Dephlegmator process with liquid additive

• US 6,336,344 B1
• Filed: 05/26/2000
• Issued: 01/08/2002
• Est. Priority Date: 05/26/1999
• Status: Active Grant

• Current Assignee: Chart Incorporated (Chart Industries Incorporated)
• Original Assignee: Chart Incorporated (Chart Industries Incorporated)
• Inventors: OʼBrien, John V.
• Primary Examiner(s): DOERRLER, WILLIAM CHARLES
• Application Number:
  US09/579,953
• Time in Patent Office: 592 Days
• Field of Search: 626/20, 626/27, 629/20, 629/28, 629/29
• US Class Current: 62/627
• 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 2200/94 Details relating to the withdrawal point
• CPC Class Codes: F25J 2205/30 using a washing, e.g. "scrubbing" or bubble column for purification purposes
• CPC Class Codes: F25J 2205/50 using absorption, i.e. with selective solvents or lean oil, heavier CnHm and including generally a regeneration step for the solvent or lean oil
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2210/42 Nitrogen
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/904 by liquid or gaseous cryogen in an open loop
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• 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 3/0223 H2/CO mixtures, i.e. synthesis gas; Water gas or shifted synthesis gas production of carbon monoxide containing gas in general C01B32/40, C10J, C10K; production of hydrogen containing gas C01B3/00
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0247 separation of CnHm with 4 carbon atoms or more
• CPC Class Codes: F25J 3/0252 separation of hydrogen production of hydrogen containing gas in general C01B3/00, e.g. separation of hydrogen or hydrogen containing gases form gaseous mixtures at low temperatures C01B3/506
• CPC Class Codes: Y10S 62/928 Recovery of carbon dioxide

Abstract

A cryogenic process for the separation of one light gas component from a heavier gas component in a gas feed stream, by injecting a liquid hydrocarbon additive stream into the top or upper portion of a dephlegmator-heat exchanger, to increase the rectification temperature, or to maintain the temperature and reduce the additive flow rate relative to the respective values required with a conventional, single stage condenser.

Claims

1. A dephlegmator-heat exchanger process for the cryogenic separation from a feed gas stream of a light gas component and a heavy gas component, which process comprises:

a) rectifying the feed gas stream in a dephlegmator-heat exchanger to provide a lean component overhead gas stream and a rich liquid stream;

b) introducing, during the rectifying step, a selected amount of a liquid hydrocarbon additive into the top or upper portion of the dephlegmator-heat exchanger to maintain the temperature of the dephlegmator-heat exchanger, with a reduced flow rate of the liquid hydrocarbon additive relative to the flow rate required for a conventional, single stage condenser, or to increase the upper temperature of the dephlegmator-heat exchanger for rectification for the same additive flow rate relative to the temperature required for a conventional, single stage condenser, or to obtain selected intermediate values of flow rate and temperature;

c) withdrawing the rich liquid stream from a lower portion of the dephlegmator-heat exchanger; and

d) withdrawing the lean overhead gas stream from an upper portion of the dephlegmator-heat exchanger.

2. The process of claim 1 wherein the feed gas stream comprises primarily an acid gas and methane.

3. The process of claim 2 wherein the acid gas comprises carbon dioxide.

4. The process of claim 1 wherein the feed gas stream comprises a gas stream containing C₂ and C₃ hydrocarbons.

5. The process of claim 4 wherein the C₂-C₃ hydrocarbons comprise ethane, or propane, or mixtures thereof.

6. The process of claim 4 wherein the C₂-C₃ hydrocarbons comprise ethylene, or propylene, or mixtures thereof;

and the feed gas stream comprises a refinery offgas stream.

7. The process of claim 4 wherein the light C₂-C₃ hydrocarbons comprise ethylene or propylene to be recovered, and the feed gas stream comprises a gas stream from an ethylene or propylene plant.

8. The process of claim 1 wherein the upper rectification temperature is increased up to about −

40°

F.

9. The process of claim 1 wherein the additive stream comprises a liquid C₄+ stream.

10. The process of claim 1 wherein the one light gas component comprises hydrogen, the feed gas stream comprises hydrogen, methane, and carbon monoxide, and the liquid hydrocarbon additive stream comprises methane.

11. The process of claim 1 wherein the amount of additive stream ranges from about 1 to 200 mole percent of the feed gas stream.

12. The process of claim 1 in which rectifying of the feed gas stream from the top or upper portion of a distillation column occurs solely by the employing of the dephlegmator-heat exchanger.

13. The process of claim 1 which includes increasing the temperature of the dephlegmator-heat exchanger by the liquid additive stream by at least 10°

F.

14. The process of claim 1 which includes operating the dephlegmator-heat exchanger as an isothermal absorption tower.

15. The process of claim 1 wherein the feed gas stream comprises a refinery offgas stream, the light gas component comprises an olefin lean vapor, and the heavy gas component comprises an olefin rich liquid.

16. The process of claim 1 which includes separating the liquid hydrocarbon additive from the liquid stream.

17. The process of claim 16 which includes recycling all or part of the recovered liquid hydrocarbon additive to the dephlegmator-heat exchanger.

18. The process of claim 10 which includes introducing the feed gas stream comprising hydrogen;

methane; and

carbon monoxide into the lower section of the dephlegmator-heat exchanger, cooling the liquid additive methane, and introducing the cooled liquid additive methane into the top or upper portion of the dephlegmator-heat exchanger.

19. The process of claim 6 which includes introducing the feed gas stream from the top or upper portion of a distillation column directly into the dephlegmator-heat exchanger.

20. The process of claim 1 which includes maintaining a rectification temperature and reducing the flow rate of the liquid hydrocarbon additive stream by up to 50 percent, relative to a conventional condenser.

21. The process of claim 1 which includes introducing the liquid hydrocarbon additive stream by injecting or spraying the additive stream into the dephlegmator-heat exchanger.

22. A dephlegmator-heat exchanger process for the cryogenic separation from a feed gas stream of a light gas component and a heavy gas component, which process comprises:

a) rectifying the feed gas stream in a dephlegmator-heat exchanger by passing the feed gas stream through at least two distillation stages in the dephlegmator-heat exchanger and distilling the feed gas stream in each distillation stage thereby transferring heat, the distillation stage providing a lean component overhead gas stream and a rich liquid stream;

b) introducing, during the rectifying step, a selected amount of a liquid hydrocarbon additive into an upper distillation chamber of the dephlegmator-heat exchanger to maintain the temperature of the dephlegmator-heat exchanger, with a reduced flow rate of the liquid hydrocarbon additive relative to the flow rate required for a conventional, single stage condenser, or to increase the upper temperature of the dephlegmator-heat exchanger for rectification for the same additive flow rate relative to the temperature required for a conventional, single stage condenser, or to obtain selected intermediate values of flow rate and temperature;

c) withdrawing the rich liquid stream from a lower portion of the dephlegmator-heat exchanger; and

d) withdrawing the lean overhead gas stream from an upper portion of the dephlegmator-heat exchanger.

23. The process of claim 22 in which rectifying of the feed gas stream from a top or upper portion of a distillation column occurs solely employing the dephlegmator-heat exchanger.

24. The process of claim 22 further including the step of operating the dephlegmator-heat exchanger as an isothermal absorption tower.

25. The process of claim 22 which further includes the steps of introducing the feed gas stream, which comprises hydrogen, methane, and carbon monoxide, into the lower portion of the dephlegmator-heat exchanger;

cooling the liquid additive, which comprises methane; and

introducing the cooled liquid additive into an upper distillation chamber of the dephlegmator-heat exchanger.