Patent Publication Number: US-2013244187-A1

Title: HIGH EFFICIENCY LOW NOx EMISSION BURNER APPARATUS

Description:
1. FIELD OF THE INVENTION 
     The present invention is directed to a high efficiency low NO x  emission burner apparatus and method. In particular, the present invention is directed to a thermal oxidizer burner apparatus and method which utilizes waste gas or tail gas from an independent source to achieve high efficiency and low emission of nitrogen oxides. 
     2. DESCRIPTION OF THE RELATED ART 
     Oxides of nitrogen form as a result of combustion emitting from burners. Various prior configurations and designs have been utilized in the past to increase the efficiency of thermal oxidizer burners and to reduce nitrogen oxides content of the flue gas effluent, There are a variety of oxides of nitrogen in flue gas effluent, such as nitrogen oxide (NO), nitrogen dioxide (NO 2 ) and others which arc together generally labeled NO x . 
     It is known that high oxygen content can increase the formation of nitrogen oxides. It is also known that increasing combustion temperatures may increase production of NO x . 
     In at least one other prior past approach, a portion of the flue gas, waste or tail gas created by the combustion emitting from the burner is mixed and recirculated with inlet combustion air. 
     European Patent No. 1,203,188 illustrates an example of premixing fuel with internally recirculated waste gases drawn from the furnace chamber and then recirculated. 
     U.S. Pat. No. 5,135,387 discloses a flue gas gathering member in a burner which forms a passage so that combustion air and recirculated flue gas are combined. 
     In flue gas recirculating systems in the past, the amount and percentage of waste gas would be dependent upon the combustion occurring in the furnace and various other factors. Additional issues have arisen in attempting to recirculate the waste gas or tail gas with the combustion air. 
     The composition of the waste gas or tail gas will vary but in one non-limiting example would be approximately 98% nitrogen with the balance being combustibles such as methane, carbon monoxide, hydrogen and various sulfur compounds. Because the waste gas or tail gas has little or no oxygen content, the introduction of waste gas or tail gas to the combustion air will influence the oxygen content. The recirculation of a portion of the waste or tail gas is known to decrease and/or control the amount of oxygen content in the combustion air. Decreasing the oxygen content decreases the partial pressure of oxygen, thereby reducing the rate of the reactions forming oxides. 
     Accordingly, it is an object and purpose of the present invention to provide a thermal oxidizer burner apparatus which utilizes flue gas from an external source separate from the ongoing combustion in the combustion chamber associated with the burner. 
     it is a further object and purpose of the present invention to provide a high efficiency low NO x  emission thermal oxidizer burner apparatus having a lobed tip nozzle within a mix chamber to thoroughly mix combustion air with waste gas or tail gas from an independent source. 
     It is a further object and purpose of the present invention to control the composition and content of waste gas or tail gas utilized by a burner. 
     It is a further object and purpose of the present invention to provide a thermal oxidizer burner wherein waste gas or tail gas is introduced through a burner plenum to a combustion chamber in stages. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a high efficiency low NO x  emission burner apparatus. A plenum chamber includes an inlet for introduction of combustion air which moves into and through the plenum chamber. 
     A combustion chamber is in fluid communication and connected to the plenum chamber. An inlet is in communication with one or more primary waste gas pipes in order to introduce waste gas or tail gas into the combustion chamber through the plenum chamber. The waste gas or tail gas will be delivered from an independent, external source not associated with the combustion herein. 
     In one preferred arrangement, the primary waste gas pipe or pipes terminate in a lobed tip nozzle which extends from one end at the waste gas pipe to an opposed end terminating in a plurality of radially extending lobes symmetrically arranged around a center axis. 
     A primary fuel gas line provides a source for fuel to the combustion reaction. 
     The waste gas inlet is also in communication with a secondary waste pipe or pipes for introduction of a portion of the waste gas or tail gas into the combustion chamber so that the introduction of waste gas is staged. 
     Additionally, in one preferred embodiment, a secondary fuel gas line or lines are in communication with the combustion chamber for staged introduction of secondary fuel gas into the combustion chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a simplified schematic diagram of a preferred embodiment of a high efficiency low NO x  emission burner apparatus constructed in accordance with the present invention; 
         FIG. 2A  illustrates a simplified view of the burner apparatus shown in  FIG. 1  from the combustion chamber into the mixing plenum and  FIGS. 2B and 2C  illustrate external views of the burner apparatus; 
         FIGS. 3 ,  4  and  5  illustrate alternate views of a lobed tip nozzle of the burner apparatus shown in  FIG. 1 ; 
         FIG. 6  illustrates an alternate preferred embodiment of the burner apparatus; and 
         FIG. 7  illustrates a further alternate preferred embodiment of the burner apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments discussed herein are merely illustrative of specific manners in which to make and use the invention and are not to be interpreted as limiting the scope of the instant invention. While the invention has been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the invention&#39;s construction and the arrangement of its components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification. 
     Referring to the drawings in detail,  FIG. 1  illustrates a sectional view of a first preferred embodiment of a high efficiency low NO x  emission thermal oxidizer burner apparatus  10  constructed in accordance with the present invention. In a preferred embodiment, a substantially tubular or cylindrical plenum chamber  12  is provided although other configurations are possible. The plenum chamber  12  includes an inlet  14  for introduction of combustion air as illustrated by arrow  16 . The combustion air may be drawn or forced into the combustion chamber through the plenum chamber  12  in a variety of ways. The combustion air moves into and through the plenum chamber  12  as illustrated by arrow  18 . Various fans or other mechanisms along with controls may be used to force or induce combustion air through the plenum chamber  12 . 
