Process for the recovery and purification of ethylene

• US 4,720,293 A
• Filed: 04/28/1987
• Issued: 01/19/1988
• Est. Priority Date: 04/28/1987
• Status: Expired due to Term

• Current Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Original Assignee: Air Products and Chemicals Incorporated (Linde Plc)
• Inventors: Grassi, Kimberly S., Rowles, Howard C., Bernhard, Dennis P.
• Primary Examiner(s): Wayner, William E.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/043,582
• Time in Patent Office: 266 Days
• Field of Search: 62/9, 62/11, 62/23, 62/24, 62/27, 62/28, 62/31, 62/32, 62/34, 62/36, 62/38, 62/39, 62/40, 62/41, 62/42, 62/44
• US Class Current: 62/630
• CPC Class Codes: C07C 11/04 Ethylene
• CPC Class Codes: C07C 7/04 by distillation
• CPC Class Codes: F25J 2200/80 using integrated mass and heat exchange, i.e. non-adiabatic rectification in a reflux exchanger or dephlegmator
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2205/82 using a reactor with combustion or catalytic reaction
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/66 Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 3/0219 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

The present invention relates to a process for the recovery of ethylene from a feed gas containing ethane, methane and other light gases, e.g. cracked gas or refinery off-gases, wherein ethylene is condensed in two stages, preferably rectified, and fed to an integrated demethanizer column. Refrigeration for the process is provided by an integrated combination of work expansion of rejected light gases, by vaporization of separated ethane at low partial pressure but high total pressure, and by a mixed refrigerant system. The process results in the separation and purification of ethylene from the feed gas stream while significantly reducing the energy consumption to do so.

Claims

1. In a process for the recovery and purification of ethylene from an ethylene containing feed stream, wherein the ethylene containing feed stream is cooled in two heat exchange stages to condense out the bulk of C₂⁺ material present in the feed stream;

the condensed C₂⁺ material is fed to a demethanizer column to remove any remaining light gases, producing a light gas stream as an overhead of the demethanizer column and a demethanized C₂⁺ stream is then fed to an ethylene-ethane separation process which produces at least an ethylene product stream and an ethane byproduct stream, the improvement comprising the utilization of three integrated refrigeration cycles wherein low level refrigeration for the second heat exchange stage is provided by work expansion, in one or more stages, of at least a portion of an uncondensed light gas stream removed from the cold end of the second heat exchange stage or an uncondensed light gas stream removed from the cold end of the second heat exchange stage and at least a portion of the light gas stream from the overhead of the demethanizer column;

intermediate level refrigeration for the demethanizer column condenser and for the cold end of the first heat exchange byproduct stream from the ethylene-ethane separation process with at least a portion of the light gas stream from the cold end of the second heat exchange stage or at least a portion of the light gas stream from the overhead of the demethanizer column, or both; and

high level refrigeration for the warm end of the first heat exchange stage is provided by a mixed refrigerant system.

2. The process according to claim 1 wherein the second heat exchange stage is a dephlegmator which produces a rectified C₂⁺ liquid as a bottoms stream and a cold end light gas streams as an overheated.

3. The process according to claim 2 wherein the C₂⁺ material condensed in the first heat exchange stage and the rectified C₂⁺ liquid condensed in the dephlegmator are fed separately to the demethanizer column.

4. The process according to claim 2 wherein the mixed refrigerant is compressed, condensed, subcooled, and then revaporized in the first heat exchange stage at one or more pressure levels to provide the high level refrigeration.

5. The process according to claim 2 wherein the mixed refrigerant is compressed, partially condensed with cooling water or ambient air, further condensed by heat exchanger with the demethanized C₂⁺ stream, subcooled and then revaporized in the first heat exchange stage at one or more pressure levels to provide the high level refrigeration.

