Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C6/00—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion
  • F23C6/04—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection
  • F23C6/045—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection with staged combustion in a single enclosure
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C7/00—Combustion apparatus characterised by arrangements for air supply
  • F23C7/002—Combustion apparatus characterised by arrangements for air supply the air being submitted to a rotary or spinning motion
  • F23C7/004—Combustion apparatus characterised by arrangements for air supply the air being submitted to a rotary or spinning motion using vanes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
  • F23D14/02—Premix gas burners, i.e. in which gaseous fuel is mixed with combustion air upstream of the combustion zone
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D14/00—Burners for combustion of a gas, e.g. of a gas stored under pressure as a liquid
  • F23D14/20—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone
  • F23D14/22—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone with separate air and gas feed ducts, e.g. with ducts running parallel or crossing each other
  • F23D14/24—Non-premix gas burners, i.e. in which gaseous fuel is mixed with combustion air on arrival at the combustion zone with separate air and gas feed ducts, e.g. with ducts running parallel or crossing each other at least one of the fluids being submitted to a swirling motion
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D17/00—Burners for combustion conjointly or alternatively of gaseous or liquid or pulverulent fuel
  • F23D17/002—Burners for combustion conjointly or alternatively of gaseous or liquid or pulverulent fuel gaseous or liquid fuel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23D—BURNERS
  • F23D23/00—Assemblies of two or more burners
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2201/00—Staged combustion
  • F23C2201/20—Burner staging
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2202/00—Fluegas recirculation
  • F23C2202/30—Premixing fluegas with combustion air
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
  • F23C2900/07001—Air swirling vanes incorporating fuel injectors

Definitions

• the invention relates generally to combustion apparatus, and more specifically relates to a burner that combines the advantageous operating characteristics of nozzle mix and premixed type burners to achieve extremely low NO x , CO and hydrocarbon emissions.
• NO x emissions from gas flames can be created either through the Zeldevitch mechanism (often called thermal NO x ) or through the formation of HCN and/or NH 3 which can then be ultimately oxidized to NO x (prompt NO x ) .
• Thermodynamic calculations typically show that NO x emissions measured from natural gas flames are well below, one to two orders of magnitude, the thermodynamic equilibrium value. This indicates that in most situations NO x formation is kinetically controlled.
• thermal NO x can be controlled by regulation of the peak flame temperature, and as shown in Figure 1 using kinetic calculations, if the temperature can be lowered enough the ⁇ O x emissions from a "true" premixed natural gas flame operating at 15% excess air can be reduced to extremely low values (less than 1 ppmv) .
• Figure 1 shows the relationship between thermal NO x and temperature since for a premixed natural gas flame with an excess of oxygen, thermal NO x is the only route by which any significant N0 X emissions are created.
• Low N0 X gas burners have been undergoing considerable development in recent years as governmental regulations have required burner manufacturers to comply with lower and lower NO x limits.
• Most of the existing low NO x gas burner designs are nozzle mix designs. In this approach the fuel is mixed with the air immediately downstream of the burner throat.
• FGR flue gas recirculation
• Delayed mixing can be effective in reducing both flame temperature and oxygen availability and consequently in providing a degree of thermal NO x control.
• delayed mixing burners are not effective in reducing prompt NO x emissions and can actually exacerbate prompt NO x emissions. Delayed mixing burners can also lead to increased emissions of CO and total hydrocarbons.
• an outer shell which includes a windbox and a constricted tubular section in fluid communication therewith.
• a generally cylindrical body is mounted in the shell, coaxially with and spaced inwardly from the tubular section so that an annular flow channel or throat is defined between the body and the inner wall of the tubular section.
• Oxidant gases are flowed under pressure from the windbox to the throat, and exit from a downstream outlet end.
• a divergent quarl is adjoined to the outlet end of the throat and define a combustion zone for the burner.
• a plurality of curved axial swirl vanes are mounted in the annular flow channel to impart swirl to the oxidant gases flowing downstream in the throat.
• Fuel gas injector means are provided in the annular flow channel proximate or contiguous to the swirl vanes for injecting the fuel gas into the flow of oxidant gases at a point upstream of the outlet end.
