Patent Application
20180038588
According to an embodiment, a combustion system includes a furnace body defining a furnace volume. A fuel and oxidant source and a perforated flame holder are positioned within the furnace volume. A support structure is fixed to the furnace body and supports the perforated flame holder at a selected distance from the fuel and oxidant source. The fuel and oxidant source outputs fuel and oxidant onto the perforated flame holder. The perforated flame holder supports a combustion reaction of the fuel and oxidant within the perforated flame holder. Because the support structure supports the perforated flame holder at the selected distance from the fuel and oxidant source, the perforated flame holder can stably support the combustion reaction of the fuel and oxidant within the perforated flame holder.
According to an embodiment, a method for operating a combustion system includes supporting, with a support structure fixed to a furnace body, a perforated flame holder at a selected distance from a fuel and oxidant source, outputting fuel and oxidant from the fuel and oxidant source, and receiving the fuel and oxidant in the perforated flame holder positioned to receive the fuel and oxidant from the fuel and oxidant source. The method further includes supporting a majority of a combustion reaction of the fuel and oxidant within the perforated flame holder.
According to an embodiment, a combustion system includes an enclosure defining an interior volume, a fuel and oxidant source disposed within the enclosure and configured to output fuel and oxidant, and a perforated flame holder disposed to receive the fuel and oxidant from the fuel and oxidant source and to support a combustion reaction of the fuel and oxidant within the perforated flame holder. The combustion system further includes a first support arm coupled between the enclosure and the perforated flame holder and configured to support the perforated flame holder within the enclosure at a selected distance from the fuel and oxidant source.
According to an embodiment, a combustion system includes a furnace wall defining a furnace volume, a fuel and oxidant source configured to output fuel and oxidant into the furnace volume, and a perforated flame holder disposed within the furnace volume and configured to hold a combustion reaction of the fuel and oxidant. A support structure is configured to hold the perforated flame holder in alignment with the fuel and oxidant output by the fuel and oxidant source.
According to an embodiment, the support structure may be a cooled support structure having an interior channel configured to pass a fluid coolant therethrough.
According to an embodiment, the support structure may be a movable support structure configured to move the perforated flame holder relative to the fuel and oxidant source.
According to an embodiment, a method of operating a combustion system includes outputting fuel and oxidant from a fuel and oxidant source and supporting, with a support structure, a perforated flame holder in alignment with the fuel and oxidant source. The fuel and oxidant are received into the perforated flame holder. The perforated flame holder holds a combustion reaction of the fuel and oxidant within the perforated flame holder.
According to an embodiment, a combustion system includes a fuel and oxidant source configured to output fuel and oxidant and a perforated flame holder configured to receive the fuel and oxidant and to hold a combustion reaction of the fuel and oxidant within the perforated flame holder. A support structure is configured to hold the perforated flame holder in alignment to receive the fuel and oxidant source and to adjust a position of the perforated flame holder. At least one sensor is configured to sense at least one parameter of the combustion reaction and to output one or more sensor signals. A controller is configured to receive the one or more sensor signals and to cause actuation of the support structure to adjust the position of the perforated flame holder based on the one or more sensor signals.
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. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the disclosure.
The fuel and oxidant source 104 outputs fuel and oxidant into the furnace volume 106. The perforated flame holder 102 receives the fuel and oxidant from the fuel and oxidant source 104 and supports a combustion reaction of the fuel and oxidant within the perforated flame holder 102.
Characteristics of the combustion reaction within the perforated flame holder 102 depend, in part, on the distance between the fuel and oxidant source 104 and the perforated flame holder 102. The support structure 108 supports the perforated flame holder 102 in a stable position at the selected distance from the fuel and oxidant source 104. In this way, the combustion reaction of the fuel and oxidant can be stably supported within the perforated flame holder 102.
Experiments performed by the inventors have shown that perforated flame holders 102 described herein can support very clean combustion. Specifically, in experimental use of systems 200 ranging from pilot scale to full scale, output of oxides of nitrogen (NOx) was measured to range from low single digit parts per million (ppm) down to undetectable (less than 1 ppm) concentration of NOx at the stack. These remarkable results were measured at 3% (dry) oxygen (O2) concentration with undetectable carbon monoxide (CO) at stack temperatures typical of industrial furnace applications (1400-1600° F.). Moreover, these results did not require any extraordinary measures such as selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), water/steam injection, external flue gas recirculation (FGR), or other heroic extremes that may be required for conventional burners to even approach such clean combustion.
According to embodiments, the burner system 200 includes a fuel and oxidant source 202 disposed to output fuel and oxidant into a combustion volume 204 to form a fuel and oxidant mixture 206. As used herein, the terms fuel and oxidant mixture and fuel stream may be used interchangeably and considered synonymous depending on the context, unless further definition is provided. As used herein, the terms combustion volume, combustion chamber, furnace volume, and the like shall be considered synonymous unless further definition is provided. The perforated flame holder 102 is disposed in the combustion volume 204 and positioned to receive the fuel and oxidant mixture 206.
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, the perforated flame holder body 208 can be bounded by an input face 212 disposed to receive the fuel and oxidant mixture 206, an output face 214 facing away from the fuel and oxidant source 202, and a peripheral surface 216 defining a lateral extent of the perforated flame holder 102. The plurality of perforations 210 which are defined by the perforated flame holder body 208 extend from the input face 212 to the output face 214. The plurality of perforations 210 can receive the fuel and oxidant mixture 206 at the input face 212. The fuel and oxidant mixture 206 can then combust in or near the plurality of perforations 210 and combustion products can exit the plurality of perforations 210 at or near the output face 214.
According to an embodiment, the perforated flame holder 102 is configured to hold a majority of the combustion reaction 302 within the perforations 210. For example, on a steady-state basis, more than half the molecules of fuel output into the combustion volume 204 by the fuel and oxidant source 202 may be converted to combustion products between the input face 212 and the output face 214 of the perforated flame holder 102. According to an alternative interpretation, more than half of the heat or thermal energy output by the combustion reaction 302 may be output between the input face 212 and the output face 214 of the perforated flame holder 102. As used herein, the terms heat, heat energy, and thermal energy shall be considered synonymous unless further definition is provided. As used above, heat energy and thermal energy refer generally to the released chemical energy initially held by reactants during the combustion reaction 302. As used elsewhere herein, heat, heat energy and thermal energy correspond to a detectable temperature rise undergone by real bodies characterized by heat capacities. Under nominal operating conditions, the perforations 210 can be configured to collectively hold at least 80% of the combustion reaction 302 between the input face 212 and the output face 214 of the perforated flame holder 102. In some experiments, the inventors produced a combustion reaction 302 that was apparently wholly contained in the perforations 210 between the input face 212 and the output face 214 of the perforated flame holder 102. According to an alternative interpretation, the perforated flame holder 102 can support combustion between the input face 212 and output face 214 when combustion is “time-averaged.” For example, during transients, such as before the perforated flame holder 102 is fully heated, or if too high a (cooling) load is placed on the system, the combustion may travel somewhat downstream from the output face 214 of the perforated flame holder 102. Alternatively, if the cooling load is relatively low and/or the furnace temperature reaches a high level, the combustion may travel somewhat upstream of the input face 212 of the perforated flame holder 102.
While a “flame” is described in a manner intended for ease of description, it should be understood that in some instances, no visible flame is present. Combustion occurs primarily within the perforations 210, but the “glow” of combustion heat is dominated by a visible glow of the perforated flame holder 102 itself. In other instances, the inventors have noted transient “huffing” or “flashback” wherein a visible flame momentarily ignites in a region lying between the input face 212 of the perforated flame holder 102 and the fuel nozzle 218, within the dilution region 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 210 of the perforated flame holder 102, between the input face 212 and the output face 214. In still other instances, the inventors have noted apparent combustion occurring downstream from the output face 214 of the perforated flame holder 102, but still a majority of combustion occurred within the perforated flame holder 102 as evidenced by continued visible glow from the perforated flame holder 102 that was observed.
The perforated flame holder 102 can be configured to receive heat from the combustion reaction 302 and output a portion of the received heat as thermal radiation 304 to heat-receiving structures (e.g., furnace walls and/or radiant section working fluid tubes) in or adjacent to the combustion volume 204. As used herein, terms such as radiation, thermal radiation, radiant heat, heat radiation, etc. are to be construed as being substantially synonymous, unless further definition is provided. Specifically, such terms refer to blackbody-type radiation of electromagnetic energy, primarily at infrared wavelengths, but also at visible wavelengths owing to elevated temperature of the perforated flame holder body 208.
