Abstract:
An apparatus and process is provided for combining fuel and combustion air to produce a mixture. The mixture is burned in a combustion chamber to produce a flame.

Description:
[0001]    This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/743,388, filed Mar. 1, 2006, which is expressly incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to burner assemblies, and particularly to a low-emission industrial burner. More particularly, the present disclosure relates to a burner and process for burning a combustible air/fuel mixture to produce a flame. 
       SUMMARY 
       [0003]    According to the present disclosure, an apparatus and process is provided for combining fuel and combustion air to produce a mixture to be burned in a combustion chamber. The mixture is a combination of a swirling air/fuel mixture and a non-swirling air/fuel mixture. 
         [0004]    The apparatus is configured to mix a first fuel stream with a laminar flow of air passing through a first airflow channel to produce a straight-line air/fuel mixture. The apparatus is also configured to mix a second fuel stream with a swirling flow of air passing through a second airflow channel to produce a swirling air/fuel mixture. An ignitor is configured and arranged to ignite a combustible mixture comprising the straight-line and swirling air/fuel mixtures in a combustion chamber to produce a stable flame. 
         [0005]    In an illustrative embodiment, a fluid-injector tube is coupled to a fluid supply and arranged to inject an auxiliary fluid stream into the combustion chamber to combine with the straight-line and swirling air/fuel mixtures to produce the combustible mixture. In illustrative embodiments, the auxiliary fluid stream comprises a fuel gas, a liquid fuel, oxidants, or inerts. It is within the scope of the present disclosure to omit this auxiliary fluid stream. 
         [0006]    The process comprises the steps of discharging a first fuel stream into a stream of air flowing in a first airflow channel to produce a non-swirling straight-line air/fuel mixture and discharging a second fuel stream into a stream of air flowing in a second airflow channel to produce a swirling air/fuel mixture. The process further comprises the step of flowing the swirling air/fuel mixture alongside the non-swirling air/fuel mixture in an air/fuel transfer channel in a direction toward a combustion chamber to generate an air-and-fuel mixture flowing in the air/fuel transfer channel. 
         [0007]    In illustrative embodiments, the process further includes the steps of using the air/fuel transfer channel to transfer mixtures discharged from the first and second airflow channels into a downstream combustion chamber and passing an auxiliary fluid stream through a fluid-injector tube extending through the first airflow channel to combine the auxiliary fluid stream with the swirling and non-swirling air/fuel mixtures to produce a combustible mixture in the combustion chamber The auxiliary fluid stream comprises one or more of a fuel gas, a liquid fuel, an oxidant, and an inert. 
         [0008]    Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The detailed description particularly refers to the accompanying figures in which: 
           [0010]      FIG. 1  is a diagrammatic view of a burner in accordance with the present disclosure showing discharge of (1) a first fuel stream into a stream of air flowing in a first airflow channel to produce a “straight-line” air/fuel mixture flowing through an air/fuel transfer channel into a combustion chamber; (2) a second fuel stream into a stream of “swirling” air flowing in a second airflow channel containing a swirler to produce a “swirling” air/fuel mixture flowing through the air/fuel transfer channel “alongside” the straight-line air/fuel mixture into the combustion chamber; and (3) an auxiliary fluid stream into the combustion chamber, and showing ignition of the straight-line and swirling air/fuel mixtures and the auxiliary fluid stream in the combustion chamber to produce a flame; 
           [0011]      FIG. 2  is a perspective exploded assembly view of components included in a burner in accordance with the present disclosure showing several air-swirl vanes mounted in a “pin-wheel” pattern on an exterior surface of a vane-support sleeve surrounding a fuel-supply tube coupled to a fuel supply to provide an annular opening into an inner (first) airflow channel formed between the fuel-supply tube and the vane-support sleeve and showing fuel jet ports formed in a downstream end of each air-swirl vane for emitting streams of fuel into swirling air swirled by the air-swirl vanes; 
