Abstract:
A burner supporting primary and secondary combustion reactions may include a primary combustion reaction actuator configured to select a location of the secondary combustion reaction. A burner may include a lifted flame holder structure configured to support a secondary combustion reaction above a partial premixing region. The secondary flame support location may be selected as a function of a turndown parameter. Selection logic may be of arbitrary complexity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority benefit from U.S. Provisional Patent Application No. 61/765,022, entitled “PERFORATED FLAME HOLDER AND BURNER INCLUDING A PERFORATED FLAME HOLDER”, filed Feb. 14, 2013; which, to the extent not inconsistent with the disclosure herein, is incorporated by reference. 
         [0002]    The present application is related to docket number 2651-172-04, entitled “PERFORATED FLAME HOLDER AND BURNER INCLUDING A PERFORATED FLAME HOLDER”, filed Feb. 14, 2014; docket number 2651-188-04, entitled “FUEL COMBUSTION SYSTEM WITH A PERFORATED REACTION HOLDER”, filed Feb. 14, 2014; and docket number 2651-204-04, entitled “STARTUP METHOD AND MECHANISM FOR A BURNER HAVING A PERFORATED FLAME HOLDER”, filed Feb. 14, 2014; which, to the extent not inconsistent with the disclosure herein, are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0003]    Combustion systems are widely employed throughout society. There is a continual effort to improve the efficiency and reduce harmful emissions of combustion systems. 
       SUMMARY 
       [0004]    Lifting a flame base to provide an increased entrainment length before the onset of combustion has been found by the inventors to reduce oxides of nitrogen (NOx) emissions. 
         [0005]    Lifting a flame base while maintaining inherent flame stability has proven challenging. 
         [0006]    According to an embodiment, a lifted flame burner includes a primary fuel source configured to support a primary combustion reaction, a secondary fuel source configured to support a secondary combustion reaction, a bluff body configured to hold the secondary combustion reaction, and a lifted flame holder disposed farther away from the primary and secondary fuel sources relative to the bluff body and aligned to be at least partially immersed in the secondary combustion reaction when the secondary combustion reaction is held by the bluff body. An electrically-powered primary combustion reaction actuator is configured to control exposure of a secondary fuel flow from the secondary fuel source to the primary combustion reaction. The electrically-powered primary combustion reaction actuator is configured to reduce or eliminate exposure of the secondary fuel flow to the primary combustion reaction when the electrically-powered primary combustion reaction actuator is activated. 
         [0007]    According to another embodiment, a method for operating a lifted flame burner includes supporting a primary combustion reaction to produce an ignition source proximate to a bluff body, providing a secondary fuel stream to impinge on the bluff body, and igniting the secondary fuel stream to produce a secondary combustion reaction. The primary combustion reaction is electrically actuated to remove or reduce effectiveness of the primary combustion reaction as an ignition source proximate to the bluff body. The secondary combustion reaction is allowed to lift and be held by a lifted flame holder. The secondary fuel stream is diluted in a region between the bluff body and the lifted flame holder. Responsive to an interruption in electrical power, the secondary combustion reaction is held by the bluff body. 
         [0008]    According to another embodiment, a method for controlling combustion can include selectively applying power to a primary combustion reaction or pilot flame actuator, and selectively applying ignition to a secondary combustion reaction with the primary combustion reaction or pilot flame as a function of the selective application of power to the primary combustion reaction or pilot flame actuator. 
         [0009]    According to another embodiment, a combustion control gain apparatus includes a first fuel source configured to support a pilot flame or primary combustion reaction, a pilot flame or primary combustion reaction actuator configured to select a primary combustion reaction or pilot flame deflection, and a secondary fuel source. The pilot flame or primary combustion reaction deflection is selected to control a secondary fuel ignition location. 
         [0010]    According to another embodiment, a combustion control gain apparatus includes a first fuel source configured to support a pilot flame or primary combustion reaction, a pilot flame or primary combustion reaction actuator configured to select a primary combustion reaction or pilot flame deflection, and a secondary fuel source. The pilot flame or primary combustion reaction deflection is selected to control a non-ignition location where the secondary fuel is not ignited. A bluff body corresponds to a secondary fuel ignition location when the primary combustion reaction or pilot flame is not deflected. A lifted flame holder corresponds to a secondary fuel ignition location when the primary combustion reaction or pilot flame is deflected. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1A  is a diagram of a burner including a lifted flame holder in a state where a secondary flame is anchored to a bluff body below the lifted flame holder, according to an embodiment. 
