Patent Application
20210310650
According to an embodiment, a row of burner tiles is provided, each having a receiving feature extending laterally therethrough. A support member extends through the receiving feature of each of the burner tiles. The burner tiles can be, for example, perforated flame holders.
According to another embodiment, each of the burner tiles includes a second receiving feature extending parallel to the first receiving feature, and a second support member extends through the second receiving feature of each of the burner tiles.
According to an embodiment, a quantity of bonding agent is positioned between the burner tiles of each adjacent pair of burner tiles of the row. According to an alternative embodiment, the bonding agent is omitted, and the tiles are held in their relative positions by the support member or members.
According to an embodiment, the support member is under tension, at least while the row of burner tiles is not at operating temperature. According to an embodiment, the tension is maintained by a fastener at each end of the support member.
According to an embodiment, the support member is generally circular in cross section.
According to an embodiment, the burner tiles of the row are aligned such that a respective face of each burner tile lies substantially in a same plane. According to an alternative embodiment, the burner tiles are positioned, relative to each other, such that the row has a substantially arcuate shape.
According to an embodiment, a perforated flame holder of a furnace is provided, including an array of burner tiles with a support member extending through the burner tiles of each row of the array of burner tiles. One or more additional support members can be positioned to extend through each of the burner tiles of a respective column of the array.
According to an embodiment, a first face of each of the burner tiles of the array of burner tiles lies in a common plane. According to an alternative embodiment, a number of the burner tiles of the array of burner tiles are offset longitudinally with respect to others of the burner tiles of the array.
According to an embodiment, a method of assembly of the perforated flame holder is provided, in which each row of burner tiles is separately installed into a furnace, such that a final assembly of the perforated flame holder is performed inside the furnace.
According to an alternative embodiment, rows of burner tiles are coupled together outside the furnace to form larger segments of the perforated flame holder, which are then separately installed in the furnace to form the perforated flame holder.
According to another alternative embodiment, all of the rows of burner tiles are coupled together outside the furnace, then the fully assembled perforated flame holder is installed in the furnace.
According to an embodiment, a perforated flame holder mounting structure is provided in the furnace, which includes coupling features configured to receive ends of the support members of each of the rows, thereby supporting the perforated flame holder within the furnace.
According to an embodiment, a perforated flame holder is provided, which includes a plurality of burner tiles. Support members extend between adjacent pairs of burner tiles in receiving features formed into facing lateral surfaces of each adjacent pair of burner tiles.
According to an embodiment, the receiving features are relieved at an angle selected to distribute stress between the support members the respective burner tiles.
According to an embodiment, each of the support members includes a strain relief member positioned and configured to distribute stress between the respective support member and the respective pair of burner tiles.
According to an embodiment, the strain relief members include sleeves of fibrous ceramic material that is formed into a flexible tube.
According to an embodiment, each of the support members includes a plurality of ridges extending lengthwise thereon.
According to an embodiment, a combustion system includes a fuel and oxidant source configured to output a fuel and an oxidant, and a perforated flame holder including a group of burner tiles arranged side by side. Each burner tile includes an input face aligned to receive the fuel and the oxidant, an output face, and a plurality of perforations extending between the input face and the output face. The perforated flame holder is configured to support a combustion reaction of the fuel and the oxidant within the perforations of the burner tiles. A first burner tile of the plurality of burner tiles includes a receiving feature. The combustion system includes a first support member extending into the first burner tile via the receiving feature and holding the perforated flame holder in alignment to receive the fuel and oxidant into the perforations.
According to an embodiment, a combustion system includes a fuel and oxidant source configured to output a fuel and an oxidant, and a perforated flame holder including a first group of burner tiles arranged side by side. Each burner tile of the first group includes an input face aligned to receive the fuel and the oxidant, an output face, a plurality of perforations extending between the input face and the output face, and a receiving feature. The perforated flame holder is configured to support a combustion reaction of the fuel and the oxidant within the perforations. The combustion system includes a plurality of support members, each extending into a respective burner tile of the first group via the receiving feature and supporting the perforated flame holder in alignment to receive the fuel and oxidant.
According to an embodiment, a method includes outputting a fuel into a furnace volume, outputting an oxidant into the furnace volume, and supporting a perforated flame holder, including a plurality of burner tiles arranged side by side in alignment to receive the fuel and oxidant by passing a support member into at least one of the burner tiles via a receiving feature of the at least one burner tile. Each burner tile includes an input face, an output face, and a plurality of perforations extending between the input face and the output face. The method includes receiving the fuel and oxidant into the perforations of each burner tile and supporting a combustion reaction of the fuel and oxidant within the perforations of each burner tile.
According to an embodiment, a device includes a first burner tile and a support member. The first burner tile includes an input face, an output face, a plurality of perforations extending between the input face and the output face, and a receiving feature. The support member extends into the burner tile via the receiving feature, the support member includes a portion protruding from the burner tile.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.
In some of the drawings, two or more elements may be indicated by reference numbers of the same numerical value, but that include a letter that is different, such as, e.g., 406x and 406y. This is to enable the detailed description to differentiate between specific elements or groups of elements that are otherwise similar or identical. However, where the description refers more generally to all of the elements, the letters may be omitted from the description. Additionally, in other drawings, the letters may be omitted from references to the same or similar elements, where there is no need in the description to differentiate between the elements.
According to embodiments, the burner system 100 includes a fuel and oxidant source 103 disposed to output fuel and oxidant into a combustion volume 104 to form a fuel and oxidant mixture 106. As used herein, the terms fuel and oxidant mixture and fuel stream may be used interchangeably and considered synonymous depending on the context, unless further definition is provided. As used herein, the terms combustion volume, combustion chamber, furnace volume, and the like shall be considered synonymous unless further definition is provided. The perforated flame holder 102 is disposed in the combustion volume 104 and positioned to receive the fuel and oxidant mixture 106.
The fuel can include hydrogen, a hydrocarbon gas, a vaporized hydrocarbon liquid, an atomized hydrocarbon liquid, or a powdered or pulverized solid. The fuel can be a single species or can include a mixture of gas(es), vapor(s), atomized liquid(s), and/or pulverized solid(s). For example, in a process heater application the fuel can include fuel gas or byproducts from the process that include carbon monoxide (CO), hydrogen (H2), and methane (CH4). In another application, the fuel can include natural gas (mostly CH4) or propane (C3H8). In another application, the fuel can include #2 fuel oil or #6 fuel oil. Dual fuel applications and flexible fuel applications are similarly contemplated by the inventors. The oxidant can include oxygen carried by air, flue gas, and/or can include another oxidant, either pure or carried by a carrier gas. The terms oxidant and oxidizer shall be considered synonymous herein.
According to an embodiment, a perforated flame holder body 108 can be bounded by an input face 112 disposed to receive the fuel and oxidant mixture 106, an output face 114 facing away from the fuel and oxidant source 103, and a peripheral surface 116 defining a lateral extent of the perforated flame holder 102. The plurality of perforations 110 which are defined by the perforated flame holder body 108 extend from the input face 112 to the output face 114. The plurality of perforations 110 can receive the fuel and oxidant mixture 106 at the input face 112. The fuel and oxidant mixture 106 can then combust in or near the plurality of perforations 110 and combustion products can exit the plurality of perforations 110 at or near the output face 114.
