxidant mixture 706.
  • heat conduction paths such as heat conduction paths 812 in FIG. 8
  • This may cause relatively more heat to be transferred from a heat-receiving region or area (such as heat receiving region 806 in FIG. 8 ) to a heat-output region or area (such as heat-output region 810 of FIG. 8 ) of the reticulated fibers 1039 via thermal radiation (shown as element 804 in FIG. 8 ).
  • individual perforations 710 may extend between an input face 712 to an output face 714 of the perforated flame holder 102.
  • Perforations 710 may have varying lengths L. According to an embodiment, because the perforations 710 branch into and out of each other, individual perforations 710 are not clearly defined by a length L.
  • the perforated flame holder 102 is configured to support or hold a combustion reaction (see element 802 of FIG. 8 ) or a flame at least partially between the input face 712 and the output face 714.
  • 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.
  • the input face 712 corresponds to an extent of the reticulated fibers 1039 proximal to the main fuel nozzle 718.
  • the output face 714 corresponds to a surface distal to the main fuel nozzle 718 or opposite the input face 712.
  • the input face 712 corresponds to an extent of the reticulated fibers 1039 distal to the main fuel nozzle 718 or opposite to the input face 712.
  • the formation of thermal boundary layers 814, transfer of heat between the perforated flame holder body 708 and the gases flowing through the perforations 710, a characteristic perforation width dimension D, and the length L can each be regarded as related to an average or overall path through the perforated reaction holder 102.
  • the dimension D can be determined as a root-mean-square of individual Dn values determined at each point along a flow path.
  • the length L can be a length that includes length contributed by tortuosity of the flow path, which may be somewhat longer than a straight line distance T RH from the input face 712 to the output face 714 through the perforated reaction holder 102.
  • the void fraction (expressed as (total perforated reaction holder 102 volume - reticulated fiber 1039 volume)/total volume)) is about 70%.
  • the method 1100 may further include measuring a temperature of the distal flame holder, and, when the temperature of the distal flame holder is at or above a predetermined threshold, reducing a pilot fuel rate of flow to reduce a 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 cause a reduction of emissions of oxides of nitrogen.
  • the method 1200 may further include detecting the combusting of the main fuel at the distal flame holder using a an electrocapacitive sensor, the electrocapacitive sensor configured to output sensor signals to a controller.
  • the controller may be configured to receive the sensor signals from the combustion sensor and to control the actuators to adjust the flow of the pilot fuel, the main fuel, and the oxidant responsive to the sensor signals and in accordance with software instructions stored in a non-transitory computer readable medium coupled to the controller.
  • the combustion system further includes a pilot flame sensor configured to sense a condition of a pilot flame and to output a sensor signal indicative of the condition of the pilot flame.
  • the combustion sensor may include the pilot flame sensor.
  • the pilot flame sensor may include an electrocapacitive sensor, an electro-resistive sensor, and/or a tomographic sensor (e.g., employing electrocapacitive tomography (ECT).)
  • the combustion system further includes an ignitor configured to generate an arc.
  • the controller may be configured to control one or more of the actuators to cause the ignitor to generate the arc to ignite the pilot flame if the electrocapacitive sensor indicates that the pilot flame is not present and all safety interlocks are met.
  • the controller is configured to adjust a size of the pilot flame response to the sensor signals from at least the combustion sensor by controlling one or more of the actuators to adjust the flow of the pilot fuel or the oxidant.
  • the combustion sensor may be configured to detect the combustion reaction at the distal flame holder and to output sensor signals to the controller responsive to a detected state of the combustion reaction.
  • the combustion sensor is configured for operation as a flashback sensor configured to detect a flashback of the combustion reaction toward the main fuel nozzle from the distal flame holder.
  • the combustion sensor may include an electrocapacitive sensor.
  • ECT electrocapacitive tomography
  • ECT sensing may be fundamentally capacitive, or may additionally or alternatively be made to measure a conductance, a resistance, an impedance, or other electrical parameter.
  • ECT may include a plurality of sensor channels, such as may be produced by moving a sensor through different positions or by using a sensor array, such as may be seen in more common (e.g., medical) tomography systems.
  • the combustion system 1300 may include a combustion sensor that includes an EC sensor or ECT device, such as the electrocapacitive sensor 1305 of FIG. 13A and FIG. 13B .
  • the electrocapacitive sensor 1305 can include a first set of electrodes 1320, including multiple pairs of electrodes 1320, positioned laterally around the distal flame holder 102 in order to sense a parameter of the distal flame holder 102.
  • the electrocapacitive sensor 1305 can also include a second set of electrodes positioned upstream from the distal flame holder 102.
  • the first set of electrodes 1320 can sense a capacitance or other parameter in a vicinity of the distal flame holder 102.
  • the second set of electrodes can sense a capacitance or other parameter upstream from the distal flame holder 102, for example at a pilot burner (e.g., 104 in FIG. 3 ) or upstream from the pilot burner.
  • the controller 730 can compare the capacitance or other parameter sensed by the first set of electrodes 1320 to the capacitance or other parameter sensed by the second set of electrodes in order to detect a combustion reaction parameter, presence of flashback, etc.
  • the combustion system 1300 may include a distal flame holder sensor that includes the electrocapacitive sensor 1305.
  • the distal flame holder sensor can share use of the first set of electrodes 1320 described in relation to the combustion sensor.
  • the first set of electrodes 1320 including pairs of electrodes positioned laterally around the distal flame holder 102 can act as both the electrocapacitive sensor 1305, and at least a portion of the combustion sensor.
  • the combustion system 1300 may include a pilot flame sensor (not shown) that includes the electrocapacitive sensor 1305.
