US-20260126246-A1 - PROCESS FOR DEHYDRATION OF A GAS STREAM PRIOR TO CRYOGENIC CO2 FRACTIONATION

Abstract

Processes for recovery of carbon dioxide from a gas stream are described. The processes reduce dehydration cost in CO 2 capture systems and minimize the formation of COS and H 2 O and enable water removal with an enhanced solvent-based absorbent operating at a lower temperature. This allows low residual water levels to be achieved in the dried gas. Also, feed streams containing high levels of CO 2 and H 2 S can be treated in an integrated system comprising a cryogenic CO 2 fractionation system, an overhead pressure swing adsorption (PSA) unit, and a CO 2 temperature swing adsorption (TSA) unit. The processes allow recovery of helium and methane as well as CO 2 and H 2 S.

Inventors

• Anh Ngo
• Audra Van Doorn
• Gregory R. Werba
• Bradley Russell
• John D. Wilkinson
• Shubhra J. Bhadra
• Nasser Khazeni
• Steven E. Zell
• Ali Hatami
• Christopher M. Dyszkiewicz
• Erick J. Bennett, III

Assignees

• UOP LLC

Dates

Publication Date

20260507

Application Date

20250827

Claims (20)

1. 1 . A process for recovery of carbon dioxide from a gas stream comprising: removing water from a gas feed stream in a dehydration unit comprising a liquid solvent-based absorbent to form a dried gas stream; and removing carbon dioxide from the dried gas stream in a cryogenic carbon dioxide fractionation system comprising a cryogenic fractionation column to form a carbon dioxide product stream.
2. 2 . The process of claim 1 further comprising: chilling the gas feed stream and optionally the dried gas stream with the carbon dioxide product stream from the cryogenic fractionation system forming a chilled gas feed stream, and optionally a chilled dried gas stream before removing the carbon dioxide.
3. 3 . The process of claim 2 wherein a temperature of the gas feed stream is less than 50° C.
4. 4 . The process of claim 1 further comprising: chilling the gas feed stream and optionally the dried gas stream with a cold stream from the cryogenic carbon dioxide fractionation system before removing carbon dioxide.
5. 5 . The process of claim 4 wherein a temperature of the gas feed stream is less than 50° C.
6. 6 . The process of claim 1 wherein a water concentration in the dried gas stream is less than 20 ppmv.
7. 7 . The process of claim 1 wherein the liquid solvent comprises triethylene glycol, ethylene glycol, diethylene glycol, methanol, or formulated glycol solvents, or combinations thereof.
8. 8 . The process of claim 1 further comprising: passing an overhead stream comprising carbon dioxide and at least one of methane, hydrogen, nitrogen, carbon monoxide, argon, hydrogen sulfide, and helium from the cryogenic carbon dioxide fractionation column to an overhead pressure swing adsorption unit; separating the overhead stream into a residue gas stream comprising carbon dioxide and at least one of methane, nitrogen, hydrogen, carbon monoxide, argon, and helium, and a tail gas stream comprising carbon dioxide; and compressing the tail gas stream and recycling the compressed tail gas stream to the cryogenic carbon dioxide fractionation system.
9. 9 . The process of claim 8 further comprising: separating the residue gas stream in a CO 2 thermal swing adsorption (TSA) unit into a CO 2 lean stream comprising at least one of methane, nitrogen, hydrogen, carbon monoxide, argon, and helium, and a regeneration gas stream comprising carbon dioxide, wherein a CO 2 concentration in the residue gas stream is less than 1 mol %; and passing the regeneration gas stream to the overhead PSA unit.
10. 10 . The process of claim 9 where a CO 2 concentration in the CO 2 lean stream is less than 100 ppmv.
11. 11 . The process of claim 9 further comprising: passing the CO 2 lean stream to a cryogenic nitrogen rejection unit (NRU) to form a nitrogen lean stream comprising methane and helium and a nitrogen rich stream; and recovering the nitrogen lean stream.
12. 12 . The process of claim 11 further comprising: passing the nitrogen-lean stream to a helium recovery unit to form a residue gas stream comprising methane and a helium-enriched product stream comprising helium; and recovering the helium-enriched product stream.
