Separation of carbon dioxide and hydrogen

Abstract

A process for separating a synthesis gas stream into a hydrogen (H 2 ) rich vapour stream and a liquid carbon dioxide (CO 2 ) stream in a CO 2 condensation plant comprising the steps of: (A) feeding a synthesis gas stream having a pressure in the range of 10 to 120 barg to a compression system of the CO 2 condensation plant thereby increasing its pressure to 150 to 400 barg and cooling the resulting high pressure (HP) synthesis gas against an external coolant to remove at least part of the heat of compression; (B) cooling the HP synthesis gas stream to a temperature in the range of −15 to −55° C. by passing the HP synthesis gas stream through a heat exchanger system in heat exchange relationship with a plurality of refrigerant streams that are produced subsequently in the process; (C) passing the cooled HP synthesis gas stream formed in step (B) either directly or indirectly to a gas-liquid separator vessel that is operated at substantially the same pressure as the heat exchanger system and withdrawing a high pressure (HP) hydrogen rich vapour stream from the top of the separator vessel and a high pressure (HP) liquid CO 2 stream from the bottom of the separator vessel; and (D) feeding the HP hydrogen rich vapour stream from step (C) to the turboexpansion system wherein the hydrogen rich vapour stream is subjected to isentropic expansion in each of the turboexpanders of the series such that hydrogen rich vapour streams are withdrawn from the turboexpanders of the series at reduced temperature and at successively reduced pressures and wherein isentropic expansion of the hydrogen rich vapour in each of the turboexpanders of the series generates motive power thereby driving a machine that is a component of the CO 2 condensation plant and/or driving an alternator of an electric generator.

1 - 18 . (canceled) 
     
     
         19 . A process for separating a synthesis gas stream into a hydrogen (H 2 ) rich vapour stream and a liquid carbon dioxide (CO 2 ) stream in a CO 2  condensation plant that comprises (a) a compression system comprising at least one compressor, (b) a heat exchanger system, (c) a gas-liquid separator vessel, and (d) a turboexpansion system comprising a plurality of turboexpanders arranged in series, the process comprising the steps of:
 (A) feeding a synthesis gas stream having a pressure in the range of 10 to 120 barg to the compression system of the CO 2  condensation plant such that the synthesis gas is increased in pressure to a pressure in the range of 150 to 400 barg and cooling the resulting high pressure (HP) synthesis gas against an external coolant to remove at least part of the heat of compression;   (B) cooling the HP synthesis gas stream formed in step (A) to a temperature in the range of −15 to −55° C. by passing the HP synthesis gas stream through the heat exchanger system in heat exchange relationship with a plurality of refrigerant streams that are produced subsequently in the process wherein the internal refrigerant streams are selected from the group consisting of cold hydrogen rich vapour streams and liquid CO 2  streams;   (C) passing the cooled HP synthesis gas stream formed in step (B) either directly or indirectly to a gas-liquid separator vessel that is operated at substantially the same pressure as the heat exchanger system and withdrawing a high pressure (HP) hydrogen rich vapour stream from at or near the top of the separator vessel and a high pressure (HP) liquid CO 2  stream from at or near the bottom of the separator vessel; and   (D) feeding the HP hydrogen rich vapour stream from step (C) to the turboexpansion system wherein the hydrogen rich vapour stream is subjected to isentropic expansion in each of the turboexpanders of the series such that hydrogen rich vapour streams are withdrawn from the turboexpanders of the series at reduced temperature and at successively reduced pressures and wherein isentropic expansion of the hydrogen rich vapour in each of the turboexpanders of the series generates motive power thereby driving a machine that is a component of the CO 2  condensation plant and/or driving an alternator of an electric generator.   
     
     
         20 . A process as claimed in  claim 19 , wherein the hydrogen rich vapour stream that exits the final turboexpander in step (D) is obtained at a pressure in the range of 25 to 45 barg. 
     
