Separation of gases

Abstract

A method of separating a carbon-dioxide-rich liquid stream from a synthesis gas including carbon dioxide and hydrogen, includes carrying out a first cooling step to cool a synthesis gas feed stream using at least one heat exchanger such that a first two-phase mixture is formed. The first two-phase mixture is passed at a first pressure and a first temperature to a first separator and a first separation is carried out to separate the first mixture into a first CCVrich liquid stream and a H2-Hcli gas stream. The H2-rich gas stream is pressurised and a second cooling step is carried out to cool the H2-rich gas stream using at least one heat exchanger such that a second two-phase mixture is formed. The second mixture is passed at a second pressure and a second temperature to a second separator, the second pressure being higher than the first pressure and a second separation is carried out to separate the second mixture into a second CO2-rich liquid stream and a further H2-rich gas stream. Preferred examples further include the step of expanding at least one of the separated H2-rich vapour streams to recover mechanical work and/or to cool the H2-rich stream and subsequently using the expanded H2-rich stream as a coolant in the separation system.

1 - 14 . (canceled) 
     
     
         15 . A method of separating a carbon-dioxide-rich liquid stream from a synthesis gas including carbon dioxide and hydrogen, the method comprising the steps of:
 a) carrying out a first cooling step to cool a synthesis gas feed stream such that a first two-phase mixture is formed;   b) passing the first two-phase mixture at a first pressure and a first temperature to a first separator,   c) carrying out a first separation to separate the first mixture into a first CO 2 -rich liquid stream and a H 2 -rich gas stream;   d) pressurizing the H 2 -rich gas stream;   e) carrying out a second cooling step to cool the H 2 -rich gas stream such that a second two-phase mixture is formed,   f) passing the second mixture at a second pressure and a second temperature to a second separator, the second pressure being higher than the first pressure;   g) carrying out a second separation to separate the second mixture into a second CO 2 -rich liquid stream and a further H 2 -rich gas stream   wherein the method further includes the step of feeding a separated hydrogen-rich vapour stream to an expansion system including an expander, wherein the hydrogen rich stream is subjected to expansion such that an expanded hydrogen rich stream is withdrawn from the expander at reduced temperature and pressure, the method further including using the expanded hydrogen rich vapour stream as a coolant.   
     
     
         16 . A method according to  claim 15 , wherein the expanded hydrogen-rich vapour stream is used to cool one or more streams selected from a hydrogen-rich gas stream, a carbon dioxide stream and a synthesis gas stream. 
     
     
         17 . A method according to  claim 15 , wherein the expander effects isentropic expansion of the hydrogen rich vapour in the expander and generates motive power. 
     
     
         18 . A method according to  claim 15 , in which the first pressure is substantially the feed pressure of the synthesis gas. 
     
     
         19 . A method according to  claim 15 , wherein the first pressure is not less than 50 bar. 
     
     
         20 . A method according to  claim 19 , wherein the first pressure is less than 150 bar, preferably less than 100 bar, and/or wherein the second pressure is greater than 100 bar, preferably 150 bar or more. 
     
     
         21 . A method according to  claim 15 , wherein the first temperature is less than −50 degrees C., and/or wherein the second temperature is less than −50 degrees C., preferably −53 degrees C. or less. 
     
     
         22 . A method according to  claim 15 , wherein the second temperature is substantially the same as the first temperature. 
     
     
         23 . A method according to  claim 15 , further including the step of carrying out a third separation of liquid carbon dioxide at a third separation stage, a two-phase mixture at the third separation stage being at a third temperature and third pressure. 
     
     
         24 . A method according to  claim 15 , wherein at least one of the cooling steps is carried out using one or more internal refrigerant streams 
     
     
         25 . A method according to  claim 15 , in which a cooling step is carried out using at least one heat exchanger, preferably a multi-channel heat exchanger carrying one or more internal and/or external refrigerants or coolants. 
     
     
         26 . A method according to  claim 15 , further including the step of expanding the H 2 -rich gas using an expander, feeding the expanded H 2 -rich stream, to a heat exchanger system including at least one for exchanging heat between at least two streams of the process, and feeding the H 2 -rich stream from the heat exchanger system to a further expander. 
     
     
         27 . A method of separating a carbon-dioxide-rich liquid stream from a synthesis gas including carbon dioxide and hydrogen, the method comprising the steps of:
 a) carrying out a first cooling step to cool a synthesis gas feed stream such that a first two-phase mixture is formed;   b) passing the first two-phase mixture at a first pressure and a first temperature to a first separator,   c) carrying out a first separation to separate the first mixture into a first CO 2 -rich liquid fraction and a first H 2 -rich vapour fraction;   d) compressing H 2 -rich vapour using at least one compressor;   e) carrying out a second cooling step to cool H 2 -rich vapour such that a second two-phase mixture is formed,   f) passing the second mixture at a second pressure and a second temperature to a second separator   g) carrying out a second separation to separate the second mixture into a second CO 2 -rich liquid fraction and a further H 2 -rich vapour stream.   
     
     
         28 . An apparatus for separating a carbon-dioxide-rich liquid stream from a synthesis gas including carbon dioxide and hydrogen, the apparatus including:
 a) two separator stages each arranged for separating a cooled two-phase mixture into a CO 2 -rich liquid fraction and a H 2 -rich gas fraction, the second separator stage being arranged downstream of the first separator stage such that a H 2 -rich fraction from the first separator stage is fed to the second separator stage;   b) a compressor arranged between the two separator stages;   c) a cooling stage for carrying out a first cooling step to cool a synthesis gas feed stream upstream of the first separator stage, and for carrying out a second cooling step to the separated H 2 -rich stream, the cooling stage including at least one heat exchanger arranged for exchanging heat between at least one separated H 2 -rich stream or CO 2 -rich stream and the synthesis gas feed   d) at least one expander for reducing the pressure of a separated H 2 -rich vapour stream, and preferably to recover mechanical work.