BURNER WITH A PERFORATED FLAME HOLDER SUPPORT STRUCTURE
A furnace has a fuel and oxidant source to create a flow of combustible fuel and oxidant mixture, a perforated flame holder on which the flow impinges, and a support structure to support the perforated flame holder in a position where it at least partially contains combustion of the fuel and oxidant mixture. The support structure mechanically engages with the interior of the furnace to support the perforated flame holder, which may be movable within the furnace via a mechanism to optimize combustion or reduce NOx. The support may contain fluid coolant. The perforated flame holder may be moved into and out of a combustion region.
The present application claims priority benefit from U.S. Provisional Patent Application No. 62/117,943, entitled “BURNER WITH PERFORATED FLAME HOLDER SUPPORT STRUCTURE”, filed Feb. 18, 2015; and U.S. Provisional Patent Application No. 62/021,549, entitled “BURNER SYSTEM INCLUDING A MOVEABLE PERFORATED FLAME HOLDER”, filed Jul. 7, 2014; which, to the extent not inconsistent with the disclosure herein, is incorporated by reference.
SUMMARYAccording to an embodiment, a furnace includes a fuel and oxidant source configured to output fuel and oxidant, a perforated flame holder configured to hold a combustion reaction supported by the fuel and oxidant source, and a support structure 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 further include a coolant space therein, the coolant space being bounded by a fluid-containment barrier, and the coolant space may be separated from combustion by the fluid-containment barrier.
According to an embodiment, heat may be removed from the perforated flame holder by putting the support structure into contact with a fluid coolant having a coolant temperature lower than a combustion temperature.
According to an embodiment, the support structure may include a mechanism configured to move the perforated flame holder relative to the furnace and/or the fuel and oxidant source.
According to an embodiment, the burner may further include an electronic controller with a processor and a sensor. The perforated flame holder may be configured to support a flame inside it when located at a distance from the fuel and oxidant source at which the fuel and oxidant flow has a predetermined range of velocities and a predetermined range of mix ratios. The electronic controller may be configured to operate a feedback loop that drives a perforated flame holder support mechanism to vary the distance between the fuel and oxidant source and the perforated flame holder. The electronic controller can thus cause the flame to be supported within the perforated flame holder.
According to an embodiment, an electronic feedback device including a processor running software embodied in a non-transitory medium can operate to drive a mechanism to move a perforated flame holder responsive to a detected condition such that a combustion reaction is held in the perforated flame holder. Holding the combustion reaction in the perforated flame holder can reduce undesirable combustion emissions.
According to an embodiment, a perforated flame holder can be supported by a mechanism configured to move at least a first portion of the perforated flame holder between a combustion region and a cooling region. Simultaneously at least another portion of the perforated flame holder can be moved from the cooling region to the combustion region so as to maintain heat output. While in the cooling region, the first perforated flame holder or portion of the perforated flame holder can be serviced and/or exchanged for a new perforated flame holder or portion thereof.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.
The furnace 1100 supports combustion to produce heat, which may be used for any suitable purpose. Furnaces are used for a wide range of industrial, commercial, and domestic applications such as steam generation for heating, propulsion, and generation of electricity; process heating used in oil refineries and other chemical plants such as for heating endothermic reactions, cracking petroleum, and heating distillation columns; metallurgical refining and production heating; kiln firing; and residential air and water heating systems. Other uses of furnaces will be apparent to those skilled in the art.
A fuel and oxidant source 1200 provides a flow of fuel and oxidant 1202 toward the perforated flame holder 1300, which is disposed transverse to the fuel and oxidant flow 1202. Although the fuel and oxidant flow 1202 is depicted, in
The fuel and oxidant mixture 1202 has an overall (e.g., mean-average) velocity in a direction (leftward in
In another embodiment, fuel and oxidant are introduced to a pre-mixing chamber, from which they pass, through a flame arrestor, into the interior space 1106 where combustion of the mixture 1202 takes place. In an embodiment, a flame arrestor (not shown) may include a body having parallel passages, openings, or tubes aligned generally with the direction of the overall velocity. In the flame arrestor, these are configured by a surface-to-volume ratio of the arrestor (and/or the surface-to-volume ratio of the parallel passages, openings, or tubes), by the thermal conductivity of the material from which the arrestor is made (e.g., metal), and by the length of the flow of the mixture 1202 through the arrestor, to exclude a flame from passing through the arrestor at a speed greater than or equal to the velocity, when the mixture 1202 has a predetermined mix ratio and the fuel has a predetermined heat value. Thus, flames are prevented from moving “backward” from the furnace interior space into the mixing chamber. The flame arrester can prevent a dangerous “flashback” condition, which can have an explosive result.
Inside the interior space 1106 of the furnace 1100, the applicants dispose a perforated flame holder 1300. In an embodiment, the perforated flame holder 1300 is configured to hold a flame and maintain stable combustion. In an embodiment, the flame holder 1300 may be configured by a surface-to-volume ratio thereof, by a thermal conductivity thereof, by a geometry thereof, and by a fluid flow length therethrough to contain a flame therein. Other factors such (as predetermined) fuel and oxidant flow velocity, fuel and oxidant mixture ratio, and fuel type, for example, can affect the ability of the perforated flame holder 1300 to hold and maintain stable combustion.
