Abstract:
An enclosed flare stack having expanded air entries for flaring waste gas. The flare stack includes an enclosure assembly having a bottom portion with expanded air entries and an upper portion through which the flared waste gas escapes. The enlarged air entries at the bottom end of the stack to reduce entry pressure loss and to increase entrained air flow when flaring waste gas. The enclosed flare stack and method of flaring waste gas also greatly reduce the height of the stack enclosure without greatly increasing the size of the flare windows.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Provisional Application No. 61/983,561 filed Apr. 24, 2014, the contents of which are hereby incorporated by reference 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to an enclosed flare stack and method of flaring waste gas, and more particularly to an enclosed flare stack having a series of enlarged air entries at a bottom end of the stack to reduce entry pressure loss and to increase entrained air flow when flaring waste gas. 
         [0003]    Flare systems are used in various industries to provide safe disposal of flammable liquids or gases. Flare systems are combustion mechanisms to burn off flammable liquids or gases. By way of example, flare systems may be used in industrial plants to burn off flammable gases released by pressure relief valves. Various types of flares exist, including elevated flares and flares that operate near grade. Near-grade level flares are often called ground flares. 
         [0004]    Enclosed ground flares must be of a certain dimensions to maintain a desired combustion volume and a certain height to generate the required draft for combustion air flow. Large ground flares are often surrounded by a ground flare “fence” or “wall” that serves to reduce the amount of light emitted by the flares. The fence also serves to limit the amount of infrared radiation from the flares, protecting personnel and equipment at grade. In addition, the fence serves to reduce the amount of noise from the flare by reflecting the noise. The fence must allow sufficient air flow through the fence to provide air flow for combustion, and must also control the wind flow so that high winds do not interfere with flare operation. 
         [0005]    One of the major costs of enclosed flares is the stack enclosure. A shorter stack enclosure is less expensive, but entrains less air, whereas an enclosure with larger air entries, or “windows” can induce more air through static draft for a given height, but in turn loses the ability to direct the air flow at a given velocity magnitude and also requires a taller external radiation fence, both of which are undesirable. 
         [0006]    It is therefore desirable to provide an enclosed flare stack and method of flaring waste gas. 
         [0007]    It is further desirable to provide an enclosed flare stack having a series of enlarged air entries at a bottom end of the stack enclosure to reduce entry pressure loss and to increase entrained air flow when flaring waste gas. 
         [0008]    It is still further desirable to provide an enclosed flare stack and method of flaring waste gas that greatly reduce the height of the stack enclosure without greatly increasing the size of the flare windows. 
         [0009]    It is yet further desirable to provide an enclosed flare stack having a lower cost design by using about 25% less enclosure material compared to current designs. 
         [0010]    It is still yet further desirable to provide an enclosed flare stack and method of flaring waste gas that increase the available air flow to the flare system without increasing the line-of-sight to the high radiation flame zone. 
         [0011]    It is still yet further desirable to provide an improved enclosed flare stack that is less visible from a distance and therefore has a lower impact to the surrounding community. 
         [0012]    It is still yet further desirable to provide an enclosure assembly for a flare stack having angled air entries at a bottom of the enclosure without the need to increase the surrounding radiation fence of the flare stack. 
         [0013]    It is still yet further desirable to provide an enclosed flare stack and method of flaring waste gas that have a low peak exit temperature from the flare stack. 
         [0014]    It is still yet further desirable to provide an enclosed flare stack and method of flaring waste gas that have a relatively low impinging temperature on the interior casing of the flare stack enclosure. 
         [0015]    Other advantages and features will be apparent from the following description, and from the claims. 
       SUMMARY OF THE INVENTION 
       [0016]    In general, in a first aspect, the invention relates to an enclosed flare stack having a flow path for flaring waste gas. The stack includes an enclosure assembly having a bottom portion with at least one expanded air entry and an upper portion through which the flared waste gas escapes. The expanded air entry includes at least one upper panel having a predetermined angle with respect to the upper portion of the enclosure assembly. The enclosed flare stack also includes a flare window adjacent to the expanded air entry of the enclosure assembly. The enclosed flare stack can also include a radiation fence that completely surrounds and circumnavigates the flare stack. Flare manifold assemblies are in fluid communication with the flare windows, and may completely or substantially surround the flow path through the flare stack. 
         [0017]    The predetermined angle between the upper panel of the expanded air entry and the upper portion of the enclosure assembly ranges between about 110 to about 160 degrees, namely about 135 degrees. The predetermined angle between the upper panel of the expanded air entry and the upper portion of the enclosure assembly can also be a generally smooth radius, downwardly sloping angle, or a concave angle toward the flow path through the enclosed flare stack. The expanded air entry continuously radially surrounds and enlarges the bottom portion of the enclosure assembly. The expanded air entry may be a plurality of expanded air entries. The expanded air entries can include side panels, open side windows or a combination thereof. In addition, the expanded air entries may be spaced from and generally parallel to each other or contiguous with each other. 
