Multiple reflux stream hydrocarbon recovery process

• US 20040159122A1
• Filed: 01/13/2004
• Published: 08/19/2004
• Est. Priority Date: 01/16/2003
• Status: Active Grant

• Current Assignee: Lummus Technology Inc.
• Original Assignee: ABB Lummus Global Inc.
• Inventors: Foglietta, Jorge H., Patel, Sanjiv N.
• Granted Patent: US 7,484,385 B2
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• 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 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• 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 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• CPC Class Codes: F25J 2240/02 Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. 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 2270/04 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 3/0209 Natural gas or substitute natural gas
• 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

Abstract

An ethane recovery process utilizing multiple reflux streams is provided. Feed gas is cooled, partially condensed, and separated into a first liquid stream and a first vapor stream. First liquid stream is expanded and sent to a demethanizer. First vapor stream is split into a first and a second separator vapor streams. First separator vapor stream is expanded and sent to demethanizer. Second separator vapor stream is partially condensed and is separated into a reflux separator liquid stream, which is sent to demethanizer, and a reflux separator vapor stream, which is condensed and sent to demethanizer. Demethanizer produces a tower bottom stream containing a substantial amount ethane and heavier components, and a tower overhead stream containing a substantial amount remaining lighter components and forms a residue gas stream. A portion of residue gas stream is cooled, condensed, and sent to the demethanizer tower as top reflux stream.

Claims

1. A process for separating a gas stream containing methane and ethane, ethylene, propane, propylene, and heavier components into a volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of ethane, ethylene, propane, propylene, and heavier components, the process comprising the steps of:

a. cooling and at least partially condensing a hydrocarbon feed stream;

b. supplying the hydrocarbon feed stream to a cold separator;

c. separating the hydrocarbon feed stream into a first vapor stream and a first liquid stream;

d. splitting the first vapor stream into a first separator overhead stream and a second separator overhead stream;

e. expanding the first separator overhead stream to produce an expanded first separator overhead stream and then supplying a demethanizer with the first liquid stream as a first tower feed stream and the expanded first separator overhead stream as a second tower feed stream;

f. cooling and at least partially condensing the second separator overhead stream and then supplying a reflux separator with the second separator overhead stream;

g. separating the second separator overhead stream into a reflux separator overhead stream and a reflux separator bottoms stream;

h. supplying the demethanizer with the reflux separator bottoms stream as a third tower feed stream;

i. cooling, substantially condensing, and then supplying the demethanizer with the reflux separator overhead stream as a fourth tower feed stream, the demethanizer producing a demethanizer overhead stream containing a substantial amount of the methane and lighter components and a demethanizer bottoms stream containing a major portion of recovered ethane, ethylene, propane, propylene, and heavier components;

j. warming and compressing the demethanizer overhead stream to produce a residue gas stream; and

k. wherein an improvement comprises removing at least a portion of the residue gas stream as a residue gas reflux stream and cooling, substantially condensing, and then supplying the residue gas reflux stream to the demethanizer as a demethanizer reflux stream.

2. The process of claim 1, wherein

a. the step of cooling a hydrocarbon stream includes splitting the hydrocarbon stream into a first inlet stream and a second inlet stream and cooling the first and second inlet streams;

and

b. the step of supplying the hydrocarbon feed stream to a cold separator includes supplying a top of a cold absorber with the first inlet stream and a bottom of the cold absorber with the second inlet stream where the first inlet stream has a temperature colder than the second inlet stream, the cold absorber having a packed bed contained therein.

3. The process of claim 1, further including subcooling and supplying at least a portion of the first liquid stream to the demethanizer at a feed location located above that of the expanded first separator overhead stream.

4. The process of claim 1, wherein the step of supplying the demethanizer with the demethanizer reflux stream includes supplying the demethanizer reflux stream at a top tower feed location.

5. The process of claim 1, wherein the steps of supplying the demethanizer with the first, second, third and fourth tower feed streams includes sending the first tower feed stream at a lowest feed location, sending the second tower feed stream at a second tower feed location that is higher than the lowest feed location, sending the third tower feed stream at a third tower feed location that is higher than the second tower feed location, and sending the fourth tower feed stream at a fourth tower feed location that is higher than the third tower feed location.

6. The process of claim 1, wherein the improvement further includes expanding the residue reflux gas stream prior to supplying the residue reflux gas stream to the demethanizer.