The perforated flame holder 1300 includes a plurality of through passages, and/or it may be porous. Perforated flame holders are described and discussed in the Applicant's Aug. 21, 2014 Publication WO2014/127311 A1, entitled “FUEL COMBUSTION SYSTEM WITH A PERFORATED REACTION HOLDER”, the contents of which, to the extent not inconsistent with the disclosure herein, are incorporated herein by reference. This publication alternatively refers to a “perforated reaction holder” as well as a “perforated flame holder”. In this application, “perforated reaction holder”, “perforated flame holder”, and “flame holder” are equivalent. The perforated flame holder of this application may be of any material, may be an electrical insulator or conductor, and may otherwise be varied. The perforated flame holder 1300 of this application may be used in any sort of external combustion heating device, for example a boiler or process furnace, herein generically referred to as a “furnace”.
Perforated flame holder 1300 may include or constitute a single integral piece that is extruded, drilled, or otherwise formed to define a plurality of perforations 1302; or, it may be discontinuous, formed from a plurality of pieces of material; or, it may be composite, for example, woven or sintered. The flame holder 1300 may include any suitable material; for example, it may include metal, ceramic, cementatious, or other refractory material. It may take any shape or form that provides (an appropriate) flow resistance, thermal mass, thermal conductivity, surface area, and etc., suitable for holding a flame inside, under given conditions of fuel heat value, mixture ratio, and flow rate through the flame holder 1300 (which is a function of the mixture velocity and other factors), or other variables. The perforated flame holder 1300 may include sheets, flakes or fibers.
The thermal, physical, and other characteristics of a flame holder, that relate to its ability to maintain a flame substantially within it under given ambient conditions such as fuel, mixture speed, mix ratio, and so on, are referred to herein as the “reaction parameters” of the flame holder.
The “perforated” embodiment of the flame holder 1300, that may include numerous through-passages, can be formed by drilling or otherwise forming holes through a solid block, by bundling lengths of tubing together, etc.
Again considering
The flame holder 1300 is disposed or held in position inside the interior space 1106 at such a position (or positions) that, in view of the fuel flow rate, mixture velocity, and other variables, flame may be contained substantially between its envelope surfaces 1310 and 1320. To hold it in such a position, a support structure 1400 is provided to support the flame holder 1300 in at least one stable position at which the flame holder 1300 receives the fuel and oxidant mixture 1202 on the input flame holder surface 1310 and discharges the flow from a output flame holder surface 1320.
The support structure 1400 engages with the flame holder 1300 and also operatively couples to the furnace 1100. According to embodiments, the support structure 1400 is operatively coupled to the interior surface 1101 of the furnace 1100, to the fuel and oxidant source 1200, to the exhaust vent 1102, and/or to another structure (e.g. a steam tube) inside the furnace 1100. Various embodiments of the support structure 1400, described herein, provide hanging (tensile) support, compression member support, moveable support, and/or cooled support to the perforated flame holder 1300. In
A viewing window or port 1104, 1105 may be disposed in the wall 1103, allowing the interior space 1106 and the flame holder 1300 to be imaged or otherwise detected by a sensor or sensors 1501 that may include cameras for flame imaging by visible light or other light, or sensors for detecting particular wavelengths of electromagnetic radiation (usually light, infrared, and ultraviolet). Other sensors 1501, such as sensors detecting the electrical conductivity of the gas in the interior space 1106, may be disposed exposed to the interior space 1106 of the furnace 1100. The sensors 1501 may provide information that is usable for feedback to adjust the furnace parameters to maintain flame or combustion inside the perforated flame holder 1300. Any suitable type of sensor may be included.
Data from the sensor(s) 1502, 1504, 1506, 1508 is used by the control processor or circuit 1510 to control the fuel and oxidant source 1200 to adjust the velocity and/or the fuel and oxidant ratio of the mixture, and the actuator 1513 can also or alternatively adjust the position of the fuel and oxidant source 1200 relative to the flame holder 1300, and/or move the flame holder 1300 relative to the furnace 1100 or the fuel and oxidant source 1200. With such a feedback mechanism, combustion can be optimized to maintain flame within the flame holder 1300, which can provide benefits for reducing oxides of nitrogen (NOx) and other pollutants.
Referring to
A tubular shape more efficiently resists bending than does a rod of the same cross section and same tension resistance. Therefore a tube or pipe can be used as a rail, as well as being used as a purely tensioned suspending member, and can support a flame holder other than in a hanging position against gravity (or in tensile opposition to other tension members). A tensioned suspending member, such as a rod or tube, can be coiled to impart a lower spring constant, which may be advantageous in some situations, for example in a marine boiler that is subject to acceleration forces and in which some shock mounting may be advantageous. (A coiled tension member 1474 is shown as part of a suspended member in
A flame holder may be suspended inside a furnace, in any orientation, by pure tension members that are suitably arranged and attached at respective points to the interior surface 1101, without any of the support members being loaded in compression or bending. In such an arrangement, tension members with a relatively low spring constant can provide for thermal expansion effects as well as shock-mounting. For example, a generally-planar flame holder might be suspended by one straight vertical tension member and two coiled tension members, where the three tension members made angles of approximately 120 degrees between them. (Three tension members 1413 are shown in
In an embodiment, the perforated flame holder 1300 can be supported entirely by compression members. Also, a flame holder can be supported by a combination of tension and compression members. One example is where the weight of the flame holder is counteracted by a torque due to tensile and compressive members. For example, a flame holder may be supported by a truss acting as a cantilever beam.
