Ethane Recovery Methods And Configurations

• US 20100011809A1
• Filed: 06/26/2007
• Published: 01/21/2010
• Est. Priority Date: 06/27/2006
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Granted Patent: US 9,316,433 B2
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/50 using multiple (re-)boiler-condensers at different heights of the column
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2215/02 Mixing or blending of fluids to yield a certain product
• CPC Class Codes: F25J 2215/60 Methane
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• 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 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/60 Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• 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
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

Contemplated methods and configurations use a cooled ethane and CO2-containing feed gas that is expanded in a first turbo-expander and subsequently heat-exchanged to allow for relatively high expander inlet temperatures to a second turbo expander. Consequently, the relatively warm demethanizer feed from the second expander effectively removes CO2 from the ethane product and prevents carbon dioxide freezing in the demethanizer, while another portion of the heat-exchanged and expanded feed gas is further chilled and reduced in pressure to form a lean reflux for high ethane recovery.

Claims

1. A gas processing plant comprising;

a first heat exchanger, a first turboexpander, and a second heat exchanger, coupled to each other in series upstream of a demethanizer and configured to cool and expand a feed gas to a pressure above a demethanizer operating pressure;

a separator fluidly coupled to the second heat exchanger and configured to separate the cooled and expanded feed gas into a liquid phase and a vapor phase;

a second turboexpander coupled to the separator and configured to expand one portion of the vapor phase to the demethanizer pressure; and

a third heat exchanger and a pressure reduction device that are coupled to each other and configured to receive and condense another portion of the vapor phase to thereby form a reflux to the demethanizer.

2. The plant of claim 1 wherein first and second heat exchangers are thermally coupled to the demethanizer to provide at least part of a reboiling duty to the demethanizer.

3. The plant of claim 1 further comprising a side reboiler of the demethanizer that is thermally coupled to at least one of a deethanizer overhead condenser and a residue gas heat exchanger.

4. The plant of claim 1 wherein the first turboexpander is mechanically coupled to a residue gas compressor.

5. The plant of claim 1 further comprising a feed gas source that is configured to provide feed gas at a pressure of at least 1500 psig.

6. The plant of claim 1 wherein the feed gas comprises at least 0.5 mol % CO2 and less than 3 mol % C3+ components.

7. The plant of claim 1 wherein the pressure above the demethanizer operating pressure is between 1000 psig and 1400 psig.

8. The plant of claim 1 wherein the first heat exchanger, the first turboexpander, and the second heat exchanger are configured to cool the feed gas to a temperature above −

10°

F.

9. The plant of claim 1 wherein the second turboexpander is configured such that the expanded portion of the vapor phase has a temperature between −

75°

F. and −

85°

F. and a pressure between 400 psig and 550 psig.

10. The plant of claim 1 wherein the third heat exchanger and the pressure reduction device are configured to condense the another portion of the vapor phase at a temperature of equal or less than −

130°

F.

11. A method of separating ethane from an ethane-containing gas, comprising:

cooling and expanding a feed gas upstream of a demethanizer from a feed gas pressure to a pressure above a demethanizer operating pressure;

separating a superheated vapor phase from the cooled and expanded feed gas and expanding one portion of the superheated vapor phase in a turboexpander to the demethanizer operating pressure; and

cooling and expanding another portion of the superheated vapor phase to generate a reflux, and feeding the reflux to the demethanizer.

12. The method of claim 11 wherein the step of expanding the feed gas is performed in a further turboexpander that is optionally mechanically coupled to a compressor.

13. The method of claim 11 wherein the step of cooling the feed gas is performed using a heat exchanger that is configured to provide rebelling heat to the demethanizer.

14. The method of claim 11 further comprising a step of providing a side reboiler with heat content from a deethanizer overhead condenser and a residue gas heat exchanger.

15. The method of claim 11 wherein the feed gas has a pressure of at least 1500 psig.

16. The method of claim 11 wherein the feed gas comprises at least 0.5 mol % CO2 and less than 3 mol % C3+ components.

17. The method of claim 11 wherein the pressure above the demethanizer operating pressure is between 1000 psig and 1400 psig.

18. The method of claim 11 wherein the cooled and expanded feed gas has a temperature above −

10°

F.

19. The method of claim 11 wherein the expanded portion of the vapor phase has a temperature between −

75°

F. and −

85°

F. and a pressure between 400 psig and 550 psig.

20. The method of claim 11 wherein the another portion of the superheated vapor phase is cooled such that the reflux has a temperature of equal or less than −

130°

F.