Production of helium from a stream of natural gas

Abstract

A method for producing a helium gas stream from a gas source containing at least helium, methane, and nitrogen is provided. The method includes introducing the gas into a double column nitrogen rejection unit.

1 .- 14 . (canceled) 
     
     
         15 . A process for producing a helium gas stream from a source gas stream comprising at least helium, methane and nitrogen, the process comprising the following steps:
 step a): introducing the source gas stream into a double-column nitrogen rejection unit, the double column comprising a high-pressure distillation column, a low-pressure distillation column and a condenser linking the high-pressure column with the low-pressure column, the condenser comprising an outlet, and the high-pressure column comprising a top, and the low-pressure column comprising a top;   step b): extracting at the outlet of the condenser at least one part of a mixture produced at the top of the high-pressure column;   step c): expanding the mixture resulting from step b) to an intermediate pressure of between 8 bar and 20 bar absolute;   step d): separating the intermediate pressure mixture resulting from step c) in a first phase separator vessel into a liquid phase and a helium-enriched gas phase;   step e): at least partially condensing the helium-enriched gas phase in a heat exchanger;   step f): separating the at least partially condensed stream resulting from step e) in a second phase separator vessel into a liquid phase and a gas phase containing more than 50% by volume of helium.   
     
     
         16 . The process of  claim 15 , further comprising a step g): using, as refrigerant, the liquid phase after expansion resulting from step f) in the heat exchanger used in step e). 
     
     
         17 . The process of  claim 16 , wherein, during step g), the liquid phase is vaporized at a pressure of between 0.1 bar and 3 bar absolute. 
     
     
         18 . The process of  claim 15 , wherein, during step a), the gas stream is introduced into the high-pressure column at at least a first feed level and a second feed level, the vapor fraction at the first feed level being smaller than the vapor fraction at the second feed level and the first feed level being introduced at a higher level of the high-pressure column than the second feed level. 
     
     
         19 . The process of  claim 16 , further comprising a step h): extracting the gas phase resulting from step f) as helium-rich product containing at least 75% by volume of helium. 
     
     
         20 . The process of  claim 19 , wherein the temperature at the outlet of the condenser in step b) is between −150° C. and −165° C. 
     
     
         21 . The process of  claim 20 , wherein the pressure in the high-pressure column is between 20 bar absolute and 50 bar absolute and the pressure in the low-pressure column is between 1 bar absolute and 5 bar absolute. 
     
     
         22 . The process of  claim 15 , wherein the temperature at which step c) is carried out is between −160° C. and −180° C. 
     
     
         23 . The process of  claim 15 , wherein the temperature at which step e) is carried out is between −180° C. and −210° C. 
     
     
         24 . The process of  claim 15 , wherein the liquid phase resulting from step d) is introduced into the low-pressure column. 
     
     
         25 . The process of  claim 15 , further comprising an additional step of producing a nitrogen-enriched stream comprising less than 2% by volume of methane from a gas stream rom the top of the low-pressure column. 
     
     
         26 . The process of  claim 15 , wherein the source gas stream comprises from 20% by volume to 80% by volume of methane, from 20% by volume to 80% by volume of nitrogen and from 0% by volume to 2% by volume of helium. 
     
     
         27 . A facility for producing helium from a gas source mixture comprising methane, helium and nitrogen, the facility comprising:
 at least one nitrogen rejection unit equipped with a double column, the double column comprising a high-pressure distillation column, a low-pressure distillation column and a condenser linking the high-pressure column with the low-pressure column, and   a helium extraction unit comprising a first phase separator vessel located upstream of a heat exchanger which is itself located upstream of a second phase separator vessel;   
       wherein the nitrogen rejection unit is located upstream of the helium extraction unit. 
     
     
         28 . The facility of  claim 27 , wherein the helium extraction unit contains neither a distillation column nor a rectification column nor a phase separator vessel with multiple feeds.