Integrated nitrogen removal in the production of liquefied natural gas using intermediate feed gas separation

Patent metadata

Field	Value
Publication number	US-10767922-B2
Application number	US-201715626301-A
Country	US
Kind code	B2
Filing date	Jun 19, 2017
Priority date	Apr 24, 2014
Publication date	Sep 8, 2020
Grant date	Sep 8, 2020

Abstract

A method and apparatus for liquefying a natural gas feed stream and removing nitrogen therefrom to produce a nitrogen-depleted LNG product, in which a natural gas feed stream is fed into the warm end of a main heat exchanger, cooled and at least partially liquefied, withdrawn from an intermediate location of the main heat exchanger and separated to form a nitrogen-enriched natural gas vapor stream and a nitrogen-depleted natural gas liquid stream, the liquid and vapor streams being reintroduced into an intermediate location of the main heat exchanger and further cooled in parallel to form a first LNG stream and a first at least partially liquefied nitrogen-enriched natural gas stream, respectively.

First claim

The invention claimed is:

1. A method for producing a nitrogen-depleted LNG product, the method comprising:
(a) introducing a natural gas feed stream into the warm end of a main heat exchanger, cooling and at least partially liquefying the natural gas feed stream, and withdrawing the cooled and at least partially liquefied stream from an intermediate location of the main heat exchanger;
(b) expanding, partially vaporizing and separating the cooled and at least partially liquefied stream to form a nitrogen-enriched natural gas vapor stream and a nitrogen-depleted natural gas liquid stream;
(c) withdrawing a portion of the nitrogen-enriched natural gas vapor stream to form a stripping gas stream;
(d) separately re-introducing a remaining portion of the nitrogen-enriched natural gas vapor stream and the nitrogen-depleted natural gas liquid stream into an intermediate location of the main heat exchanger to further cool the remaining portion of the nitrogen-enriched natural gas vapor stream and the nitrogen-depleted natural gas liquid stream in parallel, the remaining portion of the nitrogen-enriched natural gas vapor stream being further cooled and at least partially liquefied to form a first at least partially liquefied nitrogen-enriched natural gas stream and the nitrogen-depleted natural gas liquid stream being further cooled to form a first LNG stream, and withdrawing the first at least partially liquefied nitrogen-enriched natural gas stream and the first LNG stream from the cold end of the main heat exchanger;
(e) expanding and partially vaporizing the first at least partially liquefied nitrogen-enriched natural gas stream and introducing the expanded and partially vaporized stream into a distillation column to separate the expanded and partially vaporized stream to form a nitrogen-rich vapor product and a second LNG stream;
(f) introducing the stripping gas stream into the bottom of the distillation column;
(g) expanding, partially vaporizing and separating the second LNG stream and expanding, partially vaporizing and separating the first LNG stream to form a nitrogen-depleted LNG product from a liquid portion of said second LNG stream and first LNG stream and a nitrogen-enriched natural gas vapor from a vapor portion of said second LNG stream and first LNG stream, wherein said separation of the second LNG stream and separation of the first LNG stream take place in one or more LNG storage tanks or phase separators;
(h) withdrawing at least a portion of the nitrogen-enriched natural gas vapor as a recycle stream;
(i) compressing the recycle stream to form a compressed recycle stream; and
(j) returning the compressed recycle stream to the main heat exchanger to be cooled and at least partially liquefied in combination with the natural gas feed stream.

2. The method of claim 1 , wherein in step (b) the steps of expanding, partially vaporizing and separating the cooled and at least partially liquefied stream to form the nitrogen-enriched natural gas vapor stream and the nitrogen-depleted natural gas liquid stream comprise expanding and partially vaporizing the cooled and at least partially liquefied stream and separating said partially vaporized stream in a phase separator into vapor and liquid phases to form the nitrogen-enriched natural gas vapor stream and the nitrogen-depleted natural gas liquid stream.

3. The method of claim 1 , wherein in step (g) the steps of expanding, partially vaporizing and separating the second LNG stream and expanding, partially vaporizing and separating the first LNG stream to form the nitrogen-depleted LNG product and the nitrogen-enriched natural gas vapor comprise expanding the second LNG stream, expanding the first LNG stream, and transferring both of said expanded second and first LNG streams into the same LNG storage tank, in which LNG storage tank a portion of the LNG present in each of said expanded second and first LNG streams vaporizes, thereby forming the nitrogen-enriched natural gas vapor and the nitrogen-depleted LNG product.

4. The method of claim 1 , wherein the first at least partially liquefied nitrogen-enriched natural gas stream in step (e) is introduced into the top of the distillation column.

5. The method of claim 1 , wherein refrigeration for the main heat exchanger is provided by a closed loop refrigeration system, refrigerant circulated by the closed loop refrigeration system passing through and being warmed in the main heat exchanger.

Assignees

• Air Prod & Chem

Inventors

• Chen Fei
• Liu Yang
• Krishnamurthy Gowri
• Ott Christopher Michael
• Roberts Mark Julian

Classifications

• F25J3/0635

  separation of CnHm with 1 carbon atom or more · CPC title

• F25J2200/40

  Features relating to the provision of boil-up in the bottom of a column · CPC title

• F25J3/0233

  separation of CnHm with 1 carbon atom or more · CPC title

• F25J1/0042

  by liquid expansion with extraction of work · CPC title

• F25J1/0055

  originating from an incorporated cascade · CPC title