Integrated heavy hydrocarbon and BTEX removal in LNG liquefaction for lean gases

Patent metadata

Field	Value
Publication number	US-12215922-B2
Application number	US-201916421138-A
Country	US
Kind code	B2
Filing date	May 23, 2019
Priority date	May 23, 2019
Publication date	Feb 4, 2025
Grant date	Feb 4, 2025

Abstract

A method for removing heavy hydrocarbons from a feed gas by: feeding, into an absorber, a top reflux stream and a second reflux stream below the top reflux stream, wherein the absorber produces an absorber bottom product stream and an absorber overhead product stream; depressurizing and feeding the absorber bottom product stream to a stripper to produce a stripper bottom product stream and a stripper overhead product stream; cooling and feeding a portion of the absorber overhead product stream back to the absorber as the top reflux stream; and pressurizing and feeding the stripper overhead product stream back to the absorber as the second reflux stream. Systems for carrying out the method are also provided.

First claim

What is claimed is:

1. A method for removing heavy hydrocarbons from a feed gas, the method comprising:
cooling an inlet gas in a propane pre-cooling heat exchanger;
separating the cooled inlet gas to produce the feed gas and a feed liquid;
feeding, into an absorber, the feed gas, a top reflux stream, and a second reflux stream below the top reflux stream, wherein the absorber produces an absorber bottom product stream and an absorber overhead product stream;
depressurizing and feeding the absorber bottom product stream to a stripper to produce a stripper bottom product stream and a stripper overhead product stream;
cooling and feeding a portion of the absorber overhead product stream back to the absorber as the top reflux stream; and
pressurizing and feeding the stripper overhead product stream back to the absorber as the second reflux stream.

2. The method of claim 1 , further comprising:
feeding the feed liquid to the stripper; and
expanding the feed gas before feeding the feed gas to the absorber, wherein the feed gas is fed to a lower portion of the absorber.

3. The method of claim 2 , wherein expanding the feed gas comprises expanding the feed gas in a turboexpander.

4. The method of claim 1 , wherein cooling the inlet gas comprises:
after passing the inlet gas through the propane pre-cooling heat exchanger, passing the inlet gas through a cold box, wherein the cold box comprises a plurality of passes configured to provide heat exchange between the inlet gas, the absorber overhead product stream, the absorber bottom product stream, the stripper overhead product stream, and the portion of the absorber overhead product stream.

5. The method of claim 1 , further comprising:
after passing the inlet gas through the propane pre-cooling heat exchanger, passing the inlet gas through a first heat exchanger, wherein the first heat exchanger is configured to cross-exchange the inlet gas with a part of the absorber overhead product stream.

6. The method of claim 1 , wherein the propane pre-cooling heat exchanger is part of a propane pre-cooling train of a LNG liquefaction plant, the method further comprising: locating the propane pre-cooling train to a NGL extraction train that contains the absorber and the stripper.

7. The method of claim 1 , wherein a combined mass flow rate of the feed liquid and the absorber bottom product stream is less than 10% of a mass flowrate of the inlet gas.

8. The method of claim 1 , wherein the inlet gas has less than 2 gallons per thousand cubic feet of gas of C3+ components.

9. The method of claim 1 , before cooling and feeding the portion of the absorber overhead product stream back to the absorber, the method further comprising:
heating a first part of the of the absorber overhead product stream and cooling the inlet gas in a first heat exchanger;
heating a second part of the absorber overhead product stream and cooling the portion of the absorber overhead product stream in a second heat exchanger; and
heating a third part of the absorber overhead product stream and cooling the stripper overhead product stream in a third heat exchanger.

10. The method of claim 9 , further comprising:
combining the heated first, second, and third parts to form a heat exchanged absorber overhead product, and
compressing the heat exchanged absorber overhead product to form a residue gas stream at a pressure of from about 800 psig to about 900 psig, wherein the portion of the absorber overhead product stream that is fed back to the absorber as the top reflux stream is a portion of the residue gas stream.