If a flame-holder-supporting member serves as a rail that is subjected to bending loads, then coiling may greatly reduce its bending stiffness, so a straight or curved rod or tube would be preferred. (An example of a rail is 1450 in
A flame holder can be mounted to a rail by screws, clamps, sliders, rollers, wheels, gears, etc. In some embodiments, it may be advantageous to be able to adjust or move the flame holder, especially in regard to its distance from the fuel and oxidant source 1200. Therefore, the applicants contemplate that a flame holder may be supported so as to allow for motion along the rail(s).
Optionally, 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 1300. Another possibility is to use 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 1300. Still another possibility is to let the support 1400 slide on the rail, but be located by a cable, rod, or other mechanism that is not involved in the contact of the perforated flame holder 1300 and the rail (see, e.g.,
The applicants also contemplate a support that is adapted to furnaces of the type having tubes (e.g., process heaters, water-tube boilers), which are part of the interior and include part of the interior surface 1101 of the furnace. Such furnaces may have tubes that are horizontal or vertical, although the tubes are sometimes inclined, as for example when the tube is helical and the tubes is at a shallow angle. The tubes, which are often separated from a refractory wall and each other by some distance, may be disposed in a vertical plane on either side of a row of burners on the floor of a furnace, or, may fire toward a single plane of tubes from either side; there are many configurations.
A perforated flame holder 1300 may be suspended from the tubes. A support may engage with tubes via conventional hardware such as hooks, pipe clamps, and the like, and these are contemplated by the applicants to be at least part of a support for a perforated flame holder 1300. However, it may be desirable to adjust the position of a perforated flame holder 1300, or to change it in response to changing conditions, for start-up, etc.
An alternate apparatus (not illustrated) for suspending a perforated flame holder 1300 from horizontal tubes in a furnace might include a hinged track with a hook on each segment, with the hinged track being moved over rollers, as is a tank tread. The track segments could have a length such that the hooks engage the tubes sequentially. This arrangement would distribute the weight of the perforated flame holder 1300 over several tubes.
For example, if the bolts or studs 1410 shown in
Also, the fastener and strut 1420 of
As mentioned above, the perforated flame holder 1300 may, in an embodiment, be made with a ceramic element or elements and this ceramic may be held by a metal frame, as metal often is tougher than ceramic and has greater tensile strength and workability. For example, in exemplary
It will be understood that the struts need not be distinct from the perforated flame holder 1300, and a support for the perforated flame holder 1300 need not be more than an attachment (e.g., a fastener) between the furnace 1100 and the perforated flame holder 1300 proper. As just one example, one of the bolts illustrated in
In general, any of the hollow members mentioned above, such as the U-shaped tube 1450 of
Materials 1459 other than sodium can be used as a working fluid in the applicants' heat-pipe embodiment. Zinc, for example, boils at 907 C (1665 F) and is less reactive than sodium; it is about as reactive as iron, although it may burn in air, unlike iron. Its melting point is, however, higher at about 420 C (787 F). Other materials, such as thallium and calcium, might also be used. In this embodiment the hollow grid 1453 could be evacuated rather than filled with air, to enhance the heat-pipe effect. A pressure-relief valve in a vent tube leading to a remote container can be provided, to prevent explosion in case of overheating.
The heat-pipe principle could also be used in an all-metal perforated flame holder having the general configuration of a hollow volume perforated by fire tubes, as in a fire-tube boiler that contained sodium, zinc, etc. rather than water and steam. Such an embodiment of a perforated device is shown in
This device would tend to create a region of uniform temperature between a hot side and a cool side, and could be used alone or in combination with other devices in a perforated flame holder as both a thermal zone regulator and a rigid mechanical support structure for any perforated flame holder 1300 (see
In a non-illustrated variation, the grid 1452 of
Regardless of its cooling features, the perforated flame holder 1300 embodiments of
The descending portion 1457 of the grid 1453 in
Another example of this principle is in
The rollers 1424 may grip the perforated flame holder 1322 at its outer edge as shown. If the outer edge is unable to separate from the rollers (as a roller-coaster car is unable to separate from its track), then the perforated flame holder 1322 can be cantilevered and the rollers 1424 may be kept away from the combustion area, regardless of the orientation of the furnace and fuel and oxidant source 1200. Three rollers 1424 may suffice to fix the axial orientation and position of the perforated flame holder 1322.
