Method and apparatus for cooling and separating a hydrocarbon stream

Abstract

A method and apparatus for cooling and separating a hydrocarbon stream such as natural gas. The method comprises providing a hydrocarbon stream, cooling the hydrocarbon stream ( 10 ) to provide a partially liquefied hydrocarbon stream, passing at least a fraction of the partially liquefied hydrocarbon stream into a distillation column through a first inlet, providing a lower feed stream, providing a refrigerant circuit comprising at least a refrigerant stream, heating the lower feed stream against the refrigerant stream to provide a heated lower feed stream and a cooled refrigerant stream, passing the heated lower feed stream into the distillation column through a second inlet lower than the first inlet, and separating the partially liquefied hydrocarbon stream in the distillation column to provide at least a first overhead gaseous stream and a first bottom liquid stream.

1 . A method of cooling and separating a hydrocarbon stream such as natural gas comprising at least the steps of:
 (a) providing a hydrocarbon stream;   (b) cooling the hydrocarbon stream to provide a partially liquefied hydrocarbon stream, wherein at least a fraction of the cooling is provided by partially or fully evaporating a cooled refrigerant stream;   (c) passing at least a fraction of the partially liquefied hydrocarbon stream into a distillation column through a first inlet;   (d) providing a lower feed stream;   (e) providing a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream;   (f) heating the lower feed stream against the compressed fully liquefied refrigerant stream to provide a heated lower feed stream and the cooled refrigerant stream;   (g) passing the heated lower feed stream into the distillation column through a second inlet that is located gravitationally lower than the first inlet; and   (h) separating the partially liquefied hydrocarbon stream in the distillation column to provide at least a first overhead gaseous stream and a first bottom liquid stream.   
     
     
         2 . The method according to  claim 1  wherein at least a fraction of the first liquid bottom stream provides at least a fraction of the lower feed stream. 
     
     
         3 . The method according to  claim 1  wherein a fraction of the hydrocarbon stream provides at least a fraction of the lower feed stream. 
     
     
         4 . The method according to  claim 3  wherein the hydrocarbon stream is divided into at least first and second part-streams, and wherein the first part-stream is cooled to provide the partially liquefied hydrocarbon stream, and the second part-stream provides at least a fraction of the lower feed stream. 
     
     
         5 . The method according to  claim 1  wherein a fraction of the partially liquefied hydrocarbon stream provides at least a fraction of the lower feed stream. 
     
     
         6 . The method according to  claim 5  wherein the partially liquefied hydrocarbon stream is passed into a first gas/liquid separator to provide a feed stream overhead gaseous stream and a feed stream liquid bottom stream, and wherein at least a fraction of the feed stream overhead gaseous stream is provided to the first inlet of the distillation column, and at least a fraction of the feed stream liquid bottom stream is provided as at least a fraction of the lower feed stream. 
     
     
         7 . The method according to  claim 1  wherein at least a fraction of the first overhead gaseous stream is at least partly condensed and passed into a final gas/liquid separator to provide at least a final bottom stream, and wherein at least a fraction of the final bottom stream is a lower feed stream. 
     
     
         8 . The method according to  claim 1  wherein at least a fraction of the cooling in step (b) is provided by the refrigerant circuit. 
     
     
         9 . The method according to  claim 1  wherein the refrigerant circuit comprises one or more refrigerant compressors, and wherein the compressed fully liquefied refrigerant stream is provided from the refrigerant circuit downstream of a refrigerant compressor(s). 
     
     
         10 . The method according to  claim 1  wherein a refrigerant circuit comprises one or more refrigerant accumulators, and wherein the compressed fully liquefied refrigerant stream is provided from a refrigerant accumulator. 
     
     
         11 . The method according to  claim 1  wherein the compressed fully liquefied refrigerant stream is propane. 
     
     
         12 . The method according to  claim 1  wherein at least a fraction of the first overhead gaseous stream is subsequently liquefied to provide a liquefied hydrocarbon stream such as LNG. 
     
     
         13 . An apparatus for cooling and separating a hydrocarbon stream such as natural gas, comprising at least:
 a first cooling stage to cool a hydrocarbon stream and provide a partially liquefied hydrocarbon stream;   a distillation column to receive and separate at least a fraction of the partially liquefied hydrocarbon stream provided through a first inlet;   a refrigerant circuit comprising at least a compressed fully liquefied refrigerant stream;   a first heat exchanger to heat a lower feed stream against the compressed fully liquefied refrigerant stream to provide a cooled refrigerant stream and a heated lower feed stream to be passed into the distillation column through a second inlet that is located gravitationally lower than the first inlet; and   a heat exchange system in the first cooling stage arranged in the refrigerant circuit downstream of the first heat exchanger to cool the hydrocarbon stream against at least a fraction of the cooled refrigerant stream, thereby partly or fully evaporating the at least the fraction of the cooled refrigerant stream.   
     
     
         14 . A liquefaction plant comprising apparatus as claimed in  claim 13 .