11. The method of claim 9 , further comprising:
combining the heated first, second, and third parts to form a heat exchanged absorber overhead product,
wherein the heat exchanged absorber overhead product does not need recompression before a second portion of the absorber overhead product stream flows to a LNG liquefaction plant as a product feed.

12. The method of claim 1 , before cooling and feeding the portion of the absorber overhead product stream back to the absorber, the method further comprising:
heating the absorber overhead product stream in a cold box to form a heat exchanged absorber overhead product.

13. The method of claim 12 , further comprising:
compressing the absorber overhead product stream to form a residue gas stream at a pressure of from about 800 psig to about 900 psig, wherein the portion of the absorber overhead product stream that is fed back to the absorber as the top reflux stream is a portion of the residue gas stream.

14. The method of claim 13 , wherein a second portion of the absorber overhead product stream forms a product feed to a LNG liquefaction plant.

15. The method of claim 1 , wherein a second portion of the absorber overhead product stream forms a product feed to a LNG liquefaction plant.

16. The method of claim 15 , wherein the second portion has a pressure in a range of 800 psig to 900 psig.

17. The method of claim 1 , further comprising:
at least partially condensing the portion of the absorber overhead product stream prior to feeding the portion of the absorber overhead product stream back to the absorber.

18. The method of claim 1 , further comprising:
cooling and at least partially condensing a portion of the stripper overhead product stream prior to feeding the stripper overhead product stream back to the absorber.

19. The method of claim 1 , wherein the absorber is operated at a higher pressure than the stripper.

20. The method of claim 1 , wherein the top reflux stream and the second reflux stream comprise primarily methane.

21. A system for removing heavy hydrocarbons from a feed gas, the system comprising:
a propane pre-cooling heat exchanger configured to cool an inlet gas;
an absorber, wherein the absorber is configured to receive a top reflux stream and a second reflux stream within a top portion of the absorber, receive an expanded feed gas stream at a bottom portion of the absorber, and produce an absorber bottom product stream and an absorber overhead product stream;
a stripper, wherein the stripper is configured to receive a feed liquid and the absorber bottom product stream and produce a stripper overhead product stream and a stripper bottom product stream;
a pressure reduction valve configured to reduce a pressure of the absorber bottom product stream between the absorber and the stripper; and
a compressor configured to pressurize the stripper overhead product stream from the stripper to form a compressed stripper overhead product stream, wherein the compressed stripper overhead product stream is configured to pass back to the absorber as the second reflux stream.

22. The system of claim 21 , further comprising:
a cold box, wherein the cold box is configured to cool and at least partially condense the compressed stripper overhead product stream to form the second reflux stream, cool and at least partially condense a portion of the absorber overhead product stream to form the top reflux stream, and cool and partially condense the inlet gas to produce the feed gas and the feed liquid.

23. The system of claim 22 , further comprising:
a separator, wherein the separator is configured to receive and separate the inlet gas into the feed gas and the feed liquid; and
an expander, wherein the expander is configured to receive the feed gas from the separator and expand the feed gas to produce the expanded feed gas stream, wherein the expander is a turboexpa

Assignees

• Fluor Tech Corp

Inventors

• Mak John
• Thomas Jacob
• Patel Dhirav
• Graham Curt
• Zhang Irene

Classifications

• F25J2205/50

  using absorption, i.e. with selective solvents or lean oil, heavier CnHm and including generally a regeneration step for the solvent or lean oil · CPC title

• F25J2210/60

  Natural gas or synthetic natural gas [SNG] · CPC title

• F25J2210/06

  Splitting of the feed stream, e.g. for treating or cooling in different ways · CPC title

• F25J2220/64

  Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general · CPC title

• F25J2205/04

  in the feed line, i.e. upstream of the fractionation step · CPC title