Gas processing

• US 5,275,005 A
• Filed: 12/01/1992
• Issued: 01/04/1994
• Est. Priority Date: 12/01/1992
• Status: Expired due to Term

• Current Assignee: Ortloff Enigneers, Ltd.
• Original Assignee: Elcor Corporation
• Inventors: Hudson, Hank M., Wilkinson, John D., Campbell, Roy E.
• Primary Examiner(s): Bennet, Henry A.
• Assistant Examiner(s): KILNER, CHRISTOPHER B
• Application Number:
  US07/983,884
• Time in Patent Office: 399 Days
• Field of Search: 62/24, 62/25, 62/27, 62/28, 62/32, 62/36, 62/42
• US Class Current: 62/621
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• 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 2205/02 using simple phase separation in a vessel or drum
• 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 2230/60 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 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 3/0238 separation of CnHm with 2 carbon atoms or more

Abstract

A process for the recovery of C₂ components (ethylene and/or ethane) and heavier hydrocarbon components from a gas stream containing a significant quantity of components more volatile than methane (e.g., hydrogen, nitrogen, and/or others) is disclosed. The cooled, partially condensed hydrocarbon bearing gas stream is separated into a vapor containing substantial quantities of the component(s) more volatile than methane and a liquid containing predominantly hydrocarbons. The vapor is expanded to the distillation column pressure and then supplied to the column at an upper mid-column feed position. The liquid is expanded to column pressure and supplied to the column at a lower mid-column feed position. A recycle stream is withdrawn from the column at a point below the upper mid-column feed position where the bulk of the volatile components are supplied to the column. The recycle stream is compressed and cooled so that a substantial portion is condensed and then supplied to the column as reflux at the top column feed position. The major portion of this reflux is liquid methane which allows the recovery of a significant portion of the C₂ and heavier components that are in the vapors in the upper section of the distillation column. The distillation column overhead vapor contains predominantly methane and the more volatile components The major portion of the desired components is recovered in the distillation column bottom liquid product.

Claims

1. In a process for the separation of a gas, stream containing methane and components more volatile than methane, C₂ components, C₂ components and heavier hydrocarbon components, into (i) a volatile residue gas fraction containing a major portion of said methane and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₂ components, C₃ 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 supplied to at least one fractionation section in at least one feed stream for fractionation at said lower pressure whereby the major portion of said C₂ components, C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction;

the improvement wherein

(1) a recycle stream is withdrawn from a region of said fractionation section below at least one of said feed streams;

(2) said recycle stream is compressed and thereafter said compressed recycle stream is cooled sufficiently to substantially condense it;

(3) said substantially condensed compressed recycle stream is expanded and thereafter supplied to said fractionation section at a top feed position;

(4) the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams are effective to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₂ components, C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

3. The improvement according to claim 1 or 2 wherein said recycle stream is heated prior to compression.

7. The improvement according to claim 1, 2, 4 or 5 wherein there is more than one fractionation section, and wherein the recycle stream is withdrawn from a region of one of said sections wherein the temperature in said region is warmer than the temperature of at least one of the feed streams to the fractionation sections.

8. The improvement according to claim 7 wherein said recycle stream is heated prior to compression.

2. In a process for the separation of a gas stream containing methane and components more volatile than methane, C₂ components, C₃ components and heavier hydrocarbon components into (i) a volatile residue gas fraction containing a major portion of said methane, C₂ components and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₃ 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 supplied to at least one fractionation section in at least one feed stream for fractionation at said lower pressure whereby the major portion of said C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction;

the improvement wherein

(1) a recycle stream is withdrawn from a region of said fractionation section below at least one of said feed streams;

(2) said recycle stream is compressed and thereafter said compressed recycle stream is cooled sufficiently to substantially condense it;

(3) said substantially condensed compressed recycle stream is expanded and thereafter supplied to said fractionation section at a top feed position;

(4) the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams are effective to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