Referring especially to
The perforated flame holder body 208 can be characterized by a heat capacity. The perforated flame holder body 208 may hold thermal energy from the combustion reaction 302 in an amount corresponding to the heat capacity multiplied by temperature rise, and transfer the thermal energy from the heat receiving regions 306 to heat output regions 310 of the perforation walls 308. Generally, the heat output regions 310 are nearer to the input face 212 than are the heat receiving regions 306. According to one interpretation, the perforated flame holder body 208 can transfer heat from the heat receiving regions 306 to the heat output regions 310 via thermal radiation, depicted graphically as 304. According to another interpretation, the perforated flame holder body 208 can transfer heat from the heat receiving regions 306 to the heat output regions 310 via heat conduction along heat conduction paths 312. The inventors contemplate that multiple heat transfer mechanisms including conduction, radiation, and possibly convection may be operative in transferring heat from the heat receiving regions 306 to the heat output regions 310. In this way, the perforated flame holder 102 may act as a heat source to maintain the combustion reaction 302, even under conditions where a combustion reaction 302 would not be stable when supported from a conventional flame holder.
The inventors believe that the perforated flame holder 102 causes the combustion reaction 302 to begin within thermal boundary layers 314 formed adjacent to walls 308 of the perforations 210. Insofar as combustion is generally understood to include a large number of individual reactions, and since a large portion of combustion energy is released within the perforated flame holder 102, it is apparent that at least a majority of the individual reactions occur within the perforated flame holder 102. As the relatively cool fuel and oxidant mixture 206 approaches the input face 212, the flow is split into portions that respectively travel through individual perforations 210. The hot perforated flame holder body 208 transfers heat to the fluid, notably within thermal boundary layers 314 that progressively thicken as more and more heat is transferred to the incoming fuel and oxidant mixture 206. After reaching a combustion temperature (e.g., the auto-ignition temperature of the fuel), the reactants continue to flow while a chemical ignition delay time elapses, over which time the combustion reaction 302 occurs. Accordingly, the combustion reaction 302 is shown as occurring within the thermal boundary layers 314. As flow progresses, the thermal boundary layers 314 merge at a merger point 316. Ideally, the merger point 316 lies between the input face 212 and output face 214 that define the ends of the perforations 210. At some position along the length of a perforation 210, the combustion reaction 302 outputs more heat to the perforated flame holder body 208 than it receives from the perforated flame holder body 208. The heat is received at the heat receiving region 306, is held by the perforated flame holder body 208, and is transported to the heat output region 310 nearer to the input face 212, where the heat is transferred into the cool reactants (and any included diluent) to bring the reactants to the ignition temperature.
In an embodiment, each of the perforations 210 is characterized by a length L defined as a reaction fluid propagation path length between the input face 212 and the output face 214 of the perforated flame holder 102. As used herein, the term reaction fluid refers to matter that travels through a perforation 210. Near the input face 212, the reaction fluid includes the fuel and oxidant mixture 206 (optionally including nitrogen, flue gas, and/or other “non-reactive” species). Within the combustion reaction region, the reaction fluid may include plasma associated with the combustion reaction 302, molecules of reactants and their constituent parts, any non-reactive species, reaction intermediates (including transition states), and reaction products. Near the output face 214, the reaction fluid may include reaction products and byproducts, non-reactive gas, and excess oxidant.
The plurality of perforations 210 can be each characterized by a transverse dimension D between opposing perforation walls 308. The inventors have found that stable combustion can be maintained in the perforated flame holder 102 if the length L of each perforation 210 is at least four times the transverse dimension D of the perforation. In other embodiments, the length L can be greater than six times the transverse dimension D. For example, experiments have been run where L is at least eight, at least twelve, at least sixteen, and at least twenty-four times the transverse dimension D. Preferably, the length L is sufficiently long for thermal boundary layers 314 to form adjacent to the perforation walls 308 in a reaction fluid flowing through the perforations 210 to converge at merger points 316 within the perforations 210 between the input face 212 and the output face 214 of the perforated flame holder 102. In experiments, the inventors have found L/D ratios between 12 and 48 to work well (i.e., produce low NOx, produce low CO, and maintain stable combustion).
The perforated flame holder body 208 can be configured to convey heat between adjacent perforations 210. The heat conveyed between adjacent perforations 210 can be selected to cause heat output from the combustion reaction portion 302 in a first perforation 210 to supply heat to stabilize a combustion reaction portion 302 in an adjacent perforation 210.
Referring especially to
The perforated flame holder 102 can be held by a perforated flame holder support structure 222 configured to hold the perforated flame holder 102 at a dilution distance DD away from the fuel nozzle 218. The fuel nozzle 218 can be configured to emit a fuel jet selected to entrain the oxidant to form the fuel and oxidant mixture 206 as the fuel jet and oxidant travel along a path to the perforated flame holder 102 through the dilution distance DD between the fuel nozzle 218 and the perforated flame holder 102. Additionally or alternatively (particularly when a blower is used to deliver oxidant contained in combustion air), the oxidant or combustion air source can be configured to entrain the fuel and the fuel and oxidant travel through the dilution distance DD. In some embodiments, a flue gas recirculation path 224 can be provided. Additionally or alternatively, the fuel nozzle 218 can be configured to emit a fuel jet selected to entrain the oxidant and to entrain flue gas as the fuel jet travels through the dilution distance DD between the fuel nozzle 218 and the input face 212 of the perforated flame holder 102.
The fuel nozzle 218 can be configured to emit the fuel through one or more fuel orifices 226 having an inside diameter dimension that is referred to as “nozzle diameter.” The perforated flame holder support structure 222 can support the perforated flame holder 102 to receive the fuel and oxidant mixture 206 at the distance DD away from the fuel nozzle 218 greater than 20 times the nozzle diameter. In another embodiment, the perforated flame holder 102 is disposed to receive the fuel and oxidant mixture 206 at the distance DD away from the fuel nozzle 218 between 100 times and 1100 times the nozzle diameter. Preferably, the perforated flame holder support structure 222 is configured to hold the perforated flame holder 102 at a distance about 200 times or more of the nozzle diameter away from the fuel nozzle 218. When the fuel and oxidant mixture 206 travels about 200 times the nozzle diameter or more, the mixture is sufficiently homogenized to cause the combustion reaction 302 to produce minimal NOx.
The fuel and oxidant source 202 can alternatively include a premix fuel and oxidant source, according to an embodiment. A premix fuel and oxidant source can include a premix chamber (not shown), a fuel nozzle configured to output fuel into the premix chamber, and an oxidant (e.g., combustion air) channel configured to output the oxidant into the premix chamber. A flame arrestor can be disposed between the premix fuel and oxidant source and the perforated flame holder 102 and be configured to prevent flame flashback into the premix fuel and oxidant source.
The oxidant source 220, whether configured for entrainment in the combustion volume 204 or for premixing, can include a blower configured to force the oxidant through the fuel and oxidant source 202.
The support structure 222 can be configured to support the perforated flame holder 102 from a floor or wall (not shown) of the combustion volume 204, for example. In another embodiment, the support structure 222 supports the perforated flame holder 102 from the fuel and oxidant source 202. Alternatively, the support structure 222 can suspend the perforated flame holder 102 from an overhead structure (such as a flue, in the case of an up-fired system). The support structure 222 can support the perforated flame holder 102 in various orientations and directions.
The perforated flame holder 102 can include a single perforated flame holder body 208. In another embodiment, the perforated flame holder 102 can include a plurality of adjacent perforated flame holder sections that collectively provide a tiled perforated flame holder 102.
The perforated flame holder support structure 222 can be configured to support the plurality of perforated flame holder sections. The perforated flame holder support structure 222 can include a metal superalloy, a cementatious, and/or ceramic refractory material. In an embodiment, the plurality of adjacent perforated flame holder sections can be joined with a fiber reinforced refractory cement.
The perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 216 at least twice a thickness dimension T between the input face 212 and the output face 214. In another embodiment, the perforated flame holder 102 can have a width dimension W between opposite sides of the peripheral surface 216 at least three times, at least six times, or at least nine times the thickness dimension T between the input face 212 and the output face 214 of the perforated flame holder 102.
In an embodiment, the perforated flame holder 102 can have a width dimension W less than a width of the combustion volume 204. This can allow the flue gas circulation path 224 from above to below the perforated flame holder 102 to lie between the peripheral surface 216 of the perforated flame holder 102 and the furnace volume wall (not shown).
Referring again to both
In one range of embodiments, each of the plurality of perforations 210 has a lateral dimension D between 0.05 inch and 1.0 inch. Preferably, each of the plurality of perforations 210 has a lateral dimension D between 0.1 inch and 0.5 inch. For example the plurality of perforations 210 can each have a lateral dimension D of about 0.2 to 0.4 inch.
The void fraction of a perforated flame holder 102 is defined as the total volume of all perforations 210 in a section of the perforated flame holder 102 divided by a total volume of the perforated flame holder 102 including body 208 and perforations 210. The perforated flame holder 102 should have a void fraction between 0.10 and 0.90. In an embodiment, the perforated flame holder 102 can have a void fraction between 0.30 and 0.80. In another embodiment, the perforated flame holder 102 can have a void fraction of about 0.70. Using a void fraction of about 0.70 was found to be especially effective for producing very low NOx.
