Treating Liquefied Natural Gas

Abstract

Method of treating liquefied natural gas ( 1 ) to obtain a liquid stream ( 21 ) having a reduced content of components having low boiling points comprising expanding ( 3 ) the liquefied gas to expand to obtain expanded two-phase fluid; introducing the two-phase fluid into a column ( 10 ) below a gas-liquid contacting section ( 14 ); withdrawing from the bottom ( 16 ) a liquid-stream ( 17 ) having a reduced content of components having low boiling points; withdrawing from the top ( 23 ) of the column ( 10 ) a gaseous stream ( 25 ) enriched in components having low boiling points; heating the gaseous stream in a heat exchanger ( 27 ); compressing ( 30 ) the stream to fuel gas pressure to obtain fuel gas ( 33 ); separating a recycle stream ( 34 a ) from the fuel gas; at least partly condensing ( 27 ) the recycle stream to obtain a reflux stream ( 34 b ); and introducing the reflux stream ( 34 b ) into the column ( 10 ) above the contacting section ( 14 ).

1 . A method of treating liquefied natural gas supplied at liquefaction pressure containing components having low boiling points to obtain a liquid product stream having a reduced content of components having low boiling points, which method comprises the steps of: 
 (a) allowing the liquefied gas to expand to separation pressure to obtain an expanded two-phase fluid;    (b) introducing the expanded two-phase fluid into a column, the column comprising a single gas-liquid contacting section, wherein the expanded two-phase fluid is introduced below the single gas-liquid contacting section arranged in the column;    (c) collecting in the bottom of the column liquid from the two-phase fluid and withdrawing from the bottom of the column a liquid stream having a reduced content of components having low boiling points to obtain the liquid product stream;    (d) allowing vapor from the two-phase fluid to flow through the single contacting section;    (e) withdrawing from the top of the column a gaseous stream that is enriched in components having low boiling points;    (f) heating the gaseous stream obtained in step (c) in a heat exchanger to obtain a heated gaseous stream;    (g) compressing the heated gaseous stream obtained in step (f) to fuel gas pressure to obtain fuel gas;    (h) separating a recycle stream from the fuel gas obtained in step (g);    (i) at least partly condensing the recycle stream obtained in step (h) to obtain a reflux stream; and    (j) introducing the reflux stream obtained in step (i) at separation pressure into the column above the single contacting section.    
     
     
         2 . The method according to  claim 1 , wherein step (c) comprises collecting in the bottom of the column liquid from the two-phase fluid and withdrawing from the bottom of the column a liquid stream having a reduced content of components having low boiling points; introducing the liquid stream having a reduced content of components having low boiling points into a flash vessel at a low pressure; removing a second gaseous stream from the top of the flash vessel; and removing from the bottom of the flash vessel a liquid stream to obtain the liquid product stream.  
     
     
         3 . The method according to  claim 2 , further comprising heating the second gaseous stream in the heat exchanger; compressing the second gaseous stream to fuel gas pressure; and adding the second gaseous stream to the recycle stream.  
     
     
         4 . The method according to  claim 1 , wherein at least partly condensing the recycle stream in step (i) comprises indirectly heat exchanging the recycle stream with the gaseous stream(s) in the heat exchanger.  
     
     
         5 . The method according to  claim 1 , wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.  
     
     
         6 . The method according to  claim 1 , wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.  
     
     
         7 . The method according to  claim 1 , wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.  
     
     
         8 . The method according to  claim 2 , wherein at least partly condensing the recycle stream in step (i) comprises indirectly heat exchanging the recycle stream with the gaseous stream(s) in the heat exchanger.  
     
     
         9 . The method according to  claim 3 , wherein at least partly condensing the recycle stream in step (i) comprises indirectly heat exchanging the recycle stream with the gaseous stream(s) in the heat exchanger.  
     
     
         10 . The method according to  claim 2 , wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.  
     
     
         11 . The method according to  claim 3 , wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.  
     
     
         12 . The method according to  claim 4 , wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.  
     
     
         13 . The method according to  claim 2 , wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.  
     
     
         14 . The method according to  claim 3 , wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.  
     
     
         15 . The method according to  claim 4 , wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.  
     
     
         16 . The method according to  claim 5 , wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.  
     
     
         17 . The method according to  claim 2 , wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.  
     
     
         18 . The method according to  claim 3 , wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.  
     
     
         19 . The method according to  claim 4 , wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.  
     
     
         20 . The method according to  claim 5 , wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.