Flexible reflux process for high NGL recovery

• US 6,453,698 B2
• Filed: 04/12/2001
• Issued: 09/24/2002
• Est. Priority Date: 04/13/2000
• Status: Active Grant

• Current Assignee: IPSI, LLC (Bechtel Group Incorporated)
• Original Assignee: IPSI, LLC (Bechtel Group Incorporated)
• Inventors: Lee, Rong-Jywn, Yao, Jame, Elliot, Douglas G., Chen, Jong Juh, Jain, Pallav
• Primary Examiner(s): Doerrler, William C.
• Assistant Examiner(s): Drake, Malik N.
• Application Number:
  US09/833,892
• Publication Number:
  US 20010052241A1
• Time in Patent Office: 530 Days
• Field of Search: 626/20, 626/43, 626/21
• US Class Current: 62/621
• 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 2200/78 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 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2235/60 the fluid being (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 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0219 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• 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

A process for enhancing the recovery of less volatile components, from a multi component gas mixture, in a cryogenic distillation column, which involves withdrawing a stream from the cryogenic distillation column and processing it to yield a stream leaner in the component to be recovered, which will be cooled and fed to the cryogenic distillation column as a reflux. The processing step may include heating or cooling the side draw and then further contacting the side draw with another stream which is substantially condensed.

Claims

1. A process for recovering relatively less volatile components from a multi-component feed gas, while rejecting relatively more volatile components as a residue gas via a cryogenic distillation column wherein the reflux to said cryogenic distillation column is generated by steps comprising:

i) Obtaining a side draw from said cryogenic distillation column wherein said side draw is selected from the group consisting of;

a) a side liquid draw;

b) a side vapor draw;

ii) Processing said side draw to generate a first vapor stream from further separation of said side draw in one or more mass transfer stages;

said first vapor stream is lean in relatively less volatile components to be recovered; and

iii) Cooling said first vapor stream and then directing said cooled first vapor stream to the top of said cryogenic distillation column as a lean reflux.

2. A process for recovering relatively less volatile components from a multi-component feed gas, while rejecting relatively more volatile components as a residue gas via a cryogenic distillation column wherein the reflux to said cryogenic distillation column is generated by steps comprising:

i) Obtaining a first liquid stream from said cryogenic distillation column via a side liquid draw;

ii) Raising the pressure of said first liquid stream and thereafter vaporizing at least a portion of said first liquid stream by steps that include heating said first liquid stream in one or more exchangers and then separating, in one or more separation stages, said vaporized first liquid stream to generate a first vapor stream and a second liquid stream; and

iii) Cooling said first vapor stream and then directing said cooled first vapor stream to the top of said cryogenic distillation column as a lean reflux.

3. The process of claim 2 wherein said separating step further involves contacting said vaporized first liquid stream with a substantially condensed portion of said feed gas.

4. The process of claim 2 wherein said separating step further involves contacting said vaporized first liquid stream with a substantially condensed stream which can be obtained by steps comprising:

i) Cooling said feed gas stream;

ii) Separating said cool feed gas stream into a vapor portion and a liquid portion;

iii) Splitting said vapor portion into at least two portions—

a main vapor portion and a first vapor portion;

iv) Cooling and substantially condensing said first vapor portion to obtain said substantially condensed stream.

5. The process of claim 2 further comprises cooling said second liquid stream and directing said cooled second liquid stream to said cryogenic distillation column.

6. A process for recovering relatively less volatile components from a multi-component feed gas, while rejecting relatively more volatile components as a residue gas via a cryogenic distillation column wherein the reflux to said cryogenic distillation column is generated by steps comprising:

i) Obtaining a vap or stream from said cryogenic distillation column via a side vapor draw and thereafter raising the pressure of said vapor stream to form a first vapor stream;

ii) Processing s aid first vapor stream to generate a second vapor stream and a first liquid stream from said first vapor stream;

said second vapor stream is lean in relatively less volatile components to be recovered; and

iii) Cooling said second vapor stream and then directing said cooled second vapor stream to the top of said cryogenic distillation column as a lean reflux.

7. The process of claim 6 wherein said processing step (ii) further comprises cooling and partially condensing said first vapor stream in one or more heat exchangers and then separating said partially condensed first vapor stream, in one or more separation stages, to generate said second vapor stream and said first liquid stream.

8. The process of claim 6 wherein said processing step (ii) further involves contacting said first vapor stream with a substantially condensed portion of said feed gas.