         [0018]    In general, in a second aspect, the invention relates to a method of flaring waste gas using an enclosed flare stack. The method includes flowing a waste gas through the enclosed flare stack; entraining air through at least one flare windows in the flare stack; entraining additional air through at least one expanded air entry having at least one upper panel having a predetermined angle with respect to an upper portion of the flare stack; and flaring the waste gas. Similar to above, the expanded air entry may be a plurality of expanded air entries. Additionally, the predetermined angles between the upper panels of the expanded air entries and the upper portion of the flare stack may range between about 110 to about 160 degrees, be generally smooth radius, downwardly sloping angles, be concave angles toward the flow path through the enclosed flare stack or be a combination thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a perspective view of an example of an enclosure assembly having a bottom with expanded air entries surrounded by a radiation fence in accordance with an illustrative embodiment of the enclosed flare stack and method of flaring waste gas disclosed herein. 
           [0020]      FIG. 2  is a front plan view of the enclosure assembly shown in  FIG. 1 . 
           [0021]      FIG. 3  is a cross-sectional view along line  3 - 3  of the an enclosure assembly shown in  FIG. 2 . 
           [0022]      FIG. 4  is an exploded view of area  4  of the expanded air entry shown in  FIG. 3 . 
           [0023]      FIG. 5  is a front perspective view of the bottom portion of the enclosure assembly in  FIG. 2 . 
           [0024]      FIG. 6  is a front perspective view of an enclosure assembly having another example of expanded air entries in accordance with an illustrative embodiment of the enclosed flare stack and method of flaring waste gas disclosed herein. 
           [0025]      FIG. 7  is a front perspective view of an enclosure assembly having still another example of expanded air entries in accordance with an illustrative embodiment of the enclosed flare stack and method of flaring waste gas disclosed herein. 
           [0026]      FIG. 8  is a cross-sectional view along line  3 - 3  of the enclosure assembly shown in 
           [0027]      FIG. 2  having yet another example of expanded air entries in accordance with an illustrative embodiment of the enclosed flare stack and method of flaring waste gas disclosed herein. 
           [0028]      FIG. 9  is an exploded view of area  8  of the expanded air entry shown in  FIG. 8 . 
           [0029]      FIG. 10  is a front perspective view of the enclosure assembly shown in  FIG. 1  having yet another example of expanded air entries in accordance with an illustrative embodiment of the enclosed flare stack and method of flaring waste gas disclosed herein. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    The apparatuses 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. 
         [0031]    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 construction and the arrangement of the structural and function details disclosed herein without departing from the scope of the invention. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification. 
         [0032]    The description of the invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. In the description, relative terms such as “front,” “rear,” “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly”, etc.) should be construed to refer to the orientation as then described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the machine be constructed or the method to be operated in a particular orientation. Terms, such as “connected,” “connecting,” “attached,” “attaching,” “join” and “joining”, are used interchangeably and refer to one structure or surface being secured to another structure or surface or integrally fabricated in one piece. 
         [0033]    Referring to the figures of the drawings, wherein like numerals of reference designate like elements throughout the several views, and initially to  FIGS. 1 through 3 , an enclosed flare stack  10  having expanded air entries  12  for flaring waste gas. The flare stack  10  includes an enclosure assembly  14  having a generally annular bottom portion  16  with the expanded air entries  12  and a generally cylindrical upper portion  18  through which the flared waste gas escapes. As illustrated in the drawings, the upper portion  18  of the flare stack  10  has a polygonal configuration, but is not so limited as other forms, such as a circle or oval, may be utilized. Moreover, the enclosure assembly  14  may form a single main flare stack having an open end  20  at the upper portion as exemplified, or may have a closed end at the upper portion of the enclosure assembly with one or more radially extending arm assemblies (not shown) in fluid communication with the main flare stack. 
         [0034]    The enclosure assembly  14  may also include a plurality of structural supports  22  to position the bottom portion  16  of the flare stack  10  in a spaced relation from grade or ground level to form flare windows  24 . The structural supports  22  may be fabricated from steel beams or other sturdy material, and may be secured at grade or ground level by concrete footings or the like. A radiation fence  26  completely surrounds and circumnavigates the flare stack  10 , and in general, the fence  26  has a height generally equal to the height of the flare windows  24 . A series of flare manifold assemblies  28  are positioned in the flare windows  24  in fluid communication with a flow path  30  through the flare stack  10  for flaring waste gas. Similar to the radiation fence  26 , the manifold assemblies  28  may completely or substantially surround the flow path  30  through the flare stack  10 . The manifold assemblies  28  may be arranged in a wide variety of patterns and, depending on the application, the manifold assemblies  28  may be utilized simultaneously or at various different times. 