13. 13 . The process of claim 9 further comprising: compressing the regeneration gas stream from the CO 2 TSA unit.
14. 14 . The process of claim 1 further comprising: selectively removing additional water from the dried gas stream with a non-regenerative adsorber before removing the carbon dioxide.
15. 15 . The process of claim 14 further comprising: passing an overhead stream comprising-carbon dioxide and at least one of methane, hydrogen, nitrogen, carbon monoxide, argon, hydrogen sulfide, and helium from the cryogenic carbon dioxide fractionation column to an overhead pressure swing adsorption unit; separating the overhead stream into a residue gas stream comprising carbon dioxide and at least one of methane, nitrogen, hydrogen, carbon monoxide, argon, and helium, and a tail gas stream comprising carbon dioxide; and compressing the tail gas stream and recycling the compressed tail gas stream to the carbon dioxide fractionation system.
16. 16 . The process of claim 14 further comprising: chilling the dried gas stream with a cold stream from the cryogenic carbon dioxide fractionation system before removing the additional water from the dried gas stream.
17. 17 . The process of claim 1 further comprising: removing additional water from the dried gas stream with a thermal swing adsorption (TSA) unit forming a water stream before removing the carbon dioxide.
18. 18 . The process of claim 17 further comprising: chilling the dried gas stream with a cold stream from the cryogenic carbon dioxide fractionation system before removing the additional water from the dried gas stream.
19. 19 . The process of claim 1 wherein the gas stream comprises a hydrocarbon stream, a synthesis gas stream, a flue gas stream, or combinations thereof.
20. 20 . A process for recovery of carbon dioxide from a gas stream comprising: chilling the gas feed stream with a carbon dioxide product stream from a cryogenic fractionation system forming a chilled gas feed stream; removing water from the chilled gas feed stream in a dehydration unit comprising a liquid solvent-based absorbent to form a dried gas stream; chilling the dried gas stream with the carbon dioxide product stream from the cryogenic fractionation system forming a chilled gas feed stream; removing carbon dioxide from the chilled dried gas stream in a cryogenic carbon dioxide fractionation system comprising a cryogenic fractionation column to form a carbon dioxide product stream; optionally chilling the gas feed stream, or the dried gas feed stream, or the chilled dried gas feed stream, or combinations thereof with a cold stream from the cryogenic carbon dioxide fractionation system before removing the carbon dioxide from the chilled dried gas feed stream; passing an overhead stream comprising carbon dioxide and at least one of methane, hydrogen, nitrogen, carbon monoxide, argon, hydrogen sulfide, and helium from the cryogenic carbon dioxide fractionation column to an overhead pressure swing adsorption unit; separating the overhead stream into a residue gas stream comprising carbon dioxide and at least one of methane, nitrogen, hydrogen, carbon monoxide, argon, and helium, and a tail gas stream comprising carbon dioxide; compressing the tail gas stream and recycling the compressed tail gas stream to the carbon dioxide fractionation system; separating the residue gas stream in a CO 2 thermal swing adsorption (TSA) unit into a CO 2 lean stream comprising at least one of methane, nitrogen, hydrogen, carbon monoxide, argon, and helium, and a regeneration gas stream comprising carbon dioxide; passing the regeneration gas stream to the overhead PSA unit; passing the CO 2 lean stream to a cryogenic nitrogen rejection unit (NRU) to form a nitrogen lean stream comprising methane and helium and a nitrogen rich stream; passing the nitrogen-lean stream to a helium recovery unit to form a residue gas stream comprising methane and a helium-enriched product stream comprising helium; and recovering the helium-enriched product stream.

