Method and apparatus for treating a hydrocarbon stream

Abstract

The present invention relates to a method of treating a hydrocarbon stream, the method at least comprising the steps of: supplying a partly condensed feed stream ( 10 ). to a first gas/liquid separator ( 2 ) and into a gaseous stream ( 2 and a liquid stream ( 30 ); expanding the liquid stream ( 30 ) and the gaseous stream ( 20 ) and subsequently feeding them into a second gas/liquid separator ( 3 ) at a first and second feeding point ( 32 ) respectively, the second feeding point ( 32 ) being at a higher level than the first feeding point ( 31 ); feeding a liquefied natural gas stream ( 70,70 b ) into the second gas/liquid separator ( 3 ) at a third feeding point ( 33 ) being at a higher level than the second feeding point ( 32 ); removing from the top of the second gas/liquid separator ( 3 ) a C2+ lean gaseous stream ( 60 ) and from the bottom a liquid stream ( 80, 80 a ); wherein the liquefied ̂natural gas stream ( 70,70 b ) is obtained from a source ( 4 ) of liquefied natural gas from a separate plant.

1 . Method of treating a hydrocarbon stream in a plant, the method at least comprising the steps of:
 (a) supplying a partly condensed feed stream to a first gas/liquid separator;   (b) separating the feed stream in the first gas/liquid separator into a gaseous stream and a liquid stream;   (c) expanding the liquid stream obtained in step (b) and feeding it into a second gas/liquid separator at a first feeding point;   (d) expanding the gaseous stream obtained in step (b), thereby obtaining an at least partially condensed stream, and subsequently feeding it into the second gas/liquid separator at a second feeding point, the second feeding point being at a higher level than the first feeding point;   (e) feeding a liquefied natural gas stream into the second gas/liquid separator at a third feeding point, the third feeding point being at a higher level than the second feeding point;   (f) removing from the top of the second gas/liquid separator a C2+ lean gaseous stream; and   (g) removing from the bottom of the second gas/liquid separator a liquid stream;   wherein the liquefied natural gas stream as fed in step (e) is obtained from a source of liquefied natural gas from a separate plant.   
   
   
       2 . Method according to  claim 1 , wherein the liquefied natural gas stream has a temperature below −100° C. 
   
   
       3 . Method according to  claim 1 , wherein the gaseous stream obtained in step (f) is sent to a gas network. 
   
   
       4 . Method according to  claim 1 , wherein the gaseous stream obtained in step (f) is not liquefied. 
   
   
       5 . Method according to  claim 1 , wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream. 
   
   
       6 . Method according to  claim 1 , wherein the liquefied natural gas stream as fed in step (e) has been previously heat exchanged against the feed stream. 
   
   
       7 . Method according to  claim 1 , wherein the liquid stream removed from the bottom of the second gas/liquid separator is subjected to fractionation thereby obtaining two or more products including ethane. 
   
   
       8 . Method according to  claim 1 , wherein >75 mole % of the ethane present in the partially partly condensed feed stream is recovered in the liquid stream obtained in step (g). 
   
   
       9 . Method according to  claim 1 , wherein the pressure drop during expanding in step (d) is less than 15 bar. 
   
   
       10 . Method according to  claim 1 , wherein the pressure in the second gas/liquid separator is from 15 to 40 bar. 
   
   
       11 . Method according to  claim 1 , wherein the C2+ lean gaseous stream removed from the top of the second gas/liquid separator in step (f) is a gaseous stream comprising < (less than) 10 mole % hydrocarbons having 2 or more carbon atoms. 
   
   
       12 . Method according to  claim 1 , wherein the source of liquefied natural gas from a separate plant is a liquefied natural gas storage tank at a liquefied natural gas import terminal. 
   
   
       13 . Apparatus for treating a hydrocarbon stream in a plant, the apparatus at least comprising:
 a first gas/liquid separator having an inlet for a partly condensed feed stream, a first outlet for a gaseous stream and a second outlet for a liquid stream;   a second gas/liquid separator having at least a first outlet for a gaseous stream and a second outlet for a liquid stream and first, second and third feeding points, the third feeding point being at a higher level in the gas/liquid separator than the second feeding point, said second feeding point being at a higher level in the gas/liquid separator than the first feeding point;   a first expander for expanding the gaseous stream obtained from the first outlet of the first gas/liquid separator, the first expander having an outlet which is connected to the second feeding point of the second gas/liquid separator; and   a second expander for expanding the liquid stream obtained from the second outlet of the first gas/liquid separator, the second expander having an outlet which is connected to the first feeding point of the second gas/liquid separator;   wherein the third feeding point is connected to a source of liquefied natural gas from a separate plant.   
   
   
       14 . Apparatus according to  claim 13  wherein the source of liquefied natural gas from a separate plant is a liquefied natural gas storage tank at a liquefied natural gas import terminal. 
   
   
       15 . Method according to  claim 2 , wherein the gaseous stream obtained in step (f) is sent to a gas network. 
   
   
       16 . Method according to  claim 2 , wherein the gaseous stream obtained in step (f) is not liquefied. 
   
   
       17 . Method according to  claim 3 , wherein the gaseous stream obtained in step (f) is not liquefied. 
   
   
       18 . Method according to  claim 2 , wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream. 
   
   
       19 . Method according to  claim 3 , wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream. 
   
   
       20 . Method according to  claim 4 , wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream.