Hydrocarbon gas processing

• US 5,799,507 A
• Filed: 10/25/1996
• Issued: 09/01/1998
• Est. Priority Date: 10/25/1996
• Status: Expired due to Term

• Current Assignee: UOP Llc (Honeywell International Inc.)
• Original Assignee: Elcor Corporation
• Inventors: Cuellar, Kyle T., Hudson, Hank M., Wilkinson, John D.
• Primary Examiner(s): CAPOSSELA, RONALD C
• Application Number:
  US08/738,321
• Time in Patent Office: 676 Days
• Field of Search: 62/621, 62/619
• US Class Current: 62/621
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: C10L 3/10 Working-up natural gas or synthetic natural gas
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/50 using multiple (re-)boiler-condensers at different heights of the column
• 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 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 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 the recovery of propane, propylene and heavier hydrocarbon components from a hydrocarbon gas stream is disclosed. The stream is cooled and/or expanded to partially condense it, then separated to provide one or more C₃ containing liquid steams and a first vapor stream. These streams are then directed into a distillation column wherein a second vapor stream is separated to recover a product containing the major portion of the C₃ components and heavier hydrocarbon components. A distillation stream is withdrawn from the column below the feed point of the first vapor stream and is then directed into heat exchange relation with the second vapor stream to cool the distillation stream and condense at least a part of it, forming a condensed stream. At least a portion of the condensed stream is directed to the distillation column as its top feed. The quantities and temperatures of the feeds to the distillation column are effective to maintain the overhead temperature of the distillation column at a temperature whereby the major portion of the desired components is recovered.

Claims

1. In a process for the separation of a gas stream containing methane, C₂ components, C₃ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and C₂ components and a relatively less volatile fraction containing a major portion of said C₃ components and heavier hydrocarbon components, in which process

(a) said gas stream is treated in one or more heat exchange and/or expansion steps to partially condense at least a portion thereof and provide thereby at least a first vapor stream and at least one C₃ -containing liquid stream which also contains lighter hydrocarbons;

and

(b) at least one of said C₃ -containing liquid streams is directed into a distillation column wherein said liquid is separated into a second vapor stream containing predominantly methane and C₂ components and said relatively less volatile fraction containing the major portion of said C₃ components and heavier hydrocarbon components;

the improvement wherein

(1) at least a portion of said first vapor stream is directed into a mid-column feed position on said distillation column as a second feed thereto;

(2) a vapor distillation stream is withdrawn from a region of said distillation column below said first vapor stream and cooled sufficiently to condense at least a part of it, thereby forming a third vapor stream and a condensed stream;

(3) at least a portion of said condensed stream is supplied to said distillation column at a top feed position;

(4) at least a portion of said second vapor stream is directed into heat exchange relation with said vapor distillation stream, thereby to supply at least a portion of the cooling of step (2) and thereafter discharging at least a portion of said second vapor stream and said third vapor stream as said volatile residue gas fraction; and

(6) the quantities and temperatures of said feed streams to said distillation column are effective to maintain the overhead temperature of said distillation column at a temperature whereby the major portion of said C₃ components and heavier hydrocarbon components is recovered in said relatively less volatile fraction.

2. The improvement according to claim 1 wherein a liquid distillation stream is withdrawn from said distillation column at a location above the region wherein said vapor distillation stream is withdrawn, whereupon said liquid distillation stream is heated and thereafter redirected into said distillation column as a third feed thereto at a location below the region wherein said vapor distillation stream is withdrawn.

3. The improvement according to claim 1 wherein

(1) said condensed stream is divided into at least a first liquid stream and a second liquid stream;

(2) said first liquid stream is supplied to said distillation column at a top feed position; and

(3) said second liquid stream is supplied to said distillation column as a third feed thereto, said third feed location being in substantially the same region wherein said vapor distillation stream is withdrawn.

4. The improvement according to claim 3 wherein a liquid distillation stream is withdrawn from said distillation column at a location above the region wherein said vapor distillation stream is withdrawn, whereupon said liquid distillation stream is heated and thereafter redirected into said distillation column as a fourth feed thereto at a location below the region wherein said vapor distillation stream is withdrawn.

5. In an apparatus for the separation of a gas containing methane, C₂ components, C₃ components and heavier hydrocarbon components into a volatile residue gas fraction containing a major portion of said methane and C₂ components and a relatively less volatile fraction containing a major portion of said C₃ components and heavier components, in said apparatus there being

(a) one or more first heat exchange means and/or expansion means cooperatively connected to provide at least one partially condensed gas stream, providing thereby at least a first vapor stream and at least one C₃ -containing liquid which also contains lighter hydrocarbons;

and

(b) a distillation column connected to receive at least one of said C₃ -containing liquid streams which is adapted to separate said stream into a second vapor stream containing predominantly methane and C₂ components and said relatively less volatile fraction containing the major portion of said C₁ components and heavier hydrocarbon components;

the improvement wherein said apparatus includes

(1) connecting means connected to said distillation column to supply at least a portion of said first vapor stream to said distillation column at a mid-column feed position;

(2) vapor withdrawing means connected to said distillation column to receive a vapor distillation stream from a region of said distillation column below said first vapor stream;

(3) second heat exchange means connected to said vapor withdrawing means to receive said vapor distillation stream and cool it sufficiently to condense at least a part of it;

(4) separating means connected to said second heat exchange means to receive said partially condensed distillation stream and separate it, thereby to form a third vapor stream and a condensed stream, said separating means being further connected to said distillation column to supply at least a portion of said condensed stream to said distillation column at a top feed position;

(5) said distillation column being further connected to said second heat exchange means to direct at least a portion of said second vapor stream separated therein into heat exchange relation with said vapor distillation stream; and

(6) control means adapted to regulate the quantities and temperatures of said feed streams to said distillation column to maintain the overhead temperature of said distillation column at a temperature whereby the major portion of said C₃ components and heavier components is recovered in said relatively less volatile fraction.

6. The improvement according to claim 5 wherein said apparatus includes

(1) liquid withdrawing means connected to said distillation column to receive a liquid distillation stream from a region of said distillation column above that of said vapor withdrawing means;

(2) said first heat exchange means connected to said liquid withdrawing means to receive said liquid distillation stream and heat it; and

(3) said first heat exchange means being further connected to said distillation column to supply said heated stream to said distillation column at a location below that of said vapor withdrawing means.

7. The improvement according to claim 5 wherein said apparatus includes

(1) dividing means connected to said separating means to receive said condensed stream and divide it into at least first and second liquid streams, said dividing means being further connected to said distillation column to supply said first liquid stream to said distillation column at a top feed position;

and

(2) said dividing means being further connected to said distillation column to supply said second liquid stream to said distillation column at a location in substantially the same region as said vapor withdrawing means.

8. The improvement according to claim 7 wherein said apparatus includes

(1) liquid withdrawing means connected to said distillation column to receive a liquid distillation stream from a region of said distillation column above that of said vapor withdrawing means;

(2) first heat exchange means connected to said liquid withdrawing means to receive said liquid distillation stream and heat it; and

(3) said first heat exchange means being further connected to said distillation column to supply said heated stream to said distillation column at a location below that of said vapor withdrawing means.