The perforated flame holder 102 can be formed from a fiber reinforced cast refractory material and/or a refractory material such as an aluminum silicate material. For example, the perforated flame holder 102 can be formed to include mullite or cordierite. Additionally or alternatively, the perforated flame holder body 208 can include a metal superalloy such as Inconel or Hastelloy. The perforated flame holder body 208 can define a honeycomb. Honeycomb is an industrial term of art that need not strictly refer to a hexagonal cross section and most usually includes cells of square cross section. Honeycombs of other cross sectional areas are also known.
The inventors have found that the perforated flame holder 102 can be formed from VERSAGRID® ceramic honeycomb, available from Applied Ceramics, Inc. of Doraville, S.C.
The perforations 210 can be parallel to one another and normal to the input and output faces 212, 214. In another embodiment, the perforations 210 can be parallel to one another and formed at an angle relative to the input and output faces 212, 214. In another embodiment, the perforations 210 can be non-parallel to one another. In another embodiment, the perforations 210 can be non-parallel to one another and non-intersecting. In another embodiment, the perforations 210 can be intersecting. The body 308 can be one piece or can be formed from a plurality of sections.
In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from reticulated ceramic material. The term “reticulated” refers to a netlike structure. Reticulated ceramic material is often made by dissolving a slurry into a sponge of specified porosity, allowing the slurry to harden, and burning away the sponge and curing the ceramic.
In another embodiment, which is not necessarily preferred, the perforated flame holder 102 may be formed from a ceramic material that has been punched, bored or cast to create channels.
In another embodiment, the perforated flame holder 102 can include a plurality of tubes or pipes bundled together. The plurality of perforations 210 can include hollow cylinders and can optionally also include interstitial spaces between the bundled tubes. In an embodiment, the plurality of tubes can include ceramic tubes. Refractory cement can be included between the tubes and configured to adhere the tubes together. In another embodiment, the plurality of tubes can include metal (e.g., superalloy) tubes. The plurality of tubes can be held together by a metal tension member circumferential to the plurality of tubes and arranged to hold the plurality of tubes together. The metal tension member can include stainless steel, a superalloy metal wire, and/or a superalloy metal band.
The perforated flame holder body 208 can alternatively include stacked perforated sheets of material, each sheet having openings that connect with openings of subjacent and superjacent sheets. The perforated sheets can include perforated metal sheets, ceramic sheets and/or expanded sheets. In another embodiment, the perforated flame holder body 208 can include discontinuous packing bodies such that the perforations 210 are formed in the interstitial spaces between the discontinuous packing bodies. In one example, the discontinuous packing bodies include structured packing shapes. In another example, the discontinuous packing bodies include random packing shapes. For example, the discontinuous packing bodies can include ceramic Raschig ring, ceramic Berl saddles, ceramic Intalox saddles, and/or metal rings or other shapes (e.g. Super Raschig Rings) that may be held together by a metal cage.
The inventors contemplate various explanations for why burner systems including the perforated flame holder 102 provide such clean combustion.
According to an embodiment, the perforated flame holder 102 may act as a heat source to maintain a combustion reaction even under conditions where a combustion reaction would not be stable when supported by a conventional flame holder. This capability can be leveraged to support combustion using a leaner fuel-to-oxidant mixture than is typically feasible. Thus, according to an embodiment, at the point where the fuel stream 206 contacts the input face 212 of the perforated flame holder 102, an average fuel-to-oxidant ratio of the fuel stream 206 is below a (conventional) lower combustion limit of the fuel component of the fuel stream 206—lower combustion limit defines the lowest concentration of fuel at which a fuel and oxidant mixture 206 will burn when exposed to a momentary ignition source under normal atmospheric pressure and an ambient temperature of 25° C. (77° F.).
The perforated flame holder 102 and systems including the perforated flame holder 102 described herein were found to provide substantially complete combustion of CO (single digit ppm down to undetectable, depending on experimental conditions), while supporting low NOx. According to one interpretation, such a performance can be achieved due to a sufficient mixing used to lower peak flame temperatures (among other strategies). Flame temperatures tend to peak under slightly rich conditions, which can be evident in any diffusion flame that is insufficiently mixed. By sufficiently mixing, a homogenous and slightly lean mixture can be achieved prior to combustion. This combination can result in reduced flame temperatures, and thus reduced NOx formation. In one embodiment, “slightly lean” may refer to 3% O2, i.e. an equivalence ratio of ˜0.87. Use of even leaner mixtures is possible, but may result in elevated levels of O2. Moreover, the inventors believe perforation walls 308 may act as a heat sink for the combustion fluid. This effect may alternatively or additionally reduce combustion temperatures and lower NOx.
According to another interpretation, production of NOx can be reduced if the combustion reaction 302 occurs over a very short duration of time. Rapid combustion causes the reactants (including oxygen and entrained nitrogen) to be exposed to NOx-formation temperature for a time too short for NOx formation kinetics to cause significant production of NOx. The time required for the reactants to pass through the perforated flame holder 102 is very short compared to a conventional flame. The low NOx production associated with perforated flame holder combustion may thus be related to the short duration of time required for the reactants (and entrained nitrogen) to pass through the perforated flame holder 102.
According to a simplified description, the method 400 begins with step 402, wherein the perforated flame holder is preheated to a start-up temperature, TS. After the perforated flame holder is raised to the start-up temperature, the method proceeds to step 404, wherein the fuel and oxidant are provided to the perforated flame holder and combustion is held by the perforated flame holder.
According to a more detailed description, step 402 begins with step 406, wherein start-up energy is provided at the perforated flame holder. Simultaneously or following providing start-up energy, a decision step 408 determines whether the temperature T of the perforated flame holder is at or above the start-up temperature, TS. As long as the temperature of the perforated flame holder is below its start-up temperature, the method loops between steps 406 and 408 within the preheat step 402. In step 408, if the temperature T of at least a predetermined portion of the perforated flame holder is greater than or equal to the start-up temperature, the method 400 proceeds to overall step 404, wherein fuel and oxidant is supplied to and combustion is held by the perforated flame holder.
Step 404 may be broken down into several discrete steps, at least some of which may occur simultaneously.
Proceeding from step 408, a fuel and oxidant mixture is provided to the perforated flame holder, as shown in step 410. The fuel and oxidant may be provided by a fuel and oxidant source that includes a separate fuel nozzle and oxidant (e.g., combustion air) source, for example. In this approach, the fuel and oxidant are output in one or more directions selected to cause the fuel and oxidant mixture to be received by the input face of the perforated flame holder. The fuel may entrain the combustion air (or alternatively, the combustion air may dilute the fuel) to provide a fuel and oxidant mixture at the input face of the perforated flame holder at a fuel dilution selected for a stable combustion reaction that can be held within the perforations of the perforated flame holder.
Proceeding to step 412, the combustion reaction is held by the perforated flame holder.
In step 414, heat may be output from the perforated flame holder. The heat output from the perforated flame holder may be used to power an industrial process, heat a working fluid, generate electricity, or provide motive power, for example.
In optional step 416, the presence of combustion may be sensed. Various sensing approaches have been used and are contemplated by the inventors. Generally, combustion held by the perforated flame holder is very stable and no unusual sensing requirement is placed on the system. Combustion sensing may be performed using an infrared sensor, a video sensor, an ultraviolet sensor, a charged species sensor, thermocouple, thermopile, flame rod, and/or other combustion sensing apparatuses. In an additional or alternative variant of step 416, a pilot flame or other ignition source may be provided to cause ignition of the fuel and oxidant mixture in the event combustion is lost at the perforated flame holder.
Proceeding to decision step 418, if combustion is sensed not to be stable, the method 400 may exit to step 424, wherein an error procedure is executed. For example, the error procedure may include turning off fuel flow, re-executing the preheating step 402, outputting an alarm signal, igniting a stand-by combustion system, or other steps. If, in step 418, combustion in the perforated flame holder is determined to be stable, the method 400 proceeds to decision step 420, wherein it is determined if combustion parameters should be changed. If no combustion parameters are to be changed, the method loops (within step 404) back to step 410, and the combustion process continues. If a change in combustion parameters is indicated, the method 400 proceeds to step 422, wherein the combustion parameter change is executed. After changing the combustion parameter(s), the method loops (within step 404) back to step 410, and combustion continues.
Combustion parameters may be scheduled to be changed, for example, if a change in heat demand is encountered. For example, if less heat is required (e.g., due to decreased electricity demand, decreased motive power requirement, or lower industrial process throughput), the fuel and oxidant flow rate may be decreased in step 422. Conversely, if heat demand is increased, then fuel and oxidant flow may be increased. Additionally or alternatively, if the combustion system is in a start-up mode, then fuel and oxidant flow may be gradually increased to the perforated flame holder over one or more iterations of the loop within step 404.
