Sour Natural Gas Pretreating Method

Abstract

The invention relates to a method of pretreating a natural gas, water-saturated or not, essentially comprising hydrocarbons, a substantial amount of hydrogen sulfide and possibly carbon dioxide. The method according to the invention comprises an H 2 S-rich stream recycling stage.

1 ) An improved method of pretreating a natural gas under pressure containing hydrocarbons, at least one of the acid compounds hydrogen sulfide and carbon dioxide, and water, comprising: 
 a) cooling the natural gas so as to produce a liquid phase and a gas phase,    b) contacting in a distillation column the gas phase obtained in stage a) with a liquid phase obtained in stage c) so as to produce a gas phase and a liquid phase,    c) cooling the gas phase obtained in stage b) so as to produce a liquid phase and a gas phase,    characterized in that at least part of the liquid phase obtained in stage b) at the column bottom is recycled upstream from natural gas cooling stage a).    
     
     
         2 ) A method as claimed in  claim 1 , wherein at least part of the liquid phase obtained in stage b) at the column bottom is directly recycled into said distillation column.  
     
     
         3 ) A method as claimed in  claim 2 , wherein at least part of the liquid phase obtained in stage b) at the column bottom is directly recycled into said distillation column at a lower level than the gas phase intake.  
     
     
         4 ) A method as claimed in  claim 2 , wherein at least part of the liquid phase obtained in stage b) at the column bottom is directly recycled into said distillation column at a higher level than the gas phase intake.  
     
     
         5 ) A method as claimed in  claim 2 , wherein at least part of the liquid phase obtained in stage b) at the column bottom is directly recycled into said distillation column at the same level as the gas phase intake.  
     
     
         6 ) A method as claimed in  claim 1 , wherein said recycle stream is subjected to a thermal exchange stage in order to be heated.  
     
     
         7 ) A method as claimed in  claim 6 , wherein said recycle stream is subjected to a thermal exchange stage in order to be heated between 50° C. and 150° C., preferably between 75° C. and 120° C.  
     
     
         8 ) A method as claimed in  claim 1 , wherein said recycle stream is determined in such a way that, after mixing with the input gas, the H 2 S content of the effluent entering the column ranges between 15% and 50% by mole, preferably between 20% and 45% by mole.