Method for separating c2+-hydrocarbons from a hydrocarbon-rich fraction

Abstract

Described herein is a method for separating C 2+ -hydrocarbons from a hydrocarbon-rich fraction comprising partially condensing a hydrocarbon-rich fraction, and separating the hydrocarbon-rich fraction into a gaseous fraction and a liquid fraction. These fractions are subjected to a rectification fractionation to obtain a methane-rich fraction and a C 2+ -hydrocarbon-rich fraction. The methane-rich fraction is compressed, and a partial stream of the compressed methane-rich fraction is condensed is fed as reflux to rectification fractionation. In addition, before rectification fractionation, the liquid fraction is separated into two partial streams. The first partial stream is partially evaporated and then is fed to rectification fractionation. The second partial stream is undercooled and then is fed as additional reflux to rectification fractionation.

1 . A method for separating C 2+ -hydrocarbons from a hydrocarbon-rich fraction, said method comprising:
 a) partially condensing the hydrocarbon-rich fraction,   b) separating the partially condensed hydrocarbon-rich fraction into a gaseous fraction and a liquid fraction,   c) subjecting said gaseous fraction and said liquid fraction to a rectification fractionation to produce a methane-rich fraction and a C 2+ -hydrocarbon-rich fraction,   d) compressing the methane-rich fraction obtained from the rectification fractionation is compressed, and   e) condensing a partial stream of the compressed methane-rich fraction and feeding the condensed partial stream of the compressed methane-rich fraction as reflux to the rectification fractionation,   
       wherein
   said liquid fraction ( 2 ) obtained in b) is separated into a first partial stream ( 2 ′) and a second partial stream ( 4 ),   said first partial stream ( 2 ′) is partially evaporated (E 1 ) and then fed to the rectification fractionation (T), and   said second partial stream ( 4 ) is subcooled (E 2 ) and then fed as additional reflux ( 4 ′) to the rectification fractionation (T).   
 
     
     
         2 . The method according to  claim 1 , wherein said hydrocarbon-rich fraction is from natural gas. 
     
     
         3 . The method according to  claim 1 , wherein said first partial stream ( 2 ′) is partially evaporated (E 1 ) against the hydrocarbon-rich fraction ( 1 ) that is to be partially condensed. 
     
     
         4 . The method according to  claim 1 , wherein the evaporation pressure of the first partial stream ( 2 ′,  3 ) is variable (V 1 , V 2 ). 
     
     
         5 . The method according to  claim 1 , wherein said second partial stream ( 4 ) is sub-cooled (E 2 ) against the methane-rich fraction ( 10 ) obtained from the rectification fractionation (T). 
     
     
         6 . The method according to  claim 5 , wherein the sub-cooled second partial stream ( 4 ′) is fed as reflux to the rectification fractionation (T) at a feed point below the feedpoint of the condensed partial stream of the compressed methane-rich fraction used as reflux ( 16 ). 
     
     
         7 . The method according to  claim 1 , wherein
 three heating circuits—via which intermediate fractions are drawn off from the rectification fractionation, partially evaporated and fed again to the rectification fractionation—are assigned to the rectification fractionation, and   the intermediate fractions circulating in the two heating circuits located at the highest temperature levels are partially evaporated against the hydrocarbon-rich fraction that is to be partially condensed.   
     
     
         8 . The method according to  claim 1 , wherein
 three heating circuits—via which intermediate fractions are drawn off from the rectification fractionation, partially evaporated and fed again to the rectification fractionation—are assigned to the rectification fractionation, and   the intermediate fractions circulating in the two heating circuits located at the highest temperature levels are partially evaporated against the hydrocarbon-rich fraction that is to be partially condensed,   removal of the intermediate fraction circulating in the heating circuit ( 20 ,  20 ′) located at the highest temperature level is at least temporarily interrupted,   during the temporary interruption of removal of the intermediate fraction circulating in the heating circuit located at the highest temperature level, the intermediate fraction of the heating circuit ( 21 ,  21 ′) located at the medium temperature level is partially evaporated (E 1 ) at the temperature level at which the intermediate fraction circulating in the heating circuit ( 20 ,  20 ′) located at the highest temperature level was partially evaporated,   during the temporary interruption of removal of the intermediate fraction circulating in the heating circuit located at the highest temperature level, the intermediate fraction of the heating circuit ( 22 ,  22 ′) located at the lowest temperature level is partially evaporated (E 1 ) at the temperature level at which the intermediate fraction circulating in the heating circuit ( 20 ,  20 ′) located at the medium temperature level was partially evaporated, and   during the temporary interruption of removal of the intermediate fraction circulating in the heating circuit located at the highest temperature level, a partial stream ( 9 ′) of a bottom fraction ( 9 ) obtained from the rectification fractionation (T) is partially evaporated (E 3 ) against an external medium and as a bottom heating to the rectification fractionation (T).   
     
     
         9 . The method according to  claim 1 , whereby
 At least three heating circuits—via which intermediate fractions are drawn off from the rectification fractionation, partially evaporated and fed again to the rectification fractionation—are assigned to the rectification fractionation, and   At least the intermediate fractions circulating in the two heating circuits located at the highest temperature levels are partially evaporated against the hydrocarbon-rich fraction that is to be partially condensed,   removal of the intermediate fraction circulating in the heating circuit ( 20 ,  20 ′) located at the highest temperature level is at least temporarily interrupted,   during the temporary interruption of removal of the intermediate fraction circulating in the heating circuit located at the highest temperature level, a partial stream of a bottom fraction obtained from the rectification fractionation is partially evaporated against an external medium and is fed as a bottom heating to the rectification fractionation, and   during the temporary interruption of removal of the intermediate fraction circulating in the heating circuit located at the highest temperature level, the other two intermediate fractions, in each case at the temperature level at which the intermediate fraction circulating in the heating circuit located at the next-higher temperature level was partially evaporated, are partially evaporated.