Among the variations on the embodiment of
Embodiments of a perforated flame holder 1300 that is movable relative to a fuel and oxidant source 1200, transversely to the mixture flow direction, are described above in relation to cooling of the perforated flame holder 1300 and its support structure 1400, herein. Elsewhere, relative motion of a perforated flame holder 1300 and a fuel and oxidant source 1200, in a direction that is substantially parallel to the mixture 1202, have been described in relation to maintaining combustion substantially inside the perforated flame holder 1300. However, relative motion in the flow velocity direction may also be involved with raising and lowering the perforated flame holder 1300 temperature, especially with raising the temperature at the start of combustion. This is because the perforated flame holder 1300 may need to be pre-heated by a conventional flame (in which combustion occurs between the fuel and oxidant source 1200 and the input surface (not shown) of the perforated flame holder 1300); then, after the flame heater reaches the appropriate temperature, the distance and/or reaction parameters may be adjusted to keep the flame inside the perforated flame holder 1300.
In
In the illustrated device the perforated flame holder 1300 has a diameter that may not allow entry into the concave part of the burner tile 1112, but the device may be designed such that the perforated flame holder 1300 can enter the conventional burner tile 1112. Mixing devices such as fuel jets are often inside a cylindrical burner tile, but may also be disposed around its periphery, and in that case the perforated flame holder 1300 might be larger.
Those skilled in the art can modify the support and perforated flame holder 1300 of
In some embodiments, the illustrated fluid-containment structure is closed and relies on surface cooling to remove heat from the coolant (as in the descending portions 1457 of
The tube 1620 may optionally pass through the wall of a furnace 1100, also indicated schematically by a dashed line, and reach a heat radiator 1622 located in the space outside of the perforated flame holder 1600 and also outside of the furnace 1100. In this way the heat radiator 1622 is fluid-coupled to the coolant containment volume inside the perforated flame holder 1600 by the connection tube 1620.
A fuel nozzle 110 is disposed to receive fuel from a fuel source 112, coupled to a valve 138, and output a fuel jet 206 into the combustion volume 108, and also an oxidant source 114 is disposed to output combustion air into the combustion volume 108. The oxidant source 114 can consist essentially of a natural draft air source, or alternatively can receive oxidant from a blower 116. Various fuels are used in commercially available fire tube boilers. In other embodiments, the fuel might be solid, or a mix of solid, liquid, and/or gas, alone or in combination. Hot flue gas that is circulated through exemplary “fire” tubes 120, 122 that, together with the wall of the combustion pipe 106 transfer heat produced by the combustion reaction 118 to the water 104. In the illustrative example, the fire tubes including the combustion pipe 106, 120, 122 form a three pass system with hot flue gas being produced in the combustion pipe 106 flowing from left to right, a second pass of fire tube 120 supporting flue gas flow from right to left, and a third pass of fire tubes 122 supporting flue gas flow from left right. Each “turn” of flue gas direction is made in a plenum 124, 126.
In other embodiments not shown, the perforated flame holder 202 might have a different shape and/or extra parts, and may include or function as an electrode whereby electrical voltages or currents, magnetic or electric fields, flame sensors and signals therefrom, and the like may influence the flame. Such non-illustrated parts may be coupled to a processor and electrical apparatus, not shown.
The perforated flame holder 202 can be disposed substantially adjacent to the combustion pipe 106 around its entire body 210. Additionally or alternatively, the perforated flame holder 202 can be disposed at least partly separated from the combustion pipe 106 such that natural flue gas recirculation can occur.
The fuel nozzle 110 can be characterized by a nozzle diameter through which fuel is emitted. The perforated flame holder support structure 602 is operatively coupled to the perforated flame holder 400 and configured to hold the perforated flame holder 400 at a dilution distance (DD) from the fuel nozzle 110.
The shell 102 (see
The fuel nozzle 110 and the oxidant source 114 together can include an exemplary fuel assembly or fuel and oxidant source 606. The fuel assembly 606 can be operatively coupled to the cover plate 604. The cover plate 604, the fuel assembly 606, the support structure 602, and the perforated flame holder 400 can be configured to be installed relative to the combustion pipe 106 as a unit without a mechanical coupling to the combustion pipe 106. The cover plate 604, the fuel assembly 606, the support structure 602 and the perforated flame holder 400 can be configured to be retrofitted to the boiler 200 (see
In the prior art, a fuel assembly 606 may include swirl vanes 610 or equivalent structures (such as a bluff body, for example) aligned to cause vortices to form near to the fuel assembly 606, in cases where fluid fuel or composite fuel is used, as opposed to using solid fuel. The vortices operate to recycle heat released by a conventional flame back to incoming fuel and oxidant 206, 208 (see
The illustrated support structure 602 can be configured to hold the perforated flame holder 300 away from the fuel nozzle 110 at a distance sufficient to cause substantially complete mixing of the fuel and oxidant at a location where the fuel and oxidant impinge upon the perforated flame holder 300; in other embodiments, the perforated flame holder may be closer or may include additional parts, such as electrodes for example, that are disposed closer or farther. Thermal insulation 612 can be included and operatively coupled to the flame holder support structure 602. The thermal insulation 612 can be supported by the support structure 602 adjacent to the wall of the combustion pipe 106 along at least a portion of the distance (DD) between the fuel nozzle 110 and the perforated flame holder 300. In some embodiments, the thermal insulation 612 can be affixed to the combustion pipe 106 wall. Additionally or alternatively, thermal insulation 612 can be disposed adjacent to the wall of the combustion pipe 106 along at least a portion of the distance (DD) between the fuel nozzle 110 and the perforated flame holder 400. For example, the thermal insulation 612 can be formed from a 1 inch thick FIBERFRAX DURABLANKET © high temperature insulating blanket, available from UNIFRAX I LLC of Niagara Falls, N.Y.
