METHOD FOR TREATING A HYDROCARBON STREAM

• US 20090194461A1
• Filed: 05/30/2007
• Published: 08/06/2009
• Est. Priority Date: 05/30/2006
• Status: Abandoned Application

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Bras, Eduard Coenraad, Chieng, Jill Hui Chiun, Wani, Akash Damodar
• Application Number:
  US12/302,299
• Publication Number:
  US 20090194461A1
• Time in Patent Office: Days
• US Class Current: 208/368
• CPC Class Codes: C10L 3/10 Working-up natural gas or synthetic natural gas
• CPC Class Codes: C10L 3/102 of acid contaminants
• CPC Class Codes: F25J 2200/02 in a single 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 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/62 Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
• CPC Class Codes: F25J 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• 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 2240/04 Multiple expansion turbines in parallel
• CPC Class Codes: F25J 2270/904 by liquid or gaseous cryogen in an open 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 3/0238 separation of CnHm with 2 carbon atoms or more

Abstract

The present invention relates to a method for treating a natural gas feed stream, containing >10 mole % CO₂, the method at least comprising the steps of separating the feed stream (10) in a first (2) or a second (3) gas/liquid separator, removing from the top of the second gas/liquid separator (3) a gaseous stream (60), partially condensing it by heat exchanging against a cold stream (120) and feeding it (70) into a third gas/liquid separator (4) thereby obtaining a liquid stream (80) and a gaseous stream (90) and feeding the liquid stream (80) having a temperature above the freezing point of CO₂ at the prevailing conditions, into the second gas/liquid separator (3) removing from the bottom of the second gas/liquid separator (3) a liquid stream (100, 100a).

Claims

1. Method for treating a hydrocarbon stream containing >

10 mole % CO₂, the method at least comprising the steps of;

(a) supplying a partly condensed feed stream containing >

10 mole % CO₂ to a first gas/liquid separator;

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

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

(d) expanding the gaseous stream obtained in step (b), thereby obtaining an at least partially condensed stream, and subsequently feeding it into the second gas/liquid separator 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 second gas/liquid separator a gaseous stream, partially condensing it and feeding it into a third gas/liquid separator;

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

(g) feeding the liquid stream obtained in step (f), having a temperature above the freezing point of CO₂ at the prevailing conditions, into the second gas/liquid separator at a third feeding point, the third feeding point being at a higher level than the second feeding point; and

(h) removing from the bottom of the second gas/liquid separator a liquid stream;

wherein the gaseous stream removed from the second gas/liquid separator in step (e) is partially condensed by heat exchanging against a cold stream, which is selected such that the partially condensed stream obtained in step (e) has a temperature greater than or equal to −

60°

C. and wherein all streams being fed into the second gas/liquid separator fully originate from the feed stream.

2. Method according to claim 1, wherein the cold stream is selected such that the partially condensed stream obtained in step (e) has a temperature above the freezing point of CO₂ at the prevailing conditions.

3. Method according to claim 1, wherein the temperature of the liquid stream obtained in step (f) is at or above −

60°

C. near the third feeding point.

4. Method according to claim 1, wherein the cold stream is obtained from a separate source of liquefied natural gas (LNG).

5. Method according to claim 1, wherein >

75% by weight of the propane present in the partially condensed feed stream is recovered in the liquid stream obtained in step (h).

6. Method according to claim 1, wherein the partially condensed feed stream contains >

15 mole % CO₂.

7. Method according to claim 1, wherein the partially condensed feed stream has a pressure >

20 bar.

8. Method according to claim 1, wherein the pressure in the second gas/liquid separator is in the range from 10 to 50 bar.

9. Method according to claim 1, wherein the gaseous stream obtained in step (f) is sent to a gas network.

10. Method according to claim 1, wherein the gaseous stream obtained in step (f) is liquefied thereby obtaining a liquefied hydrocarbon stream.

11. Method according to claim 1, wherein the liquid stream removed from the bottom of the second gas/liquid separator is subjected to distillation thereby obtaining two or more distilled streams.

12. Method according to claim 1, wherein the partially condensed feed stream has been previously cooled against a cold stream.

13. Method according to claim 1, wherein the temperature of the liquid stream obtained in step (f) is at or above −

55°

C. near the third feeding point.

14. Method according to claim 1, wherein the cold stream is selected such that the partially condensed stream obtained in step (e) has a temperature from −

60°

C. to −

40°

C.

15. Method according to claim 1, wherein the cold stream is selected such that the partially condensed stream obtained in step (e) has a temperature greater than or equal to −

55°

C.

16. Method according to claim 2, wherein the temperature of the liquid stream obtained in step (f) is at or above −

60°

C. near the third feeding point.

17. Method according to claim 2, wherein the cold stream is obtained from a separate source of liquefied natural gas (LNG).

18. Method according to claim 3, wherein the cold stream is obtained from a separate source of liquefied natural gas (LNG).

19. Method according to claim 2, wherein >

75% by weight of the propane present in the partially condensed feed stream is recovered in the liquid stream obtained in step (h).

20. Method according to claim 3, wherein >

75% by weight of the propane present in the partially condensed feed stream is recovered in the liquid stream obtained in step (h).