• the fuel gas injection means comprise a plurality of spaced gas injectors, each being defined by a gas ejection hole and means to feed the gas thereto.
• the ratio of the number of gas ejection holes to the projected (i.e. transverse cross-sectional) area of the annular flow channel which is fed fuel gas by the injector means is at least 200/ft 2 .
• One or more turbulence enhancing means may optionally be mounted in the throat at at least one of the upstream or downstream sides of the swirl vanes. These serve to induce fine scale turbulence into the flow to promote microscale mixing of the oxidant and fuel gases prior to combustion at the quarl.
• the gas injectors can be located at the leading or trailing edges of the swirl vanes, and inject the fuel gas in the direction of the tangential component of the flow imparted by the swirl vanes.
• the gas injectors can also be disposed on a plurality of hollow concentric rings which are mounted in the throat downstream of the swirl vanes.
• the injected can similarly comprise openings disposed in opposed concentric bands on the walls which define the inner and outer radii of the annular flow channel.
• the gas injectors can also be located at the surfaces of the swirl vanes, with the vanes being hollow structures fed by a suitable manifold.
• the geometry of the burner is such that the product of the swirl number S and the quarl outlet to inlet diameter ratio C/B is in the range of 1.0 to 3.0.
• a method is provided for injection of gaseous fuel in a forced draft burner of the type which includes an annular throat of outer diameter B, having an inlet connected to receive a forced flow of air and recirculated flue gases, and an outlet adjoined to a divergent quarl.
• the gaseous fuel is injected at an axial coordinate which is spaced less than B in the upstream direction from the axial coordinate at which the quarl divergence begins; and sufficient mixing of the gaseous fuel with the air and recirculated flue gases is provided that these components are well-mixed down to a molecular scale at the axial coordinate of ignition. This procedure results in extremely low N0 X , CO and hydrocarbon emissions from the burner.
• the swirl vanes which are mounted with their leading edges parallel to the axial flow of fuel and oxidant gases, and then slowly curve to the final desired angle, have a constant radius of curvature along the curved portion of the vane, whereby the curved portion is a section of a cylinder. This shape simplifies manufacturing using conventional metal fabricating techniques.
• FIGURE 1 is a graphical depiction showing calculated NO x versus adiabatic flame temperature for a premixed flame with 15% excess air;
• FIGURE 2 is a further graph showing kinetic calculation of prompt NO x (HCN and NH 3 ) ;
• FIGURE 3 is a schematic longitudinal cross-sectional view, through a first embodiment of apparatus in accordance with the present invention.
• FIGURE 4 is a schematic view similar to Figure 3, but showing only sufficient of the apparatus to illustrate a modification of same in which turbulence enhancing means are provided;
• FIGURE 5 is a schematic longitudinal cross-sectional view similar to Figure 3, and showing a further embodiment of apparatus in accordance with the invention
• FIGURE 6 is a perspective view of the apparatus of Figure 5;
• FIGURE 7 is a cross-sectional schematic view similar to Figure 4 and showing a further arrangement for the fuel gas injection means
• FIGURE 7A is a simplified partially sectional perspective view of a portion of a swirl vane, showing a further arrangement for the fuel gas injection means;
• FIGURE 8 is a graphical depiction showing the effect of mixing rates on N0 X emissions
• FIGURE 9 is a graph showing the relationship between carbon monoxide and NO x for apparatus in accordance with the invention, as compared with conventional nozzle mix devices;
• FIGURE 10 is a graph depicting the calculated effect of stoichiometry on N0 X for premixed flames;
• FIGURE 11 a perspective view appears of a further embodiment of burner apparatus in accordance with the present invention.
• FIGURE 12 is a longitudinal cross-sectional view through the apparatus of Figure 11;
• FIGURES 13 and 14 are respectively front and rear-end views of the apparatus of Figures 12 and 13.
• FIGURE 15 is a perspective view of a further embodiment of burner apparatus in accordance with the present invention.
• FIGURE 16 is an elevational view simplified and partially in cross-section of a further embodiment of burner apparatus in accordance with the present invention.
