Cat cracker gas plant process for increased olefins recovery

• US 6,576,805 B2
• Filed: 06/05/2001
• Issued: 06/10/2003
• Est. Priority Date: 02/22/1999
• Status: Expired due to Term

• Current Assignee: Stone & Webster Process Technology, Inc. (Technip Energies NV)
• Original Assignee: Stone & Webster Process Technology, Inc. (Technip Energies NV)
• Inventors: Keady, Ginger S., Garbouchian, Berj, Puerto, Juan
• Primary Examiner(s): Griffin, Walter D.
• Assistant Examiner(s): Nguyen, Tam M.
• Application Number:
  US09/874,172
• Publication Number:
  US 20010044565A1
• Time in Patent Office: 735 Days
• Field of Search: 585/802, 585/803, 585/809, 208/347, 208/351, 208/354
• US Class Current: 585/802
• CPC Class Codes: B01D 3/143 by two or more of a fractionation, separation or rectification step
• CPC Class Codes: C10G 7/02 Stabilising gasoline by removing gases by fractioning
• CPC Class Codes: C10G 70/00 Working-up undefined normally gaseous mixtures obtained by processes covered by groups C10G9/00, C10G11/00, C10G15/00, C10G47/00, C10G51/00
• CPC Class Codes: C10G 70/041 by distillation
• CPC Class Codes: C10G 70/043 by fractional condensation
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/04 Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2230/30 Compression 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 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion 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 2270/66 Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• 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

The invention relates to a new process for more efficient separation and recovery of light olefins such as ethylene and propylene from a fluid catalytic cracking unit. The new process invention for recovering olefins from a mixture of cracked hydrocarbons from a fluid catalytic cracker comprises the steps of: (a) providing a mixture of cracked hydrocarbons including methane, ethylene, ethane, propylene, propane, butylene, butane and heavier hydrocarbons such as naphtha produced in a fluid catalytic cracker; (b) separating said mixture into (i) a first stream comprising substantially all of said ethane, ethylene, and methane and a major portion of said propane and propylene and (ii) a second stream comprising a portion of said butylene and butane, and a major portion of said heavier hydrocarbons; and (c) processing said first stream to recover the ethylene and propylene therefrom, and the details of such process described herein.

Claims

1. A process for recovering olefins from hydrocarbons produced in a fluid catalytic cracking unit, the process comprising:

a. providing hydrocarbons produced in a fluid catalytic cracking unit, said hydrocarbons comprising ethylene, ethane, propylene, propane, butane, butylene, and C₅ and heavier components;

b. pressurizing said hydrocarbons to a pressure in the range of approximately 120 psig to 300 psig;

c. cooling said pressurized hydrocarbons;

d. feeding said cooled, pressurized hydrocarbons to a separator operated at a temperature in the range of approximately 80 degrees F. to 120 degrees F. and a pressure in the range of approximately 120 psig to 270 psig;

e. yielding from said separator a gas stream comprising a major portion of the propane and lighter components of said hydrocarbons and substantially all of the ethylene in said hydrocarbons;

f. separating hydrogen and methane from said gas stream, thereby forming an ethylene and heavier stream;

g. separating ethane and lighter components from said ethylene and heavier stream, thereby forming an ethane and lighter stream and a propylene and heavier stream;

h. yielding from said separator a liquid stream that comprises a portion of said propylene, propane and heavier components of said hydrocarbons;

i. feeding said liquid stream from said separator to a stripper tower;

j. operating said stripper tower to remove as a stripper overhead stream a major portion of the propane and lighter components from said liquid stream fed to said stripper tower;

k. feeding said stripper overhead stream into the hydrocarbons entering said separator; and

l. yielding from said stripper tower bottom a de-propanized liquid stream.

2. The process of claim 1, wherein said stripper tower is operated to remove as a stripper overhead stream substantially all of the propane and lighter components from said liquid stream fed to said stripper tower.

3. The process of claim 1, wherein said stripper tower is operated at a temperature in the range of approximately 50 degrees F. to 75 degrees F. above the water dew point.

