Hydrocarbon gas processing

• US 9,021,832 B2
• Filed: 12/28/2010
• Issued: 05/05/2015
• Est. Priority Date: 01/14/2010
• Status: Active Grant

• Current Assignee: UOP Llc (Honeywell International Inc.)
• Original Assignee: Ortloff Enigneers, Ltd.
• Inventors: Pierce, Michael C., Wilkinson, John D., Hudson, Hank M.
• Primary Examiner(s): PETTITT, JOHN F
• Application Number:
  US12/979,563
• Publication Number:
  US 20110167868A1
• Time in Patent Office: 1,589 Days
• Field of Search: 626/20, 626/28, 626/18, 626/11, 626/21, 626/30, 626/32
• US Class Current: 62/620
• 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 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• 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 2200/94 Details relating to the withdrawal point
• 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 2230/30 Compression of the feed stream
• 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 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 and an apparatus are disclosed for recovering ethane, ethylene, and heavier hydrocarbon components from a hydrocarbon gas stream. The stream is cooled, expanded to lower pressure, and supplied to a first fractionation tower at a mid-column feed position. A distillation liquid stream is withdrawn from the first fractionation tower below the feed position of the expanded stream, heated, and directed into a second fractionation tower that produces an overhead vapor stream and a bottom liquid stream. The overhead vapor stream is cooled to condense it, with a portion of the condensed stream directed to the second fractionation tower as its top feed and the remainder directed to the first fractionation tower at a lower column feed position. The bottom liquid stream from the second fractionation tower is cooled and directed to the first fractionation tower as its top feed.

Claims

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

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

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

(c) said further cooled stream is directed into a first distillation column and fractionated at said lower pressure whereby the components of said relatively less volatile fraction are recovered;

the improvement wherein

(1) said further cooled expanded stream is directed to said first distillation column at a mid-column feed position;

(2) a distillation liquid stream is withdrawn from a region of said first distillation column below said mid-column feed position;

(3) said distillation liquid stream is heated, and thereafter directed into a second distillation column and fractionated into an overhead vapor stream and a bottom liquid stream;

(4) said overhead vapor stream is cooled to condense substantially all of it, thereby forming a condensed stream;

(5) said condensed stream is divided into a first portion and a second portion, whereupon said first portion is directed to said second distillation column at a top feed position;

(6) said second portion is directed to said first distillation column at a lower column feed position below said region wherein said distillation liquid stream is withdrawn from said first distillation column;

(7) said bottom liquid stream is cooled, thereby to supply at least a portion of the heating of step (3);

(8) said cooled bottom liquid stream is directed to said first distillation column at a top feed position;

(9) the quantities and temperatures of said feed streams to said second distillation column are effective to maintain the overhead temperature of said second distillation column at a temperature whereby said overhead vapor stream is predominantly C₃ hydrocarbon components and more volatile components, and said bottom liquid stream is predominatly C₄-C₅hydrocarbon components, and

(10) the quantities and temperatures of said feed streams to said first distillation column are effective to maintain the overhead temperature of said first distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

2. The process according to claim 1 wherein

said gas stream is cooled sufficiently to partially condense it;

and

(a) said partially condensed gas stream is separated thereby to provide a vapor stream and at least one liquid stream;

(b) said vapor stream is expanded to said lower pressure and is supplied to said first distillation column at said mid-column feed position;

(c) at least a portion of said at least one liquid stream is expanded to said lower pressure and is supplied to said first distillation column at a lower mid-columnm feed position below said mid-column feed position; and

(d) said distillation liquid stream is withdrawn from a region of said first distillation column below said mid-column feed position and above said lower mid-column feed position.

3. The process according to claim 1 wherein

said cooled stream is divided into first and second streams;

and

(a) said second stream is expanded to said lower pressure and is supplied to said first distillation column at said mid-column feed position;

(b) said first stream is expanded to an intermediate pressure and thereafter combined with said cooled bottom liquid stream to form a combined stream;

(c) said combined stream is cooled and thereafter expanded to said lower pressure; and

(d) said expanded cooled combined stream is directed to said first distillation column at said top feed position.

