Gas separation process

• US 6,405,561 B1
• Filed: 06/06/2001
• Issued: 06/18/2002
• Est. Priority Date: 05/15/2001
• Status: Expired due to Term

• Current Assignee: Black & Veatch International Company (Black & Veatch Corporation)
• Original Assignee: Black & Veatch Pritchard Incorporated
• Inventors: Mortko, Robert A., Currence, Kevin L.
• Primary Examiner(s): CAPOSSELA, RONALD C
• Application Number:
  US09/875,308
• Time in Patent Office: 377 Days
• Field of Search: 626/30, 626/31
• US Class Current: 62/631
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• 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 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 2270/02 Internal refrigeration with liquid vaporising loop
• 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 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 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

A process for separating a feed gas stream containing methane, C₂ components, C₃ components, and heavier components into a volatile gas stream containing a major portion of the methane and C₂ components and a less volatile stream containing a major portion of the C₃ and heavier components by adjusting the temperature and pressure of the feed gas stream and charging it to a separator/absorber where the gas stream is separated into a first gas stream containing a major portion of the methane and C₂ components with a minor content of C₃ and heavier components and a first liquid stream containing a major portion of the C₃ and heavier components with a lesser concentration of C₂ and lighter components with the first liquid stream being fractionated in a deethanizer into an overhead stream and a bottoms stream with the bottoms stream containing primarily C₃ and heavier components with the overhead stream containing primarily C₂ and lighter components being at least partially condensed and separated into a liquid reflux stream, a second liquid stream and a vaporous stream. The second liquid stream is passed to an upper portion of the separator/absorber for use therein to absorb C₃ and heavier components from a gas stream in the separator/absorber.

Claims

1. In a process for separating a feed gas stream containing methane, C₂ components, C₃ components and heavier components into a volatile gas stream containing a major portion of the methane and C₂ components and a less volatile stream containing a major portion of the C₃ and heavier components by adjusting the temperature and pressure of the feed gas stream to a suitable temperature for separation into an absorber gas stream and a first liquid stream in a separator/absorber with the absorber gas stream containing a major portion of the methane and C₂ components and the first liquid stream containing a major portion of the C₃ and heavier components, the first liquid stream being charged to a deethanizer from which a bottoms liquid product comprising primarily the C₃ and heavier components is recovered with the deethanizer overhead consisting primarily of C₂ and lighter components, the improvement comprising:

a) cooling the deethanizer overhead to produce a partially condensed stream;

b) separating the cooled deethanizer overhead stream into a liquid stream comprising principally C₂ components and a residue gas stream; and

,

c) cooling a portion of the liquid stream in heat exchange with the absorber gas stream to produce a subcooled liquid stream and passing the subcooled liquid stream to an upper portion of the separator/absorber for contact with a gas stream rising through the separator/absorber to absorb C₃ and heavier components therefrom.

2. The improvement of claim 1 wherein a pressure in the deethanizer is at least 25 psi greater than a pressure in the separator/absorber.

3. The improvement of claim 1 wherein the pressure in the deethanizer is at least 100 psi greater than the pressure in the separator/absorber.

4. The process of claim 1 wherein the separator/absorber contains at least one theoretical stage of mass transfer.

5. A process for separating a feed gas stream containing methane, C₂ components, C₃ components and heavier components into a volatile gas stream containing a major portion of the methane and C₂ components and a less volatile stream containing a major portion of the C₃ and heavier components, the process comprising:

a) cooling the feed gas stream to a temperature sufficient to condense the majority of the C₃ components in the feed gas stream by heat exchange with at least one of a first liquid stream containing C₃ and heavier components and a refrigerant stream to produce a cooled feed gas stream;

b) passing the cooled feed gas stream to a separator/absorber to produce the first liquid stream as a bottoms product and a separator/absorber overhead residue gas stream;

c) passing the first liquid stream to a deethanizer tower operating at a pressure at least 25 psi above the pressure in the separator/absorber;

d) separating the first liquid stream into a deethanizer bottoms stream containing a majority of the C₃ and heavier components and a deethanizer overhead gas stream;

e) cooling the deethanizer overhead gas stream to partially condense the deethanizer overhead gas stream by heat exchange with a refrigerant stream to produce a deethanizer liquid reflux stream, a second liquid stream and a deethanizer residue gas stream; and

,

f) cooling the second liquid stream by heat exchange with the separator/absorber overhead residue gas stream to produce a subcooled second liquid stream and passing the subcooled second liquid stream into an upper portion of the separator/absorber.

