Process for the production of dilute ethylene

• US 10,365,038 B2
• Filed: 09/15/2016
• Issued: 07/30/2019
• Est. Priority Date: 09/15/2016
• Status: Active Grant

• Current Assignee: Lummus Technology LLC
• Original Assignee: Lummus Technology Inc.
• Inventors: Schwint, Kevin John, Ram, Sanjeev
• Primary Examiner(s): Raymond, Keith M
• Application Number:
  US15/266,430
• Publication Number:
  US 20180073803A1
• Time in Patent Office: 1,048 Days
• CPC Class Codes: C07C 11/04 Ethylene
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: C07C 7/09 by fractional condensation
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• 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 2215/62 Ethane or ethylene
• 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 2270/88 Quasi-closed internal refrigeration or heat pump cycle, if not otherwise provided
• 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 3/0238 separation of CnHm with 2 carbon atoms or more
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more
• CPC Class Codes: Y02P 30/40 Ethylene production

Abstract

Processes and systems for recovery of a dilute ethylene stream are illustrated and described. More specifically, embodiments disclosed herein relate to processes and systems for separation of a dilute ethylene stream from an offgas or other vapor streams, where the ultra-low temperature refrigeration for the desired separations is provided by the offgas itself, and only moderately-low temperature externally supplied propylene refrigerants (for example, at −40° C. to 15° C.) are necessary.

Claims

1. A process for producing a dilute ethylene stream, the process comprising:

cooling and partially condensing a feedstock comprising hydrogen, methane, ethane, ethylene, and C₃₊ hydrocarbons;

separating the cooled and partially condensed feedstock into a vapor feed stream and a liquid feed stream, wherein the liquid feed stream comprises a portion of the ethylene contained in the feedstock;

separating the vapor feed stream in a deethanizer to recover an overhead stream and a bottoms product stream comprising the C₃₊ hydrocarbons;

separating the liquid feed stream into a first vapor fraction and a first liquid fraction;

cooling and partially condensing the overhead stream via indirect heat exchange with a refrigerant comprising at least a portion of the first liquid fraction;

separating the first liquid fraction, after the indirect heat exchange, into a second vapor fraction and a second liquid fraction;

compressing the first vapor fraction and the second vapor fraction to form a compressed refrigerant stream; and

cooling the compressed refrigerant stream via indirect heat exchange with the second liquid fraction and feeding the second liquid fraction to the deethanizer.

2. The process of claim 1, further comprising separating the cooled and partially condensed overhead stream into a liquid reflux stream and an overhead vapor dilute ethylene product stream.

3. The process of claim 1, further comprising separating the cooled compressed refrigerant stream into a third vapor fraction and a third liquid fraction.

4. The process of claim 3, further comprising feeding the third vapor fraction to the deethanizer.

5. The process of claim 4, further comprising combining the third liquid fraction with the liquid feed stream.

6. A process for producing a dilute ethylene stream, the process comprising:

cooling and partially condensing a feedstock comprising hydrogen, methane, ethane, ethylene, and C₃₊ hydrocarbons;

separating the cooled and partially condensed feedstock into a vapor feed stream and a liquid feed stream, wherein the liquid feed stream comprises a portion of the ethylene contained in the feedstock;

separating the vapor feed stream in a deethanizer to recover an overhead stream and a bottoms product stream comprising the C₃₊ hydrocarbons;

separating the liquid feed stream into a first vapor fraction and a first liquid fraction;

cooling and partially condensing the overhead stream via indirect heat exchange with the first liquid fraction, forming a warmed first liquid fraction;

separating the cooled and partially condensed overhead stream into a liquid reflux stream and an overhead vapor dilute ethylene product stream;

separating the warmed first liquid fraction into a second vapor fraction and a second liquid fraction;

compressing the first vapor fraction and the second vapor fraction to form a compressed refrigerant stream;

cooling the compressed refrigerant stream via indirect heat exchange with the second liquid fraction and feeding the second liquid fraction to the deethanizer;

separating the cooled compressed refrigerant stream into a third vapor fraction and a third liquid fraction;

feeding the third vapor fraction to the deethanizer;

combining the third liquid fraction with the liquid feed stream.

7. The process of claim 6, further comprising:

withdrawing a portion of the first vapor fraction prior to compressing the remaining portion of the first vapor fraction; and

withdrawing a portion of the second vapor fraction prior to compressing the remaining portion of the second vapor fraction.

8. The process of claim 6, wherein compressing the first vapor fraction and the second vapor fraction to form a compressed refrigerant stream comprises:

compressing the second vapor fraction in a first stage compressor to form a partially compressed second vapor fraction;

combining the partially compressed second vapor fraction with the first vapor fraction; and

compressing the combined fractions in a second stage compressor to form the compressed refrigerant stream.

9. The process of claim 6, wherein the cooling and partially condensing the feedstock comprises contacting the feedstock in indirect heat exchange with the overhead vapor dilute ethylene product stream.

10. The process of claim 9, wherein the cooling and partially condensing the feedstock further comprises contacting the feedstock in indirect heat exchange with a C₃ refrigerant stream at a temperature in the range from −

50°

C. to −

30°

C.

11. The process of claim 6, further comprising:

cooling and partially condensing an ethylene-containing feedstock;

separating the cooled and partially condensed ethylene-containing feedstock to form a condensate stream and a vapor portion;

treating the vapor portion to remove contaminants and forming the feedstock comprising hydrogen, methane, ethane, ethylene, and C₃₊ hydrocarbons.

12. The process of claim 11, wherein the contaminants comprise one or more of water, oxygen-containing hydrocarbons, nitrogen-containing hydrocarbons, or mercury.

13. The process of claim 11 wherein the cooling the ethylene-containing feedstock comprises contacting the ethylene-containing feedstock in indirect heat exchange with the overhead vapor dilute ethylene product stream to form a warmed overhead vapor dilute ethylene product stream.

14. The process of claim 13, wherein the cooling the compressed refrigerant stream via indirect heat exchange further comprises contacting the compressed refrigerant stream in indirect heat exchange with the warmed overhead vapor dilute ethylene product stream.

15. The process of claim 13, wherein the cooling the ethylene-containing feedstock further comprises contacting the ethylene-containing feedstock in indirect heat exchange with a C₃ refrigerant stream at a temperature in the range from 0°

C. to 20°

C.

16. The process of claim 15, wherein the cooling the compressed refrigerant stream via indirect heat further comprises contacting the compressed refrigerant stream in indirect heat exchange with a C₃ refrigerant stream at a temperature in the range from 0°

C. to 20°

C.

17. The process of claim 16, wherein the cooling the compressed refrigerant stream via indirect heat further comprises contacting the compressed refrigerant stream in indirect heat exchange with a second C₃ refrigerant stream at a temperature in the range from −

50°

C. to −

30°

C.

18. The process of claim 6, further comprising feeding at least a portion of the overhead vapor dilute ethylene product stream to an alkylation reaction zone.

19. The process of claim 18, further comprising feeding a portion of the overhead vapor dilute ethylene product stream to a combustion system as a fuel gas.

20. The process of claim 19, further comprising controlling an overhead pressure of the deethanizer by varying a flow rate of the overhead vapor dilute ethylene product stream withdrawn as a fuel gas and a flow rate of the overhead vapor dilute ethylene product stream fed to the alkylation reaction zone.