           [0012]      FIG. 3  is a sectional view of the burner taken along line  3 - 3  of  FIG. 2  after assembly of the components shown in  FIG. 1  showing placement of the air-swirl vanes and the vane-support sleeve in an annular space defined between the fuel-supply tube and a surrounding air-supply duct to “split” the air flowing through an air-supply duct toward a combustion chamber formed in a downstream burner cone and sleeve into (1) a “straight-line” air stream flowing in the annular inner (first) airflow channel formed between an exterior surface of the fuel-supply tube and an interior surface of the vane-support sleeve and mixing with fuel streams discharged through a first set of fuel jet ports located in the annular inner first airflow channel and (2) a “swirling” air stream flowing in an annular outer (second) airflow channel (containing a swirler defined by the air-swirl vanes) formed between an exterior surface of the vane-support sleeve and an interior surface of the air-supply duct and mixing with fuel streams discharged through a second set of fuel jet ports formed in the air-swirl vanes to establish a swirling air/fuel mixture surrounding the straight-line air/fuel mixture and cooperating with the straight-line air-fuel mixture (and with an auxiliary fluid stream passing through a small-diameter fluid-injector tube extending through the fuel-supply tube) to establish a combustible air/fuel mixture that flows through an air/fuel transfer channel arranged to extend from the air-swirl vanes to the combustion chamber and located between the exterior surface of the fuel-supply tube and the interior surface of the air-supply duct and ignites in the combustion chamber to produce a stable flame associated with a downstream end of the fuel-supply tube; 
           [0013]      FIG. 4  is an enlarged perspective view of the air-supply duct of  FIGS. 2 and 3 , with portions broken away, showing air flowing from the air plenum through a small-diameter annular opening into the inner (first) airflow channel and through a surrounding large-diameter annular opening into the outer (second) airflow channel and showing discharge of a second stream of fuel through the second set of jet ports to mix with swirling air discharged from the annular outer (second) airflow channel to produce a swirling air/fuel mixture flowing in a spiraling pattern in the downstream air/fuel transfer channel; 
           [0014]      FIG. 5  is a perspective view of the air-supply duct of  FIG. 4  taken from a different point of view showing the straight-line air/fuel mixture flowing along the cylindrical exterior surface of the fuel-supply tube and showing the swirling air/fuel mixture flowing in a spiraling pattern along the cylindrical interior surface of the air supply tube and around the straight-line air/fuel mixture and showing an auxiliary fluid stream being discharged from a small-diameter fluid-injector tube extending through a downstream end of the larger-diameter fuel-supply tube; 
           [0015]      FIG. 6  is a diagrammatic view showing a center circle representing the fuel-supply tube and containing a smaller circle representing the fluid-injector tube, a “small-diameter” annular zone around the fuel-supply tube containing the straight-line air/fuel mixture, a “large-diameter” annular zone surrounding the small-diameter annular zone and containing the swirling air/fuel mixture, and a circular “shear” interface (shown in phantom) between the small-diameter and large-diameter annular zones; 
           [0016]      FIG. 7  is a top plan view of the burner shown in  FIG. 3 , with portions broken away, showing the auxiliary fluid stream flowing from the fluid-injector tube into the combustion chamber, along a “center-line” path through the burner, and showing an “interface” between the straight-line air/fuel mixture flowing through the air/fuel transfer channel into the combustion chamber and the swirling air/fuel mixture surrounding the straight-line air/fuel mixture and flowing in a spiraling pattern through the air/fuel transfer channel into the combustion chamber; 
