Method and system for recovery of methane from hydrocarbon streams

Abstract

The invention relates to a method for recovery of methane from hydrocarbon streams comprising the following steps: a. Introducing a feed fluid stream (F), which comprises methane fluid, at least one hydrocarbon free fluid, wherein in particular said at least one hydrocarbon free fluid is nitrogen, and at least one hydrocarbon fluid, into a demethanizer system ( 1 ); b. Separating said feed fluid stream (F) in the demethanizer system ( 1 ) into a carbon rich fraction (C), comprising hydrocarbons with a carbon content of C2 and higher, and a separation stream (S), comprising methane fluid and at least one hydrocarbon free fluid; c. Introducing said separation stream (S) into a hydrocarbon-free fluid separation system ( 2 ), in particular in a cryogenic hydrocarbon-free fluid separation system ( 2 ′), more particularly into a cryogenic nitrogen rejection system ( 2 ″); wherein said separation stream (S) is compressed by a compressor system ( 6 ) before said separation stream (S) is introduced in said hydrocarbon-free fluid separation system ( 2 ), wherein said separation stream is compressed to a pressure of 12 bar to 80 bar; d. Separating said separation stream (S) in said free fluid separation system ( 2 ) into a methane stream (M) and a hydrocarbon-free fluid stream (HF) and a respective system for recovery of methane from hydrocarbon streams.

1 . A method for recovery of methane from hydrocarbon streams comprising the following steps:
 a. Introducing a feed fluid stream (F), which comprises methane fluid, at least one hydrocarbon free fluid, wherein in particular said at least one hydrocarbon free fluid is nitrogen, and at least one hydrocarbon fluid, into a demethanizer system ( 1 );   b. Separating said feed fluid stream (F) in the demethanizer system ( 1 ) into a carbon rich fraction (C), comprising hydrocarbons with a carbon content of C 2  and higher, and a separation stream (S,) comprising methane fluid and at least one hydrocarbon free fluid;   c. Introducing said separation stream (S) into a hydrocarbon-free fluid separation system ( 2 ), in particular in a cryogenic hydrocarbon-free fluid separation system ( 2 ′), more particularly into a cryogenic nitrogen rejection system ( 2 ″); wherein said separation stream (S) is compressed by a compressor system ( 6 ) before said separation stream (S) is introduced in said hydrocarbon-free fluid separation system ( 2 ), wherein said separation stream is compressed to a pressure of 25 bar to 80 bar;   d. Separating said separation stream (S) in said free fluid separation system ( 2 ) into a methane stream (M) and a hydrocarbon-free fluid stream (HF).   
     
     
         2 . The method according to  claim 1 , wherein said feed fluid stream (F) derives from a synthesis system ( 3 ), which uses methane as a reactant, in particular said synthesis system ( 3 ) is a system for oxidative coupling of methane. 
     
     
         3 . The method according to any one of the  claims 1  to  2 , wherein said methane stream (M) is recycled and reused as a reactant, wherein in particular said methane stream (M) is transferred to said synthesis system ( 3 ). 
     
     
         4 . The method according to any of the previous claims, wherein said separation stream (S) is compressed by said compressor system ( 6 ) to a pressure of 25 bar to 75 bar, preferably to a pressure of 25 bar to 60 bar, more preferably to a pressure of 25 bar to 40 bar, particularly to a pressure of 30 bar, before said separation stream (S) is introduced in said hydrocarbon-free fluid separation system ( 2 ). 
     
     
         5 . The method according to  claim 1 , wherein said carbon rich fraction (C) from the demethanizer system ( 1 ) is transferred to a C2-splitter ( 7 ), for separation and isolation of hydrocarbon compounds with different carbon contents of said carbon rich fraction (C) from each other. 
     
     
         6 . The method according to any one of the  claims 1  to  5 , wherein at least parts of the feed fluid stream (F) are liquidized in a cooling system before the introduction into a demethanizer unit ( 10 ) of the demethanizer system ( 1 ). 
     
