Abstract:
A burner assembly has a burner head and a deflector plate extending radially therefrom and across a firetube housing for supporting the burner assembly therein. The deflector plate has a plurality of angled vanes for re-directing secondary combustion air flowing through the housing. Secondary air is deflected away from a nozzle tip at the burner head to minimize lifting of the flame by the deflector plate or by a low pressure ring formed around the nozzle tip above the deflector plate for creating an area of low pressure. Preferably, a combination of the deflector plate and low pressure ring provides a stable flame positioned at the nozzle tip under low-fire and high-fire conditions enabling use of a pilotless ignition and flame sensing system which is consistent under low and high fire conditions. More preferably, the deflector plate supports the igniter and optionally a heat return tube for heat tracing of the freeze-prone burner assembly components.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to the field of burners and particularly to gas burners used in industrial heaters.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is well known in a variety of industries to use heaters having burner assemblies for a number of different applications, including kilns, drying apparatus, furnaces and for preventing freezing of tanks and pipelines. In the oil and gas industry, heaters are particularly used in regions where low ambient temperatures may result in freezing of storage tanks or in production and process pipelines. Further process heaters are used which may be used when knocking water out of oil and when heating salt baths and the like. Gas burner assemblies are typically arranged in a housing or firetube which extends into a storage or holding tank to be heated.  
         [0003]     In prior art natural draft or “non-forced draft” situations, primary combustion air is drawn into a mixing chamber or mixer head of the gas burner assembly as a result of the velocity of the flammable gas entering the mixing chamber or venturi. The premixed gas/air fuel mixture exits the venturi at a burner nozzle, typically a rosebud nozzle, where the mixture is ignited. Secondary combustion air is drawn into the housing and around the burner assembly as a result of draft. The secondary air, intended to aid in combustion, may adversely affect the operation of the burner assembly. Large volumes of secondary air creating a large turbulent draft at the burner head may result in the flame being lifted from the burner nozzle or may blow out a flame at the nozzle. Attempts to reduce or dampen the amount of secondary air entering the burner can substantially shutoff the flow of secondary air which compromises the efficiency of the burner.  
         [0004]     Further, variability in operation can adversely affect the consistency of ignition and flame sensing. Typically, burners may be operated in high-fire and low-fire situations. In a low-fire situation, the pressure of fuel entering the burner is relatively low compared to a high-fire situation. Conventional burners which are set to operate under low-fire conditions can experience lifting of the flame from the burner nozzle should they be used in a high-fire situation. Thus, in conventional burners, ignition and flame sensing, which are optimized for one flame characteristic, become problematic as the position of the flame alters. Use of a pilot has provided a consistent flame source and ignition sensing. In variable firing conditions, should the fuel/air ratio and secondary air flow be sufficiently unstable at the burner nozzle, remote lighting of the burner becomes difficult. As a result, the industry has typically relied on manual lighting of such burners which has resulted in significant hazard to personnel performing the task.  
         [0005]     Additionally, freezing is a common problem with natural draft burner assemblies. Typically, areas of low pressure adjacent the orifice of the burner may result in freezing at the orifice or in the gas lines which feed the orifice. Low flow of fuel at pilot assemblies are even more prone to freezing  
         [0006]     Clearly, there is interest in the industry to provide a reliable burner which remains lit under ambient conditions, is safe to ignite and operate and permits flame-sensing in both low fire and high fire situations, does not freeze in low ambient temperature and is efficient.  
       SUMMARY OF THE INVENTION  
       [0007]     A burner assembly according to one embodiment of the invention comprises a pilotless ignition and flame sensing system and a burner head having a nozzle tip situated in a secondary air housing and which is equally operable at low and high fire. The nozzle tip discharges a mixture of primary air and gaseous fuel which is separated from the secondary air flowing therearound for stabilizing flame at the nozzle tip. A flame ionization sensor senses flame at the nozzle tip throughout low and high fire operation, obviating the need for a pilot. Secondary air is separated from the nozzle tip by directing the secondary air away from the tip such as through a conical ring situated on the burner head or by an air deflector ring which also serves to swirl the secondary air circumferentially in the housing or in a preferred embodiment, by a combination of both the low pressure ring and the deflector plate manufactured as a unitary structure with the nozzle head. More preferably, the burner assembly comprises a tubular barrel having a mixing chamber at the gas inlet end and a nozzle tip having a plurality of orifices at the burner head end. The mixing chamber can received aspirated primary combustion air, preferably through a plurality of air orifices, or through a forced air inlet.  