• FIGURE 17 is a top-plan view of the apparatus of Figure 16 which is partially in section;
• FIGURE 18 is an elevational view showing details of one of the swirl vanes which may utilize in the present invention.
• FIGURE 19 is a top-plan view of the swirl vane of Figure 18.
• FIGURE 20 is an in-view of the apparatus 51 of Figure 11 showing certain relationships between the swirl vane and the remaining portions of the apparatus.
• FIG. 3 is a longitudinal highly schematic view of forced burner apparatus 10 in accordance with the present invention.
• Apparatus 10 includes an outer shell 8 having a plenum or windbox 12 and an adjoined tubular section 13. Air and recirculated flue gases 17 are provided under positive pressure by conventional fan means (not shown) via a conduit 11 to burner windbox 12, from which they proceed into the burner throat 14.
• the latter is a constricted annular space defined between outer cylindrical wall 18 of section 13, and an inner coaxial cylindrical body 16.
• the latter functions as a bluff body, and may take the form of or include an oil gun 15 (which gives the burner both gas and oil firing capabilities) ; or can simply be an open or closed end tube in the case of a gas only burner.
• a set of swirl vanes 20 are mounted in the throat 14.
• the swirl vanes can be approximately twenty in number, although greater or lesser numbers of vanes can be used depending upon the burner size and specific conditions under which the burner may be operated.
• Swirl vanes 20 are designed to impart a specific amount of swirl (S) to the flow with a minimum pressure loss.
• Fuel gas injection means 21 are provided proximate swirl vanes 20.
• hollow tubes 22 are attached, each of which is provided with a series of small holes 24 which serve as ejection ports for fuel gas, e.g. natural gas.
• the fuel gas is fed to the series of tubes 22 by a fuel gas feed manifold 26 which extends in toroidal fashion about the axis of apparatus 10 and is connected to provide an input to each tube 22.
• the totality of gas injection holes in effect define a grid of injection points.
• the object of this arrangement is to provide extremely rapid mixing with the air/FGR mixture.
• the mixing is effected rapidly enough to minimize regions of fluid having a stoichiometry of less than 0.6 downstream of the ignition point. In the apparatus 10 shown, this occurs at an approximate axial point 25.
• an igniter is only used for start-up. Once the main flame is established, the igniter is removed and the flame is self-stabilizing.
• the ignition point is determined by the temperature and mass flow rate of the internal recirculation gases, which in turn is determined by the burner geometry and the amount of external FGR that is used.
• the high degree of mixing should be achieved down to a molecular scale.
• the grid of gas injection points is designed to provide a minimum of 200 injection points per square foot of the projected area of a transverse cross- section taken through the throat 14 at the plane of the grid, with the mutual spacing of the injection points being such as to provide uniform mixing with the oxidant gases.
• the injection points are located to inject the gas in the direction of the tangential component of the flow imparted by the swirl vanes 20. In this approach the gas injection also acts to enhance the swirl number of the flow.
• the diameter (A) of the cylindrical body 16 defines the inner diameter of the swirling flow.
• FIG. 4 A modification of the apparatus of Figure 3 is shown in the partial view of Figure 4.
• a turbulence enhancer 27 has been mounted in the throat 14 downstream of the swirl vanes 20.
• the turbulence enhancer may take the form of a fine mesh screen, its function being to generate fine scale mixing as the fuel/air/FGR mixture passes through the screen.
• the screen openings will be no greater than 1 mm.
• FIG. 5 A further embodiment of the invention appears in Figure 5.
• the gas injection means 21, i.e. consisting of the same basic arrangement as aforementioned, is such that the hole carrying tubes 22 are now mounted at the trailing edge of the swirl vanes 20.
• the turbulence enhancer 27, i.e. a fine screen is provided.
• the screen is located a minimum of 30 gas injection hole diameters downstream of the gas injection grid 21 in order to provide adequate distance for macromixing to occur.
• tubes 22 can also extend along radials, i.e. the tubes would be vertically oriented as shown in Figure 3.