           [0012]      FIG. 1B  is a diagram of the burner including the lifted flame holder of  FIG. 1A  in a state where the secondary flame is anchored to the lifted flame holder above the bluff body, according to an embodiment. 
           [0013]      FIG. 2  is a side-sectional diagram of a burner including coanda surfaces along which a primary combustion reaction may flow responsive to deflection or non-deflection of the primary combustion reaction, according to an embodiment. 
           [0014]      FIG. 3  is a top view of a burner including a lifted flame holder wherein a primary combustion reaction actuator includes an ionic wind device, according to an embodiment. 
           [0015]      FIG. 4  is a diagram of a lifted flame holder, according to an embodiment. 
           [0016]      FIG. 5  is a diagram of a burner including a lifted flame holder, according to another embodiment. 
           [0017]      FIG. 6  is a block diagram of a burner including a lifted flame holder and a feedback circuit configured to sense operation of the lifted flame holder, according to an embodiment. 
           [0018]      FIG. 7  is a flow chart depicting a method for operating a burner including a primary combustion reaction actuator configured to select a secondary combustion location, according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the disclosure. 
         [0020]      FIG. 1A  is a side-sectional diagram of a portion of a burner  100  including a lifted flame holder  108  in a state where a secondary flame (also referred to as a secondary combustion reaction)  101  is anchored to a bluff body  106  below the lifted flame holder  108 , according to an embodiment.  FIG. 1B  is a side-sectional diagram of the portion of the burner  100  including the lifted flame holder  108  in a state where the secondary flame  101  is anchored to the lifted flame holder  108  above the bluff body  106 , according to an embodiment. In the pictured embodiment, the lifted flame holder  108  and the bluff body  106  are toroidal in shape. Only one side of the burner is shown, the other side being a substantial mirror image. 
         [0021]    The lifted flame burner  100  includes a primary fuel source  102  configured to support a primary combustion reaction  103 . A secondary fuel source  104  is configured to support a secondary combustion reaction  101 , and includes a groove  112  that extends around the inner surface of the bluff body, and a plurality of holes  114  that exit at the top of the bluff body. The bluff body  106  is configured to hold the secondary combustion reaction  101 . The lifted flame holder  108  is disposed farther away from the primary and secondary fuel sources  102 ,  104  relative to the bluff body  106  and aligned to be at least partially immersed in the secondary combustion reaction  101  when the secondary combustion reaction is held by the bluff body  106 . 
         [0022]    An electrically-powered primary combustion reaction actuator  110  can be configured to control exposure of a secondary fuel flow from the secondary fuel source  104  to the primary combustion reaction  103 . The electrically-powered primary combustion reaction actuator  110  can be configured to reduce or eliminate exposure of the secondary fuel flow to the primary combustion reaction  103  when the electrically-powered primary combustion reaction actuator  110  is activated. Similarly, the electrically-powered primary combustion reaction actuator  110  can be configured to cause or increase exposure of the secondary fuel flow to the primary combustion reaction  103  when the electrically-powered primary combustion reaction actuator  110  is not activated. For example, the electrically-powered primary combustion reaction actuator  110  can be configured as an electrically-powered primary combustion reaction deflector  110 . The electrically-powered primary combustion reaction deflector  110  is configured to deflect momentum or buoyancy of the primary combustion reaction  103  when the electrically-powered primary combustion reaction deflector  110  is activated. 
         [0023]    According to an embodiment, the deflected momentum or buoyancy of the primary combustion reaction  103  caused by the activated primary combustion reaction deflector  110  can be selected to cause the secondary combustion reaction to lift from being held by the bluff body  106  to being held by the lifted flame holder  108 . Additionally and/or alternatively, the electrically-powered primary combustion reaction deflector  110  can be configured to deflect the primary combustion reaction  103  away from a stream of secondary fuel output by the secondary fuel source  104  when the electrically-powered primary combustion reaction deflector  110  is activated. The deflection of the primary combustion reaction  103  away from the stream of secondary fuel can be selected to delay ignition of the secondary fuel. 
         [0024]      FIG. 2  is a side-sectional diagram of a burner  200  including coanda surfaces  202 ,  204  along which a primary combustion reaction can flow, according to an embodiment. The burner  200  includes a bluff body  106 . The bluff body  106  includes the two coanda surfaces  202 ,  204 . 
         [0025]    A primary fuel source  102  is aligned to cause the primary combustion reaction to occur substantially along the first coanda surface  202  when the electrically-powered primary combustion reaction deflector  110  is not activated. The electrically-powered primary combustion reaction deflector  110  is configured to cause the primary combustion reaction to occur substantially along the second coanda surface  204  when the electrically-powered primary combustion reaction deflector  110  is activated. 
