Helium production in lng plants

Abstract

A process for separating a helium-rich fraction from a liquefied natural gas stream, is disclosed. In an embodiment, the process includes expansion of a liquefied natural gas stream and separation of the helium-rich fraction. The helium-rich fraction is heated countercurrent to a natural gas stream to be cooled and liquefied. The natural gas stream liquefied in a heat exchange countercurrent to the helium-rich fraction to be heated is fed prior to and/or in the separation of the helium-rich fraction. The total enthalpy of the mixture of the two aforementioned natural gas streams brought to the separation of the helium-rich fraction is variable.

1 - 6 . (canceled) 
   
   
       7 . A process for separating a helium-rich fraction from a liquefied natural gas stream, comprising the steps of:
 a) expansion of a liquefied natural gas stream and separation of the helium-rich fraction;   b) heating of the helium-rich fraction countercurrent to a natural gas stream to be cooled and liquefied; and   c) feeding of the natural gas stream liquefied in a heat exchange countercurrent to the helium-rich fraction to be heated prior to and/or in the separation of the helium-rich fraction;   d) wherein the total enthalpy of the mixture of the two aforementioned natural gas streams brought to the separation of the helium-rich fraction is variable.   
   
   
       8 . The process according to  claim 7 , wherein a temperature of the natural gas stream liquefied in the heat exchange countercurrent to the helium-rich fraction to be heated is variable. 
   
   
       9 . The process according to  claim 7 , wherein a volume flow of the helium-rich fraction taken to the heat exchange and/or a volume flow of the natural gas stream taken to the heat exchange to be cooled and liquefied, is varied such that a helium yield from the helium-rich fraction remains essentially constant and/or is maximized. 
   
   
       10 . The process according to  claim 7 , wherein at least one partial stream of the natural gas stream to be cooled and liquefied and/or at least one partial stream of the helium-rich fraction to be heated is taken past the heat exchange between the helium-fraction to be heated and the natural gas stream to be cooled and liquefied. 
   
   
       11 . The process according to  claim 7 , wherein the heat exchange between the helium-rich fraction to be heated and the natural gas stream to be cooled and liquefied takes place in at least one coil heat exchanger and/or at least one TEMA heat exchanger. 
   
   
       12 . The process according to  claim 7 , wherein the separation of the helium-rich fraction is implemented in a separator or a wash column. 
   
   
       13 . A process for separating a helium-rich fraction from a liquefied natural gas stream, comprising the steps of:
 expanding a liquefied natural gas stream;   cooling and liquefying a natural gas stream in a heat exchanger;   providing the liquefied natural gas stream and the cooled and liquefied natural gas stream as a mixture to a separator; and   separating a helium-rich fraction from the mixture in the separator;   wherein the helium-rich fraction is provided from the separator to the heat exchanger for cooling and liquefying the natural gas stream and wherein a total enthalpy of the mixture is variable.   
   
   
       14 . The process according to  claim 13 , further comprising the steps of controlling a volume of the natural gas stream cooled and liquefied in the heat exchanger and controlling a volume of the helium-rich fraction provided from the separator to the heat exchanger. 
   
   
       15 . The process according to  claim 13 , further comprising the step of controlling a yield of helium in the helium-rich fraction by adjusting a temperature of the cooled and liquefied natural gas stream. 
   
   
       16 . The process according to  claim 14 , wherein the step of controlling the volume of the natural gas stream cooled and liquefied in the heat exchanger and the step of controlling the volume of the helium-rich fraction provided from the separator to the heat exchanger include the step of bypassing a portion of the natural gas stream and the helium-rich fraction around the heat exchanger.