  • the pilot flame sensor and the combustion sensor can share use of electrodes positioned upstream from the distal flame holder 102 or laterally around the distal flame holder 102.
  • Two or more of the pilot flame sensors, the combustion sensor, and the distal flame holder sensor can share electrodes 1320 of an electrocapacitive sensor 1305.
  • the fuel and oxidant source 702 includes, for example, a fuel nozzle configured to output the main fuel and oxidant onto the distal flame holder 102.
  • the distal flame holder 102 holds a combustion reaction of the fuel and oxidant primarily adjacent to and/or within the distal flame holder 102.
  • the electrocapacitive 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 electrocapacitive sensor 1305 is configured to make images of the distal flame holder 102 based on the capacitance between the electrodes 1320.
  • the images represent slices of the distal flame holder 102 based on the capacitances between the electrodes 1320.
  • the capacitance between pairs of electrodes 1320 depends, in part, on the dielectric constant of the material(s) between the pairs of electrodes 1320.
  • the dielectric constant within the perforations of the distal flame holder 102 can change based on the characteristics of the combustion reaction within the perforations. Therefore, the images produced by the electrocapacitive sensor 1305 can give an indication of a temperature within the perforations or a concentration or flow of fuel, oxidant, and flue gasses at various locations corresponding to the distal flame holder 102 based on the dielectric constant at the various locations of the distal flame holder 102.
  • the controller 730 can analyze the images and adjust the combustion reaction based on the images.
  • the controller 730 is configured to cause the electrocapacitive 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 to adjust the characteristics of the combustion reaction based on the analysis of the one or more images.
  • FIG. 13B is a top view of the distal flame holder 102 and the electrocapacitive sensor 1305, according to an embodiment.
  • the electrocapacitive sensor 1305 includes multiple pairs of electrodes 1320 positioned laterally around the distal flame holder 102.
  • Each pair of electrodes 1320 includes two electrodes 1320 opposite one another, with the distal flame holder 102 positioned between the pair of electrodes 1320 or in a fringing field therebetween.
  • the controller 730 controls each pair of electrodes 1320 to make a plurality of images (or an aggregate image) of the distal flame holder 102, according to an embodiment.
  • the electrodes 1320a and 1320a are a pair, the electrodes 1320b and 1320b are a pair, the electrodes 1320c and 1320c are a pair, the electrodes 1320d and 1320d are a pair, the electrodes 1320e and 1320e are a pair, and the electrodes 1320f and 1320f are a pair.
  • the electrocapacitive sensor 1305 can generate electrocapacitive tomography images based on a capacitance between the pairs of electrodes 1320.
  • 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 opposite each other in a first orientation substantially perpendicular to a primary direction of a flow of the main fuel toward the distal flame holder 102.
  • the first pairs of electrodes 1320 can include the pair of electrodes 1320a and the pair of electrodes 1320b.
  • the first pairs of electrodes 1320a and 1320b sense the capacitance of the distal flame holder 102 along an X direction substantially perpendicular to a primary direction of flow of the main fuel and the oxidant toward the distal flame holder 102.
  • the primary direction of flow of the main fuel and the oxidant toward the distal flame holder 102 can correspond to a Z direction.
  • 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 opposite each other in a second orientation substantially perpendicular to both the first orientation and the primary direction of the flow of the main fuel.
  • the second pairs of electrodes 1320 can include the pair of electrodes 1320c and the pair of electrodes 1320d.
  • the second pairs of electrodes 1320c and 1320d sense the capacitance of the distal flame holder 102 along a Y direction substantially perpendicular to the primary direction of flow of the main fuel and the oxidant and substantially perpendicular to orientation of the first pairs of electrodes 1320a and 1320b.
  • the plurality of electrodes 1320 can include pairs of electrodes 1320 oriented transverse to both the first pairs of electrodes 1320a and 1320b and the second pairs of electrodes 1320c and 1320d.
  • the transverse pairs of electrodes 1320 can include the pair of electrodes 1320e and the pair of electrodes 1320f.
  • an electrocapacitive sensor in accordance with principles of the present disclosure can include pairs of electrodes positioned in configurations other than laterally around a distal flame holder 102.
  • An electrocapacitive sensor can include pairs of electrodes positioned upstream from the distal flame holder 102, downstream from the distal flame holder 102, or in other locations depending on the particular aspect of a combustion system that the electrocapacitive sensor is intended to sense or monitor. Accordingly, other sensors described or contemplated in relation to embodiments disclosed herein (e.g., sensors 734, 1414) can include electrocapacitive sensors where suitable.
  • Each burner module 1401 may respectively include a distal flame holder 102 configured to hold a combustion reaction supported by the main fuel stream 1404 when the distal flame holder 102 is at or above a predetermined temperature.
  • the predetermined temperature may be equal to or greater than a main fuel auto-ignition temperature.
  • Each burner module 1401 may include a pilot burner 1408 configured to pre-heat the distal flame holder 102 to the predetermined temperature, according to an embodiment.
  • the pilot burner 1408 of each burner module 1401 may include a continuous pilot burner that also may operate to ignite the main fuel.
  • the distal flame holder 102 may be separated from the main fuel nozzle(s) 1402 and from the pilot burner 1408 by respective non-zero distances (D1, D2).
  • At least one heating rate may be selected to cause a rise in sensible temperature of the distal flame holder 102 to the 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 total fuel consumed per unit of time is provided by the main fuel source 1402.
  • the common combustion air source 1405 is configured to provide natural draft combustion air to each burner module (1401) of the one or more burner modules 1401.
  • the low emissions modular burner system 1400 further includes one or more separate main fuel valves 1410 for each burner module 1401, each main fuel valve 1410 including separate main fuel valve actuators configured to operate responsive to receiving control signals, and further includes a control system 1412 configured to output respective control signals to each of the separate main fuel valve actuators.
