Abstract:
A flare tip for the burning and disposal of combustible waste gases including internal spin vanes is provided. By providing a plurality of internal spin vanes within the waste gas inlet of a flare tip, the efficiency of combustion of waste gas can be increased.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/452,005, filed Mar. 11, 2011, and entitled “Flare Tip Having Internal Spin Vanes”. U.S. Provisional Patent Application No. 61/452,005, filed Mar. 11, 2011, is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure relates generally to a flare tip for the burning and disposal of flammable waste gases and more particularly, to a flare tip including internal spin vanes. 
       BACKGROUND 
       [0003]    Gas flares are commonly located at production facilities, refineries, processing plants, and the like for disposing of flammable waste gases and other flammable gas streams that are diverted due to venting requirements, shut-downs, upsets, and/or emergencies. Such flares are often operated in a smokeless or near smokeless manner, which can be largely achieved by making sure that the flammable gas to be discharged and burned (“flare gas”) is admixed with enough air to sufficiently oxidize the gas. 
         [0004]    A typical flare apparatus includes a flare stack, which can extend high above the ground, and a flare tip mounted on the flare stack. An elevated flare tip is a device often used in industrial applications to burn combustible materials in an elevated location. Advanced flare tips use various methods in an attempt to provide sufficient oxygen in the combustion zone of the flare tip to help minimize the formation of smoke. In some larger flare tips, the exit of the flare tip is larger, and sometimes much larger, than the size of the waste gas riser that supplies the waste gas that includes the combustible material. Because the diameter of the flare tip is often larger than the flare riser, the waste gas velocity can be much higher in the center of the flare tip than at the perimeter of the flare tip. The higher flow of waste gas in the center of the flare tip can increase the oxygen requirements at the center of the flare tip, which can increase the propensity of the flare to smoke. 
       SUMMARY 
       [0005]    The disclosure relates generally to a flare tip for the burning and disposal of combustible gases and more particularly, to a flare tip including internal spin vanes. 
         [0006]    In an illustrative embodiment, a flare apparatus for burning and disposal of combustible waste gases is provided. The flare apparatus may include a flare tip having a waste gas conduit. The waste gas conduit may have a base portion defining a waste gas inlet and an upper portion defining a waste gas outlet. In some cases, the base portion of the waste gas conduit can have an outer diameter that is smaller than an outer diameter of the upper portion, but this is not required. The flare apparatus may include a plurality of spin vanes for inducing a spin in the waste gas entering the flare tip. In some instances, the plurality of spin vanes may be disposed within the base portion of the waste gas conduit. The spin vanes can be disposed at an angle relative to a longitudinal axis of the flare tip. The number, size, and angle of the spin vanes may vary depending upon a variety of factors including, for example, waste gas composition, waste gas flow rate, waste gas pressure, the available smokeless medium, the allowable heat and grade, as well as other factors. The flare apparatus may also include an outer shell defining a plenum surrounding the flare tip, if desired. 
         [0007]    The above summary is not intended to describe each and every example or every implementation of the disclosure. The Description that follows more particularly exemplifies various illustrative embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]    The following description should be read with reference to the drawings. The drawings, which are not necessarily to scale, depict selected illustrative embodiments and are not intended to limit the scope of the disclosure. The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments in connection with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a partial, cross-sectional view of a flare tip in accordance with an illustrative embodiment of the present disclosure; 
           [0010]      FIG. 2  is a side, cross-sectional view of a flare tip in accordance with an illustrative embodiment of the present disclosure; 
           [0011]      FIG. 3  is a detailed, plan view of a flare tip base including a plurality of internal spin vanes in accordance with an illustrative embodiment of the present disclosure; 
           [0012]      FIG. 4  is an end, cross-sectional view of a flare tip in accordance with an illustrative embodiment of the present disclosure; 
           [0013]      FIGS. 5A-5D  show the burn profiles of a waste gas stream using a modified flare tip including spin vanes; 
           [0014]      FIGS. 5E-5F  show the velocity contours within a waste gas stream produced using the same modified flare tip used to produce the burn profiles of  FIGS. 5A-5D . 
           [0015]      FIGS. 6A-6D  show the burn profiles of a waste gas stream using a flare tip including spin vanes and a twenty-four inch velocity seal; 
           [0016]      FIGS. 6E-6F  show the velocity contours within a waste gas stream produced using the same modified flare tip used to produce the burn profiles of  FIGS. 6A-6D ; and 
           [0017]      FIGS. 6G-6H  show the velocity contours within the waste gas stream measured just above the velocity seal of the same modified flare tip used to produce the burn profiles and velocity profiles of  FIGS. 6A-6F . 
       