4. The process of claim 1, wherein said stripper tower is operated at a pressure in the range of approximately 120 psig to 275 psig and with a bottoms temperature in the range of approximately 200 degrees F. to 350 degrees F.

5. The process of claim 1, wherein said stripper tower is operated at a pressure in the range of approximately 150 psig to 220 psig and with a bottoms temperature in the range of approximately 250 degrees F. to 320 degrees F.

6. The process of claim 1, wherein said stripper tower is operated with no external reflux stream at the top of the tower.

7. The process of claim 1, further comprising:

m. feeding said de-propanized liquid stream to a debutanizer tower;

n. operating said debutanizer tower at a bottoms temperature in the range of approximately 250 degrees F. to 350 degrees F. and a pressure in the range of approximately 60 psig to 150 psig;

o. yielding from said debutanizer tower an overhead stream comprising butane and butylene; and

p. yielding from said debutanizer tower a bottoms stream comprising C₅ and heavier components.

8. A process for recovering olefins from hydrocarbons produced in a fluid catalytic cracking unit, the process comprising:

a. providing a fluid catalytic cracking reactor effluent stream to a Main Fractionator distillation tower, said reactor effluent stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, butylene, butane, and C₅ and heavier components;

b. operating said Main Fractionator tower to produce therefrom (i) a wet gas stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, butylene, and butane, and (ii) a Main Fractionator overhead liquid stream comprising predominantly C₅ and heavier components;

c. pressurizing the chemical components of said wet gas stream to a pressure in the range of approximately 120-300 psig;

d. pressuring the chemical components of said Main Fractionator overhead liquid stream to a pressure in the range of approximately 120-300 psig;

e. cooling the chemical components of said wet gas stream to a temperature in the range of approximately 80-120 degrees F.;

f. cooling the chemical components of said Main Fractionator overhead liquid stream to a temperature in the range of approximately 80-120 degrees F.;

g. feeding the chemical components of said wet gas stream and said Main Fractionator overhead liquid steam to a separator vessel operated at a pressure of approximately 120-270 psig;

h. yielding from said separator vessel (i) a first stream comprising a major portion of said propylene and propane from said reactor effluent and substantially all of said ethane, ethylene, methane, and hydrogen from said reactor effluent, and (ii) a second stream comprising C₅ and heavier compounds; and

wherein the second stream further comprises a portion of the propylene and propane from said reactor effluent;

i. feeding said second stream from said separator vessel to a stripper tower;

j. operating said stripper tower to remove as a stripper overhead stream a major portion of the propane and propylene from said second stream fed to said stripper tower;

k. feeding said stripper overhead stream into the hydrocarbons entering said separator vessel; and

l. yielding from said stripper tower bottom a de-propanized liquid stream.

9. The process of claim 8, wherein said first stream yielded from said separator comprises substantially all of said propylene and said propane from said reactor effluent.

10. A process for recovering olefins from hydrocarbons produced in a fluid catalytic cracking unit, the process comprising:

a. providing a fluid catalytic cracking reactor effluent stream to a Main Fractionator distillation tower, said reactor effluent stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, butylene, butane, and C₅ and heavier components;

b. operating said Main Fractionator tower to produce, therefrom (i) a wet gas stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, butylene, and butane, and (ii) a Main Fractionator overhead liquid stream comprising predominantly C₅ and heavier components;

c. pressurizing the chemical components of said wet gas stream to pressure in the range of approximately 120-300 psig;

d. pressuring the chemical components of said Main Fractionator overhead liquid stream to pressure in the range of approximately 120-300 psig;

e. cooling the chemical components of said wet gas stream to a temperature in the range of approximately 80-120 degrees F.;

f. cooling the chemical components of said Main Fractionator overhead liquid stream to a temperature in the range of approximately 80-120 degrees F.;

g. feeding the chemical components of said wet gas stream and said Main Fractionator overhead liquid steam to a separator vessel operated at a pressure of approximately 120-270 psig;