  • the control system 1412 further includes an interface 1514 (see FIG. 15 ) between the control system 1412 and an input channel.
  • the input channel may include a physical (e.g., electrically conductive) connection or a wireless connection.
  • 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.
  • the interface 1514 includes an interface to one or more sensors disposed to sense physical parameters related to each burner module 1401 and environs. Sensors (e.g., 1414 in FIG. 14 ) and operation thereof, may include capacitance coupled (e.g., patch) electrodes (which may alternatively be referred to as antennas) cooperating to emit and receive a radio frequency signal across a region intended to hold a combustion reaction.
  • capacitance coupled e.g., patch
  • a change in capacitance corresponds to a change in charged species concentration, which has been found to be covariant with the presence or absence of combustion.
  • the electrodes may be disposed in sufficient number, and be positioned, to provide a tomographic scan of the combustion region.
  • the sensors 1414 may be connected to the control system 1412 by a communication channel 1415.
  • the communication channel may wired (e.g., electrically conductive).
  • the communication channel 1415 may provide a voltage and/or current to electrodes of the sensors 1414.
  • the interface 1514 may be configured to receive a signal corresponding to a burner capacity requirement.
  • the control system 1412 may further include one or more burner module sensor inputs 1515a, 1515b, each of the one or more burner module sensor inputs 1515a, 1515b being configured to receive a signal corresponding to a burner module status, wherein the burner module status is provided by sensor hardware 1414.
  • the control system 1412 may further include a microcontroller or other logic processor 1516, a computer readable memory 1518, and a module sequencer 1520 (which may optionally be embodied as or by the logic processor 1516 and the computer readable memory 1518 when executing module sequencing functions) configured to select a subset of the one or more burner modules 1401for ignition.
  • the control system 1412 may further include a respective one or more main fuel valve driver outputs, each operatively coupled to one of the separate main fuel valve actuators 1410.
  • the one or more burner module sensor inputs 1515a, 1515b are configured to receive input from one or more sensors, such as the sensor hardware 1414, or from one or more sensors external to the burner module(s) (1401).
  • the one or more sensors may include a demand sensor including one or more of a condensate pressure sensor, a heating energy demand sensor, and a condensate presence sensor.
  • a control circuit 1512 may include a module sequencer 1520.
  • the module sequencer 1520 may include a state machine configured to changeably sequence an actuation of the one or more burner modules 1401. For example, it may be desirable to periodically change an assignment of the burner modules to different positions in an actuation sequence in accord with demand.
  • a last module turned on in the previous module sequence may also operate as the first/only module turned on during a turn-down state.
  • the assignment of burner modules 1401 need not be identical with respect to capacity, age (e.g., cycle count), and design.
  • a start-up sequence may be at least partially identical with each base demand/surge capacity cycle.
  • the inventors contemplate various arrangements, actuation sequences, and selections of the assignment of burner modules 1401may offer specific advantages to particular application characteristics.
  • the low emissions modular burner system 1400 further includes a run sequencer 1522.
  • the control circuit 1512 may include the run sequencer 1522.
  • the run sequencer 1522 may include a state machine configured to sequence steps in a burner module start-up schedule for one or more of the burner modules 1401. Start-up schedules may be stored in the memory 1518 and periodically updated via the interface 1514 that includes a network interface. Illustrative methods and aspects for start-up sequencing are described with respect to several of the other figures included herein.
  • Sensors 1414 are described herein as performing sensory functions or functioning as signal outputs.
  • the power module 1526 may be employed to amplify such signal, e.g., for the aforementioned emission and receipt of radio frequency signals across a combustion region.
  • sensors 1414 may provide a signal for generating data, e.g., a flame tomogram.
  • dedicated sensor inputs 1515a, 1515b may be utilized.
  • the sensors 1414 may provide a subset of many data signals that communicate via interface 1514 of the control circuitry 1512.
  • the interface 1514 may provide wireless or wired connections using various communication protocols, which may permit the sensors 1414 to communicate via a standard method such as USB, WiFi, ethernet, or the like.
  • the low emissions modular burner system 1400 may further include a demand module 1528.
  • demand for system capacity is received in substantially real time via a network interface included in the interface 1514.
  • the demand module 1528 may be configured to supervise automatic operation of the one or more burner module(s) 1401selectively based on at least one of a stored schedule and a received demand signal.
  • the demand module 1528 may consist essentially of a data value in a register of the memory 1518.
  • the demand module 1528 may include a real time clock and, as data, a scheduled system capacity.
  • the demand module 1528 may operate as a supervisory state configured to automatically operate the modular burner system 1400 according to seasonal and/or periodic demand dynamics.
  • operation of the interface 1514 may be more crucial.
  • portions of the module sequencer 1520 may be virtualized and cloud-accessed.
  • the logic processor 1516 is configured to read and execute computer executable instructions supported by a non-transitory computer readable memory 1518 to receive capacity input data corresponding to the burner capacity requirement signal, read module status sensor data from sensor(s) corresponding to at least one burner module to verify that a selected one or more of the burner module(s) 1401 is ready for firing, select the subset of the one or more burner modules 1401 for firing, and drive at least one of the separate main fuel valve (1410) actuators corresponding to the selected one or more burner module(s) to open so as to provide fuel to a combustion reaction supported by the one or more burner module(s)1401.
  • control system 1412 further includes a demand sensor.
  • the demand sensor may include a heating energy demand sensor.