As mentioned above, in some cases the flame holder support structure 602 and the perforated flame holder 300 may be retrofitted to a boiler which already has associated with it a cover plate 604, held to the exterior wall 103 (usually by threaded fasteners 608) and a fuel assembly 606 held onto the cover plate 604. In such a case, the support structure 602 may be attached by various methods, such as welding the support structure 602 to the inside surface of the cover plate 604 (not illustrated), or drilling holes in the cover plate 604 and bolting the support structure 602 to the cover plate 604 with additional threaded fasteners 608 (such extra holes and fasteners are not shown in the drawing). The distal end of the support structure (the end farthest into the combustion pipe 106) may be mechanically supported and located by such an attachment. However, the inventors also contemplate that the support structure proximal end may be operatively coupled to at least one of the shell 102 (here, exterior wall 103) and the combustion pipe 106, as well as the cover plate 604. The distal end of the support structure 602, closer to the perforated flame holder 400, may be suspended in the space inside the combustion pipe 106, either coaxially or not coaxially, and with any amount of annular space between the support structure 602 and the inside of the combustion pipe 106. If the clearance space is minimal, then the inside of the combustion pipe 106 may support or help to support the support structure 602 against gravity (if the boiler is horizontal or slanted; if the boiler is vertical, then such support may not be needed).
In any case, the support structure should be positively located, so that it will not migrate due to vibration, for example.
Ideally, an existing boiler should be retrofitted with the least downtime and without requiring machine work. One embodiment of the support structure 602, which requires no machining or modification, no special tools, and no modification of existing parts for retrofitting with the perforated flame holder 400, includes a flange 614. This flange, which is unitary with or attached to the support structure 602, extends into the space between the outside surface of the exterior wall 103 of the shell 102, and the inward-facing surface of the cover plate 604. The flange 614 may replace, or augment, a gasket (not shown) which ordinarily or might otherwise be provided in that space for sealing purposes. The flange 614 not only seals, but also functions for mechanical support, and so may be made of strong metal such as steel; it may include a circular ridge or bead, like the beads in some internal combustion engine head gaskets, which may allow for sealing between the outside surface of the exterior wall 103 and the inward-facing surface of the cover plate 604. The flange 614 might also include, in this region, rings of elastomer or other soft gasket material, and/or grooves to accept such. The flange 614 may extend past the threaded fasteners 608 as shown, and include holes to pass the fasteners 608 through. These holes may provide one means for locating the support structure 602 relative to the combustion device.
The flange 614 may be considered as including three areas: an outer annular portion that is clamped tightly between the cover plate 604 and the exterior wall 103, by the threaded fasteners 608; an inner annular portion that is fastened to the support structure 602; and an intermediate annular portion that is neither fastened nor clamped. The outer annular portion is securely held, and the inner annular portion is fixed to a rigid body, namely the support structure 602.
If the combustion tube 106 is vertical, then there is no torque on the support structure 602, and the flange 614 may not need to resist any forces; but if the combustion tube 106 is tilted or horizontal, then there may be torque due to gravity at the proximal end of the support structure 602, and the flange 614 may need to resist it.
If the intermediate annular portion is narrow, then the flange 614 may be able to hold the support structure 602 against tilting. This is because the flange 614, in order to exert a torque on the support structure 602, needs only to resist bending, stretching, or failure due to shear force.
At the lower side of the flange 614, the gravity force may push the support structure 602 against the inside of the cover plate 604, so that the flange 614 needs to exert little force. However, at the upper side, the gravity force may tend to pull the support structure 602 away from the inside of the cover plate 604, and the flange 614 must resist this force.
It is evident that the intermediate portion may be subjected to only a shearing force if the intermediate portion is very narrow, but also to stretching and bending forces if the intermediate portion is broad. Assuming that the flange 614 is strong enough to resist plastic deformation or failure due to any of these forces, the movement of the support structure 602 may be least when there is only one: namely, shear, which predominates when the intermediate portion is narrow. Furthermore, if the intermediate portion is wide, and is able to assume an angle between the inner edge of the exterior wall 103 and the outer edge of the proximal end of the support structure 602, then the amount of tensile stretching of the intermediate portion may be minimal at the beginning of the displacement of the support structure away from the cover plate. This is because of the trigonometric fact that the cosine of a small angle is approximately one; at small angles, the amount of stretching is minimal, and therefore the flange 614 does not resist the motion of the support structure away from the cover plate. Thus, the support structure may tilt more under the force of gravity as the intermediate portion grows wider.
