Process for liquefying a hydrocarbon-rich fraction

Abstract

Described herein is a process for liquefying a hydrocarbon-rich fraction, in particular natural gas, is described, in which the hydrocarbon-rich fraction that is to be liquefied is cooled in indirect heat exchange against a multistage precooling circuit, the refrigerant of the precooling circuit is at least 95% by volume carbon dioxide, the cooled hydrocarbon-rich fraction is liquefied and subcooled in indirect heat exchange against a mixed cycle, and the mixed refrigerant of the mixed cycle comprises exclusively the component(s) nitrogen, methane and/or ethane.

1 . A process for liquefying a hydrocarbon-rich fraction, comprising:
 cooling the hydrocarbon-rich fraction that is to be liquefied (A-B) in indirect heat exchange (E 1 B-E 4 B) against a multistage precooling circuit ( 1 - 9 ,  30 - 37 ,  40 - 47 ),   wherein the refrigerant of the precooling circuit is at least 95% by volume carbon dioxide, and   liquefying and subcooling the cooled hydrocarbon-rich fraction (C) is in indirect heat exchange (E 7 , E 8 , E 10 ) against a mixed cycle ( 10 - 19 ),   wherein the mixed refrigerant of the mixed cycle comprises exclusively component(s) selected from nitrogen, methane and ethane.   
     
     
         2 . The process according to  claim 1 , wherein said hydrocarbon-rich fraction is natural gas. 
     
     
         3 . The process according to  claim 1 , wherein the carbon dioxide circulating in the precooling circuit ( 1 - 9 ,  30 - 37 ,  40 - 47 ) is compressed in two separate compressor casings (C 1 A, C 1 B), a low-pressure casing (C 1 A) and a high-pressure casing (C 1 B), wherein the exit pressure of the low-pressure casing (C 1 A) is below the critical pressure of carbon dioxide. 
     
     
         4 . The process according to  claim 2 , wherein the exit pressure of the high-pressure casing (C 1 B) is operated at a final pressure of at least 90 bar. 
     
     
         5 . The process according to  claim 2 , wherein the exit pressure of the high-pressure casing (C 1 B) is operated at a final pressure of at least 100 bar. 
     
     
         6 . The process according to  claim 1 , wherein the mixed refrigerant circulating in the mixed cycle ( 10 - 19 ) is compressed to a pressure above the critical pressure thereof (C 2 ). 
     
     
         7 . The process according to  claim 1 , wherein the temperature(s) of the hydrocarbon-rich fraction that is to be liquefied, of the carbon dioxide and/or of the mixed refrigerant is/are adjusted in such a manner that the drive powers of the compressors (C 1 A, C 1 B) of the precooling circuit ( 1 - 9 ,  30 - 37 ,  40 - 47 ) and of the compressor or compressors (C 2 ) of the mixed cycle differ by a maximum of 10%. 
     
     
         8 . The process according to  claim 7 , wherein the temperature(s) of the hydrocarbon-rich fraction that is to be liquefied, of the carbon dioxide and/or of the mixed refrigerant is/are adjusted in such a manner that the drive powers of the compressors (C 1 A, C 1 B) of the precooling circuit ( 1 - 9 ,  30 - 37 ,  40 - 47 ) and of the compressor or compressors (C 2 ) of the mixed cycle differ by a maximum of 5%. 
     
     
         9 . The process according to  claim 1 , wherein the hydrocarbon-rich fraction that is to be liquefied, before the cooling and liquefaction thereof, is subjected to an adsorptive water removal (Y), and wherein the liquefied hydrocarbon-rich fraction (D, D′) is expanded (V 2 ) and the resulting gaseous fraction is compressed to the pressure of the hydrocarbon-rich fraction that is to be liquefied (A, A′) and fed thereto, wherein the compressed gaseous fraction, before the feeding thereof, serves for regenerating the dryer or dryers of said adsorptive water removal (Y). 
     
     
         10 . The process according to  claim 1 , wherein the refrigerant of the precooling circuit is at least 99% by volume carbon dioxide. 
     
     
         11 . The process according to  claim 1 , wherein higher hydrocarbons, and optionally hydrocarbons at risk of freezing, are removed from the precooled hydrocarbon-rich fraction that is to be liquefied (C).