           [0017]      FIG. 8  is an enlarged sectional view taken along line  8 - 8  of  FIG. 3  showing radially outward flow of fuel from the fuel-supply tube through apertures formed in the fuel-supply tube into short radiated first-stage fuel transfer tubes and then into the annular inner (first) airflow channel through fuel jet ports formed in the short radiated first-stage fuel transfer tubes to generate a straight-line air/fuel mixture flowing in the air/fuel transfer channel toward the combustion chamber and showing further radially outward flow of fuel from the short radiated first-stage fuel transfer tube into longer angled second-stage fuel transfer tubes formed in downstream ends of the air-swirl vanes and then into the annular outer (second) airflow channel through fuel jet ports formed in the angled second-stage fuel transfer tubes to generate a “swirling” air/fuel flowing mixture in the air/fuel transfer channel toward the combustion chamber; 
           [0018]      FIG. 9  is a sectional view taken along line  9 - 9  of  FIG. 8  showing discharge of fuel through fuel jet ports formed in the short radiated first-stage fuel transfer tubes into the annular inner airflow channel; 
           [0019]      FIG. 10  is a sectional view taken along line  10 - 10  of  FIG. 8  showing discharge of fuel through fuel jet ports formed in the longer angled second-stage fuel transfer tubes into the annular outer airflow channel; and 
           [0020]      FIG. 11  is a perspective and diagrammatic view showing flow of the swirling air/fuel mixture in a spiraling pattern about the straight-line air/fuel mixture. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    An air-fuel combustion system  10  for burning a mixture of air and fuel to produce a flame  12  in a combustion chamber  14  is shown diagrammatically in  FIG. 1  and illustratively in  FIG. 3 . A “straight-line” air/fuel mixture  16  produced by mixing a first fuel stream  21  with a non-swirling laminar flow of air flowing in a first airflow channel  31  combines in combustion chamber  14  with a “swirling” air/fuel mixture  18  produced by mixing a second fuel stream  22  with swirling air flowing in a second airflow channel  32  as shown diagrammatically in  FIG. 1  and illustratively in  FIGS. 4-7 . An auxiliary fluid stream  23  is also discharged into combustion chamber  14  through a fluid-injector tube  26  in an illustrative embodiment to mix with mixtures  16  and  18  to produce combustible mixture  19 . Combustible mixture  19  is ignited by ignitor/pilot  24  to produce a stable flame  12  in combustion chamber  14  as shown diagrammatically in  FIG. 1  and illustratively in  FIG. 3 . 
         [0022]    Any suitable fuel can be provided by fuel supply  11 A. Fluid supply  11 B may be configured to supply various fluids including fuel gases, liquid fuels, inert gases, or oxidants to combustion chamber  14  via fluid-injection tube  26 . Fuels may be supplied by fluid supply  11 B as gases or liquids to create waste burning, combination fuel, or dual fuel embodiments. Inerts such as steam or flue gas may be supplied by fluid supply  11 B to assist in the reduction of pollutant formations. Oxidants such as air or oxygen may be supplied by fluid supply  11 B to boost burner capacity or increase flame temperatures. In an illustrative embodiment, fuel gas is provided by fuel supply  11 A and oil is provided by fuel supply  11 B. It is within the scope of this disclosure to use one fuel supply in lieu of two supplies  11 A,  11 B. 
         [0023]    As suggested in  FIG. 1 , in an illustrative embodiment, combustion air  27  flows from air supply  28  through air plenum  29  into an air-supply duct  30  containing first and second airflow channels  31 ,  32 . “Duct,” as used herein, means a pipe, tube, or channel that conveys a substance. Fuel  20  discharged from a fuel supply  11 A is split to produce (1) a first fuel stream  21  that mixes with combustion air  131  flowing through first airflow channel  31  and (2) a second fuel stream  22  that mixes with combustion air  132  flowing through second airflow channel  32  as suggested in  FIG. 1 . 
         [0024]    A swirler  36  is associated with second airflow channel  32  and configured to provide means for swirling combustion air  132  flowing in second airflow channel  32  in a direction toward combustion chamber  14 . In the illustrative embodiment, swirler  36  is arranged to swirl only combustion air and not fuel or an air/fuel mixture. Also, in an illustrative embodiment, swirler  36  includes a sleeve  74  arranged to define a boundary between first and second airflow channels  31 ,  32  as suggested in  FIG. 3 . 
