Cat cracker gas plant process for increased olefins recovery

• US 6,271,433 B1
• Filed: 02/22/1999
• Issued: 08/07/2001
• 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 Engineering Corporation
• Inventors: Keady, Ginger S., Garbouchian, Berj, Puerto, Juan
• Primary Examiner(s): Griffin, Walter D.
• Assistant Examiner(s): Nguyen, Tam M.
• Application Number:
  US09/255,281
• Time in Patent Office: 897 Days
• Field of Search: 585/802, 585/803, 585/809, 208/351, 208/354, 208/347
• 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 cracked 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 effluent stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, butylene, butane, naphtha, water, and a contaminant selected from the group consisting of hydrogen sulfide, carbon dioxide, oxygen, mercury, carbonyl sulfide (COS), ammonia and arsenic;

b. operating said Main Fractionator tower to produce therefrom a wet gas stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, C₄s (comprising butylene and butane), naphtha, water, and a contaminant, and a Main Fractionator overhead liquid stream including predominantly naphtha;

c. pressurizing said wet gas stream and said Main Fractionator overhead liquid stream to a pressure in the range of 120-300 psig;

d. cooling said wet gas stream and said Main Fractionator overhead liquid stream to a temperature in the range of 80-120 degrees F.;

e. feeding said wet gas stream and said Main Fractionator overhead liquid stream to a separator vessel operated at a pressure of 120-270 psig;

f. yielding from said separator vessel a first stream containing a major portion of said propane and propane and contaminant and substantially all of said ethane, ethylene, methane, and hydrogen and a first portion of said C₄s and naphtha, and (ii) a second stream including a second portion of said C₄s and naphtha;

g. treating said first stream to remove a major portion of said contaminant;

h. pressurizing said first stream to 350-600 psig;

i. cooling said first stream to 50-65 degrees F., thereby partially condensing said first stream to produce a sweet liquid fraction and a sweet gas fraction;

j. separating said sweet gas fraction from said sweet liquid fraction;

k. drying said sweet gas fraction to remove water and produce a dry gas stream;

l. drying said sweet liquid fraction to remove water and produce a dry liquid stream;

m. cooling said dry gas stream to form a first chilled vapor stream and a first chilled liquid stream;

n. separating said first chilled vapor stream and said first chilled liquid stream;

o. further cooling said first chilled vapor stream to form a second chilled vapor stream containing substantially all of said methane and hydrogen from said wet gas and a second chilled liquid stream;

p. feeding said dry liquid stream and said first chilled liquid stream to a Demethanizer tower;

q. producing from said Demethanizer tower a Demethanizer bottoms stream comprising a major portion of said ethylene, a major portion of said ethane, a major portion of said propylene, a major portion of said propane and substantially all of said first portion of said C₄s and naphtha;

r. feeding said Demethanizer bottoms stream to a Deethanizer tower;

s. producing from said Deethanizer tower a Deethanizer overhead stream comprising a major portion of said ethylene and ethane and a Deethanizer bottoms stream comprising a major portion of said propylene and propane, and substantially all of said first portion of said C₄s and naphtha;

t. feeding said Deethanizer bottoms stream to a Depropanizer tower;

u. producing from said Depropanizer tower a Depropanizer overhead stream comprising a major portion of said propylene and propane and a Depropanizer bottoms stream comprising substantially all of said first portion of said C₄s and naphtha;

v. stripping propane and propylene from said second stream from said separator vessel to form a stripped C₄ and heavier stream;

w. feeding said Depropanizer bottoms stream and said stripped C₄ and heavier stream to a Debutanizer tower;

x. producing from said Debutanizer tower a Debutanizer overhead stream comprising a major portion of said C₄s and a Debutanizer bottoms stream comprising a major portion of said naphtha.

3. The process of claim 1 or 2 wherein said fluid catalytic cracking unit is a Deep Catalytic Cracking Unit and the reactor effluent stream provided to the Main Fractionator tower comprises at least 14-21 weight percent propylene and at least 2-6 weight percent ethylene.

2. A process for recovering olefins from a mixture of cracked 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, naphtha, water, and a contaminant selected from the group consisting of hydrogen sulfide, carbon dioxide, oxygen, mercury, carbonyl sulfide (COS), ammonia and arsenic;

b. operating said Main Fractionator tower to produce therefrom a wet gas stream comprising hydrogen, methane, ethylene, ethane, propylene, propane, C₄s (comprising butylene and butane), naphtha, water, and a contaminant, and a Main Fractionator overhead liquid stream including predominantly naphtha;

c. pressurizing said wet gas stream and said Main Fractionator overhead liquid stream to a pressure in the range of 120-300 psig;

d. cooling said wet gas stream and said Main Fractionator overhead liquid stream to a temperature in the range of 80-120 degrees F.;

e. feeding said wet gas stream and said Main Fractionator overhead liquid stream to a separator vessel operated at a pressure of 120-270 psig;

f. yielding from said separator vessel a first stream containing a major portion of said propane and propane and contaminant and substantially all of said ethane, ethylene, methane, and hydrogen and a first portion of said C₄s and naphtha, and (ii) a second stream including a second portion of said C₄s and naphtha;

g. chilling said first stream to produce a chilled liquid phase stream and a hydrogen-rich chilled gas phase stream;

h. separating said chilled liquid phase stream and a chilled gas phase stream;

i. drying said chilled liquid phase stream;

j. drying said chilled gas phase stream to produce a dried chilled gas phase stream;

k. separating a major portion of said hydrogen from said dried chilled gas phase stream;

l. feeding said chilled liquid phase stream to a Deethanizer tower;

m. producing from said Deethanizer tower a Deethanizer overhead stream comprising a major portion of said methane, ethylene and ethane and a Deethanizer bottoms stream comprising a major portion of said propylene and propane, and substantially all of said first portion of said C₄s and naphtha; and

n. stripping propane and propylene from said second stream from said separator vessel to form a stripped C₄s and heavier stream.