Treating Liquefied Natural Gas

• US 20080066492A1
• Filed: 07/12/2005
• Published: 03/20/2008
• Est. Priority Date: 07/12/2004
• Status: Abandoned Application

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Buijs, Cornelis, Klein Nagelvoort, Robert, Pek, Johan
• Application Number:
  US11/632,105
• Publication Number:
  US 20080066492A1
• Time in Patent Office: Days
• US Class Current: 62/612
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/40 Features relating to the provision of boil-up in the bottom of a column
• CPC Class Codes: F25J 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• 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 2215/04 Recovery of liquid products
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2235/60 the fluid being (a mixture of) hydrocarbons
• 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 2245/90 the recycled stream being boil-off gas from storage
• 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 2270/42 Quasi-closed internal or closed external nitrogen refrigeration cycle
• CPC Class Codes: F25J 2290/40 Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
• CPC Class Codes: F25J 2290/62 Details of storing a fluid in a tank
• 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 3/0257 separation of nitrogen from air F25J3/04, production of nitrogen in general C01B21/00

Abstract

Method of treating liquefied natural gas (1) to obtain a liquid stream (21) having a reduced content of components having low boiling points comprising expanding (3) the liquefied gas to expand to obtain expanded two-phase fluid; introducing the two-phase fluid into a column (10) below a gas-liquid contacting section (14); withdrawing from the bottom (16) a liquid-stream (17) having a reduced content of components having low boiling points; withdrawing from the top (23) of the column (10) a gaseous stream (25) enriched in components having low boiling points; heating the gaseous stream in a heat exchanger (27); compressing (30) the stream to fuel gas pressure to obtain fuel gas (33); separating a recycle stream (34a) from the fuel gas; at least partly condensing (27) the recycle stream to obtain a reflux stream (34b); and introducing the reflux stream (34b) into the column (10) above the contacting section (14).

Claims

1. A method of treating liquefied natural gas supplied at liquefaction pressure containing components having low boiling points to obtain a liquid product stream having a reduced content of components having low boiling points, which method comprises the steps of:

(a) allowing the liquefied gas to expand to separation pressure to obtain an expanded two-phase fluid;

(b) introducing the expanded two-phase fluid into a column, the column comprising a single gas-liquid contacting section, wherein the expanded two-phase fluid is introduced below the single gas-liquid contacting section arranged in the column;

(c) collecting in the bottom of the column liquid from the two-phase fluid and withdrawing from the bottom of the column a liquid stream having a reduced content of components having low boiling points to obtain the liquid product stream;

(d) allowing vapor from the two-phase fluid to flow through the single contacting section;

(e) withdrawing from the top of the column a gaseous stream that is enriched in components having low boiling points;

(f) heating the gaseous stream obtained in step (c) in a heat exchanger to obtain a heated gaseous stream;

(g) compressing the heated gaseous stream obtained in step (f) to fuel gas pressure to obtain fuel gas;

(h) separating a recycle stream from the fuel gas obtained in step (g);

(i) at least partly condensing the recycle stream obtained in step (h) to obtain a reflux stream; and

(j) introducing the reflux stream obtained in step (i) at separation pressure into the column above the single contacting section.

2. The method according to claim 1, wherein step (c) comprises collecting in the bottom of the column liquid from the two-phase fluid and withdrawing from the bottom of the column a liquid stream having a reduced content of components having low boiling points;

introducing the liquid stream having a reduced content of components having low boiling points into a flash vessel at a low pressure;

removing a second gaseous stream from the top of the flash vessel; and

removing from the bottom of the flash vessel a liquid stream to obtain the liquid product stream.

3. The method according to claim 2, further comprising heating the second gaseous stream in the heat exchanger;

compressing the second gaseous stream to fuel gas pressure; and

adding the second gaseous stream to the recycle stream.

4. The method according to claim 1, wherein at least partly condensing the recycle stream in step (i) comprises indirectly heat exchanging the recycle stream with the gaseous stream(s) in the heat exchanger.

5. The method according to claim 1, wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.

6. The method according to claim 1, wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.

7. The method according to claim 1, wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.

8. The method according to claim 2, wherein at least partly condensing the recycle stream in step (i) comprises indirectly heat exchanging the recycle stream with the gaseous stream(s) in the heat exchanger.

9. The method according to claim 3, wherein at least partly condensing the recycle stream in step (i) comprises indirectly heat exchanging the recycle stream with the gaseous stream(s) in the heat exchanger.

10. The method according to claim 2, wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.

11. The method according to claim 3, wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.

12. The method according to claim 4, wherein compressing the heated gaseous stream to fuel gas pressure to obtain fuel gas in step (g) further includes removing the heat of compression.

13. The method according to claim 2, wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.

14. The method according to claim 3, wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.

15. The method according to claim 4, wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.

16. The method according to claim 5, wherein the recycle stream separated from the fuel gas in step (h) is compressed to an elevated pressure before it is at least partly condensed.

17. The method according to claim 2, wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.

18. The method according to claim 3, wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.

19. The method according to claim 4, wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.

20. The method according to claim 5, wherein the supplied liquefied natural gas comprises less than 7 mol % of components having low boiling points.