METHODS AND CONFIGURATION OF AN NGL RECOVERY PROCESS FOR LOW PRESSURE RICH FEED GAS

• US 20160231052A1
• Filed: 02/09/2016
• Published: 08/11/2016
• Est. Priority Date: 02/09/2015
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Granted Patent: US 10,077,938 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: C10L 3/12 Liquefied petroleum gas liquefying by pressure and cold treatment F25J
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/04 in a dual 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 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/02 Mixing or blending of fluids to yield a certain product
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• 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 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/60 Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• CPC Class Codes: F25J 2280/02 Control in general, load changes, different modes ("runs"), measurements
• 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
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

Separating propane and heavier hydrocarbons from a feed stream by cooling the feed stream, introducing the chilled feed stream into a feed stream separation unit, pumping the separator bottom stream, introducing the pressurized separator bottom stream into a stripper column, reducing the pressure of the separator overhead stream, introducing the letdown separator overhead stream into an absorber column, collecting a stripper overhead stream from the stripper column, chilling the stripper overhead stream, reducing the pressure of the chilled stripper overhead stream, introducing the letdown stripper overhead stream into the absorber column, collecting an absorber bottom stream, pumping the absorber bottom stream, heating the absorber bottom stream, introducing the heated absorber bottom stream into the stripper column, and collecting the stripper bottom stream from the stripper column. The stripper column bottom stream includes the propane and heavier hydrocarbons and less than about 2.0% of ethane by volume.

Claims

1. A method for operating a natural gas liquids (NGL) recovery system, the method comprising:

separating a propane and heavier hydrocarbon stream from a feed stream comprising methane, ethane, and propane to yield an ethane-containing residue gas stream, wherein separating the propane and heavier hydrocarbons from the feed stream comprises;

cooling the feed stream to yield a chilled feed stream;

introducing the chilled feed stream into a feed stream separation unit to yield a feed stream separator bottom stream and a feed stream separator overhead stream;

pumping the feed stream separator bottom stream to yield a pressurized feed stream separator bottom stream;

introducing the pressurized feed stream separator bottom stream into a stripper column;

reducing the pressure of the feed stream separator overhead stream to yield a letdown feed stream separator overhead stream;

introducing the letdown feed stream separator overhead stream into an absorber column;

collecting a stripper column overhead stream from the stripper column;

chilling the stripper column overhead stream to yield a chilled stripper column overhead stream;

reducing the pressure of the chilled stripper column overhead stream to yield a letdown stripper column overhead stream;

introducing the letdown stripper column overhead stream into the absorber column;

collecting an absorber bottom stream from the absorber column;

compressing the absorber bottom stream to yield a compressed absorber bottom stream;

heating the absorber bottom stream to yield a heated absorber bottom stream;

introducing the heated absorber bottom stream into the stripper column; and

collecting a stripper column bottom stream from the stripper column, wherein the stripper column bottom stream forms the propane and heavier hydrocarbon stream and wherein the propane and heavier hydrocarbon stream comprises propane and heavier hydrocarbons and less than about 2.0% of ethane by volume.

2. The method of claim 1, wherein cooling the feed stream comprises introducing the feed stream into a first heat exchanger and a second heat exchanger.

3. The method of claim 2, wherein heating the absorber bottom stream comprises introducing the absorber bottom stream into a third heat exchanger.

4. The method of claim 3, wherein chilling the stripper column overhead stream comprises introducing the stripper column overhead stream into the third heat exchanger, a fourth heat exchanger, and the first heat exchanger.

5. The method of claim 1, wherein reducing the pressure of the separator overhead stream comprises passing the separator overhead stream through a first valve.

6. The method of claim 1, wherein reducing the pressure of the chilled stripper column overhead stream comprises passing the chilled stripper column through a second valve.

7. The method of claim 1, wherein separating the propane and heavier hydrocarbons from the feed stream further comprises:

collecting an absorber overhead stream from the absorber, wherein the absorber overhead stream forms the ethane-containing residue gas stream.

8. The method of claim 7, further comprising:

compressing the absorber overhead stream to yield a compressed absorber overhead stream; and

chilling the compressed absorber overhead stream to yield a chilled absorber overhead stream.

9. The method of claim 8, wherein chilling the compressed absorber overhead stream comprises introducing the compressed absorber overhead stream into a fifth heat exchanger.

10. The method of claim 8, further comprising:

separating ethane from the ethane-containing residue gas stream, wherein separating ethane from the ethane-containing residue gas stream comprises;

cooling a first portion of the ethane-containing residue gas stream to yield a cooled first portion residue gas stream;

reducing the pressure of the cooled first portion residue gas stream to yield a letdown first portion residue gas stream;

introducing the letdown first portion residue gas stream into a demethanizer column;

cooling a second portion of the ethane-containing residue gas stream to yield a cooled second portion residue gas stream;

introducing the cooled second portion residue gas stream into a residue gas separation unit to yield a residue gas separator bottom stream and a residue gas separator overhead stream;

reducing the pressure of the residue gas separator bottom stream to yield a letdown residue gas separator bottom stream;

introducing the letdown residue gas separator bottom stream into a lower portion of the demethanizer column;

decreasing the pressure of the residue gas separator overhead stream to yield a letdown residue gas separator overhead stream;

introducing the letdown residue gas separator overhead stream into an upper portion of the demethanizer column; and

collecting a demethanizer column bottom stream, wherein the demethanizer column bottom stream comprises at least 98% ethane by volume.