         [0025]    In an illustrative embodiment, air-supply duct  30  is formed to include an air-conductor passageway  130  containing swirler  36  as shown, for example, in  FIGS. 1 and 3 . An upstream end of air-supply duct  30  is arranged to communicate with air plenum  29  to allow combustion air  27  to flow from air plenum  29  into air-conducting passageway  130  so as to intercept swirler  36 . 
         [0026]    An air/fuel transfer channel  40  is interposed between air-supply duct  30  and combustion chamber  14  in an illustrative embodiment as shown diagrammatically in  FIG. 1  and illustratively in  FIG. 3 . A fluid-injector tube  26  is coupled to fluid supply  11 B and arranged to extend through air/fuel transfer channel  40  to conduct an auxiliary fluid stream  23  into combustion chamber  14  as shown diagrammatically in  FIG. 1  and illustratively in  FIG. 3 . Air/fuel transfer channel  40  provides means for conducting straight-line air/fuel mixture  16  and swirling air/fuel mixture  18  to combustion chamber  14  where mixtures  16 ,  18  cooperate with auxiliary fluid stream  23  to define combustible mixture  19 . In an illustrative embodiment, shown in  FIGS. 5 and 6 , straight-line air/fuel mixture  16  flows into combustion chamber  14  through a small-diameter inner annular zone  41  (defined by small dimension  141 ) located in air/fuel transfer channel  40  and swirling air/fuel mixture  18  flows into combustion chamber  14  through a large-diameter outer annular zone  42  (defined by larger dimension  142 ) surrounding small-diameter inner annular zone  41  and lying in air/fuel transfer channel  40 . 
         [0027]    A somewhat “cylindrical” shear layer stabilization boundary  43  is created between inner and outer annular zones  41 ,  42  in air/fuel transfer channel  40  and an inlet region  44  provided in combustion chamber  14  as suggested diagrammatically in  FIG. 6  and illustratively in  FIG. 5 . Ignition of straight-line and swirling air/fuel mixtures  16 ,  18  and auxiliary fluid stream  23  in combustion chamber  14  using ignitor  24  produces a stable flame  12 . Flame attachment of flame  12  is provided by reacting boundary layers along shear layer stabilization boundary  43  located between inner and outer annular zones  41 ,  42  to define a “zero-velocity” flow zone containing at least the root of flame  12 . In other words, flame  12  is attached by reacting swirling air/fuel mixture  18  and annular straight-line air/fuel mixture  16  accelerated by fluid-injector tube  26  working in combination with the resultant zero velocity flow zone. Flame attachment is enhanced by the presence of an annular flow guide provided by fluid-injector tube  26 . Fluid-injector tube  26  also enhances the stable operation range of burner  10  by providing low-flow recirculation eddies. 
         [0028]    Air-fuel combustion system  10  includes an air-supply housing  50  comprising a small-diameter front plate  52 , a large-diameter rear plate  54 , and a frustoconical shell  56  arranged to extend between front and rear plates  52 ,  54  as suggested in  FIGS. 2 and 3 . A gasket  53  is interposed between front plate  52  and a circular flange provided on a small-diameter end of frustoconical shell  56  as suggested in  FIGS. 3 and 7  to establish a sealed connection between front plate  52  and shell  56 . 
         [0029]    An elongated pipe  38  includes both air-supply duct  30  and air/fuel transfer channel  40  in an illustrative embodiment as shown in  FIG. 3 . Elongated pipe  38  is fixed to extend into an interior region  57  formed in frustoconical shell  56  so that at least air-supply duct  30  lies in that interior region  57  as shown in  FIG. 3 . Air-supply housing  50  also includes an air inlet pipe  58  having one end adapted to receive combustion air from air supply  28  and another end coupled to frustoconical shell  56  to discharge combustion air from air supply  28  through an aperture formed in frustoconical shell  56  into an air plenum  29  provided inside air-supply housing  50  as suggested in  FIG. 3 . In an illustrative embodiment, front plate  52 , frustoconical shell  56 , and elongated pipe  38  cooperate to define air plenum  29  as shown, for example, in  FIG. 3 . Elongated pipe  38  is arranged to cause a downstream end of air/fuel transfer channel  40  to open into combustion chamber  14  as shown, for example, in  FIG. 3 . 
