Method and Apparatus for Liquefying a Natural Gas Stream

• US 20090064713A1
• Filed: 04/10/2006
• Published: 03/12/2009
• Est. Priority Date: 04/12/2005
• Status: Abandoned Application

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: De Jong, Emilius Carolus Joanes Nicolaas, Buijs, Cornelis, Dam, Willem
• Application Number:
  US11/918,162
• Publication Number:
  US 20090064713A1
• Time in Patent Office: Days
• US Class Current: 62/613
• 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 1/0042 by liquid expansion with extraction of work
• CPC Class Codes: F25J 1/0055 originating from an incorporated cascade
• CPC Class Codes: F25J 1/0214 as a dual level refrigeration cascade with at least one MCR cycle
• CPC Class Codes: F25J 1/0216 using a C3 pre-cooling cycle
• CPC Class Codes: F25J 1/0238 Purification or treatment step is integrated within one refrigeration cycle only, i.e. the same or single refrigeration cycle provides feed gas cooling (if present) and overhead gas cooling
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• CPC Class Codes: F25J 2220/62 Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2220/64 Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons

Abstract

The present invention relates to a method of liquefying a natural gas stream, wherein the natural gas stream (10) is provided at a pressure of 10-80 bar, supplied to a gas/liquid separator (31), and separated into a vaporous stream (40) and a liquid stream (30). The vaporous stream (40) is compressed to a pressure of at least 70, 84 bar heat exchanged against the vaporous stream (40), and liquefied to obtain a liquefied natural gas stream (100).

Claims

1. A method of liquefying a natural gas stream, the method comprising the steps of:

(a) providing a feed stream containing natural gas at a pressure of 10-80 bar;

(b) supplying the feed stream provided in step (a) to a gas/liquid separator;

(c) separating the feed stream in the gas/liquid separator into a vaporous stream and a liquid stream, the vaporous stream being enriched in methane relative to the feed stream, and the liquid stream being reduced in methane relative to the feed stream;

(d) compressing the vaporous stream obtained in step (c) thereby obtaining a compressed stream having a pressure of at least 70 bar;

(e) liquefying the compressed stream obtained in step (d) thereby obtaining a liquefied natural gas stream;

wherein the compressed stream obtained in step (d), before it is liquefied in step (e), is heat exchanged against the vaporous stream obtained in step (c),

and wherein the pressure of the feed stream as provided in step (a) is not increased until the compressing in step (d).

2. The method according to claim 1, wherein in step (d) the pressure is increased to at least 86 bar.

3. The method according to claim 1, wherein the vapour stream obtained in step (c) has a C₅⁺ content of below 0.5 mol %.

4. The method according to claim 1, wherein the compressed stream obtained in step (d) is cooled, before it is heat exchanged against the vaporous stream obtained in step (c).

5. The method according to claim 1, wherein the feed stream provided in step (a), before supplying to the gas/liquid separator in step (b), is expanded.

6. The method according to claim 5, wherein an expander for expanding the feed stream is functionally coupled to a compressor for compressing the vaporous stream in step (d).

11. The method according to claim 1, wherein in step (d) the pressure is increased to at least 84 bar.

12. The method according to claim 1, wherein in step (d) the pressure is increased to at least 90 bar.

17. The method according to claim 2, wherein the vapour stream obtained in step (c) has a C₅⁺ content of below 0.5 mol %.

18. The method according to claim 11, wherein the vapour stream obtained in step (c) has a C₅⁺ content of below 0.5 mol %.

19. The method according to claim 12, wherein the vapour stream obtained in step (c) has a C₅⁺ content of below 0.5 mol %.

20. The method according to claim 1, wherein the vapour stream obtained in step (c) has a C₅⁺ content of below 0.1 mol %.

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

means for providing a feed stream containing natural gas at a pressure of 10-80 bar;

a gas/liquid separator for separating the feed stream into a vaporous stream and a liquid stream, the vaporous stream being enriched in methane relative to the feed stream, and the liquid stream being reduced in methane relative to the feed stream;

a compressor for increasing the pressure of the vaporous stream obtained in the gas/liquid separator to a pressure of at least 70 bar, thereby obtaining a compressed stream;

a heat exchanger for heat exchanging the compressed stream against the vaporous stream obtained from the gas/liquid separator; and

a liquefaction unit for liquefying an effluent from the heat exchanger having a pressure of at least 70 bar, the liquefaction unit comprising at least one cryogenic heat exchanger.

8. The apparatus according to claim 7, wherein the apparatus further comprises an expander for expanding the feed stream before it is supplied to the gas/liquid separator.

9. The apparatus according to claim 8, wherein the compressor and expander are functionally coupled.

10. The apparatus according to claim 7, wherein no compressor is present between the means for providing the feed stream at a pressure of 10-80 bar and the compressor for increasing the pressure of the vaporous stream.

13. A method of liquefying a natural gas stream, the method comprising the steps of:

(a) providing a feed stream containing natural gas at a pressure of 10-50 bar;

(b) supplying the feed stream provided in step (a) to a gas/liquid separator;

(c) separating the feed stream in the gas/liquid separator into a vaporous stream and a liquid stream, the vaporous stream being enriched in methane relative to the feed stream, and the liquid stream being reduced in methane relative to the feed stream;

(d) compressing the vaporous stream obtained in step (c) thereby obtaining a compressed stream having a pressure of at least 70 bar;

(e) liquefying the compressed stream obtained in step (d) thereby obtaining a liquefied natural gas stream;

wherein the compressed stream obtained in step (d), before it is liquefied in step (e), is heat exchanged against the vaporous stream obtained in step (c),

and wherein the pressure of the feed stream as provided in step (a) is not increased until the compressing in step (d).

14. The method according to claim 13, wherein in step (d) the pressure is increased to at least 84 bar.

15. The method according to claim 13, wherein in step (d) the pressure is increased to at least 86 bar.

16. The method according to claim 13, where in step (d) the pressure is increased to at least 90 bar.