    
    
     DESCRIPTION 
       [0018]    The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected illustrative embodiments and are not intended to limit the scope of the disclosure. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized. 
         [0019]      FIGS. 1-4  show various cross-sectional views of an illustrative flare apparatus  10 . As shown in  FIGS. 1 and 2 , the flare apparatus  10  may include a flare tip  14  having a base portion   18  defining a waste gas inlet  22  and an upper portion  26  defining a waste gas outlet  30 . In certain embodiments, such as shown in  FIGS. 1 and 2 , the base portion  18  has an outer diameter smaller than an outer diameter of the upper portion  26 , but this is not required. 
         [0020]    As best shown in  FIG. 3 , a plurality of spin vanes  36  may be disposed within, for example, the base portion  18 . The spin vanes  36  may induce a spin on the waste gas entering the flare tip  14  through the waste gas inlet  22 . The energy needed to produce the spin comes from the kinetic energy present in the flowing waste gas. In many instances, no additional equipment is necessary to induce a spin on the waste gas entering the flare tip  14 . 
         [0021]    In many flare tip designs, more oxygen for combustion is available near the perimeter of the flare tip  14  than is available near the center of the flare tip  14 . When a spin is induced in the waste gas entering the flare tip  14 , the resulting centrifugal action may distribute the waste gas more toward the outer edges or perimeter of the flare tip  14 . By shifting waste gas flow closer to the perimeter of the flare tip  14 , where more oxygen is often available, the propensity for the waste gas to smoke when burned may be reduced. 
         [0022]    Flare tips are often customized depending upon the application, and it is contemplated that the number, size, and angle of the spin vanes  36  may vary. The number, size, and angle of the spin vanes  36  disposed within the flare tip  14  may vary depending upon a variety of factors including, for example: the waste gas composition, diameter of the waste gas inlet  22 , waste gas flow velocity, waste gas pressure, the available smokeless medium, the allowable heat and grade, as well as other factors. 
         [0023]    In general, the larger the diameter of the waste gas inlet  22 , the larger the number and/or size of the spin vanes  36  may be used. Typically, the diameter of the waste gas inlet  22  can range from about 8 inches to about 72 inches, depending upon the application, but this is just an example range. Depending upon the diameter of the waste gas inlet  22  and the amount of spin needed to distribute the waste gas to the perimeter of the flare tip  14 , the number of spin vanes   36  disposed within the base portion  18  of the flare tip  14  may range from, for example, 2 to 36 spin vanes. In other embodiments, the number of spin vanes  36  can range from 24 to 36 spin vanes, from 12 to 24 spin vanes, and from 2 to 12 spin vanes, or any other suitable range. In the illustrated embodiment shown in  FIGS. 1-3 , eight spin vanes  36  are utilized. The size of the spin vanes  36  can also be varied depending on, for example, the diameter of the waste gas inlet   22  and the number of spin vanes  36  provided. In some embodiments, the width of the spin vanes   36  can range from 1 inch to about 18 inches, but again, these are just examples. In other embodiments, the width of the spin vanes  36  can range from about 8 inches to about 18 inches, from about 4 to about 8 inches, and from about 1 inch to about 4 inches. 
         [0024]    The angle relative to the longitudinal axis  40  ( FIG. 2 ) at which each of the spin vanes   36  are disposed within the base portion  18  of the flare tip  14  can also vary, depending on the application. In certain embodiments, the angle of the spin vanes  36  relative to the longitudinal axis  40  of the flare tip  14  may be equal to or less than about 60° and more particularly, ranges from about 20° to about 60° or from about 20° to about 40°. In other embodiments, the angle of the spin vanes  36  relative to the longitudinal axis  40  of the flare tip  14  is about 30°. Thus, it is contemplated that the angle of the spin vanes may be any suitable value or within any suitable range. In some cases, it is contemplated that the angle of the spin vanes  36  may change or vary from the upstream end of the spin vanes  36  to the downstream end, while in other cases, the angle may be constant. In some cases, waste gas composition can also affect the angle, size and number of spin vanes  36  that are desired for a particular application. 
         [0025]    As shown in  FIGS. 1-4 , the flare apparatus  10  can also include a one or more combustion air conduits  44  for supplying combustion air to the flare tip  14 . In some embodiments, as illustrated, the combustion air conduits  44  may be disposed within and in fluid communication with the upper portion  26  of the flare tip  14 . In some instances, spaces are provided between the combustion air conduits  44  to, for example, allow the waste gas to travel up and past the combustion air conduits  44 . In some embodiments, the combustion air conduit(s)   44  may be provided external to, but still in fluid communication with the flare tip  14 . The combustion air conduits  44  can be fabricated from, for example, carbon steel or stainless steel piping, and may be capable of delivering air and/or steam to the flare tip  14 , depending upon the application. 
         [0026]    In some instances, the flare apparatus  10  may include an outer shell  48  defining a plenum   52  surrounding the flare tip  14  ( FIGS. 1 and 2 ), but this is not required. According to one embodiment, as illustrated, the outer shell  48  can include a generally cylindrical lower portion  52  and a frustoconical upper portion  56  defining an opening  60 . In certain embodiments, such as shown in  FIG. 1 , the opening  60  of the upper portion  56  of the outer shell  48  can be elevated relative to the waste gas outlet  30  defined by the flare tip  14 . In some cases, atmospheric air can be forced through the plenum  52  surrounding the flare tip  14 . 
         [0027]    Spin vanes, as discussed herein, may be combined with other tips of flare tip internal structures such as, for example, velocity seals. 
       EXAMPLES 
     Example 1 
       [0028]    A computational fluid dynamic study (CFD) of the combustion of a propane gas stream was conducted using a modified flare tip including five-inch wide internal spin vanes. The operating parameters utilized to conduct this study are provided in Table 1. 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Parameter 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Propane Flow 
                 60,000 
                 lbs/hr 
               
