NGL Recovery from Natural Gas Using a Mixed Refrigerant

• US 20120137726A1
• Filed: 12/01/2011
• Published: 06/07/2012
• Est. Priority Date: 12/01/2010
• Status: Active Grant

• Current Assignee: Black & Veatch International Company (Black & Veatch Corporation)
• Original Assignee: Black & Veatch Corporation
• Inventors: Currence, Kevin L., Mortko, Robert A.
• Granted Patent: US 9,777,960 B2
• Time in Patent Office: Days
• US Class Current: 62/613
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• 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 2270/04 Internal refrigeration with work-producing gas expansion loop
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/66 Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• 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

Abstract

An NGL recovery facility utilizing a single, closed-loop mixed refrigerant cycle for recovering a substantial portion of the C₂ and heavier or C₃ and heavier NGL components from the incoming gas stream. Less severe operating conditions, including a warmer refrigerant temperature and a lower feed gas pressure, contribute to a more economical and efficient NGL recovery system.

Claims

1. A process for recovering natural gas liquids (NGL) from a feed gas stream, said process comprising:

(a) cooling and at least partially condensing said feed gas stream via indirect heat exchange with a mixed refrigerant stream to thereby provide a cooled feed gas stream;

(b) separating said cooled feed gas stream into a first residue gas stream enriched in methane and lighter components and a first liquid product stream enriched in C₂ and heavier components in a first vapor-liquid separation vessel;

(c) separating said first liquid product stream into a second residue gas stream and a second liquid product stream in a second vapor-liquid separation vessel; and

(d) recovering at least a portion of said second liquid product stream obtained in step (c) as an NGL product stream.

2. The process of claim 1, wherein said feed gas stream has a pressure less than 600 psig prior to said cooling of step (a).

3. The process of claim 1, wherein said cooled feed gas stream has a temperature of no less than −

165°

F. prior to said separating of step (b).

4. The process of claim 1, wherein the temperature of said mixed refrigerant stream has a temperature of not less than −

175°

F. prior to said cooling of step (a).

5. The process of claim 1, further comprising, compressing a stream of mixed refrigerant to thereby provide a compressed mixed refrigerant stream;

cooling said compressed mixed refrigerant stream to thereby provide a cooled mixed refrigerant stream; and

expanding said cooled mixed refrigerant stream to thereby provide an expanded mixed refrigerant stream, wherein said mixed refrigerant stream utilized to perform said cooling of step (a) comprises at least a portion of said expanded mixed refrigerant stream.

6. The process of claim 5, wherein the pressure of said compressed mixed refrigerant stream is no more than 550 psig.

7. The process of claim 1, further comprising introducing an absorber liquid into said first vapor-liquid separation vessel, wherein said absorber liquid comprises at least a portion of said first bottoms liquid product stream.

8. The process of claim 1, further comprising expanding said first residue gas stream to thereby provide an expanded residue gas stream and heating said expanded residue gas stream to thereby provide at least a portion of said cooling of step (a).

9. The process of claim 8, wherein said first residue gas stream comprises at least about 80 percent of the total amount of methane and lighter components originally present in said feed gas stream prior to said cooling of step (a) and wherein said expanded residue gas stream has a vapor fraction greater than 0.85.

10. The process of claim 1, wherein said NGL product stream comprises at least 80 percent of the total amount of C₃ and heavier components originally present in said feed gas stream prior to said cooling of step (a) and wherein said NGL product stream comprises less than 20 mole percent of C₂ and lighter components.

11. The process of claim 1, wherein said NGL product stream comprises at least 50 percent of the total amount of C₂ and heavier components originally present in said feed gas stream prior to said cooling of step (a).

12. The process of claim 1, wherein said mixed refrigerant comprises two or more components selected from the group consisting of methane, ethylene, ethane, propylene, propane, isobutane, n-butane, isopentane, and n-pentane.

14. The process of claim 1, wherein said recovering of step (d) comprises subjecting said NGL product stream to further fractionation in one or more distillation columns to thereby produce one or more additional product streams enriched in C₂, C₃, and/or C₄ and heavier components.

15. A process for recovering natural gas liquids (NGL) from a hydrocarbon-containing feed gas stream, said process comprising:

(a) compressing a mixed refrigerant stream with a refrigeration compressor to thereby provide a compressed mixed refrigerant stream having a pressure less than 550 psig;

(b) cooling said compressed mixed refrigerant stream in a first heat exchanger to thereby provide a cooled mixed refrigerant stream;

(c) passing said cooled mixed refrigerant stream through an expansion device to thereby provide an expanded refrigerant stream;

(d) cooling said hydrocarbon-containing feed gas stream via indirect heat exchange with said expanded refrigerant stream to thereby provide a cooled feed gas stream;

(e) separating said cooled feed gas stream into a first residue gas stream and a first liquid product stream; and

(f) recovering an NGL product stream from at least a portion of said liquid product stream,

wherein the temperatures of said compressed mixed refrigerant stream, said cooled mixed refrigerant stream, and said expanded refrigerant stream during each of steps (a) through (d) are sufficient to condense at least a portion of the C₂ components or at least a portion of the C₃ components originally present in said hydrocarbon-containing feed stream.