  • each burner module 1401 further includes a pilot fuel source configured to provide a pilot fuel, a pilot fuel igniter (e.g., 1406) configured to ignite a flow of the pilot fuel, and a distal pilot or start-up burner (e.g., constituting pilot burner 1408) configured to hold a pilot flame supported by the pilot fuel, a pilot fuel source flow rate being selected to provide a pilot flame sized to raise the temperature of the distal flame holder 102 to the predetermined temperature.
  • the predetermined temperature is equal to or greater than a main fuel auto-ignition temperature.
  • the terms pilot, pilot burner, distal pilot and start-up burner and pre-heating apparatus shall be considered synonymous unless context dictates otherwise.
  • the main igniter 1406 comprises the distal pilot.
  • the main igniter 1406 includes the distal flame holder 102 when the distal flame holder 102 is heated to the predetermined temperature by the distal pilot 1408. That is, the fuel and combustion air may ignite on contact with the pre-heated distal flame holder 102 rather than by a separate igniter.
  • the predetermined temperature is the main fuel auto-ignition temperature.
  • the distal pilot burner 1408 is configured to be controlled to provide the pilot flame sized to raise the distal flame holder 102 to the pre-determined temperature during a burner module start-up cycle, and to not provide the pilot flame sized to raise the distal flame holder 102 to the pre-determined temperature at times other than during the burner module start-up cycle.
  • the distal pilot burner 1408 is configured to decrease to a pilot flame capacity at times other than during the burner module start-up cycle.
  • the distal pilot burner 1408 is configured to stop supporting a combustion reaction at times other than during the burner module start-up cycle.
  • 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 decreased to a pilot flame capacity at times other than during the burner module start-up cycle.
  • 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.
  • the pilot burner 1408 is configured to guarantee combustion of the main fuel, e.g., 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 embodiments, the pilot fuel and the main fuel may consist essentially of the same fuel.
  • a 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 main fuel supply and to receive combustion air via the housing 1403, a distal flame holder 102 positioned inside the housing 1403, and a main fuel nozzle 1402 configured to receive a flow of main fuel from the inlet, and to emit a main fuel stream toward the distal flame holder 102.
  • each of the one or more burner modules 1401 is configured to be freestanding, supported only by a coupling at the inlet.
  • the burner module 1401 is configured to be coupled to the burner and to be supported thereby.
  • the main fuel nozzle is one of a plurality of main fuel nozzles 1402, each of the main fuel nozzles 1402 configured to receive a flow of the main fuel from the inlet, and to emit a main fuel stream 1404 toward a respective portion of the distal flame holder 102.
  • the modular burner 1401 further includes a plurality of the main fuel valves 1410 operatively coupled between a common fuel line and a respective one of the plurality of main fuel nozzles 1402 and configured to independently control operation of the respective main nozzle 1402. That is, whereas FIG. 14 illustrates a main fuel valve 1410 shared by each of the main fuel nozzles 1402, an embodiment may include a separate-and separately controllable-main fuel valve 1410 for each main fuel nozzle 1402.
  • the modular burner 1401 further includes a distal pilot burner 1408 positioned between the distal flame holder 102 and the main fuel nozzle(s) 1402 for each burner module.
  • the modular burner 1401 may be a retrofit burner positioned within the housing 1407, the retrofit burner including the distal flame holder 102 and the main fuel nozzle(s) 1402.
  • Each distal pilot burner 1408 may include a plurality of pilot nozzles arranged in an array.
  • the distal pilot burner 1408 is configured to support a pilot flame between the distal pilot burner 1408 and the distal flame holder 102.
  • the main fuel nozzle(s) 1402 may include an aperture having a size that is variable.
  • the main fuel nozzle(s) 1402 may be configured to regulate a velocity of the main fuel stream.
  • the modular burner 1401 further includes an actuator operatively coupled to the main fuel nozzle(s) 1402 and configured to control the size of the aperture.
  • the main fuel nozzle(s) 1402 may each include a main nozzle outlet and a control element, the control element being positioned to occlude some portion of the main nozzle outlet, and wherein movement of the control element varies a degree to which the main nozzle outlet is occluded by the control element.
  • each burner module has a heating capacity of about 8 MBtu/Hr.
  • FIG. 16 is a block diagram of a burner system 1600, according to an embodiment.
  • the burner system 1600 includes a distal flame holder 1602 (corresponding to 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 delivery of an oxidant 1606a, and one or more main fuel nozzle(s) 1618 for main delivery of a fuel 1606b.
  • the fuel 1606b and the oxidant 1606a mix in the mixing tube 1610 en route to the distal flame holder 1602, creating a fuel and oxidant mixture 1607.
  • the distal flame holder 1602 is disposed and oriented to receive and (when at an operating temperature) to ignite the fuel and oxidant mixture 1607.
  • the oxidant conduit 1604 provides a pathway for the oxidant 1606a (e.g., air), and directs the oxidant 1606a toward the distal flame holder 1602.
  • the main fuel nozzle(s) 1618 direct the fuel 1606b toward the distal flame holder 1602.
  • the main fuel nozzle(s) 1618 may receive the fuel 1606b from a fuel reservoir or pipeline (not shown, each or both referred to herein as a fuel supply) via a main fuel supply line 1608.
  • the burner system 1600 may include a single main fuel nozzle 1618 or a plurality of the main fuel nozzle(s) 1618, each disposed and configured as described herein.
  • the fuel 1606b emitted by the main fuel nozzle(s) 1618, and the oxidant 1606a emitted by the oxidant conduit 1604 become mixed 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 element 706 in FIG. 7 ) to permit efficient and uniform combustion within the distal flame holder 1602 at the operating temperature.
  • the burner system 1600 may include a pilot burner 1612.
