Hydrocarbon gas processing

• US 4,869,740 A
• Filed: 05/17/1988
• Issued: 09/26/1989
• Est. Priority Date: 05/17/1988
• Status: Expired due to Fees

• Current Assignee: Torgo Ltd.
• Original Assignee: Elcor Corporation
• Inventors: Hudson, Hank M., Wilkinson, John D., Campbell, Roy E.
• Primary Examiner(s): Capossela, Ronald C.
• Application Number:
  US07/194,822
• Time in Patent Office: 497 Days
• Field of Search: 62/23, 62/24, 62/32, 62/36, 62/38, 62/39, 62/42
• US Class Current: 62/621
• CPC Class Codes: C07C 7/04 by distillation
• CPC Class Codes: F25J 2200/02 in a single 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 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/80 using integrated mass and heat exchange, i.e. non-adiabatic rectification in a reflux exchanger or dephlegmator
• 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 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• CPC Class Codes: F25J 2230/30 Compression of the feed stream
• 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 2240/40 Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/02 Internal refrigeration with liquid vaporising loop
• 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

Abstract

A process for the recovery of ethane and heavier hydrocarbon components from a hydrocarbon gas stream is disclosed. The stream is divided into first and second streams. The first stream is cooled to condense substantially all of it and is thereafter expanded to a pressure below that of the distillation column. After expansion, the cooled first stream is directed in heat exchange relation with a warmer distillation stream rising from fractionation stages of the distillation column. The warmed first stream is then separated to provide a cold vapor and a liquid stream. The liquid is supplied to the column at a first mid-column feed position and the cold vapor is supplied to the column at a second mid-column feed position. The second stream is expanded to the column pressure and is then supplied to the column at a third mid-column feed position. The distillation stream is cooled by the first stream sufficiently to partially condense it . The partially condensed distillation stream is then separated to provide volatile residue gas and a reflux stream feed. The reflux stream feed is supplied to the column at a top column feed position. In instances where the second stream is expanded in a work expansion machine, any condensation formed prior to work expansion is combined either in whole or in part with the first stream prior to cooling and/or expansion, or supplied either in whole or in part to the column as a condensed stream at a fourth mid-column feed position, or some combination thereof. The temperatures of the feeds to the column are effective to maintain the column overhead temperature at a temperature whereby the major portion of the C₂ + components is recovered.

Claims

1. In a process for the separation of a gas containing methane, C₂ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C₂ components and heavier components, in which process

(a) said gas is cooled under pressure to provide a cooled stream;

(b) said cooled stream is expanded to a lower pressure whereby it is further cooled; and

(c) said further cooled stream is fractionated at said lower pressure whereby the major portion of said C₂ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction;

the improvement wherein said gas is cooled sufficiently to partially condense it; and

(1) said partially condensed gas is separated thereby to provide a vapor stream and a condensed stream;

(2) said vapor stream is thereafter divided into gaseous first and second streams;

(3) said gaseous first stream is combined with at least a portion of said condensed stream to form a combined stream and said combined stream is cooled to condense substantially all of it and is thereafter expanded to a pressure below the fractionation pressure;

(4) the expanded cooled combined stream is then directed in heat exchange relation with a warmer distillation stream which rises from fractionation stages of a distillation column;

(5) the distillation stream is cooled by said combined stream sufficiently to partially condense it and said partially condensed distillation stream is separated thereby to provide said volatile residue gas and a reflux stream, said reflux stream is supplied to said distillation column at a top column feed position;

(6) the combined stream is separated thereby to provide a cold vapor stream and a liquid stream, the liquid stream is pumped to said column at a first mid-column feed position;

(7) the cold vapor stream is compressed and fed to the column at a second mid-column feed position;

(8) the gaseous second stream is expanded to said fractionation pressure and is supplied to said distillation column at a third mid-column feed position; and

(9) the temperatures of said feeds to the column are effective to maintain column overhead temperature at a temperature whereby the major portion of said C₂ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

2. The improvement according to claim 1 wherein the distillation column is a lower portion of a fractionation tower and wherein

(a) the distillation stream is cooled by the expanded cooled combined stream and

(b) the cooled distillation stream is separated to provide the volatile residue gas and the reflux stream

in a portion of the tower above the distillation column and wherein said reflux stream flows to the top fractionation stage of the distillation column.

