Configurations and methods for improved NGL recovery

• US 7,051,552 B2
• Filed: 11/07/2002
• Issued: 05/30/2006
• Est. Priority Date: 11/09/2001
• Status: Expired due to Term

• Current Assignee: Fluor Enterprises Incorporated (Fluor Corporation)
• Original Assignee: Flour Technologies Corporation
• Inventors: Mak, John
• Primary Examiner(s): DOERRLER, WILLIAM CHARLES
• Application Number:
  US10/478,349
• Publication Number:
  US 20040237580A1
• Time in Patent Office: 1,300 Days
• Field of Search: 626/20, 626/21, 626/25, 626/32
• US Class Current: 62/621
• CPC Class Codes: B01D 53/002 by condensation
• CPC Class Codes: B01D 53/263 by absorption
• CPC Class Codes: C10L 3/10 Working-up natural gas or synthetic natural gas
• 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 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2205/60 using adsorption on solid adsorbents, e.g. by temperature-swing adsorption [TSA] at the hot or cold end
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• CPC Class Codes: F25J 2220/68 Separating water or hydrates
• 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 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

Abstract

Feed gas (1) in an improved NGL processing plant is cooled below ambient temperature and above hydrate point of the feed gas to condense heavy components (6) and a significant portion of water (4) contained in the feed gas. The water (4) is removed in a feed gas separator (101) and the condensed liquids are fed into an integrated refluxed stripper (104) that operates as a drier/demethanizer for the condensed liquids, and the uncondensed portion (5) containing light components is further dried (106) and cooled prior to turboexpansion (23) and demethanization (112). Consequently, processing of heavy components in the cold section is eliminated, and feed gas with a wide range of compositions can be efficiently processed for high NGL recovery at substantially the same operating conditions and optimum expander efficiency.

Claims

1. A plant comprising:

a feed cooler cooling a feed gas comprising water and C₅₍₊₎ components, and a feed separator that removes at least some of the water and C₅₍₊₎ components from the cooled feed gas;

an intermediate separator fluidly coupled to the feed separator separating an at least partially dehydrated gas in to a C₅₍₊₎ depleted gas and a C₃₍₊₎ liquid;

a turboexpander receiving at least part of the C₅₍₊₎ depleted gas; and

a refluxed stripper comprising an absorption section, a dehydration section, and a stripping section, and receiving a C₅₍₊₎ liquid from the feed separator and further receiving the C₃₍₊₎ liquid from the intermediate separator as a reflux.

2. The plant of claim 1 further comprising a gas drier that receives and dries a gas from the feed separator thereby generating the at least partially dehydrated gas.

3. The plant of claim 2 wherein the at least partially dehydrated gas is further cooled by at least one of a first heat exchanger and a second heat exchanger, wherein cooling in the first heat exchanger is provided by a reboiler circuit from a demethanizer, and wherein cooling in the second heat exchanger is provided by an overhead product of the demethanizer and an overhead product gas from the stripper.

4. The plant of claim 2 wherein another part of the part of the C₅₍₊₎ depleted gas is cooled by a third heat exchanger, wherein cooling in the third heat exchanger is provided by the overhead product of the demethanizer, and wherein the cooled another part of the part of the C₅₍₊₎ depleted gas is used as a reflux for the demethanizer.

5. The plant of claim 1 wherein the feed separator is a three-phase separator.

6. The plant of claim 1 wherein the dehydration section comprises a triethylene glycol (TEG) dehydration section comprising a vapor-TEG contacting device.

7. The plant of claim 1 wherein the feed cooler cools the feed gas that to a temperature above a hydration point.

8. The plant of claim 7 wherein the feed gas is natural gas.

9. The plant of claim 7 wherein the feed gas comprises ethane, propane, and heavier components, and wherein recovery of the ethane and propane from the feed gas is at least 87% and 97%, respectively.

10. A plant comprising:

a demethanizer receiving a C₅₍₊₎ depleted gas from an intermediate separator, wherein a first portion of the C₅₍₊₎ depleted gas is expanded in a turboexpander, and wherein a second portion of the C₅₍₊₎ depleted gas is cooled and used as a demethanizer reflux;

wherein a feed separator separates a feed gas into the C₅₍₊₎ depleted gas and a liquid portion;

wherein at least one of a first heat exchanger and a second heat exchanger are configured to cool the C₅₍₊₎ depleted gas, and wherein the intermediate separator is configured to produce the first and second portions of the C₅₍₊₎ depleted gas from the cooled C₅₍₊₎ depleted gas; and

a gas drier that dries the C₅₍₊₎ depleted gas prior to cooling.

11. The plant of claim 10 wherein cooling in the first heat exchanger is provided by a reboiler circuit from the demethanizer, and wherein cooling in the second heat exchanger is provided by an overhead product of the demethanizer and an overhead product gas from the stripper.

12. The plant of claim 10 wherein cooling of the second portion of the C₅₍₊₎ depleted gas is provided by a third heat exchanger, and wherein cooling in the third heat exchanger is provided by an overhead product of the demethanizer.

13. The plant of claim 10 further comprising a stripper that receives the liquid portion from the feed separator, and wherein the stripper further receives a C₃₍₊₎ liquid from the intermediate separator as a reflux.

14. The plant of claim 13 wherein the stripper further includes a dehydration section.

15. The plant of claim 14 wherein the dehydration section comprises a triethylene glycol (TEG) dehydration section comprising a vapor-TEG contacting device.

16. The plant of claim 10 wherein the feed separator receives a feed gas that is cooled to a temperature above a hydration point.

17. The plant of claim 16 wherein the feed separator further separates at least a portion of water contained in the feed gas from the feed gas.

18. A plant comprising a stripper that receives a water saturated C₅₍₊₎ liquid and further comprises a mid-tower dehydration stage, wherein the stripper is operated as a separate demethanizer, and wherein the stripper receives a reflux from an intermediate separator that provides a C₅₍₊₎ depleted gas to a demethanizer.

19. The plant of claim 18 wherein the intermediate separator receives an at least partially dehydrated gas that is separated from a feed gas in a feed gas separator.

20. The plant of claim 18 wherein the feed gas separator further produces the water saturated C₅₍₊₎ liquid.