         [0035]    As illustrated in  FIGS. 1 through 5 , the expanded air entries  12  may be made by expanding the bottom portion  16  of the enclosure assembly  14  immediately above the flare windows  24  to a larger area in order to increase the rate of entrained air while flaring waste gas. The expanded air entries  12  may be constructed from steel and refractory or insulation lining similar to the enclosure assembly  14 . The expanded air entries  12  can be constructed from upper panels  32  having generally predetermined angles A with respect to the upper portion  18  of the enclosure assembly  14 . The upper panels  32  may be retained in place by horizontal bracing  34 , which can be generally parallel to grade and by cross bracing  36  extending between the horizontal bracing  34 . Brackets and/or other fasteners may be utilized to facilitate connections. As illustrated for this example of the enclosed flare stack  10 , the predetermined angles A between the upper panels  32  of the expanded air entries  12  and the upper portion  18  of the flare stack  10  may range from between about 110 to about 160 degrees or generally about 135 degrees. The expanded air entries  12  may include side panels  38  that extend between the upper panels  32  and the horizontal bracing  34  to generally enclose the expanded air entries  12 . In this configuration, the side panels  38  are spaced from and generally parallel to each other on opposed sides of the expanded air entries  12 . This arrangement of side panels  38  results in air flow space between adjacent expanded air entries  12 . Alternatively, as shown in  FIG. 6 , the expanded air entries  12  can have open side windows  40 , which allow increased air intake to entrain with the flaring waste gas with minimal additional radiation. By way of yet another example, as shown in  FIG. 7 , the upper panels  32  extend between adjacent structural supports  22  with the expanded air entries  12  being contiguous with each other. 
         [0036]    Turning now to  FIGS. 8 through 10 , the expanded air entries  12  are illustrated predetermined angles A forming generally smooth radius, downwardly sloping bell curves between the upper panels  32  and the upper portion  18  of the enclosure assembly  14  or concave angles toward the flow path  30  through the enclosed flare stack  10 . The concave upper panels  32  may be retained in place by horizontal bracing  34  and cross bracing  36 , with suitable fasteners utilized to facilitate connections. The expanded air entries  12  may include side panels  38  or may include open side windows  40 . Further, the expanded air entries  12  may be spaced from and generally parallel to each other or the expanded air entries  12  may be contiguous with each other. 
         [0037]    Whereas, the apparatuses 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 scope of this invention. 
       SPECIFIC EMBODIMENTS 
       [0038]    While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims. 
         [0039]    A first embodiment of the invention is an enclosed flare stack having a flow path for flaring waste gas, the stack comprising an enclosure assembly having a bottom portion with at least one expanded air entry and an upper portion through which the flared waste gas escapes, the expanded air entry comprising at least one upper panel having a predetermined angle with respect to the upper portion of the enclosure assembly; and a flare window adjacent to the expanded air entry of the enclosure assembly. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a radiation fence that completely surrounds and circumnavigates the flare stack. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph further comprising a plurality of flare manifold assemblies in fluid communication with the flare windows. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph the manifold assemblies completely or substantially surround the flow path through the flare stack. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the predetermined angle between the upper panel of the expanded air entry and the upper portion of the enclosure assembly ranges between about 110 and about 160 degrees. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the predetermined angle is about 135 degrees. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the predetermined angle between the upper panel of the expanded air entry and the upper portion of the enclosure assembly further comprises a generally smooth radius, downwardly sloping angle. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the predetermined angle between the upper panel of the expanded air entry and the upper portion of the enclosure assembly further comprises a concave angle toward the flow path through the enclosed flare stack. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the expanded air entry continuously radially surrounds and enlarges the bottom portion of the enclosure assembly. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the expanded air entry is a plurality of expanded air entries. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the predetermined angles between the upper panels of the expanded air entries and the upper portion of the enclosure assembly range between about 110 and about 160 degrees, are generally smooth radius, downwardly sloping angles, are concave angles toward the flow path through the enclosed flare stack or are a combination thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the predetermined angle is about 135 degrees. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the expanded air entries further side panels, side windows or a combination thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the expanded air entries are spaced from and generally parallel to each other. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the air entries are contiguous with each other. 
         [0040]    A second embodiment of the invention is a method of flaring waste gas using an enclosed flare stack, the method comprising the steps of flowing a waste gas through the enclosed flare stack; entraining air through at least one flare windows in the flare stack; entraining additional air through at least one expanded air entry in the flare stack, the expanded air entry comprising at least one upper panel having a predetermined angle with respect to an upper portion of the flare stack; and flaring the waste gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the expanded air entry is a plurality of expanded air entries. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the predetermined angles between the upper panels of the expanded air entries and the upper portion of the flare stack ranges between about 110 and about 160 degrees, are generally smooth radius, downwardly sloping angles, are concave angles toward the flow path through the enclosed flare stack or are a combination thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the predetermined angle is about 135 degrees. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the expanded air entries further side panels, side windows or a combination thereof 
         [0041]    Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. 
         [0042]    In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.