Method for liquefying a hydrocarbon stream

Abstract

A hydrocarbon stream is liquefied in a method wherein a feed stream is provided, from which feed stream a first stream and a second stream are produced. The first stream is liquefied in a main liquefaction system to provide a first liquefied stream, while the second stream is cooled separately to provide a cooled second stream. The first liquefied stream is combined with the cooled second stream to produce a combined stream, which is separated in a gas/liquid separator into a liquefied hydrocarbon product stream and a gaseous stream. The gaseous stream is warmed to a temperature of above −40° C. by heat exchanging against any other stream used in the method, wherein the warming of the gaseous stream employs at least heat exchanging against the second stream to provide at least part of the cooling of the second stream.

1 . A method of liquefying a hydrocarbon stream, the method at least comprising the steps of:
 (a) providing a feed stream;   (b) producing, from the feed stream, a first stream and a second stream;   (c) liquefying the first stream in a main liquefaction system to provide a first liquefied stream;   (d) cooling the second stream of step (b) to provide a cooled second stream;   (e) combining the first liquefied stream of step (c) with the cooled second stream of step (d) to produce a combined stream;   (f) separating the combined stream in a gas/liquid separator into a liquefied hydrocarbon product stream and a gaseous stream;   (g) warming the gaseous stream of step (f) to a temperature above −40° C. by heat exchanging against any other stream used in the method, wherein the warming of the gaseous stream comprises at least heat exchanging against the second stream of step (b) to provide at least part of the cooling of step (d).   
     
     
         2 . The method as claimed in  claim 1 , wherein said producing of the first stream and the second stream comprises passing the feed stream through a first cooling stage. 
     
     
         3 . The method as claimed in  claim 2 , wherein the passing of the feed stream through the first cooling stage yields a pre-cooled stream, whereby the first stream and second stream are produced from the pre-cooled stream. 
     
     
         4 . The method as claimed in  claim 3 , wherein said producing of the first stream and the second stream comprises dividing the pre-cooled stream into at least the first stream and the second stream. 
     
     
         5 . The method as claimed in  claim 1 , wherein said producing of the first stream and the second stream comprises dividing the feed stream into at least the first stream and the second stream. 
     
     
         6 . The method as claimed in  claim 1 , said warming in step (g) is achieved by passing the gaseous stream through one or more heat exchangers. 
     
     
         7 . The method as claimed in  claim 6 , wherein the heat exchanging of the gaseous stream against the second stream of step (b) comprises passing the second stream through at least one of the one or more heat exchangers. 
     
     
         8 . The method as claimed in  claim 6 , wherein the temperature of the gaseous stream immediately after having passed through the one or more heat exchangers is above 0° C. 
     
     
         9 . The method as claimed in  claim 1 , further comprising the step of:
 (h) using the warmed gaseous stream as a fuel gas stream.   
     
     
         10 . The method as claimed in  claim 1 , wherein after step (e) and before step (f) the combined stream is passed into the gas/liquid separator. 
     
     
         11 . The method as claimed in  claim 1 , wherein the pressure of the first liquefied stream is reduced prior to step (e). 
     
     
         12 . The method as claimed in  claim 1 , wherein the pressure of the combined stream of step (e) is reduced before said separating in step (f). 
     
     
         13 . The method as claimed in  claim 1 , wherein the first stream, in step (b), is produced in the form of two or more part-first streams. 
     
     
         14 . The method as claimed in  claim 13 , wherein the part-first streams are separately liquefied to produce separate liquefied part-streams, and wherein the separate liquefied part-streams are combined prior to, simultaneously with, or after step (e). 
     
     
         15 . The method as claimed in  claim 14 , wherein the pressure of each liquefied part-stream is reduced prior to step (e). 
     
     
         16 . The method as claimed in  claim 1 , wherein the first stream comprises at least a majority of the feed stream. 
     
     
         17 . The method as claimed in  claim 1 , wherein the second stream comprises preferably between 1-5 mass % of the feed stream. 
     
     
         18 . The method as claimed in  claim 1 , wherein the second stream is cooled to a temperature sufficiently low to provide a combined liquefied stream upon said combining in step (e) with the first liquefied stream. 
     
     
         19 . The method as claimed in  claim 1 , wherein the second stream is cooled in step (d) to a temperature of less than −100° C. 
     
     
         20 . The method as claimed in  claim 1 , wherein the second stream is cooled in step (d) to about the same temperature as that of the first liquefied stream. 
     
     
         21 . The method as claimed in  claim 1 , wherein the temperature above −40° C. in step (g) is a temperature above −30° C. 
     
     
         22 . The method as claimed in  claim 1 , wherein the temperature above −40° C. in step (g) is a temperature above 0° C.