7. A process for separating a gas stream containing methane and ethane, ethylene, propane, propylene and heavier components into a volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of ethane, ethylene, propane, propylene and heavier components, the process comprising the steps of:

a. cooling and at least partially condensing a hydrocarbon feed stream;

b. separating the hydrocarbon feed stream into a first vapor stream and a first liquid stream

c. splitting the separator overhead stream into a first separator overhead stream and a second separator overhead stream;

d. expanding the first separator overhead stream to produce an expanded first separator overhead stream and then supplying a demethanizer with the first liquid stream as a first tower feed stream and the expanded first separator overhead stream as a second tower feed stream, the demethanizer producing a demethanizer overhead stream containing a substantial amount methane and lighter components and a demethanizer bottoms stream containing a major portion of recovered ethane, ethylene, propane, propylene and heavier components;

e. warming and compressing the demethanizer overhead stream to produce a residue gas stream; and

f. wherein an improvement comprises the following;

removing at least a portion of the residue gas stream as a residue gas reflux stream;

combining the second separator overhead stream with the residue gas reflux stream to produce a combined reflux stream and then cooling and partially condensing the combined reflux gas stream to form a partially condensed combined reflux gas stream;

supplying the partially condensed combined reflux gas stream to a reflux separator producing a reflux separator overhead stream and a reflux separator bottoms stream;

supplying the demethanizer with the reflux separator bottoms stream as a third tower feed stream; and

cooling, substantially condensing and then supplying the demethanizer with the reflux separator overhead stream as a fourth tower feed stream.

8. The process of claim 7, wherein

a. the step of cooling a hydrocarbon feed stream includes splitting the hydrocarbon stream into a first inlet stream and a second inlet stream and cooling the first and second inlet streams;

and

b. the step of supplying the hydrocarbon feed stream to a cold separator includes supplying a top of the cold absorber with the first inlet stream and a bottom of the cold absorber with the second inlet stream where the first inlet stream has a temperature colder than the second inlet stream, the cold absorber having a packed bed contained therein.

9. The process of claim 7, further including subcooling and supplying at least a portion of the first liquid stream to the demethanizer at a feed location located above that of the expanded first separator overhead stream.

10. The process of claim 9, further including the step of subcooling and supplying at least a portion of the residue reflux stream to the demethanizer at a feed location located above that of the expanded first separator overhead stream.

11. The process of claim 7, wherein the steps of supplying the demethanizer with the first, second, third and fourth tower feed streams includes sending the first tower feed stream at a lowest feed location, sending the second tower feed stream at a second tower feed location that is higher than the lowest feed location, sending the third tower feed stream at a third tower feed location that is higher than the second tower feed location, and sending the fourth tower feed stream at a fourth tower feed location that is higher than the third tower feed location.

12. A process for separating a gas stream containing methane and ethane, ethylene, propane, propylene and heavier components into a volatile gas fraction containing a substantial amount of the methane and a less volatile fraction containing a large portion of ethane, ethylene, propane, propylene and heavier components, the process comprising the steps of:

a. splitting a hydrocarbon feed stream into a first inlet stream, a second inlet stream and a third inlet stream and cooling the first, second, and third inlet streams;

b. supplying the first inlet stream and the second inlet stream to a cold separator;

c. separating the first inlet stream and the second inlet stream to produce a first vapor stream and a first liquid stream;

d. expanding the first vapor stream to produce an expanded first vapor stream and then supplying a demethanizer with the first liquid stream as a first tower feed stream and the expanded first vapor stream as a second tower feed stream;

e. cooling and at least partially condensing the third inlet stream and then supplying a reflux separator with the third inlet stream and producing a reflux separator overhead stream and a reflux separator bottoms stream;

f. supplying the demethanizer with the reflux separator bottoms stream as a third tower feed stream;

g. cooling and substantially condensing and then supplying the demethanizer with the reflux separator overhead stream as a fourth tower feed stream, the demethanizer producing a demethanizer overhead stream containing a substantial amount methane and lighter components and a demethanizer bottoms stream containing a major portion of recovered ethane, ethylene, propane, propylene and heavier components;

h. warming and compressing the demethanizer overhead stream to produce a residue gas stream; and

i. wherein an improvement comprises removing at least a portion of the residue gas stream as a residue gas reflux stream and cooling, substantially condensing and then supplying the residue gas reflux stream to the demethanizer as a reflux stream.

13. The process of claim 12, wherein the step of supplying the first inlet stream and the second inlet stream to a cold separator includes supplying a top of a cold absorber with the first inlet stream and a bottom of the cold absorber with the second inlet stream where the first inlet stream has a temperature colder than the second inlet stream, the cold absorber having a packed bed contained therein.

14. The process of claim 12, further including subcooling and supplying at least a portion of the first liquid stream to the demethanizer at a feed location located above that of the expanded first separator overhead stream.

15. The process of claim 12, wherein the steps of supplying the demethanizer with the first, second, third and fourth tower feed streams includes sending the first tower feed stream at a lowest feed location, sending the second tower feed stream at a second tower feed location that is higher than the lowest feed location, sending the third tower feed stream at a third tower feed location that is higher than the second tower feed location, and sending the fourth tower feed stream at a fourth tower feed location that is higher than the third tower feed location.

