METHOD AND APPARATUS FOR LIQUEFYING A NATURAL GAS STREAM

• US 20090277218A1
• Filed: 04/10/2007
• Published: 11/12/2009
• Est. Priority Date: 04/12/2006
• Status: Active Grant

• Current Assignee: Shell USA Incorporated (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Poh, Chun Kit, Kevenaar, Mark Antonius
• Granted Patent: US 9,726,425 B2
• Time in Patent Office: Days
• US Class Current: 62/612
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0035 by gas expansion with extraction of work
• CPC Class Codes: F25J 1/0045 by vaporising a liquid return stream
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0087 Propane; Propylene
• CPC Class Codes: F25J 1/0237 integrating refrigeration provided for liquefaction and purification/treatment of the gas to be liquefied, e.g. heavy hydrocarbon removal from natural gas details related to rectification F25J3/02; details related to partial condensation F25J3/06; working-up natural gas C10L3/10
• CPC Class Codes: F25J 2200/04 in a dual 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 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• 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 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 2260/02 Integration in an installation for exchanging heat, e.g. for waste heat recovery
• CPC Class Codes: F25J 2260/20 Integration in an installation for liquefying or solidifying a fluid stream
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• 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 2270/60 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

The present invention relates to a method of liquefying a hydrocarbon stream such as a natural gas stream, the method at least comprising the steps of: supplying a partly condensed hydrocarbon feed stream (10) to a first gas/liquid separator (2); separating the feed stream (10) in the first gas/liquid separator (2) into a gaseous stream (20) and a liquid stream (30); expanding the gaseous stream (20) thereby obtaining an expanded stream (40) and feeding it (40) into a second gas/liquid separator (3); feeding the liquid stream (30) into the second gas/liquid separator (3); removing from the bottom of the second gas/liquid separator a liquid stream (60) and feeding it into a fractionation column (5); removing from the top of the second gas/liquid separator (3) a gaseous stream (50) and passing it to a compressor (6) thereby obtaining a compressed stream (70); cooling the compressed stream (70) thereby obtaining a cooled compressed stream (80); heat exchanging the cooled compressed stream (80) against a stream being downstream of the first gas/liquid separator (2) and upstream of the fractionation column (5).

Claims

1. A method of liquefying a hydrocarbon stream, the method at least comprising the steps of:

(a) supplying a partly condensed hydrocarbon feed stream to a first gas/liquid separator;

(b) separating the feed stream in the first gas/liquid separator into a gaseous stream and a liquid stream;

(c) expanding the gaseous stream obtained in step (b) thereby obtaining an expanded stream and feeding it into a second gas/liquid separator at a first feeding point;

(d) feeding the liquid stream obtained in step (b) into the second gas/liquid separator at a second feeding point;

(e) removing from the bottom of the second gas/liquid separator a liquid stream and feeding it into a fractionation column;

(f) removing from the top of the second gas/liquid separator a gaseous stream and passing it to a compressor thereby obtaining a compressed stream having a pressure above 50 bar;

(g) cooling the compressed stream obtained in step (f) thereby obtaining a cooled compressed stream;

(h) heat exchanging the cooled compressed stream obtained in step (g) against a stream being downstream of the first gas/liquid separator and upstream of the fractionation column; and

(i) liquefying the cooled compressed stream, after heat exchanging in step (h), thereby obtaining a liquefied stream.

2. The method according to claim 1, wherein in step (h) the cooled compressed stream is heat exchanged against the liquid stream removed in step (e) from the second gas/liquid separator.

3. The method according to claim 1, wherein in step (h) the cooled compressed stream is heat exchanged against at least a part of the expanded stream obtained in step (c).

4. The method according to claim 1, wherein from the top of the fractionation column a gaseous stream is removed that is heat exchanged against at least a part of the bottom stream from the second gas/liquid separator.

5. The method according to claim 1, wherein the gaseous stream removed in step (f) from the top of the second gas/liquid separator is heat exchanged against the feed stream, before it is fed to the compressor.

6. The method according to claim 5, wherein the gaseous stream removed from the fractionation column, after heat exchanging against at least a part of the bottom stream from the second gas/liquid separator, is heat exchanged against the gaseous stream removed from the second gas/liquid separator.

13. The method according to claim 1, wherein the hydrocarbon stream is a natural gas stream.

14. The method according to claim 1, wherein the heat exchanging in step (h) is directly heat exchanging.

16. The method according to claim 2, wherein in step (h) the cooled compressed stream is heat exchanged against at least a part of the expanded stream obtained in step (c).

17. The method according to claim 2, wherein from the top of the fractionation column a gaseous stream is removed that is heat exchanged against at least a part of the bottom stream from the second gas/liquid separator.

18. The method according to claim 3, wherein from the top of the fractionation column a gaseous stream is removed that is heat exchanged against at least a part of the bottom stream from the second gas/liquid separator.

19. The method according to claim 2, wherein the gaseous stream removed in step (f) from the top of the second gas/liquid separator is heat exchanged against the feed stream, before it is fed to the compressor.

20. The method according to claim 3, wherein the gaseous stream removed in step (f) from the top of the second gas/liquid separator is heat exchanged against the feed stream, before it is fed to the compressor.

7. An apparatus for liquefying a hydrocarbon stream, the apparatus at least comprising:

a first gas/liquid separator having an inlet for a partly condensed hydrocarbon feed stream, a first outlet for a gaseous stream and a second outlet for a liquid stream;

a second gas/liquid separator having at least a first outlet for a gaseous stream and a second outlet for a liquid stream and first and second feeding points;

an expander for expanding the gaseous stream obtained from the first outlet of the first gas/liquid separator, thereby obtaining an expanded stream, the outlet of the expander being connected to a feeding point of the second gas/liquid separator;

a fractionation column having at least a first outlet for a gaseous stream and a second outlet for a liquid stream and a first feeding point for receiving a liquid stream removed from the second outlet of the second gas/liquid separator;

a compressor for compressing the gaseous stream removed from the first outlet of the second gas/liquid separator thereby obtaining a compressed stream;

a cooler for cooling the compressed stream obtained from the compressor thereby obtaining a cooled compressed stream;

a first heat exchanger for heat exchanging the cooled compressed stream against a stream being downstream of the first gas/liquid separator and upstream of the fractionation column; and

a liquefaction unit for liquefying the cooled compressed stream, downstream of the first heat exchanger, the liquefaction unit comprising at least one cryogenic heat exchanger.

8. An apparatus according to claim 7, wherein the cooled compressed stream can be heat exchanged in the first heat exchanger against the liquid stream removed from the second gas/liquid separator.

9. An apparatus according to claim 7, wherein the cooled compressed stream can be heat exchanged in the first heat exchanger against at least a part of the expanded stream.

10. An apparatus according to claim 7, further comprising a second heat exchanger between the second outlet of the second gas/liquid separator and the first feeding point of the fractionation column, in which second heat exchanger a gaseous stream removed from the top of the fractionation column can be heat exchanged against at least a part of the bottom stream from the second gas/liquid separator.

11. An apparatus according to claim 7, further comprising a third heat exchanger in which the gaseous stream removed from the top of the second gas/liquid separator can be heat exchanged against the feed stream, before it is fed to the compressor.

12. An apparatus according to claim 10, further comprising a heat exchanger for heat exchanging the gaseous stream removed from the fractionation column, after heat exchanging in the second heat exchanger, against the gaseous stream removed from the second gas/liquid separator.

15. An apparatus according to claim 7, wherein heat exchanging is direct heat exchanging.