Method and apparatus for liquefying a gaseous hydrocarbon stream

Patent metadata

Field	Value
Publication number	US-9625208-B2
Application number	US-66858208-A
Country	US
Kind code	B2
Filing date	Jul 10, 2008
Priority date	Jul 12, 2007
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

A method and apparatus for liquefying a gaseous hydrocarbon stream such as natural gas. The method comprises at least the steps of providing a feed stream ( 10 ) and dividing the feed stream ( 10 ) to provide at least a first stream ( 20 ) and a second stream ( 30 ). The first stream ( 20 ) is liquefied using heat exchange against a liquid nitrogen stream ( 40 ) to provide a first liquefied hydrocarbon stream ( 60 ) and an at least partly evaporated nitrogen stream ( 70 ). The second stream ( 20 ) is cooled and liquefied by heat exchanging against the at least partly evaporated nitrogen stream ( 70 ) to provide a second cooled hydrocarbon stream ( 80 ).

First claim

What is claimed is:

1. A method of liquefying a gaseous hydrocarbon stream, the method at least comprising the steps of:
(a) providing a feed stream comprising the gaseous hydrocarbon stream at an elevated pressure;
(b) dividing the feed stream of step (a) to provide at least a first stream and a second stream;
(c) expanding the first stream or compressing the second stream, or both;
(d) cooling and liquefying the first stream downstream of step (c) by heat exchanging exclusively against a liquid nitrogen stream that is at a pressure of less than 10 bara, to provide a first liquefied hydrocarbon stream and an at least partly evaporated nitrogen stream; and
(e) cooling and liquefying the second stream downstream of step (c) by heat exchanging against the at least partly evaporated nitrogen stream of step (d) without invoking a significant change in pressure of the evaporated nitrogen stream other than a de minemus operational pressure loss caused by the present heat exchanging of step (e) and passing the evaporated nitrogen stream from the heat exchanging of step (d) to the present heat exchanging of step (e), wherein the cooling of the first stream and second stream is carried out at different pressures.

2. A method as claimed in claim 1 , wherein step (e) is followed by step (f): expanding the second liquefied hydrocarbon stream to provide an expanded second liquefied hydrocarbon stream.

3. A method as claimed in claim 2 , wherein step (f) is followed by step (g): combining the first liquefied hydrocarbon stream with the expanded second liquefied hydrocarbon stream to provide a combined hydrocarbon stream.

4. A method as claimed in claim 1 , wherein in step (c) the first stream is expanded prior to step (d), thereby reducing the pressure to a pressure of between 1 and 15 bar.

5. A method as claimed in claim 1 , wherein in step (c) the second stream is compressed prior to step (e), to at least 120% of the elevated pressure in step (a).

6. A method as claimed in claim 5 , wherein the second stream is compressed to a pressure of between 80 and 140 bar.

7. A method as claimed in claim 1 , wherein the liquid nitrogen stream is provided from one or more storage tanks.

8. A method as claimed in claim 7 , wherein the liquid nitrogen stream is provided from one or more storage tanks on a sea-going vessel, and the volume of the liquid nitrogen stream for step (d) is equivalent to the volume of the liquid fractions of the first liquefied hydrocarbon stream and the second liquefied hydrocarbon stream together.

9. A method as claimed in claim 8 , wherein the one or more storage tanks can store and transport the first liquefied hydrocarbon stream and the second cooled hydrocarbon stream.

10. A method as claimed in claim 1 , wherein the first stream comprises 30 mass % to 70 mass % of the feed steam.

11. A method as claimed in claim 1 , wherein the feed stream in step (a) is provided from a natural gas liquids extraction system, and wherein the at least partly evaporated nitrogen stream of step (d) is divided into two or more fractions to create at least a first separate nitrogen stream and a second separate nitrogen stream, which second separate nitrogen stream is employed to provide cooling to the natural gas liquids extraction system.

12. A method as claimed in claim 1 , wherein the second stream in step (e) is cooled and liquefied without invoking a significant pressure reduction in the second stream during the cooling and liquefying, other than a de minemus operational pressure loss caused by the heat exchanging, thereby providing the second liquefied hydrocarbon stream at substantially the same pressure as the pressure of the second stream after step (C).

13. An apparatus for liquefying a hydrocarbon stream, the apparatus comprising:
a stream splitter to divide the hydrocarbon stream into at least a first stream and a second stream;
a pressure modification stage comprising a first expander to receive and expand the first stream or a compressor to receive and compress the second stream, or both;
a first cooling system, downstream of the pressure modification stage, through which the first stream and a liquid nitrogen stream that is at a pressure of less than 10 barn can heat exchange to provide a first liquefied hydrocarbon stream and an at least partly evaporated nitrogen stream;
a second cooling system, downstream of the pressure modification stage, through which the second stream, at a higher pressure than the first stream, and the at least partly evaporated nitrogen stream can heat exchange, to provide a second liquefied hydrocarbon stream and a warmed nitrogen stream at substantially the same pressure as the at, least partly evaporated nitrogen stream, and
a connection conduit, free from pressure modification means and fluidly connecting the first cooling system to the second cooling system, to allow the at least partly evaporated nitrogen stream to pass from the first cooling system to the second cooling system without invoking a significant change in pressure other than a de minemus operational pressure loss caused by the evaporated nitrogen stream from the first cooling system to the second cooling system.

14. An apparatus as claimed in claim 13 , further comprising: a second expander to expand the second liquefied hydrocarbon stream.

15. An apparatus as claimed in claim 14 , further comprising: a combiner to combine the first liquefied hydrocarbon stream and the second cooled hydrocarbon stream downstream of the second expander.

16. An apparatus as claimed in claim 13 , wherein the second cooling system is free of pressure modification means such that the second liquefied hydrocarbon stream downstream of the second coding system is at substantially the same pressure as the pressure of the second stream upstream of the second cooling system other than a de minemus operational pressure loss caused by the second cooling system.

17. A method as claimed in claim 1 , wherein the liquid nitrogen stream in step (d) is at a pressure of less than 2 bara.

Assignees

• Chantant Francois
• Shell Oil Co

Inventors

• Chantant Francois

Classifications

• F25J2200/74

  Refluxing the column with at least a part of the partially condensed overhead gas · CPC title

• F25J1/0022

  Hydrocarbons, e.g. natural gas · CPC title

• F25J1/0221

  using the cold stored in an external cryogenic component in an open refrigeration loop · CPC title

• F25J1/0042

  by liquid expansion with extraction of work · CPC title

• F25J2270/904

  by liquid or gaseous cryogen in an open loop · CPC title