• the mixture of air, recirculated flue gas and fuel gas are flowed into a divergent quarl 28, which may be formed of a suitable refractory in view of the high temperature combustion taking place within such flame zone.
• the quarl has a sufficient diameter expansion, i.e. the ratio C/B (see Figure 3) , to provide the desired flame stability.
• FIG. 6 An isometric perspective depiction of the Figure 5 embodiment of apparatus 10 appears in Figure 6, which shows the relative location of the furnace windbox 12, the location of the swirl vanes 20 in the air/FGR throat 14 and the location of the turbulence enhancer 27.
• the turbulence enhancer need not necessarily be used with the present invention, although in many instances it will assist in providing the desired enhanced mixing.
• FIG. 7 A further embodiment of the present invention is depicted in the partial longitudinal cross-sectional schematic view of Figure 7.
• This apparatus is generally similar to that of Figures 5 and 6 except that in this instance the gas injection means instead of or in addition to comprising tubes located just downstream of the trailing edges or just upstream of the leading edges of the swirl vanes, comprises a pair of hollow rings or torroids, which are mounted to reside within throat 14.
• the outer ring 30 carries a plurality of gas ejection openings, oriented to eject gas in an axial direction.
• the smaller hollow ring 32 similarly carries a series of ejecting holes disposed to eject gas away from the axis of apparatus 10.
• the ejection holes on each of rings 30 and 32 direct the fuel gas toward the opposed ring, to assist in mixing. Additional rings of this type may be used in pairs or otherwise. For small burner sizes this arrangement can simplify to gas injection from holes provided at the inner and outer walls of the annular flow channel which defines the throat 14.
• Figure 7A shows a further fuel gas injector arrangement.
• a small section 35 is shown toward a lateral edge 37 of a swirl vane.
• the vane is hollow as seen at 39 and is fed fuel gas under pressure from an open end 41 connected to a gas feed manifold (not shown) .
• the fuel gas is ejected from a plurality of holes 43 provided at the surface of the swirl vane.
• Typical hole size of each injector is -approximately 1/16" or smaller, and the number of injection holes will typically range from 625 to 1043 for ratios of the gas/air velocity ranging from 3 to 5. However, different gas/air velocity ratios may be used generating different numbers of injectors according to the method described below.
• the injection grid should be spaced uniformly in the azimuthal direction, but varied in the radial direction to give equal number of injectors per annulus cross-sectional area (i.e. the area increases with radius squared.
• the injector hole size is based on the entrainment rate of the air/FGR mixture into the gas jets.
• the volume of the air and FGR mixture is 15 times the volume of the air and the desired mixing distance is 4".
• the diameter of the gas jets can be calculated according to the entrainment rate:
• the diameter of the gas jet is 0.087".
• the gas jet diameter should be smaller than 0.087".
• the number of gas jets can be defined by the ratio of the gas/air velocity used. Typically the velocity ratio will be in the range 3/1 to 5/1 and will depend on the available gas pressure and the direction of gas injection relative to the air velocity.
• the number of gas injectors can be defined by the relative total area of air/FGR area to the gas area and the ratio of the gas/air injection velocity. Th-' - number is given by:
• Number of gas injector .quare foot 1/ (volume ratio oxidant/gas»gas/air velocity ratio»area single gas injector ft 2 ) .
• the number of gas injectors per square foot of air/FGR cross-sectional area is 782.
• the number of injectors should consequently be at least 782.
• the dimensions of the annular region defined by the ratio of the inner diameter of the swirl vanes divided by the outer diameter of the swirl vanes, i.e. the ratio A:B in Figure 3, is preferably in the range of 0.6 to 0.8.
• the product of the swirl number (S) with the quarl outlet-to-inlet ratio, i.e. the factor S»(C/B) is preferably in the range of 1.0 to 3.0 in order to assure the adequate mixing of interest to the invention.
• the outlet of the quarl can be shaped to provide control of the flame shape.
• the outlet of the quarl can be parallel to the burner throat to minimize the rate of expansion of the flame in a narrow furnace.
• the quarl as mentioned, can be constructed from refractory material or can form part of a water wall where water cooling is utilized.
