Process for C.sub.2 recovery

• US 4,895,584 A
• Filed: 01/12/1989
• Issued: 01/23/1990
• Est. Priority Date: 01/12/1989
• Status: Expired due to Term

• Current Assignee: Linde Boc Process Plants LLC (Linde Plc)
• Original Assignee: Pro-Quip Corp. (Linde Plc)
• Inventors: Key, Ronald D., Buck, Loren L.
• Primary Examiner(s): Capossela, Ronald C.
• Application Number:
  US07/296,432
• Time in Patent Office: 376 Days
• Field of Search: 62/23, 62/24, 62/27, 62/28, 62/29, 62/31
• 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 2200/30 using a side column in a single pressure 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 2205/04 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 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 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• 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

An improved process for separating a hydrocarbon bearing feed gas containing methane and lighter, C₂ (ethylene and ethane) and heavier components into a fraction containing predominantly methane and lighter components and a fraction containing predominantly C₂ and heavier hydrocarbon components including the steps of cooling and partially condensing and delivering the feed stream to a separator to provide a first residue vapor and a C₂ containing liquid, directing a portion of the C₂ containing liquid into a heavy ends fractionation column wherein the liquid is separated into a second hydrocarbon bearing vapor residue and a C₂ containing product, conducting a portion of the first residue vapors with at least part of the partially condensed second residue into a light ends fractionating column to thereby obtain third residue vapors and liquids, supplying the liquids recovered from the light ends fractionating column to the heavy ends fractionation column as the liquid feed thereto and directing part of the C₂ containing liquid from the first step into intimate contact with the second residue, which liquid provides additional liquefied methane which acts with the partially condensed second residue as a direct contact refrigerant to thereby condense C₂ and heavier components while the methane itself is evaporated in the light ends fractionation column.

Claims

1. An improved process for separating a hydrocarbon bearing feed gas containing ethane and C₂ (ethylene and/or ethane) components into a fraction containing predominantly methane and lighter components and a fraction containing a predominant portion of the C₂ and heavier components, comprising the steps of:

(a) cooling and partially condensing the feed gas and delivering it to a separator to provide thereby a first residue vapor and a C₂ -containing liquid, which liquid also contains lighter hydrocarbons including appreciable methane;

(b) directing at least part of the C₂ -containing liquid into a heavy ends fractionation column wherein said liquid is separated into a second hydrocarbon bearing residue vapor containing predominantly methane and a C₂ -containing product;

(c) passing the second residue through a heat exchanger to condense at least a major portion of the methane content thereof;

(d) contacting at least part of said first residue vapors with at least part of the partially condensed second residue in a light ends fractionation column to thereby obtain third residue vapors and liquids;

(e) supplying the liquids thereby recovered from the light ends fractionating column to the heavy end fractionation column as a liquid feed thereto; and

(f) directing at least part of the C₂ -containing liquid from step (a) into intimate contact with the second residue prior to step (d), which liquid provides additional liquefied methane which acts with said partially condensed second residue as a direct contact refrigerant to thereby condense C₂ and heavier components while the methane itself is evaporated in the light ends fractionation column.

2. The improved process according to claim 1 wherein the light ends fractionation column of step (c) includes fractionation means for vapor-liquid counter-current contact wherein said partly condensed second residue in conjunction with at least a portion of the C₂ containing liquid from step (a) is introduced into said light ends fractionation column above said fractionation means, whereby the liquid portion of it passes downwardly through said fractionation means and said first residue vapors is supplied to said light ends fractionation column below said fractionation means, whereby the first residue vapor rises through said fractionation means in counter-current contact with the liquid portion of the partly condensed second residue and said C₂ containing liquid admixed therewith in step (e).

3. The improved process according to claim 2 wherein the fractionation means in said light ends fractionation column provide the equivalent of at least one theoretical distillation stage arranged to contact at least part of said first residue vapors with the liquid portion of the partly condensed second residue and said C₂ containing liquid admixed therewith in step (e).

4. The process of claim 1 including the step of:

cooling the C₂ -containing liquid from step (a).

5. The proces of claim 1 including the step of:

cooling the combined second residue and C₂ -containing liquid from step (a) before the same is delivered into the light ends fractionation column.

6. The process of claim 1 including the step of:

directing the third residue recovered from the light ends fractionation column into heat exchange relation with said second residue from the heavy end fractionation column.

7. The process of claim 1 including the step of:

passing the first residue from step (a) through an expansion means to decrease the pressure and reduce the temperature of the first residue before the same is delivered to the light ends fractionation column.

8. The process of claim 1 including the step of reducing the temperature of the second residue before the same is directed into contact with at least part of the C₂ -containing liquid from step (a) in step (e).

9. The process of claim 8 wherein the step of reducing the temperature of the second residue includes the steps of:

(a) passing the second residue through a heat exchanger;

(b) compressing the second residue after step (a);

(c) expanding the compressed residue of step (b) to reduce the temperature thereof;

(d) passing the reduced temperature residue of step (c) through the heat exchanger of step (a); and

(e) directing the second residue from step (d) into contact with at least part of the C₂ -containing liquid in step (e).

10. An apparatus for separating a hydrocarbon feed gas containing at least methane and C₂ components into a fraction containing a predominant portion of methane and lighter components and a fraction containing a predominant portion of the C₂ and heavier components, comprising:

(a) separator means for receiving hydrocarbon feed gas and for providing at a first outlet a first residue vapor and at a second outlet C₂ -containing liquid, which liquid also contains lighter hydrocarbons;

(b) a heavy ends fractionation column means connected to receive at least a portion of said C₂ -containing liquids, the heavy ends fractionation column means being adapted to separate the C₂ -containing liquids into a second residue containing lighter hydrocarbons and a C₂ -containing liquid product;

(c) light ends fractionation column means connected to receive at least part of said first residue vapors and at least part of the liquid portion of the partially condensed second residue and to co-mingle said vapor and liquid in at least one contacting stage, and including separation means for separating the vapor and liquid after contact in said stage, and being further connected to supply the liquids separated therein to said heavy end fractionation column means as a liquid feed thereto; and

(d) means of co-mingling at least a portion of said C₂ -containing liquid from said separator means with said second residue before said second residue is introduced into said light ends fractionation column means.

11. The apparatus according to claim 10 wherein said light ends fractionation column means includes fractionation means for counter-current vapor-liquid contact and wherein said light ends fractionation column means is connected to receive the portion of said first residue vapors to be treated therein below said fractionation means and to receive the portion of said liquids from the partially condensed second residue to be treated therein above said fractionation means, said fractionation means thereby being adapted so that the first residue vapors rise therethrough in counter-current contact with partially condensed second residue.

12. The apparatus according to claim 11 wherein said fractionation means in said light ends fractionation column means includes vapor-liquid contacting means which are the equivalent of at least one theorretical distillation stage.

13. An apparatus according to claim 10 including:

heat exchange means connected to receive said second residue and to partially condense it.

14. An apparatus according to claim 13 wherein said heat exchange means connected to receive said second residue and to partially condense it includes the arrangement wherein said light ends fractionation column means is connected to direct third residue vapors separated therein through said heat exchange means.

15. An apparatus according to claim 10 including:

expansion means connected to receive first residue from said separator means having means to reduce the pressure of and reduce the temperature of the first residue before the same is directed into said light ends fractionation column means.

16. An apparatus according to claim 15 wherein said expansion means is in the form of a turbo expander.