Process and apparatus for treating natural gas

• US 4,004,430 A
• Filed: 09/30/1974
• Issued: 01/25/1977
• Est. Priority Date: 09/30/1974
• Status: Expired due to Term

• Current Assignee: The Lummus Company
• Original Assignee: The Lummus Company
• Inventors: Marshall, Louis, Solomon, Stephen M., Shaievitz, Sidney
• Primary Examiner(s): Lutter, Frank W.
• Assistant Examiner(s): Sever, Frank
• Application Number:
  US05/510,367
• Time in Patent Office: 848 Days
• Field of Search: 62/9, 62/11, 62/32, 62/34, 62/36, 62/38, 62/40, 62/41, 62/42, 62/23, 62/24, 62/26, 62/31, 62/44, 62/28, 62/18
• US Class Current: 62/621
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: C07C 9/06 Ethane
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• CPC Class Codes: F25J 2230/20 Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2240/02 Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• CPC Class Codes: F25J 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• 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

Abstract

There is disclosed a process and apparatus for recovering ethane and heavier hydrocarbons from natural gas by heating the natural gas stream prior to the expansion and introduction thereof into a demethanizer operating under cryogenic conditions. Ethane and the heavier hydrocarbons are recovered from the demethanizer as well as a residual gaseous methane stream which is compressed to a pipeline receiving pressure by the work of expansion without requiring a booster compressor.

Claims

1. A process for treating gaseous natural gas stream including carbon dioxide and water vapor to recover ethane, which comprises:

a. heating said gaseous natural gas stream;

b. expanding said gaseous natural gas stream;

c. passing said expanded natural gas stream through a drying section to remove water vapor;

d. introducing into a demethanizer zone said dried and expanded natural gas stream of step (c) to separate a methane-enriched gaseous stream from an ethane-enriched stream;

e. withdrawing said ethane-enriched stream from said demethanizer zone;

f. withdrawing said methane-enriched gaseous stream from said demethanizer zone; and

g. compressing at least a major portion of said methane-enriched stream to a delivery pressure by the work produced by expanding said gaseous natural gas stream.

2. The process as defined in claim 1 wherein said delivery pressure equals the pressure of said gaseous natural gas stream

3. The process as defined in claim 1 wherein said expanded gaseous natural gas is cooled prior to introduction into said demethanizer zone.

4. The process as defined in claim 3 wherein said expanded gaseous natural gas stream is at a pressure of between about 450 to 500 psia. prior to introduction into said demethanizer zone.

5. The process as defined in claim 4 wherein a major portion of said carbon dioxide in said gaseous natural gas stream is withdrawn from said dementhanizer zone in said methane-enriched gaseous stream.

6. The process as defined in claim 1 wherein a minor portion of said methane-enriched gaseous stream is passed in indirect contact with a heat transfer medium to recover the cold potential of said minor portion of said methane-enriched gaseous stream.

7. The process as defined in claim 6 wherein said minor portion of said methane-enriched gaseous stream is utilized to regenerate a desiccant utilized to remove water from said expanded natural gas stream.

8. The process as defined in claim 7 wherein said minor portion of said methane-enriched gaseous stream is utilized to provide the energy requirements of the process.

9. The process as defined in claim 1 wherein said expanded natural gas feed to said demethanizer zone is at a pressure of between about 450 to 500 psia.

10. An apparatus for treating a gaseous natural gas stream including water vapor to recover ethane and heavier hydrocarbon which comprises:

a. means for heating said gaseous natural gas stream;

b. expander means for reducing the pressure of said gaseous natural gas stream;

c. drier means for removing water therefrom;

d. a demethanizer for separating said expanded natural gas stream into a methane-enriched gaseous stream and an ethane-enriched stream; and

e. compressor means for raising the pressure of said methane-enriched gaseous stream.