• NO x emissions can be reduced to less than 10 ppm with about 25% FGR (as compared to 50% for the nozzle mix injector) . If desired, the NO x emissions can be reduced to less than 4 ppm using about 50% FGR.
• Figure 9 shows the relationship between NO x and CO emissions for the tests described above. As the mixing improved and lower NO x emissions could be obtained, the CO emissions were also reduced. For the rapid mix cases (3) and (4) , less than 4 ppm NO x emissions could be obtained with CO emissions less than the detection limits of the analyzer (1 ppm) .
• the present invention provides methods of obtaining a high degree of mixing upstream of the ignition point while maintaining a gas injection point downstream of the axial swirl vanes (i.e. the burner would effectively remain a nozzle mix burner avoiding the drawbacks of a premix burner) .
• the method of rapid mixing is combined with a burner and quarl geometry which provides strong internal recirculation of hot combustion products to the root of the flame, and an extremely stable flame.
• the combination of the parameters S»(C/B) being between 1.0 and 3.0 and the annular ratio of the swirling flow between 0.6 and 0.8 provides a suitable internal recirculation pattern and the required flame stability.
• the rapid mixing of fuel and air may be combined with air staging to reduce NO x emissions while minimizing the amount of FGR which may be required.
• kinetic calculations show that at an FGR rate of 20%, a reduction in NO x emissions from 20 ppmv to 8 ppmv can be achieved if rapid mix conditions can be created.
• Figure 10 also shows that operations at stoichiometries of 0.5 must be avoided if prompt NO x is to be eliminated.
• FIG 11 an isometric perspective view appears of a further embodiment of burner apparatus 51 in accordance with the present invention.
• This Figure may be considered simultaneously with Figures 12, 13 and 14, which are respectively longitudinal cross-sectional; and front and rear end views of apparatus 51.
• Apparatus 51 may be compared with the apparatus 10 in Figure 6, from which it will be seen that certain similarities are present, but also a number of differing features.
• combustion air (which can be mixed with recirculated flue gas) is provided to the windbox 53 through a cylindrical conduit 55.
• Windbox 53 adjoins a tubular section 57 which terminates at a flange 59, which as in prior embodiments is secured to a divergent quarl 58 ( Figure 12) .
• fuel gas is provided by an external manifold 26.
• the inner co-axial cylindrical body 61 is comprised of a central hollow cylindrical tube 63 intended for receipt of an oil gun or a sight glass and a surrounding tubular member or cylinder 65 which is spaced from the outside wall of tube 63 and closed at each end, by closures 67.
• a hollow annular space 68 is thereby formed between tubular member 63 and cylinder 65, which serves as a manifold 68 for the fuel gas which is provided to such space via connector 69.
• the cylindrical body 61 is positioned and spaced within wind box 53 and tubular section 61 by passing 5 through flanges, one of which is seen at 71. The latter is secured to a plate 73 at the end of the wind box by bolts 75 and suitable fasteners (not shown) . This arrangement enables easy disassembly, as for servicing and the like.
• a series of swirl vanes 77 are again provided in the annular space or throat 79 which is defined between tubular body 61 (specifically, between the outer wall of cylinder 65) and the inner wall of tubular member 57.
• gas injector means are provided which take the form of a plurality of tubes 81, each of which is provided with multiple holes 83, this arrangement being in such respect similar to the device shown in Figure 3. It will be evident that the tubes 81, 0 being hollow members, are in communication at their open one end with the interior of the gas manifold 68 defined within member 5, which therefore serves as a feed source for the fuel ,__s.
• the fuel gas is discharged in the irection of the openings 83, so that in each instance m> fuel is injected into the throat directly at the leading edges of the swirl vanes and in the direction of the tangential component of the flow imparted by the swirl vanes 77. Accordingly, the gas injection also acts to enhance the swirl number of the flow.
• FIG 15 a further perspective view appears of burner apparatus in accordance with the invention.
• the apparatus 85 in Figure 15 is in most respects similar to apparatus 51 in Figures 11 through 14, and identical components are identified by corresponding reference 5 numerals.
