METHOD AND APPARATUS FOR TREATING A HYDROCARBON STREAM

• US 20100064725A1
• Filed: 10/23/2007
• Published: 03/18/2010
• Est. Priority Date: 10/24/2006
• Status: Abandoned Application

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Chieng, Jill Hui Chiun, Wani, Akash Damodar
• Application Number:
  US12/446,622
• Publication Number:
  US 20100064725A1
• 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 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 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 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 2270/904 by liquid or gaseous cryogen in an open loop
• CPC Class Codes: F25J 2290/12 Particular process parameters like pressure, temperature, ratios
• 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

In a method of treating a hydrocarbon stream, such as a natural gas stream, a partly condensed feed stream (10) is supplied to a first gas/liquid separator (2), where it is separated into a gaseous stream (20) and a liquid stream (30). The liquid stream (30) is expanded and fed (40) into a second gas/liquid separator (3), and the gaseous stream (20) is split into at least two sub-streams (50, 70). A first sub-stream (50) of the at least two sub-streams is expanded, thereby obtaining an at least partially condensed first sub-stream (60), and subsequently fed (60) into the second gas/liquid separator (3). A second sub-stream (70) of the at least two sub-streams is cooled against a cold stream (120), thereby obtaining an at least partially condensed second sub-stream (90, 90a), which is fed (90, 90a) into the second gas/liquid separator (3) from which a gaseous stream (130) and a liquid stream (100, 100a) are removed. The at least partially condensed second sub-stream (90, 90a) may have a temperature of below −95° C.

Claims

1. Method of treating a hydrocarbon stream, the method at least comprising the steps of:

(a) supplying a partly condensed 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 liquid stream obtained in step (b) and feeding it into a second gas/liquid separator;

(d) splitting the gaseous stream into at least two sub-streams;

(e) expanding a first sub-stream obtained in step (d), thereby obtaining an at least partially condensed first sub-stream, and subsequently feeding it into the second gas/liquid separator;

(f) cooling a second sub-stream obtained in step (d) against a cold stream, thereby obtaining an at least partially condensed second sub-stream, and subsequently feeding the at least partially condensed second sub-stream into the second gas/liquid separator;

(g) removing from the second gas/liquid separator a gaseous stream; and

(h) removing from the second gas/liquid separator a liquid stream.

2. Method according to claim 1, wherein the at least partially condensed second sub-stream obtained in step (f) has a temperature below −

95°

C.

3. Method according to claim 2, wherein said temperature is above −

125°

C.

4. Method according to claim 1, wherein the gaseous stream removed from the second gas/liquid separator in step (g) is warmed by heat exchanging against the second sub-stream before the second sub-stream is cooled against the cold stream.

5. Method according to claim 1, wherein in step (d) a split ratio is used such that a ratio for the second sub-stream to the gaseous stream is obtained in the range of 0.3 to 0.9.

6. Method according to claim 1, wherein the cold stream is not a refrigerant stream being cycled in a closed refrigerant cycle.

7. Method according to claim 1, wherein the cold stream is obtained from a separate source of a liquefied hydrocarbon product.

8. Method according to claim 1, wherein >

75 mol % of the ethane present in the partially condensed feed stream is recovered in the liquid stream obtained in step (h).

9. Method according to claim 1, wherein the pressure in the second gas/liquid separator is from 15 to 30 bar.

10. Method according to claim 1, wherein at least a part of the gaseous stream obtained in step (g) is sent to a gas network.

11. Method according to claim 1, wherein at least a part of the gaseous stream obtained in step (g) is liquefied thereby obtaining a liquefied hydrocarbon stream.

12. Method according to claim 1, wherein at least a part of the liquid stream removed from the bottom of the second gas/liquid separator is subjected to fractionation thereby obtaining two or more fractionated streams.

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

17. Method according to claim 1, wherein the at least partially condensed second sub-stream obtained in step (f) has a temperature below −

100°

C.

18. Method according to claim 1, wherein the at least partially condensed second sub-stream obtained in step (f) has a temperature below −

110°

C.

19. Method according to claim 17, wherein said temperature is above −

125°

C.

20. Method according to claim 18, wherein said temperature is above −

125°

C.

14. Apparatus for treating a hydrocarbon stream, the apparatus at least comprising:

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

a splitter connected to the first outlet of the first gas/liquid separator for splitting the gaseous stream into at least a first sub-stream and a second sub-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, second and third inlets;

a first expander connected to the second outlet of the first gas/liquid separator for expanding the liquid stream;

a second expander for expanding the first sub-stream obtained from the splitter;

a first heat exchanger between the splitter and an inlet of the second gas/liquid separator, in which first heat exchanger the second sub-stream can be cooled against a cold stream.

15. Apparatus according to claim 14, wherein the cold stream can be obtained from a separate source of a liquefied hydrocarbon product.

16. Apparatus according to claim 14, further comprising a second heat exchanger between the splitter and the first heat exchanger, in which second heat exchanger the gaseous stream obtained from the first outlet of the second gas/liquid separator can be warmed against the second sub-stream.