According to an embodiment, the perforated flame holder 102 is configured to hold a majority of the combustion reaction 202 within the perforations 110. For example, on a steady-state basis, more than half the molecules of fuel output into the combustion volume 104 by the fuel and oxidant source 103 may be converted to combustion products between the input face 112 and the output face 114 of the perforated flame holder 102. According to an alternative interpretation, more than half of the heat or thermal energy output by the combustion reaction 202 may be output between the input face 112 and the output face 114 of the perforated flame holder 102. As used herein, the terms heat, heat energy, and thermal energy shall be considered synonymous unless further definition is provided. As used above, heat energy and thermal energy refer generally to the released chemical energy initially held by reactants during the combustion reaction 202. As used elsewhere herein, heat, heat energy and thermal energy correspond to a detectable temperature rise undergone by real bodies characterized by heat capacities. Under nominal operating conditions, the perforations 110 can be configured to collectively hold at least 80% of the combustion reaction 202 between the input face 112 and the output face 114 of the perforated flame holder 102. In some experiments, the inventors produced a combustion reaction 202 that was apparently wholly contained in the perforations 110 between the input face 112 and the output face 114 of the perforated flame holder 102. According to an alternative interpretation, the perforated flame holder 102 can support combustion between the input face 112 and output face 114 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 114 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 112 of the perforated flame holder 102.
While a “flame” is described in a manner intended for ease of description, it should be understood that in some instances, no visible flame is present. Combustion occurs primarily within the perforations 110, but the “glow” of combustion heat is dominated by a visible glow of the perforated flame holder 102 itself. In other instances, the inventors have noted transient “huffing” or “flashback” wherein a visible flame momentarily ignites in a region lying between the input face 112 of the perforated flame holder 102 and a fuel nozzle 118, within the dilution region DD. 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 110 of the perforated flame holder 102, between the input face 112 and the output face 114. In still other instances, the inventors have noted apparent combustion occurring downstream from the output face 114 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 202 and output a portion of the received heat as thermal radiation 204 to heat-receiving structures (e.g., furnace walls and/or radiant section working fluid tubes) in or adjacent to the combustion volume 104. As used herein, terms such as radiation, thermal radiation, radiant heat, heat radiation, etc. are to be construed as being substantially synonymous, unless further definition is provided. Specifically, such terms refer to blackbody-type radiation of electromagnetic energy, primarily at infrared wavelengths, but also at visible wavelengths owing to elevated temperature of the perforated flame holder body 108.
Referring especially to
The perforated flame holder body 108 can be characterized by a heat capacity. The perforated flame holder body 108 may hold thermal energy from the combustion reaction 202 in an amount corresponding to the heat capacity multiplied by temperature rise, and transfer the thermal energy from the heat receiving regions 206 to the heat output regions 210 of the perforation walls 208. Generally, the heat output regions 210 are nearer to the input face 112 than are the heat receiving regions 206. According to one interpretation, the perforated flame holder body 108 can transfer heat from the heat receiving regions 206 to the heat output regions 210 via thermal radiation, depicted graphically as 204. According to another interpretation, the perforated flame holder body 108 can transfer heat from the heat receiving regions 206 to the heat output regions 210 via heat conduction along heat conduction paths 212. The inventors contemplate that multiple heat transfer mechanisms including conduction, radiation, and possibly convection may be operative in transferring heat from the heat receiving regions 206 to the heat output regions 210. In this way, the perforated flame holder 102 may act as a heat source to maintain the combustion reaction 202, even under conditions where a combustion reaction would not be stable when supported from a conventional flame holder.
The inventors believe that the perforated flame holder 102 causes the combustion reaction 202 to begin within thermal boundary layers 214 formed adjacent to the walls 208 of the perforations 110. Insofar as combustion is generally understood to include a large number of individual reactions, and since a large portion of combustion energy is released within the perforated flame holder 102, it is apparent that at least a majority of the individual reactions occur within the perforated flame holder 102. As the relatively cool fuel and oxidant mixture 106 approaches the input face 112, the flow is split into portions that respectively travel through individual perforations 110. The hot perforated flame holder body 108 transfers heat to the fluid, notably within the thermal boundary layers 214 that progressively thicken as more and more heat is transferred to the incoming fuel and oxidant mixture 106. After reaching a combustion temperature (e.g., the auto-ignition temperature of the fuel), the reactants continue to flow while a chemical ignition delay time elapses, over which time the combustion reaction 202 occurs. Accordingly, the combustion reaction 202 is shown as occurring within the thermal boundary layers 214. As flow progresses, the thermal boundary layers 214 merge at a merger point 216. Ideally, the merger point 216 lies between the input face 112 and the output face 114 that define the ends of the perforations 110. At some position along the length of a perforation 110, the combustion reaction 202 outputs more heat to the perforated flame holder body 108 than it receives from the perforated flame holder body 108. The heat is received at the heat receiving region 206, is held by the perforated flame holder body 108, and is transported to the heat output region 210 nearer to the input face 112, where the heat is transferred into the cool reactants (and any included diluent) to bring the reactants to the ignition temperature.
In an embodiment, each of the perforations 110 is characterized by a length L defined as a reaction fluid propagation path length between the input face 112 and the output face 114 of the perforated flame holder 102. As used herein, the term reaction fluid refers to matter that travels through a perforation 110. Near the input face 112, the reaction fluid includes the fuel and oxidant mixture 106 (optionally including nitrogen, flue gas, and/or other “non-reactive” species). Within the combustion reaction 202 region, the reaction fluid may include plasma associated with the combustion reaction 202, molecules of reactants and their constituent parts, any non-reactive species, reaction intermediates (including transition), and reaction products. Near the output face 114, the reaction fluid may include reaction products and byproducts, non-reactive gas, and excess oxidant.
The plurality of perforations 110 can be each characterized by a transverse dimension D between opposing perforation walls 208. The inventors have found that stable combustion can be maintained in the perforated flame holder 102 if the length L of each perforation 110 is at least four times the transverse dimension D of the perforation. In other embodiments, the length L can be greater than six times the transverse dimension D. For example, experiments have been run where L is at least eight, at least twelve, at least sixteen, and at least twenty-four times the transverse dimension D. Preferably, the length L is sufficiently long for the thermal boundary layers 214 to form adjacent to the perforation walls 208 in a reaction fluid flowing through the perforations 110 to converge at merger points 216 within the perforations 110 between the input face 112 and the output face 114 of the perforated flame holder 102. In experiments, the inventors have found L/D ratios between 12 and 48 to work well (i.e., produce low NOx, produce low CO, and maintain stable combustion).
The perforated flame holder body 108 can be configured to convey heat between adjacent perforations 110. The heat conveyed between adjacent perforations 110 can be selected to cause heat output from the combustion reaction portion 202 in a first perforation 110 to supply heat to stabilize a combustion reaction portion 202 in an adjacent perforation 110.
Referring especially to
The perforated flame holder 102 can be held by a perforated flame holder support structure 122 configured to hold the perforated flame holder 102 at a dilution distance DD away from the fuel nozzle 118. The fuel nozzle 118 can be configured to emit a fuel jet selected to entrain the oxidant to form the fuel and oxidant mixture 106 as the fuel jet and oxidant travel along a path to the perforated flame holder 102 through the dilution distance DD between the fuel nozzle 118 and the perforated flame holder 102. Additionally or alternatively (particularly when a blower is used to deliver oxidant contained in combustion air), the oxidant or combustion air source can be configured to entrain the fuel and the fuel and oxidant travel through the dilution distance DD. In some embodiments, a flue gas recirculation path 124 can be provided. Additionally or alternatively, the fuel nozzle 118 can be configured to emit a fuel jet selected to entrain the oxidant and to entrain flue gas as the fuel jet travels through the dilution distance DD between the fuel nozzle 118 and the input face 112 of the perforated flame holder 102.
