Method for liquefying a hydrocarbon-rich flow while simultaneously obtaining a c3/c4-rich fraction

Abstract

A process for liquefying a flow of natural gas with simultaneous recovery of a C 3 /C 4 -rich fraction is described, whereby the liquefaction of the flow of natural gas is carried out in heat exchange for at least one refrigerant and/or mixed refrigerant flow, and the flow of natural gas that is to be liquefied, after precooling, is subjected to a rectifying column, in which higher hydrocarbons are separated from the flow of natural gas, and then is subjected to further cooling and liquefaction, whereby a C 2+ -rich fraction that is recovered in the subsequent cooling of the flow of natural gas is fed to the rectifying column as a reflux liquid. According to the invention, a C 4 /C 5 -rich fraction ( 20, 35 ) is fed directly and/or indirectly to rectifying column (T 1 ) as an additional reflux liquid, whereby the feed point of the C 4 /C 5 -rich [fraction ( 20, 35 ) is located at the top of rectifying column (T 1 ) or is identical to the feed point of the C 2+ -rich fraction ( 5 ).]

1 . Process for liquefying a hydrocarbon-rich flow, in particular a flow of natural gas, with simultaneous recovery of a C 3 /C 4 -rich fraction, whereby the liquefaction of the hydrocarbon-rich flow is carried out in heat exchange for at least one refrigerant and/or mixed refrigerant flow, and the hydrocarbon-rich flow that is to be liquefied, after precooling, is subjected to a rectifying column, in which higher hydrocarbons are separated from the hydrocarbon-rich flow that is to be liquefied, and then is subjected to further cooling and liquefaction, whereby a C 2+ -rich fraction that is recovered in the subsequent cooling of the hydrocarbon-rich flow is fed to the rectifying column as a reflux liquid, characterized in that a C 4  /C 5 -rich fraction ( 20 ,  35 ) is fed to rectifying column (T 1 ) as an additional reflux liquid, whereby the feed point of the C 4 /C 5 -rich fraction ( 20 ,  35 ) is located above the feed point of C 2+ -rich fraction ( 5 ), and a mass transfer zone (M) is provided between the feed point of the C 4 /C 5  -rich fraction ( 20 ,  35 ) and the feed point of C 2+ -rich fraction ( 5 ).  
   
   
       2 . Process according to  claim 1 , in which the higher hydrocarbons that are recovered in the rectifying column are separated by rectification in several steps, whereby one of these steps comprises the feeding of higher hydrocarbons in a depropanizer (T 2 ), wherein the C 4 /C 5 -rich fraction ( 20 ,  35 ) that is fed to rectifying column (T 1 ) as an additional reflux liquid is recovered in a depropanizer side column (T 3 ), which is fed to a C 4+ -rich fraction ( 14 ) that is drawn off from depropanizer (T 2 ).  
   
   
       3 . Process according to  claim 1 , in which the higher hydrocarbons that are recovered in the rectifying column are separated by rectification in several steps, whereby one of these steps comprises the feeding of higher hydrocarbons in a debutanizer, wherein the C 4 /C 5 -rich fraction ( 20 ,  35 ) that is fed to rectifying column (T 1 ) as an additional reflux liquid is recovered in the debutanizer.  
   
   
       4 . Process according to  claim 1 , wherein the C 4 /C 5 -rich fraction ( 20 ,  35 ) that is fed to rectifying column (T 1 ) as an additional reflux liquid is recovered in a side column (T 4 ) of rectifying column (T 1 ) by a C 4+ -rich fraction ( 30 ) being fed to this side column (T 4 ) from rectifying column (T 1 ).  
   
   
       5 . Process according to one of the preceding  claims 1  to  4 , wherein the C 4 /C 5 -rich fraction ( 20 ,  35 ) that is fed to rectifying column (T 1 ) as an additional reflux liquid is cooled before the feeding thereof (E 5 , E 7 ).  
   
   
       6 . Process according to  claim 5 , wherein the C 4 /C 5 -rich fraction ( 20 ,  35 ) that is fed to rectifying column (T 1 ) as an additional reflux liquid is at least partially condensed in its cooling (E 5 , E 7 ).  
   
   
       7 . Process according to one of the preceding  claims 1  to  6 , wherein the benzene content of the C 4 /C 5 -rich fraction ( 20 ,  35 ) that is fed to rectifying column (T 1 ) as an additional reflux liquid is less than 500 ppm, preferably less than 300 ppm.