     
         21 . A process as claimed in  claim 19 , wherein liquid carbon dioxide is exported from the process at a pressure in the range of 100 to 175 barg. 
     
     
         22 . A process as claimed in  claim 19 , wherein the synthesis gas stream is fed to the compression system at a pressure in the range of 10 to 60 bar. 
     
     
         23 . A process as claimed in  claim 19 , wherein the isentropic expansion of the hydrogen rich vapour in each of the turboexpanders of the series is used to drive a compressor of the compression system and/or to drive a turbine of an electric generator. 
     
     
         24 . A process as claimed in  claim 19 , wherein the machine that is driven by the turboexpanders in step (D) is a compressor of the compression system and/or a pump. 
     
     
         25 . A process as claimed in  claim 19 , wherein the pressure drop across the heat exchanger system in step (B) is less than 1.5 bar. 
     
     
         26 . A process as claimed in  claim 19 , wherein the heat exchanger system comprises at least one multichannel heat exchanger and the IiP synthesis gas stream is passed through a channel in the multichannel heat exchanger in heat exchange relationship with a plurality of internal refrigerant streams that are passed through further channels in the multichannel heat exchanger. 
     
     
         27 . A process as claimed in  claim 26 , wherein the multichannel heat exchanger is a diffusion-bonded heat exchanger, in particular, a printed circuit heat exchanger. 
     
     
         28 . A process as claimed  claim 19 , wherein the heat exchanger system comprises a plurality of stand-alone heat exchangers arranged in series and the HP synthesis gas stream is cooled in step (B) as it is passed through the heat exchangers of the series by heat exchange with a plurality of internal refrigerant streams that are fed to the first and successive heat exchangers of the series at successively lower temperatures. 
     
     
         29 . A process as claimed in  claim 19 , wherein the HP liquid CO 2  stream that is withdrawn from the gas-liquid separator in step (C) is obtained at the liquid CO 2  export pressure and the HP liquid CO 2  stream is then passed through the heat exchanger system in heat exchange relationship with the HP synthesis gas stream before being exported from the process and sequestered and/or used in a chemical process. 
     
     
         30 . A process as claimed in  claim 19 , wherein the HP liquid CO 2  stream of step (C) is obtained at a pressure above the liquid CO 2  export pressure and is reduced in pressure to the liquid CO 2  export pressure before being passed to a flash separation vessel where a hydrogen rich vapour stream is withdrawn from at or near the top of the flash separation vessel and a liquid CO 2  stream is withdrawn from at or near the bottom of the flash separator vessel and the liquid CO 2  stream is then passed through the heat exchanger system in heat exchange relationship with the HP synthesis gas stream before being exported from the process and sequestered and/or used in a chemical process. 
     
     
         31 . A process as claimed in  claim 30 , wherein the hydrogen rich vapour stream that is withdrawn from the flash separation vessel is combined with a hydrogen rich vapour stream of similar pressure that is withdrawn from one of the turboexpanders in step (D) and/or is combined with a synthesis gas feed stream of similar pressure that is obtained by passing the synthesis gas feed stream through the compression system in step (A). 
     
     
         32 . A process as claimed in  claim 19 , wherein the hydrogen rich vapour stream that exits the final turboexpander in step (D) is obtained at a pressure in the range of 1 to 200 barg, preferably 10 to 100 barg. 
     
     
         33 . A process as claimed in  claim 19 , wherein the hydrogen rich vapour stream that exits the final turboexpander in step (D) is obtained at a pressure in the range of 25 to 45 barg, preferably, 30 to 35 barg and is passed as fuel gas to a combustor of at least one gas turbine of a power plant. 
     