The fuel nozzle 118 can be configured to emit the fuel through one or more fuel orifices 126 having an inside diameter dimension that is referred to as “nozzle diameter.” The perforated flame holder support structure 122 can support the perforated flame holder 102 to receive the fuel and oxidant mixture 106 at the distance DD away from the fuel nozzle 118 greater than 20 times the nozzle diameter. In another embodiment, the perforated flame holder 102 is disposed to receive the fuel and oxidant mixture 106 at the distance DD away from the fuel nozzle 118 between 100 times and 1100 times the nozzle diameter. Preferably, the perforated flame holder support structure 122 is configured to hold the perforated flame holder 102 at a distance about 200 times or more of the nozzle diameter away from the fuel nozzle 118. When the fuel and oxidant mixture 106 travels about 200 times the nozzle diameter or more, the fuel and oxidant mixture 106 is sufficiently homogenized to cause the combustion reaction 202 to produce minimal NOx.
The fuel and oxidant source 103 can alternatively include a premix fuel and oxidant source, according to an embodiment. A premix fuel and oxidant source can include a premix chamber (not shown), a fuel nozzle configured to output fuel into the premix chamber, and an oxidant (e.g., combustion air) channel configured to output the oxidant into the premix chamber. A flame arrestor can be disposed between the premix fuel and oxidant source and the perforated flame holder 102 and be configured to prevent flame flashback into the premix fuel and oxidant source.
The oxidant source 120, whether configured for entrainment in the combustion volume 104 or for premixing, can include a blower configured to force the oxidant through the fuel and oxidant source 103.
The perforated flame holder support structure 122 can be configured to support the perforated flame holder 102 from a floor or wall (not shown) of the combustion volume 104, for example. In another embodiment, the perforated flame holder support structure 122 supports the perforated flame holder 102 from the fuel and oxidant source 103. Alternatively, the perforated flame holder support structure 122 can suspend the perforated flame holder 102 from an overhead structure (such as a flue, in the case of an up-fired system). The perforated flame holder support structure 122 can support the perforated flame holder 102 in various orientations and directions.
The perforated flame holder 102 can include a single perforated flame holder body 108. 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 122 can be configured to support the plurality of perforated flame holder sections. The perforated flame holder support structure 122 can include a metal superalloy, a cementatious, and/or ceramic refractory material. In an embodiment, the plurality of adjacent perforated flame holder sections can be joined with a fiber reinforced refractory cement.
The perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 116 at least twice a thickness dimension T between the input face 112 and the output face 114. In another embodiment, the perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 116 at least three times, at least six times, or at least nine times the thickness dimension T between the input face 112 and the output face 114 of the perforated flame holder 102.
In an embodiment, the perforated flame holder 102 can have a width dimension W less than a width of the combustion volume 104. This can allow the flue gas recirculation path 124 from above to below the perforated flame holder 102 to lie between the peripheral surface 116 of the perforated flame holder 102 and the combustion volume wall (not shown).
Referring again to both
In one range of embodiments, each of the plurality of perforations 110 has a lateral dimension D between 0.05 inch and 1.0 inch. Preferably, each of the plurality of perforations 110 has a lateral dimension D between 0.1 inch and 0.5 inch. For example the plurality of perforations 110 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 110 in a section of the perforated flame holder 102 divided by a total volume of the perforated flame holder 102 including the perforated flame holder body 108 and perforations 110. The perforated flame holder 102 should have a void fraction between 0.10 and 0.90. In an embodiment, the perforated flame holder 102 can have a void fraction between 0.30 and 0.80. In another embodiment, the perforated flame holder 102 can have a void fraction of about 0.70. Using a void fraction of about 0.70 was found to be especially effective for producing very low NOx.
The perforated flame holder 102 can be formed from a fiber reinforced cast refractory material and/or a refractory material such as an aluminum silicate material. For example, the perforated flame holder 102 can be formed to include mullite or cordierite. Additionally or alternatively, the perforated flame holder body 108 can include a metal superalloy such as Inconel or Hastelloy. The perforated flame holder body 108 can define a honeycomb. Honeycomb is an industrial term of art that need not strictly refer to a hexagonal cross section and most usually includes cells of square cross section. Honeycombs of other cross sectional areas are also known.
The inventors have found that the perforated flame holder 102 can be formed from VERSAGRID® ceramic honeycomb, available from Applied Ceramics, Inc. of Doraville, S.C.
The perforations 110 can be parallel to one another and normal to the input and the output faces 112, 114. In another embodiment, the perforations 110 can be parallel to one another and formed at an angle relative to the input and the output faces 112, 114. In another embodiment, the perforations 110 can be non-parallel to one another. In another embodiment, the perforations 110 can be non-parallel to one another and non-intersecting. In another embodiment, the perforations 110 can be intersecting. The perforated flame holder body 108 can be one piece or can be formed from a plurality of sections. Embodiments described herein relate to a perforated flame holder 102 that is formed from a plurality of sections, referred to as tiles.
In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from reticulated ceramic material. The term “reticulated” refers to a netlike structure. Reticulated ceramic material is often made by dissolving a slurry into a sponge of specified porosity, allowing the slurry to harden, and burning away the sponge and curing the ceramic.
In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from a ceramic material that has been punched, bored or cast to create channels.
In another embodiment, the perforated flame holder 102 can include a plurality of tubes or pipes bundled together. The plurality of perforations 110 can include hollow cylinders and can optionally also include interstitial spaces between the bundled tubes. In an embodiment, the plurality of tubes can include ceramic tubes. Refractory cement can be included between the tubes and configured to adhere the tubes together. In another embodiment, the plurality of tubes can include metal (e.g., superalloy) tubes. The plurality of tubes can be held together by a metal tension member circumferential to the plurality of tubes and arranged to hold the plurality of tubes together. The metal tension member can include stainless steel, a superalloy metal wire, and/or a superalloy metal band.
The perforated flame holder body 108 can alternatively include stacked perforated sheets of material, each sheet having openings that connect with openings of subjacent and superjacent sheets. The perforated sheets can include perforated metal sheets, ceramic sheets and/or expanded sheets. In another embodiment, the perforated flame holder body 108 can include discontinuous packing bodies such that the perforations 110 are formed in the interstitial spaces between the discontinuous packing bodies. In one example, the discontinuous packing bodies include structured packing shapes. In another example, the discontinuous packing bodies include random packing shapes. For example, the discontinuous packing bodies can include ceramic Raschig ring, ceramic Berl saddles, ceramic Intalox saddles, and/or metal rings or other shapes (e.g., Super Raschig Rings) that may be held together by a metal cage.
The inventors contemplate various explanations for why burner systems 100 including the perforated flame holder 102 provide such clean combustion.
According to an embodiment, the perforated flame holder 102 may act as a heat source to maintain a combustion reaction 202 even under conditions where a combustion reaction 202 would not be stable when supported by a conventional flame holder. This capability can be leveraged to support combustion using a leaner fuel-to-oxidant mixture than is typically feasible. Thus, according to an embodiment, at the point where the fuel stream 106 contacts the input face 112 of the perforated flame holder 102, an average fuel-to-oxidant ratio of the fuel stream 106 is below a (conventional) lower combustion limit of the fuel component of the fuel stream 106—lower combustion limit defines the lowest concentration of fuel at which a fuel and oxidant mixture 106 will burn when exposed to a momentary ignition source under normal atmospheric pressure and an ambient temperature of 25° C. (77° F.).
The perforated flame holder 102 and systems including the perforated flame holder 102 described herein were found to provide substantially complete combustion of CO (single digit ppm down to undetectable, depending on experimental conditions), while supporting low NOx. According to one interpretation, such a performance can be achieved due to a sufficient mixing used to lower peak flame temperatures (among other strategies). Flame temperatures tend to peak under slightly rich conditions, which can be evident in any diffusion flame that is insufficiently mixed. By sufficiently mixing, a homogenous and slightly lean mixture can be achieved prior to combustion. This combination can result in reduced flame temperatures, and thus reduced NOx formation. In one embodiment, “slightly lean” may refer to 3% O2, i.e., an equivalence ration of ˜0.87. Use of even leaner mixtures is possible but may result in elevated levels of O2. Moreover, the inventors believe the perforation walls 208 may act as a heat sink for the combustion fluid. This effect may alternatively or additionally reduce combustion temperatures and lower NOx.