4. In a process for the separation of a gas stream containing methane and components more volatile than methane, C₂ components, C₃ components and heavier hydrocarbon components into (i) a volatile residue gas fraction containing a major portion of said methane and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₂ components, C₃ 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 supplied to at least one fractionation section in at least one feed stream for fractionation at said lower pressure whereby the major portion of said C₂ components, C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction;

the improvement wherein

(1) a recycle stream is withdrawn from a region of said fractionation section below at least one of said feed streams;

(2) said recycle stream is compressed and thereafter said compressed recycle stream is cooled sufficiently to partially condense it;

(3) said partially condensed compressed recycle stream is separated thereby to provide a vapor stream and a condensed stream;

(4) said condensed stream is expanded and thereafter supplied to said fractionation section at an upper mid-column feed position;

(5) said vapor stream is cooled sufficiently to substantially condense it;

(6) said substantially condensed vapor stream is expanded and thereafter supplied to said fractionation section at a top feed position;

(7) the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams are effective to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₂ components, C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

6. The improvement according to claim 4 or 5 wherein said recycle stream is heated prior to compression.

5. In a process for the separation of a gas stream containing methane and components more volatile than methane, C₂ components, C₃ components and heavier hydrocarbon components into (i) a volatile residue gas fraction containing a major portion of said methane, C₂ components and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₃ 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 supplied to at least one fractionation section in at least one feed stream for fractionation at said lower pressure whereby the major portion of said C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction;

the improvement wherein

(1) a recycle stream is withdrawn from a region of said fractionation section below at least one of said feed streams;

(2) said recycle stream is compressed and thereafter said compressed recycle stream is cooled sufficiently to partially condense it;

(3) said partially condensed compressed recycle stream is separated thereby to provide a vapor stream and a condensed stream;

(4) said condensed stream is expanded and thereafter supplied to said fractionation section at an upper mid-column feed position;

(5) said vapor stream is cooled sufficiently to substantially condense it;

(6) said substantially condensed vapor stream is expanded and thereafter supplied to said fractionation section at a top feed position;

(7) the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams are effective to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

9. In an apparatus for the separation of a gas stream containing methane and components more volatile than methane, C₂ components, C₃ components and heavier hydrocarbon components, into (i) a volatile residue gas fraction containing a major portion of said methane and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₂ components, C₃ 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 further expand it to a lower pressure, whereby said stream is further cooled; and

(c) at least one fractionation section connected to said first expansion means to receive the further cooled stream therefrom in at least one feed;

the improvement wherein said apparatus includes

(1) withdrawing means connected to said fractionation section to receive a recycle stream from a region of said fractionation section below at least one of said feed streams;

(2) compressing means connected to said withdrawing means to receive said recycle stream and compress it;

(3) second cooling means connected to said compressing means to receive said compressed recycle stream and cool it sufficiently to substantially condense it;

(4) second expansion means connected to said second cooling means to receive said substantially condensed compressed recycle stream and expand it, said second expansion means being further connected to said fractionation section to supply said expanded substantially condensed recycle stream to said fractionation section at a top feed position; and

(5) control means adapted to regulate the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₂ components, C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

10. In an apparatus for the separation of a gas stream containing methane and components more volatile than methane, C₂ components, C₃ components and heavier hydrocarbon components, into (i) a volatile residue gas fraction containing a major portion of said methane, C₂ components and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₃ 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 further expand it to a lower pressure, whereby said stream is further cooled; and

(c) at least one fractionation section connected to said first expansion means to receive the further cooled stream therefrom in at least one feed;

the improvement wherein said apparatus includes

(1) withdrawing means connected to said fractionation section to receive a recycle stream from a region of said fractionation section below at least one of said feed streams;

(2) compressing means connected to said withdrawing means to receive said recycle stream and compress it;

(3) second cooling means connected to said compressing means to receive said compressed recycle stream and cool it sufficiently to substantially condense it;

(4) second expansion means connected to said second cooling means to receive said substantially condensed compressed recycle stream and expand it, said second expansion means being further connected to said fractionation section to supply said expanded substantially condensed recycle stream to said fractionation section at a top feed position; and

(5) control means adapted to regulate the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

11. The improvement according to claim 9 or 10 wherein said apparatus includes heating means connected to said withdrawing means to receive said recycle stream and heat it, said heating means being further connected to said compressing means to supply said heated recycle stream thereto.

