Propane recovery process

• US 5,685,170 A
• Filed: 10/09/1996
• Issued: 11/11/1997
• Est. Priority Date: 11/03/1995
• Status: Expired due to Fees

• Current Assignee: Jacobs Canada Incorporated (Jacobs Solutions, Inc.)
• Original Assignee: Mcdermott Engineers & Constructors Limited
• Inventors: Sorensen, James N.
• Primary Examiner(s): Capossela, Ronald C.
• Application Number:
  US08/727,894
• Time in Patent Office: 398 Days
• Field of Search: 62/625, 62/632, 62/635
• US Class Current: 62/625
• CPC Class Codes: B01D 53/1418 Recovery of products
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: C07C 9/08 Propane
• CPC Class Codes: C10G 5/04 with liquid absorbents
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/08 in a triple pressure main column system
• 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 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion loop
• 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 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

Increased recovery of propane, butane and other heavier components found in a natural gas stream is achieved by installing an absorber upstream from an expander and a separator. The separator is downstream from the expander and returns the liquid stream generated by the separator back to the absorber. Additionally, the recovery of propane, butane and other heavier components is enhanced by combining the upper gas stream from a distillation column with the upper gas stream from the absorber prior to injecting this combination into the separator. The upper gas stream removed from the separator is then subsequently processed for the recovery of a predominately methane and ethane gas stream while the bottom liquid stream from the absorber is subsequently distilled for the generation of a stream consisting predominately of propane, butane and other heavy hydrocarbon components. Alternate embodiments include an additional reflux separator in the system, or substitution of an additional absorber for the separator.

Claims

1. In a propane recovery process, the method comprising the steps of:

providing an absorber for receiving a natural gas stream and passing it upwardly therethrough, said absorber separating the natural gas stream into an upper gas stream and a bottom liquid stream;

providing an expander downstream from said absorber for receiving and expanding the upper gas stream from said absorber;

locating a separator downstream from said expander for receiving a liquid-gas stream from expansion with said expander;

separating the liquid-gas stream with said separator into an upper gas stream and a lower liquid stream;

removing the liquid stream from said separator;

returning said liquid stream from said separator to said absorber which is positioned upstream from said separator and injecting it into an upper region of said absorber, said liquid stream being passed downwardly in said absorber for absorbing propane and heavier hydrocarbon compounds in said absorber;

removing the upper gas stream from said separator for compression into a residue gas;

delivering the bottom liquid stream from said absorber to distilling means located downstream from said separator for generating a bottom propane rich liquid product stream and an upper methane and ethane gas stream; and

removing the bottom propane rich liquid product stream from said distilling means.

2. In the propane recovery process as set forth in claim 1, the method further comprising the step of cross-exchanging said liquid stream from said separator with the upper methane and ethane gas stream removed from said distilling means in a heat exchanger prior to returning said liquid stream to said absorber.

3. In the propane recovery process as set forth in claim 2, the method further comprising the step of cross-exchanging the upper gas stream from said separator with said natural gas stream prior to delivery of said natural gas stream to said absorber.

4. In the propane recovery process as set forth in claim 3, the method further comprising the step of combining said upper methane and ethane gas stream from said distilling means with a separate methane-rich gas stream from said absorber and injecting said combined streams into said separator for subsequent separation into the liquid stream and the upper gas stream.

5. In the propane recovery process as set forth in claim 4, the method further comprising the step of expanding said separate methane-rich gas stream from said absorber prior to combining same with said gas stream from said distillation column.

6. In a propane recovery system, an apparatus comprising:

an absorber for receiving a natural feed gas stream, said absorber providing a downwardly flowing liquid stream for absorbing propane and heavier hydrocarbon compounds therein, said absorber passing the natural feed gas stream upwardly in a counter current manner for providing an upper methane and ethane gas stream;

expansion means positioned downstream from said absorber, said expansion means receiving the upper methane and ethane gas stream for expanding the upper methane and ethane gas stream to produce a liquid-gas stream;

means for separating situated downstream from said expansion means, said separating means receiving the liquid-gas stream therefrom and dividing the liquid-gas stream into an upper gas stream and a lower liquid stream, said absorber receiving the lower liquid stream in an upper region thereof;

compression means located downstream from said separating means, said compression means receiving the upper gas stream from said separating means for compressing the upper gas stream into a residue gas; and

distilling means located downstream from said absorber and receiving a bottom liquids stream therefrom, said distilling means providing a bottom propane product stream and an upper methane and ethane gas stream.