     A combustion chamber  20  is in fluid communication with and connected to the plenum chamber  12 . Thermal oxidation occurs in the combustion chamber. The combustion chamber  20  may be cylindrical or tubular or take other configurations. In a preferred arrangement, the combustion chamber is coaxial with the plenum chamber  12  although other configurations are possible. 
     An inlet  28  is in communication with one or more primary waste gas pipes or tubes  30  in order to introduce waste gas or tail gas into the combustion chamber  20  through the plenum chamber  12  as illustrated by arrow  32 . The waste gas or tail gas may be delivered from an independent, external source not associated with the combustion herein. A non-limiting example of a tail gas or waste gas from an independent source would be waste gas or tail gas from a sulfur recovery unit as a part of a petrochemical or natural gas processing plant. 
     At least a portion of the primary waste gas pipe or pipes  30  may be coaxial with the cylindrical plenum chamber  12 . The primary waste gas pipe or pipes  30  terminate in a lobed tip nozzle  34 , to be described herein in detail, or terminate in an open ended device or other mixing device. Accordingly, primary waste gas is delivered and mixed with the combustion air through the plenum chamber  12 . 
     A primary fuel gas line or lines  40  provide a source for fuel to the combustion reaction. Natural gas or various other types of fuel might be employed within the spirit and scope of the invention. 
     In one preferred embodiment, the waste gas inlet  28  is in communication with a secondary waste gas pipe or tube  50  for introduction of a portion of waste gas or tail gas into the combustion chamber  20 . Accordingly, introduction of the waste gas or tail gas is staged. 
     Additionally, in one preferred embodiment, a secondary fuel gas line or lines  60  are in communication with the combustion chamber  20  for introduction of secondary fuel gas into the combustion chamber  20 . Accordingly, introduction of fuel gas is staged. Natural gas or other various types of fuel might be employed within the spirit or scope of the invention. 
     Refractory material or refractory tiles  52  may be used between the fuel gas lines. 
       FIG. 2A  illustrates an end view taken from the combustion chamber  20  into the plenum chamber  12  of the apparatus  10  shown in  FIG. 1  while  FIGS. 2B and 2C  illustrate external views of the apparatus  10 . 
       FIGS. 3 ,  4  and  5  illustrate alternate views of the lobed tip nozzle  34  apart from the apparatus  10 . The lobed tip nozzle  34  is connected at inlet end  42  to the primary waste gas pipe  30 . The lobed tip nozzle  34  extends from the inlet end  42  at the primary waste gas pipe to an opposed outlet end  44  terminating in a plurality of radially extending lobes  36  symmetrically arranged around a center axis. The lobes  36  are rounded protuberances projecting radially outward from the axis. 
     The primary waste gas flows through the nozzle  34  as illustrated by arrows  46 . 
     The cross-sectional area of the inlet end  42  of the lobed nozzle  34  is approximately the same as the cross-sectional area of the outlet end  44  of the nozzle whereas the perimeter of the outlet end  44  is greater than the perimeter of the inlet end  42 , thereby increasing the surface area of contact of both fluid streams passing through or surrounding the nozzle, in this case waste or tail gas and combustion air respectively, thereby increasing the rate of mixing of the two fluid streams. 
     In the arrangement, shown in  FIG. 1 , the secondary fuel gas from secondary fuel gas line or lines  60  mixes with combustion air and the primary fuel gas and waste gas before introduction of secondary waste gas. 
     Accordingly, the arrangement of the present invention causes a thorough mixing of the combustion air, the fuel gas and the waste gas in order to better modulate, control and predict NO x , carbon monoxide and unburned hydrogen emissions from the combustion chamber. The arrangement disclosed in  FIGS. 1 through 5  will tend to minimize carbon monoxide (CO) and unburned hydrocarbon emissions. 
       FIG. 6  discloses an alternate preferred embodiment  70  of the burner apparatus  10 . The arrangement is similar to that in  FIGS. 1 through 5  with the exception of the introduction of the secondary fuel gas and secondary tail gas or waste gas in conjunction with an alternate arrangement of refractory tile  62 . In the alternate embodiment shown in  FIG. 6 , the secondary fuel gas delivered through secondary fuel gas line  60  mixes with the secondary tail gas or waste gas through secondary waste gas pipe or pipes  50  and then simultaneously mixes with the combustion air, primary fuel gas and primary waste gas. 
       FIG. 7  illustrates a further, alternate preferred embodiment  80  of the present invention. The alternate embodiment shown in  FIG. 7  is similar to the arrangement of the foregoing with the exception of the secondary fuel gas and secondary waste gas introduction in conjunction with a further alternate arrangement of refractory tile  72 . In the alternate embodiment shown in  FIG. 7 , the secondary tail gas or waste gas delivered through secondary waste pipe  50  fully or partially mixes with the secondary fuel gas delivered through secondary fuel gas line  60  prior to or before mixing with the combustion air, primary fuel gas through primary fuel gas line  40  and primary waste gas from the primary waste gas pipe or pipes  30 . The arrangement disclosed in  FIG. 7  will tend to minimize NO x  emissions. 
     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.