15. The improvement according to claim 9, 10, 12 or 13 wherein said apparatus includes more than one fractionation section and wherein said withdrawing means are connected to one of said sections to withdraw said recycle stream from a region of the section wherein the temperature in the region is warmer than the temperature of at least one of the feed streams to the fractionation sections.

16. The improvement according to claim 15 wherein said apparatus includes heating means connected to said withdrawing means to receive said recycle stream and heat it, said heating means being further connected to said compressing means to supply said heated recycle stream thereto.

12. In an apparatus for the separation of a gas stream containing methane and components more volatile than methane, C₂ components, C₃ components and heavier hydrocarbon components, into (i) a volatile residue gas fraction containing a major portion of said methane and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₂ components, C₃ 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 further expand it to a lower pressure, whereby said stream is further cooled; and

(c) at least one fractionation section connected to said first expansion means to receive the further cooled stream therefrom in at least one feed;

the improvement wherein said apparatus includes

(1) withdrawing means connected to said fractionation section to receive a recycle stream from a region of said fractionation section below at least one of said feed streams;

(2) compressing means connected to said withdrawing means to receive said recycle stream and compress it;

(3) second cooling means connected to said compressing means to receive said compressed recycle stream and cool it sufficiently to partially condense it;

(4) separating means connected to said second cooling means to receive said partially condensed compressed recycle stream and separate it into a vapor stream and a condensed stream;

(5) second expansion means connected to said separating means to receive said condensed stream and expand it, said second expansion means being further connected to said fractionation section to supply said expanded condensed stream to said fractionation section at an upper mid-column feed position;

(6) third cooling means connected to said separating means to receive said vapor stream and cool it sufficiently to substantially condense it;

(7) third expansion means connected to said third cooling means to receive said substantially condensed vapor stream and expand it, said third expansion means being further connected to said fractionation section to supply said expanded substantially condensed vapor stream to said fractionation section at a top feed position; and

(8) control means adapted to regulate the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₂ components, C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

14. The improvement according to claim 12 or 13 wherein said apparatus includes heating means connected to said withdrawing means to receive said recycle stream and heat it, said heating means being further connected to said compressing means to supply said heated recycle stream thereto.

13. In an apparatus for the separation of a gas stream containing methane and components more volatile than methane, C₂ components, C₃ components and heavier hydrocarbon components, into (i) a volatile residue gas fraction containing a major portion of said methane, C₂ components and components more volatile than methane and (ii) a relatively less volatile fraction containing a major portion of said C₃ 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 further expand it to a lower pressure, whereby said stream is further cooled; and

(c) at least one fractionation section connected to said first expansion means to receive the further cooled stream therefrom in at least one feed;

the improvement wherein said apparatus includes

(1) withdrawing means connected to said fractionation section to receive a recycle stream from a region of said fractionation section below at least one of said feed streams;

(2) compressing means connected to said withdrawing means to receive said recycle stream and compress it;

(3) second cooling means connected to said compressing means to receive said compressed recycle stream and cool it sufficiently to partially condense it;

(4) separating means connected to said second cooling means to receive said partially condensed compressed recycle stream and separate it into a vapor stream and a condensed stream;

(5) second expansion means connected to said separating means to receive said condensed stream and expand it, said second expansion means being further connected to said fractionation section to supply said expanded condensed stream to said fractionation section at an upper mid-column feed position;

(6) third cooling means connected to said separating means to receive said vapor stream and cool it sufficiently to substantially condense it;

(7) third expansion means connected to said third cooling means to receive said substantially condensed vapor stream and expand it, said third expansion means being further connected to said fractionation section to supply said expanded substantially condensed vapor stream to said fractionation section at a top feed position; and

(8) control means adapted to regulate the quantity and pressure of said compressed recycle stream and the temperatures of said feed streams to maintain the overhead temperature of said fractionation section at a temperature whereby the major portion of said C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.