4. The process according to claim 2 wherein

(a) said vapor stream is divided into first and second streams;

(b) said second stream is expanded to said lower pressure and is supplied to said first distillation column at said mid-column feed position;

(c) said first stream is expanded to an intermediate pressure and thereafter combined with said bottom liquid stream to form a combined stream;

(d) said combined stream is cooled and thereafter expanded to said lower pressure; and

(e) said expanded cooled combined stream is directed to said first distillation column at said top feed position.

5. The process according to claim 2 or 4 wherein said expanded at least a portion of said at least one liquid stream is heated and thereafter supplied to said first distillation column at said another lower mid-column feed position below said mid-column feed position.

6. The process according to claim 1, 2, 3, or 4 wherein

(1) said overhead vapor stream is cooled sufficiently to partially condense it;

(2) said partially condensed overhead vapor stream is separated thereby to provide a residual vapor stream and said condensed stream; and

(3) said residual vapor stream is directed to said first distillation column at another lower column feed position below said region wherein said distillation liquid stream is withdrawn from said distillation column.

7. The process according to claim 5 wherein

(1) said overhead vapor stream is cooled sufficiently to partially condense it;

(2) said partially condensed overhead vapor stream is separated thereby to provide a residual vapor stream and said condensed stream; and

(3) said residual vapor stream is directed to said first distillation column at another lower column feed position below said region wherein said distillation liquid stream is withdrawn from said first distillation column.

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

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

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

(c) a first distillation column connected to receive said further cooled stream, said first distillation column being adapted to separate said further cooled stream into said volatile residue gas fraction and said relatively less volatile fraction;

the improvement wherein said further cooled expanded stream is directed to said first distillation column at a mid-column feed position, and said apparatus includes

(1) liquid withdrawing means connected to said first distillation column to receive a distillation liquid stream from a region of said first distillation column below said mid-column feed position;

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

(3) second distillation column connected to said heat exchange means to receive said heated distillation liquid stream and fractionate it into an overhead vapor stream and a bottom liquid stream;

(4) second cooling means connected to said second distillation column to receive said overhead vapor stream and cool it sufficiently to substantially condense it, thereby forming a condensed stream;

(5) dividing means connected to said second cooling means to receive said condensed stream and divide it into at least a first portion and a second portion;

(6) said dividing means connected to said second distillation column to supply said first portion to said second distillation column at a top feed portion;

(7) said dividing means being further connected to said first distillation column to supply said second portion to said first distillation column at a lower column feed position below said region where said liquid withdrawing means is connected to said first distillation column to withdraw said distillation liquid stream;

(8) said heat exchange means being further connected to said second distillation column to receive said bottom liquid stream and cool it, thereby to supply at least a portion of the heating of step (2),said heat exchange means being further connected to said first distillation column to supply said cooled bottom liquid stream to said first distillation column at a top feed position;

(9) first control means adapted to regulate the quantities and temperatures of said feed to streams to said second distillation column to maintain the overhead temperature of said second distillation column at a whereby said overhead vapor stream is predominantly C₃ hydrocarbon components and more volatile components, and said bottom liquid stream is predominantly C₄-C₅ hydrocarbon components; and

(10) second control means adapted to regulate the quantities and temperatures of said feed streams to said first distillation column to maintain the overhead temperature of said first distillation column at a temperature whereby the major portions of the components in said relatively less volatile fraction are recovered.

9. The apparatus according to claim 8 wherein

said apparatus includes

(a) said first cooling means being adapted to cool said gas stream under pressure sufficiently to partially condense it;

(b) separating means connected to said first cooling means to receive said partially condensed gas stream and separate it into a vapor stream and at least one liquid stream;

(c) said expansion means being connected to said separating means to receive said vapor stream and expand it to said lower pressure, said expansion means being further connected to said first distillation column to supply said expanded vapor stream to said first distillation column at said mid-column feed position;

(d) another expansion means connected to said separating means to receive at least a portion of said at least one liquid stream and expand it to said lower pressure, said another expansion means being further connected to said first distillation column to supply said expanded liquid stream to said first distillation column at a lower mid-column feed position below said mid-column feed position; and

(e) said liquid withdrawing means connected to said first distillation column to receive a distillation liquid stream from a region of said first distillation column below said mid-column feed position and above said lower mid-column feed position.