According to another interpretation, production of NOx can be reduced if the combustion reaction 202 occurs over a very short duration of time. Rapid combustion causes the reactants (including oxygen and entrained nitrogen) to be exposed to NOx-formation temperature for a time too short for NOx formation kinetics to cause significant production of NOx. The time required for the reactants to pass through the perforated flame holder 102 is very short compared to a conventional flame. The low NOx production associated with perforated flame holder combustion may thus be related to the short duration of time required for the reactants (and entrained nitrogen) to pass through the perforated flame holder 102.
According to a simplified description, the method 300 begins with step 302, wherein the perforated flame holder is preheated to a start-up temperature, TS. After the perforated flame holder is raised to the start-up temperature, the method proceeds to step 304, wherein the fuel and oxidant are provided to the perforated flame holder and combustion is held by the perforated flame holder.
According to a more detailed description, step 302 begins with step 306, wherein start-up energy is provided at the perforated flame holder. Simultaneously or following providing start-up energy, a decision step 308 determines whether the temperature T of the perforated flame holder is at or above the start-up temperature, TS. As long as the temperature of the perforated flame holder is below its start-up temperature, the method loops between steps 306 and 308 within the preheat step 302. In decision step 308, if the temperature T of at least a predetermined portion of the perforated flame holder is greater than or equal to the start-up temperature, the method 300 proceeds to overall step 304, wherein fuel and oxidant is supplied to and combustion is held by the perforated flame holder.
Step 304 may be broken down into several discrete steps, at least some of which may occur simultaneously.
Proceeding from decision step 308, a fuel and oxidant mixture is provided to the perforated flame holder, as shown in step 310. The fuel and oxidant may be provided by a fuel and oxidant source that includes a separate fuel nozzle and oxidant (e.g., combustion air) source, for example. In this approach, the fuel and oxidant are output in one or more directions selected to cause the fuel and oxidant mixture to be received by the input face of the perforated flame holder. The fuel may entrain the combustion air (or alternatively, the combustion air may dilute the fuel) to provide a fuel and oxidant mixture at the input face of the perforated flame holder at a fuel dilution selected for a stable combustion reaction that can be held within the perforations of the perforated flame holder.
Proceeding to step 312, the combustion reaction is held by the perforated flame holder.
In step 314, heat may be output from the perforated flame holder. The heat output from the perforated flame holder may be used to power an industrial process, heat a working fluid, generate electricity, or provide motive power, for example.
In optional step 316, the presence of combustion may be sensed. Various sensing approaches have been used and are contemplated by the inventors. Generally, combustion held by the perforated flame holder is very stable and no unusual sensing requirement is placed on the system. Combustion sensing may be performed using an infrared sensor, a video sensor, an ultraviolet sensor, a charged species sensor, thermocouple, thermopile, flame rod, and/or other combustion sensing apparatuses. In an additional or alternative variant of step 316, a pilot flame or other ignition source may be provided to cause ignition of the fuel and oxidant mixture in the event combustion is lost at the perforated flame holder.
Proceeding to decision step 318, if combustion is sensed not to be stable, the method 300 may exit to step 324, wherein an error procedure is executed. For example, the error procedure may include turning off fuel flow, re-executing the preheating step 302, outputting an alarm signal, igniting a stand-by combustion system, or other steps. If, in decision step 318, combustion in the perforated flame holder is determined to be stable, the method 300 proceeds to decision step 320, wherein it is determined if combustion parameters should be changed. If no combustion parameters are to be changed, the method loops (within step 304) back to step 310, and the combustion process continues. If a change in combustion parameters is indicated, the method 300 proceeds to step 322, wherein the combustion parameter change is executed. After changing the combustion parameter(s), the method loops (within step 304) back to step 310, and combustion continues.
Combustion parameters may be scheduled to be changed, for example, if a change in heat demand is encountered. For example, if less heat is required (e.g., due to decreased electricity demand, decreased motive power requirement, or lower industrial process throughput), the fuel and oxidant flow rate may be decreased in step 322. Conversely, if heat demand is increased, then fuel and oxidant flow may be increased. Additionally, or alternatively, if the combustion system is in a start-up mode, then fuel and oxidant flow may be gradually increased to the perforated flame holder over one or more iterations of the loop within step 304.
Referring again to
Various heating apparatuses have been used and are contemplated by the inventors. In some embodiments, the heater 128 can include a flame holder configured to support a flame disposed to heat the perforated flame holder 102. The fuel and oxidant source 103 can include a fuel nozzle 118 configured to emit a fuel stream 106 and an oxidant source 120 configured to output oxidant (e.g., combustion air) adjacent to the fuel stream 106. The fuel nozzle 118 and oxidant source 120 can be configured to output the fuel stream 106 to be progressively diluted by the oxidant (e.g., combustion air). The perforated flame holder 102 can be disposed to receive a diluted fuel and oxidant mixture 106 that supports a combustion reaction 202 that is stabilized by the perforated flame holder 102 when the perforated flame holder 102 is at an operating temperature. A start-up flame holder, in contrast, can be configured to support a start-up flame at a location corresponding to a relatively unmixed fuel and oxidant mixture that is stable without stabilization provided by the heated perforated flame holder 102.
The burner system 100 can further include a controller 130 operatively coupled to the heater 128 and to a data interface 132. For example, the controller 130 can be configured to control a start-up flame holder actuator configured to cause the start-up flame holder to hold the start-up flame when the perforated flame holder 102 needs to be pre-heated and to not hold the start-up flame when the perforated flame holder 102 is at an operating temperature (e.g., when T≥TS).
Various approaches for actuating a start-up flame are contemplated. In one embodiment, the start-up flame holder includes a mechanically-actuated bluff body configured to be actuated to intercept the fuel and oxidant mixture 106 to cause heat-recycling and/or stabilizing vortices and thereby hold a start-up flame; or to be actuated to not intercept the fuel and oxidant mixture 106 to cause the fuel and oxidant mixture 106 to proceed to the perforated flame holder 102. In another embodiment, a fuel control valve, blower, and/or damper may be used to select a fuel and oxidant mixture flow rate that is sufficiently low for a start-up flame to be jet-stabilized; and upon reaching a perforated flame holder 102 operating temperature, the flow rate may be increased to “blow out” the start-up flame. In another embodiment, the heater 128 may include an electrical power supply operatively coupled to the controller 130 and configured to apply an electrical charge or voltage to the fuel and oxidant mixture 106. An electrically conductive start-up flame holder may be selectively coupled to a voltage ground or other voltage selected to attract the electrical charge in the fuel and oxidant mixture 106. The attraction of the electrical charge was found by the inventors to cause a start-up flame to be held by the electrically conductive start-up flame holder.
In another embodiment, the heater 128 may include an electrical resistance heater configured to output heat to the perforated flame holder 102 and/or to the fuel and oxidant mixture 106. The electrical resistance heater 128 can be configured to heat up the perforated flame holder 102 to an operating temperature. The heater 128 can further include a power supply and a switch operable, under control of the controller 130, to selectively couple the power supply to the electrical resistance heater 128.
An electrical resistance heater 128 can be formed in various ways. For example, the electrical resistance heater 128 can be formed from KANTHAL® wire (available from Sandvik Materials Technology division of Sandvik AB of Hallstahammar, Sweden) threaded through at least a portion of the perforations 110 defined formed by the perforated flame holder body 108. Alternatively, the heater 128 can include an inductive heater, a high-energy beam heater (e.g., microwave or laser), a frictional heater, electro-resistive ceramic coatings, or other types of heating technologies.
