Multiple Reflux Stream Hydrocarbon Recovery Process

• US 20090113930A1
• Filed: 12/30/2008
• Published: 05/07/2009
• Est. Priority Date: 01/16/2003
• Status: Active Grant

• Current Assignee: Lummus Technology Inc.
• Original Assignee: Lummus Technology Inc.
• Inventors: Foglietta, Jorge H., Patel, Sanjiv N.
• Granted Patent: US 7,856,847 B2
• Time in Patent Office: Days
• US Class Current: 62/618
• 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 of ethane and heavier components, and a tower overhead stream containing a substantial amount of 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.

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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 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 of 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 at a fourth tower feed location that is higher than the third tower feed location.

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