Partial pre-mix flare burner and method

Abstract

A flare burner that is particularly suitable for use in connection with ground flares and other types of flares in which it is important to control the height of the flame envelope created by the burner is provided. The flare burner includes a pre-mix zone including a pre-mix chamber into which air is entrained. A uniform mixture of fuel and air is formed in the pre-mix zone and caused to exit an air/fuel outlet in the top of the pre-mix chamber. In one embodiment, the amount of air in the fuel/air mixture that exits the air/fuel outlet is in excess of the stoichiometric amount of air required to support combustion of the fuel in the mixture. Fuel is injected around the perimeter of the air/fuel outlet, combustion is initiated and a flame envelope is created. By injecting a mixture of fuel and air that includes excess air into the center of the flame envelope, combustion of the central portion of the flame envelope is accelerated which allows more fuel to be flared with a given flame envelope height. The invention also includes a ground flare and a method of flaring fuel with a flare burner.

1 . A flare burner, comprising:
 a pre-mix zone including a pre-mix chamber, said pre-mix chamber having a top, a bottom, a sidewall connecting said top to said bottom, an air inlet disposed in one of said bottom and said sidewall and an air/fuel outlet disposed in said top;   a supplemental fuel inlet for injecting fuel into said pre-mix zone, said supplemental fuel inlet being located in a position with respect to said pre-mix zone such that the injection of fuel from said supplemental fuel inlet into said pre-mix zone entrains air into said pre-mix zone whereby a mixture of fuel and air is formed in said pre-mix zone and caused to exit said air/fuel outlet of said pre-mix chamber; and   a main fuel outlet located in a position with respect to said top of said pre-mix chamber such that fuel can be injected from said main fuel outlet around the perimeter of said air/fuel outlet of said pre-mix chamber.   
   
   
       2 . The flare burner of  claim 1  wherein said air inlet is disposed in said bottom of said pre-mix chamber. 
   
   
       3 . The flare burner of  claim 1  wherein said main fuel outlet is spaced outwardly from said pre-mix chamber to provide an air entrainment space therebetween. 
   
   
       4 . The flare burner of  claim 1  further comprising a fuel membrane disposed around the outside perimeter of said pre-mix chamber, said membrane including a fuel inlet and being in fluid communication with said main fuel outlet. 
   
   
       5 . The flare burner of  claim 4  wherein said fuel membrane and said main fuel outlet are spaced outwardly from said pre-mix chamber to provide an air entrainment space therebetween. 
   
   
       6 . The flare burner of  claim 4  wherein said membrane is also in fluid communication with said supplemental fuel inlet. 
   
   
       7 . The flare burner of  claim 1  further comprising a fuel feed conduit in fluid communication with said supplemental fuel inlet and said main fuel outlet for conducting fuel to said supplemental fuel inlet and said main fuel outlet. 
   
   
       8 . The flare burner of  claim 1  wherein said main fuel outlet comprises a plurality of fuel ports disposed around the perimeter of said air/fuel outlet of said pre-mix chamber. 
   
   
       9 . The flare burner of  claim 4  wherein said pre-mix chamber, including said air/fuel outlet, and said fuel membrane and said main fuel outlet each have a round cross-section such that fuel can be injected annularly from said main fuel outlet around the perimeter of said air/fuel outlet. 
   
   
       10 . The flare burner of  claim 1  wherein said sidewall of said pre-mix chamber includes an interior surface and an exterior surface, said interior surface having a section that is a Coanda surface. 
   
   
       11 . The flare burner of  claim 10  wherein said supplemental fuel inlet is located in a position with respect to said pre-mix chamber such that fuel can be injected from said supplemental fuel inlet onto said Coanda surface. 
   
   
       12 . The flare burner of  claim 4  wherein said sidewall of said pre-mix chamber includes an interior surface and an exterior surface, said interior surface having a section that is a Coanda surface. 
   
   
       13 . The flare burner of  claim 12  wherein:
 said air inlet is disposed in said bottom of said pre-mix chamber and said pre-mix chamber, including said air inlet, and said membrane and said supplemental fuel inlet each have a round cross-section; and   said Coanda surface annularly extends around said interior surface of said sidewall of said pre-mix chamber.   
   