7. In the propane recovery system as set forth in claim 6, wherein said separating means comprises a separator.

8. In the propane recovery system as set forth in claim 7, wherein said distilling means comprises a deethanizer.

9. In the propane recovery system as set forth in claim 8, wherein the upper methane and ethane gas stream from said deethanizer is injected into said separator.

10. In the propane recovery system as set forth in claim 6, wherein said expansion means comprises a turbo-expander.

11. In the propane recovery system as set forth in claim 6, wherein said absorber comprises a reboiled absorber having a plurality of equilibrium absorption stages therein.

12. In the propane recovery system as set forth in claim 11, wherein said separating means comprises a reflux separator.

13. In the propane recovery system as set forth in claim 12, the apparatus further comprising a second reflux separator positioned downstream from said distilling means, said second reflux separator receiving the upper methane and ethane gas stream from said distilling means for generating an upper gas stream and a lower liquid stream, the lower liquid stream being returned to an upper region of said distilling means, the upper gas stream being combined with the upper gas stream from said first reflux separator for producing a residue gas.

14. In the propane recovery system as set forth in claim 13, the apparatus further comprising at least one heat exchanger for cooling the natural feed gas stream and warming the upper gas stream from said first reflux separator.

15. In the propane recovery system as set forth in claim 14, the apparatus further comprising a second heat exchanger receiving the combined upper gas streams from the first and second reflux separators for cooling the natural feed gas stream.

16. In the propane recovery system as set forth in claim 15, the apparatus further comprising a first and a second dividing means, said first dividing means dividing the natural gas feed stream into an upper and lower natural gas feed stream prior to cooling, said second dividing means dividing the upper natural gas feed stream into three streams prior to cooling and introducing the feed streams into said absorber.

21. In the propane recovery system as set forth in claim 6, wherein said absorber comprises a separator.

22. In the propane recovery system as set forth in claim 21, wherein recycled liquids combine with said natural gas feed stream prior to the delivery of said natural gas feed stream to said separator.

17. In a propane recovery system, an apparatus comprising:

a first absorber for receiving a natural feed gas stream on a plurality of absorption stages, said absorber providing a downwardly flowing liquid stream for absorbing propane and heavier hydrocarbon compounds therein, said absorber passing the natural gas feed stream upwardly in a counter current manner for providing an upper methane and ethane gas stream;

expansion means positioned downstream from said first absorber, said expansion means receiving the upper methane and ethane gas stream to produce a liquid-gas stream;

a second absorber situated downstream from said expansion means, said second absorber receiving the liquid/gas stream therefrom and dividing the liquid/gas stream into an upper gas stream and a lower liquid stream, said first absorber receiving the lower liquid stream in an upper region thereof;

compression means located downstream from said second absorber, said compression means receiving the upper gas stream from said second absorber for compressing the upper gas stream into a residue gas stream; and

distilling means located downstream from said first absorber and receiving a bottom liquids stream therefrom, said distilling means providing a bottom propane product stream and an upper methane and ethane gas stream.

18. In the propane recovery system as set forth in claim 17, the apparatus further comprising a reflux separator positioned downstream from said distilling means, said reflux separator receiving the upper methane and ethane gas stream from said distilling means for generating an upper gas stream and a lower liquid stream, the lower liquid stream being returned to an upper region of said distilling means, the upper gas stream being provided to an upper region of said second absorber.

19. In the propane recovery system as set forth in claim 18, the apparatus further comprising a heat exchanger positioned downstream from said reflux separator for cooling the upper gas stream, said heat exchanger receiving the lower liquid stream from said second absorber and using the lower liquid stream for cooling the upper gas stream.

20. In the propane recovery system as set forth in claim 19, wherein said distilling means comprises a deethanizer.