  • the pilot burner 1612 disposed proximate the distal flame holder and provides a pilot flame which may maintain ignition of the fuel and oxidant mixture 1607.
  • the pilot burner 1612 may receive fuel from a pilot fuel supply line 1614.
  • the pilot burner 1612 may be in fluid connection with the main fuel supply line 1608.
  • the mixing tube may be disposed a predetermined distance from a floor of the burner system, and may be configured to receive at least the combustion air via the oxidant conduit 1604.
  • a source of flue gas diluent 1616 is contemplated.
  • the inventors have observed that the introduction of a mixing tube facilitates a recirculation of flue gas-as a substantial flue gas diluent-from downstream of the distal flame holder 1602.
  • the flue gas 1616 is educed to a proximal end (i.e., the main nozzle end) of the mixing tube 1610 by a flow of main fuel and combustion oxidant between the main fuel nozzle(s) 1618 and the distal flame holder 1602 through the mixing tube 1610.
  • the recirculated flue gas 1616 mixes with the fuel and the combustion air before reaching the distal flame holder 1602.
  • the non-reactive elements of the resulting mixture minimize a potential for flashback upstream from the distal flame holder 1602 while permitting additional combustion of the reactive elements of the flue gas, thus reducing, e.g., NOx and other potential pollutants.
  • a 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 nozzle(s) 1612), and a mixing tube 1710.
  • the main fuel nozzles 1618 may be arranged in fluid connection with a main fuel source 1732.
  • flow of 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 in fluid connection with a pilot fuel source 1730.
  • flow of pilot fuel from the pilot fuel source 1730 may be controlled via a pilot fuel control valve 1734.
  • the distal pilot burner(s) 1704 may be configured to support a pilot flame by outputting a pilot fuel received via a pilot fuel pipe 1712 from the pilot fuel source 1730.
  • the pilot fuel pipe 1712 may be disposed inside the mixing tube 1710 or-advantageously for maintenance, temperature regulation, etc.-outside the mixing tube 1710.
  • the pilot fuel pipe 1712 may form a portion of a support for the mixing tube 1710.
  • the distal pilot burner(s) 1704 may be supported by and receive fuel via the pilot fuel pipe 1712.
  • the pilot fuel pipe 1712 extends into the furnace volume 1701 via the opening 1740 in the floor 1738 of the furnace.
  • Each distal pilot burner 1704 may include a pilot manifold formed in any of several shapes.
  • the pilot manifold is formed in a Y shape. See also the discussion above corresponding to, e.g., FIGS. 3-6 with respect to pilot burner configurations.
  • each distal pilot burner 1704 includes one or more manifolds that define a plurality of fuel orifices 1718 having a large collective area to collectively support a low momentum pilot flame (not shown).
  • the main fuel output by the main fuel nozzles 1618 and combustion air form a combustible mixture that expands in breadth as it flows from a proximal position of the main fuel nozzles 1618 to the distal position of the distal pilot burner(s) 1704.
  • the plurality of fuel orifices 1718 may be disposed across the furnace volume 1701 sufficiently broadly to cause contact of the pilot flame with the main fuel and combustion air mixture across the breadth of the combustible mixture.
  • the main fuel nozzles 1618 may be configured to output fuel in co-flow with the air.
  • a distal 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 pass fuel from inside the fuel manifold to the furnace volume 1701.
  • the plurality of segments 1719 may be formed as respective tubes configured to freely pass the fuel delivered from the pilot fuel pipe 1712 into the fuel manifold.
  • at least a portion of the tubes is arranged as spokes radiating from a center disposed substantially at a centerline along the axis.
  • at least a portion of the tubes is arranged as an "X", a rectangle, an "H", a wagon wheel, or a star.
  • a distal pilot burner 1704 includes a manifold including a curvilinear tube.
  • the curvilinear tube is arranged as a spiral, " ", " , or " ⁇ ".
  • the mixing tube 1712 may be arranged about a longitudinal axis of flow between the main fuel nozzles 1618 and the distal flame holder 1602.
  • the mixing tube 1710 may include a bell-shaped or flared portion 1714 at an end proximate the main fuel nozzles 1618.
  • the bell-shaped or flared portion 1714 may be disposed a predetermined distance from a floor 1738 of the burner system, and may be configured to receive at least the combustion air via an opening 1740 in the floor 1738.
  • a source of flue gas diluent is contemplated.
  • the inventors have observed that the introduction of a mixing tube facilitates a recirculation of flue gas-as a substantial flue gas diluent-from downstream of the distal flame holder 1602, and/or including combustion products of a pilot flame held at the pilot burner 1704.
  • the flue gas is educed to a proximal end (i.e., the floor end) of the mixing tube 1710 by a flow of main fuel and combustion oxidant between the floor 1738 and the distal flame holder 1602 through the mixing tube 1710.
  • the recirculated flue gas mixes with the fuel and the combustion air before reaching the distal flame holder 1602.
  • the non-reactive elements of the resulting mixture minimize a potential for flashback upstream from the distal flame holder 1602 while permitting additional combustion of the reactive elements of the flue gas, thus reducing, e.g., NOx and other potential pollutants.
  • the mixing tube 1710 may have a diameter appropriate for providing a mixture of fuel and oxidant (e.g., fuel and oxidant mixture 1607) to at least most of the input face (e.g., input face 712 of FIG. 7 ) of the distal flame holder 1602.
  • the opening at the proximal end of the mixing tube 1710, closest to the main fuel nozzles 1618, may have a largest diameter sized in correspondence to either the opening 1740 in the floor 1738 or sufficient to receive fuel input from each of the main fuel nozzles 1618.
  • the largest diameter of the bell-shaped or flared portion 1714 may correspond to either the opening 1740 in the floor 1738 or may correspond to at least the farthest distance between main fuel nozzles 1618.