Referring again to
Various heating apparatuses have been used and are contemplated by the inventors. In some embodiments, the heater 228 can include a flame holder configured to support a flame disposed to heat the perforated flame holder 102. The fuel and oxidant source 202 can include a fuel nozzle 218 configured to emit a fuel stream 206 and an oxidant source 220 configured to output oxidant (e.g., combustion air) adjacent to the fuel stream 206. The fuel nozzle 218 and oxidant source 220 can be configured to output the fuel stream 206 to be progressively diluted by the oxidant (e.g., combustion air). The perforated flame holder 102 can be disposed to receive a diluted fuel and oxidant mixture 206 that supports a combustion reaction 302 that is stabilized by the perforated flame holder 102 when the perforated flame holder 102 is at an operating temperature. A start-up flame holder, in contrast, can be configured to support a start-up flame at a location corresponding to a relatively unmixed fuel and oxidant mixture that is stable without stabilization provided by the heated perforated flame holder 102.
The burner system 200 can further include a controller 230 operatively coupled to the heater 228 and to a data interface 232. For example, the controller 230 can be configured to control a start-up flame holder actuator configured to cause the start-up flame holder to hold the start-up flame when the perforated flame holder 102 needs to be pre-heated and to not hold the start-up flame when the perforated flame holder 102 is at an operating temperature (e.g., when T≧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 206 to cause heat-recycling and/or stabilizing vortices and thereby hold a start-up flame; or to be actuated to not intercept the fuel and oxidant mixture 206 to cause the fuel and oxidant mixture 206 to proceed to the perforated flame holder 102. In another embodiment, a fuel control valve, blower, and/or damper may be used to select a fuel and oxidant mixture flow rate that is sufficiently low for a start-up flame to be jet-stabilized; and upon reaching a perforated flame holder 102 operating temperature, the flow rate may be increased to “blow out” the start-up flame. In another embodiment, the heater 228 may include an electrical power supply operatively coupled to the controller 230 and configured to apply an electrical charge or voltage to the fuel and oxidant mixture 206. An electrically conductive start-up flame holder may be selectively coupled to a voltage ground or other voltage selected to attract the electrical charge in the fuel and oxidant mixture 206. The attraction of the electrical charge was found by the inventors to cause a start-up flame to be held by the electrically conductive start-up flame holder.
In another embodiment, the heater 228 may include an electrical resistance heater configured to output heat to the perforated flame holder 102 and/or to the fuel and oxidant mixture 206. The electrical resistance heater can be configured to heat up the perforated flame holder 102 to an operating temperature. The heater 228 can further include a power supply and a switch operable, under control of the controller 230, to selectively couple the power supply to the electrical resistance heater.
An electrical resistance heater 228 can be formed in various ways. For example, the electrical resistance heater 228 can be formed from KANTHAL® wire (available from Sandvik Materials Technology division of Sandvik AB of Hallstahammar, Sweden) threaded through at least a portion of the perforations 210 defined by the perforated flame holder body 208. Alternatively, the heater 228 can include an inductive heater, a high-energy beam heater (e.g. microwave or laser), a frictional heater, electro-resistive ceramic coatings, or other types of heating technologies.
Other forms of start-up apparatuses are contemplated. For example, the heater 228 can include an electrical discharge igniter or hot surface igniter configured to output a pulsed ignition to the oxidant and fuel. Additionally or alternatively, a start-up apparatus can include a pilot flame apparatus disposed to ignite the fuel and oxidant mixture 206 that would otherwise enter the perforated flame holder 102. The electrical discharge igniter, hot surface igniter, and/or pilot flame apparatus can be operatively coupled to the controller 230, which can cause the electrical discharge igniter or pilot flame apparatus to maintain combustion of the fuel and oxidant mixture 206 in or upstream from the perforated flame holder 102 before the perforated flame holder 102 is heated sufficiently to maintain combustion.
The burner system 200 can further include a sensor 234 operatively coupled to the control circuit 230. The sensor 234 can include a heat sensor configured to detect infrared radiation or a temperature of the perforated flame holder 102. The control circuit 230 can be configured to control the heating apparatus 228 responsive to input from the sensor 234. Optionally, a fuel control valve 236 can be operatively coupled to the controller 230 and configured to control a flow of fuel to the fuel and oxidant source 202. Additionally or alternatively, an oxidant blower or damper 238 can be operatively coupled to the controller 230 and configured to control flow of the oxidant (or combustion air).
The sensor 234 can further include a combustion sensor operatively coupled to the control circuit 230, the combustion sensor being configured to detect a temperature, video image, and/or spectral characteristic of a combustion reaction held by the perforated flame holder 102. The fuel control valve 236 can be configured to control a flow of fuel from a fuel source to the fuel and oxidant source 202. The controller 230 can be configured to control the fuel control valve 236 responsive to input from the combustion sensor 234. The controller 230 can be configured to control the fuel control valve 236 and/or oxidant blower or damper to control a preheat flame type of heater 228 to heat the perforated flame holder 102 to an operating temperature. The controller 230 can similarly control the fuel control valve 236 and/or the oxidant blower or damper to change the fuel and oxidant mixture 206 flow responsive to a heat demand change received as data via the data interface 232.
According to an embodiment, the fuel nozzle 504 outputs a stream 507 of fuel and/or a mixture of fuel and oxidant onto the perforated flame holder 102. The oxidant can be provided to the furnace volume independent of the fuel nozzle 504. The perforated flame holder 102 supports a combustion reaction of the fuel and oxidant 507 within the perforated flame holder 102.
The characteristics of the combustion reaction within the perforated flame holder 102 depend, in part, on a distance that the fuel and/or fuel and oxidant travel between the fuel nozzle 504 and the perforated flame holder 102. The perforated flame holder 102 may not support the combustion reaction of the fuel and oxidant if the perforated flame holder 102 is not positioned at a proper distance from the fuel nozzle 504. The support structure 508 is configured to support the perforated flame holder 102 in a stable position at the selected distance from the fuel nozzle 504.
The support structure 508 includes one or more support arms 509 fixed to the floor 514 and coupled to the perforated flame holder 102. According to an embodiment, the support structure 508 includes two support arms 509 coupled to opposite sides of the perforated flame holder 102.
According to an embodiment, the support structure 508 is fixed to a side of the perforated flame holder 102. Alternatively, the perforated flame holder 102 can rest on the support structure 508.
According to an embodiment, the support structure 508 is fixed to the floor 514 by one or more screws or bolts. Alternatively, the support structure 508 can be fixed to the floor by a refractory cement material, by fitting into slots or grooves in the floor 514, or by gravity alone, for example.
According to an embodiment, the support structure 508 can include multiple finger members 515 (shown in
According to an embodiment, the support structure 508 can be covered by a thermal insulator and coupled to a structure for extracting heat from the insulated structure. Such structures for extracting heat (not shown) may include the use of a fluid coolant such as air, flue gas, steam, or water. Heat may optionally be extracted from the fluid coolant electronically using a Peltier cooler or by other means known to those skilled in the art. In transient operation, thermal insulation alone may allow the structural material to remain sufficiently cool. These or other methods can help prevent the support structure 508 from overheating to the point of becoming structurally unsound, thereby jeopardizing the stability of the positioning of the perforated flame holder 102. For example, the inventors have found that ordinary high temperature steel materials may undergo plastic deformation under the influence of furnace temperatures. Providing insulation and/or fluid coolant are contemplated to provide sufficient protection to avoid plastic deformation.
According to an embodiment, the support structure 508 can be coupled to the perforated flame holder 102 by one or more of gravity; a refractory cement material; superalloy or ceramic screws, bolts, pins, or clamps; or by fitting into grooves or slots in the perforated flame holder 102, for example.
According to an embodiment, the support structure 508 can include one or more of a metal superalloy (such as Inconel or Hastelloy), a ceramic material, a refractory brick, a refractory material, or a fiber reinforced refractory material.
According to an embodiment, the support structure 508 includes support arms coupled between the floor 514 and the perforated flame holder 102.
According to an embodiment, the brackets 513 can be fixed to the perforated flame holder 102 by gravity, screws, bolts, or pins, refractory cement, or other suitable mechanisms or materials for fixing a bracket to a support arm. The brackets 513 can include a metal or a metal superalloy, a ceramic or refractory material, and/or other materials suitable for being placed in a high temperature combustion environment. The brackets 513 can be of the same material as the support arms 509 and/or continuous with the support arms 509.
According to an embodiment, the finger members 515 are rods, bars, or other relatively long and thin structure suitable for supporting the perforated flame holder 102. As shown more clearly in a top view of
According to an embodiment, the brackets 513 can be fixed to the perforated flame holder 102 by a refractory cement material, metal, superalloy, or ceramic screws, bolts, pins, or clamps; or by fitting into grooves or slots in the perforated flame holder 102, for example. The brackets 513 can include a metal or a metal superalloy, a ceramic or refractory material, and/or other materials suitable for being placed in a high temperature combustion environment. The brackets 513 can be of the same material as the support arms 509.