         [0008]     In a broad aspect of the invention, a burner assembly is provided for mounting in a housing and forming an annular space therebetween, the burner assembly having a nozzle tip mounted in a burner head at a first distal end of a tubular barrel, the tubular barrel having a primary combustion air inlet and a fuel inlet at a second proximal end for providing a flow of primary combustion air and fuel in the tubular barrel directed toward the nozzle tip and a flow of secondary combustion air in the annular space directed towards the nozzle tip, the burner assembly comprising: a deflector for deflecting the flow of secondary combustion air in the annular space away from at least the nozzle tip for stabilizing at least a position of a flame thereon. Preferably, a conical low pressure ring is positioned circumferentially about the nozzle tip and extends radially outwardly from the burner head for substantially separating the flow of primary combustion air and fuel from the flow of secondary combustion air at the nozzle tip creating an area of low pressure at the nozzle tip relative to a pressure of the secondary air in the annulus whereby lifting of the flame from the nozzle tip is reduced.  
         [0009]     In another embodiment, a pilotless burner assembly comprises the burner assembly as described above and further comprises an igniter supported in the air deflector for remotely igniting the burner assembly which is positioned adjacent the burner tip and therefore separated from the secondary air. Preferably the igniter further comprises flame sensor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic side view of a burner according to an embodiment of the invention and positioned for operation in a firetube or housing;  
         [0011]      FIG. 2   a  is a side view of the burner assembly removed from the housing for clarity;  
         [0012]      FIG. 2   b  is a plan view of a deflector plate positioned at a nozzle of the burner according to  FIG. 1 , the housing being removed for clarity;  
         [0013]      FIG. 3  is a bottom perspective view of a burner according to  FIG. 1  positioned in the housing, an igniter and heat return tube removed for clarity;  
         [0014]      FIG. 4  is a side view of a nozzle portion of the burner according to  FIG. 1 , the housing removed for clarity and illustrating a heat return tube for preventing freezing of the burner by heat tracing;  
         [0015]      FIG. 5  is a schematic side view of a mixer head according to  FIG. 1 ;  
         [0016]      FIG. 6  is a plan view of the mixer head according to  FIG. 5  shown along section lines A-A;  
         [0017]      FIG. 7  is a sectional view of the mixer head according to  FIG. 5  shown along section lines B-B; and  
         [0018]      FIG. 8  is a sectional view of the mixer head according to  FIG. 5  shown along section lines C-C. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     Having reference to  FIGS. 1-8 , a burner assembly  1  according to an embodiment of the invention is shown.  
         [0020]     As shown in  FIG. 1 , the burner assembly  1  comprises a tubular barrel  2  which is mounted in the bore of a firetube or other such housing  3 , forming an annulus  5  therebetween. The tubular barrel  2  conducts primary fuel gas G from a gas inlet  6  at a base or proximal end  8  of the tubular barrel  2  to a burner head  1   2  at a distal end  11  of the tubular barrel  2 . The barrel  2  is typically of conventional configuration. The gas at the gas inlet  6  is fed at a first pressure P 1  through an orifice  50  to a mixer head  7  ( FIGS. 5, 7  and  8 ) at the proximal end  8 . Primary combustion air A p  is drawn into the mixer head  7  via natural draft and the combined air A p  and gas G are mixed therein and flow through the tubular barrel  2  at a second pressure P 2  to an orifice or plurality of orifices  1   0  in the burner head  12 . The air and gas discharge from the burner head  12  at a nozzle tip  13  and, when ignited, form a flame  15 .  
         [0021]     Secondary combustion air A s  is aspirated or drawn into the annulus  5  and flows therein toward the nozzle tip  1   3  at a third pressure P 3 , to mix with the primary air A p  and fuel G and enhance combustion of the primary air A p  and fuel G in a combustion zone C at the nozzle tip  13  and in the housing  3  extending outwardly therefrom. Depending upon the draft created by a pressure differential along the burner assembly  1 , the velocity of the secondary air A s  is altered. A chimney effect in an exhaust stack for the heated system (not shown), aids in creating a draft.  
         [0022]     In low pressure fuel or low-fire conditions, the velocity of secondary air A s  is relatively low compared to a high-fire condition. If unrestricted, the flow of secondary air A s  up the annulus  5  and past the nozzle tip  13  can adversely affect the flame  15 .  
         [0023]     In order to stabilize at least a position of the flame  15  relative to the nozzle tip  13 , means are provided to deflect the flow of secondary air A s  away from at least the nozzle tip  13 .  
         [0024]     In a preferred embodiment, best seen in  FIG. 4 , the means for deflecting the flow of secondary air A s  is a radially outwardly extending low pressure ring  14  extending from the burner head  12 . The low pressure ring  14  is shaped such as an inverted, truncated frustrum of a cone and is positioned circumferentially about the nozzle tip  13  of the burner head  12 . A diameter of the low pressure ring  14  increases as it extends downstream and away from the nozzle tip  13 .  