         [0026]    According to an embodiment, the first coanda surface  202  is aligned to cause the primary combustion reaction to cause ignition of the secondary fuel substantially coincident with the bluff body  106 . The second coanda surface  204  is aligned to cause the primary combustion reaction to cause ignition of the secondary fuel between the bluff body  106  and the lifted flame holder  108 . Additionally or alternatively, the second coanda surface  204  can be aligned to cause the primary combustion reaction to cause ignition of the secondary fuel substantially coincident with the lifted flame holder  108 . Additionally or alternatively, the second coanda surface  204  can be aligned to cause the primary combustion reaction or products from the primary combustion reaction to combine with the secondary combustion reaction without causing ignition of the secondary combustion reaction. 
         [0027]    Referring to  FIGS. 1A ,  1 B, and  2 , the electrically-powered primary combustion reaction deflector  110  can include an ionic wind device (as illustrated). The ionic wind device includes a charge-ejecting electrode such as a corona electrode (also referred to as a serrated electrode)  116 . According to an embodiment, the serrated electrode  116  is configured to be held at between 15 kilovolts and 50 kilovolts when the electrically-powered primary combustion reaction deflector  110  is activated. The ionic wind device also includes a smooth electrode  118 . The smooth electrode  118  is configured to be held at or near electrical ground (at least) when the electrically-powered primary combustion reaction deflector  110  is activated. The ionic wind device is preferably disposed in a region of space characterized by a temperature below the primary combustion reaction temperature. Keeping the ambient temperature around or the surface temperature of the charge-ejecting electrode  116  relatively low was found by the inventors to improve the rate of charge ejection at a given voltage. The charge ejection voltage can be determined according to Peek&#39;s Law. 
         [0028]    A lifting distance d from the bluff body  106  to at least a portion of the lifted flame holder  108  can be selected to cause partial premixing of the secondary combustion reaction when the secondary combustion reaction is held by the lifted flame holder  108 . The lifting distance d from the bluff body  106  to at least a portion of the lifted flame holder  108  can be selected to cause the combination of the primary combustion reaction and the secondary combustion reaction to output reduced oxides of nitrogen (NOx) when the secondary combustion reaction is held by the lifted flame holder  108 . For example, the lifting distance d can be selected to cause the stream of secondary fuel output by the secondary fuel source  104  to entrain sufficient air to result in the secondary combustion reaction being at about 1.3 to 1.5 times a stoichiometric ratio of oxygen to fuel. 
         [0029]    According to an embodiment, the lifting distance d can be about 4.25 inches. Greater lifting distance d can optionally be selected by providing a lifted flame holder support structure (not shown) configured to hold the lifted flame holder  108  at a greater height above the bluff body  106 . The lifted flame holder support structure can itself be supported from the bluff body  106  or a furnace floor (not shown). 
         [0030]    According to an embodiment, the electrically-powered primary combustion reaction actuator  110  is configured to cause the secondary flame  101  to be reduced in height when the electrically-powered primary combustion reaction actuator  110  is activated compared to the secondary flame height when the electrically-powered primary combustion reaction actuator  110  is not activated. 
         [0031]    The primary fuel nozzle is aligned to cause the secondary combustion reaction to be ignited by the primary combustion reaction when the primary combustion reaction actuator  110  is not actuated. The primary fuel combustion reaction can be held by the bluff body  106  when the electrical power is turned off or fails. 
         [0032]    In other words, according to this embodiment, as long as electrical power is present in the system, the primary combustion reaction deflector  110  remains energized and operates to prevent the primary combustion reaction  103  from igniting the secondary combustion reaction  101  in the region of the bluff body  106 . This permits the secondary combustion reaction  101  to be held instead by the lifted flame holder  108 . However, in the event of a loss of power, the primary combustion reaction deflector  110  no longer acts on the primary combustion reaction  103 , which, because of the alignment of the primary fuel nozzle  102  ignites the fuel from the secondary fuel source  104  and causing the secondary combustion reaction to be held by the bluff body  106 . 