According to an embodiment, the fuel nozzle 504 outputs a stream 507 of fuel and/or a mixture of fuel and oxidant 507 onto the perforated flame holder 102. The perforated flame holder 102 supports a combustion reaction of the fuel and oxidant 507 within the perforated flame holder 102.
The characteristics of the combustion reaction within the perforated flame holder 102 depend, in part, on a distance that the fuel and oxidant 507 travel between the fuel nozzle 504 and the perforated flame holder 102. The perforated flame holder 102 may not support the combustion reaction of the fuel and oxidant 507 if the perforated flame holder 102 is not positioned a proper distance from the fuel nozzle 504. The support structure 608 is configured to support the perforated flame holder 102 in a stable position at a selected distance from the fuel nozzle 504.
The support structure 608 includes two or more portions each fixed to the sidewall 512 and coupled to the perforated flame holder 102. According to an embodiment, the support structure 608 includes two support structure portions 609 coupled to opposite sides of the perforated flame holder 102.
According to an embodiment, the support structure 608 is fixed to a side of the perforated flame holder 102. Alternatively, the perforated flame holder 102 can rest on the support structure 608. According to an embodiment, the support structure 608 may include two or more layers of support arms 609 arranged in alternating directions, such as in a crisscrossed arrangement.
According to an embodiment, the support structure 608 is coupled to the sidewall 512 by gravity. In another embodiment the support structure 608 can be coupled to the sidewall 512 by one or more ceramic screws, bolts, or pins. Alternatively or additionally, the support structure 608 can be fixed to the sidewall 512 by a refractory cement material, by fitting into slots or grooves in the sidewall 512.
According to an embodiment, the support structure 608 can include multiple finger members 515 (shown and described in relation to
According to an embodiment, the support structure 608 can be covered by a thermal insulator and coupled to a method for extracting heat from the insulated structure. Such means of extracting heat (not shown) may include the use of a fluid coolant such as air, steam, or water. Heat may also be extracted electronically using a Peltier cooler or by other methods or structures known to those skilled in the art. In transient operation, thermal insulation alone may allow the structural material to remain sufficiently cool. These or other methods can help prevent the support structure 608 from overheating to the point of becoming structurally unsound, thereby jeopardizing the stability of the positioning of the perforated flame holder 102.
According to an embodiment, the support structure 608 can be coupled to the perforated flame holder 102 by one or more of gravity; a refractory cement; superalloy or ceramic screws, bolts, clamps, or pins; or by fitting into grooves or slots in the perforated flame holder 102; for example.
According to an embodiment, the support structure 608 can include one or more of a metal superalloy (such as Inconel or Hastelloy), a ceramic material, a refractory brick, a refractory material, or a fiber reinforced refractory material.
According to an embodiment, the support structure 608 includes support arms coupled between the wall 512 and the perforated flame holder 102.
According to an embodiment, the support arms 609 are finger members 515 such as rods, tubes, bars, or other relatively long and thin structure suitable for supporting the perforated flame holder 102. The support arms 609 pass through the walls 512 and are supported thereby. As shown more clearly in a top view of
According to an embodiment, the fuel nozzle 504 outputs a stream of fuel and/or a mixture of fuel and oxidant 507 onto the perforated flame holder 102. The perforated flame holder 102 supports a combustion reaction of the fuel and oxidant 507 within the perforated flame holder 102.
The characteristics of the combustion reaction within the perforated flame holder 102 depend, in part, on a distance that the fuel and oxidant 507 travel between the fuel nozzle 504 and the perforated flame holder 102. The perforated flame holder 102 may not support the combustion reaction of the fuel and oxidant 507 if the perforated flame holder 102 is not positioned a proper distance from the fuel nozzle 504. The support structure 708 is configured to support the perforated flame holder 102 in a stable position at a selected distance from the fuel nozzle 504.
The support structure 708 includes one or more support arms 709 each fixed to the ceiling 516 and coupled to the perforated flame holder 102. According to an embodiment, the support structure 708 includes two support arms 709 coupled to opposite sides of the perforated flame holder 102.
According to an embodiment, the support structure 708 is fixed to a side of the perforated flame holder 102. Alternatively, the perforated flame holder 102 can rest on the support structure 708.
According to an embodiment, the support structure 708 is fixed to the ceiling 516 by one or more superalloy or ceramic screws, bolts, or pins. Alternatively, the support structure 708 can pass through the ceiling 516 from outside the furnace body, or can be coupled into slots or grooves in the ceiling 516.
According to an embodiment, the support structure 708 can include multiple finger members 515 on which the perforated flame holder 102 rests. The finger members 515 can be configured to allow the fuel and oxidant 507 to pass between the thin finger members 515 to enter into the perforated flame holder 102 without significantly inhibiting the fuel and oxidant 507 from entering into the perforated flame holder 102. According to an embodiment, the perforated flame holder 102 can include multiple perforated flame holder sections fixed together. Each perforated flame holder section can be positioned on and supported by at least one of the thin finger members 515.
According to an embodiment, the support structure 708 can be covered by a thermal insulator and coupled to a method for extracting heat from the insulated structure. Such means of extracting heat (not shown) may include the use of a fluid coolant such as air, flue gas, steam, or water. Heat may also be extracted electronically using a Peltier cooler or by other structures or methods known to those skilled in the art. In transient operation, thermal insulation alone may allow the structural material to remain sufficiently cool. These or other methods can help prevent the support structure 708 from overheating to the point of becoming structurally unsound, thereby jeopardizing the stability of the positioning of the perforated flame holder 102.
According to an embodiment, the support structure 708 can be coupled to the perforated flame holder 102 by gravity, a refractory cement, superalloy or ceramic screws, bolts, clamps, or pins, or by fitting into grooves or slots in the perforated flame holder 102.
According to an embodiment, the support structure 708 can include one or more of a metal superalloy (such as Inconel or Hastelloy), a ceramic material, a refractory brick, a refractory material, or a fiber reinforced refractory material.
According to an embodiment, the support structure 708 includes support arms coupled between the ceiling 516 and the perforated flame holder 102.
The brackets 716 can include a metal or a metal superalloy, a ceramic or refractory material, and/or other materials suitable for being placed in a high temperature combustion environment. The brackets 716 can be of the same material as and/or continuous with the support arms 709.
According to an embodiment, the finger members 715 are rods, bars, or other relatively long and thin structure suitable for supporting the perforated flame holder 102. The finger members 715 are spaced apart from each other in such a way as to permit the fuel and oxidant 507 to enter the perforated flame holder 102. The finger members 715 can be discreet members positioned on the brackets 713 or a unitary grid positioned on the brackets 713. The finger members 715 can be fixed to the brackets 713 or can merely rest on the brackets 713. The finger members 715 can include a metal or a metal superalloy, a ceramic or refractory material, and/or other materials suitable for being placed in a high temperature combustion environment. The fingers 715 can be of the same material as the brackets 713 and/or the support arms 709.
The fuel and oxidant source 104 outputs fuel and oxidant onto the perforated flame holder 102. The perforated flame holder 102 receives the fuel and oxidant 507 and supports a combustion reaction of the fuel and oxidant 507 within the perforated flame holder 102.
Characteristics of the combustion reaction within the perforated flame holder 102 depend, in part, on a distance between the fuel and oxidant source 104 and the perforated flame holder 102. The cooled support structure 808 supports the perforated flame holder 102 in a stable position at the selected distance from the fuel and oxidant source 104.
According to an embodiment, the cooled support structure 808 can include an interior channel, such as a tube, a channel, or chamber through which the fluid coolant 812 can pass. In particular, the coolant source 814 can circulate or pass the fluid coolant 812 through the cooled support structure 808, thereby cooling the cooled support structure 808 and/or the perforated flame holder 102 and maintaining the cooled support structure 808 at a selected temperature or below a failure temperature.
According to an embodiment, the fluid coolant 812 can be a liquid and/or a gas. The coolant 812 can include water, flue gas, water vapor, or any other suitable fluid for cooling tubes 909 (shown in
According to an embodiment, the cooled support structure 908 includes tubes 909 passing through the sidewall 512 of the furnace body and coupled to a coolant source 814. Each tube 909 includes an interior channel 911 through which fluid coolant 812 can pass. The coolant source 814 passes the fluid coolant 812 through the tubes 909. The perforated flame holder 102 rests on the tubes 909.
As the fluid coolant 812 is passed through the interior channels 911 of the tubes 909 the fluid coolant 812 absorbs heat from the tubes 909, thereby cooling the tubes 909. As the tubes 909 are cooled, the perforated flame holder 102 is also cooled. In this way, the temperature of the tubes 909 forming the support structure 908 can be kept within a selected temperature range.
According to an embodiment, the tubes 909 can include a refractory material such as quartz, silicon carbide, or another material capable of withstanding a high temperature combustion environment.
According to an embodiment, the tubes 909 are connected with U shaped connectors outside the furnace walls 512 such that the tubes 909 form a single tube through which the fluid coolant 812 can pass. Alternatively, each tube 909 can be a separate tube coupled to the coolant source 814 and through which the fluid coolant 812 passes.