3. The improvement according to claim 1 wherein the reflux stream is directed through a pump to the distillation column.

4. The improvement according to claim 1 wherein the distillation stream is (a) cooled to partially condense it and (b) separated in a dephlegmator to provide said volatile residue gas and a reflux stream and wherein the reflux stream flows from the dephlegmator to the top fractionation stage of the distillation column.

17. The improvement according to claim 1, 5 or 11 wherein said cold vapor stream is cooled after compression.

18. The improvement according to claim 17 wherein said liquid stream cools said cold vapor stream after compression.

19. The improvement according to claim 1, 5 or 11 wherein the stream directed in heat exchange relation with the distillation stream is cooled prior to expansion by said liquid stream.

20. The improvement according to claim 1, 9 or 16 wherein at least a portion of the condensed stream is expanded to said lower pressure and is supplied to said distillation column at a fourth mid-column feed position.

21. The improvement according to claim 20 wherein said cold vapor stream is cooled after compression.

22. The improvement according to claim 20 wherein at least portions of at two of said liquid stream, said cold vapor stream, said second stream and said condensed stream are combined to form a second combined stream and said second combined stream is supplied to said column at a mid-column feed position.

24. The improvement according to claim 1, 9 or 16 wherein,

(a) said condensed stream is cooled and divided into first and second portions;

(b) said first portion is expanded to said lower pressure and supplied to said column at a mid-column feed position; and

(c) the second portion is supplied to said column at a higher mid-column feed position.

25. The improvement according to claim 24 wherein

(a) at least part of said second portion is combined with said first stream to form a combined stream and said combined stream is directed in heat exchange relation with said distillation stream and then separated to provide said cold vapor stream and said liquid stream;

and

(b) the remainder of said second portion is expanded to said lower pressure and supplied to said column at another mid-column feed position.

26. The improvement according to claim 24 wherein the first portion is expanded, directed in heat exchange relation with said condensed stream and then supplied to said column at a lower mid-column feed position.

27. The improvement according to claim 24 wherein said second portion is expanded to said lower pressure and at least part of said expanded second portion is combined with said expanded cooled first stream to form a combined stream and said combined stream is directed in heat exchange relation with said distillation stream and then separated to provide said cold vapor stream and said liquid stream.

5. In a process for the separation of a gas containing methane, C₂ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C₂ components and heavier components, in which process

(a) said gas is cooled under pressure to provide a cooled stream;

(b) said cooled stream is expanded to a lower pressure whereby it is further cooled; and

(c) said further cooled stream is fractionated at said lower pressure whereby the major portion of said C₂ components and heavier components is recovered in said relatively less volatile fraction;

the improvement wherein prior to cooling, said gas is divided into gaseous first and second streams and

(1) said gaseous first stream is cooled to condense substantially all of it and is thereafter expanded to a pressure below the fractionation pressure;

(2) said gaseous second stream is cooled under pressure and is thereafter expanded to said lower pressure;

(3) the expanded cooled first stream is directed in heat exchange relation with a warmer distillation stream which rises from fractionation stages of a distillation column;

(4) the distillation stream is cooled by said first stream sufficiently to partially condense it and said partially condensed distillation stream is separated thereby to provide said volatile residue gas and a reflux stream, said reflux stream is supplied to said distillation column at a top column feed position;

(5) the first stream is separated thereby to provide a cold vapor stream and a liquid stream, the liquid stream is pumped to said distillation column at a first mid-column feed position;