   
       14 . The flare burner of  claim 13  wherein said supplemental fuel inlet is located in a position with respect to said pre-mix chamber such that fuel can be annularly injected from said supplement fuel inlet onto said Coanda surface. 
   
   
       15 . The flare burner of  claim 10  wherein said interior surface includes two opposing sections that are Coanda surfaces, and said supplemental fuel inlet is in a position with respect to said pre-mix chamber such that fuel can be injected from said supplement fuel inlet onto each of said Coanda surfaces. 
   
   
       16 . The flare burner of  claim 1  wherein said pre-mix chamber has a length to inside hydraulic diameter ratio in the range of from about 0.25:1 to about 4:1. 
   
   
       17 . The flare burner of  claim 1  wherein said pre-mix chamber has a length to inside hydraulic diameter ratio of about 1:1 or less. 
   
   
       18 . A flare burner, comprising:
 a pre-mix zone including a pre-mix chamber, said pre-mix chamber having a top, a bottom, a sidewall connecting said top to said bottom, an air inlet disposed in said bottom, an air/fuel outlet disposed in said top and a length to inside hydraulic diameter ratio in the range of from about 0.25:1 to about 4:1;   a supplemental fuel inlet for injecting fuel into said pre-mix zone, said supplemental fuel inlet being located in a position with respect to said pre-mix zone such that the injection of fuel from said supplemental fuel inlet into said pre-mix zone entrains air into said pre-mix zone whereby a mixture of fuel gas and air is formed in said pre-mix zone and caused to exit said air/fuel outlet of said pre-mix chamber;   a main fuel outlet located in a position with respect to said top of said pre-mix chamber such that fuel can be injected from said main fuel outlet around the perimeter of said air/fuel outlet of said pre-mix chamber; and   a fuel feed conduit in fluid communication with said supplemental fuel inlet and said main fuel outlet for conducting fuel to said supplemental fuel inlet and said main fuel outlet.   
   
   
       19 . The flare burner of  claim 18  wherein said pre-mix chamber, including said air inlet and said air/fuel outlet, and said main fuel outlet have round cross-sections. 
   
   
       20 . The flare burner of  claim 18  wherein said main fuel outlet is spaced outwardly from said pre-mix chamber to provide an air entrainment space therebetween. 
   
   
       21 . The flare burner of  claim 19  further comprising an annular fuel membrane disposed around the outside perimeter of said pre-mix chamber, said membrane being in fluid communication with said main fuel outlet and having a top, a bottom and a sidewall connecting said top to said bottom. 
   
   
       22 . The flare burner of  claim 21  wherein said main fuel outlet is attached to said top of said fuel membrane and comprises a plurality of fuel ports extending around the perimeter of said air/fuel outlet of said pre-mix chamber. 
   
   
       23 . The flare burner of  claim 22  wherein said fuel membrane and said main fuel outlet are spaced outwardly from said pre-mix chamber to provide an air entrainment space therebetween. 
   
   
       24 . The flare burner of  claim 18  wherein said pre-mix chamber has a length to inside hydraulic diameter ratio of about 1:1 or less. 
   
   
       25 . The flare burner of  claim 24  wherein said supplemental fuel inlet is spaced below said air inlet of said pre-mix chamber. 
   
   
       26 . The flare burner of  claim 18  wherein said air/fuel outlet of said pre-mix chamber is spaced above said main fuel outlet. 
   
   
       27 . A ground flare comprising a plurality of flare burners, an enclosure extending around the flare burners and a fuel supply line for supplying fuel to the flare burners, wherein at least one of the flare burners includes:
 a pre-mix zone including a pre-mix chamber having a top, a bottom, a sidewall connecting said top to said bottom, an air inlet disposed in one of said bottom and said sidewall and an air/fuel outlet disposed in said top;   a supplemental fuel inlet for injecting fuel into said pre-mix zone, said supplemental fuel inlet being located in a position with respect to said pre-mix zone such that the injection of fuel from said supplemental fuel inlet into said pre-mix zone entrains air into said pre-mix zone whereby a mixture of fuel gas and air is formed in said pre-mix zone and caused to exit said air/fuel outlet of said pre-mix chamber; and   a main fuel outlet located in a position with respect to said top of said pre-mix chamber such that fuel can be injected from said main fuel outlet around the perimeter of said air/fuel outlet of said pre-mix chamber.   
   