  • a length of the mixing tube may be selected to permit sufficient time and/or distance for appropriate mixing of the fuel and the oxidant before reaching the distal flame holder 1602.
  • a burner system includes a distal flame holder configured to hold 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 mixture with the oxidant in a dilution region between the main fuel nozzle and the distal flame holder when a temperature of the distal flame holder is above a predetermined temperature, and a mixing tube disposed in the dilution region, and being open 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 flow of the oxidant and fuel to educe flue gas into the mixing tube for mixing with fuel and oxidant.
  • 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.
  • the burner system further includes a pilot burner configured to support a pilot flame between the outlet of the mixing tube and the distal flame holder.
  • the mixing tube includes a flared portion at the mixing tube inlet.
  • the flue gas recirculation path may include at least a toroidal volume between the mixing tube and a wall of the combustion volume.
  • the flue gas may be educed into the fuel and oxidant stream at the mixing tube inlet for dilution of the fuel and oxidant stream.
  • the burner system further a continuous pilot disposed adjacent to the distal flame holder, the continuous pilot being configured to heat the distal flame holder to the predetermined temperature, and a controller operatively coupled to the main fuel source, the controller configured to receive an indication of a temperature of the distal flame holder and to control the flow of the main fuel responsive to the indication of the temperature.
  • the burner system further includes 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.
  • FIG. 18 is an illustration showing a horizontally-fired burner system 1800 including a distal pilot burner 1804 and a mixing tube 1810, according to an embodiment.
  • the inventors have observed, in a variety of furnace applications, undesirable combustion oscillations occurring between a distal flame holder 1802 and a fuel and oxidant (combustion air) source 1820.
  • a fuel and oxidant (combustion air) source 1820 Although not necessarily restricted to a confined furnace configuration-e.g., a water heater, boiler, or once-through steam generator (OTSG)-such applications are representative environments that can permit such combustion oscillations.
  • OTSG once-through steam generator
  • insufficiently and/or non-uniformly cooled oxidant e.g., flue gas
  • the flashback reduces the efficiency of the burner 1800 at least in part because heat from this premature combustion is not (in a gas-fired burner) radiant heat, is not sufficiently absorbed by the distal flame holder 1802 and/or boiler tubes, and is thus wasted. Combustion products from the flashback can dilute the mixture and thus temporarily snuff the flashback combustion. Hence the oscillating nature of flashback.
  • the distal pilot burner 1804 may 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 position sufficiently near to the distal flame holder 1802 to provide heat benefits from a diffusion pilot flame 1808 to the distal flame holder 1802.
  • the distal pilot burner 1804 may be disposed adjacent to the distal flame holder 1802 in a combustion volume 1801.
  • the distal flame holder 1802 may be formed of a plurality of columns including refractory materials.
  • the distal pilot burner 1804 is configured to maintain a diffusion pilot flame 1808 during combustion of main fuel in a combustion reaction held by the distal flame holder 1802.
  • the main fuel and the combustion air may be supplied by the fuel and combustion air source 1820 disposed a distance upstream from the distal pilot burner 1804.
  • the distance between main fuel nozzles 1806 of the fuel and combustion air source 1820 and the distal pilot burner 1804 may be at least 50 times a diameter of the main fuel nozzles 1806, at least 100 times a diameter of the main fuel nozzles 1806, or at least 200 times the diameter of the main fuel nozzles 1806.
  • the horizontally-fired burner system 1800 may include a mixing tube 1810 disposed between the fuel and combustion air source 1820 and the 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 a 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 the proximal end thereof for mixture with the fuel and the combustion air.
  • the horizontally-fired burner system 1800 includes the distal pilot burner 1804 disposed adjacent to the plurality of columns.
  • the distal pilot burner 1804 may be configured to successively provide a pre-heating flame to raise a temperature of the distal flame holder 1802 to at least an auto-ignition temperature of main fuel prior to introduction of the main fuel, and to maintain the diffusion pilot flame 1808 during combustion of the main fuel in the combustion reaction held by the distal flame holder 1802.
  • the distal pilot burner 1804 may be configured to support a large combustion reaction during pre-heating of the distal flame holder 1802 and to support a smaller combustion reaction during subsequent combustion of the main fuel.
  • a horizontally-fired burner system disclosed may include a controller 1812 (corresponding to, e.g., control system 1412 described herein) configured to receive sensor inputs, e.g., from sensor 1815, and to control output of fuel and combustion air.
  • the controller 1812 may control use of the distal pilot burner 1804.
  • the controller 1812 may control an actuator (not shown) that controls rate and/or amount of fuel provided to the distal pilot burner 1804 based on, e.g., sensor inputs showing temperature of the distal flame holder 1802, presence or absence or quality of a flame at the distal flame holder 1802 and/or at the distal pilot burner 1804.
  • combustion system in accordance with principles of the present disclosure can include sensors and actuators other than those disclosed herein, other combinations of sensors and actuators, as well as other kinds of actions to be taken by the controller (e.g., 730 of FIG. 7 ) responsive to sensor signals.