         [0025]     The secondary combustion air A s  flowing through the annulus  5  from the proximal end  8  of the burner assembly  1  to the distal end  11  of the burner assembly  1  and approaching the nozzle tip  13  is deflected outwardly by the low pressure ring  14 , typically creating a turbulence pattern in the flow of the secondary air A s  which aids in establishing a local area of low pressure P 4  at the nozzle tip  13  and particularly at the plurality of orifices  10 . The low pressure P 4  at the tip  13  is low relative to the pressure P 3  of the secondary air A s . Further, the low pressure ring  14  separates the flow of secondary air A s  from the flow of primary air A p  and fuel G exiting the orifices  10  at the nozzle tip  13  which further aids in maintaining the area of low pressure P 4 . The area of low pressure P 4  acts to minimize lifting of the flame  15  from the nozzle tip  13 , resulting in increased stability and reliability of the flame  15  regardless the pressure P 2  and velocity of the primary combustion air A p  and fuel G in the burner assembly  1  and the draft in the housing  3 . Further, the low pressure ring  14  aids in preventing the flame from being extinguished by the secondary combustion air A s .  
         [0026]     Preferably, the nozzle head  12  and the low pressure ring  14  are formed as a unitary structure.  
         [0027]     Alternately, as shown in  FIGS. 1-4 , the means for deflecting the flow of secondary air A s  in the annulus  5  away from at least the nozzle tip  13  is included as part of an air deflector plate  20  which extends radially outwardly from the burner head  12 . The deflector plate  20  extends from the burner head  12 , such as from an underside  21 , and extends radially from the burner head  12  across the annulus  5 . The deflector plate has an inner mounting ring  29  adjacent the burner head and extending circumferentially therearound. Preferably, the inner ring  29  can act to restrict and deflect the flow of secondary combustion air A s  away from and around the nozzle tip  13 .  
         [0028]     As shown in  FIGS. 2   a,    2   b  and  3 , the air deflector plate  20  comprises a plate base  22 , preferably extending radially from the burner head  12  and across a diameter of the housing  3 . The burner head  12  can be conveniently supported concentrically in the housing  3  by the air deflector plate  20 .  
         [0029]     A plurality of angled deflectors or vanes  23  are formed about the plate base  22 , each vane  23  being formed adjacent one of a plurality of radially extending openings  24  formed in the plate base  22 . The plate base  22  and the openings  24  act to dampen or reduce the pressure P 3  the secondary combustion air A s  reaching the burner head  12  and nozzle tip  13 . Further, the angled vanes  23  act to direct the secondary combustion air A s  outward and circumferentially to the walls of the housing  3 , creating a turbulence pattern therein which substantially fills the housing  3  at the combustion zone C for improved mixing of the primary air A p  and fuel G therein. Preferably, angled vanes  23  also act to restrict and deflect the flow of secondary combustion air A s  away from and around the nozzle tip  13 .  
         [0030]     Thus, higher efficiency combustion is achieved as a greater amount of the available fuel G is burned in the housing  3 . Further, the deflection of at least a portion of the gas/air mixture to the outer walls of the housing  3  caused by the turbulence patterns as described establishes a flame pattern which extends to about the diameter of the housing  3  aiding in a more complete combustion of the gas/air mixture therein.  
         [0031]     An angle of the vanes  23  of the deflector plate  20  may be adjustable so as to control the amount of secondary air A s  reaching the housing  3  and the combustion zone C therein and thus the combustion efficiency of the burner assembly  1 . Controlling the rate of secondary combustion A s  air further acts to control the draft of the burner assembly  1  which increases the retention time in the housing  3  and permits more efficient heat transfer therein.  
         [0032]     Most preferably, as shown in  FIGS. 1, 3  and  4 , the means for deflecting the flow of secondary air A s  in the annulus  5  away from at least the nozzle tip  13  comprises both the low pressure ring  14  and the deflector plate  20 . In this embodiment, the nozzle head  12 , low pressure ring  14  and deflector plate  20  are preferably manufactured as a unitary nozzle structure.  
         [0033]     As shown in  FIGS. 1 and 2   a,  aventuri sleeve  25  may be positioned within the tubular barrel  2  to accelerate the flow of primary combustion air A p  and fuel G therein causing turbulence which results in enhanced mixing of the primary combustion air A p  and fuel G prior to reaching the orifices  10 .  