Other forms of start-up apparatuses are contemplated. For example, the heater 128 can include an electrical discharge igniter or hot surface igniter configured to output a pulsed ignition to the oxidant and fuel. Additionally, or alternatively, a start-up apparatus can include a pilot flame apparatus disposed to ignite the fuel and oxidant mixture 106 that would otherwise enter the perforated flame holder 102. The electrical discharge igniter, hot surface igniter, and/or pilot flame apparatus can be operatively coupled to the controller 130, which can cause the electrical discharge igniter or pilot flame apparatus to maintain combustion of the fuel and oxidant mixture 106 in or upstream from the perforated flame holder 102 before the perforated flame holder 102 is heated sufficiently to maintain combustion.
The burner system 100 can further include a sensor 134 operatively coupled to the control circuit 130. The sensor 134 can include a heat sensor configured to detect infrared radiation or a temperature of the perforated flame holder 102. The control circuit 130 can be configured to control the heating apparatus 128 responsive to input from the sensor 134. Optionally, a fuel control valve 136 can be operatively coupled to the controller 130 and configured to control a flow of fuel to the fuel and oxidant source 102. Additionally, or alternatively, an oxidant blower or damper 138 can be operatively coupled to the controller 130 and configured to control flow of the oxidant (or combustion air).
The sensor 134 can further include a combustion sensor operatively coupled to the control circuit 130, the combustion sensor being configured to detect a temperature, video image, and/or spectral characteristic of a combustion reaction 202 held by the perforated flame holder 102. The fuel control valve 136 can be configured to control a flow of fuel from a fuel source 118 to the fuel and oxidant source 102. The controller 130 can be configured to control the fuel control valve 136 responsive to input from the combustion sensor 134. The controller 130 can be configured to control the fuel control valve 136 and/or the oxidant blower or damper 138 to control a preheat flame type of heater 128 to heat the perforated flame holder 102 to an operating temperature. The controller 130 can similarly control the fuel control valve 136 and/or the oxidant blower or damper 138 to change the fuel and oxidant mixture 106 flow responsive to a heat demand change received as data via the data interface 132.
Each of the burner tiles 402 includes at least one receiving feature 404 extending into the burner tile 402 laterally from a lateral surface of the burner tile 402. In some embodiments, the receiving feature 404 may extend entirely through a burner tile 402. In other embodiments, the receiving feature 404 may extend into but not through the burner tile 402. In the embodiment of
Depending, in part, upon the material and manufacturing method used to produce the burner tiles 402, the receiving features 404 can be formed in a number of different ways. Examples of processes for forming the receiving features 404 include formation by movable or loose cores (in embodiments in which a casting process is used to make the burner tiles 402), drilling, conventional machining, electrical discharge machining, waterjet machining, etc. The receiving features 404 can be formed prior to firing or sintering, i.e., in embodiments in which the burner tiles 402 are made from ceramic materials, or can be formed in otherwise complete burner tiles 402.
The perforated flame holder 102 includes a plurality of support members 406. A support member 406x extends through the first receiving feature 404x of each of the burner tiles 402 of a respective row, while a transverse support member 406y extends through the second receiving feature 404y of each of the burner tiles 402 of a respective column of the array. In embodiments in which the rows of burner tiles 402 are different in length from the columns, the support members 406x differ from the transverse support members 406y at least with respect to their respective lengths. In other embodiments, they may be substantially identical.
In the embodiment of
The support members 406 are preferably made of an alloy that is capable of tolerating sustained high temperatures, examples of which include, Inconel, Monel, Hastelloy, Stellite, etc. According to an embodiment, the support members 406 serve to reinforce a bond, formed by a bonding agent such as a refractory adhesive or cement, between the burner tiles 402, thereby reducing the likelihood of a failure of the bond. According to another embodiment, the bonding agent is omitted, and the burner tiles 402 are held in position solely by the support members 406. Omitting the bond between the burner tiles 402 can reduce the likelihood that damage to a single burner tile 402 will render the entire perforated flame holder 102 irreparable. Instead, the support members 406 that support the damaged burner tile 402 can be withdrawn far enough to release that burner tile 402, a new burner tile 402 positioned in its place, and the support members 406 reinserted.
In some embodiments, one or more of the receiving features 404 may extend through multiple perforations 110 in the body 108 of a burner tile 402. As a result, the receiving feature 404 may be discontinuous, as it passes through one perforation 110 after another. Nevertheless, for the purposes of the description and claims, where a plurality of individual openings extending between perforations 110 of a single burner tile 402 are in alignment with each other so as to define one, continuous, straight passage through the burner tile 402, the openings are considered to be comprised by a single receiving feature 404. Additionally, although, in many embodiments, the support members 406 may extend through, and partially obstruct some of the perforations 110 of the burner tile 402, most of the perforations 110 remain completely unobstructed. Thus, for the purposes of the specification and claims, the perforations 110, in such embodiments, are considered to be substantially unobstructed.
In one embodiment, each support member 406 extends only partially into a single burner tile 402. Each receiving feature 404 may extend only a few cells or perforations 110 deep into the burner tile 402. The support members 406 can be ceramic dowels that extend partially into the burner tiles 402.
In one embodiment, the perforated flame holder 102 can include a first group of burner tiles 402 and a second group of burner tiles 402. The first group of burner tiles 402 can include the three burner tiles 402 on the right side of the perforated flame holder 102. The second group of burner tiles 402 can include the three burner tiles 402 on the left side of the perforated flame holder 102. Each of the support members 406y can extend through both a burner tile 402 of the first group and an aligned burner tile 402 of the second group via the receiving features 404 of the burner tiles 402. Alternatively, each support member 406y can pass only partially through a single burner tile 402 such that there can be a single support member 406y for each respective burner tile 402 of both the first and second groups.
In one embodiment, the support members 406 hold the perforated flame holder 102 in alignment above the fuel and oxidant source 103 of
In one embodiment, with reference to
In one embodiment, with reference to
In one alternative embodiment, with reference to
In one embodiment, the support members 404 are elongated support members.
According to an embodiment, the orientation of the perforated flame holder 102 relative to the directions X, Y, Z shown in
According to an embodiment, the perforated flame holder 102 can be utilized in a horizontally fired burner system in which fuel and oxidant is output in a horizontal direction, such as that shown in
According to an embodiment, in a horizontally fired burner system, the phrase “side by side” can include burner tiles 402 being positioned both above adjacent burner tiles 402 and laterally from adjacent burner tiles 402. For example, in a side by side arrangement, a single burner tile 402 could be arranged side by side with a burner tile 402 above it, a burner tile 402 below it, and two burner tiles 402 on either lateral side.
As set forth above in relation to
Support members 602 may have a variety of sectional shapes, including oval, flattened teardrop, polygonal, etc.
As set forth above in relation to
The perforated flame holder mounting structure 702 includes coupling features 704 positioned and shaped to receive respective ends of the support members 406 of the perforated flame holder 102. In the embodiment shown, the coupling features 704 are notches formed in the perforated flame holder mounting structure 702. The ends of the support members 406 rest on the bottoms of the respective coupling features 704, which thereby serve to support the perforated flame holder 102 in a selected position and orientation within the combustion volume 104.
As noted above, the receiving features 404x and 404y are offset longitudinally, so that the corresponding support members 406x and 406y can cross within the burner tiles 402 without intersecting. Accordingly, coupling features 704x, positioned to receive the ends of the support members 406x, have a first depth, while coupling features 704y, positioned to receive the ends of the transverse support members 406y, have a second depth that is greater than the first depth. Thus, the perforated flame holder 102 is fully supported along each side.
