Method and Apparatus for Liquefying a Natural Gas Stream

Abstract

The present invention relates to a method of liquefying a natural gas stream, wherein the natural gas stream ( 10 ) is provided at a pressure of 10-80 bar, supplied to a gas/liquid separator ( 31 ), and separated into a vaporous stream ( 40 ) and a liquid stream ( 30 ). The vaporous stream ( 40 ) is compressed to a pressure of at least 70, 84 bar heat exchanged against the vaporous stream ( 40 ), and liquefied to obtain a liquefied natural gas stream ( 100 ).

1 . A method of liquefying a natural gas stream, the method comprising the steps of:
 (a) providing a feed stream containing natural gas at a pressure of 10-80 bar;   (b) supplying the feed stream provided in step (a) to a gas/liquid separator;   (c) separating the feed stream in the gas/liquid separator into a vaporous stream and a liquid stream, the vaporous stream being enriched in methane relative to the feed stream, and the liquid stream being reduced in methane relative to the feed stream;   (d) compressing the vaporous stream obtained in step (c) thereby obtaining a compressed stream having a pressure of at least 70 bar;   (e) liquefying the compressed stream obtained in step (d) thereby obtaining a liquefied natural gas stream;   wherein the compressed stream obtained in step (d), before it is liquefied in step (e), is heat exchanged against the vaporous stream obtained in step (c),   and wherein the pressure of the feed stream as provided in step (a) is not increased until the compressing in step (d).   
   
   
       2 . The method according to  claim 1 , wherein in step (d) the pressure is increased to at least 86 bar. 
   
   
       3 . The method according to  claim 1 , wherein the vapour stream obtained in step (c) has a C 5   +  content of below 0.5 mol %. 
   
   
       4 . The method according to  claim 1 , wherein the compressed stream obtained in step (d) is cooled, before it is heat exchanged against the vaporous stream obtained in step (c). 
   
   
       5 . The method according to  claim 1 , wherein the feed stream provided in step (a), before supplying to the gas/liquid separator in step (b), is expanded. 
   
   
       6 . The method according to  claim 5 , wherein an expander for expanding the feed stream is functionally coupled to a compressor for compressing the vaporous stream in step (d). 
   
   
       7 . An apparatus for liquefying a natural gas stream, the apparatus at least comprising:
 means for providing a feed stream containing natural gas at a pressure of 10-80 bar;   a gas/liquid separator for separating the feed stream into a vaporous stream and a liquid stream, the vaporous stream being enriched in methane relative to the feed stream, and the liquid stream being reduced in methane relative to the feed stream;   a compressor for increasing the pressure of the vaporous stream obtained in the gas/liquid separator to a pressure of at least 70 bar, thereby obtaining a compressed stream;   a heat exchanger for heat exchanging the compressed stream against the vaporous stream obtained from the gas/liquid separator; and   a liquefaction unit for liquefying an effluent from the heat exchanger having a pressure of at least 70 bar, the liquefaction unit comprising at least one cryogenic heat exchanger.   
   
   
       8 . The apparatus according to  claim 7 , wherein the apparatus further comprises an expander for expanding the feed stream before it is supplied to the gas/liquid separator. 
   
   
       9 . The apparatus according to  claim 8 , wherein the compressor and expander are functionally coupled. 
   
   
       10 . The apparatus according to  claim 7 , wherein no compressor is present between the means for providing the feed stream at a pressure of 10-80 bar and the compressor for increasing the pressure of the vaporous stream. 
   
   
       11 . The method according to  claim 1 , wherein in step (d) the pressure is increased to at least 84 bar. 
   
   
       12 . The method according to  claim 1 , wherein in step (d) the pressure is increased to at least 90 bar. 
   
   
       13 . A method of liquefying a natural gas stream, the method comprising the steps of:
 (a) providing a feed stream containing natural gas at a pressure of 10-50 bar;   (b) supplying the feed stream provided in step (a) to a gas/liquid separator;   (c) separating the feed stream in the gas/liquid separator into a vaporous stream and a liquid stream, the vaporous stream being enriched in methane relative to the feed stream, and the liquid stream being reduced in methane relative to the feed stream;   (d) compressing the vaporous stream obtained in step (c) thereby obtaining a compressed stream having a pressure of at least 70 bar;   (e) liquefying the compressed stream obtained in step (d) thereby obtaining a liquefied natural gas stream;   wherein the compressed stream obtained in step (d), before it is liquefied in step (e), is heat exchanged against the vaporous stream obtained in step (c),   and wherein the pressure of the feed stream as provided in step (a) is not increased until the compressing in step (d).   
   
   
       14 . The method according to  claim 13 , wherein in step (d) the pressure is increased to at least 84 bar. 
   
   
       15 . The method according to  claim 13 , wherein in step (d) the pressure is increased to at least 86 bar. 
   
   
       16 . The method according to  claim 13 , where in step (d) the pressure is increased to at least 90 bar. 
   
   
       17 . The method according to  claim 2 , wherein the vapour stream obtained in step (c) has a C 5   +  content of below 0.5 mol %. 
   
   
       18 . The method according to  claim 11 , wherein the vapour stream obtained in step (c) has a C 5   +  content of below 0.5 mol %. 
   
   
       19 . The method according to  claim 12 , wherein the vapour stream obtained in step (c) has a C 5   +  content of below 0.5 mol %. 
   
   
       20 . The method according to  claim 1 , wherein the vapour stream obtained in step (c) has a C 5   +  content of below 0.1 mol %.