System and process for the recovery of propylene and ethylene from refinery offgases

• US 6,308,532 B1
• Filed: 01/20/2000
• Issued: 10/30/2001
• Est. Priority Date: 11/20/1998
• Status: Expired due to Term

• Current Assignee: Chart Incorporated (Chart Industries Incorporated)
• Original Assignee: Chart Industries Incorporated
• Inventors: Hopewell, Richard B.
• Primary Examiner(s): CAPOSSELA, RONALD C
• Application Number:
  US09/463,466
• Time in Patent Office: 649 Days
• Field of Search: 626/20, 629/35
• US Class Current: 62/620
• CPC Class Codes: C07C 11/02 Alkenes
• CPC Class Codes: C07C 15/46 Styrene; Ring-alkylated styrenes
• CPC Class Codes: C07C 7/04 by distillation
• CPC Class Codes: C07C 7/20 Use of additives, e.g. for stabilisation
• CPC Class Codes: C10G 70/041 by distillation
• CPC Class Codes: C10G 70/06 by gas-liquid contact
• CPC Class Codes: F25J 2200/80 using integrated mass and heat exchange, i.e. non-adiabatic rectification in a reflux exchanger or dephlegmator
• CPC Class Codes: F25J 2200/94 Details relating to the withdrawal point
• CPC Class Codes: F25J 2205/50 using absorption, i.e. with selective solvents or lean oil, heavier CnHm and including generally a regeneration step for the solvent or lean oil
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2215/64 Propane or propylene
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• 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
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more
• CPC Class Codes: F25J 3/0247 separation of CnHm with 4 carbon atoms or more
• CPC Class Codes: Y02P 30/40 Ethylene production

Abstract

A system and process for the recovery of ethylene and propylene from a gas stream, such as a refinery offgas stream. The process comprises withdrawing, cooling, and recovering an overhead vapor stream from a single distillation column. The process includes withdrawing a liquid C₃+, C₄+, C₅+ or C₆+ bottoms product stream and recycling a portion of the bottoms steam to maintain an overhead column condenser at temperature refrigeration levels of above −140° F. and withdrawing a vapor side stream rich in propylene or ethylene-propylene.

Claims

1. A process for the recovery of an olefin from a gas feed stream comprising hydrocarbons and minor amounts of olefins, which process comprises:

a) introducing the gas feed stream into a single recovery distillation column having an upper tray section and with an overhead condenser and reflux drum;

b) withdrawing an overhead vapor stream from said column;

c) cooling and partially condensing the overhead vapor stream in the overhead condenser, to provide an overhead vapor-liquid;

d) phase-separating the overhead vapor-liquid in the reflux drum;

e) withdrawing from the reflux drum, an olefin-lean, overhead vapor stream and recycling the separated liquid from the reflux drum to the column;

f) withdrawing from said column, a liquid C₃+, C₄+, C₅+, or C₆+ bottoms product stream;

g) recycling at least a portion of the liquid bottoms product stream to the overhead condenser or the upper tray section of said column, to maintain the temperature of the overhead condenser above about −

140°

F. refrigeration temperature; and

h) withdrawing an olefin-rich, vapor phase, side product stream rich in a selected olefin.

2. The process of claim 1 wherein the gas feed stream comprises a refinery offgas stream derived from a Fuel Catalytic Cracker Unit (FCCU), or Coker unit, or mixture thereof.

3. The process of claim 1 which includes pretreating the gas feed stream by waterwashing, removing acid gases, and dehydrating the gas feed stream.

4. The process of claim 1 wherein the selected olefin comprises ethylene, propylene, or ethylene and propylene mixtures.

5. The process of claim 1 wherein the gas feed stream comprises up to about 20 percent (20%) by volume of ethylene and up to about 11 percent (11%) by volume of propylene.

6. The process of claim 1 for the recovery of propylene, ethylene, or ethylene-propylene mixtures, which process includes employing a carbon steel column, carbon steel shell and tube heat exchangers, and the process is free of employing turboexpanders.