According to an embodiment, the perforated flame holder mounting structure 702 is sized to closely fit around the perforated flame holder 102. This holds the burner tiles 402 in close contact, even if the burner tiles 402 are not bonded, or otherwise held together.
The coupling features 704 are shown in
As set forth above in relation to
Tensioned support members 802 may reduce the likelihood of damage to burner tiles 402 during service and handling. For example, when a perforated flame holder 800—or a row of burner tiles 402—is supported at opposite edges in a horizontal orientation, a bending stress is produced along its length. During handling of the perforated flame holder 800, the bending stress can fluctuate, and can momentarily spike, even with careful handling. During such spikes, the material of the burner tiles 402 can fracture, or a refractory cement bond can fail. In either case, damage to the perforated flame holder 800 or row of burner tiles 402 may render it unusable. However, even in embodiments in which the support member 802 itself is not sufficiently stiff to substantially limit flexion of the perforated flame holder 800 under tension, it can significantly increase the stiffness and structural strength of the perforated flame holder 800, reducing the likelihood of damage during handling.
The retaining washer 824 is shown as having a shape that is similar to the shape of the threaded nut 806 of
The embodiment shown in
It should be noted that typically, the ceramic or composite materials used for burner tiles has a much lower coefficient of thermal expansion than the refractory alloys that might be used for support members. For example, ceramics made from alumina or Mullite generally have coefficients of thermal expansion of around 3×10−6/° F., and cordierite has a coefficient of less than 0.1×10−6/° F. In contrast, alloys such as Monel, Hastelloy, and Inconel each have a coefficient of thermal expansion of around 7×10−6/° F., or more. Perforated flame holders typically operate at temperatures exceeding 1500° F., and often exceeding 2000° F. If the support members (406, 802, 822, etc.) fit closely within the receiving features 404 at room temperature, there is a danger that as the perforated flame holder heats to its normal operating temperature, the greater expansion of the support members 822 will crack or break the material of the burner tiles. Accordingly, it is preferable that the receiving features 404 be dimensioned slightly larger than the dimensions of the support members 822, so as to accommodate the expansion of the support members 822.
Similarly, an allowance for lengthwise expansion of support members 822 is preferable, where clearance might otherwise be a problem. For example, referring to
In the embodiments disclosed above, perforated flame holders are shown with the burner tiles in substantially planar configurations, with their respective lateral faces lying in common planes. However, in some furnace configurations, it may be desirable to have a perforated flame holder whose face is not planar, but that instead has some other selected shape. According to various embodiments, the burner tiles of a perforated flame holder can be offset, longitudinally, with respect to other burner tiles, in order to modify the shape of the perforated flame holder.
As set forth above in relation to
In the embodiment shown, the longitudinal separation of the burner tiles 402 is such that a single support member 802 cannot extend through all of the burner tiles 402 of the row 900. Accordingly, the row 900 includes first and second support members 802x1, 802x2, which are offset longitudinally, with respect to each other. The first support member 802x1 extends through all but the outermost burner tiles 402, while the second support member 802x2 extends through two burner tiles 402 at each end of the row 900, coupling the outermost burner tiles 402 to the remaining burner tiles 402 of the row 900.
Transverse receiving features 404y are configured to receive respective support members 404 when the row 900 is combined with additional rows of burner tiles 402 to form a perforated flame holder, to hold the rows in close contact. Perforated flame holder support brackets 902 are configured to support the row 900, together with the other rows of a perforated flame holder, in a combustion volume, and to prevent lateral movement of the rows or of individual burner tiles 402 along the X axis.
In some embodiments in which the burner tiles 402 of the row 900 are bonded to each other, the first support member 802x1 may be omitted. The second support member 802x2 reinforces the row 900 and retains the arcuate shape of the row 900 during handling, while a bonding agent between the burner tiles 402 holds the inner tiles in place. Once the row 900 is installed in a combustion volume, the perforated flame holder support brackets 902 provide the necessary lateral support.
The row 900 is shown with support members 802 and threaded nuts 806. However, this is by way of example only. According to various embodiments, other support members, as well as other fasteners can be employed, including, for example, the support members and fasteners previously disclosed herein.
According to various additional embodiments, perforated flame holders having other symmetrical and asymmetrical shapes can be made by selection of the number of rows of burner tiles, and the number, size, shape, and relative longitudinal displacement of the burner tiles of each row of the respective perforated flame holders.
As set forth above in relation to
Each of a first plurality of support members 406x extends through each of the burner tiles 1204 of a respective one of the plurality of rows 1202. Each of a second plurality of support members 406y extends transversely through each of the burner tiles 1204 of a respective column 1206 of tiles of the perforated flame holder 1200. Because the burner tiles 1204 of the perforated flame holder 1200 are arranged in a hexagonal grid, the columns of the grid lie at an angle of 60 or 120 degrees, relative to the rows 1202 of the grid.
In the example shown, the burner tiles 1204 are configured as perforated flame holders 102, as described in detail above with reference to
According to respective embodiments, various methods are provided for assembling, handling, and installing perforated flame holders like those disclosed herein. For example, according to an embodiment, a technician assembles pluralities of burner tiles and support members to form rows, then assembles the rows to form a perforated flame holder or segments thereof. According to another embodiment, a technician obtains pre-assembled rows of burner tiles, or pre-assembled segments, each having a plurality of rows, then assembles these to form the perforated flame holder. According to a further embodiment, the technician obtains a preassembled perforated flame holder. According to an embodiment, the pre-assembled rows, segments, or perforated flame holder include pre-positioned support members. According to another embodiment, the technician positions some or all of the support members after obtaining the pre-assembled rows, segments, or perforated flame holder.
According to an embodiment, a fully assembled perforated flame holder is installed as a unit into the combustion volume of a furnace. Support members extending through at least each row of burner tiles of the perforated flame holder stiffen the perforated flame holder and reduce the likelihood of damage during installation. According to an embodiment, at least some of the additional stiffness is a result of tension applied to the support members.
The perforated flame holder is similarly protected during service of the furnace. For example, where it becomes necessary to remove the perforated flame holder from the furnace, the support members again provide additional strength and stiffness, enabling removal of the perforated flame holder from the furnace and, later, reinstallation, while reducing the likelihood of damage during handling.
According to another embodiment, rows of burner tiles are coupled together outside the furnace to form segments of the perforated flame holder, which are then separately installed in the furnace to form the perforated flame holder. According to a further embodiment, each of the rows of burner tiles is installed separately into the furnace to form the perforated flame holder. Embodiments in which the perforated flame holder is installed in pieces, either as individual rows, or as larger segments, are particularly useful where the perforated flame holder is relatively large. Very large perforated flame holders can be difficult to manipulate, particularly within the confines of a combustion volume, which increases the danger of damage to the plate. By moving segments or rows of a perforated flame holder at a time, instead of the entire plate at once, installation or removal is simplified. The smaller pieces are less unwieldy, and the risk of damage is reduced.
Because damage to a perforated flame holder is often irreparable, or at least costly, the use of support members in accordance with the principles of the invention can reduce maintenance costs. According to an embodiment in which the tiles of the individual rows are bonded together but the rows are not bonded, damage to one tile can be repaired by replacement of the corresponding row, rather than of the entire perforated flame holder.