Therefore, to make the support structure 602 as stable as possible without requiring any modification of the other parts, the gap between the support structure and the inside of the exterior wall 103 should be minimized. Thus, one aspect of reaching the inventors' goal is to make the proximal end of the support structure 602 to fit as closely as possible inside the exterior wall 103 and/or the cover plate. The width of the intermediate portion is therefore less than a predetermined thickness, where the predetermined number depends of the thickness, shear modulus, tensile modulus, the weight of the support structure, the position of the center of gravity of the support structure, and other factors, which will be apparent to those skilled in the art. The predetermined thickness may be less than n inches, where n is a positive integer; or may be less than 1/n inches, where n is again an integer; or may be less than m/n inches, where m is an integer <n.
In most cases, the thickness of the flange 614 may not be a critical design issue, because the thickness can, in most cases, be increased to the point where support is not a design problem. For example, if the tolerance on the proximal opening into the combustion volume 108 is wide, or if several different openings are to be accommodated with one flange 614, then the thickness can merely be increased as needed.
The great advantage of the flange 614 is that it may require no modification of the other parts when installing a support structure 602. In particular, the existing cover plate 604 may require no modification.
It is to be noted that the illustrated support structure has application to combustion devices that lack a combustion pipe; one example would be a water-tube boiler, which lacks any well-defined surface surrounding the combustion volume 108. However, in cases where the applicants' concept is to be applied to combustion devices that include the exemplary illustrated combustion pipe 106, then a mechanical coupling to such a combustion pipe may be provided.
The spring 670 is fixed by a screw 671, but any permanent or temporary attachment can be used. As shown, the spring 670 is fixed near to the distal end of the support structure 602 but projects backward toward the proximal end, which may reduce the maximum temperature to which the spring 670 is exposed. If the combustion pipe 106 is metal in contact with water, then it may cool the spring 670. The spring 670 includes an up-turned proximal end so as to avoid catching when the support structure might be withdrawn.
As can be seen in
Each wheel 676 may be made retractable into the body of the support structure 602 (not shown in
The drawing shows that the spring 672 is unitary with or fastened to the wheel carriage 674 that supports the wheel 676; these two may be combined into one integral piece of metal, by folding a sheet of metal, for example. At the end of the spring far from the wheel 676, the spring 672 is fastened to the support structure 602 (not shown in
Thus, by properly deploying the wheels 676 and by properly biasing them with weights 679, the weight of the support structure 602 can be effectively canceled, so that the support structure 602 levitates and, as a consequence, automatically centers itself under the influence of the forces due solely to the springs 670, 672 (which, if these forces are equal and equally spaced, would center the support structure 602 inside the combustion pipe 106).
A cover (not shown) may be provided to keep flames away from the wheel 676 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.
There may be three gear trains (or a different number) embedded in the flange 614, and each gear train may rotate the proximal end of a respective rod 620. Each of the exemplary three rods 620 is rotatable by being fastened to or unitary with a respective rod-end gear 622, that is trapped within a respective end-gear cavity 616 formed by: a hole or molded depression in the flange 614; the inside surface of the cover plate 604; and/or a proximal surface of a part of the support structure 602 lying beyond the distal surface of the flange 614.
Each rod-end gear 622 is engaged with at least one drive gear 624 in a respective gear train, that drives the rod-end gear 622. The one or more drive gears 624 are engaged with one another successively as needed to the point where one of them extends beyond the outer edge of the cover plate 604. At that point, the gear train can be driven by a motor gear 626 meshing with the outermost drive gear 624. In some cases not shown, due to the geometry of the exterior wall 103 and the cover plate 604, no drive gears may be needed, as the rod-end gear 622 will protrude from under the edge of the cover plate 604.
The three rods 620, being simultaneously turned by their respective gear trains, can cause the perforated flame holder 400 to move in the axial direction (along the dot-dash line in
In the region of the intermediate annular portion, which, as discussed above, helps to resist torque when the support structure 602 is horizontal, the three sheets 6141, 6142, and 6143 may be rigidly fastened together by spot-welding, strong adhesives, and/or fasteners, or the like. Most preferably for resisting torque, the rods 620 can be arranged so that, when viewed axially, the uppermost region of the intermediate portion of the flange 614 (which is the region subjected to the most mechanical stress) is far from the rods 620. For example, one rod may be in the lowermost region and two others disposed at 120 degrees either side. It will be understood that the middle sheet 6142 may be present everywhere except where gears are present, so that the stiffness of the basket 614 is maximized.
In the rest of the flange 614, the mechanical strength requirements are lower, but sealing is a desirable option. Ideally, the flange 614 might not allow combustion products to exit the combustion volume 108, or outside air to leak in. To this end, any gaps between the sheets 6141, 6142, and 6143 may be filled with sealant. Another option is a stuffing box 6144 through which the rod 620 passes.
On the outside, for each of the several gear trains and rods 620, there may be provided a drive motor incorporating a motor gear 626 meshing with the outermost drive gear 624. The drive motor may include feet (not shown) with holes positioned so that one or more of the threaded fastener 608 may serve to locate the drive motor. Then, the drive motors for the several rods 620 may be simultaneously controlled to move in synchrony so that the perforated flame holder 400 may move along the direction of the dot-dash line in
An advantage of the embodiment shown in
A large load on the gears is only likely to result if the distal threaded portion of the rod 620 freezes onto the female threads 618 due to corrosion, buildup of combustion products, etc. Such problems can be prevented by moving the perforated flame holder 400 through a short distance at regular intervals, and this can be programmed into whatever device controls the drive motors.