6. The process of claim 5 wherein the refrigerant comprises propane.

7. The process of claim 5 where the pressure of the deethanizer is at least 100 psi greater than the pressure in the separator/absorber.

8. The process of claim 5 wherein the pressure in the deethanizer is at least about 200 psi greater than the pressure in the separator/absorber.

9. The process of claim 5 wherein the separator/absorber contains at least one theoretical stage of mass transfer.

10. A process for separating a feed gas stream containing methane, C₂ components, C₃ components and heavier components into a volatile gas stream containing a major portion of the methane and C₂ components and a less volatile stream containing a major portion of the C₃ and heavier components, the process comprising:

a) cooling the feed gas stream to a temperature sufficient to condense the majority of the C₃ components in the feed gas stream by heat exchange with at least one of a first liquid stream containing C₃ and heavier components, a second liquid stream containing C₃ and heavier components, a residue gas stream, and a refrigerant stream to produce a cooled feed gas stream;

b) passing the cooled feed gas stream to a separator to produce a separator gas stream and the first liquid stream;

c) optionally further cooling the separator gas stream by heat exchange or expansion and passing it to a separator/absorber wherein a second liquid stream is produced as a bottoms stream and wherein a separator/absorber overhead residue gas stream is produced;

d) passing the first liquid stream and the second liquid stream to a deethanizer tower operating at a pressure at least 25 psi above the separator/absorber pressure;

e) separating the first and the second liquid streams into a deethanizer bottoms stream containing a majority of the C₃ and heavier components and a deethanizer overhead gas stream;

f) cooling the deethanizer overhead gas stream to partially condense the deethanizer overhead gas stream by heat exchange with a refrigerant stream to produce a deethanizer liquid reflux stream, a third liquid stream and a deethanizer residue gas stream; and

,

g) cooling the third liquid stream by heat exchange with the separator/absorber overhead residue gas stream to produce a subcooled third liquid stream and passing the subcooled third liquid stream into an upper portion of the separator/absorber.

11. The process of claim 10 wherein the refrigerant comprises propane.

12. The process of claim 10 wherein the pressure of the deethanizer is at least 100 psi greater than the pressure in the separator/absorber.

13. The process of claim 10 wherein the pressure of the deethanizer is at least 200 psi greater than the pressure in the separator/absorber.

14. The process of claim 10 wherein the separator/absorber contains at least one theoretical stage of mass transfer.

15. A process for separating a feed gas stream containing methane, C₂ components, C₃ components and heavier components into a volatile gas stream containing a major portion of the methane and C₂ components and a less volatile stream containing a major portion of the C₃ and heavier components, the process comprising:

a) cooling the feed gas stream to a temperature sufficient to condense the majority of the C₃ components in the feed gas stream by heat exchange with at least one of a first liquid stream containing C₃ and heavier components, a second liquid stream containing C₃ and heavier components, a residue gas stream, and a refrigerant stream to produce a cooled gas stream;

b) passing the cooled gas stream to a first separator to produce a first separator gas stream and a first separator liquid stream;

c) optionally further cooling the first separator gas stream by heat exchange or expansion and passing it to a separator/absorber wherein the second liquid stream is produced as a bottoms stream and wherein a separator/absorber overhead residue gas stream is produced;

d) passing the first separator liquid stream to a second separator at a lower pressure than the first separator and separating a second separator residue gas stream and a second separator liquid stream;

e) passing the first separator liquid stream and the second separator liquid stream to a deethanizer tower operating at a pressure at least 25 psi above the separator/absorber pressure;

f) separating the first and the second separator liquid streams into a deethanizer bottoms stream containing a majority of the C₃ and heavier components and a deethanizer overhead gas stream;

g) cooling the deethanizer overhead gas stream to partially condense the deethanizer overhead gas stream by heat exchange with a refrigerant stream to produce a deethanizer liquid reflux stream, a third liquid stream and a deethanizer residue gas stream; and

,

j) cooling the third liquid stream by heat exchange with the separator/absorber overhead residue gas stream to produce a subcooled third liquid stream and passing the subcooled third liquid stream into an upper portion of the separator/absorber.

16. The process of claim 15 wherein the refrigerant comprises propane.

17. The process of claim 15 wherein the pressure of the deethanizer is at least 100 psi greater than the pressure in the separator/absorber.

18. The process of claim 15 wherein the pressure in the deethanizer is at least 200 psi greater than the pressure in the separator/absorber.

19. The process of claim 15 wherein the separator/absorber contains at least one theoretical stage of mass transfer.