Method for liquefying a hydrocarbon-rich fraction

Abstract

A method for liquefying a hydrocarbon-rich fraction, in particular natural gas, by indirect heat exchange with the refrigerant blend of a refrigerant blend circuit is described, wherein the refrigerant blend is compressed, separated into a liquid phase which is rich in higher-boiling components (HMR) of the refrigerant blend and a gas phase which is rich in lower-boiling components (LMR) of the refrigerant blend, and said phases are mixed before the indirect heat exchange. According to the invention, indirect heat exchange proceeds in at least two heat exchangers (E 3, E 4 ), wherein the first heat exchanger (E 4 ) serves to precool and the second heat exchanger (E 3 ) to liquefy the hydrocarbon-rich fraction, and the first heat exchanger is supplied with a refrigerant blend which comprises 5 to 50% of the liquid phase ( 3, 15 ) which is rich in higher-boiling components (HMR) of the refrigerant blend and said blend is combined with the gas phase ( 6, 14 ) which is rich in lower-boiling components (LMR) of the refrigerant blend in such a way that an HMR/LMR mixing ratio of between 1.2 and 10 is established.

1 . A method for liquefying a hydrocarbon-rich fraction by indirect heat exchange with a refrigerant blend of a refrigerant blend circuit, said method comprising:
 performing said indirect heat exchange between said hydrocarbon-rich fraction and said refrigerant blend in at least two heat exchangers (E 3 , E 4 ) comprising a first heat exchanger (E 3 ) and a second heat exchanger (E 3 ),   wherein said first heat exchanger (E 4 ) serves to precool said hydrocarbon-rich fraction, and said second heat exchanger (E 3 ) serves to liquefy said hydrocarbon-rich fraction ( 200 - 203 ),   wherein said refrigerant blend is compressed, separated into a liquid phase, which is rich in higher-boiling components (HMR) of the refrigerant blend, and a gas phase, which is rich in lower-boiling components (LMR) of the refrigerant blend, and said liquid phase and said gas phase are mixed before said indirect heat exchange, and   wherein said first heat exchanger (E 4 ) is supplied with a first portion of said refrigerant blend and said second heat exchanger (E 4 ) is supplied with a second portion of said refrigerant blend, wherein said first portion of said refrigerant blend comprises 5 to 50% of said liquid phase ( 3 ,  15 ) rich in higher-boiling components and an amount of said gas phase ( 6 ,  14 ) rich in lower-boiling components (LMR) in such a way that an HMR/LMR mixing ratio of between 1.2 and 10 is established in said portion of the said refrigerant blend.   
     
     
         2 . The method according to  claim 1 , wherein said portion of said refrigerant blend supplied to said first heat exchanger (E 4 ) comprises 10 to 30% of said liquid phase rich in higher-boiling components. 
     
     
         3 . The method according to  claim 1 , wherein the HMR/LMR mixing ratio of said portion of said refrigerant blend is between 2 and 5 is established. 
     
     
         4 . The method according to  claim 2 , wherein the HMR/LMR mixing ratio of said portion of said refrigerant blend is between 2 and 5 is established. 
     
     
         5 . A method according to  claim 1 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the first heat exchanger (E 4 ). 
     
     
         6 . A method according to  claim 2 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the first heat exchanger (E 4 ). 
     
     
         7 . A method according to  claim 3 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the first heat exchanger (E 4 ). 
     
     
         8 . A method according to  claim 4 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the first heat exchanger (E 4 ). 
     
     
         9 . A method according to  claim 1 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         10 . A method according to  claim 2 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         11 . A method according to  claim 3 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         12 . A method according to  claim 4 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         13 . A method according to  claim 5 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         14 . A method according to  claim 6 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         15 . A method according to  claim 7 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         16 . A method according to  claim 8 , wherein a sub-stream ( 13 ,  17 ) of said gas phase ( 6 ) is supplied to the refrigerant blend ( 12 ,  16 ) at the cold end of the second heat exchanger (E 3 ). 
     
     
         17 . A method according to  claim 1 , wherein said first and second portions of the refrigerant blend are vaporized by said indirect heat exchange in said first and second heat exchangers, respectively, and then the first and second portions of the of the refrigerant blend are combined and the resultant combined stream is sent to a first separator D 1  where a gaseous fraction and a liquid fraction are separated, and the compression of the refrigerant blend is performed by compressing the gaseous fraction from said first separator D 1  in an at least two-stage compressor unit C, a separator D 1  upstream of the compressor unit C, a second separator D 2  is positioned downstream of the first compressor stage and a third separator D 3  is positioned downstream of the second compressor stage,
 a gaseous fraction removed from the second separator D 2  is compressed in the second compressor stage and a liquid fraction removed from the second separator D 2  forms said liquid phase, and 
 a gaseous fraction removed from the third separator D 3  forms said gas phase, and a liquid fraction removed from the third separator D 3  is recycled to said second separator D 2 . 
 
     
     
         18 . A method according to  claim 1 , wherein the hydrocarbon-rich fraction to be liquefied is particular natural gas.