         [0033]      FIG. 3  is a top view of a burner  300  including a lifted flame holder  108 , a bluff body  106 —positioned behind the lifted flame holder in the view of  FIG. 3  and shown in hidden lines—and a primary combustion reaction deflector  110  that includes an ionic wind device, according to an embodiment. The lifted flame holder  108  and the bluff body  104  can each have a toroid shape, a portion of which is shown in  FIG. 3 . The ionic wind device includes a charge ejecting electrode (such as a serrated electrode)  116  configured to be held at a high voltage and a smooth electrode  118  configured to be held at or near voltage ground. The serrated electrode  116  and the smooth electrode  118  define a line or a plane that intersects the primary fuel source  102 . When energized, the charge ejecting electrode  116  ejects ions that are strongly attracted toward the counter-charged smooth electrode  118 . Ions moving from the charge electrode  116  toward the smooth electrode  118  entrain air, which moves along the same path. Although most of the ions contact the smooth electrode and discharge, the entrained air, i.e., ionic wind, continues along the same path toward the primary fuel source  102  and the primary combustion reaction supported thereby. The primary combustion reaction is in turn entrained or carried by the movement of air to circulate in a groove  112  formed in an interior surface of the toroidal bluff body  106 , preventing the primary combustion reaction from entering holes in the bluff body  106 . When power is removed from the ionic wind device, the primary combustion reaction is no longer deflected by air moving laterally along the bluff body  106 , and is thus permitted to emerge through a plurality of holes  114  in a top surface of the bluff body  106  when the electrically-powered primary combustion reaction deflector  110  is not activated. 
         [0034]    The burner  300  includes a plurality of primary fuel sources  102 , secondary fuel sources  104 , and primary combustion reaction deflectors  110  distributed evenly around the bluff body  106 , as shown in part in  FIG. 3 . The pluralities of elements are preferably configured to operate in concert with each other, for more effective operation. For example, each of the primary combustion reaction deflectors  110  is oriented in the same direction (facing clockwise, as viewed from above in the example of  FIG. 3 ), and energized simultaneously. Thus, air movement in the groove  112  produced by an ionic wind generated by one of the plurality of primary combustion reaction deflectors  110  reinforces air movement generated by others of the plurality, which increases the effectiveness of each of the devices. 
         [0035]      FIG. 4  is a diagram of a lifted flame holder  108 , according to an embodiment. The lifted flame holder  108  of  FIG. 4  includes a volume of refractory material  402 . The volume of refractory material  402  can be selected to allow the secondary combustion reaction to occur at least partially within a plurality of partially bounded passages  404  extending through the flame holder  108 . The plurality of partially bounded passages  404  includes a plurality of vertically-aligned cylindrical voids through the refractory material  402 . The refractory material  402  can be formed in a toric shape or as a section of a toric shape (as shown), for example. The lifted flame holder  108  can be about two to three inches thick, for example. The bounded passages  404  were formed by drilling the cylindrical voids through the refractory material. The inventors used drill bits ranging from ⅜ inch to about ¾ inch to drill the cylindrical voids, according to various embodiments. The inventors contemplate various alternative ways to form the lifted flame holder  108  and the cylindrical voids. For example, the cylindrical voids can be cast in place. 
         [0036]      FIG. 5  is a diagram of a burner  500  that includes a lifted flame holder  108 , according to an embodiment. According to the embodiment, the electrically-powered primary combustion reaction actuator  110  includes a primary combustion reaction control valve  502  and a secondary combustion reaction control valve  504 . The primary combustion reaction control valve  502  is preferably configured as a normally-open valve that is actuated to a reduced flow rate when electrical power is applied to the control valve. Optionally, the primary combustion reaction control valve  502  can be closed when the secondary combustion reaction is held by the lifted flame holder  108 . 
         [0037]      FIG. 6  is a block diagram of a burner  600  including a lifted flame holder  108  and a feedback circuit  601  configured to sense operation of the lifted flame holder, according to an embodiment. The feedback circuit  601  is configured to sense the presence or absence of a secondary combustion reaction at the lifted flame holder  108 . The feedback circuit  601  is configured to interrupt electrical power to the electrically-actuated primary combustion reaction  110  when the secondary combustion reaction is not held by the lifted flame holder  108 . Additionally and/or alternatively, the feedback circuit  600  can be configured to interrupt electrical power to the electrically-powered primary combustion reaction actuator  110  when the lifted flame holder  108  is damaged or fails. 
         [0038]    According to an embodiment, the feedback circuit  601  includes a detection electrode  602 . The detection electrode  602  is configured to receive an electrical charge imparted onto the secondary combustion reaction by the electrically-powered primary combustion reaction actuator  110  and/or a combustion reaction charge source, and to produce a voltage signal that corresponds to a value of the received charge. A node  604  of a voltage divider  605  is operatively coupled to the detection electrode  602 , and is configured to provide a voltage that is proportional to the voltage signal produced by the detector  602 , which is thus indicative of the presence or absence of a secondary combustion reaction  101  held by the lifted flame holder  108 . 
