METHOD AND APPARATUS FOR LIQUEFYING A HYDROCARBON STREAM

• US 20090107174A1
• Filed: 03/16/2007
• Published: 04/30/2009
• Est. Priority Date: 03/24/2006
• Status: Active Grant

• Current Assignee: Shell USA Incorporated (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Lee, Hsiao Teing, Ambari, Intan Agustina
• Granted Patent: US 8,434,326 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 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• 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 2230/60 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 2240/30 Dynamic liquid or hydraulic expansion with extraction of work, e.g. single phase or two-phase turbine
• 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 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

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 feed stream (10) having a pressure above 60 bar to a first separator (2) wherein it is separated into a gaseous stream (20) and a liquid stream (30); expanding the liquid stream (30) and the gaseous stream (20) and subsequently feeding them into the distillation column (3); removing from the distillation column (3) a gaseous overhead stream (80), partially condensing it, feeding it (90) into a second separator (8) thereby obtaining a liquid stream (100) and a gaseous stream (110), feeding the liquid stream (100) into the distillation column (3) and liquefying the gaseous stream (110) thereby obtaining a liquefied stream (200); wherein the gaseous overhead stream (80) is partially condensed by heat exchanging against the expanded gaseous stream (60) before it (70) is fed into the distillation column (3); and wherein the gaseous stream (110) is removed from the second separator but before it (160) is liquefied, is heat exchanged against the feed stream (10a), thereby partially condensing the feed stream (10a).

Claims

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

(a) supplying a partly condensed feed stream having a pressure above 60 bar to a first gas/liquid separator;

(b) separating the feed stream in the first gas/liquid separator into a gaseous stream, which gaseous stream is removed from the first gas/liquid separator at a first outlet, and a liquid stream;

(c) expanding the liquid stream obtained in step (b) and feeding it into a distillation column at a first feeding point;

(d) expanding the gaseous stream removed at the first outlet of the first gas/liquid separator in step (b), thereby obtaining an expanded stream which is at least partially condensed, and subsequently feeding it into the distillation column at a second feeding point, the second feeding point being at a higher level than the first feeding point;

(e) removing from the top of the distillation column a gaseous stream, partially condensing it and feeding it into a second gas/liquid separator;

(f) separating the stream fed in the second gas/liquid separator in step (e) thereby obtaining a liquid stream and a gaseous stream;

(g) feeding the liquid stream obtained in step (f) into the distillation column at a third feeding point, the third feeding point being at a higher level than the second feeding point; and

(h) liquefying the gaseous stream obtained in step (f) thereby obtaining a liquefied stream;

wherein the gaseous stream removed from the distillation column in step (e) is partially condensed by heat exchanging against the stream expanded in step (d) before it is fed into the distillation column at the second feeding point; and

wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream of step (a) before it is liquefied in step (h), thereby partially condensing the feed stream.

2. The method according to claim 1, wherein the gaseous stream obtained in step (b) is not cooled before it is expanded in step (d).

3. The method according to claim 1, wherein the liquid stream obtained in step (b) is heat exchanged against the feed stream before it is fed into the first gas/liquid separator in step (a).

4. The method according to claim 1, wherein the pressure of the gaseous stream obtained in step (f), is increased to a pressure of at least 70 bar, before it is liquefied.

5. The method according to claim 1, wherein a liquid stream is removed from the bottom of the distillation column, which liquid stream is subjected to further fractionation.

6. The method according to claim 1, wherein the gaseous stream is directly heat exchanged against the feed stream of step (a).

7. The method according to claim 1, wherein the partly condensed feed stream as supplied in step (a) has a temperature of below −

35°

C.

15. The method according to claim 2, wherein the liquid stream obtained in step (b) is heat exchanged against the feed stream before it is fed into the first gas/liquid separator in step (a).

16. The method according to claim 2, wherein the pressure of the gaseous stream obtained in step (f) is increased to a pressure of at least 70 bar, before it is liquefied.

17. The method according to claim 3, wherein the pressure of the gaseous stream obtained in step (f) is increased to a pressure of at least 70 bar, before it is liquefied.

18. The method according to claim 1, wherein the pressure of the gaseous stream obtained in step (f) is increased to a pressure of at least 84 bar, before it is liquefied.

19. The method according to claim 1, wherein the pressure of the gaseous stream obtained in step (f) is increased to a pressure of at least 86 bar, before it is liquefied.

20. The method according to claim 1, wherein the pressure of the gaseous stream obtained in step (f) is increased to a pressure of at least 90 bar, before it is liquefied.

8. An apparatus for liquefying a hydrocarbon stream such as a natural gas stream, the apparatus at least comprising:

a first gas/liquid separator having an inlet for a partly condensed feed stream having a pressure above 60 bar, a first outlet for a gaseous stream and a second outlet for a liquid stream;

a distillation column having at least a first outlet for a gaseous stream and a second outlet for a liquid stream and first, second and third feeding points, the third feeding point being at a higher level than the second feeding point and the second feeding point being at a higher level than the first feeding point;

a first expander for expanding the gaseous stream obtained from the first outlet of the first gas/liquid separator;

a second expander between the second outlet of the first gas/liquid separator and the first feeding point of the distillation column, for expanding the liquid stream obtained from the second outlet of the first gas/liquid separator;

a first heat exchanger between the first expander and the second feeding point of the distillation column, arranged to receive the expanded stream from the first expander;

a second gas/liquid separator having an inlet for the stream obtained at the first outlet of the distillation column, a first outlet for a gaseous stream and a second outlet for a liquid stream, the second outlet being connected to the third feeding point of the distillation column;

a liquefaction unit for liquefying the gaseous stream obtained at the first outlet of the second gas/liquid separator, the liquefaction unit comprising at least one cryogenic heat exchanger; and

a further heat exchanger for heat exchanging the gaseous stream obtained at the first outlet of the second gas/liquid separator against the feed stream, before it is liquefied in the liquefaction unit;

wherein the first heat exchanger is placed between the first outlet of the distillation column and the inlet of the second gas/liquid separator.

9. An apparatus according to claim 8, wherein between the first outlet of the first gas/liquid separator and the first expander no cooler is present.

10. An apparatus according to claim 8, comprising a second heat exchanger between the second expander and the first feeding point of the distillation column.

11. An apparatus according to claim 10, wherein the feed stream can be cooled in the second heat exchanger against the liquid stream obtained from the second outlet of the first gas/liquid separator.

12. An apparatus according to claim 10, wherein the further heat exchanger comprises a third heat exchanger between the second heat exchanger and the first inlet of the gas/liquid separator in which the gaseous stream obtained at the first outlet of the second gas/liquid separator can be heat exchanged against the feed stream.

13. An apparatus according to claim 12, wherein the further heat exchanger comprises a fourth heat exchanger upstream of the second heat exchanger in which the gaseous stream obtained at the first outlet of the second gas/liquid separator, after being heat exchanged in the third heat exchanger, can be further heat exchanged against the feed stream.

14. An apparatus according to claim 8, wherein the second outlet of the distillation column is connected to a fractionation unit.