Description

RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application Ser. No. 63/715,152, filed on Nov. 1, 2024, the entirety of which is incorporated herein by reference. BACKGROUND There is increasing interest in capture and sequestration or utilization of carbon dioxide (CO2) from industrial processes in order to avoid CO2 emissions to the atmosphere. Carbon dioxide capture systems are currently being developed and commercialized for various applications, including flue gas streams from power generation plants, off gas streams from cement kilns and steel plants, and syngas streams from hydrogen production plants, among others. In addition to such industrial processes, carbon dioxide can also be recovered from sour natural gas extracted from underground reservoirs; the captured CO2 can be re-injected into a reservoir for sequestration or enhanced oil recovery, thereby avoiding direct CO2 emissions associated with the natural gas extraction. Various processes have been considered for CO2 capture in such industrial processes, including solvent-based systems (e.g., amine units) and cryogenic CO2 fractionation. Feed gas to the cryogenic process must generally be dried to remove moisture to a low level (e.g., <20 ppmv or lower) in order to prevent freezing in the downstream cryogenic system. Current practice is to use a solid adsorbent-based thermal swing adsorption (TSA) unit for this dehydration, often with a molecular sieve zeolite as the dessicant. However, these TSA units can be expensive. There is a need for a lower cost dehydration system to help reduce the overall cost of carbon capture. It is well known in the art that solvent-based dehydration units offer certain benefits compared to molecular sieve TSA systems for gas dehydration, including a lower capital cost. These solvent based systems often use triethylene glycol (TEG) as the solvent and are commonly used in the natural gas processing industry for gas drying. However, the residual water concentration in the dried gas from a TEG unit is typically not suitable for the stringent requirements of a cryogenic system. Solvent dehydrators have therefore not generally been used upstream of a cryogenic process since a very low water specification is required to prevent freezing. However, in contrast to most cryogenic processes (such as liquefied natural gas recovery, nitrogen rejection units, air separation plants, etc), CO2 fractionation operates at a higher temperature (about −55° C. is the lowest temperature in the process) and does not require water removal to the level required by most cryogenic units operating at much lower temperatures (e.g, <1 ppmv). Accordingly, solvent dehydrators can be considered as a lower cost alternative for use in cryogenic CO2 capture units if appropriately designed to achieve a relatively low residue gas water specification (such as <20 ppmv). This can be accomplished by using an appropriate solvent and suitable operating conditions (such as feed gas temperature, regenerator temperature, use of stripping gas, and the like). Some natural gas streams contain high concentrations of CO2 and H2S (sour natural gas), and in some cases these natural gas streams can also contain valuable quantities of helium which can be recovered. Processing these streams can lead to the formation of carbonyl sulfide (COS) and H2O via the reverse hydrolysis reaction (COS+H2O=CO2+H2S), leading to a potential water breakthrough in the molecular sieve dehydration unit and freezing in the downstream cryogenic CO2 fractionation unit. There can also be a risk of COS and H2O formation at other locations of the plant, which could also cause high water content in the gas circulating in the CO2 fractionation unit, and a higher risk of freezing. Therefore, there is a need for improved processes for CO2 removal and helium recovery in gas streams having high concentrations of CO2 and H2S. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of one embodiment of a process for recovering carbon dioxide according to the present invention. DESCRIPTION The present invention meets the above needs by providing processes which reduce dehydration cost in CO2 capture systems and minimize the formation of COS and H2O and enable water removal with an enhanced solvent-based absorbent operating at a lower temperature. This allows low residual water levels to be achieved in the dried gas. Also, feed streams containing high levels of CO2 and H2S can be treated in an integrated system comprising a cryogenic CO2 fractionation system, an overhead pressure swing adsorption (PSA) unit, and a CO2 temperature swing adsorption (TSA) unit. The process allows recovery of helium as well as CO2 and H2S from helium rich natural gas reservoirs containing high CO2 and H2S levels, such as those found in Wyoming and elsewhere. The integrated process is designed with multiple features to minimize the formation of COS/H2O. The process includes the use of a dehy