(6) the cold vapor stream is compressed and fed to the column at a second mid-column feed position;

(7) the expanded cooled second stream is supplied to said distillation column at a third mid-column feed position; and

(8) the temperatures of said feeds to the column are effective to maintain column overhead temperature at a temperature whereby the major portion of said C₂ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

6. The improvement according to claim 5 wherein the distillation column is a lower portion of a fractionation tower and wherein

(a) the distillation stream is cooled by the expanded cooled first stream and

(b) the cooled distillation stream is separated to provide the volatile residue gas and the reflux stream

in a portion of the tower above the distillation column and wherein said reflux stream flows to the top fractionation stage of the distillation column.

7. The improvement according to claim 5 wherein the reflux stream is directed through a pump to the distillation column.

8. The improvement according to claim 5 wherein the distillation stream is (a) cooled to partially condense it and (b) separated in a dephlegmator to provide said volatile residue gas and a reflux stream and wherein the reflux stream flows from the dephlegmator to the top fractionation stage of the distillation column.

9. The improvement according to claim 5 wherein the second stream is expanded to said lower pressure in a work expansion machine and wherein

(a) prior to work expansion, said second stream is a partially condensed stream;

(b) said partially condensed second stream is separated thereby to provide another vapor stream and a condensed stream;

(c) said other vapor stream is expanded in the work expansion machine and supplied to said distillation column at a second mid-column feed position; and

(d) at least a portion of said condensed stream is combined with said first stream to form a combined stream which is cooled to condense substantially all of it and is thereafter expanded to a pressure below the fractionation pressure and wherein said expanded combined stream is then directed in heat exchange relation with said distillation stream.

10. The improvement according to claim 5 wherein the second stream is expanded to said lower pressure in a work expansion machine and wherein

(a) prior to work expansion, said second stream is a partially condensed stream;

(b) said partially condensed second stream is separated thereby to provide another vapor stream and a condensed stream;

(c) said other vapor stream is expanded in the work expansion machine and supplied to said distillation column at a second mid-column feed position; and

(d) said condensed stream is expanded to said fractionation pressure and is supplied to said distillation column at a fourth mid-column feed position.

11. In a process for the separation of a gas containing methane, C₂ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C₂ components and heavier components, in which process

(a) said gas is cooled under pressure to provide a cooled stream;

(b) said cooled stream is expanded to a lower pressure whereby it is further cooled; and

(c) said further cooled stream is fractionated at said lower pressure whereby the major portion of said C₂ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction;

the improvement wherein following cooling, said cooled stream is divided into first and second streams and

(1) said first stream is cooled to condense substantially all of it and is thereafter expanded to a pressure below the fractionation pressure;

(2) said second stream is expanded to said lower pressure;

(3) the expanded cooled first stream is directed in heat exchange relation with a warmer distillation stream which rises from fractionation stages of a distillation column;

(4) the distillation stream is cooled by said first stream sufficiently to partially condense it and said partially condensed distillation stream is separated thereby to provide said volatile residue gas and a reflux stream, said reflux stream is supplied to said distillation column at a top column feed position;

(5) the first stream is separated thereby to provide a cold vapor stream and a liquid stream, the liquid stream is pumped to said column at a first mid-column feed position;

(6) the cold vapor stream is compressed and fed to the column at a second mid-column feed position;

(7) the expanded second stream is supplied to said distillation column at a third mid-column feed position; and

(8) the temperatures of said feeds to the column are effective to maintain column overhead temperature at a temperature whereby the major portion of said C₂ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

12. The improvement according to claim 11 wherein the distillation column is a lower portion of a fractionation tower and wherein

(a) the distillation stream is cooled by the expanded cooled first stream and

(b) the cooled distillation stream is separated to provide the volatile residue gas and the reflux stream

in a portion of the tower above the distillation column and wherein said reflux stream flows to the top fractionation stage of the distillation column.