9. The process of claim 6 wherein said processing step (ii) further involves contacting said first vapor stream with a substantially condensed stream which can be obtained by steps comprising:

i) Cooling said feed gas stream;

ii) Separating said cool feed gas stream into a vapor portion and a liquid portion;

iii) Splitting said vapor portion into at least two portions—

a main vapor portion and a first vapor portion; and

iv) Cooling and substantially condensing said first vapor portion to obtain said substantially condensed stream.

10. The process of claim 6 further comprising cooling said first liquid stream and directing said cooled first liquid stream to said cryogenic distillation column.

11. An apparatus for recovering relatively less volatile components from a multi-component feed gas, while rejecting relatively more volatile components as a residue gas comprising:

i) A distillation column having a plurality of feed and recovery trays;

ii) Means for introducing a cooled feed gas/condensate into said distillation column at one or more of said feed trays;

iii) Means for withdrawing a side draw from one or more of said recovery trays wherein said side draw can be selected from the group consisting of;

a) a liquid draw;

b) a vapor draw;

iv) A device for increasing the pressure of said side draw;

v) Means for processing said pressurized side draw to generate a first vapor stream from further separation of said pressurized side draw via one or more mass transfer devices;

wherein said first vapor stream is lean in relatively less volatile components to be recovered; and

vi) A heat exchanger for cooling said first vapor stream to substantial condensation and thereafter directing it to the top of said distillation column as a lean reflux to enhance the recovery of relatively less volatile components.

12. The apparatus of claim 11 wherein said means for processing said pressurized side draw further comprising:

i) A heat exchanger for indirectly exchanging energy from said pressurized side draw to form a partially condensed stream; and

ii) A separator for separating said partially condensed stream to generate a first vapor stream which is lean in relatively less volatile less components to be recovered.

13. The apparatus of claim 11 wherein said means for processing said pressurized side draw further comprising:

i) A heat exchanger for indirectly exchanging energy from said pressurized side draw to form a partially condensed stream; and

ii) An absorber comprising one or more mass transfer stages wherein said partially condensed stream contacts with a substantially condensed stream obtained from a portion of said feed gas; and

thereafter fractionating it into a first vapor stream and a first liquid stream;

said first vapor stream is lean in relatively less volatile components to be recovered.

14. The apparatus of claim 13 wherein said substantially condensed stream can be further obtained in an apparatus comprising:

i) A heat exchanger for cooling said feed gas;

ii) A separator for separating said cooled feed gas into a vapor portion and a liquid portion;

iii) A device for splitting said vapor portion into at least two portions—

a main vapor portion and a first vapor portion; and

iv) A heat exchanger for cooling and substantially condensing said first vapor portion to obtain said substantially condensed stream.

15. A process for recovering relatively less volatile components from a multi-component feed gas, while rejecting relatively more volatile components as a residue gas via a cryogenic distillation column wherein the reflux to said cryogenic distillation column is generated by steps comprising:

i) Obtaining a first liquid stream from said cryogenic distillation column via a side liquid draw;

ii) Vaporizing at least a portion of said first liquid stream by steps that include heating said first liquid stream in one or more exchangers;

iii) Contacting said vaporized first liquid stream with a substantially condensed stream obtained from a portion of said feed gas to generate a first vapor stream which is lean in relatively less volatile components to be recovered; and

iv) Cooling said first vapor stream and then directing said cooled first vapor stream to the top of said cryogenic distillation column as a reflux.

16. The process of claim 15 wherein said substantially condensed stream can be obtained by steps comprising:

i) Cool said feed gas stream;

ii) Separating said cooled feed gas stream into a vapor portion and a liquid portion;

iii) Splitting said vapor portion into at least two portions—

a main vapor portion and a first vapor portion; and

iv) Cooling and substantially condensing said first vapor portion to obtain said substantially condensed stream.

17. A process for recovering relatively less volatile components from a multi-component feed gas, while rejecting relatively more volatile components as a residue gas via a cryogenic distillation column wherein the reflux to said cryogenic distillation column is generated by steps comprising:

i) Obtaining a first vapor stream from said cryogenic distillation column via a side vapor draw;

ii) Contacting said first vapor stream with a substantially condensed stream obtained from a portion of said feed gas to generate a first vapor stream which is lean in relatively less volatile components to be recovered; and

iii) Cooling said first vapor stream and then directing said cooled first vapor stream to the top of said cryogenic distillation column as a reflux.

18. The process of claim 17 wherein said substantially condensed stream can be obtained by steps comprising:

i) Cooling said feed gas stream;

ii) Separating said cooled feed gas stream into a vapor portion and a liquid portion;

iii) Splitting said vapor portion into at least two portions—

a main vapor portion and a first vapor portion; and

iv) Cooling and substantially condensing said first vapor portion to obtain said substantially condensed stream.