6. In a process for the recovery and purification of ethylene from an ethylene containing feed stream, wherein the ethylene containing feed stream is cooled in two heat exchange stages to condense out the bulk of C₂⁺ material present in the feed stream;

the condensed C₂⁺ material is fed to a distillation column to remove any remaining light gases, producing a light gas stream as an overhead of the distillation column and a demethanized C₂⁺ stream as a bottoms of the distillation column;

the demethanized C₂⁺ stream is then fed to an ethylene-ethane splitter column to separate the demethanized C₂⁺ stream into at least an ethylene product stream and a C₂⁺ liquid byproduct stream, the improvement comprising the utilization of three integrated refrigeration cycles wherein low level refrigeration for the second heat exchange stage is provided by work expansion, in one or more more stages, of at least a portion of an uncondensed light gas stream removed from the cold end of the second heat exchange stage or an uncondensed light gas stream removed from the cold end of the second heat exchange stage and at least a portion of the light gas stream from the overhead of the distillation column;

intermediate level refrigeration for the distillaton column condenser and for the cold end of the first heat exchange stage is provided by mixing at least a portion of the C₂⁺ liquid byproduct stream for the ethylene-ethane splitter column with at least a portion of the light gas stream from the cold end of the second heat exchange stage or at least a portion of the light gas stream from the overhead of the distillation column, or both; and

high level refrigeration for the warm end of the first heat exchange stage is provided by a mixed refrigerant system.

7. The process according to claim 6 wherein the second heat exchange stage is a dephlegmator which produces a rectified C₂⁺ liquid as a bottoms stream and a cold end light gas stream as an overhead.

8. The process according to claim 7 wherein the C₂⁺ material condensed in the first heat exchange stage and the rectified C₂⁺ liquid condensed in the dephlegmator are fed separately to the distillation column.

9. The process according to claim 7 wherein the mixed refrigerant is compressed, condensed, subcooled, and then revaporized in the first heat exchange stage at one or more pressure levels to provide the high level refrigeration.

10. The process according to claim 7 wherein the mixed refrigerant is compressed, partially condensed with cooling water or ambient air, further condensed by heat exchange with the demethanized C₂⁺ stream, subcooled and then revaporized in the first heat exchange stage at one or more pressure levels to provide the high level refrigeration.

11. In a process for the recovery and purification of ethylene from an ethylene containing feed stream, wherein the ethylene containing feed stream is cooled in two heat exchange stages to condense out the bulk of C₂⁺ material present in the feed stream;

the condensed C₂⁺ material is fed to a first distillation column to remove any remaining light gases, producing a light gas stream as an overhead of the first distillation column and a demethanized C₂⁺ stream as a bottoms of the first distillation column;

the demethanized C₂⁺ stream is then fed to second distillation column to remove the C₃⁺ portion of the demethanized C₂⁺ stream, producing at least a mixed ethylene-ethane stream as an overhead of the second distillation column and a C₃⁺ stream as a bottom of the second distillation column; and

the mixed ethylene-ethane stream is fed to an ethylene-ethane splitter column to separate the mixed ethylene-ethane stream into at least an ethylene product stream and an ethane liquid byproduct stream;

the improvement comprising the utilization of three integrated refrigeration cycles wherein low level refrigeration for the second heat exchange stage is provided by work expansion, in one or more stages, of at least a portion of an uncondensed light gas stream removed from the cold end of the second heat exchange stage or an uncondensed light gas stream removed from the cold end of the second heat exchange stage and at least a portion of the light gas stream from the overhead of the first distillation column;

intermediate level refrigeration for the first distillation column condenser and for the cold end of the first heat exchange stage is provided by mixing at least a portion of the ethane liquid byproduct stream from the ethylene-ethane splitter column with at least a portion of the light gas stream from the cold end of the second heat exchange stage or at least a portion of the light gas stream from the overhead of the first distillation column, or both; and

high level refrigeration for the warm end of the first heat exchange stage is provided by a mixed refrigerant system.

12. The process according to claim 11 wherein the second heat exchange stage is a dephlegmator which produces a rectified C₂⁺ liquid as a bottoms stream and a cold end light gas stream as an overhead.

13. The process according to claim 12 wherein the C₂₊ material condensed in the first heat exchange stage and the rectified C₂⁺ liquid condensed in the dephlegmator are fed separately to the first distillation column.

14. The process according to claim 12 wherein the mixed refrigerant is compressed, condensed, subcooled, and then revaporized in the first heat exchange stage at one or more pressure levels to produce the high level refrigeration.

15. The process according to claim 12 wherein the mixed refrigerant is compressed, partially condensed with cooling water or ambient air, further condensed by heat exchange with the demethanized C₂⁺ stream, subcooled and then revaporized in the first heat exchange stage at one or more pressure levels to provide the high level refrigeration.

16. The process according to claim 12 wherein the ethane liquid byproduct is subcooled prior to being mixed with the light gases.

17. The process according to claim 12 wherein the combined ethane-light gas stream is recompressed in a compressor driven by a light gas expander.