Separation of carbon dioxide and hydrogen

Abstract

A process is described for removing carbon dioxide from a synthesis gas feed stream in a cryogenic separation plant. In an example described the synthesis gas feed stream ( 3 ) comprises 40 to 65 mole % hydrogen and is fed to a single stage or a first stage of a series of separation stages ( 120, 103, 104 ) at a pressure in the range of 46 to 90 bar absolute. The single stage or a stage of the series is operated at a temperature in the range of −53 to −48° C. and a pressure in the range of 44 to 90 bar absolute. In some examples, the single stage or the combined stages of the series remove 70 to 80% of the total moles of carbon dioxide in the synthesis gas feed stream. Liquefied C02 product stream(s) discharged from the stage (s) ( 7,10,13 ) of the cryogenic separation plant may be sequestrated and/or used in a chemical process ( 71 ).

1 . A process for removing carbon dioxide from a synthesis gas feed stream in a cryogenic separation plant that comprises either a single cryogenic separation stage or at least two cryogenic separation stages arranged in series, with the stages in the series being designated stage 1 through stage N, the letter N representing the number of stages in the series, the single stage or each stage of the series comprising the steps of (a) condensing carbon dioxide from the synthesis gas by cooling the synthesis gas by non-contact heat exchange with an external refrigerant to produce liquefied carbon dioxide, and (b) separating the liquefied carbon dioxide from the synthesis gas, with the single separation stage discharging a liquefied carbon dioxide product stream and a hydrogen enriched synthesis gas stream or, with each of the stages in the series cooling the synthesis gas to a successively lower temperature as the synthesis gas progresses from stage 1 to stage N, thereby separately removing a liquefied carbon dioxide product stream from each of the stages, with stage N discharging a hydrogen enriched synthesis gas vapour stream, characterized in that:
 (i) the synthesis gas feed stream comprises 40 to 65 mole % hydrogen and is fed to the single stage or the first stage of the series at a pressure in the range of 46 to 76 bar absolute; 
 (ii) the single stage or stage N of the series is operated at a temperature in the range of −53 to −48° C. and a pressure in the range of 44 to 74 bar absolute such that the single stage or the combined stages of the series remove 70 to 80% of the total moles of carbon dioxide in the synthesis gas feed stream; and 
 (iii) the liquefied CO 2  product stream(s) discharged from the stage(s) of the cryogenic separation plant is sequestrated and/or used in a chemical process. 
 
     
     
         2 . A process as claimed in  claim 1  wherein the liquid CO 2  product stream(s) is used for enhanced oil recovery before being sequestered. 
     
     
         3 . A process as claimed in  claim 1  wherein 75 to 80% of the total moles of carbon dioxide in the synthesis gas feed stream is separated in the cryogenic separation plant. 
     
     
         4 . A process as claimed in  claim 1  wherein the synthesis gas stream comprises hydrogen, carbon dioxide, and hydrogen sulfide and the hydrogen sulfide is condensed from the synthesis gas stream in the single cryogenic separation stage or each of the cryogenic separation stages of the series and the hydrogen sulfide is removed from the single stage or each of the stages of the series in the liquefied carbon dioxide product stream(s). 
     
     
         5 . A process as claimed in  claim 4  wherein the single stage or the combined stages of the series remove 80 to 90% of the total moles of hydrogen sulfide from the synthesis gas feed stream. 
     
     
         6 . A process as claimed in  claim 1  wherein the synthesis gas feed stream is cooled upstream of the cryogenic separation plant to a temperature in the range of 20 to 50° C. thereby condensing out a condensate and the condensate is separated from the cooled synthesis gas stream. 
     
     
         7 . A process as claimed in  claim 6  wherein the synthesis gas feed stream is dried prior to being passed to the CO 2  condensation plant such that the synthesis gas feed stream has a water content of less than 1 ppm on a molar basis. 
     
     
         8 . A process as claimed in  claim 1  wherein the synthesis gas feed stream is passed to a pre-cooling heat exchanger of the CO 2  condensation plant where the synthesis gas feed stream is pre-cooled against a cold process stream selected from a liquid CO 2  product stream and a cold H 2  enriched synthesis gas vapour stream. 
     
     
         9 . A process as claimed in  claim 8  wherein the synthesis gas feed stream is pre-cooled in a multichannel heat exchanger by passing the synthesis gas feed stream through at least one channel of the multichannel heat exchanger and a plurality of cold process streams through further channels of the multichannel heat exchanger. 
     
     
         10 . A process as claimed in  claim 1  wherein the pressure drop across the single stage or the series of stages of the cryogenic separation plant is in the range of 2 to 10 bar. 
     
     
         11 . A process as claimed in  claim 1  wherein the hydrogen enriched synthesis gas vapour stream that exits the separator of the single cryogenic separation stage or that exits stage N of the series of cryogenic separation stages is passed through a channel of the multichannel heat exchanger in heat exchanger relationship with the synthesis gas feed stream and is then cooled by expansion to lower pressure in a first turboexpander before being fed to a further channel in the multichannel heat exchanger and the hydrogen enriched vapour stream is optionally cooled by expansion to a lower pressure in a second turboexpander before being fed to a further channel of the multichannel heat exchanger thereby pre-cooling the synthesis gas feed stream to a temperature in the range of −15 to −35° C. 
     