According to an embodiment, the support structure can be fixed to a sidewall, a ceiling, or a floor of a furnace defining the furnace volume. Because the support structure is fixed to one or more selected portions of the furnace body, the support structure can stably support the perforated flame holder at a selected distance from the fuel and oxidant source.
A fuel and oxidant source 104 provides a flow of fuel and oxidant mixture 206. Although the flow of the fuel and oxidant mixture 206 is depicted in
The perforated flame holder 102 is disposed transverse to the direction of flow of the fuel and oxidant mixture 206. The perforated flame holder is configured to receive the fuel and oxidant mixture 206 and hold the combustion reaction 302 of the fuel and oxidant mixture 206 within the perforated flame holder 102. According to an embodiment, the perforated flame holder 102 can be configured to support a majority of the combustion reaction 302 within the perforated flame holder 102.
The support structure 1108 can be configured to hold the perforated flame holder 102 at a selected position within the furnace wall 110. In particular, the support structure 1108 can support the perforated flame holder 102 in alignment with the fuel and oxidant source 104 so that the perforated flame holder receives the fuel and oxidant mixture 206 from the fuel and oxidant source 104 and support the combustion reaction of the fuel and oxidant mixture 206 within the perforated flame holder 102. The position of the perforated flame holder 102 can be selected based on one or more of a fuel flow rate, fuel nozzle diameter, mixture velocity, fuel type, emissions requirements, and/or other variables.
According to an embodiment, the support structure 1108 is coupled to the interior surface 1112 of the furnace wall 110. Additionally or alternatively, the support structure 1108 can be coupled to the fuel and oxidant source 104, to the exhaust vent 1114, and/or to another structure (e.g., a steam tube) inside the combustion system 1100. In this way, the support structure 1108 can support the perforated flame holder 102 in a selected position relative to the fuel and oxidant source 104 within the interior space 1106.
According to an embodiment, the support structure 1108 can include bolts 1120, struts 1122, and/or a metal rim 1124. Each bolt 1120 may pass into or through the furnace wall to couple a strut 1122 to the furnace wall 110. The struts 1122 may additionally or alternatively be coupled to the metal rim 1124 at attachment points 1126. The metal rim 1124 may directly contact the perforated flame holder 102. The components of the support structure 1108 may support the perforated flame holder 102 at a selected position within the interior space 1106.
According an embodiment, the support structure 1108 can include structures additional or alternative to those shown in
According to an embodiment, the combustion system 1100 may include one or more sensors 234 configured to detect one or more parameters of the combustion reaction held by the perforated flame holder 102. The sensor(s) 234 may, for example, be positioned external to the furnace wall 110 to sense parameter(s) of the combustion reaction 302 through one or more windows or ports 1118. Additionally or alternatively, one or more sensors 234 may be located within the interior space 1106 defined by the furnace wall 110. The sensor(s) 234 can include one or more cameras or other image capture devices configured to sense infrared, visible, and/or ultraviolet radiation emitted by the combustion reaction 302 and/or the perforated flame holder 102. Additionally or alternatively, the sensor(s) 234 can include a temperature sensor, an electrical conductivity, resistance, inductance, or capacitance sensor (e.g. a “flame rod”), or other kinds of sensors capable of sensing parameters related to the combustion reaction 302 of the perforated flame holder 102 that can be usable for feedback to adjust the furnace parameters to maintain the combustion reaction 302 inside the perforated flame holder 102. Any suitable types of sensors may be included.
The combustion system 1100 may also include tubes, fittings, and the like not shown in
According to an embodiment, the furnace wall 110 may include an outer steel shell and an inner lining of firebrick 1212. The bolts 1120 of the support structure 1108 can fix the firebrick 1212 to the furnace wall 110. Thus, the bolts 1120 can serve the dual purpose of being a part of the support structure 1108 that supports the perforated flame holder 102, as well as fixing the firebrick 1212 to the furnace wall 110. The bolts 1120 can have a length that is sufficiently long to both fix the firebrick 1212 to the furnace wall 110 and to support the strut(s) 1122. Thus, bolts 1120 can be longer than conventional bolts used for fixing the firebrick 1212 to the furnace wall 110 so that extra nuts may be used to attach the strut 1122 thereto. The bolts of the type shown in
The fuel and oxidant source 104 can output the fuel and oxidant mixture 206 onto the perforated flame holder 102. The perforated flame holder 102 receives the fuel and oxidant mixture 206 from the fuel and oxidant source 104 and supports a combustion reaction 302 of the fuel and oxidant mixture 206 within the perforated flame holder 102.
The movable support structure 1408 can be configured to support the perforated flame holder 102 in a stable position at one or more selected distances from the fuel and oxidant source 104. Characteristics of the combustion reaction within the perforated flame holder 102 may depend in part on the distance between the fuel and oxidant source 104 and the perforated flame holder 102. The movable support structure 1408 can move the perforated flame holder 102 to adjust parameters of the combustion reaction 302, for example to improve stability of the combustion reaction 302 or to adjust the temperature of the perforated flame holder 102. In this way, the movable support structure 1408 can adjust the position of the perforated flame holder 102 to promote desired behavior of the combustion reaction 302.
According to an embodiment, the combustion system 1400 can include an actuator 1410 coupled to the movable support structure 1408. The actuator 1410 can move the movable support structure 1408. A controller 230 can control the actuator 1410 through instructions input by a technician and/or by software instructions executed by the controller 230.
According to an embodiment, the movable support structure 1408 can include tension bearing members such as rods, tubes, cables, wires, chains, and/or other structures that can support the perforated flame holder 102 in the selected position and/or adjust the position of the perforated flame holder 102. The tension bearing members can extend parallel to the direction of output of the fuel and oxidant mixture 206. This may allow the movable support structure 1408 to easily move the perforated flame holder 102 toward and away from the fuel and oxidant source 104 to affect the action of the perforated flame holder 102, and/or to preheat the perforated flame holder 102 via a conventional flame.
In an embodiment, the perforated flame holder 102 may be suspended in a large, vertically-fired furnace by chains or cables that run through furnace-wall openings, such as the exhaust vent 1114, to a windlass mechanism or the like. Heavy chains may be advantageous for such use because they may provide some positional stability. Pure tension members such as cables or chains may also support the perforated flame holder 102, in the manner of a gondola supported on an aerial cable. The perforated flame holder 102 may be supported on one or several such tension members that run parallel to one another (similar to a suspension bridge), and may include a mechanism for moving the perforated flame holder 102 along their length. The chain(s) may be engaged with a mechanism that engages the chain and works along from link to link (not shown). Also, relatively stiff rods or tubes can replace the flexible cables or chains, which may reduce the amount of tension needed to support the perforated flame holder 102 against its weight or against fluid forces. Rods and tubes may alternatively, or in conjunction, be used as rails rather than as suspension members.
According to an embodiment, the movable support structure 1408 may include a rail configured to enable moving the position of the perforated flame holder 102. For example, a strut may run along the interior surface of the furnace wall 110, extend to a second bolt or stud to which it may be attached in a similar manner, and serve as a rail. Two or more such rails, mutually parallel and spaced around the circumference of the interior surface 1112 of the furnace wall 110, may be sufficient to constitute a track on which the perforated flame holder 102 can slide or roll, or be clamped into a fixed but adjustable position. A single, wide rail may alternatively be used.
According to an embodiment, the movable support structure 1408 can include screws, clamps, sliders, rollers, wheels, gears, etc., for mounting the perforated flame holder 102 to the rail(s) in a movable fashion. In this way, the movable support structure 1408 can enable the perforated flame holder 102 to move along the rail or rails between selected positions. Additionally or alternatively, one or more of the rails can be rotatable and threaded to intercept a female thread or nut fixedly coupled to the perforated flame holder 102. According to an embodiment, the movable support structure 1408 can include a rack-and-pinion or worm-and-wheel arrangement, with teeth provided on the rail meshing with a worm or pinion gear coupled to the perforated flame holder 102. Additionally or alternatively, the movable support structure 1408 can include a structure configured to slide on the rail(s) in conjunction with a cable, rod, or other mechanism that is not involved in the contact of the perforated flame holder 102 and the rail(s).
According to an embodiment, the movable support structure 1408 can be adapted to furnaces of a type having tubes (e.g., process heaters, water-tube boilers), which are disposed in the interior 1106 and/or form part of the interior surface 1112 of the furnace wall 110. Such furnaces may have tubes that are horizontal, vertical, and/or inclined. For example, the tube may be of a helical shape and be positioned at a shallow angle. The tubes, which may be separated from a refractory wall and/or each other by some distance, may be disposed in a vertical plane on each side of a row of burners on the floor of the furnace. Alternatively, a burner may fire toward a plane of tubes from one or two sides. Other configurations are also contemplated. The movable support structure 1408 can suspend the perforated flame holder 102 from the tubes. The movable support structure 1408 may engage with tubes via conventional hardware such as hooks, pipe clamps, and the like. The movable support structure 1408 can enable movement of the perforated flame holder 102 to a selected position within the furnace.
