Process and apparatus for C3 recovery

• US 6,311,516 B1
• Filed: 01/27/2000
• Issued: 11/06/2001
• Est. Priority Date: 01/27/2000
• Status: Expired due to Term

• Current Assignee: Linde Engineering North America, Inc. (Linde Plc)
• Original Assignee: Linde Process Plants, Inc. (Linde Plc)
• Inventors: Brantingham, Steven C., Key, Ronald D.
• Primary Examiner(s): Doerrler, William
• Assistant Examiner(s): Drake, Malik N.
• Application Number:
  US09/492,189
• Time in Patent Office: 649 Days
• Field of Search: 626/19, 626/20
• US Class Current: 62/619
• 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 2200/74 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 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 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 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 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

An improved process for separating a hydrocarbon bearing feed gas containing methane and lighter, C₂ (ethylene and/or ethane), C₃ (propylene and/or propane) and heavier components into a fraction containing predominantly C₂ and lighter components and a fraction containing predominantly C₃ 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 C₃ containing liquid, directing a portion of the C₃ containing liquid into a heavy-ends fractionation column wherein the liquid is separated into a second hydrocarbon bearing vapor residue, a second C₂ containing liquid stream, and a C₃ containing product. Directing part of the second liquid into the lights-ends fractionation column, which liquid provides additional liquefied C₂'"'"'s which act as a direct contact refrigerant to thereby condense C₃'"'"'s and heavier components while the C₂'"'"'s are evaporated in the light-ends fractionation 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 a feed thereto.

Claims

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

(a) the feed gas is cooled in one or more heat exchangers providing thereby a first residue vapor and a first C₃ containing liquid which liquid also contains lighter hydrocarbons;

and

(b) a portion of the first C₃ containing liquids is directed into a heavy ends fractionation column wherein said liquid is separated into a second residue containing lighter hydrocarbons and a C₃ containing product;

the improvements comprising;

(1) cooling said second residue to condense at least a portion thereof into a C₂ containing liquid stream and a fourth residue vapor;

(2) separating the fourth residue vapor produced in step (1) from the C₂ containing liquid stream;

(3) further cooling at least a part of the said C₂ containing liquid;

(4) intimately contacting at least part of the said first residue vapors with at least part of the said cooled C₂ containing liquid in a fractionation device having at least one contacting stage and thereafter separating a third residue vapor and a resulting second C₃ containing liquid from said fractionation device;

(5) supplying the liquids thereby recovered into heat exchange relation with said C₂ containing liquid stream to supply a portion of the cooling of step (3) and thereafter into the heavy ends fractionation column as a feed thereto;

(6) supplying the fourth residue vapors thereby recovered into heat exchange relation with said C₂ containing liquid stream to supply a portion of the cooling of step (3) and thereafter discharging said residue gases.

2. The improvement according to claim 1 wherein said contacting step (4) is carried out in a light ends fractionation column that includes fractionation means for vapor/liquid counter-current contact and

(i) wherein said cooled C₂ containing liquid is introduced into said light end fractionation column above said fractionation means, whereby the cooled C₂ containing liquid passes downwardly through said fractionation means;

(ii) supplying at least part of the first residue vapors 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 cooled C₂ containing liquid.

3. The improvement according to claim 2 wherein the fractionation means in said light ends fractionation column provides the equivalent of at least one theoretical distillation stage arranged to contact at least part of said first residue vapors with the C₂ containing liquid stream.

4. The process of claim 1 including the step of cooling the C₂ containing liquid from step (2) prior to delivery of the C₂ containing liquid to the light ends fractionation column.

5. The process of claim 1 including the step of directing the fourth residue recovered from the light ends fractionation column into heat exchange relation with said C₂ containing liquid stream.

6. The process of claim 1 including the step of directing the second C₃ containing liquid recovered from the light ends fractionation column into heat exchange relation with said C₂ containing liquid stream.

7. The process of claim 1 including the step of combining the third and fourth residue gases prior to their discharge.

8. An apparatus for separating a feed gas containing at least methane, C₂ components and C₃ components into a fraction containing a predominant portion of C₂ and lighter components and a fraction containing a predominant portion of the C₃ and heavier components, comprising:

(a) separator means for receiving feed gas and for providing at a first outlet a first residue vapor and at a second outlet a C₃ containing liquid which liquid also contains lighter hydrocarbons;

(b) a heavy ends fractionation column means connected to receive at least a portion of said C₃ containing liquids, the heavy ends fractionation column means being adapted to separate the C₃ containing liquids into a second residue containing lighter hydrocarbons and a C₃ containing liquid product;

(c) heat exchanger system to cool and at least partially condense the second residue from the heavy ends fractionation column into a possible third residue and a C₂ containing liquid stream;

(d) heat exchange system to further cool the C₂ containing liquids;

(e) light ends fractionation column means connected to receive at least part of said first residue vapors and at least part of the said cooled C₂ containing liquids and to co-mingle said vapor and liquid in at least one contacting stage, and including the separation means for separating the vapor and liquid after contact in said stage, and being further connected to supply, via heat exchange, the liquids separated therein to said heavy ends fractionation column as a feed thereto.

9. The apparatus according to claim 8 wherein said light ends fractionation column includes fractionation means for counter-current vapor-liquid contact and wherein said light ends fractionation column 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 cooled C₂ containing liquids above said fractionation means, said fractionation means thereby being adapted so that the first residue vapors rise there-through in counter-current contact with cooled C₂ containing liquids.

10. The apparatus according to claim 9 wherein said fractionation means in said light ends fractionation column includes vapor-liquid contacting means which are the equivalent of at least one theoretical distillation stage.

11. An apparatus according to claim 8 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.

12. An apparatus according to claim 8 wherein the heat exchange system includes a heat exchange means connected to receive said C₂ containing liquids and cool them.

13. An apparatus according to claim 12 wherein said heat exchange means connected to receive said C₂ containing liquids and cool them includes an arrangement wherein said light ends fractionation column means is connected to direct fourth residue vapors therein through said heat exchange means.

14. An apparatus according to claim 12 wherein said heat exchange means connected to receive said C₂ containing liquids and cool them includes an arrangement wherein said light ends fractionation column means is connected to direct second C₃ containing liquids therein through said heat exchange means.