     
         12 . A process as claimed in  claim 11  wherein the hydrogen enriched synthesis vapour stream discharged from the single cryogenic separation stage or the final cryogenic separation stage (Stage N) of the cryogenic separation plant comprises at least 70 mole % hydrogen, preferably, at least 80 mole % hydrogen and the expanded hydrogen enriched vapour stream is used as a fuel stream for the combustor of a gas turbine that drives an electric generator thereby producing electricity provided that the hydrogen enriched vapour stream is not expanded to a pressure below the desired fuel gas feed pressure for the combustor. 
     
     
         13 . A process as claimed in  claim 1  wherein the liquid CO 2  stream that is removed from the single cryogenic separation stage or the combined liquid CO 2  stream that is removed from the series of cryogenic separation stages comprises at least 90 mole % CO 2 , in particular, at least about 94 mole % CO 2 , the liquid CO2 stream or combined liquid CO2 stream is fed to a rectification column and a liquid CO2 product stream comprising less than 1% by volume hydrogen is removed from at or near the bottom of the rectification column. 
     
     
         14 . A process as claimed in  claim 1  wherein the liquefied CO 2  product stream is transferred by pipeline to a reception facility of an oil field or gas field where the CO2 product stream is injected into a reservoir of the oil field or gas fluid. 
     
     
         15 . A process for separating a synthesis gas stream into a hydrogen rich vapour stream and a carbon dioxide rich stream, the process including the steps of:
 a) cooling a synthesis gas stream to a temperature at which at which a two-phase mixture is formed,   b) passing the cooled stream formed in step (a) either directly or indirectly to a gas-liquid separator vessel, the feed to the gas-liquid separator vessel having a pressure of less than 150 barg   c) withdrawing a hydrogen rich vapour stream from the separator vessel and a liquid CO 2  stream from the separator vessel; and   d) feeding a separated hydrogen rich vapour stream to an expansion system including a plurality of expanders arranged in series, wherein the hydrogen rich vapour stream is subjected to expansion in each of the expanders of the series such that an expanded hydrogen rich vapour stream is withdrawn from each of the expanders at reduced temperature and at successively reduced pressures; and   e) using at least one 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 expanders effect isentropic expansion of the hydrogen rich vapour in each of the expanders of the series and generate motive power. 
     
     
         18 . A method according to  claim 15 , further including increasing the pressure of the separated carbon dioxide stream. 
     
     
         19 . A method according to  claim 15 , further including passing the separated hydrogen rich stream directly or indirectly to a further gas-liquid separator vessel and withdrawing a second separated hydrogen rich vapour stream from the separator vessel and a second liquid CO 2  stream from the separator vessel. 
     
     
         20 . A process for separating a gas stream into a hydrogen rich vapour stream and a carbon dioxide rich stream, the process including the steps of:
 a) cooling a gas stream to a temperature at which at which a two-phase mixture is formed,   b) passing the cooled stream formed in step (a) either directly or indirectly to a first gas-liquid separator vessel, the feed to the gas-liquid separator vessel having a pressure of less than 150 barg   c) withdrawing a hydrogen rich vapour stream from the separator vessel and a liquid CO 2  stream from separator vessel;   d) passing the hydrogen rich vapour stream formed in step (c) either directly or indirectly to a second gas-liquid separator vessel, and withdrawing a second hydrogen rich vapour stream from the separator vessel and a liquid CO 2  stream from the separator vessel; and   e) feeding a separated hydrogen rich vapour stream to an expansion system including at least one expander, wherein the hydrogen rich vapour stream is subjected to expansion in the expander of the system such that an expanded hydrogen rich vapour stream is withdrawn from the expander at reduced temperature and at pressure; and   f) using an expanded hydrogen-rich vapour stream as a coolant.   
     
     
         21 . A method according to  claim 20 , further including cooling the separated hydrogen-rich stream upstream of the second separator vessel. 
     
     
         22 . A process for removing carbon dioxide from a synthesis gas feed stream in a cryogenic separation plant that comprises either a single cryogenic separation stage or at least two cryogenic separation stages arranged in series, with the stages in the series being designated stage 1 through stage N, the letter N representing the number of stages in the series, the single stage or each stage of the series comprising the steps of (a) condensing carbon dioxide from the synthesis gas by cooling the synthesis gas by non-contact heat exchange with an external refrigerant to produce liquefied carbon dioxide, and (b) separating the liquefied carbon dioxide from the synthesis gas, with the single separation stage discharging a liquefied carbon dioxide product stream and a hydrogen enriched synthesis gas stream or, with each of the stages in the series cooling the synthesis gas to a successively lower temperature as the synthesis gas progresses from stage 1 to stage N, thereby separately removing a liquefied carbon dioxide product stream from each of the stages, with stage N discharging a hydrogen enriched synthesis gas vapour stream, wherein:
 (i) the synthesis gas feed stream comprises 40 to 65 mole % hydrogen and is fed to the single stage or the first stage of the series at a pressure in the range of 46 to 90 bar absolute;   (ii) the single stage or stage N of the series is operated at a temperature in the range of −53 to −48° C. and a pressure in the range of 44 to 90 bar absolute such that the single stage or the combined stages of the series remove 70 to 80% of the total moles of carbon dioxide in the synthesis gas feed stream; and   (iii) the liquefied CO 2  product stream(s) discharged from the stage(s) of the cryogenic separation plant is sequestrated and/or used in a chemical process.   
     
