Abstract:
A flare stack operating on the Coanda principle in which provision is made for cooling of a Coanda body terminating the gas flue by a flow of cooling fluid within the Coanda body. The pressure in the flare stack is held constant by a mechanism disposed outside of the main flue of the flare stack.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to gas flares that operate on the Coanda principle. An exemplary such gas flare is shown in U.S. Pat. No. 4,634,372 issued Jan. 6, 1987. In such gas flares, a Coanda body is positioned across a flare stack to form an annular slot between the Coanda body and the pipe forming the gas conduit for the flare stack. The slot height is variable by use of springs within the flare stack to maintain a constant pressure in the flare stack. Such conventional flare stacks are subject to damage when a flame stabilizes on the surface of the Coanda body, and the springs are subject to damage and fouling by virtue of being exposed continuously to the corrosive and contaminated gases of the flare gas.  
         SUMMARY OF THE INVENTION  
         [0002]    This invention, in its various independent aspects, provides an improved flare stack. In a first aspect of the invention, provision is made for cooling of a Coanda body terminating a flare stack by a flow of cooling fluid within the Coanda body. In a second aspect of the invention, the pressure in the flare stack is held constant by a mechanism disposed outside of the main flue of the flare stack. When pressure is low, the gas flue is closed, thus eliminating the need for purging of the flare stack.  
           [0003]    These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    There will now be described preferred embodiments of the invention, with reference to the drawings, by way of illustration only and not with the intention of limiting the scope of the invention, in which like numerals denote like elements and in which:  
         [0005]    [0005]FIGS. 1A and 1B together show a Coanda flare stack according to the invention;  
         [0006]    [0006]FIG. 2 is a perspective view of the top end of a fluid circulation system for use with the Coanda flare stack of FIGS. 1A and 1B;  
         [0007]    [0007]FIG. 3 is a perspective view showing how conduits in the fluid circulation system of FIG. 2 enter and exit the flare stack of FIGS. 1A and 1B;  
         [0008]    [0008]FIG. 4A is a perspective view of a first tensioning device for placing tension on the Coanda body shown in FIG. 1A;  
         [0009]    [0009]FIG. 4B is a perspective view of a second tensioning device for placing tension on the Coanda body shown in FIG. 1A; and  
         [0010]    [0010]FIG. 5 shows a heat exchanger and pump for the fluid circulation system. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0011]    In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word in the sentence are included and that items not specifically mentioned are not excluded. The use of the indefinite article “a” in the claims before an element means that one of the elements is specified, but does not specifically exclude others of the elements being present, unless, unless the context clearly requires that there be one and only one of the elements.  
         [0012]    Referring to FIGS. 1A and 2, there is shown a flare stack of the Coanda type, which has a Coanda body  10  disposed adjacent the flare end  11  of a gas flue  12 . Gas flue  12  receives gas from, for example an oil-gas separator, through pipe  13 . The shape of the Coanda body  10 , and its design, as well as the gas flue  12 , otherwise than as indicated in this patent document is conventional. The Coanda body  10  is supported by a cooling fluid circuit that includes a cooling fluid supply conduit  16  and a cooling fluid removal conduit  14 . The cooling fluid removal conduit  14  is disposed concentrically within the cooling fluid supply conduit  16  to form an annular gap  15  through which cooling fluid enters the Coanda body  10 . The cooling fluid supply conduit  16  is located centrally within the gas flue  12  by upper vanes  17 A and lower vanes  17 B acting as spacers and is connected at its lower end to a tensioning cable  19 . The supply conduit  16  is free to move up and down within the gas flue  12  and is secured as by welding to the spherical Coanda body  10 .  
         [0013]    As part of the cooling fluid circuit, a cylindrical jacket  20  surrounds the flare end  11  of the gas flue  12 . The cylindrical jacket  20  forms an annular volume at the flare end  11  of the gas flue that is divided by a barrier  22 . A tip coolant supply line  24  is connected to the coolant fluid return line  14  and delivers coolant to the jacket  20  on one side of the barrier  22 . The coolant flows around the annular volume defined by the jacket  20  and the flare end  11  and returns to heat exchanger  26  at the base of the gas flue  12  through tip coolant return line  28 .  