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Claims (16)

  1. Brennersystem, umfassend:
    - einen Pilotbrenner (104, 1704), der in einem Ofen an einer abgelegenen Position entlang einer Strömungsachse (A) eines Hauptbrennstoffs und einer Verbrennungsluft angeordnet ist, wobei der Pilotbrenner (104, 1704) einen Brennstoffverteiler mit mehreren miteinander verbundenen Segmenten (219, 1719) umfasst, wobei jedes Segment (219, 1719) mehrere Brennstofföffnungen (218, 1718) aufweist, die dazu ausgelegt sind, Brennstoff von innerhalb des Brennstoffverteilers zu einem Ofenverbrennungsraum zu leiten;
    - eine oder mehrere Hauptbrennstoffdüsen (106, 1618), die an einer nahe gelegenen Position entlang der Strömungsachse (A) angeordnet und dazu ausgelegt sind, einen Hauptbrennstoff auszugeben;
    - einen abgelegenen Flammenhalter (102, 1602), der an einer dritten Position entlang der Brennstoff- und Verbrennungsluftströmungsachse (A) angeordnet ist, abgelegener von den Hauptbrennstoffdüsen (106, 1618) als der Pilotbrenner (104, 1704); und
    wobei der Pilotbrenner (104, 1704) dazu ausgelegt ist, eine Pilotflamme (108) zu stützen; und wobei die eine oder die mehreren Hauptbrennstoffdüsen (106, 1618) dazu ausgelegt sind, eine Hauptflamme (110) stromabwärts von der Pilotflamme (108) und in Kontakt mit der Pilotflamme (108) zu stützen; wobei der Pilotbrenner (104, 1704) dazu ausgelegt ist, zu bewirken, dass der Hauptbrennstoff und die Verbrennungsluft durch die Pilotflamme (108) gezündet werden.
  2. Brennersystem nach Anspruch 1,
    wobei der Pilotbrenner (104, 1704) mehrere Brennstofföffnungen (218, 1718) mit einer ausreichend großen kollektiven Fläche definiert, um gemeinsam eine Pilotflamme mit geringem Impuls (108) zu unterstützen.
  3. Brennersystem nach Anspruch 1,
    wobei die mehreren Segmente (219, 1719) als jeweilige Rohre ausgebildet sind, die dazu ausgelegt sind, den von einem Brennstoffrohr gelieferten Brennstoff frei in den Brennstoffverteiler zu leiten.
  4. Brennersystem nach Anspruch 3,
    wobei mindestens ein Teil der Rohre als Speichen angeordnet ist, die von einem Zentrum ausgehen, das im Wesentlichen an einer Mittellinie entlang der Achse (A) angeordnet ist.
  5. Brennersystem nach einem der vorhergehenden Ansprüche,
    wobei der Pilotbrenner (104, 1704) eine Diffusionsflamme an der abgelegenen Stelle mindestens 100 Hauptbrennstoffdüsendurchmesser vom Boden des Ofens unterstützt.
  6. Brennersystem nach Anspruch 1,
    wobei der Pilotbrenner (104, 1704) mindestens ein Rohr beinhaltet, das quer zu der Brennstoff- und Verbrennungsluftströmungsachse (A) angeordnet ist.
  7. Brennersystem nach Anspruch 6, ferner umfassend:
    - einen oder mehrere Abschnitte aus netzförmiger Keramik (226), die über dem mindestens einen Rohr angeordnet sind.
  8. Brennersystem nach Anspruch 1,
    wobei der abgelegene Flammenhalter (102) einen perforierten Flammenhalter umfasst.
  9. Brennersystem nach Anspruch 8,
    wobei der perforierte Flammenhalter (102) Perforationen umfasst, die als Durchgänge zwischen netzförmigen Fasern (1039) oder in einem netzförmigen Schaum gebildet sind.
  10. Verfahren zum Betreiben eines Brennersystems, umfassend:
    - Bereitstellen von Wärme an einen abgelegenen Flammenhalter (102, 1602) von einer Pilotflamme (108), die von einem Pilotbrenner (104, 1704) getragen wird, der einen Brennstoffverteiler mit mehreren miteinander verbundenen Segmenten (219, 1719) umfasst, wobei jedes Segment mehrere Brennstofföffnungen (218, 1718) aufweist, die dazu ausgelegt sind, Brennstoff von innerhalb des Brennstoffverteilers zu einem Ofenverbrennungsraum zu leiten, wobei die Pilotflamme (108) durch einen Pilotbrennstoff betrieben wird, wobei der abgelegene Flammenhalter (102, 1602) und der Pilotbrenner (104, 1704) entlang einer Strömungsachse (A) eines Hauptbrennstoffs und Verbrennungsluft in einem Ofen und in der Nähe zueinander angeordnet sind, wobei der Pilotbrenner (104, 1704) zwischen dem abgelegenen Flammenhalter (102, 1602) und einer oder mehreren Hauptbrennstoffdüsen (106, 1618) angeordnet ist, wobei ein Abstand zwischen dem Pilotbrenner (104, 1704) und dem abgelegenen Flammenhalter (102, 1602) kleiner ist als ein Abstand zwischen dem Pilotbrenner (104, 1704) und der oder den Hauptbrennstoffdüsen (106, 1618);
    - Einführen von gemischtem Hauptbrennstoff und Luft in den abgelegenen Flammenhalter (102, 1602); und Halten mindestens eines Teils einer Verbrennungsreaktion des gemischten Hauptbrennstoffs und Luft mit dem abgelegenen Flammenhalter (102, 1602), während der Pilotbrenner (104, 1704) weiterhin die Pilotflamme (108) trägt.
  11. Verfahren nach Anspruch 10,
    wobei das Einführen von gemischtem Hauptbrennstoff und Luft in den abgelegenen Flammenhalter (1602) das Einleiten, an einem nahe gelegenen Ende eines Mischrohrs (1710), des Hauptbrennstoffs über die eine oder die mehreren Hauptbrennstoffdüsen (1618) und der Luft beinhaltet;
    wobei das nahe gelegene Ende des Mischrohrs (1710) nahe der einen oder den mehreren Hauptbrennstoffdüsen (1618) angeordnet ist und ein abgelegenes Ende des Mischrohrs (1710) nahe dem abgelegenen Flammenhalter (1602) angeordnet ist, wobei das Mischrohr (1710) von dem nahe gelegenen Ende zum abgelegenen Ende offen ist.