     
         7 . The method according to any one of the  claims 1  to  6 , wherein said feed fluid stream (F) is separated in said cooling system into a liquid feed fluid stream and a gaseous feed fluid stream, wherein said liquid feed fluid stream is transferred to said demethanizer unit ( 10 ) and said gaseous feed fluid stream is transferred to an expander-booster system, in which said gaseous feed fluid stream is expanded to a lower pressure before introducing said gaseous feed fluid stream into said demethanizer unit ( 10 ). 
     
     
         8 . The method according to any one of the  claims 1  to  7 , wherein said demethanizer system ( 1 ) system is operated at a pressure of 6 to 40 bar. 
     
     
         9 . The method according to any one of the  claims 1  to  7 , wherein said demethanizer unit ( 10 ) of said demethanizer system ( 1 ) is operated at a pressure of 9 to 25 bar, in particular at a pressure of approximately 13 bar. 
     
     
         10 . The method according to  claim 1 , wherein said separation stream (S) is introduced in at least one high pressure column ( 21 ), which is arranged in said hydrocarbon free fluid separation system ( 2 ), and in which said separation stream (S) is separated in a methane rich bottom liquid and an essentially pure hydrocarbon-free overhead, wherein said methane rich bottom liquid is transferred into at least one low pressure column ( 22 ), which is arranged in said hydrocarbon free fluid separation system ( 2 ), in which said methane rich bottom liquid is separated into a methane rich liquid and hydrocarbon-free gas. 
     
     
         11 . The method according to  claim 10 , wherein said hydrocarbon free overhead from the high pressure column ( 21 ) is at least partially condensed on a heat exchanger ( 5 ) and said a methane rich liquid from the low pressure column ( 22 ) is at least partially vaporized on said heat exchanger ( 5 ), providing a liquid fraction and a methane gas fraction, wherein said heat exchanger ( 5 ) is situated between said high pressure column ( 21 ) and said low pressure column ( 22 ). 
     
     
         12 . The method according to any one of the  claims 10  to  11 , wherein said high pressure column ( 21 ) is operated at a pressure of 6 to 40 bar, in particular at a pressure of approximately 20 bar, and at a temperature of −160 to −90° C., in particular at a temperature of approximately −140° C., and wherein said low pressure column ( 22 ) is operated at a pressure of 1 to 5 bar, in particular at a pressure of approximately 2 bar, and at a temperature of −220 to −180° C., in particular at a temperature of approximately −190° C. 
     
     
         13 . A system for recovery of methane from hydrocarbon streams comprising
 a. a demethanizer system ( 1 ), which is designated to separate a feed fluid stream (F), which comprises methane fluid, at least one hydrocarbon-free fluid, wherein in particular said at least one hydrocarbon-free fluid is nitrogen, and at least one hydrocarbon fluid, into
 i. a carbon rich fraction (C), which comprises hydrocarbons with a carbon content of C 2  and higher, and 
 ii. a separation stream (S), which comprises methane fluid and at least one hydrocarbon free fluid, and 
   b. a hydrocarbon-free fluid separation system ( 2 ), in particular a cryogenic hydrocarbon free fluid separation system ( 2 ′), more particularly a cryogenic nitrogen rejection system ( 2 ″), which is designated to separate said separation stream (S) into a methane stream (M) and a hydrocarbon free stream (HF), and   c. a compressor system ( 6 ) that is configured to compress said separation stream (S) to a pressure of 25 bar to 80 bar before said separation stream (S) is introduced in said hydrocarbon-free fluid separation system ( 2 ).   
     
     
         14 . The system according to  claim 13 , wherein the compressor system ( 6 ) is configured to compress said separation stream (S) to a pressure of 25 bar to 75 bar, preferably to a pressure of 25 bar to 60 bar, more preferably to a pressure of 25 bar to 40 bar, particularly to a pressure of 30 bar, before said separation stream (S) is introduced in said hydrocarbon-free fluid separation system ( 2 ). 
     
     
         15 . The system according to  claim 13  or  14 , wherein said system comprises a synthesis system ( 3 ), which uses methane as a reaction educt and provides said feed fluid stream (F), wherein in particular said synthesis system ( 3 ) is a system for oxidative coupling of methane.