Helium Extraction from Natural Gas

Abstract

A crude helium stream is recovered from a natural gas feed by distillation. Refrigeration from expanding a portion of the bottoms liquid is used to partially condense the helium-enriched overhead vapor and generate a crude helium vapor and a helium-containing liquid stream that is recycled to the distillation column to maximize helium recovery. The helium-depleted natural gas stream can be returned at pressure for utilization or transportation.

We claim: 
     
         1 . A process for recovering helium from a natural gas feed comprising methane, nitrogen, and helium, said process comprising:
 cooling said natural gas feed to produce a cooled natural gas feed which is at least partially condensed;   separating the cooled natural gas feed in a distillation column system to produce a helium-enriched overhead vapor and a helium-depleted bottoms liquid;   cooling said helium-enriched overhead vapor to produce a partially condensed overhead stream;   separating said partially condensed overhead stream in an overhead separator to produce a crude helium vapor and a recycle liquid;   expanding at least a portion of the helium-depleted bottoms liquid to produce a first helium-depleted bottoms fraction;   wherein cooling duty for cooling said helium-enriched overhead vapor is provided at least in part by indirect heat exchange with said first helium-depleted bottoms fraction.   
     
     
         2 . Process of  claim 1  wherein the pressure of said cooled natural gas feed is reduced to achieve a ratio of liquid to vapor density in the distillation column greater than 4. 
     
     
         3 . Process of  claim 1  wherein the pressure of said cooled natural gas feed is reduced to achieve a liquid phase surface tension in the distillation column greater than 0.5 dyne/cm. 
     
     
         4 . Process of  claim 1  wherein the difference between the pressure of the top of the distillation column system and the pressure of said overhead separator is no more than 1 bar. 
     
     
         5 . Process of  claim 1  wherein the re-boiling duty for said distillation column system is provided at least in part by indirect heat exchange with the natural gas feed. 
     
     
         6 . Process of  claim 1  wherein said recycle liquid is introduced to the distillation column. 
     
     
         7 . Process of  claim 6  wherein the recycle liquid is introduced to the distillation column at the same or lower stage as the location where the cooled natural gas is fed to the distillation column. 
     
     
         8 . Process of  claim 1  further comprising the step of expanding at least a portion of said helium-depleted bottoms liquid to produce a second helium-depleted bottoms fraction. 
     
     
         9 . Process of  claim 8  wherein the pressure of said second helium-depleted bottoms fraction is higher than the pressure of said first helium-depleted bottoms fraction. 
     
     
         10 . Process of  claim 8  further comprising the steps of warming said second helium-depleted bottoms fraction to provide at least a portion of the refrigeration to cool and condense said natural gas feed and produce a warmed second helium-depleted bottoms fraction;
 and expanding said warmed second helium-depleted bottoms fraction to provide power and produce an expanded second helium-depleted bottoms fraction. 
 
     
     
         11 . Process of  claim 8  further comprising combining and compressing said first and second helium-depleted bottoms fractions, or streams derived therefrom, to produce a helium-depleted natural gas stream. 
     
     
         12 . Process of  claim 8  further comprising the steps of pressurizing at least a portion of said helium-depleted bottoms liquid to produce a third helium-depleted bottoms fraction;
 and warming said third helium-depleted bottoms fraction to provide at least a portion of the refrigeration to cool and condense said natural gas feed. 
 
     
     
         13 . Process of  claim 12  further comprising combining and compressing said first, second, and third helium-depleted bottoms fraction, or streams derived therefrom, to produce a helium-depleted natural gas stream. 
     
     
         14 . A natural gas processing plant for recovering helium from a natural gas feed comprising methane, nitrogen, and helium, said plant comprising:
 a heat exchanger system;   a distillation column system comprising a vapor outlet and a liquid outlet;   a first conduit for transferring a cooled natural gas feed from said heat exchanger system to said distillation column;   a second conduit for transferring a helium-enriched overhead vapor from said vapor outlet of said distillation column to said heat exchanger system;   an overhead separator comprising a vapor outlet and a liquid outlet;   a third conduit for transferring a partially condensed overhead from said heat exchanger system to said overhead separator;   a fourth conduit for transferring a first helium-depleted bottoms fraction from said liquid outlet of said distillation system to said heat exchanger system;   Wherein said fourth conduit comprises a pressure reduction device.   
     
     
         15 . The natural gas processing plant of  claim 14  wherein said first conduit comprises a pressure reduction device. 
     
     
         16 . The natural gas processing plant of  claim 14  further comprising a fifth conduit for transferring a recycle liquid from said liquid outlet of said overhead separator to said distillation column. 
     
     
         17 . The natural gas processing plant of  claim 16  wherein said fifth conduit connects to said distillation column at the same stage as or a lower stage than where said first conduit connects to said distillation column. 
     
     
         18 . The natural gas processing plant of  claim 14  further comprising a sixth conduit for transferring a second helium-depleted bottoms fraction from said liquid outlet of said distillation system to said heat exchanger system, wherein said sixth conduit further comprises a pressure reduction device. 
     
     
         19 . The natural gas processing plant of  claim 18  further comprising:
 an expander; 
 a seventh conduit for transferring a warmed second helium-depleted bottoms fraction from said heat exchanger to said expander; 
 and an eighth conduit for transferring an expanded second helium-depleted bottoms fraction from said expander to said heat exchanger system. 
 
     
     
         20 . The natural gas processing plant of  claim 18  further comprising:
 a pump; 
 a ninth conduit for transferring a third helium-depleted bottoms fraction from said liquid outlet of said distillation system to said pump; 
 and a tenth conduit for transferring a pressurized third helium-depleted bottoms fraction from said pump to said heat exchanger system. 
 
     
     
         21 . The natural gas processing plant of  claim 18  further comprising:
 a return compressor; 
 and an eleventh conduit for transferring a low-pressure return stream from said heat exchanger system to said return compressor. 
 
     
     
         22 . The natural gas processing plant of  claim 21  further comprising a twelfth conduit for transferring a medium-pressure return stream from said heat exchanger system to said return compressor. 
     
     
         23 . The natural gas processing plant of  claim 21  further comprising:
 a mixing device; 
 a thirteenth conduit for transferring a compressed helium-depleted natural gas stream from said return compressor to said mixing device; 
 and a fourteenth conduit for transferring a medium-pressure return stream from said heat exchanger system to said mixing device.