Flexible reflux process for high NGL recovery

• US 20010052241A1
• Filed: 04/12/2001
• Published: 12/20/2001
• Est. Priority Date: 04/13/2000
• Status: Active Grant

• Current Assignee: IPSI, LLC (Bechtel Group Incorporated)
• Original Assignee: IPSI, LLC (Bechtel Group Incorporated)
• Inventors: Jain, Pallav, Yao, Jame, Elliot, Douglas G., Chen, Jong Juh, Lee, Rong-Jywn
• Granted Patent: US 6,453,698 B2
• Time in Patent Office: Days
• 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 first liquid stream from said cryogenic distillation column via a side liquid draw;

ii) Processing said first liquid stream to generate a first vapor stream;

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

2. The process of

claim 1

wherein said processing step (ii) comprises 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.

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

wherein the processing step (ii) further comprises raising the pressure of said first liquid stream prior to the vaporizing step.

6. The process of

claim 2

further comprises cooling said second liquid stream and directing said cooled second liquid stream to said cryogenic distillation column.

7. 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 where in 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) Processing said first vapor stream to generate a second vapor stream and a first liquid stream;

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

8. The process of

claim 7

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.

9. The process of

claim 7

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

10. The process of

claim 7

wherein said processing step (ii) 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.

11. The process of

claim 7

in which said processing step (ii) includes raising the pressure of said first vapor stream.

12. The process of

claim 7

further comprising cooling said first liquid stream and directing said cooled first liquid stream to said cryogenic distillation column.

13. 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 or more of said feed trays;

(iii) Means for withdrawing a liquid or vapor from one or more of said recovery trays;

(iv) Means for processing said side liquid or vapor draw from said distillation column to generate at least one reflux stream for said distillation column.

14. The apparatus of

claim 13

, wherein said means for processing said side liquid or vapor draw comprises:

(i) Means for raising the pressure of said side liquid or vapor draw;

(ii) Means for heat exchange with said side liquid or vapor draw;

(iii) Means for separating said side liquid or vapor draw in one or more separation stages to generate at least one reflux stream for said distillation column.