         [0030]    A pilot-mount fixture  60  is coupled to one side of frustoconical shell  56  to mate with a first aperture  59  formed in shell  56 . A viewer-mount fixture  62  for combustion chamber viewer  64  is coupled to another side of shell  56  to mate with a second aperture  61  formed in shell  56 . An air probe fixture  63  is coupled to shell  56  as shown, for example, in  FIG. 3  to mate with a third aperture  63  formed in shell  56 . An air flow measurer  163  is coupled to air probe fixture  63  and used to measure the flow rate of air  27  in air-supply duct  30 . 
         [0031]    A fuel-supply tube  66  is arranged to extend through a passageway formed in elongated pipe  38  and fluid-injector tube  26  is arranged to extend through a fuel-conductor passageway  166  formed in fuel-supply tube  66  along a “center line” path  126  through burner  10  as shown in  FIG. 3 . Fuel-supply tube  66  includes an outer end  67  coupled to an inlet tube  68  that is connected to fuel supply  11 A by supply line  65  and an inner end  69  arranged to extend into an interior region of air-supply housing  50 . Outer end  67  of fuel-supply tube  66  extends through an aperture formed in front plate  52  of air-supply housing  50  as shown, for example, in  FIGS. 2 and 3 . Supply line  65 , fuel-supply tube  66 , and inlet tube  68  cooperate to define a fuel-supply duct  17  configured to conduct fuel  20  from fuel supply  11 A to first and second airflow channels  21 ,  22 . 
         [0032]    As shown, for example, in  FIGS. 2 ,  4 , and  8 , swirler  36  comprises several air-swirl vanes  70  mounted in a “pin-wheel” pattern on an exterior surface  72  of an annular vane-support sleeve  74 . In an illustrative embodiment, each air-swirl vane  70  has a helical shape as suggested in  FIGS. 2-4 . 
         [0033]    In an illustrative embodiment, vane-support sleeve  74  is cylindrical and formed to include a duct-receiver passageway  174  extending therethrough and receiving a portion of fuel-supply tube  66  therein as suggested, for example, in  FIGS. 2 ,  3 , and  8 . As suggested, for example, in  FIGS. 3 ,  4 , and  8 , vane-support sleeve  74  is arranged to separate and define a boundary between first and second airflow channels  31 ,  32  locating first airflow channel  31  in a space between an exterior surface  75  of fuel-supply tube  66  and an interior surface  73  of vane-support sleeve  74  and locating second airflow channel  32  in a space between an exterior surface  72  of vane-support sleeve  74  and an interior surface  77  of air-supply duct  30 . 
         [0034]    Vane-support sleeve  74  is arranged to lie inside air-conductor passageway  130  formed in air-supply duct  30  of elongated pipe  38  and to receive and surround a mid-portion  263  of fuel-supply tube  66  as suggested in  FIGS. 3 and 8 . Radially extending standoffs  76  are arranged to extend between a cylindrical exterior surface  75  of fuel-supply tube  66  and a cylindrical interior surface  73  of vane-support sleeve  74  to define an elongated, annular, first airflow channel  31  therebetween as suggested in  FIGS. 4 and 8 . Cylindrical exterior surface  72  of vane-support sleeve  74  lies inside and in spaced-apart relation to a cylindrical interior surface  77  of air-supply duct  30  to define an elongated, annular, second airflow channel  32  therebetween as suggested in  FIGS. 4 and 8 . 