• the method of fuel gas introduction is different from that shown in Figures 11 through 14, and in fact uses principles similar to those shown in the apparatus of Figure 7. Specifically, it will be seen that the fuel gas introduced by connector 69 to the interior gas manifold 68 (see Figure 12) defined between tubular member 65 and the inner tube 63, is injected into throat 79 by a series of holes or openings 87 which are disposed in a band extending circumferentially about the tubular member 65.
• a second gas manifold 95 is formed as an annular space surrounding tube 57, by a cylinder 89 which is closed at both ends 91 and 93. The annular gas manifold 95 is thus seen to be present between cylinder 89 and tubular member 57.
• An inlet for fuel gas is again provided by a connector 97.
• a second series of holes or openings 99 are disposed in a band about the wall of cylinder 57, so that fuel gas may be injected from manifold 95 through such openings 99. In this instance, the gas is injected radially but toward the axis 101 of the apparatus.
• the holes on the one hand at 99 and at the other at 87 provide opposed gas injection between the bands of holes, to produce a high degree of turbulence and mixing directly at the trailing edges of swirl vanes 77.
• the arrangement shown is particularly suitable where the apparatus 85 is of relatively compact dimensions.
• FIGS 16 and 17 elevational and plan views appear of further apparatus 110 in accordance with the invention. These views are somewhat simplified and schematic in nature and may be considered simultaneously in connection with this description.
• Windbox 112 as best seen in Figure 16, is fed combu. tion air and flue gas in the direction 114 (by pressurizing means not shown) .
• the entirety of the windbox is not shown, but is rather broken away at its upper end.
• the arrangement of apparatus 110 enables a more compact device than certain of the prior apparatus discussed. Specifically, it will be seen that a constricted tubular section 115 is provided, which is in direct communication with the interior of wind box 112 through the open end defined by diverging flange 116.
• the flange 116 while shown to diverge linearly, can also be dish-shaped to assist in air flow. Combustion air proceeds through the annular space 118 defined between tubular memoer 115 and the generally cylindrical body 120 mounted coaxially within said member. Cylindrical body 120 consists of a central tube 122 within which is received an oil gun 124 terminating in a nozzle 126. Oil is provided to gun 124 by port 125. Tube 122 in turn is surrounded by a spaced tubular member 130. The spacing between tube 130 and tube 122 defines an annular space 132 the function of which will be indicated below. Tube 130 is, in turn, surrounded toward its forward end by a further cylinder 134 which is closed at each end and defines within same an annular fuel receiving manifold 136.
• the gas injector means in the present device 110 comprises a series of prism-like hollow members 139 which are mounted transversely to cylinder 134 and intersect and are open to the interior manifold space 136 within same.
• the members 139 are provided on their lateral faces with openings 140 which substantially correspond in function to the openings 83 in Figure 11.
• the members 139 are directly in contact with and contiguous with the leading edges of swirl vanes 142, so that the gas is injected directly at such leading edge.
• a diverging quarl 144 is provided at the outlet end of burner throat 118.
• an elbow-shaped conduit 148 connects the interior of one side of windbox 112 to the interior annular space 132.
• a manually or non-manually operated gate valve 150 may be actuated to open or close a flow path between the windbox 112 and space 132. When the valve is in an open position, an air flow is provided into space 132 which then proceeds forwardly in the device and passes about the periphery of the oil nozzle 126. Steam or other actuating gas (such as compressed air) may be fed to the rear of the tube 131 to assist tas is known in the art) in spraying or atomizing the oil into the combustion volume. The air stream flow moving past nozzle 126 prevents or limits coke and ash particles from depositing on the oil gun during oil firing.
• FIG. 18 a vane 160 is shown which may be considered to be one of the vanes 77 in apparatus 51 of Figure 11. This is representative of the swirl vanes which may be used in any of the•apparatus depicted in the drawings herein.
• the shadow line version of the vane as seen at 162 indicates the form of the vane in plan view before it is bent to achieve a desired curvature in accordance with the invention.
• the vane 160 is seen to be secured, as previously discussed in connection with apparatus 51, to the injector tube 83 as, for example, by being welded to same.