13. The improvement according to claim 11 wherein the reflux stream is directed through a pump to the distillation column.

14. The improvement according to claim 11 wherein the distillation stream is (a) cooled to partially condense it and (b) separated in a dephlegmator to provide said volatile residue gas and a reflux stream and wherein the reflux stream flows from the dephlegmator to the top fractionation stage of the distillation column.

15. The improvement according to claim 11 wherein the second stream is cooled after said division and prior to the expansion to said lower pressure.

16. The improvement according to claim 11 wherein the second stream is expanded to said lower pressure in a work expansion machine and wherein

(a) prior to work expansion, said second stream is a partially condensed stream;

(b) said partially condensed second stream is separated thereby to provide another vapor stream and a condensed stream;

(c) said other vapor stream is expanded in the work expansion machine and supplied to said distillation column at a second mid-column feed position; and

(d) at least a portion of said condensed stream is combined with said first stream to form a combined stream which is cooled to condense substantially all of it and is thereafter expanded to a pressure below the fractionation pressure and wherein said expanded combined stream is then directed in heat exchange relation with said distillation stream.

23. The improvement according to claim 5 or 11 wherein at least portions of least two of said liquid stream, said cold vapor stream and said second stream are combined to form a combined stream and said combined stream is supplied to said column at a mid-column feed position.

29. The improvement according to claim 11 wherein the second stream is expanded to said lower pressure in a work expansion machine and wherein

(a) prior to work expansion, said second stream is a partially condensed stream;

(b) said partially condensed second stream is separated thereby to provide another vapor stream and a condensed stream;

(c) said other vapor stream is expanded in the work expansion machine and supplied to said distillation column at a second mid-column feed position; and

(d) said condensed stream is expanded to said fractionation pressure and is supplied to said distillation column at a fourth mid-column feed position.

28. In a process for the separation of a gas containing methane, C₂ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C₂ components and heavier components, in which process

(a) said gas is cooled under pressure to provide a cooled stream;

(b) said cooled stream is expanded to a lower pressure whereby it is further cooled; and

(c) said further cooled stream is fractionated at said lower pressure whereby the major portion of said C₂ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction;

the improvement wherein said gas is cooled sufficiently to partially condense it; and

(1) said partially condensed gas is separated thereby to provide a vapor stream and a condensed stream;

(2) said vapor stream is thereafter divided into gaseous first and second streams;

(3) said gaseous first stream is cooled to condense substantially all of it and is thereafter expanded to a pressure below the fractionation pressure;

(4) the expanded cooled first stream is then directed in heat exchange relation with a warmer distillation stream which rises from fractionation stages of a distillation column;

(5) the distillation stream is cooled by said first stream sufficiently to partially condense it and said partially condensed distillation stream is separated thereby to provide said volatile residue gas and a reflux stream, said reflux stream is supplied to said distillation column at a top column feed position;

(6) the first stream is separated thereby to provide a cold vapor stream and a liquid stream, the liquid stream is pumped to said column at a first mid-column feed position;

(7) the cold vapor stream is compressed and fed to the column at a second mid-column feed position;

(8) the gaseous second stream is expanded to said fractionation pressure and is supplied to said distillation column at a third mid-column feed position;

(9) said condensed stream is expanded to said fractionation pressure and is supplied to said distillation column at a fourth mid-column feed position; and

(10) the temperatures of said feeds to the column are effective to maintain column overhead temperature at a temperature whereby the major portion of said C₂ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

30. In an apparatus for the separation of a gas containing methane, C₂ components and heavier hydrocarbons into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C₂ components and heavier components, in said apparatus there being

(a) a first cooling means to cool said gas under pressure connected to provide a cooled stream under pressure;

(b) a first expansion means connected to receive at least a portion of said cooled stream under pressure and to expand it to a lower pressure, whereby said stream is further cooled; and

(c) a distillation column connected to said first expansion means to receive the further cooled stream therefrom;

the improvement wherein said apparatus includes

(1) first to cool said feed gas under pressure sufficiently to partially condense it;