     
         23 . A process as claimed in  claim 22  wherein the synthesis gas feed stream is passed to a heat exchanger system where the synthesis gas feed stream is against a colder process stream selected from a liquid CO 2  product stream and a H 2  enriched stream, and preferably the synthesis gas feed stream is cooled in a multichannel heat exchanger by passing the synthesis gas feed stream through at least one channel of the multichannel heat exchanger and a plurality of colder process streams through further channels of the multichannel heat exchanger. 
     
     
         24 . A process as claimed in  claim 23  wherein a hydrogen enriched gas vapour stream that exits the separator is passed through a channel of a multichannel heat exchanger in heat exchanger relationship with the synthesis gas feed stream and is then cooled by expansion to lower pressure in a first turboexpander before being fed to a further channel in the multichannel heat exchanger and the hydrogen enriched vapour stream is optionally cooled by expansion to a lower pressure in a second turboexpander before being fed to a further channel of the multichannel heat exchanger. 
     
     
         25 . A process as claimed in  claim 22  wherein the hydrogen-rich stream is used as a fuel stream for the combustor of a gas turbine. 
     
     
         26 . A process as claimed in  claim 22  wherein the liquefied CO 2  product stream is transferred by pipeline to a reception facility of an oil field or gas field where the CO2 product stream is injected into a reservoir of the oil field or gas fluid. 
     
     
         27 . A process for removing carbon dioxide from a gas feed stream in a cryogenic separation plant that comprises either a single cryogenic separation stage or at least two cryogenic separation stages arranged in series, with the stages in the series being designated stage 1 through stage N, the letter N representing the number of stages in the series, the single stage or each stage of the series comprising the steps of (a) condensing carbon dioxide from the gas by cooling the gas by non-contact heat exchange with a refrigerant to produce liquefied carbon dioxide, and (b) separating the liquefied carbon dioxide from the gas or, with each of the stages in the series cooling the synthesis gas to a successively lower temperature as the synthesis gas progresses from stage 1 to stage N, thereby separately removing a liquefied carbon dioxide product stream from each of the stages, with stage N discharging a gas vapour stream. 
     
     
         28 . A system for separating a synthesis gas stream into a hydrogen rich vapour stream and a carbon dioxide rich stream, the system including:
 a) a cooling system arranged to cool a gas stream to a temperature at which a two-phase mixture is formed,   b) a gas-liquid separator vessel arranged to receive the two-phase mixture either directly or indirectly from the cooling system, at a pressure of less than 150 bar, the output of the separator vessel being a hydrogen rich vapour stream and a liquid CO 2  stream; and   c) an expansion system arranged downstream of the separator vessel to receive a hydrogen rich vapour stream, the expansion system including a plurality of expanders arranged in series such that the hydrogen rich vapour stream is subjected to expansion in each of the expanders of the series such that a hydrogen rich vapour stream can be withdrawn from each of the expanders at reduced temperature and at successively reduced pressures   d) a flow path for feeding an expanded hydrogen rich stream to the cooling system.   
     
     
         29 . A system for separating a synthesis gas stream into a hydrogen rich vapour stream and a carbon dioxide rich stream, the system including:
 a) a cooling system arranged to cool a synthesis gas stream to a temperature at which at which a two-phase mixture is formed,   b) a first gas-liquid separator vessel arranged to receive the cooled stream either directly or indirectly, the feed to the gas-liquid separator vessel having a pressure of less than 150 barg, and to output a first hydrogen rich stream and a liquid CO 2  stream;   c) a second gas-liquid separator vessel downstream of the first separator for receiving the first hydrogen rich stream either directly or indirectly, and outputting a second hydrogen rich stream from the separator vessel and a liquid CO 2  stream from the separator vessel; and   d) an expansion system including at least one expander, arranged, preferably downstream of the second separator vessel, to receive a the hydrogen rich vapour stream and subjected it to expansion in the expander of the system such that an expanded hydrogen rich vapour stream can be withdrawn from the expander at reduced temperature and at pressure; and   e) a flow path for feeding an expanded hydrogen-rich vapour stream to the cooling system.   
     
     
         30 . A system according to  claim 29 , further including a compressor or pump arranged to increase the pressure of a separated carbon dioxide stream. 
     
     
         31 . (canceled) 
     
     
         32 . (canceled)