               
                   
                 Propane Temp 
                 100° 
                 F. 
               
               
                   
                 Air Flow 
                 100,000 
                 ACFM 
               
               
                   
                 Air Temp 
                 100° 
                 F. 
               
               
                   
                 Wind Speed/Direction 
                 10 
                 ft/sec left-right 
               
               
                   
                   
               
             
          
         
       
     
         [0029]      FIGS. 5A-5D  show the burn profiles of a combustion gas stream using the modified flare tip.  FIGS. 5A-5B  show the air volume fraction within the gas stream, and  FIGS. 5C-5D  show the volume fraction of propane within the combustion gas stream.  FIGS. 5E-5F  show the velocity contours within the gas stream produced using the modified flare tip. 
         [0030]    The burn profiles shown in  FIGS. 5A-5F  exhibit improved velocity profiles when comparing the modified flare tip including the internal spin vanes to a flare tip without spin vanes (not shown). Additionally, the burn profiles shown in  FIGS. 5A-5F  show improved mixing between the waste gas (propane gas) and the surrounding atmosphere. 
       Example 2 
       [0031]    A similar CFD study to that discussed in Example 1 was conducted using a modified flare tip including five-inch wide internal spin vanes and a twenty-four inch velocity seal. The operating parameters utilized to conduct the study are provided below in Table 2. 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Parameter 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Propane Flow 
                 60,000 
                 lbs/hr 
               
               
                   
                 Propane Temp 
                 100° 
                 F. 
               
               
                   
                 Air Flow 
                 100,000 
                 ACFM 
               
               
                   
                 Air Temp 
                 100° 
                 F. 
               
               
                   
                 Wind Speed/Direction 
                 10 
                 ft/sec left-right 
               
               
                   
                   
               
             
          
         
       
     
         [0032]      FIGS. 6A-6D  show the burn profiles of a combustion gas stream using the modified flare tip including a twenty-four inch velocity seal.  FIGS. 6A-56B  show the air volume fraction within the gas stream, and  FIGS. 6C-6D  show the volume fraction of propane within the combustion gas stream.  FIGS. 6E-6H  show the velocity contours within the gas stream produced using the modified flare tip including a twenty-four inch velocity seal. 
         [0033]    Again, the burn profiles and velocity profiles shown in  FIGS. 6A-6H  show improved mixing between the waste gas (propane gas) and the surrounding atmosphere. 
         [0034]    As a result of the CFD studies, it is believed that by providing internal spin vanes within the flare tip, the velocity profile within the flare tip is improved, improving mixing between the waste gas and the surrounding atmosphere. 
         [0035]    The disclosure should not be considered limited to the particular examples described above. Various modifications, equivalent processes, as well as numerous structures to which the disclosure can be applicable will be readily apparent to those of skill in the art upon review of the instant specification. Other steps may be provided, or steps may be eliminated, from the described methods, and other components may be added to, or removed from, the described devices. Also, in the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.