For example, in an embodiment in which the rows are held together by two or more transverse support members—as described above, for example, with reference to
As set forth above in relation to
The support members 1302 are in the form of short pins that act primarily as shear members to hold the burner tiles 402 in their proper positions within the perforated flame holder 1300. The pins 1302 can be made from any of a number of different materials, including, for example, alumina, mullite, cordierite, ceramic binder, combinations of these and/or other suitable materials, etc. According to an embodiment, the pins 1302 are made of the same material used to make the burner tiles 402. The pins 1302 are preferably made of a material whose coefficient of thermal expansion is substantially equal to that of the material of the burner tiles 402—although other materials can be used, provided that the relative sizes of the receiving features 1304 and pins 1302 are selected to accommodate differences in thermal expansion rates. According to an embodiment, the receiving features 1304 are round, with a diameter of about ½ inch and a depth exceeding one inch, and the pins 1302 are round, with a diameter of about % inch and a length of about two inches.
Refractory cement can be used to fix the pins 1302 in place, in which case the perforated flame holder 1300 is substantially rigid, and strengthened by the pins 1302. Alternatively, the perforated flame holder 1300 can be assembled without adhesive or cement, which can result in some relative movement of the burner tiles 402, but also enables the removal and replacement of individual burner tiles 402, rather than requiring the replacement of the entire perforated flame holder 1300. According to an embodiment, a wire or strap is positioned around the perforated flame holder 1300, and tensioned to hold the burner tiles 402 in position during installation, and to prevent any of the burner tiles 402 from separating enough to permit a pin 1302 to slip entirely from the corresponding receiving feature 1304.
According to an embodiment, the burner tiles 402 include respective pluralities of perforations 110 defined by perforation walls 208. In the example shown, the perforations 110 are substantially square, with perforation walls 208x extending parallel to a first (longitudinal) axis, and perforation walls 208y extending parallel to a second axis, substantially perpendicular to the first axis. The receiving features 1304a, 1304b are slightly larger in diameter than the pin 1302. This may provide several potential benefits. For example, one possible advantage is that typical manufacturing processes can result in slight variations in dimensions of the burner tiles 402, and/or the exact positions of the receiving features 1304. In the case of a perforated flame holder 1300 that has a number of burner tiles 402, these slight variations can result in some minimal misalignment of the receiving features 1304 of some of the burner tiles 402. The oversized receiving features 1304 can compensate for such misalignment in a manner that is generally more cost effective than the employment of more expensive processes that would be required to achieve higher tolerances.
Another potential advantage is that, during operation of a furnace, the temperature of a perforated flame holder 1300 in the furnace can vary significantly at different locations of the plate 1300, particularly during startup and shutdown of the furnace. The loose fit of the pins 1302 in the receiving features 1304 can permit some limited relative movement of the burner tiles 402 caused by different degrees of thermal expansion, as some parts of the perforated flame holder 1300 heat or cool faster than others.
Finally, even though the pins 1302 may be made from the same material as the burner tiles 402, the pins 1302 are much stronger than the perforation walls 208 of the burner tiles 402 because the pins 1302 are far more massive than the walls 208. Thus, perforation walls 208 can be very easily broken by the pins 1302 during assembly of the perforated flame holder 1300 if there is any binding or tightness. The slightly oversized receiving features 1304 help reduce the likelihood of such damage.
As set forth above in relation to
During testing of prototype systems, the inventors found that the use of pins in receiving features was very effective in supporting the burner tiles of large perforated flame holders, and resulted in a reduction of damage to perforated flame holders during installation and service, and also reduced the cost and extent of repairs when such became necessary.
However, the inventors also noted that the burner tiles used in the tests often showed small cracks in the material of the burner tiles, extending upward in the lateral walls of the tiles from the receiving features to the upper surface of the tiles. The inventors believe that the cracks are caused by stresses imposed by the pins, as explained below with reference to
As set forth above in relation to
The angled outer portion 1502 of the receiving features 1304 serves to distribute the stress across a broader surface area, compared to the embodiment described with reference to
As set forth above in relation to
According to an embodiment, the outside dimensions of the strain relief member 1604 are selected to be equal to or larger than the dimensions of the receiving features 1304, so that the strain relief member 1604 engages the receiving features 1304 with a limited friction or interference fit.
As set forth above in relation to
At their outermost edges, the ridges 1706 preferably have a thickness that is much less than a thickness TW of the perforation walls 208 that define the receiving feature 1304. According to an embodiment, the ridges 1706 have a smallest thickness that is less than about 10% the thickness TW of the perforation walls 208. Because the ridges 1706 have a smallest thickness that is much less than the thickness TW of the perforation walls 208, they are relatively quite fragile. Thus, when the burner tiles 402 of the perforated flame holder 1700 move with relation to each other, and stress is applied—as described above with respect to
As set forth above in relation to
The spline 1804 can be flat and sufficiently broad as to occupy most of the combined depths of the grooves 1802a and 1802b. While shown as having lateral sides that are square, according to various embodiments, the lateral edges of the spline 1804 can have any shape that does not interfere with its operation, such as, e.g., rounded, chamfered, bull nosed, etc.
One potential advantage of the spline 1804 is that it can serve to distribute the stress load over a broad surface area, and reduce or prevent the occurrence of stress cracks in burner tiles 402.
According to an embodiment, the grooves 1802 extend the length of the burner tiles 402. According to another embodiment, the grooves 1802a, 1802b extend less than half the length of the respective burner tiles 402a, 402b.
According to an embodiment, the spline 1804 extends the length of an entire row of burner tiles 402 of the perforated flame holder 1800, and engages the grooves 1802 of each of the burner tiles 402 of two facing rows of burner tiles 402 of the perforated flame holder 1800. According to another embodiment, the spline 1804 is substantially equal in length to the grooves 1802. According to respective alternative embodiments, the length-to-height ratio of the spline 1804 is less than 2:1, less than 4:1, and less than 10:1.
The spline 1804 can be sized to extend the entire length of the grooves 1802, or to extend beyond the burner tiles 402a, 402b and engage the grooves of additional burner tiles 402. However, it is not essential that the spline 1804 occupy the entire length of the burner tiles 402. For example, according to an embodiment, the grooves 1802 extend the full length of the burner tiles 402, while the splines 1804 are less than half the length of the grooves 1802.
The grooves 1802 can be formed in any of a number of different ways. For example, a cutting tool such as an end mill, router, or flat bed tile saw can be used to form a groove 1802 of any length in a lateral face of a burner tile 402. Such a groove 1802 can be made to extend the entire length of the burner tile 402, or to be shorter than the length of the burner tile 402.
The spline 1804 can be sized to extend the entire length of the grooves 1802, or to extend beyond the burner tiles 402a, 402b and engage the grooves of additional burner tiles 402. However, it is not essential that the spline 1804 occupy the entire length of the burner tiles 402. For example, according to an embodiment, the grooves 1802 may extend the full length of the burner tiles 402, while the splines 1804 are a fraction of the length of the grooves 1802.
On the one hand, it may be most economical to manufacture the burner tiles 402 with the channels 1802 extending their entire lengths. On the other hand, the splines 1804 occlude perforations 110 of the burner tiles 402 along their length, and in many embodiments, a relatively short spline 1804 is sufficient to adequately distribute the stress load. Where a channel 1802 is unoccupied by a spline 1804, the perforations 110 of the burner tile 402 will operate adequately to hold a flame under most conditions.
As set forth above in relation to
According to an embodiment, the perforated flame holder body 108 can include reticulated fibers 1939. The reticulated fibers 1939 can define branching perforations 110 that weave around and through the reticulated fibers 1939. According to an embodiment, the perforations 110 are formed as passages through the reticulated ceramic fibers 1939.
According to an embodiment, the reticulated fibers 1939 can include alumina silicate. According to an embodiment, the reticulated fibers 1939 can be formed from extruded mullite or cordierite. According to an embodiment, the reticulated fibers 1939 can include Zirconia. According to an embodiment, the reticulated fibers 1939 can include silicon carbide.