10. The apparatus according to claim 8 wherein

said apparatus includes

(a) another dividing means connected to said first cooling means to receive said cooled stream and dividing it into first and second streams;

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

(c) another expansion means connected to said first dividing means to receive said first stream and expand it to an intermediate pressure;

(d) combining means connected to said another expansion means said heat exchange means to receive said expanded first stream and said cooled bottom liquid stream and form a combined stream;

(e) third cooling means connected to said combining means to receive said combined stream and cool it; and

(f) further expansion means connected to said third cooling means to receive said cooled combined stream and expand it to said lower pressure, said further expansion means being further connected to said first distillation column to supply said expanded cooled combined stream to said first distillation column at said top feed position.

11. The apparatus according to claim 9 wherein

(a) another dividing means connected to said separating means to receive said vapor stream and divide it into first and second streams;

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

(c) further expansion means connected to said first dividing means to receive said first stream and expand it to an intermediate pressure;

(d) combining means connected to said further expansion means and said heat exchange means to receive said expanded first stream and said cooled bottom liquid stream and form a combined stream;

(e) third cooling means connected to said combining means to receive said combined stream and cool it; and

(f) additional expansion means connected to said third cooling means to receive said cooled combined stream and expand it to said lower pressure, said additional expansion means being further connected to said first distillation column to supply said expanded cooled combined stream to said first distillation column at said top feed position.

12. The improvement according to claim 8 wherein

(1) said second cooling means is adapted to cool said overhead vapor stream sufficiently to partially condense it;

(2) a separating means is connected to said second cooling means to receive said partially condensed overhead vapor stream and separate it into a residual vapor stream and said condensed stream;

(3) said dividing means is adapted to be connected to said separating means to receive to said condensed stream;

and

(4) said separating means is connected to said first distillation column to supply said residual vapor stream to said first distillation column at another lower column feed position below said region where said liquid withdrawing means is connected to said first distillation column to withdraw said distillation liquid stream.

13. The apparatus according to claim 9 wherein

(1) said second cooling means is adapted to cool said overhead vapor stream sufficiently to partially condense it;

(2) another separating means is connected to said second cooling means to receive said partially condensed overhead vapor stream and separate it into a residual vapor stream and said condensed stream;

(3) said dividing means is adapted to be connected to said another separating means to receive said condensed stream;

and

(4) said another separating means is connected to said first distillation column to supply said residual vapor stream to said first distillation column at another lower column feed position below said region where said liquid withdrawing means is connected to said first distillation column to withdraw said distillation liquid stream.

14. The apparatus according to claim 10 wherein

(1) said second cooling means is adapted to cool said overhead vapor stream sufficiently to partially condense it;

(2) a separating means is connected to said second cooling means to receive said partially condensed overhead vapor stream and separate it into a residual vapor stream and said condensed stream;

(3) said second dividing means is adapted to be connected to said separating means to receive said condensed stream; and

(4) said separating means is connected to said first distillation column to supply said residual vapor stream to said first distillation column at another lower column position below said region where said liquid withdrawing means is connected to said first distillation column to withdraw said distillation liquid stream.

15. The apparatus according to claim 11 wherein

(1) said second cooling means is adapted to cool said overhead vapor stream sufficiently to partially condense it;

(2) another separating means is connected to said second cooling means to receive said partially condensed overhead vapor stream and separate it into a residual vapor stream and said condensed stream;

(3) said dividing means is adapted to be connected to said another separating means to receive condensed stream; and

(4) said another separating means is connected to said first distillation column to supply said residual vapor stream to said first distillation column at another lower column feed position below said region where said liquid withdrawing means is connected to said first distillation column to withdraw said distillation liquid stream.

16. The apparatus according to claim 9, 11, 13, or 15 wherein a heating means is connected to said second expansion means to receive said expanded liquid stream and heat it,said heating means being further connected to said first distillation column to supply said heated expanded liquid stream to said first distillation column at said lower mid-column feed position.