   
       28 . The ground flare of  claim 27  wherein said air inlet is disposed in said bottom of said pre-mix chamber. 
   
   
       29 . The ground flare of  claim 27  wherein said main fuel outlet is spaced outwardly from said pre-mix chamber to provide an air entrainment space therebetween. 
   
   
       30 . The ground flare of  claim 27  wherein said flare burner further comprises a fuel membrane disposed around the outside perimeter of said pre-mix chamber, said membrane including a fuel inlet and being in fluid communication with said main fuel outlet. 
   
   
       31 . The ground flare of  claim 30  wherein said fuel membrane and said main fuel outlet are spaced outwardly from said pre-mix chamber to provide an air entrainment space therebetween. 
   
   
       32 . The ground flare of  claim 30  wherein said membrane is also in fluid communication with said supplemental fuel inlet. 
   
   
       33 . The ground flare of  claim 27  further comprising a fuel feed conduit in fluid communication with said supplemental fuel inlet and said main fuel outlet for conducting fuel to said supplemental fuel inlet and said main fuel outlet. 
   
   
       34 . The ground flare of  claim 27  wherein said main fuel outlet comprises a plurality of fuel ports disposed around the perimeter of said air/fuel outlet of said pre-mix chamber. 
   
   
       35 . The ground flare of  claim 30 , wherein said pre-mix chamber, including said air/fuel outlet, and said fuel membrane and said main fuel outlet each have a round cross-section whereby fuel can be annularly injected from said main fuel outlet around the perimeter of said air/fuel outlet. 
   
   
       36 . The ground flare of  claim 27  wherein said sidewall of said pre-mix chamber includes an interior surface and an exterior surface, and said interior surface having a section that is a Coanda surface. 
   
   
       37 . The ground flare of  claim 36  wherein said supplemental fuel outlet is located in a position with respect to said pre-mix chamber such that fuel can be injected from said supplemental fuel outlet onto said Coanda surface. 
   
   
       38 . The ground flare of  claim 30  wherein said sidewall of said pre-mix chamber includes an interior surface and an exterior surface, said interior surface having a section that is a Coanda surface. 
   
   
       39 . The ground flare of  claim 38  wherein:
 said air inlet is disposed in said bottom of said pre-mix chamber and said pre-mix chamber, including said air inlet, and said fuel membrane and said supplemental fuel inlet each have a round cross-section; and   said Coanda surface annularly extends around said interior surface of said sidewall of said pre-mix chamber.   
   
   
       40 . The ground flare burner of  claim 39  wherein said supplemental fuel inlet is in a position with respect to said pre-mix chamber such that fuel can be annularly injected from said supplemental fuel inlet onto said Coanda surface. 
   
   
       41 . The ground flare burner of  claim 36  wherein said interior surface includes two opposing sections that are Coanda surfaces, and said supplemental fuel inlet is in a position with respect to said pre-mix chamber such that fuel can be injected from said supplement fuel inlet onto each of said Coanda surfaces. 
   
   
       42 . In a method of flaring fuel with a flare burner wherein fuel to be flared is injected through a fuel outlet of the burner into a combustion zone and ignited to create a flame envelope and combust the fuel, the improvement comprising:
 introducing a portion of the fuel to be burned into a pre-mix zone of said burner in a manner that entrains air into said pre-mix zone and creates a mixture of air and fuel within said pre-mix zone; and   injecting said mixture of air and fuel from said pre-mix zone into a central portion of said flame envelope.   
   
   
       43 . The method of  claim 42  wherein the amount of air entrained into said pre-mix zone and injected into said central portion of said flame envelope is in the range of from about 125% to about 300% of the stoichiometric amount of air required to support combustion of the fuel introduced into said pre-mix zone. 
   
   
       44 . The method of  claim 43  wherein the amount of air entrained into said pre-mix zone and injected into said central portion of said flame envelope is in the range of from about 150% to about 300% of the stoichiometric amount of air required to support combustion of the fuel introduced into said pre-mix zone. 
   
   
       45 . The method of  claim 42  wherein the amount of the fuel introduced into said pre-mix zone is in the range of from about 5% to about 50. % of the total amount of fuel to be flared by said flare burner. 
   
   
       46 . The method of  claim 45  wherein the amount of the fuel introduced into said pre-mix zone is in the range of from about 10% to about 30% of the total amount of fuel to be flared by said flare burner.