The term “reticulated fibers” refers to a netlike structure. According to an embodiment, the reticulated fibers 1939 are formed from an extruded ceramic material. In reticulated fiber embodiments, the interaction between the fuel and oxidant mixture 106, the combustion reaction 202, and heat transfer to and from the perforated flame holder body 108 can function similarly to the embodiment shown and described above with respect to
According to an embodiment, the reticulated fiber network is sufficiently open for downstream reticulated fibers 1939 to emit radiation for receipt by upstream reticulated fibers 1939 for the purpose of heating the upstream reticulated fibers 1939 sufficiently to maintain combustion of a fuel and oxidant mixture 106. Compared to a continuous perforated flame holder body 108, heat conduction paths 212 between reticulated fibers 1939 are reduced due to separation of the reticulated fibers 1939. This may cause relatively more heat to be transferred from the heat-receiving region 206 (heat receiving area) to the heat-output region 210 (heat output area) of the reticulated fibers 1939 via thermal radiation 204.
According to an embodiment, individual perforations 110 may extend from an input face 112 to an output face 114 of the perforated flame holder 102. Perforations 110 may have varying lengths L. According to an embodiment, because the perforations 110 branch into and out of each other, individual perforations 110 are not clearly defined by a length L.
According to an embodiment, the perforated flame holder 102 is configured to support or hold a combustion reaction 202 or a flame at least partially between the input face 112 and the output face 114. According to an embodiment, the input face 112 corresponds to a surface of the perforated flame holder 102 proximal to the fuel nozzle 118 or to a surface that first receives fuel. According to an embodiment, the input face 112 corresponds to an extent of the reticulated fibers 1939 proximal to the fuel nozzle 118. According to an embodiment, the output face 114 corresponds to a surface distal to the fuel nozzle 118 or opposite the input face 112. According to an embodiment, the input face 112 corresponds to an extent of the reticulated fibers 1939 distal to the fuel nozzle 118 or opposite to the input face 112.
According to an embodiment, the formation of boundary layers 214, transfer of heat between the perforated reaction holder body 108 and the gases flowing through the perforations 110, a characteristic perforation width dimension D, and the length L can be regarded as related to an average or overall path through the perforated reaction holder 102. In other words, the dimension D can be determined as a root-mean-square of individual Dn values determined at each point along a flow path. Similarly, 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 TRH from the input face 112 to the output face 114 through the perforated reaction holder 102. According to an embodiment, the void fraction (expressed as (total perforated reaction holder 102 volume−fiber 1939 volume)/total volume) is about 70%.
According to an embodiment, the reticulated ceramic perforated flame holder 102 is a tile about 1″×4″×4″. According to an embodiment, the reticulated ceramic perforated flame holder 102 includes about 10 pores per inch, meaning that a line laid across the surface of the perforated flame holder 102 would cross about 10 pores per inch. Other materials and dimensions can also be used for a reticulated ceramic perforated flame holder 102 in accordance with principles of the present disclosure.
According to an embodiment, the reticulated ceramic perforated flame holder 102 can include shapes and dimensions other than those described herein. For example, the perforated flame holder 102 can include reticulated ceramic tiles 402 that are larger or smaller than the dimensions set forth above. Additionally, the reticulated ceramic perforated flame holder 102 can include shapes other than generally cuboid shapes.
According to an embodiment, the reticulated ceramic perforated flame holder 102 can include multiple reticulated ceramic burner tiles 402. The multiple reticulated ceramic tiles can be joined together such that each ceramic tile is in direct contact with one or more adjacent reticulated ceramic burner tiles 402. The multiple reticulated ceramic tiles 402 can collectively form a single perforated flame holder 102. Alternatively, each reticulated ceramic burner tile 402 can be considered a distinct perforated flame holder 102.
According to an alternate embodiment, the combustion system 1900 can include a horizontally fired combustion system in which the fuel and oxidant source 103 outputs the fuel and oxidant mixture 106 horizontally, and the reticulated ceramic perforated flame holder 102 is oriented to receive the fuel and oxidant horizontally.
According to an embodiment, the portion of the support member 406 that protrudes from the burner tile 402 is configured to be received into a receiving feature 404 of the second burner tile 402. When the support member 406 is positioned in the receiving feature 404 of the second burner tile 402, the two burner tiles 402 are coupled together. The two burner tiles 402, when coupled together, form a perforated flame holder 102. Alternatively, each individual burner tile 402 can be a perforated flame holder 102.
According to an embodiment, the burner tile 402 can include multiple receiving features 404, each configured to receive a support member 406 substantially similar to the support member 406 shown in
According to an embodiment, the support member 406, is configured to couple to a support structure to hold the burner tile 402 in alignment to receive a mixture of fuel and air. According to an embodiment, the burner tile 402 can include multiple support members 406 configured to couple to the support structure.
Arrows indicating X, Y, and Z-axes are provided in many of the drawings. These are intended to aid a viewer in recognizing the relationship of the drawings with each other. Except as explained below, neither the arrows nor the orientation of the structures depicted in the drawings is intended to suggest any necessary orientation of physical structures on which the claims read. Accordingly, unless defined otherwise, the claims can be read on any structure that otherwise conforms to the claim language, without regard to its orientation.
As used herein, the term longitudinal refers to a direction or dimension along an axis that is substantially parallel to a general direction of flow of fuel and combustion gases through or around a burner tile or perforated flame holder, such as, e.g., the perforated flame holder 102 described with reference to
In many of the drawings, elements are designated with a reference number followed by a letter, e.g., “218a, 218b.” In such cases, the letter designation is used where it may be useful in the corresponding description to differentiate between otherwise similar or identical elements. Where the description omits the letter from a reference, and refers to such elements by number only, this can be understood as a general reference to all the elements identified by that reference number, unless other distinguishing language is used.
Ordinal numbers, e.g., first, second, third, etc., are used in the claims according to conventional claim practice, i.e., for the purpose of clearly distinguishing between claimed elements or features thereof. The use of such numbers does not suggest any other relationship, e.g., order of operation or relative position of such elements, etc. Furthermore, an ordinal number used to refer to an element in a claim does not necessarily correlate to a number used in the specification to refer to an element of a disclosed embodiment on which that claim reads, nor to numbers used in unrelated claims to designate similar elements or features.
The abstract of the present disclosure is provided as a brief outline of some of the principles of the invention according to one embodiment, and is not intended as a complete or definitive description of any embodiment thereof, nor should it be relied upon to define terms used in the specification or claims. The abstract does not limit the scope of the claims.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated, including the combination of elements selected from different disclosed embodiments to create further embodiments. 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 claims.
The present application is a U.S. Continuation-in-Part application which claims priority benefit under 35 U.S.C. § 120 (pre-AIA) of co-pending International Patent Application No. PCT/US2017/046372, entitled “PERFORATED FLAME HOLDER SUPPORT MEMBER FOR STRUCTURAL INTEGRITY,” filed Aug. 10, 2017 (docket number 2651-283-04). International Patent Application No. PCT/US2017/046372 claims priority benefit from U.S. Provisional Patent Application No. 62/376,776, entitled “PERFORATED FLAME HOLDER SUPPORT MEMBER FOR STRUCTURAL INTEGRITY,” filed Aug. 18, 2016 (docket number 2651-283-02), now expired. Each of the foregoing applications, to the extent not inconsistent with the disclosure herein, is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 20190257516 A1 | Aug 2019 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61765022 | Feb 2013 | US | |
| 61931407 | Jan 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2014/016632 | Feb 2014 | US |
| Child | 14741264 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2017/046372 | Aug 2017 | US |
| Child | 16279032 | US | |
| Parent | 14741264 | Jun 2015 | US |
| Child | PCT/US2017/046372 | US |
