METHOD AND APPARATUS FOR TREATING A HYDROCARBON STREAM

• US 20100162753A1
• Filed: 08/21/2007
• Published: 07/01/2010
• Est. Priority Date: 08/23/2006
• 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:
  US12/438,032
• Publication Number:
  US 20100162753A1
• Time in Patent Office: Days
• US Class Current: 62/611
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2205/30 using a washing, e.g. "scrubbing" or bubble column for purification purposes
• 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 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0214 Liquefied 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 of treating a hydrocarbon stream, the method at least comprising the steps of: supplying a partly condensed feed stream (10). to a first gas/liquid separator (2) and into a gaseous stream (2 and a liquid stream (30); expanding the liquid stream (30) and the gaseous stream (20) and subsequently feeding them into a second gas/liquid separator (3) at a first and second feeding point (32) respectively, the second feeding point (32) being at a higher level than the first feeding point (31); feeding a liquefied natural gas stream (70,70b) into the second gas/liquid separator (3) at a third feeding point (33) being at a higher level than the second feeding point (32); removing from the top of the second gas/liquid separator (3) a C2+ lean gaseous stream (60) and from the bottom a liquid stream (80, 80a); wherein the liquefied ̂natural gas stream (70,70b) is obtained from a source (4) of liquefied natural gas from a separate plant.

Claims

1. Method of treating a hydrocarbon stream in a plant, 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 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) feeding a liquefied natural gas stream 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;

(f) removing from the top of the second gas/liquid separator a C2+ lean gaseous stream; and

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

wherein the liquefied natural gas stream as fed in step (e) is obtained from a source of liquefied natural gas from a separate plant.

2. Method according to claim 1, wherein the liquefied natural gas stream has a temperature below −

100°

C.

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

4. Method according to claim 1, wherein the gaseous stream obtained in step (f) is not liquefied.

5. Method according to claim 1, wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream.

6. Method according to claim 1, wherein the liquefied natural gas stream as fed in step (e) has been previously heat exchanged against the feed stream.

7. Method according to claim 1, wherein the liquid stream removed from the bottom of the second gas/liquid separator is subjected to fractionation thereby obtaining two or more products including ethane.

8. Method according to claim 1, wherein >

75 mole % of the ethane present in the partially partly condensed feed stream is recovered in the liquid stream obtained in step (g).

9. Method according to claim 1, wherein the pressure drop during expanding in step (d) is less than 15 bar.

10. Method according to claim 1, wherein the pressure in the second gas/liquid separator is from 15 to 40 bar.

11. Method according to claim 1, wherein the C2+ lean gaseous stream removed from the top of the second gas/liquid separator in step (f) is a gaseous stream comprising <

(less than) 10 mole % hydrocarbons having 2 or more carbon atoms.

12. Method according to claim 1, wherein the source of liquefied natural gas from a separate plant is a liquefied natural gas storage tank at a liquefied natural gas import terminal.

15. Method according to claim 2, wherein the gaseous stream obtained in step (f) is sent to a gas network.

16. Method according to claim 2, wherein the gaseous stream obtained in step (f) is not liquefied.

17. Method according to claim 3, wherein the gaseous stream obtained in step (f) is not liquefied.

18. Method according to claim 2, wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream.

19. Method according to claim 3, wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream.

20. Method according to claim 4, wherein the gaseous stream obtained in step (f) is heat exchanged against the feed stream.

13. Apparatus for treating a hydrocarbon stream in a plant, 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 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 feeding points, the third feeding point being at a higher level in the gas/liquid separator than the second feeding point, said second feeding point being at a higher level in the gas/liquid separator than the first feeding point;

a first expander for expanding the gaseous stream obtained from the first outlet of the first gas/liquid separator, the first expander having an outlet which is connected to the second feeding point of the second gas/liquid separator; and

a second expander for expanding the liquid stream obtained from the second outlet of the first gas/liquid separator, the second expander having an outlet which is connected to the first feeding point of the second gas/liquid separator;

wherein the third feeding point is connected to a source of liquefied natural gas from a separate plant.

14. Apparatus according to claim 13 wherein the source of liquefied natural gas from a separate plant is a liquefied natural gas storage tank at a liquefied natural gas import terminal.