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.
Claims
1. A furnace, comprising:
- a fuel and oxidant source configured to output fuel and oxidant,
- a perforated flame holder configured to hold a combustion reaction supported by the fuel and oxidant source; and
- a support structure configured to hold the perforated flame holder in alignment with the fuel and oxidant output by the fuel and oxidant source;
- wherein the support structure comprises a mechanical coupling between the perforated flame holder and an attachment point of the furnace.
2. The furnace of claim 1, wherein the mechanical coupling comprises a cooling fluid channel configured to convey cooling fluid to at least a portion of the support structure, an actuator configured to cause a position change of at least a portion of the support structure, or a cooled actuator configured to cause a position change of at least a portion of the support structure.
3. The furnace of claim 1, wherein the perforated flame holder is configured by thermal and structural reaction parameters thereof to contain a flame therein at the location, when the fuel and oxidant has a predetermined mix ratio and a predetermined velocity, and the fuel has a predetermined heat value.
4. The furnace of claim 1, wherein the perforated flame holder has a substantially uniform thickness between a first flame holder surface and a second flame holder surface.
5. The furnace of claim 1, wherein the support structure further comprises a strut extending from an interior surface of the furnace to the perforated flame holder through an intervening space.
6. The furnace of claim 5, wherein the strut is canted in a direction opposite to a velocity of the fuel and oxidant from the fuel and oxidant source.
7. The furnace of claim 1, wherein the support structure further comprises a fastener attached to a wall of the furnace.
8. The furnace of claim 7, wherein the fastener further comprises a weld.
9. The furnace of claim 7, wherein the fastener further comprises a bolt or stud.
10. The furnace of claim 2, wherein the support structure further comprises a tension member.
11. The furnace of claim 2, wherein the support structure further comprises a compression member.
12. The furnace of claim 1, wherein the support structure further comprises a rail.
13. The furnace of claim 2, wherein the attachment point of the furnace further comprises at least one furnace tube with which the support structure is mechanically coupled.
14. The furnace of claim 13, wherein the furnace further comprises a fire-tube boiler and the furnace tube further comprises the attachment point.
15. The furnace of claim 2, wherein the support structure is attachable to and detachable from the furnace at the attachment point.
16. The furnace of claim 1, wherein the furnace further comprises a burner tile, and the support structure is configured to couple to the burner tile.
17. The furnace of claim 1, wherein an interior surface of the furnace further comprises an area that faces into, or is adjacent to an opening into or out of, an interior space of the furnace, and wherein the support structure engages with a plate to which the fuel and oxidant source is mounted, and the plate is configured to the opening.
18. The furnace of claim 1, wherein the support structure further comprises a coolant space therein, the coolant space being bounded by a fluid-containment barrier;
- the coolant space being separated from combustion by the fluid-containment barrier.
19. The furnace of claim 18, further comprising coolant disposed in the coolant space.
20. The furnace of claim 18, wherein the support structure is metallic and the perforated flame holder is non-metallic.
21. The furnace of claim 18, wherein the fluid-containment barrier further comprises a fluid connection between the coolant space and a space outside of the perforated flame holder.
22. The furnace of claim 21, wherein the fluid connection further comprises a coolant conduit passing through a wall of the furnace.
23. The furnace of claim 22, wherein the support structure further comprises the coolant conduit.
24. The furnace of claim 22, wherein an attachment point of the furnace comprises the coolant conduit.
25. The furnace of claim 24, wherein the coolant conduit further comprises a hollow bolt passing through the wall of the furnace.
26. The furnace of claim 21, further comprising a heat radiator located in the space outside of the perforated flame holder and a space outside of the furnace, and wherein the radiator is fluid-coupled to the coolant space by the fluid connection.
27. A method of removing heat from a furnace, the furnace comprising:
- a fuel and oxidant source configured to output fuel and oxidant,
- a perforated flame holder configured to hold a combustion reaction supported by the fuel and oxidant source; and
- a support structure configured to hold the perforated flame holder in alignment with the fuel and oxidant output by the fuel and oxidant source, the support structure further comprising a coolant space therein, the coolant space being bounded by a fluid-containment barrier and separated from combustion by the fluid-containment barrier;
- the method comprising:
- supporting the perforated flame holder to receive a flow of fuel and oxidant with a flame holder support structure;
- holding a combustion reaction supported by the fuel and oxidant with the perforated flame holder; and
- cooling the perforated flame holder support structure by placing the flame holder support structure in contact with a fluid coolant having a coolant temperature lower than a combustion temperature.
28. The method of removing heat from the perforated flame holder of claim 27, further comprising moving the fluid coolant relative to the perforated flame holder support structure.
29. The method of removing heat from the perforated flame holder of claim 27, wherein the fluid coolant includes air.
30. The method of removing heat from the perforated flame holder of claim 27, wherein the fluid coolant includes a liquid.