11. The method of claim 10, wherein cooling the first portion of the ethane-containing residue gas stream comprises introducing the first portion of the ethane-containing residue gas stream into a sixth heat exchanger.

12. The method of claim 10, wherein cooling the second portion of the ethane-containing residue gas stream comprises introducing the second portion of the ethane-containing residue gas stream into a demethanizer reboiler heat exchanger.

13. The method of claim 10, wherein reducing the pressure of the cooled first portion residue gas stream comprises introducing the cooled first portion residue gas stream into a third valve.

14. The method of claim 10, further comprising:

collecting a demethanizer column overhead stream, wherein the demethanizer column overhead stream comprises a substantially ethane-free residue gas stream; and

returning a portion of the substantially ethane-free residue gas stream to the demethanizer column.

15. The method of claim 1, wherein the propane and heavier hydrocarbon stream comprises at least about 95 vol. % of the propane present within the feed stream.

16. The method of claim 1, wherein the propane and heavier hydrocarbon stream comprises at least about 99 vol. % of the C4 and heavier hydrocarbons present within the feed stream.

17. A natural gas liquids (NGL) recovery system comprising:

a deep dewpointing subsystem (DDS) configured to separate a propane and heavier hydrocarbon stream from a feed stream comprising methane, ethane, and propane to yield an ethane-containing residue gas stream, the DDS comprising;

a first heat exchanger configured to receive the feed stream and to output a chilled feed stream;

a feed stream separation unit configured to receive the chilled feed stream and to output a feed stream separator bottom stream and a feed stream separator overhead stream;

a first compressor configured to compress the feed stream separator bottom stream and to output a compressed feed stream separator bottom stream;

a second heat exchanger configured to chill the compressed feed stream separator bottom stream to yield a chilled feed stream separator bottom stream;

a first valve configured to reduce the pressure of the feed stream separator overhead stream to yield a letdown feed stream separator overhead stream;

an absorber column configured to receive the letdown feed stream separator overhead stream into the absorber column and to produce an absorber bottom stream;

a second compressor configured to receive the absorber bottom stream to output a compressed absorber bottom stream;

a stripper column configured to receive the chilled feed stream separator bottom stream and the compressed absorber bottom stream and to output a stripper column overhead stream and a stripper column bottom stream;

a third heat exchanger configured to chill the stripper column overhead stream and to heat the compressed absorber bottom stream and to output a first chilled stripper column overhead stream and a heated absorber bottom stream;

a fourth heat exchanger configured to further chill the first chilled stripper column overhead stream and to output a second chilled stripper column overhead stream,

wherein the first heat exchanger is configured to further chill the second chilled stripper column overhead stream and to output a third chilled stripper column overhead stream,

a second valve configured to reduce the pressure of the third chilled stripper column overhead stream to yield a compressed stripper column overhead stream,

wherein the absorber column is further configured to receive the compressed stripper column overhead stream, and

wherein the stripper column bottom stream forms the propane and heavier hydrocarbon stream and wherein the propane and heavier hydrocarbon stream comprises propane and heavier hydrocarbons and less than about 2.0% of ethane by volume.

18. The system of claim 17, wherein the absorber column is further configured to output an absorber overhead stream, wherein the absorber overhead stream forms the ethane-containing residue gas stream.

19. The system of claim 18, wherein the DDS further comprises:

a second compressor configured to receive the absorber overhead stream and to output a compressed absorber overhead stream; and

the first heat exchanger configured to chill the compressed absorber overhead stream and to output a chilled absorber overhead stream.

20. The system of claim 19, further comprising:

an ethane-recovery subsystem (ERS) configured to separate ethane from the ethane-containing residue gas stream, wherein the ERS comprises;

a sixth heat exchanger configured to cool a first portion of the ethane-containing residue gas stream and to output a cooled first portion residue gas stream;

a third valve configured to reduce the pressure of the cooled first portion residue gas stream to output a letdown first portion residue gas stream;

a demethanized column configured to receive the letdown first portion residue gas stream;

a demethanizer reboiler heat exchanger configured to cool a second portion of the ethane-containing residue gas stream and to output a cooled second portion residue gas stream;

a residue gas separation unit configured to receive the cooled second portion residue gas stream and to output a residue gas separator bottom stream and a residue gas separator overhead stream;

a fourth valve configured to reduce the pressure of the residue gas separator bottom stream to output a letdown residue gas separator bottom stream;

wherein the demethanizer column is further configured to receive the letdown residue gas separator bottom stream into a lower portion thereof;

a turbo-expander configured to decrease the pressure of the residue gas separator overhead stream and to output a letdown residue gas separator overhead stream;

wherein the demethanizer column is further configured to receive the letdown residue gas separator overhead stream into an upper portion thereof; and

wherein the demethanizer column is further configured to output a demethanizer column bottom stream comprising at least 98% ethane by volume.

21. The system of claim 20, wherein the demethanizer column is further configured to output a demethanizer column overhead stream, wherein the demethanizer column overhead stream comprises a substantially ethane-free residue gas stream.

22. The system of claim 17, wherein the propane and heavier hydrocarbon stream comprises at least about 95 vol. % of the propane present within the feed stream.

23. The system of claim 17, wherein the propane and heavier hydrocarbon stream comprises at least about 99 vol. % of the C4 and heavier hydrocarbons present within the feed stream.