Abstract:
A high efficiency natural draft gas burner that uses a plate attached to the burner tube to block secondary air from being introduced into a firetube or confined space vessel, ensuring that only inspired air nearly homogenously mixed with fuel is ignited at the burner tip. The venturi may be sized and shaped to ensure proper mixing of the inspired air and fuel, thus reducing emissions. This proper mixing combined with the lack of secondary air may reduce the fuel consumption and CO 2  emissions of the burner by as much as 75%.

Description:
CROSS REFERENCE 
       [0001]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    This invention relates generally to a burner and more particularly, but not by way of limitation, to a high efficiency natural draft gas burner that produces low NO R , CO, and CO 2  emissions for firetube and other applications. 
         [0004]    Description of the Related Art 
         [0005]    Natural draft gas burners can be very inefficient. They typically use 10 to 30% inspirated air through the burner, with the rest being secondary air. The problem with this arrangement is that the secondary air must be heated. The air at the inlet to the fire tube is at ambient temperature, and thus fuel must be wasted raising the temperature of this air. Furthermore, the secondary air is often insufficiently mixed with the fuel, and commonly the less the air and the fuel are mixed, the higher the resulting CO and NO x  emissions. Thus, better mixing yields lower emissions. Additionally, when the burner is not being fired without a device to shut off the secondary air, the secondary air removes heat from the process thus requiring the burner to fire more often or at higher firing rates to keep the process at the correct operating temperature. 
         [0006]    Based on the foregoing, it is desirable to provide a burner that requires no secondary air, in which all air required for combustion is inspirated through the burner. 
         [0007]    It is further desirable for such a burner to require less fuel thus producing less CO 2  emissions. 
         [0008]    It is further desirable for such a burner to efficiently mix fuel and air to produce lower CO and NO x  emissions. 
       SUMMARY OF THE INVENTION 
       [0009]    In general, in a first aspect, the invention relates to a burner assembly comprising: an air inlet; a fuel inlet; a venturi in fluid communication with the air inlet and the fuel inlet; a burner tip in fluid communication with the venturi, where the burner tip is housed in a firetube or confined space; and a plate or other blocking device surrounding the burner tip such that the plate limits secondary air from entering the firetube or confined space. Air enters the burner assembly via the air inlet and travels through the venturi. Fuel enters the burner assembly via the fuel inlet which inspirates air and mixes the air in the venturi to produce a near homogenous air-fuel mixture. The air-fuel mixture then exits the burner assembly via the burner tip. 
         [0010]    The burner assembly may further comprise a pilot assembly, where the pilot assembly is positioned to ignite the air-fuel mixture as it exits the burner tip. The burner assembly may further comprise a tube joining the venturi to the burner tip such that the air-fuel mixture exits the venturi, travels through the tube, and then travels through the burner tip. 
         [0011]    The air-fuel mixture may be near homogenous. The burner assembly may use less fuel and produce fewer emissions than a burner assembly without the isolating plate. Indeed, the burner assembly may produce substantially no CO emissions and less than 10 parts per million NOx emissions while CO 2  emissions are reduced in direct proportion to reduction of fuel usage. Emissions may vary dependent on fuel composition and O 2  content in the air. 
         [0012]    The venturi may comprise a curved inlet, a straight section for inspirating air and mixing of the fuel and air, and a divergent section for pressure recovery. The venturi should be designed by someone skilled in the art such that the venturi generates a pressure recovery in excess of 10 inches W.C. 
         [0013]    The burner assembly may further comprise a single fire tube; a single plenum; a second air inlet; a second fuel inlet; a second venturi in fluid communication with the second air inlet and the second fuel inlet; and a second burner tip in fluid communication with the second venturi, where burner tips are surrounded by a common plate such that the plate prevents secondary air from entering the firetube. Both burner tips may be housed in the single fire tube and air for both air inlets may pass through the single plenum. Indeed, a single fire tube may house any number of burner assemblies sharing a common or multiple plenum(s). 
         [0014]    The burner assembly may further comprise a flame arrestor element, a plenum, and an air control damper, such that air passes through the flame arrestor element, the plenum, and the air control damper prior to entering the venturi inlet. The burner assembly may further comprise insulation installed on the hot, downstream side of the secondary air isolating plate. Said insulation may also be used to seal the isolating plate to the inside of the firetube to reduce air leakage between the outside diameter of the isolating plate and the inside diameter of the firetube. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a top cutaway view of the high efficiency burner; 
           [0016]      FIG. 2  is a side cutaway view of the high efficiency burner; 
           [0017]      FIG. 3  is a front view of the high efficiency burner as indicated in  FIG. 2 ; 
           [0018]      FIG. 4  is a rear view of the high efficiency burner mounting plate as indicated in  FIG. 2 ; 
           [0019]      FIG. 5  is a cutaway view of a typical multi-burner version of the high efficiency burner; and 
           [0020]      FIG. 6  is a front view of the typical multi-burner version of the high efficiency burner. 
       