(2) first separation means connected to said first cooling means to receive said partially condensed feed and to separate it into a vapor and a condensed stream;

(3) dividing means connected to said first separation means to receive said vapor and to divide said vapor into first and second streams;

(4) combining means connected to combine said condensed stream and said first stream into a combined stream;

(5) second cooling means connected to said combining means to receive said combined stream and to cool it sufficiently to substantially condense it;

(6) second expansion means connected to said second cooling means to receive said substantially condensed combined stream and to expand it to a pressure below the fractionation pressure;

(7) heat exchange means connected to said second expansion means to receive said expanded combined stream and to heat it, said heat exchange means being further connected to said distillation column at a point to receive a distillation stream rising from fractionation stages of the distillation column and to cool and partially condense said distillation stream;

said heat exchange means being further connected to second and third separation means;

(8) said second separation means being connected to said heat exchange means to receive said combined stream and to separate it into a cold vapor stream and a liquid stream, said second separation means being further connected to (a) pumping means and (b) compressing means;

(9) said pumping means being further connected to said distillation column at a first mid-column feed position to supply said liquid stream to said distillation column;

(10) said compressing means being further connected to said distillation column at a second mid-column feed position to supply said cold vapor stream to said distillation column;

(11) said third separation means being connected to said heat exchange means to receive said partially condensed distillation stream and to separate it into said volatile residue gas fraction and a reflux stream, said third separation means being further connected to said distillation column to supply said reflux stream to the distillation column at a top column feed position;

(12) first expansion means being connected to said dividing means to receive said second stream and expand it to said lower pressure, said first expansion means being further connected to said distillation column to supply said expanded stream to said column at a third mid-column feed position; and

(13) control means adapted to regulate the temperatures of said combined stream, said second stream and said reflux stream to maintain column overhead temperature at a temperature whereby the major portion of said C₂ components and heavier components is recovered in said relatively less volatile fraction.

33. The improvement according to claim 30, 31 or 32 wherein the distillation column is a lower portion of a fractionation tower and wherein the heat exchange means is positioned in a portion of the tower above the distillation column.

34. The improvement according to claim 30, 31 or 32 wherein a dephlegmator is connected to said second expansion means to receive the expanded stream and to provide for the heating of said expanded stream, said dephlegmator being further connected to said distillation column at a point to

(i) receive a distillation stream rising from fractionation stages of the distillation column whereby said expanded stream cools and partially condenses said distillation stream as said expanded stream is heated and whereby said partially condensed distillation stream is separated to provide said volatile residue gas and said reflux stream and;

(ii) supply the reflux stream formed in the dephlegmator to the top fractionation stage of the distillation column; and

wherein said dephlegmator is further connected to separation means;

said separation means being connected to said dephlegmator to receive said heated expanded stream and to separate it into said cold vapor stream and said liquid stream, said separation means being further connected to (a) said pumping means and (b) said compressing means.

35. The improvement according to claim 30, 31 or 32 wherein said apparatus includes another heat exchange means connected to receive said compressed cold vapor stream and to cool it, said other heat exchange means being further connected to said column to supply said cooled compressed stream to said column at a mid-column feed position.

31. In an apparatus for the separation of a feed gas containing methane, C₂ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C₂ components and heavier components;

in said apparatus there being

(a) a first cooling means to cool said gas under pressure connected to provide a cooled stream under pressure;

(b) a first expansion means connected to receive at least a portion of said cooled stream under pressure and to expand it to a lower pressure, whereby said stream is further cooled; and

(c) a distillation column connected to said expansion means to receive the further cooled stream therefrom;

the improvement wherein said apparatus includes

(1) dividing means prior to said first cooling means to divide said feed gas into a first gaseous stream and a second gaseous stream;

(2) second cooling means connected to said dividing means to receive said first stream and to cool it sufficiently to substantially condense it;

