Closed cycle mixed refrigerant systems

Abstract

The present invention provides for a process for providing cooling and controlling the refrigeration in a cooling loop used in the production of liquefied natural gas. A cooling loop in contact with a heat exchanger contains a refrigerant composition and by controlling the amount of a component in the refrigerant composition, the necessary level of cooling provided to the heat exchanger can be maintained.

1 . A method for providing refrigeration to a natural gas liquefaction process wherein a cooling loop containing a refrigerant composition is directed through a heat exchanger comprising controlling said refrigerant composition continuously by changing the liquid level in a warm end phase separator. 
   
   
       2 . The method as claimed in  claim 1  wherein said refrigerant composition contains iso-pentane. 
   
   
       3 . The method as claimed in  claim 1  wherein the liquid level in said warm end phase separator decreases as the heat transfer required of said heat exchanger increases. 
   
   
       4 . The method as claimed in  claim 1  wherein said liquid level is controlled on-line. 
   
   
       5 . The method as claimed in  claim 1  wherein the liquid level in said warm end phase separator increases as the heat transfer required of said heat exchanger decreases. 
   
   
       6 . The method as claimed in  claim 1  wherein said heat exchanger and said warm end phase separator are in fluid communication. 
   
   
       7 . The method as claimed in  claim 1  wherein said cooling loop and said heat exchanger are in fluid communication. 
   
   
       8 . The method as claimed in  claim 2  wherein said control is performed by changing the amount of iso-pentane present in said refrigerant composition. 
   
   
       9 . A method for providing cooling to a process for producing liquefied natural gas comprising the steps:
 a) contacting a stream of liquefied natural gas with a heat exchanger;   b) contacting said heat exchanger with a cooling loop containing a refrigerant composition;   c) adjusting the composition of said refrigerant by controlling the amount of a heavier condensable component in said refrigerant composition in response to performance variations in said heat exchanger; and   d) recovering liquefied natural gas.   
   
   
       10 . The method as claimed in  claim 9  wherein said heavier condensable component is iso-pentane. 
   
   
       11 . The method as claimed in  claim 9  wherein said performance variations in said heat exchanger are selected from the group consisting of a temperature increase in said heat exchanger and a temperature decrease in said heat exchanger. 
   
   
       12 . The method as claimed in  claim 9  wherein the amount of said heavier condensable component in said refrigerant composition will increase in response to an increase in temperature in said heat exchanger. 
   
   
       13 . The method as claimed in  claim 9  wherein the amount of said heavier condensable component in said refrigerant composition will decrease in response to a decrease in temperature in said heat exchanger. 
   
   
       14 . A method for providing refrigeration to a natural gas liquefaction process wherein a cooling loop comprising two warm end separators and a cold end separator are in fluid connection with each other comprising controlling the liquid level in said warm end separators. 
   
   
       15 . The method as claimed in  claim 14  wherein said cooling loop contacts a heat exchanger. 
   
   
       16 . The method as claimed in  claim 14  wherein said refrigerant composition contains iso-pentane. 
   
   
       17 . The method as claimed in  claim 14  wherein the liquid level in said warm end separators decreases as the heat transfer required of said heat exchanger increases. 
   
   
       18 . The method as claimed in  claim 14  wherein said liquid level is controlled on-line. 
   
   
       19 . The method as claimed in  claim 14  wherein the liquid level in said warm end separators increases as the heat transfer required of said heat exchanger decreases. 
   
   
       20 . The method as claimed in  claim 16  wherein said control is performed by changing the amount of iso-pentane present in said refrigerant composition. 
   
   
       21 . The method as claimed in  claim 14  wherein a first warm end separator is in fluid communication with a second warm end separator. 
   
   
       22 . A method for providing refrigeration to a natural gas liquefaction process wherein a cooling loop comprising a warm end separator and a cold end separator are in fluid connection with each other comprising the steps:
 a) controlling the liquid level in said warm end separator;   b) removing vapor from said cold end separator;   c) heat exchanging said vapor with a separate liquid nitrogen storage system; and   d) returning the liquid from said exchange of step c) to a heat exchanger.   
   
   
       23 . The method as claimed in  claim 22  wherein said controlling of said liquid level is performed on-line. 
   
   
       24 . The method as claimed in  claim 22  wherein the liquid level in said warm end separator is controlled by changing the amount of iso-pentane present in said liquid. 
   
   
       25 . The method as claimed in  claim 22  wherein said cooling loop contacts a heat exchanger. 
   
   
       26 . The method as claimed in  claim 22  wherein the liquid level in said warm end separators decreases as the heat transfer required of said heat exchanger increases. 
   
   
       27 . A method for providing refrigeration to a natural gas liquefaction process wherein a cooling loop comprising a warm end separator and a cold end separator are in fluid communication with each other comprising controlling the liquid level in said warm end separator and controlling the flow of natural gas from a separator to a heat exchanger. 
   
   
       28 . The method as claimed in  claim 27  wherein the liquid level in said warm end separator is controlled by changing the amount of iso-pentane present in said liquid. 
   
   
       29 . The method as claimed in  claim 27  wherein said controlling of said liquid level is performed on-line. 
   
   
       30 . The method as claimed in  claim 27  wherein the flow of natural gas from a separator to a heat exchanger is controlled by the temperature of said separator where a gas stream will enter said heat exchanger and a bottom liquid stream is directed from said separator for reentry into said separator. 
   
   
       31 . The method as claimed in  claim 30  wherein said bottom liquid stream comprises butane, propane and pentane. 
   
   
       32 . The method as claimed in  claim 30  wherein said gas stream from said separator after exiting said heat exchanger is directed into said separator.