31. The method of removing heat from the perforated flame holder of claim 30, further comprising boiling the liquid within the coolant space.
32. The method of removing heat from the perforated flame holder of claim 27, wherein the fluid coolant includes sodium.
33. The method of removing heat from the perforated flame holder of claim 27, further comprising moving the coolant to a heat radiator outside of the furnace.
34. The furnace of claim 1, wherein the support structure further comprises a mechanism configured to move the perforated flame holder relative to the furnace and/or the fuel and oxidant source.
35. The furnace of claim 34, wherein the mechanism is configured to move the perforated flame holder into and/or out of a cooling region wherein the perforated flame holder and/or the support structure is cooled.
36. The furnace of claim 35, wherein the mechanism moves the perforated flame holder continually or continuously over a path that passes through a fuel and oxidant-impingement region and the cooling region.
37. The furnace of claim 34, wherein the support structure further comprises a rail, and the perforated flame holder is mounted on the rail by a slider mechanism.
38. The furnace of claim 34, wherein the perforated flame holder revolves or rotates.
39. The furnace of claim 38, wherein the perforated flame holder further comprises a belt of hinged links.
40. The furnace of claim 34, wherein the mechanism is configured to vary a distance between the perforated flame holder and the fuel and oxidant source by moving the perforated flame holder, relative to the furnace, in a direction that is parallel to a flow of fuel and oxidant and/or transverse to a first flame holder surface.
41. The furnace of claim 40, wherein the fuel and oxidant source is non-movable relative to the furnace.
42. The furnace of claim 34, wherein the mechanism moves the perforated flame holder, and further comprising an additional mechanism that moves the fuel and oxidant source relative to the furnace.
43. The furnace of claim 34, wherein the support structure is mounted on a burner tile, and the mechanism moves the perforated flame holder relative to the burner tile.
44. The furnace of claim 34, wherein the mechanism puts the support structure into sliding or rolling contact with an interior surface of the furnace.
45. The furnace of claim 44, wherein the contact is made at least partially by a wheel comprised in the mechanism.
46. The furnace of claim 44, wherein the mechanism further comprises a rail mounted on the interior surface of the furnace and the support structure slides or rolls on the rail.
47. The furnace of claim 46, wherein the rail is substantially parallel to an axis of a cylindrical or prismatic portion of the interior surface.
48. The furnace of claim 34, wherein at least one of the support structure or the mechanism further comprises a compression member in contact with an attachment point of the furnace.
49. The furnace of claim 34, wherein at least one of the support structure or the mechanism further comprises a tension member in contact with an attachment point of the furnace.
50. The furnace of claim 34, wherein the mechanism rotates the perforated flame holder within the furnace.
51. The furnace of claim 50, wherein the perforated flame holder is rotated about an axis that that is not parallel to a direction of flow of fuel and oxidant.
52. The furnace of claim 34, wherein the support structure engages with a mounting plate to which the fuel and oxidant source is mounted, and the support structure further comprises the mechanism.
53. The furnace of claim 52, wherein the support structure further comprises a flange disposed between the plate and the interior surface.
54. The furnace of claim 34, wherein the mechanism further comprises an actuator.
55. The furnace of claim 54, wherein the actuator further comprises a motor.
56. The furnace of claim 34, wherein the mechanism further comprises a screw and/or a gear.
57. The furnace of claim 34, wherein the mechanism further comprises a feedback loop further comprising a processor and a sensor;
- wherein the perforated flame holder is configured by thermal and structural reaction parameters thereof to contain a flame therein when located at a distance from the fuel and oxidant source at which the flow has a predetermined velocity and a predetermined mix ratio, and the fuel has a predetermined heat value; and
- wherein the feedback loop varies the distance under control of the processor to maintain the flame within the perforated flame holder.
58. A method of reducing combustion emissions emitted by a furnace, the furnace comprising:
- configuring a perforated flame holder by thermal and structural reaction parameters thereof to contain a flame therein at a position, when a fuel-oxidant mixture from the fuel and oxidant source has a predetermined mix ratio and a predetermined velocity, and the fuel has a predetermined heat value;
- providing an electronic feedback device operatively coupled to a flame sensor and the mechanism; and
- moving the perforated flame holder, under control of the feedback device reacting to signals from the flame sensor, to contain the flame inside the perforated flame holder and/or to reduce emissions.
59. The method of reducing combustion emissions of claim 58, wherein the electronic feedback device further comprises a processor running software embodied in a non-transitory medium.
60. The method of removing heat from the perforated flame holder of claim 58, comprising:
- using the mechanism to move at least a portion of the perforated flame holder between a flame and a cooling region.
Type: Application
Filed: Jul 7, 2015
Publication Date: Jan 7, 2016
Inventors: DOUGLAS W. KARKOW (DES MOINES, WA), JOSEPH COLANNINO (BELLEVUE, WA), ROBERTO RUIZ (SAMMAMISH, WA), NICHOLAS S. BROMER (MARIETTA, PA), CHRISTOPHER A. WIKLOF (EVERETT, WA)
Application Number: 14/793,726