  12. Verfahren nach Anspruch 11, ferner umfassend:
    - Einleiten eines Rauchgases in das nahe gelegene Ende des Mischrohrs (1710).
  13. Verfahren nach Anspruch 11 oder 12,
    wobei der Pilotbrenner (1704) zwischen dem abgelegenen Flammenhalter (1602) und dem abgelegenen Ende des Mischrohrs (1710) angeordnet ist.
  14. Modulares Brennersystem mit geringen Emissionen, umfassend:
    - ein oder mehrere Brennermodule (1401), die jeweils das Brennersystem nach Anspruch 1 umfassen, wobei jedes Brennermodul Folgendes beinhaltet:
    - eine Hauptbrennstoffquelle (232), die getrennt von allen anderen Brennstoffquellen ventilgesteuert ist und dazu ausgelegt ist, selektiv einen Strom des Hauptbrennstoffs über die eine oder die mehreren Hauptbrennstoffdüsen (1402) zur Verdünnung durch einen Strom von Verbrennungsluft zuzuführen,
    - einen Hauptbrennstoffzünder (1406), der dazu ausgelegt ist, eine Zündung des von der Hauptbrennstoffquelle (232) ausgestoßenen Hauptbrennstoffstroms zu bewirken,
    - einen abgelegenen Flammenhalter (102), der von der Hauptbrennstoffquelle (232) und dem Hauptbrennstoffzünder (1406) durch jeweilige Nicht-Null-Abstände getrennt ist, wobei der abgelegene Flammenhalter (102) dazu ausgelegt ist, eine Verbrennungsreaktion zu halten, die durch den Hauptbrennstoffstrom unterstützt wird, wenn der abgelegene Flammenhalter (102) eine vorbestimmte Temperatur oder darüber aufweist, und
    - der Pilotbrenner (104, 1408) des Brennersystems nach Anspruch 1 als Vorheizeinrichtung ausgelegt ist, um den abgelegenen Flammenhalter (102) auf die vorbestimmte Temperatur vorzuheizen;
    - eine gemeinsame Verbrennungsluftquelle, die dazu ausgelegt ist, die Verbrennungsluft jedem der mehreren Brennermodule (1401) bereitzustellen; und
    - eine Wand (1407), die alle des einen oder der mehreren Brennermodule (1401) umgibt, wobei die Wand (1407) dazu ausgelegt ist, Verbrennungsfluide, die dem einen oder den mehreren Brennermodulen (1401) entsprechen, seitlich zurückzuhalten.
  15. Modulares Brennersystem mit niedriger Emission nach Anspruch 14, ferner umfassend:
    - ein oder mehrere separate Hauptbrennstoffventile (1410), die jeweils einen separaten Hauptbrennstoffventilaktuator beinhalten, der dazu ausgelegt ist, als Reaktion auf das Empfangen von Steuersignalen zu arbeiten; und
    ferner umfassend:
    - ein Steuersystem (1412), das dazu ausgelegt ist, jeweilige Steuersignale an jeden der separaten Ventilaktuatoren auszugeben;
    wobei das Steuersystem (1412) ferner Folgendes umfasst:
    - eine Schnittstelle (1514) zwischen dem Steuersystem (1412) und einem Eingangskanal, wobei die Schnittstelle (1514) dazu ausgelegt ist, ein Signal zu empfangen, das einer Brennerkapazitätsanforderung entspricht;
    - einen oder mehrere Brennermodulsensoreingänge (1515a, 1515b), wobei jeder des einen oder der mehreren Brennermodulsensoreingänge (1515a, 1515b) dazu ausgelegt ist, ein Signal zu empfangen, das einem Brennermodulstatus entspricht, wobei der Brennermodulstatus durch Sensorhardware bereitgestellt wird;
    - einen Mikrocontroller (1516), einen computerlesbaren Speicher (1518) und einen Modulsequenzierer (1520), die dazu ausgelegt sind, eine Teilmenge des einen oder der mehreren Brennermodule (1401) zur Zündung auszuwählen; und
    - einen jeweiligen einen oder mehrere Hauptbrennstoffventiltreiberausgänge, die jeweils mit einem der separaten Hauptbrennstoffventilaktuatoren wirkgekoppelt sind.
  16. Modulares Brennersystem mit geringer Emission nach Anspruch 15,
    wobei der Mikrocontroller (1516) dazu ausgelegt ist, computerausführbare Anweisungen zu lesen und auszuführen, die durch einen nichtflüchtigen computerlesbaren Speicher unterstützt werden, um:
    - Kapazitätseingabedaten entsprechend dem Brennerkapazitätsanforderungssignal zu empfangen;
    - Modulstatussensordaten aus einem oder mehreren Sensoren auszulesen, die mindestens einem Brennermodul entsprechen, um zu verifizieren, dass ein oder mehrere ausgewählte Brennermodule (1401) zum Brennen bereit sind;
    - die Teilmenge des einen oder der mehreren Brennermodule (1401) zum Brennen auszuwählen; und
    - mindestens eines der separaten Hauptbrennstoffventilaktuatoren anzusteuern, die der ausgewählten Teilmenge des einen oder der mehreren Brennermodule (1401) entsprechen, um sich zu öffnen, um Brennstoff für eine Verbrennungsreaktion bereitzustellen, die durch die Teilmenge des einen oder der mehreren Brennermodule (1401) unterstützt wird.
EP20803052.8A 2019-05-07 2020-05-07 Pilotstabilisierter brenner Active EP3966503B1 (de)

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