Method and Apparatus for Deriching a Stream of Liquefied Natural Gas

Abstract

The present invention relates to a method of deriching a stream of liquefied natural gas by extracting a natural gas liquid comprising inter alia the steps of: heating the stream of liquefied natural gas ( 1 ) in a first heat exchanger arrangement ( 5 ); splitting it into at least a first portion ( 17 ) and a second portion ( 19 ); passing the first portion ( 17 ) to a distillation column ( 21 ) and passing the second portion ( 19 ) to a second heat exchanger arrangement ( 26 ) and then supplying it ( 20 ) to the distillation column ( 21 ) from which a natural gas liquid stream ( 35 ) and an overhead vapour stream ( 40 ) are withdrawn; —passing the overhead vapour stream ( 40 ) to the second heat exchanger arrangement ( 26 ) to form an intermediate deriched condensate stream ( 49 ) of which at least a portion is thereafter passed to the distillation column.

1 . A method of deriching a stream of liquefied natural gas by extracting a natural gas liquid from the stream of liquefied natural gas, the method at least comprising the steps of:
 heating a feed stream containing the stream of liquefied natural gas in a first heat exchanger arrangement to form an intermediate feed stream;   splitting the intermediate feed stream into at least a first portion and a second portion;   passing the first portion to a distillation column and feeding it via a first feeding point;   passing the second portion to a second heat exchanger arrangement wherein it is further heated, and then supplying it to the distillation column via a second feeding point;   withdrawing a liquid stream containing the natural gas liquid from a lower portion of the distillation column;   withdrawing an overhead vapour stream from an upper portion of the distillation column;   passing the overhead vapour stream to the second heat exchanger arrangement where it is cooled against the second portion of the intermediate feed stream to form an intermediate deriched stream of which at least a portion is thereafter passed to the first heat exchanger arrangement and further cooled against the feed stream to form a product stream of deriched natural gas;   wherein during cooling of the overhead vapour stream in the second heat exchanger arrangement it is partially condensed to form an intermediate condensate, of which at least a portion is passed to the distillation column via a third feeding point, and an intermediate vapour which is passed to the first heat exchanger arrangement.   
   
   
       2 . The method of  claim 1 , wherein said heating of the feed stream in the first heat exchanger arrangement comprises partly vapourizing the feed stream whereby the intermediate feed stream comprises a mixture of liquid intermediate feed fraction and vaporous intermediate feed fraction; and wherein at least the liquid intermediate feed fraction is split into at least the first and second portions. 
   
   
       3 . The method of  claim 2 , wherein the mixture is passed to a feed separating vessel from which the liquid intermediate feed fraction and the vaporous intermediate feed fraction are respectively drawn before splitting it into the at least first and second portions. 
   
   
       4 . The method of  claim 1 , wherein the second feeding point is located gravitationally lower than the first feeding point. 
   
   
       5 . The method of  claim 1 , wherein the third feeding point is gravitationally lower than the first feeding point. 
   
   
       6 . The method of  claim 1 , wherein the third feeding point is gravitationally higher than the second feeding point. 
   
   
       7 . The method of  claim 1 , wherein the overhead vapour stream is compressed before passing it to the second heat exchanger arrangement. 
   
   
       8 . The method of  claim 1 , wherein the product stream of de-riched natural gas is subsequently re-gasified. 
   
   
       9 . A deriched liquefied natural gas stream obtained by the method of  claim 1 . 
   
   
       10 . An apparatus for deriching a stream of liquefied natural gas by extracting a natural gas liquid from the stream of liquefied natural gas, the apparatus at least comprising:
 a first heat exchanger arrangement arranged to receive a feed stream containing the stream of liquefied natural gas and provided with an outlet to discharge an intermediate feed stream;   a second heat exchanger arrangement in fluid communication with the outlet of the first heat exchanger arrangement;   a distillation column having at least first, second and third feeding points, a lower portion provided with a discharge opening for withdrawing a liquid stream containing the natural gas liquid, and an upper portion provided with an overhead vapour outlet in fluid communication with the first heat exchanger arrangement via at least the second heat exchanger arrangement;   a distributor connected to the outlet of the first heat exchanger arrangement, the distributor having a first outlet being connected to the first feeding point of the distillation column, and a second outlet being connected to the second feeding point of the distillation column via the second heat exchanger arrangement; and   a first gas/liquid separator downstream of the overhead vapour outlet and between the second heat exchanger arrangement and first heat exchanger arrangement, the first separator having an outlet connected to the third feeding point of the distillation column and an outlet in fluid communication with the first heat exchanger arrangement.   
   
   
       11 . The apparatus of  claim 10 , further comprising a second gas/liquid separator having an inlet connected to the outlet of the first heat exchanger and a bottom outlet connected to the distributor. 
   
   
       12 . The apparatus of  claim 10 , further comprising a compressor between the outlet of the distillation column and the second heat exchanger arrangement. 
   
   
       13 . The method of  claim 2 , wherein the second feeding point is located gravitationally lower than the first feeding point. 
   
   
       14 . The method of  claim 3 , wherein the second feeding point is located gravitationally lower than the first feeding point. 
   
   
       15 . The method of  claim 2 , wherein the third feeding point is gravitationally lower than the first feeding point. 
   
   
       16 . The method of  claim 3 , wherein the third feeding point is gravitationally lower than the first feeding point. 
   
   
       17 . The method of  claim 4 , wherein the third feeding point is gravitationally lower than the first feeding point. 
   
   
       18 . The method of  claim 2 , wherein the third feeding point is gravitationally higher than the second feeding point. 
   
   
       19 . The method of  claim 3 , wherein the third feeding point is gravitationally higher than the second feeding point. 
   
   
       20 . The method of  claim 4 , wherein the third feeding point is gravitationally higher than the second feeding point.