According to an embodiment, the combustion system 1500 may include horizontal tubes 1512 adjacent two facing refractory walls of a furnace wall 110. A vertically-fired perforated flame holder 102 may be suspended from the tubes 1512 by the movable support structure 1508. The movable support structure 1508 may enable the vertically-fired perforated flame holder 102 to be raised and lowered from a floor on which are disposed one or more fuel and oxidant sources 104. The movable support structure 1508 may include a plurality of large gear wheels 1514, which may be driven by their respective drive shafts 1522 from a common driver, using linkages, chains, belts, gear trains, and/or individual motors as are known in the art.
According to an embodiment, an alternate movable support structure 1508 for suspending the perforated flame holder 102 from horizontal tubes 1512 in the furnace may include a hinged track with a hook on each segment, with the hinged track being moved over the rollers, similar to a tank tread (e.g., see
According to an embodiment, there may be three wheels 1614, one of which may be spring-loaded by a spring 1616 tending to clamp the tube 1512 between the wheels 1614. One or more of the illustrated rolling supports 1612 may be attached to the perforated flame holder 102 in various ways to serve as a means for adjusting the vertical position of the perforated flame holder 102. The rolling support 1612 may be modified with rough wheel surfaces for gripping, motors, gears, and so on. Additionally or alternatively, the rolling support 1612 may be used in conjunction with a cable, rod, chain or other pure tension member that may control or adjust the vertical position of the perforated flame holder 102 while the rolling support 1612 serves to locate the perforated flame holder 102 within the horizontal plane.
According to an embodiment, the movable support structure 1808 includes C-shaped grapples 1816 coupled to the rim 1814 of the burner tile 1812. The movable support structure 1808 can further include vertical posts 1818 coupled to the grapples 1816. The vertical posts 1818 can be coupled to the metal rim 1124 by sliders 1822. The support structure 1808 may grip the metal rim 1124 or may be forced onto the metal rim 1124 by tension and/or compression members, such as springs or struts. The vertical posts 1818 may be aligned generally with the velocity of the fuel and oxidant mixture 206 coming from the fuel and oxidant source 104 inside the burner tile 1812, on which the perforated flame holder 102 is movable toward or away from the burner tile 1812 on the sliders 1822.
According to an embodiment, the sliders 1822 may include gears or wheels engaging the illustrated serrations or rack-gear teeth along a side of each vertical post 1818. Other known mechanisms for adjusting the position of the perforated flame holder 102 may also be used. Alternatively, the perforated flame holder 102 may be removably clamped, welded, or otherwise permanently or adjustably fixed in a position by conventional means.
According to an embodiment, the perforated flame holder 102 has a diameter that does not allow complete entry of the perforated flame holder 102 into a concave part of the burner tile 1812. Alternatively, the perforated flame holder 102 can enter the conventional burner tile 1812.
Those skilled in the art will understand, in light of the present disclosure, that the movable support structure 1808 and the perforated flame holder 102 can be configured for a rectangular burner tile, for a row of burners, and so on, merely by changing the shape. All such other shapes for movable support structure 1808, the perforated flame holder 102, and a burner tile 1812 fall within the scope of the present disclosure.
In an embodiment, a shell can include an exterior wall 1924 peripheral to the combustion pipe 1912. A cover plate 1914 may be operatively coupled to the exterior wall 1924. The perforated flame holder support structure 1908 can be operatively coupled to the cover plate 1914. The cover plate 1914, the support structure 1908, and the perforated flame holder 102 may be configured to be installed in the combustion pipe 1912 as a unit without a mechanical coupling to the combustion pipe 1912.
Additionally, or alternatively, the cover plate 1914, the fuel and oxidant source 104, the support structure 1908, and the perforated flame holder 102 may be configured to be retrofitted to the boiler 1900. The cover plate 1914, the fuel and oxidant source 104, the support structure 1908, and the perforated flame holder 102 can be configured to be installed in and uninstalled from the boiler 1900 as a unit for purposes of changing the perforated flame holder 102. The cover plate 1914 can be coupled to the exterior wall 1924 of the shell using threaded fasteners 1916, for example.
The illustrated support structure 1908 of
As mentioned above, in some embodiments, the perforated flame holder support structure 1908 and the perforated flame holder 102 may be retrofitted to a boiler which already has associated with it a cover plate 1914, held to the exterior wall 1924 (for example, by threaded fasteners 1916) and a fuel and oxidant source 104 held onto the cover plate 1914. In such a case, the perforated flame holder support structure 1908 may be attached by various methods, such as welding the support structure 1908 to an inside surface of the cover plate 1914 (not illustrated). Alternatively, the support structure 1908 may be attached by drilling holes in the cover plate 1914 and bolting the support structure 1908 to the cover plate 1914 with additional threaded fasteners (such extra holes and fasteners are not shown in the drawing). A distal end of the support structure 1908 (located farthest into the combustion pipe 1912) may be mechanically supported and located by such an attachment. The support structure 1908 proximal end may be operatively coupled to the combustion pipe 1912, in addition or alternative to the cover plate 1914. The distal end of the support structure 1908, located closer to the perforated flame holder 102, may be suspended in a space inside the combustion pipe 1912, either coaxially or not coaxially, and with an annular space between the support structure 1908 and the inside of the combustion pipe 1912.
According to an embodiment, an existing boiler may be retrofitted with the perforated flame holder support structure 1908 with little downtime and without requiring machine work. Such a support structure may include a flange 1928. The flange 1928 may be unitary with or attached to the support structure 1908, and may extend into a space between the outside surface of the exterior wall 1924 of the shell and the inward-facing surface of the cover plate 1914. The flange 1928 may replace, or augment, a gasket (not shown), which may be provided in that space for sealing purposes. In addition to an ability to seal, the flange 1928 can also provide a mechanical support, and so may be made of strong metal such as steel.
The flange 1928 can include three areas: an outer annular portion that can be clamped tightly between the cover plate 1914 and the exterior wall 1924 of the combustion pipe 1912, such as by the threaded fasteners 1916; an inner annular portion that can be fastened to the support structure 1908; and an intermediate annular portion that is neither fastened nor clamped.
In the embodiment shown in
As can be seen in
Each wheel 2116 may be made retractable into the body of the support structure 2108, which may be done to allow the support structure 2108 to be inserted through a proximal opening of the least diameter (or opening width if the space to be inserted into is not cylindrical), and provide the same advantage as mentioned above for the spring 2112.
The spring 2112 can be unitary with or fastened to the wheel carriage 2114 that supports the wheel 2116; these two may be combined into one integral piece of metal, by folding a sheet of metal, for example. On the other side of the wheel 2116 an arm 2115 can be attached to carry a weight 2120. The weight 2120 may be adjusted in size and/or placement to provide an outward or inward weight force on the wheel or wheels 2116 jointly, such that the sum of the weight forces counteracts gravity force acting on the support structure 2108.
It will be apparent that the screw 2014, also seen in
Thus, by properly deploying the wheels 2116 and by properly biasing them with weights 2120, the weight of the support structure 2108 can be effectively canceled, so that the support structure 2108 may levitate and, as a consequence, automatically center itself under the influence of the forces due solely to the springs 2012, 2112 (which, if these forces are equal and equally spaced, can center the support structure 808 inside the combustion pipe 1912).
A cover (not shown) may be provided to keep flames away from the wheel 2116 and reduce its operating temperature. The cover may also act as a structural reinforcement if, for example, formed as a stiffening rib of bent sheet metal or metal plate.
As mentioned above, the dilution distance DD can extend from the perforated flame holder 102 to the fuel nozzle 1922. It may be desirable to vary this distance. Therefore, the support structure 2208 may have a more-distal cylindrical portion in which the perforated flame holder 102 can slide (or, a prismatic portion if the perforated flame holder 102 has a non-circular outline, and is to fit snugly and/or slide inside the combustion pipe). Alternatively, the support structure 2208 may include a base portion and a sliding portion, where the perforated flame holder 102 may be fixed to the sliding portion, and the sliding portion may slide on an outside of the base portion, in the manner of an engine cylinder sliding on a piston. These portions may be either cylindrical, as are pistons and cylinders, or prismatic (regardless of the shape of the perforated flame holder 102).
In an embodiment illustrated in
In the region of the intermediate annular portion, which, as discussed above, can help to resist torque when the support structure 2208 is horizontal, the three sheets 2216, 2218, and 2220 may be rigidly fastened together by spot-welding, strong adhesives, and/or fasteners, or the like. Most preferably for resisting torque, the rods 2226 can be arranged so that, when viewed axially, the uppermost region of the intermediate portion of the flange 1928 (which can be the region subjected to the most mechanical stress) may be far from the rods 2226. For example, one rod may be in the lowermost region and two others disposed at 120 degrees on either side.
