Configuration and process for NGL recovery using a subcooled absorption reflux process

• US 7,377,127 B2
• Filed: 05/08/2002
• Issued: 05/27/2008
• Est. Priority Date: 05/08/2002
• Status: Active Grant

• Current Assignee: Fluor Enterprises Incorporated (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Primary Examiner(s): Tyler; Cheryl
• Assistant Examiner(s): PETTITT, JOHN F
• Application Number:
  US10/478,705
• Publication Number:
  US 20040206112A1
• Time in Patent Office: 2,211 Days
• Field of Search: 626/20, 626/32, 629/28, 629/29, 626/30, 626/35, 626/21
• US Class Current: 62/630
• 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 2200/38 using pre-separation or distributed distillation before a main column system, e.g. in a at least a double 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 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• 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 2205/50 using absorption, i.e. with selective solvents or lean oil, heavier CnHm and including generally a regeneration step for the solvent or lean oil
• 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 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• CPC Class Codes: F25J 2220/68 Separating water or hydrates
• CPC Class Codes: F25J 2235/60 the fluid being (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 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 2290/40 Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
• 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
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

An NGL recovery plant includes a demethanizer (7) in which internally generated and subcooled lean oil absorbs CO₂ and C₂ from a gas stream (11), thereby preventing build-up and freezing problems associated with CO₂, especially where the feed gas has a CO₂ treatment at ethane recoveries above 90% and propane recoveries of at least 99%.

Claims

1. A plant comprising:

a column comprising a rectification section and an absorption section, wherein the column is fluidly coupled to a first separator that is configured to separate a feed into a lean oil liquid and a vapor;

a turbo-expander configured to expand a first portion of the vapor and fluidly coupled to the column to provide the expanded first portion to the absorption section, and an exchanger fluidly coupled to the separator and configured to cool a second portion of the vapor wherein the exchanger is fluidly coupled to the column to provide the cooled second portion as a reflux to the rectification section;

a second separator that is configured to receive a cooled natural gas feed and to separate the cooled natural gas feed into a vapor portion of the natural gas, a liquid portion of the natural gas, and water, and wherein the feed of the first separator comprises at least some of the vapor portion of the natural gas;

a feed stripping column that is configured to receive the liquid portion of the natural gas, that is configured to form a bottom product comprising natural gas liquids, and that is configured to produce a stripping column overhead product that is optionally dried, and introduced into the column; and

wherein the exchanger is further configured to subcool the lean oil liquid to a temperature sufficient to condense and absorb carbon dioxide and C2 components in the column and to provide the subcooled lean oil liquid to the absorption section.

2. The plant of claim 1 further comprising a molecular sieve drier that is configured to dry the vapor portion of the natural gas.

3. The plant of claim 1 further comprising a second exchanger that is configured to cool the vapor portion of the natural gas using an overhead product of the rectification section of the column and an optional external refrigerant.

4. The plant of claim 1 further comprising an expansion device that is configured to let down in pressure a portion of the lean oil liquid to thereby provide refrigeration content to the feed of the separator.

5. The plant of claim 1 wherein the exchanger is further configured to cool the second portion of the vapor and the lean oil liquid using an overhead product of the rectification section of the column.

6. The plant of claim 1 wherein the column is configured to further comprise a stripping section that is configured to remove at least a portion of methane that is absorbed in the lean oil liquid and to produce a bottom product comprising natural gas liquids.

7. The plant of claim 4 wherein the column is configured to further comprise a stripping section that is configured to remove at least a portion of methane that is absorbed in the lean oil liquid, and to produce a bottom product comprising natural gas liquids, and wherein the stripping section is further configured to receive the portion of the lean oil liquid that is let down in pressure.

8. The plant of claim 1 wherein the column is fluidly coupled to a first stripping column that is configured to receive the lean oil liquid and to remove at least a portion of methane absorbed in the lean oil liquid and to produce a bottom product comprising natural gas liquids.

9. The plant of claim 4 wherein the column is fluidly coupled to a first stripping column that is configured to receive receives the lean oil liquid and to remove at least a portion of methane absorbed in the lean oil liquid and to produce a bottom product comprising natural gas liquids, and wherein the absorption section of the column is configured to receive the portion of the lean oil liquid that is let down in pressure.

10. The plant of claim 1 further comprising a second stripping column that is configured to receive the liquid portion of the natural gas, that is configured to form a bottom product comprising natural gas liquids, and that is configured to produce a stripping column overhead product that is optionally dried, and introduced into the column.

11. The plant of claim 1 wherein the cooled natural gas comprises at least 2 mol % carbon dioxide.

12. The plant of claim 1 wherein the cooled natural gas comprises at least 10 mol % carbon dioxide.

13. A method of operating a plant, comprising:

providing a column comprising a rectification section and an absorption section;

separating a feed in a first separator into a lean oil liquid and a vapor;

separating in a second separator a cooled natural gas feed into a vapor portion of the natural gas, a liquid portion of the natural gas, and water, and wherein the feed of the first separator comprises at least some of the vapor portion of the natural gas;

separating in a feed stripping column the liquid portion of the natural gas into a bottom product comprising natural gas liquids and a stripping column overhead product, and introducing the stripping column overhead product into the column;

dividing the vapor in a first portion and a second portion, wherein the first vapor portion is expanded in a turbo-expander and introduced into the absorption section, and wherein the second vapor portion is cooled and introduced into the rectification section as a reflux; and

cooling the lean oil liquid and introducing the cooled liquid into the absorption section at a temperature sufficient to condense and absorb carbon dioxide and C2 components in the column to thereby reduce a carbon dioxide concentration in the rectification section of the column.

14. The method of claim 13 further comprising cooling at least one of the second vapor portion and the lean oil liquid using an overhead product of the rectification section of the column.

15. The method of claim 13 further comprising cooling the feed using an overhead product of the rectification section of the column.

16. The method of claim 13 further comprising providing a first and a second distillation column, wherein the first distillation column comprises a rectifier section and an absorption section, and wherein the second distillation column comprises a stripping section, thereby allowing operation in an ethane recovery mode or operation in a propane recovery mode.

17. The method of claim 13 wherein the cooled natural gas comprises at least 2 mol % carbon dioxide.

18. The method of claim 13 wherein the cooled natural gas comprises at least 10 mol % carbon dioxide.