         [0034]     In an embodiment shown in  FIG. 4 , at least a first port  30  is formed in the air deflector plate  20  to accommodate and support an ignition system, preferably a pilotless ignition system such as an igniter/flame rod  31  for igniting the primary fuel/air mixture exiting the plurality of orifices  10  in the burner head  12 . The flame/igniter rod  31  preferably incorporates flame sensing using flame ionization technology. Due to the isolation of the nozzle tip  13  from the direct flow of secondary air A s , a consistent flame  15  is maintained at the nozzle tip  13  and will be detected by the flame sensor regardless whether the burner assembly  1  is operated at low-fire or high-fire conditions. Thus, the burner assembly  1  can be reliably and remotely lit using the igniter/flame rod  31 . Incorporation of the igniter/flame rod  31  eliminates the need for a conventional pilot and additional troublesome components associated therewith which are conventionally subject to freezing.  
         [0035]     Preferably, the igniter/flame rod  31  is arranged to pass along the housing  3  from the proximal end  8  of the tubular barrel  2 , through the air deflector plate  20  and to be positioned with a sparking tip  32  oriented at an optimal sparking distance (such as about ⅛″) from the nozzle tip  13 .  
         [0036]     Also with reference to  FIG. 4 , in another embodiment, at least one additional port  32  is formed in the air deflector plate  20  to support a heat return tube  40 . The heat return tube  40 , typically a flexible metal tube, extends from and is in communication with the mixer head  7  at the base  8  of the burner assembly  1 . An intermediate length of the heat return tube  40  extends along at least the fuel feed line  6 , along the gas inlet orifice  50  to the tubular barrel  2  and along the tubular barrel  2  to extend outward through the additional port  32  into the housing  3  adjacent the burner tip  13 , positioning a first intake end  41  adjacent or within the combustion zone C. The heat return tube  40  draws heated combustion gases from the housing  3  into the first intake end  41  of the heat return tube  40  and the heated combustion gases are communicated therealong to a second end  42  at the mixer head  7  to conduct heat and prevent freezing of the components of the burner assembly  1  which are adjacent the heat return tube  40 . A pressure differential between the mixer head  7  and housing  3  at the combustion zone C acts to draw the combustion gases into and along the heat return tube  40 .  
         [0037]     As shown in  FIGS. 5-8 , the mixer head  7  preferably comprises a tubular housing  60  having a solid base  61  through which a plurality of orifices  62  are formed. Primary combustion air is aspirated through the air orifices  62 . The air orifices  62  extend into a mixing chamber  63  formed in the tubular housing  60 . The mixing chamber  63  is positioned intermediate the air orifices  62  and the tubular barrel  2  which is connected thereto. The gas inlet orifice  50  is formed at a center of the base  61  through which fuel G is introduced to the mixing chamber  63  from the gas inlet  6 . Fuel/primary combustion air G/A p  combined in the mixing chamber  63  are discharged into the tubular barrel  2 . The plurality of orifices  62  act to minimize or prevent gusts of primary combustion air A p  from entering the mixer  7  which is particularly advantageous in low velocity fuel conditions.  
         [0038]     An air shutter  26  is provided at the base  61  of the mixer head  7  for controlling the amount of primary combustion air A p  entering the air orifices  62 . Preferably the air shutter  26  is threaded onto a gas inlet nipple  64  extending outward from the mixer base  61 . The air shutter  26  can be moved along the nipple  64  away from and toward the base  61  of the mixer  7  to permit more or less air to pass thereby into the air orifices  62 .  
         [0039]     Preferably, the fuel orifice  50  is provided in a fuel orifice insert  65  which is threadably connected into the mixer base  61 . The size of the fuel orifice  50  can be altered by swapping the insert  65  for an insert  65  having a different size fuel orifice  50 .  
         [0040]     Alternatively, in another embodiment of the invention as shown in  FIGS. 5, 6  and  8 , the burner assembly  1  further comprises an auxiliary air inlet  51  in the mixer head  7  through which primary combustion air A p  may be forced into the flow of fuel G in the mixer head  7  prior to entering the tubular barrel  2 . In this situation, the air shutter  26  at the base  8  of the burner assembly  1  can be closed completely and the flow of primary combustion air A p  is controlled through the forcible addition of air through the auxiliary air inlet  51 . The flow of fuel gas G is controlled by adjusting the size of the fuel orifice  50  in the mixer head  7 . In this embodiment, the burner assembly  1  can operate as a forced draft burner assembly, which may be preferable in cases where a more precise control of the primary combustion air/fuel ratio A p /G is required. Secondary air A s  continues to be aspirated as in the natural draft embodiment.  
         [0041]     Applicant has found this unique burner assembly operates at efficiencies in the order of 7-10% more efficient than other natural draft burners and can operate efficiently at pressures ranging from about 0.25 psig to about 15 psig. Burners employing this unique design can be manufactured to range in size from about 1″×6″ to about 2″×24″. Those skilled in the art would appreciate these specifications are guidelines only and the burner of the present invention is not limited to these dimensions or pressure ranges.