         [0014]    The Coanda body  10  responds to gas pressure in the gas flue  12  by lifting off the flare end  11  to form an adjustable annular gap  18  between the Coanda body  10  and the flare end  11  of the gas flue  12 . Gas emitted from the flare end  11  passes through the adjustable annular gap  18  and around the Coanda body  10 . The Coanda body  10  is fluid cooled by the cooling fluid circuit. As shown in FIGS. 1B and 5, the cooling fluid circuit includes heat exchanger  26 , fluid reservoir  30 , and pump  32 . Fluid is pumped into the supply conduit  16  along line  34  from reservoir  30  using pump  32  operated by electric motor  38 . The electric motor  38  also operates a fan  40  that blows air through the heat exchanger  26  to cool fluid flowing in the heat exchanger  26 . Heated fluid returned from the Coanda body  10  flows through return conduit  14 , tip coolant supply line  24 , jacket  20 , and tip coolant return line  28  to fluid heat exchanger  26  and from there to reservoir  30 . The reservoir  30  may be controllably heated as required to prevent freeze up in cold conditions.  
         [0015]    Referring to FIGS. 3, 4A and  4 B, the Coanda body  10  is supported on a pivot arm  40  that is pivotally linked to both the conduit  16  and the gas flue  12 . To maintain a constant gas pressure in the gas flue, a cable  42  is secured through a connector  44  to the lower end of the conduit  16  and to a tensioning device  46 . The cable  42  runs out of the gas flue around a pulley  48 . The tensioning device  46  does not have to be connected to the Coanda body  10  through the conduits  14  or  16 , but it is convenient to do so. In the example shown in FIG. 3, the Coanda body  10  and tensioning device  46  are connected through the supply conduit  16 . The return conduit  14  is fixed to the supply conduit  16  and to the Coanda body  10  as shown in FIGS. 1A and 3, but in this embodiment is not connected directly to the tensioning device  46 . As shown in FIG. 3, the return conduit  14  connects to conduit  24  and exits the gas flue  12  removable cover  50 . The length of the cable  42  may be adjusted by opening removable cover  52  on housing  53  and adjusting the cable  42  with conventional cable adjustor  54 .  
         [0016]    The tensioning device  46  may be a single acting cylinder that is kept pressurized at a constant pressure (FIG. 4A) or may be a diaphragm type device  46 B (FIG. 4B) attached to cable  42  and similarly kept pressurized at constant pressure. Constant pressure on the tensioning device  46 ,  46 B may be obtained using a conventional pressure regulator  47  (FIG. 4B). The pressure may be set for example to 50 psi, and is preferably kept above 10 psi. The pressure setting on the tensioning device  46 ,  46 B is then essentially the same as the maintained pressure at the tip of the gas flue  12 . The cable  42  in FIG. 4B is attached at one end to the diaphragm of the tensioning device  46 B and passes through gas tight housing  53 B, which is provided with a removable cover  52 B for access to a cable adjustor (not shown, but same as cable adjustor  54 ), around a pulley (not shown, but same as pulley  48 ) and through the gas flue  12  to connector  44 . The constant pressure on the piston or diaphragm opposes gas pressure in the gas flue  12  and tends to pull the Coanda body onto the flare tip  11 . Maintaining a constant pressure in the tensioning device  46  maintains a constant back pressure on gas in the gas flue  12 . When the gas pressure in the gas flue  12  falls below the constant gas pressure, the tensioning device  46  closes the gap  18 , and thus raises the pressure in the gas flue.  
         [0017]    When pressure in the gas flue is low, the gap  18  is reduced to zero and the gas flu  12  is closed. As pressure builds up in the gas flue  12 , the Coanda body  10  is lifted off the gas flue  12 , thus releasing gas from the gas flue  12 . Closing of the gap  18  at low gas flue pressure eliminates the need to add gas continuously to the gas flue to purge it of any air.  
         [0018]    A person skilled in the art could make immaterial modifications to the invention described in this patent document without departing from the essence of the invention that is intended to be covered by the scope of the claims that follow.