Recovery Of Helium From Nitrogen-Rich Streams

Abstract

Overall power consumption in a cryogenic distillation process for recovering helium from nitrogen-rich gases comprising helium may be reduced if the feed to the distillation column system is at least substantially condensed by indirect heat exchange against a first bottoms liquid at first pressure, and a second bottoms liquid at a second pressure that is different from the first pressure.

1 . A process for recovering helium from a nitrogen-rich feed gas comprising helium, said process comprising:
 cooling a pressurized nitrogen-rich feed gas comprising helium to produce cooled feed; and   separating said feed in a first distillation column system operating at an elevated operating pressure to produce helium-enriched overhead vapor and nitrogen-enriched bottoms liquid(s);   
       wherein said feed to the first distillation column system is at least partially condensed; and 
       wherein said cooling of said feed gas is achieved by indirect heat exchange against at least a first nitrogen-enriched bottoms liquid at a first elevated pressure and a second nitrogen-enriched bottoms liquid at a second elevated pressure that is different from said first elevated pressure. 
     
     
         2 . The process of  claim 1 , wherein said first elevated pressure is equal to the elevated operating pressure of said first distillation column system. 
     
     
         3 . The process of  claim 1 , wherein said first elevated pressure is from about 2 bar to about 35 bar. 
     
     
         4 . The process of  claim 1 , wherein the second elevated pressure is less than the elevated operating pressure of said first distillation column system. 
     
     
         5 . The process of  claim 4 , wherein the second elevated pressure is from more than 1 bar to about 30 bar. 
     
     
         6 . The process of  claim 4  comprising expanding bottoms liquid to produce said second portion of said bottoms liquid. 
     
     
         7 . The process of  claim 1 , wherein said feed gas is at subcritical pressure. 
     
     
         8 . The process of  claim 7 , wherein said feed gas is cooled by indirect heat exchange against said first bottoms liquid and then at least partially condensed by indirect heat exchange against said second bottoms liquid. 
     
     
         9 . The process of  claim 1 , wherein the second elevated pressure is greater than the elevated operating pressure of said first distillation column system. 
     
     
         10 . The process of  claim 9 , wherein the second elevated pressure is from about 3 bar to about 150 bar. 
     
     
         11 . The process of  claim 9  comprising pumping bottoms liquid to produce said second bottoms liquid. 
     
     
         12 . The process of  claim 1 , wherein said feed gas is at supercritical pressure. 
     
     
         13 . The process of  claim 12 , wherein said feed gas is cooled by indirect heat exchange against said first bottoms liquid and then further cooled by indirect heat exchange against said second bottoms liquid. 
     
     
         14 . The process of  claim 12 , comprising expanding said cooled feed prior to feeding said cooled feed to said first distillation column system. 
     
     
         15 . The process of  claim 1 , wherein the feed to the first distillation column system has a vapor fraction of no more than 0.5. 
     
     
         16 . The process of  claim 15 , wherein the feed to the first distillation column system is at least substantially fully condensed. 
     
     
         17 . The process of  claim 1 , wherein said pressurized nitrogen-rich feed gas is at a pressure greater than said elevated operating pressure of said first distillation column, said process comprising expanding said at least partially condensed feed prior to separation. 
     
     
         18 . The process of  claim 1 , wherein the pressure of said pressurized nitrogen-rich feed gas is from about 2 bar to about 200 bar. 
     
     
         19 . The process of  claim 1 , wherein said elevated operating pressure of the distillation column system is from about 2 bar to about 35 bar. 
     
     
         20 . The process of  claim 1  comprising expanding vaporized bottoms liquid, or a fluid derived therefrom, to produce expanded nitrogen-enriched gas and using said expanded gas to provide a part of the refrigeration duty of the process. 
     
     
         21 . The process of  claim 1 , wherein said second bottoms liquid is at least partially vaporized as a result of said indirect heat exchange against said feed gas, said process comprising:
 warming said vaporized bottoms liquid by indirect heat exchange to produce warmed nitrogen-enriched gas; and   expanding said warmed nitrogen-enriched gas to produce expanded nitrogen-enriched gas; and   cooling said feed gas by indirect heat exchange with said expanded nitrogen-enriched gas to produce cooled feed gas.   
     
     
         22 . The process of  claim 1  comprising:
 expanding a third nitrogen-enriched bottoms liquid to produce expanded nitrogen-enriched fluid; 
 vaporizing said expanded nitrogen-enriched fluid by indirect heat exchange against condensing nitrogen in said first distillation column system to produce nitrogen-enriched gas; 
 expanding said nitrogen-enriched gas to produce expanded nitrogen-enriched gas; and 
 condensing nitrogen gas in said first distillation column system by indirect heat exchange against said expanded nitrogen-enriched gas to produce liquid reflux for said first distillation column system. 
 