h. yielding from said separator vessel (i) a first stream comprising a major portion of said propylene and propane from said reactor effluent and substantially all of said ethane, ethylene, methane, and hydrogen from said reactor effluent, and (ii) a second stream comprising propane and heavier compounds;

i. processing said first stream from said separator to separate therefrom substantially all of said methane and hydrogen thereby producing an ethylene and heavier stream comprising a major portion of said ethylene, ethane, propylene and propane from said reactor effluent stream;

j. feeding said ethylene and heavier stream to a deethanizer tower;

k. producing from said deethanizer tower a deethanizer overhead stream comprising a major portion of said ethylene and ethane from said reactor effluent stream and a deethanizer bottoms stream comprising a major portion of said propylene and propane from said reactor effluent stream;

l. feeding said deethanizer bottoms stream to a depropanizer tower;

m. producing from said depropanizer tower a depropanizer overhead stream comprising propylene and propane and a depropanizer bottoms stream comprising butylene and heavier components;

n. feeding said second stream from said separator vessel to a stripper tower;

o. operating said stripper tower to remove as a stripper overhead stream a major portion of the propane from said second stream fed to said stripper tower;

p. feeding said stripper overhead stream into the hydrocarbons entering said separator vessel; and

q. yielding from said stripper tower bottom a de-propanized liquid stream.

12. The process of claim 10, wherein the amount of ethylene recovered in said C₂ minus stream is greater than 85 percent of the ethylene in said hydrocarbons.

13. The process of claim 10, wherein the amount of propylene recovered in said Depropanizer overhead stream is greater than 98.5 percent of the propylene in said reactor effluent stream.

11. A process for recovering olefins from a mixture of hydrocarbons from a fluid catalytic cracking unit comprising the steps of:

a. providing a fluid catalytic cracking reactor effluent stream to a Main Fractionator distillation tower, said reactor effluent stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, butylene, butane, naptha, and water;

b. operating said Main Fractionator to produce (i) a wet gas stream comprising hydrogen, methane, ethylene, propylene, propane, butylene, butane, naptha, and water, and (ii) a Main Fractionator overhead liquid stream including predominantly naptha;

c. feeding said wet gas stream and said Main Fractionator overhead liquid stream to a separator vessel operated at a pressure of 120-270 psig and a temperature in the range of 80-120 degrees F.;

d. yielding from said separator vessel (i) a first stream containing a major portion of said propane and propylene and substantially all of said ethane, ethylene, methane, and hydrogen and a portion of said water, and (ii) a second stream comprising butylene and heavier components;

e. removing water from said first stream;

f. chilling said first stream, thereby condensing a portion thereof and forming a liquid hydrogen-lean stream and a gaseous hydrogen-rich stream;

g. feeding said liquid hydrogen-lean stream to a Deethanizer tower;

h. operating said Deethanizer tower at a pressure of approximately 225-450 psig and a bottoms temperature of approximately 120-200 degrees F.;

i. producing from said Deethanizer tower (i) a Deethanizer tower overhead stream comprising a major portion of the methane, ethylene, and ethane from said wet gas and Main Fractionator overhead liquid streams, and (ii) a Deethanizer bottoms stream comprising a major portion of the propane and propylene from the wet gas and Main Fractionator overhead liquid streams;

j. stripping propane and propylene from said second stream from said separator vessel to form a stripped butylene and heavier stream; and

k. recycling the propane and propylene stripped from said second stream such that said stripped propane and propylene are processed in said separator.

14. The process of claim 8 or 11, wherein said fluid catalytic cracking unit is a Deep Catalytic Cracking Unit and the reactor effluent stream to the Main Fractionator tower comprises at least 14-21 weight percent propylene and at least 2-6 weight percent ethylene.

15. The process of claim 8 or 11, wherein said fluid catalytic cracking unit is a Deep Catalytic Cracking Unit and the reactor effluent stream to the Main Fractionator tower comprises at least 11-25 weight percent propylene and at least 2-6 weight percent ethylene.