         [0035]    As suggested in  FIGS. 3 and 4 , vane-support sleeve  74  is placed in an annular space between fuel-supply tube  66  and the surrounding air-supply duct  30  of elongated pipe  38  to “split” combustion air  27  flowing through air-supply duct  30  toward combustion chamber  14  formed in a downstream burner discharge cone  113  and sleeve  114 . Combustion air  27  is split into (1) a “straight-line” air stream  131  (characterized, for example, by laminar flow) flowing in annular inner (first) airflow channel  31  and (2) a “swirling” air stream  132  flowing in annular outer (second) airflow channel  32 . 
         [0036]    A first fuel stream  21  is discharged into straight-line air stream  131  as suggested diagrammatically in  FIG. 1  to produce straight-line air/fuel mixture  16 . In an illustrative embodiment shown, for example, in  FIGS. 8 and 9 , fuel-supply tube  66  is formed to include a series of circumferentially and uniformly spaced-apart apertures  80 . The fuel delivery system further includes a fuel sprayer  83  configured to provide means for discharging fuel  20  flowing in fuel-supply duct  17  and exiting from fuel-supply tube  66  through apertures  80  into each of first and second airflow channels  31 ,  32 . In an illustrative embodiment, fuel sprayer  83  is located in a space provided between downstream ends of air-swirl vanes  70  and air/fuel transfer duct  40  and in air-conductor passageway  130  as suggested, for example, in  FIGS. 3 and 4 . 
         [0037]    In an illustrative embodiment, fuel sprayer  83  includes a series of short radiated first-stage fuel transfer tubes  82  coupled to fuel-supply tube  66  as shown in  FIGS. 8 and 9 . Each first-stage fuel transfer tube  82  is aligned with one of the apertures  80  to receive fuel discharged through that aperture  80  and is formed to include a side-discharge aperture  84  opening into first airflow channel  31 . First fuel stream  21  flows through first-stage side-discharge apertures (i.e., a first set of fuel jet ports)  84  into first airflow channel  31  to mix with combustion air  131  flowing in first airflow channel  31  to produce straight-line air/fuel mixture  16 . In an illustrative embodiment, first fuel stream  21  is about 10% of fuel  20  discharged from fuel supply  11 A into fuel-supply tube  66 . 
         [0038]    A second fuel stream  22  is discharged by fuel sprayer  83  into swirling air stream  132  as suggested diagrammatically in  FIG. 1  to produce swirling air/fuel mixture  18 . In an illustrative embodiment shown, for example, in  FIGS. 8 and 10 , longer angled second-stage fuel transfer tubes  86  are included in fuel sprayer  83  and coupled to downstream ends of air-swirl vanes  70 . Each second-stage fuel transfer tube  86  is coupled to an open-ended distal portion of one of the short radiated first-stage fuel transfer tubes  82  as suggested in  FIG. 8  to receive any fuel discharged therefrom. Each second-stage fuel transfer tube  86  is formed to include a series of first and second side-discharge apertures (i.e., a second set of fuel jet ports)  87 ,  88  opening into second airflow channel  32 . Second fuel stream  22  flows through first and second side-discharge apertures  87 ,  88  formed in second-stage fuel transfer tubes  86  to mix with combustion air  132  flowing in second airflow channel  32  to produce swirling air/fuel mixture  18 . In an illustrative embodiment, the second fuel stream is about 90% full of fuel  20  discharged from fuel supply  11 A into fuel-supply tube  66 . 
         [0039]    An ignition controller  90  is provided and coupled to ignitor/pilot  24  as shown, for example, in  FIG. 7 . Ignition controller  90  can be used to activate ignitor/pilot  24  and produce a spark or flame to ignite the combustible mixture  19  defined by straight-line air/fuel mixture  16 , swirling air/fuel mixture  18 , and auxiliary fluid stream  23  extant in combustion chamber  14 . A stable flame  18  is produced and can be viewed and monitored using combustion chamber viewer  64  as suggested in  FIG. 7 .