(3) second expansion means connected to said second cooling means to receive the substantially condensed first stream therefrom and to expand it to a pressure below the fractionation pressure;

(4) heat exchange means connected to said second expansion means to receive said expanded first stream and to heat it, said heat exchange means being further connected to said distillation column at a point to receive a distillation stream rising from fractionation stages of the distillation column wherein said heat exchange means cools and partially condenses said distillation stream;

;

said heat exchange means being further connected to first and second separation means;

(5) said first separation means being connected to said heat exchange means to receive said first stream and to separate it into a cold vapor stream and a liquid stream, said first separation means being further connected to (a) pumping means and (b) compressing means;

(6) said pumping means being further connected to said distillation column at a first mid-column feed position to supply said liquid stream to said distillation column;

(7) said compressing means being further connected to said distillation column at a second mid-column feed position to supply said cold vapor stream to said distillation column;

(8) said second separation means being connected to said heat exchange means to receive said partially condensed distillation stream and to separate it into said volatile residue gas fraction and a reflux stream, said second separation means being further connected to said distillation column to supply said reflux stream to the distillation column at a top column feed position;

(9) said first cooling means being connected to said dividing means to receive said second stream and to cool it;

(10) said first expansion means being connected to said first cooling means to receive said cooled second stream and to expand and further cool it;

said first expansion means being further connected to said distillation column to supply said second stream to the column at a third mid-column feed position; and

(11) control means adapted to regulate the temperatures of said first stream, said second stream and said reflux stream to maintain column overhead temperature at a temperature whereby the major portion of said C₂ components and heavier components is recovered in said relatively less volatile fraction.

32. In an apparatus for the separation of a gas containing methane, C₂ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and a relatively less volatile fraction containing a major portion of said C₂ components and heavier components;

in said apparatus there being

(a) a first cooling means to cool said gas under pressure connected to provide a cooled stream under pressure;

(b) a first expansion means connected to receive at least a portion of said cooled stream under pressure and to expand it to a lower pressure, whereby said stream is further cooled; and

(c) a distillation column connected to said expansion means to receive the further cooled stream therefrom;

the improvement wherein said apparatus includes

(1) dividing means after said first cooling means to divide said cooled stream into a first stream and a second stream;

(2) second cooling means connected to said dividing means to receive said first stream and to cool it sufficiently to substantially condense it;

(3) second expansion means connected to said second cooling means to receive the substantially condensed first stream therefrom and to expand it to a pressure below the fractionation pressure;

(4) heat exchange means connected to said second expansion means to receive said expanded first stream and to heat it, said heat exchange means being further connected to said distillation column at a point to receive a distillation stream rising from fractionation stages of the distillation column wherein said heat exchange means cools and partially condenses said distillation stream;

said heat exchange means being further connected to first and second separation means;

(5) said first separation means being connected to said heat exchange means to receive said first stream and to separate it into a cold vapor stream and a liquid stream, said first separation means being further connected to (a) pumping means and (b) compressing means;

(6) said pumping means being further connected to said distillation column at a first mid-column feed position to supply said liquid stream to said distillation column;

(7) said compressing means being further connected to said distillation column at a second mid-column feed position to supply said cold vapor stream to said distillation column;

(8) said second separation means being connected to said heat exchange means to receive said partially condensed distillation stream and to separate it into said volatile residue gas fraction and a reflux stream, said second separation means being further connected to said distillation column to supply said reflux stream to the distillation column at a top column feed position;

(9) said first expansion means being connected to said dividing means to receive said second stream and to expand and cool it;

said first expansion means being further connected to said distillation column to supply said second stream to the column at a third mid-column feed position; and

(10) control means adapted to regulate the temperatures of said first stream, said second stream and said reflux stream to maintain column overhead temperature at a temperature whereby the major portion of said C₂ components and heavier components is recovered in said relatively less volatile fraction.