16. A process for separating a gas stream containing methane and ethane, ethylene, propane, propylene and heavier components and heavier hydrocarbons into a volatile gas fraction containing a substantial amount of the methane and a less volatile fraction containing a large portion of ethane, ethylene, propane, propylene and heavier components, the process comprising the steps of:

a. splitting a hydrocarbon feed into a first inlet stream, a second inlet stream, and a third inlet stream, and cooling the first and second inlet streams;

b. supplying the first inlet stream and the second inlet stream to a cold separator;

c. separating the first inlet stream and the second inlet stream into a first vapor stream and a first liquid stream;

d. expanding the first vapor stream to produce an expanded first vapor stream and then supplying a demethanizer with the first liquid stream as a first tower feed stream and the expanded first vapor stream as a second tower feed stream, the demethanizer producing a demethanizer overhead stream containing a substantial amount methane and lighter components and a demethanizer bottoms stream containing a major portion of recovered ethane, ethylene, propane, propylene and heavier components;

e. warming and compressing the demethanizer overhead stream to produce a residue gas stream; and

f. wherein an improvement comprises the following;

removing at least a portion of the residue gas stream as a residue gas reflux stream;

combining the third inlet stream with the residue gas reflux stream to produce a combined reflux stream and then cooling and partially condensing the combined reflux gas stream to form a partially condensed combined reflux gas stream;

supplying the partially condensed combined reflux gas stream to a reflux separator producing a reflux separator overhead stream and a reflux separator bottoms stream;

supplying the demethanizer with the reflux separator bottoms stream as a third tower feed stream; and

cooling, and substantially condensing and then supplying the demethanizer with the reflux separator overhead stream as a fourth tower feed stream.

17. The process of claim 16, wherein the step of supplying the first inlet stream and the second inlet stream to a cold separator includes supplying a top of a cold absorber with the first inlet stream and a bottom of the cold absorber with the second inlet stream where the first inlet stream has a temperature colder than the second inlet stream, the cold absorber having a packed bed contained therein.

18. The process of claim 16, further including subcooling and supplying at least a portion of the first liquid stream to the demethanizer at a feed location located above that of the expanded first separator overhead stream.

19. The process of claim 16, wherein the steps of supplying the demethanizer with the first, second, third and fourth tower feed streams includes sending the first tower feed stream at a lowest feed location, sending the second tower feed stream at a second tower feed location that is higher than the lowest feed location, sending the third tower feed stream at a third tower feed location that is higher than the second tower feed location, and sending the fourth tower feed stream at a fourth tower feed location that is higher than the third tower feed location.

20. An apparatus for separating a gas stream containing methane and ethane, ethylene, propane, propylene, and heavier components into a volatile gas fraction containing a substantial amount of the methane and lighter components and a less volatile fraction containing a large portion of ethane, ethylene, propane, propylene, and heavier components, the apparatus comprising:

a. a first exchanger for cooling and at least partially condensing a hydrocarbon feed stream;

b. a cold separator for separating the hydrocarbon feed stream into a first vapor stream and a first liquid stream;

c. a demethanizer for receiving the first liquid stream as a first tower feed stream, an expanded first separator overhead stream as a second tower feed stream, a reflux separator bottoms stream as a third tower feed stream, and a reflux separator overhead stream as a fourth tower feed stream, the demethanizer producing a demethanizer overhead stream containing a substantial amount of the methane and lighter components and a demethanizer bottoms stream, the demethanizer bottoms stream containing a major portion of recovered ethane, ethylene, propane, propylene, and heavier components;

d. an expander for expanding the first separator overhead stream to produce the expanded first separator overhead stream for supplying to the demethanizer;

e. a second cooler for cooling and at least partially condensing the second separator overhead stream;

f. a reflux separator for separating the second separator overhead stream into the reflux separator overhead stream and the reflux separator bottoms stream;

g. a third cooler for cooling and substantially condensing the reflux separator overhead stream;

h. a first heater for warming the demethanizer overhead stream; and

i. a booster compressor for compressing the demethanizer overhead stream to produce a residue gas stream.

21. The apparatus according to claim 20, further comprising:

a. a booster compressor for boosting a pressure of the residue gas stream; and

b. a fourth cooler for cooling residue gas stream.

22. The apparatus according to claim 20, wherein the demethanizer is a reboiled absorber.

23. The apparatus according to claim 20, wherein the cold separator is a cold absorber having a packed bed contained therein.

24. The apparatus according to claim 20, wherein the third cooler and the first heater comprise a combined heat exchanger that can simultaneously provide cooling for the reflux separator overhead stream and provide heating for the demethanizer overhead stream.

25. The apparatus according to claim 20, further comprising:

a. a first expansion valve for expanding the separator bottoms stream to produce first tower feed stream;

b. a second expansion valve for expanding the reflux separator bottoms stream to produce third tower feed stream; and

c. a third expansion valve for expanding the reflux separator overhead stream to produce the fourth tower feed stream.

26. The apparatus according to claim 25, further comprising:

a. a fourth expansion valve for expanding a cooled residue gas reflux stream.