Method for combusting fuel in a fired heater

Abstract

A method for combusting fuel in a fired heater having one or more burners, the method comprising: (a) combusting at least a portion of the fuel in the presence of an oxidizer in the burners, generating heat and producing a flue gas; and (b) recycling at least a portion of the flue gas to the burners; wherein step (a) and step (b) are conducted in a manner such that the combusting takes place in a combustion regime represented by 4 , 500 ≥ 7554.8 - 933.72  x + 64.960  x 2 + .47705  y - .55680  z - 1579.2 w ≥ 2 , 500 ; wherein w represents a mole fraction of oxygen in the oxidizer, x represents a recycle ratio of the flue as measured in moles of flue gas/mole of oxidizer; wherein y represents a temperature of the flue gas in Fahrenheit recycled to the burners; and wherein z represents a heating value of the fuel in Btu/scf LHV.

That which is claimed is:  
     
         1 . A method for combusting fuel in a fired heater having one or more burners, the method comprising: 
 (a) combusting at least a portion of said fuel in the presence of an oxidizer in said burners, generating heat and producing a flue gas; and    (b) recycling at least a portion of said flue gas to said burners;    wherein step (a) and step (b) are conducted in a manner such that combusting takes place in a combustion regime represented by            4   ,     500   ≥     7554.8   -     933.72      x     +     64.960        x   2       +     .47705      y     -     .55680      z     -     1579.2   w       ≥   2     ,     500   ;                       wherein w represents a mole fraction of oxygen in the oxidizer;    wherein x represents a recycle ratio of said flue as measured in moles of flue gas/mole of oxidizer;    wherein y represents a temperature of the flue gas, in Fahrenheit, recycled to said burners; and    wherein z represents a heating value of said fuel in Btu/scf LHV.    
     
     
         2 . The method of  claim 1 , further comprising the step of heating a hydrocarbon process fluid from the heat generated in step (a).  
     
     
         3 . The method of  claim 1 , wherein 1.0≦x≦8.0.  
     
     
         4 . The method of  claim 1 , wherein 2.6≦x≦6.0.  
     
     
         5 . The method of  claim 2 , wherein 1.0≦x≦8.0.  
     
     
         6 . The method of  claim 2 , wherein 2.6≦x≦6.0.  
     
     
         7 . The method of  claim 1 , wherein said oxidizer is oxygen-enriched air.  
     
     
         8 . The method of  claim 1 , wherein said oxidizer is substantially pure oxygen.  
     
     
         9 . The method of  claim 2 , wherein said oxidizer is oxygen-enriched air.  
     
     
         10 . The method of  claim 2 , wherein said oxidizer is substantially pure oxygen.  
     
     
         11 . A method for combusting fuel in a fired heater having one or more burners, the method comprising: 
 (a) combusting at least a portion of said fuel in the presence of an oxidizer in said burners producing a flue gas; and    (b) recycling at least a portion of said flue gas to said burners;    wherein step (a) and step (b) are conducted in a manner such that combusting takes place in a combustion regime represented by            4   ,     500   ≥     7554.8   -     933.72      x     +     64.960        x   2       +     .47705      y     -     .55680      z     -     1579.2   w       ≥   2     ,     500   ;                       wherein w represents a mole fraction of oxygen in the oxidizer, wherein 0.900≦w≦0.995;    wherein x represents a recycle ratio in moles flue gas/mole of oxidizer, wherein 1.0≦x≦8.0;    wherein y represents a temperature, in Fahrenheit, of the flue gas recycled to said burners wherein 300° F.≦y≦1,200° F.; and    wherein z represents a heating value in Btu/scf LHV of said fuel wherein 100 Btu/scf≦z≦2,200 Btu/scf.    
     
     
         12 . The method of  claim 11 , wherein said combustion regime is represented by  
       
         
           
             
               3 
               , 
               
                 500 
                 ≥ 
                 
                   7554.8 
                   - 
                   
                     933.72 
                      
                     x 
                   
                   + 
                   
                     64.960 
                      
                     
                       x 
                       2 
                     
                   
                   + 
                   
                     .47705 
                      
                     y 
                   
                   - 
                   
                     .55680 
                      
                     z 
                   
                   - 
                   
                     1579.2 
                     w 
                   
                 
                 ≥ 
                 2 
               
               , 
               500. 
             
           
           
           
               
           
         
       
     
     
         13 . The method of  claim 11 , wherein the fired heater has a heat flux rate ranging from about 10,000 Btu/hr/sq ft. to about 12,000 Btu/hr/sq ft.  
     
     
         14 . The method of  claim 12 , wherein the fired heater has a heat flux rate ranging from about 10,000 Btu/hr/sq ft. to about 12,000 Btu/hr/sq ft.  
     
     
         15 . A method for operating a fired heater having a radiant section, the method comprising: 
 (a) combusting a fuel in the presence of substantially pure oxygen in one or more burners of said fired heater producing a flue gas; and    (b) recycling at least a portion of said flue gas to one or more burners;    wherein the radiant section operates at a pressure greater than ambient pressure.    
     
     
         16 . The method of  claim 15 , wherein the radiant section operates at a pressure of at least about 0.05″ of H 2 O.  
     
     
         17 . The method of  claim 15 , wherein the radiant section operates at a pressure from at least about 0.05″ of H 2 O to about 0.10″ of H 2 O.  
     
     
         18 . A method for monitoring and controlling the combustion of fuel in a fired heater comprising a fuel feed stream, an oxygen feed stream and a recycle feed stream, the method comprising the steps of: 
 (a) monitoring said fuel, producing fuel composition data;    (b) feeding at least a portion of said fuel to said fired heater;    (c) combusting said fuel in the presence of substantially pure oxygen in one or more burners of said fired heater producing a flue gas having a temperature y, as measured in Fahrenheit; and    (d) recycling at least a portion of said flue gas at a recycling ratio x, as measured in moles of flue gas/mole of oxygen, to the fired heater;    wherein said fuel, substantially pure oxygen, and flue gas are fed into said fired heater in at least stoichiometric amounts wherein combusting takes place in a combustion regime represented by            4   ,     500   ≥     7554.8   -     933.72      x     +     64.960        x   2       +     .47705      y     -     .55680      z     -     1579.2   w       ≥   2     ,   500.                     
     
     
         19 . The method of  claim 18 , wherein said fuel is continuously monitored by a chromatograph.  
     
     
         20 . The method of  claim 19 , wherein said chromatograph is operatively linked to a microprocessor.  
     
     
         21 . The method of  claim 20 , wherein said fuel composition data is sent from said chromatograph to said microprocessor wherein said heating value of said fuel is determined by said microprocessor based on said fuel composition data.  
     
     
         22 . The method of  claim 21 , wherein said microprocessor is operatively linked to a heater controller wherein said heater controller operates a fuel flow control valve, an oxygen flow control valve, and a recycle flow control valve based on one or more signals from the microprocessor, thereby controlling the amount of fuel, substantially pure oxygen and flue gas fed into the fired heater.