• FIG. 19 The corresponding plan view of the vane of Figure 18 is seen in Figure 19, which again shows the vane before and after the bending to achieve the desired shape for use in the invention.
• the end view of Figure 201 shows the vane in its installed position in apparatus 51.
• Corresponding parts as discussed in Figure 11, are identified by corresponding reference numerals.
• the burner apparatus of the invention uses the fixed curved axial swirl vanes in the burner throat 79 to impart a given swirl level to the flow.
• the vanes are called axial swirl vanes because of the manner in which they convert an axial flow to a swirling flow.
• the swirl vanes used in the burner are designed to provide the desired flow pattern with a minimum pressure drop. Additionally, the vane is shaped to simplify manufacturing using conventional metal fabricating techniques.
• Swirling flows are commonly used in burners to improve flame stability and to improve fuel and air mixing.
• a swirling flow When a swirling flow is expanded, an internal recirculation zone is created which recirculates hot combustion products to incoming air and fuel, thus providing an ignition source.
• the objective of a swirl generator is to provide a certain level of rotation to the flow in order to provide the required amount of internal recirculation with a minimum energy requirement (pressure drop) .
• the swirl vanes also act as a mixing device for the gas and air/FGR mixture. When the gas is injected at the leading edge of the vane, fine scale turbulence is created as the flow acquires rotation generating the desired rapid mixing between the gas and oxidant.
• the leading edge of the vane is parallel to the axial flow.
• the fluid is accordingly slowly curved to the final angle.
• a constant radius of curvature is used along the surface of the curved portion of the vane (the curved portion of the vane is a section of a cylinder) .
• the swirl vane assembly is annular with an inner to outer radius R,/R 3 (as shown in Figure 20) in the range of 0.6 to 0.7.
• the exit angle of the vane is constant along the height of the vane producing a constant flow angle of the azimuthal to axial velocity (W/U) .
• a straight vane section oriented at the final flow angle is attached to the trailing edge of the curved section. This is shown at ABC in Figure 19.
• the straight vane section is designed to produce a constant overlap between the vanes as a function of the vane height.
• the vane is curved with a constant radius of curvature until the exit angle is achieved (point A) .
• the vane then continues at a fixed angle (straight portion) .
• the length of the straight portion varies with the vane height.
• the length of the straight portion of the vane along the inner tube is given by the distance from points A to B, while the length along the outer tube is given by the distance from points A to C.
• the vane is curved in a circular arc with the radius of curvature given by:
• R c (Overlap Factor) (6.28 • R,) /N/(1-cos(a) ) where:
• N total number of vanes
• a vane exit angle
• a typical % overlap to be used in equation (1) is 50%, but may be any number greater than about 20%.
• a typical exit angle is 45 degrees but may vary in the range 30 to 60 degrees.
• a straight section is added to the vane.
• the shape of the straight section of the vane which continues at the vane exit angle, a is determined according to the following criteria.
• the straight vane length is a small fraction of the curved vane length (5 to 10% of the curved vane, length would be a typical fraction) .
• the length of the straight vane along the outer surface is determined such that the distance Y 2 , Figure 20, is the same as the distance Yi *R 2 /Rj along the inner surface.
• the length of the straight vane section at any intermediate radius Rlie is determined such that Y n is equal to Yj -R n /R- ; .
• the vane 160 may be fabricated by several techniques. These include cutting out the flat vane shape and following the curved portion of the vane; cutting out the flat vane shape and stamping the final shape; and casting the blade directly into the final shape.

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• 1994
  • 1994-07-12 WO PCT/US1994/007745 patent/WO1995002789A1/en not_active Application Discontinuation
  • 1994-07-12 AU AU73283/94A patent/AU7328394A/en not_active Abandoned
  • 1994-07-12 BR BR9407484A patent/BR9407484A/pt not_active Application Discontinuation
  • 1994-07-12 CA CA002167320A patent/CA2167320C/en not_active Expired - Fee Related
  • 1994-07-12 EP EP94923414A patent/EP0707698A1/en not_active Ceased

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