7. The process of claim 1 which includes recovering, in the olefin-rich product side stream, greater than about 98 percent (98%) by volume of propylene in the gas feed stream and greater than about 90 percent (90%) by volume of ethylene in the gas feed stream.

8. The process of claim 1 which includes employing the overhead vapor stream for regeneration gas in dehydrating the gas feed stream or as a fuel gas.

9. The process of claim 1 which includes condensing the olef in-rich vapor side stream and recovering use ethylene, propylene, or ethylene-propylene mixtures.

10. The process of claim 1 wherein a selected olefin comprises ethylene, propylene, or ethylene-propylene mixtures, and heavy liquid bottoms stream comprises primarily C₃+ to C₄+ hydrocarbons.

11. The process of claim 1 wherein the selected olefin comprises propylene, ethylene, or ethylene-propylene mixtures, and the liquid recycle stream comprises primarily C₅+ to C₆+ hydrocarbons.

12. The process of claim 1 which includes maintaining the overhead condenser at a temperature range of about 0°

F. to 140°

F.

13. The process of claim 1 which includes recycling the column bottoms liquid stream in the molar ratio range from 0.03 to 1.0, with reference to the feed stream.

14. The process of claim 1 wherein the single column operates at a pressure of about 150 to 550 psig.

15. The process of claim 1 wherein the selected olefin comprises ethylene and which process includes maintaining the overhead condenser temperature at about −

114°

F. or warmer.

16. The process of claim 1 wherein the selected olefin comprises propylene and which process includes maintaining the overhead condenser temperature from about −

40°

F. or warmer.

17. The process of claim 1 wherein the feed gas steam comprises a synthesis gas stream produced by steam cracking of hydrocarbons for the production of ethylene.

18. The process of claim 1 which includes, intermediate the column in a side reboiler and below the point of feed stream introduction withdrawing, reboiling, and recycling a liquid side stream, to enhance the concentration of the selected olefin.

19. The process of claim 1 which includes withdrawing, in the side product vapor stream, ethane and propane with the selected olefin.

20. The process of claim 1 which includes removing the acid gas, in the gas feed stream, downstream of the recovery distillation column.

21. The process of claim 1 which includes employing the overhead vapor stream for the dehydration of the gas feed stream.

22. The process of claim 1 wherein the operating pressure of the recovery distillation column is about 250 to 260 psig.

23. A process for the recovery of an ethylene-propylene mixture or propylene from a refinery offgas feed stream, which process comprises:

a) introducing a waterwashed, dehydrated, refinery offgas feed stream, with acid gases removed, into a single recovery distillation column with an overhead condenser, reflux drum, and distillation trays, the offgas feed stream comprising C₁+ hydrocarbons, ethylene, and propylene;

b) withdrawing an overhead vapor stream from the recovery column;

c) cooling and partially condensing the overhead vapor stream in the overhead reflux condenser, to provide a vapor-liquid overhead stream;

d) phase-separating the vapor-liquid overhead stream in the reflux drum;

e) withdrawing from the reflux drum, a lean, stripped, overhead vapor stream essentially free of ethane, propane, ethylene and propylene;

f) withdrawing from, reboiling, and recycling to the column below the feed stream introduction, a side reboiler stream to enhance the concentration of the propylene and ethylene;

g) withdrawing a heavy liquid C₃+ to C₆+ product stream from the bottom of the recovery column and recycling at least a portion of the liquid product stream to the overhead condenser or upper tray section of the recovery distillation column, to maintain the temperature of the overhead condenser at a level of about 0°

F. to −

115°

F.;

h) withdrawing a vapor side stream from the recovery column from trays between the side reboiler, the side stream comprising ethylene and propylene or propylene;

i) condensing the vapor side stream; and

j) recovering the ethylene-propylene mixture or propylene as a condensed recovery product stream.

24. The process of claim 23 which includes withdrawing the liquid side stream from an intermediate upper tray of the column, recycling the reboiled side stream to the next lower tray of the column, and withdrawing the olefin-rich side product stream from between said intermediate upper and lower trays.