According to an embodiment, gaps between the sheets 2216, 2218, and 2220 may be filled with sealant. Another option is a stuffing box through which the rod 2226 may pass.
On the outside, for each of the several gear trains and rods 2226, there may be provided a drive motor incorporating a motor gear 2312 meshing with the outermost drive gear 2224. The drive motor may include feet (not shown) with holes positioned so that one or more of the threaded fasteners 1916 may serve to locate the actuator 1410, such as a drive motor. Actuators 1410 for the several rods 2226 may be simultaneously controlled to move in synchrony so that the perforated flame holder 102 may move without becoming skewed.
One advantage of the embodiment shown in
According to an embodiment, there may be three gear trains (or a different number) embedded in the flange 1928, and each gear train may rotate the proximal end of a respective rod 2226. Each of the exemplary three rods 2226 can be rotatable by being fastened to or unitary with a respective rod-end gear 2223, that is trapped within a respective end-gear cavity formed by: a hole or molded depression in the flange 1928; the inside surface of the cover plate 1914; and/or a proximal surface of a part of the support structure 1408 lying beyond the distal surface of the flange 1928.
Each rod-end gear 2223 can be engaged with at least one drive gear 2224 in a respective gear train that drives the rod-end gear 2223. The one or more drive gears 2224 can be engaged with one another successively as needed to the point where one of them extends beyond the outer edge of the cover plate 1914. At that point, the gear train can be driven by a motor gear 2312 meshing with the outermost drive gear 2224. (In some cases not shown, due to the geometry of the exterior wall 1924 and the cover plate 1914, no drive gears may be needed, as the rod-end gear 2223 may protrude from under the edge of the cover plate 1914.)
The three rods 2226, being simultaneously turned by their respective gear trains, can cause the perforated flame holder 102 to move in an axial direction to vary the dilution distance DD if the rods 2226 are each similarly threaded and engage female threads 2214 of the perforated flame holder 102, a peripheral frame 2228 of the perforated flame holder 102, or a sliding portion of the support structure 2208, mentioned above.
Data or signals from the sensor(s) 2412, 2414, 2416, and/or 2418 can be used by the controller 230 to select one of a plurality of positions for the perforated flame holder 102. The movable support structure 2408 can adjust the position of the perforated flame holder 102 relative to the fuel and oxidant source 104.
A furnace can become quite hot, and not only a rail, but also a strut or a tensioned or compressed suspending member, can be embodied as a hollow tube or pipe 2516 into which fluid coolant is introduced so as to keep the suspending member cool enough to avoid heat failure. Water or other fluid coolant 812 can be injected, flow, or be pumped into the tube or rail 2516 to keep its temperature safely below a softening temperature, even while the furnace is hot enough to soften the material from which it is made. In an embodiment, the coolant fluid 812 is circulated to a location external to the furnace volume. In another embodiment, the coolant fluid 812 is vented into the furnace.
According to an embodiment, the bolts 2612 or struts 2614 can be bored, or fabricated from pipes or tubes, thus allowing the fluid coolant 812 to be introduced into the furnace through them, and the fluid coolant 812 to be transferred to other members of the cooled support structure 2608, if they are also hollow.
According to an embodiment, a blind bore in the bolt 2612 makes hydraulic contact with a second bore in the strut 2614, via a conical press-fit as shown. These bores illustrate interior channels 2616. Nuts are not shown, but a lower nut may hold firebrick in place, while an upper nut may compress the strut 2614 onto the conical portion of the bolt 2612 and thereby hold it in a position with friction, as well as sealing the hydraulic passage. Optionally, the blind bore 2616 can be configured to make hydraulic contact with a second bore 2616 at a location corresponding to threads, with the second bore formed in a nut.
According to an embodiment, the tube 2712 can be welded to a steel furnace wall 2510. The tube 2712 can protrude over a continuous layer of refractory material 2716 held in place by anchors 2718. The tube 2712 can pass through holes in the furnace wall 810. Couplings 2714 are disposed on ends of the tube 2712 for attaching to a source and drain of fluid coolant.
According to an embodiment, the cooled support structure 3408 can rotate the perforated flame holder 3402 around its geometrical axis, bringing new areas of the perforated flame holder 3402 into the combustion region above the fuel and oxidant source 104.
According to an embodiment, the perforated flame holder body 208 can include reticulated fibers 3539. The reticulated fibers 3539 can define branching perforations 210 that weave around and through the reticulated fibers 3539. According to an embodiment, the perforations 210 are formed as passages through the reticulated ceramic fibers 3539.
According to an embodiment, the reticulated fibers 3539 can include alumina silicate. According to an embodiment, the reticulated fibers 3539 can be formed from extruded mullite or cordierite. According to an embodiment, the reticulated fibers 3539 can include Zirconia. According to an embodiment, the reticulated fibers 3539 can include silicon carbide.
The term “reticulated fibers” refers to a netlike structure. According to an embodiment, the reticulated fibers 3539 are formed from an extruded ceramic material. In reticulated fiber embodiments, the interaction between the fuel and oxidant 206, the combustion reaction 302, and heat transfer to and from the perforated flame holder body 208 can function similarly to the embodiment shown and described above with respect to
According to an embodiment, the reticulated fiber network 3539 is sufficiently open for downstream reticulated fibers 3539 to emit radiation 304 for receipt by upstream reticulated fibers 3539 for the purpose of heating the upstream reticulated fibers 3539 sufficiently to maintain combustion of a fuel and oxidant 206. Compared to a continuous perforated flame holder body 208, heat conduction paths 312 between fibers 3539 are reduced due to separation of the fibers 3539. This may cause relatively more heat to be transferred from the heat-receiving region 306 (heat receiving area) to the heat-output region 310 (heat output area) of the reticulated fibers 3539 via thermal radiation 304.
According to an embodiment, individual perforations 210 may extend from an input face 212 to an output face 214 of the perforated flame holder 102. Perforations 210 may have varying lengths L. According to an embodiment, because the perforations 210 branch into and out of each other, individual perforations 210 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 302 or a flame at least partially between the input face 212 and the output face 214. According to an embodiment, the input face 212 corresponds to a surface of the perforated flame holder 102 proximal to the fuel nozzle 218 or to a surface that first receives fuel. According to an embodiment, the input face 212 corresponds to an extent of the reticulated fibers 3539 proximal to the fuel nozzle 218. According to an embodiment, the output face 214 corresponds to a surface distal to the fuel nozzle 218 or opposite the input face 212. According to an embodiment, the input face 212 corresponds to an extent of the reticulated fibers 3539 distal to the fuel nozzle 218 or opposite to the input face 212.
According to an embodiment, the formation of boundary layers 314, transfer of heat between the perforated reaction holder body 208 and the gases flowing through the perforations 210, 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 212 to the output face 214 through the perforated reaction holder 102. According to an embodiment, the void fraction (expressed as (total perforated reaction holder 102 volume−fiber 3539 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 square inch of surface area. 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 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 tiles. 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 tiles. Additionally or alternatively all or a portion of the multiple reticulated ceramic tiles may be held adjacent to one another but not in direct contact with one another by a perforated flame holder support structure, many embodiments of which are disclosed herein. The multiple reticulated ceramic tiles can collectively form a single perforated flame holder 102. Alternatively, each reticulated ceramic tile can be considered a distinct perforated flame holder 102.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
The present application is a U.S. Continuation-in-Part patent application of co-pending U.S. patent application Ser. No. 15/047,557, entitled “BURNER WITH A PERFORATED FLAME HOLDER SUPPORT STRUCTURE,” filed Feb. 18, 2016 (docket number 2651-224-03). Co-pending U.S. patent application Ser. No. 15/047,557 claims priority benefit from U.S. Provisional Patent Application No. 62/117,941, entitled “BURNER WITH A PERFORATED FLAME HOLDER SUPPORT STRUCTURE,” filed Feb. 18, 2015 (docket number 2651-224-02). The present application also claims priority benefit from and is a continuation-in-part of co-pending International Patent Application No. PCT/US2016/018532, entitled “BURNER WITH A PERFORATED FLAME HOLDER SUPPORT STRUCTURE,” filed Feb. 18, 2016 (docket number 2651-221-04). Co-pending International Patent Application No. PCT/US2016/018532 claims priority benefit from U.S. Provisional Patent Application No. 62/117,943, entitled “BURNER WITH A PERFORATED FLAME HOLDER SUPPORT STRUCTURE,” filed Feb. 18, 2015 (docket number 2651-221-02). Co-pending U.S. patent application Ser. No. 15/047,557, co-pending International Patent Application No. PCT/US2016/018532, U.S. Provisional Patent Application No. 62/117,941, and U.S. Provisional Patent Application No. 62/117,943 are each, to the extent not inconsistent with the disclosure herein, incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62117941 | Feb 2015 | US | |
| 62117943 | Feb 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15047557 | Feb 2016 | US |
| Child | 15668562 | US | |
| Parent | PCT/US2016/018532 | Feb 2016 | US |
| Child | 15047557 | US |