     
     
         23 . The process of  claim 22  comprising:
 expanding a fourth nitrogen-enriched bottoms liquid to produce further expanded nitrogen-enriched fluid; and 
 vaporizing said further expanded nitrogen-enriched fluid by indirect heat exchange against condensing nitrogen in said first distillation column system to produce further nitrogen-enriched gas. 
 
     
     
         24 . The process of  claim 1 , wherein said second bottoms liquid is vaporized as a result of said indirect heat exchange against said feed gas, said process comprising:
 expanding said vaporized bottoms liquid to produce expanded nitrogen-enriched gas; and   condensing nitrogen gas in said first distillation column system by indirect heat exchange with said expanded nitrogen-enriched gas to produce liquid reflux for said first distillation column system and warmed nitrogen-enriched gas.   
     
     
         25 . The process of  claim 24  comprising:
 expanding a third nitrogen-enriched bottoms liquid to produce further expanded nitrogen-enriched fluid; and 
 vaporizing said further expanded nitrogen-enriched fluid by indirect heat exchange against condensing nitrogen in said first distillation column system to produce further nitrogen-enriched gas. 
 
     
     
         26 . The process of  claim 24  comprising expanding a fourth nitrogen-enriched bottoms liquid to form an expanded fluid; and separating said expanded fluid into a vapor phase and a liquid phase. 
     
     
         27 . The process of  claim 26 , wherein said vapor phase is warmed by indirect heat exchange to produce a gaseous nitrogen product. 
     
     
         28 . The process of  claim 26 , comprising sub-cooling said fourth portion of said bottoms liquid prior to expansion to form said expanded two phase fluid. 
     
     
         29 . The process of  claim 28 , wherein said fourth bottoms liquid is sub-cooled by indirect heat exchange against expanded nitrogen-enriched gas 
     
     
         30 . The process of  claim 1 , wherein the process is autorefrigerated. 
     
     
         31 . The process of  claim 1 , wherein said feed gas is taken from a natural gas liquid (NGL) recovery column. 
     
     
         32 . The process of  claim 1  comprising:
 cooling and at least partially condensing pressurized dry, carbon dioxide-free natural gas to produce at least partially condensed natural gas; and 
 separating said at least partially condensed natural gas in a second distillation column system operating at an elevated operating pressure to produce C 2+ -depleted overhead vapor and C 2+ -enriched bottoms liquid, 
 
       wherein said C 2+ -depleted overhead vapor is said nitrogen-rich feed gas. 
     
     
         33 . The process of  claim 32 , wherein said natural gas comprises at least 70% nitrogen (N 2 ). 
     
     
         34 . The process of  claim 32 , wherein said pressurized dry, carbon dioxide-free natural gas is at a pressure of from about 2 bar to about 200 bar. 
     
     
         35 . The process of  claim 32 , wherein said elevated pressure of said second distillation column system is less than the pressure of said pressurized dry, carbon dioxide-free natural gas, said process comprising expanding said at least partially condensed natural gas to said elevated pressure of said second distillation column system prior to separation. 
     
     
         36 . The process of  claim 32 , wherein said elevated operating pressure of said second distillation column system is from about 2 bar to about 35 bar. 
     
     
         37 . The process of  claim 1  comprising:
 warming said helium-enriched overhead vapor by indirect heat exchange to produce helium-enriched gas; and 
 purifying said helium-enriched gas to produce pure helium gas. 
 
     
     
         38 . The process of  claim 37 , wherein said helium-enriched gas is purified by a pressure swing adsorption (PSA) process. 
     
     
         39 . The process of  claim 38 , wherein tail gas from said PSA process is recycled to said first distillation column system after suitable pressure and temperature adjustment. 
     
     
         40 . The process of  claim 1 , wherein said feed gas comprises methane, said process comprising recovering methane from said bottoms liquid to produce fuel gas or LNG. 
     
     
         41 . The process of  claim 1  comprising separating bottoms liquid in a third distillation column system operating at elevated operating pressure(s) to produce nitrogen overhead vapor and methane-enriched bottoms liquid. 
     
     
         42 . The process of  claim 41  comprising warming said nitrogen overhead vapor by indirect heat exchange to produce warmed nitrogen gas. 
     
     
         43 . The process of  claim 41  comprising recycling a portion of said nitrogen gas to said third distillation column system after suitable pressure and temperature adjustment. 
     
     
         44 . The process of  claim 42  comprising expanding a portion of said nitrogen gas to produce expanded nitrogen gas, and warming said expanded nitrogen gas by indirect heat exchange to produce warmed expanded nitrogen gas. 
     
     
         45 . The process of  claim 41  comprising warming and evaporating said methane-enriched bottoms liquid by indirect heat exchange to produce fuel gas. 
     
     
         46 . The process of  claim 41 , wherein said third distillation column system additionally produces a nitrogen-enriched overhead vapor, said process comprising condensing said nitrogen-enriched overhead vapor to produce condensed vapor and removing a portion of said condensed vapor as a liquid nitrogen product. 
     