    
    
       [0021]    Other advantages and features will be apparent from the following description and from the claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The devices and methods discussed herein are merely illustrative of specific manners in which to make and use this invention and are not to be interpreted as limiting in scope. 
         [0023]    While the devices and methods have been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the construction and the arrangement of the devices and components without departing from the spirit and scope of this disclosure. It is understood that the devices and methods are not limited to the embodiments set forth herein for purposes of exemplification. 
         [0024]    In general, in a first aspect, the invention relates to a high efficiency burner, as shown in the drawings. As shown in  FIGS. 1 and 2 , air may enter through a plenum  1  and fuel may enter through a fuel inlet  2 . The air and fuel may be mixed in a venturi  3  to produce a near homogenous mixture that travels down the tube  4  to the burner tip  5 , where it exits and is lit through direct ignition, manually, or by a pilot assembly  6 . A plate  7  may block all or substantially all secondary air, ensuring that substantially only inspired air is used by the burner. 
         [0025]    A typical natural draft burner uses 70 to 90% secondary air, and thus the temperature in the front leg of the fire tube is near ambient and minimal heat is dispersed along the length of the front leg of the firetube. Because the present invention does not use secondary air, the temperature at the inlet and in the front leg of the firetube may be approximately 1000° F., thus increasing the efficiency of the burner and firetube heat transfer. In fact, the present invention may use 75% less fuel thus saving 75% of CO 2  emissions compared to a typical burner. 
         [0026]    The lack of secondary air, combined with a particular configuration of the venturi  3  and burner tip  5 , may also ensure near homogenous mixing of the fuel and air, thus promoting more complete combustion of the fuel and a resultant reduction in CO and NO x  emissions. The NOx emissions may be less than 10 parts per million, while the CO emissions may be zero and the CO 2  emissions are reduced in direct proportion to the reduction of fuel usage. This is well below California&#39;s requirement of less than 50 ppm CO emissions and less than 20 ppm NO x  emissions, as described in California Air Resources Board (CARB) Rule 1146. Thus, the user can save money both through using less fuel and by taking advantage of cap and trade of CO 2  reduction. 
         [0027]    The venturi  3  may comprise a curved inlet  8 , a straight section  9  for mixing of the fuel and air, and a divergent section  10  for pressure recovery. The venturi  3  may be designed by someone skilled in the art such that the venturi  3  generates a pressure recovery in excess of 10 inches W.C. The divergent section  10  may be connected to tube  4 , which may have any desired length to properly place the burner tip in the firetube. The diameter of the burner tip  5  may depend on the firing rate. The burner tip  5  may be comprised of a plurality of orifices, as seen in  FIG. 3 . Burner performance may be altered by changing the open area of the burner tip  5 . The burner tip  5  may have enough open area or flow paths for the fuel and air mixture to go through without too much restriction or turbulence, but with enough restriction such that the flame does not flash back behind the burner tip  5 . 
         [0028]    The size and design of burner tip  5  may further be affected by the size of the fire tube  12  or other confined space vessel with which the burner is used. A single fire tube  12  may house up to four or more burners of the present invention with a common plenum  1 . For example,  FIGS. 5 and 6  show two burners sharing a common plenum  1  and firetube  12 . 
         [0029]    A flame arrestor element  13  may precede the air plenum  1 . An air inlet  14  may attach to the air plenum  1  via a plenum mounting flange  15 . An air control damper  25  may control the amount of air passing through each venturi or common air inlet  14 . The air control damper  25  may be set during initial adjustment when starting the burner and may require no further adjustment while in normal operations, allowing emissions from the burner to remain constant during normal operations. The burner may mount to the fire tube  12  through a front plate  16 . Other elements passing through or mounted to the front plate  16 , as shown in  FIG. 4 , may include a sight glass  17 ; a pilot scanner port  18 , which may be included to satisfy NFPA&#39;s requirement of a flame proving device; and/or a pilot mounting flange  20 . 
         [0030]    The pilot assembly  6 , if it is present, may be an industry standard pilot assembly, including a pilot gas inlet  21 , a pilot orifice  22 , a pilot venturi  23 , a pilot tip  24 , an ignitor connection  19 , a pilot ignitor rod  26 , a pilot air plenum  27 , and a pilot flame arrestor element  28 . A pilot air blocking plate  29  may prevent secondary air from entering the firetube through the pilot assembly  6 . 
         [0031]    Direct ignition of the burner may be accomplished by spark ignitor in or near the burner tip, thus eliminating the pilot assembly  6  and pilot fuel usage. 
         [0032]    The secondary air blocking plate  7  may be backed by insulation  30 , which may be held in place with one or more insulation retaining pins  31  and reduce air leakage around plate  7 . 
         [0033]    All parts of the high efficiency burner may be made of aluminum or stainless steel, which requires no paint and is low maintenance. The only maintenance required for the burner may be keeping the fuel nozzle  11  and the arrester element  13  clean. Other materials may be used, but may require maintenance. Preferably, the plenum  1  and the flame arrestor  13  are aluminum and the rest of the burner is stainless steel. 
         [0034]    The high efficiency burner may be scalable. The size of the venturi  3  may depend on how much fuel, and fuel pressure, the user desires to put through it. 
         [0035]    The present invention requires no force draft, no electricity, and no fan. Alternately, as someone skilled in the art knows, a fan may be added to convert the burner to a forced draft burner without altering the emissions performance. The fan may be assisted by the air aspirated by the venturi to reduce the fan size and motor size required, as well as reducing CO 2  emissions due to reduced electricity required to drive the fan. 
         [0036]    Whereas, the devices and methods have been described in relation to the drawings and claims, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.