     
         34 . A process as claimed in  claim 19 , wherein the cooled HP synthesis gas stream formed in step (B) has a temperature in the range of −30 to −40° C. and is passed to a cryogenic separation system that comprises a single cryogenic separation stage comprised of a heat exchanger that employs an external refrigerant and a gas-liquid separator vessel wherein the pressure drop across the cryogenic separation stage is in the range of 0.1 to 5 bar; the heat exchanger of the cryogenic separation stage has an operating temperature in the range of −40 to −55° C.; and wherein the HP hydrogen rich vapour stream and the HP liquid CO 2  stream of step (C) are withdrawn from the gas-liquid separator vessel of the cryogenic separation stage. 
     
     
         35 . A process as claimed in  claim 19 , wherein the cooled HP synthesis gas stream that is formed in step (B) has a temperature in the range of −15 to −30° C. and is passed to a cryogenic separation system comprising a plurality of, cryogenic separation stages that are arranged in series wherein each cryogenic separation stage of the series is comprised of a heat exchanger that employs an external refrigerant and a gas-liquid separation vessel; the cryogenic separation stages of the series are operated at progressively lower temperatures and with a pressure drop across the series of cryogenic separation stages in the range of 0.1 to 5 bar; the HP hydrogen rich vapour stream and the HP liquid CO 2  stream of step (C) are withdrawn from the gas-liquid separator vessel of the final cryogenic separation stage in the series; and additional HP liquid CO 2  streams are withdrawn from each of the preceding cryogenic separation stages in the series. 
     
     
         36 . A process as claimed in  claim 19 , wherein the synthesis gas stream is compressed in the compression system to a pressure in the range of 175 to 360 barg, preferably, 250 to 360 barg, more preferably, 300 to 360 barg, in particular, 330 to 360 barg. 
     
     
         37 . A process as claimed in  claim 19 , wherein the synthesis gas is compressed in a multistage compressor system comprising a plurality of compressors arranged in series wherein a heat exchanger is provided after each compressor of the series and wherein the synthesis gas is cooled in each heat exchanger against an external coolant selected from the group consisting of air, water or a cold process stream selected from the H 2  rich vapour stream formed in step (C) or the final H 2  rich vapour stream from step (D). 
     
     
         38 . A process as claimed in  claim 19 , wherein the synthesis gas feed stream is a sour synthesis gas stream comprising H 2 S and wherein a major portion of the H 2 S partitions into the liquid CO 2  phase and is sequestered with the liquid CO 2  stream(s) and residual H 2 S in the final H 2  rich vapour stream is removed downstream of the CO 2  condensation plant by passing the final H 2  rich vapour stream through a bed comprising a particulate adsorbent material or through a scrubber wherein the H 2  rich vapour stream contacts a liquid absorbent. 
     
     
         39 . A process as claimed in  claim 19 , wherein the liquid CO 2  product stream is used as injection fluid for an oil reservoir by injecting the liquid CO 2  down an injection well and into the oil reservoir thereby displacing hydrocarbons towards an associated production well. 
     
     
         40 . A carbon dioxide condensation plant for separating carbon dioxide and hydrogen from a synthesis gas stream, the plant comprising:
 (a) means for providing a synthesis gas feed stream;   (b) a compression system for compressing the synthesis gas feed stream to a pressure in the range of 150 to 400 barg;   (c) a heat exchanger system for cooling the compressed synthesis gas stream to a temperature in the range of −15 to −55° C. against a plurality of internal refrigerant streams thereby partially condensing the compressed synthesis gas stream;   (d) a gas-liquid separator vessel for separating the partially condensed compressed synthesis gas stream into a hydrogen rich vapour stream and liquid CO 2  stream with minimal pressure drop across the gas-liquid separator vessel;   (e) a turboexpander system comprising a plurality of turboexpanders arranged in series for expanding the separated hydrogen rich vapour stream to successively lower pressures wherein the turboexpander system is adapted to produce a hydrogen rich vapour stream from the final turboexpander in the series at a pressure at or above the minimum fuel gas feed pressure to the combustor of a gas turbine of a power plant and wherein each turboexpander in the series is adapted to provide a hydrogen rich vapour stream that is used as an internal refrigerant stream for the heat exchanger system.