     
         47 . The process of  claim 41 , wherein the or each elevated pressure of said third distillation column system is less than the pressure of the bottoms liquid, said process comprising expanding said bottoms liquid to the or one of the elevated pressures of said third distillation column system prior to separation. 
     
     
         48 . The process of  claim 41 , wherein said elevated pressure of said third distillation column system is from about 1 bar to about 35 bar. 
     
     
         49 . A process substantially as hereinbefore described with reference to the accompanying examples and/or drawings. 
     
     
         50 . Apparatus for recovering helium from a nitrogen-rich feed gas comprising helium, said apparatus comprising:
 a distillation column system for operation at an elevated operating pressure to separate at least partially condensed feed gas into helium-enriched overhead vapor and nitrogen-enriched bottoms liquid(s);   an overhead condenser for partially condensing helium-enriched overhead vapor by indirect heat exchange to produce helium-enriched vapor as product and liquid for reflux in the column system;   a first heat exchange system for cooling feed gas by indirect heat exchange with a first nitrogen-enriched bottoms liquid to produce cooled feed gas and vapor for the column system;   a first pressure reduction device for reducing the pressure of a second nitrogen-enriched bottoms liquid to produce reduced pressure bottoms liquid;   a second heat exchange system for cooling said cooled feed gas by indirect heat exchange against said reduced pressure bottoms liquid to produce at least partially condensed feed gas and vaporized bottoms liquid; and   a second pressure reduction device for reducing the pressure of said at least partially condensed feed gas to produce at least partially condensed feed gas at reduced pressure for use as said feed to the distillation column system.   
     
     
         51 . The apparatus of  claim 50  comprising a third pressure reduction device for reducing the pressure of a third nitrogen-enriched bottoms liquid to produce reduced pressure bottoms liquid for vaporization by indirect heat exchange in said overhead condenser to produce nitrogen-enriched vapor. 
     
     
         52 . The apparatus of  claim 51  comprising an expander for expanding said nitrogen-enriched vapor to produce expanded nitrogen-enriched vapor for warming by indirect heat exchange in said overhead condenser to produce warmed nitrogen-enriched vapor. 
     
     
         53 . The apparatus of  claim 51  comprising a fourth pressure reduction device for reducing the pressure of a fourth nitrogen-enriched bottoms liquid to produce reduced pressure bottoms liquid for vaporization by indirect heat exchange in said overhead condenser to produce nitrogen-enriched vapor. 
     
     
         54 . The apparatus of  claim 50  comprising an expander for expanding said vaporized bottoms liquid to produce expanded nitrogen-enriched vapor for warming by indirect heat exchange in said overhead condenser to produce warmed nitrogen-enriched vapor. 
     
     
         55 . The apparatus of  claim 54  comprising:
 a fourth pressure reduction device for reducing the pressure of a fourth portion of said nitrogen-enriched bottoms liquid to produce reduced pressure bottoms liquid; and 
 a storage vessel for storing said reduced pressure bottoms liquid. 
 
     
     
         56 . Apparatus for recovering helium from a nitrogen-rich feed gas comprising helium, said apparatus comprising:
 a distillation column system for operation at an elevated operating pressure to separate at least partially condensed feed gas into helium-enriched overhead vapor and nitrogen-enriched bottoms liquid;   an overhead condenser for partially condensing helium-enriched overhead vapor by indirect heat exchange to produce helium-enriched vapor as product and liquid for reflux in the column system;   a first pump for pumping a second nitrogen-enriched bottoms liquid to produce pumped bottoms liquid;   a first heat exchange system for cooling feed gas by indirect heat exchange with said pumped bottoms liquid to produce cooled feed gas and nitrogen-enriched vapor;   a second heat exchange system for cooling said cooled feed gas by indirect heat exchange against a first nitrogen-enriched bottoms liquid to produce at least partially condensed feed gas and vapor for the column system; and   a pressure reduction device for reducing the pressure of said at least partially condensed feed gas to produce at least partially condensed feed gas at reduced pressure for use as said feed to the distillation column system.   
     
     
         57 . The apparatus of  claim 56  comprising a second pressure reduction device for reducing the pressure of a third nitrogen-enriched bottoms liquid to produce reduced pressure bottoms liquid for vaporization by indirect heat exchange in said overhead condenser to produce nitrogen-enriched vapor. 
     
     
         58 . The apparatus of  claim 57  comprising an expander for expanding said nitrogen-enriched vapor to produce expanded nitrogen-enriched vapor for warming by indirect heat exchange in said overhead condenser to produce warmed nitrogen-enriched vapor. 
     
     
         59 . The apparatus of  claim 57  comprising a third pressure reduction device for reducing the pressure of a fourth nitrogen-enriched bottoms liquid to produce reduced pressure bottoms liquid for vaporization by indirect heat exchange in said overhead condenser to produce nitrogen-enriched vapor. 
     
     
         60 . Apparatus substantially as hereinbefore described with reference to the accompanying examples and/or drawings.