         [0039]    A logic circuit  606  is operatively coupled to the sensor  604 , and is configured to cause application of a voltage from a voltage source  608  to the primary combustion reaction actuator  110  while a voltage signal is present at the node  604 . A loss of the voltage signal from the detection electrode  602  causes the voltage at the node  604  to drop, in response to which the logic circuit  606  interrupts electrical power to the electrically-powered primary combustion reaction actuator  110 . The actuator  110 , in turn, stops deflecting the primary combustion reaction  103 , which begins to ignite the secondary combustion reaction  101  at the bluff body  106 . 
         [0040]      FIG. 7  is a flow chart depicting a method  700  for operating a burner including a primary combustion reaction actuator configured to select a secondary combustion location, according to an embodiment. 
         [0041]    The method  700  for operating a lifted flame burner can include step  702 , in which a primary combustion reaction is supported to produce an ignition source proximate to a bluff body. In step  704 , a secondary fuel stream is provided to impinge on the bluff body. Proceeding to step  706 , the secondary fuel stream is ignited to produce a secondary combustion reaction. In step  708 , the primary combustion reaction is electrically actuated to remove or reduce effectiveness of the primary combustion reaction as an ignition source proximate to the bluff body. Proceeding to step  710 , the secondary combustion is allowed to lift and be held by a lifted flame holder. 
         [0042]    In step  712  the secondary fuel stream is diluted in a region between the bluff body and the lifted flame holder. Diluting the secondary fuel stream in the region between the bluff body and the lifted flame holder can cause the lifted secondary combustion reaction to occur at a lower temperature than the secondary combustion reaction held by the bluff body. Additionally and/or alternatively, diluting the secondary fuel stream in the region between the bluff body and the lifted flame holder can cause the lifted secondary combustion reaction to output reduced oxides of nitrogen (NOx) compared to the secondary combustion reaction when held by the bluff body. Diluting the secondary fuel stream in the region between the bluff body and the lifted flame holder can also cause the lifted secondary combustion reaction to react to substantial completion within a reduced overall secondary combustion flame height, as compared to the secondary combustion reaction when held by the bluff body. 
         [0043]    Referring to step  708 , in which the primary combustion reaction is electrically actuated to remove or reduce effectiveness of the primary combustion reaction as an ignition source proximate to the bluff body, step  708  can include deflecting the primary combustion reaction. The primary combustion reaction can be deflected, for example, with an ionic wind generator. 
         [0044]    Deflecting the primary combustion reaction with an ionic wind generator can include moving the primary combustion reaction from a first coanda surface to a second coanda surface. Additionally and/or alternatively, deflecting the primary combustion reaction with an ionic wind generator can include directing the primary combustion reaction along a groove in the bluff body. Deflecting the primary combustion reaction with an ionic wind generator preferably includes reducing output of the primary combustion reaction through holes formed in the bluff body. 
         [0045]    Referring to step  708 , removing or reducing effectiveness of the primary combustion reaction as an ignition source proximate to the bluff body can include reducing fuel flow to the primary combustion reaction. 
         [0046]    The method  700  can include step  714 , in which an interruption in electrical power to the primary combustion reaction actuator is received. Proceeding to step  716 , in response to the interruption in electrical power, the secondary combustion reaction is caused to be held by the bluff body. 
         [0047]    Referring to  FIGS. 1A-7 , the method  700  for controlling combustion can include selectively applying power to a primary combustion reaction or pilot flame actuator. Additionally and/or alternatively, the method  700  can include selectively applying ignition to a secondary combustion reaction with the primary combustion reaction or pilot flame as a function of the selective application of power to the primary combustion reaction or pilot flame actuator. 
         [0048]    According to an embodiment, a combustion control gain apparatus can include a first fuel source. The first fuel source may be configured to support a pilot flame or primary combustion reaction. 
         [0049]    The combustion control gain apparatus includes a pilot flame or a primary combustion reaction actuator  110 . The pilot flame or primary combustion reaction actuator  110  is configured to select a primary combustion reaction or pilot flame deflection. Additionally, a secondary fuel source  104  is included. The pilot flame or primary combustion reaction deflection is selected to control a secondary fuel ignition location. 
         [0050]    Additionally and/or alternatively, the pilot flame or primary combustion reaction deflection can be selected to control a non-ignition location where the secondary fuel is not ignited. 
         [0051]    A bluff body  106  can include a secondary fuel ignition location when the primary combustion reaction  103  or pilot flame is not deflected. 
         [0052]    A lifted flame holder  108  can correspond to a secondary fuel ignition location when the primary combustion reaction  103  or pilot flame is deflected. 
         [0053]    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.