16. The process of claim 15, wherein the pressure of said hydrocarbon-containing feed gas stream is less than 600 psig prior to said cooling of step (d).

17. The process of claim 16, wherein the temperature of said cooled feed gas stream is not less than −

165°

F.

18. The process of claim 15, wherein said mixed refrigerant stream comprises two or more components selected from the group consisting of methane, ethylene, ethane, propylene, propane, isobutane, n-butane, isopentane, and n-pentane.

19. The process of claim 18, wherein said mixed refrigerant stream comprises less than 20 mole percent of methane and substantially no nitrogen.

20. The process of claim 15, further comprising further separating said first liquid product stream into a second residue vapor stream and a second liquid product stream in a second vapor-liquid separation vessel;

combining said first residue gas stream and said second residue gas stream to form a combined residue gas stream;

expanding said combined residue gas stream to thereby provide an expanded residue gas stream, wherein said expanded residue gas stream comprises at least 50 mole percent of the methane and lighter components originally present in said hydrocarbon-containing feed gas prior to said cooling of step (d) and has a vapor fraction of at least 0.85.

21. The process of claim 15, further comprising further separating said first liquid product stream into a second residue vapor stream and a second liquid product stream in a second vapor-liquid separation vessel, wherein said separating of said first liquid product stream in said second separation vessel includes selectively operating said second vapor-liquid separation vessel in an C₂ recovery mode or a C₂ rejection mode.

22. A natural gas liquids (NGL) recovery facility for recovering ethane and heavier components from a hydrocarbon-containing feed gas stream using a single closed-loop mixed refrigeration cycle, said facility comprising:

a feed gas compressor defining a feed suction port and a feed discharge port, said feed gas compressor operable to compress said hydrocarbon-containing feed gas stream to pressure of not more than 600 psig;

a primary heat exchanger defining a first cooling pass for cooling the compressed feed gas stream;

a first vapor-liquid separation vessel defining a first fluid inlet, a first upper vapor outlet, and a first lower liquid outlet, wherein said first fluid inlet is coupled in fluid flow communication with said first cooling pass, wherein said first vapor-liquid separation vessel is operable to separate the cooled feed gas stream into a first residue gas stream withdrawn via said first upper vapor outlet and a first liquid stream withdrawn via first lower liquid outlet;

a second vapor-liquid separation vessel defining a second fluid inlet, a second upper vapor outlet, and a second lower liquid outlet, wherein said second fluid inlet is coupled in fluid flow communication with said first lower liquid outlet of said first vapor-liquid separation vessel, wherein said second-vapor liquid separation vessel is operable to separate the first liquid stream withdrawn from said first vapor-liquid separation vessel into a second residue gas stream and an NGL product stream; and

a single closed-loop mixed refrigeration cycle, said cycle comprising—

a refrigerant compressor defining a suction inlet and a discharge outlet for compressing a stream of mixed refrigerant;

a first refrigerant cooling pass in fluid flow communication with said discharge outlet of said refrigerant compressor, said first refrigerant cooling pass being disposed in said primary heat exchanger and operable to cool at least a portion of the compressed stream of mixed refrigerant;

an expansion device defining a high pressure inlet and a low pressure outlet for expanding the cooled mixed refrigerant stream, wherein said high pressure inlet is coupled in fluid flow communication with said first refrigerant cooling pass;

a first refrigerant warming pass in fluid flow communication with said low pressure outlet of said expansion device, said first refrigerant warming pass being disposed within said primary heat exchanger and operable to warm the expanded mixed refrigerant stream via indirect heat exchange with the compressed mixed refrigerant stream in said first refrigerant cooling pass and/or the compressed feed gas stream in said first cooling pass, wherein said first refrigerant warming pass is in fluid flow communication with said suction inlet of said refrigerant compressor.

23. The facility of claim 22, wherein said first vapor-liquid separation vessel is an absorber column defining an upper absorber liquid inlet, wherein said upper absorber liquid inlet is coupled in fluid flow communication with said second upper vapor outlet of said second vapor-liquid separation vessel and/or said first lower liquid outlet of said absorber column.

24. The facility of claim 22, further comprising a refrigerant condenser defining a warm refrigerant inlet and a cool refrigerant outlet;

a refrigerant separator defining a fluid inlet, a vapor outlet, and a liquid outlet; and

a refrigerant mixing point, wherein said discharge outlet of said refrigerant compressor is coupled in fluid flow communication with said warm refrigerant inlet of said refrigerant condenser and said fluid inlet of said refrigerant separator is coupled in fluid flow communication with said cool refrigerant outlet of said refrigerant condenser, wherein said refrigerant separator is operable to separate an at least partially condensed refrigerant stream introduced into said refrigerant separator via said fluid inlet into a refrigerant vapor stream withdrawn from said vapor outlet and a refrigerant liquid stream withdrawn from said liquid outlet, wherein said refrigerant mixing point is operable to combine at least a portion of said refrigerant vapor stream with at least a portion of said refrigerant liquid stream prior to or within said first refrigerant cooling pass.

25. The facility of claim 22, further comprising a cracking unit located upstream of said NGL recovery facility, wherein at least a portion of said hydrocarbon-containing feed gas originates from said cracking unit.