FLEXIBLE NGL RECOVERY METHODS AND CONFIGURATIONS

• US 20140260420A1
• Filed: 03/13/2014
• Published: 09/18/2014
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: MAK, John
• Granted Patent: US 9,423,175 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 2200/72 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 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• CPC Class Codes: F25J 2200/94 Details relating to the withdrawal point
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2215/02 Mixing or blending of fluids to yield a certain product
• CPC Class Codes: F25J 2215/60 Methane
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• 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 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 2280/02 Control in general, load changes, different modes ("runs"), measurements
• 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

A natural gas liquids plant uses a demethanizer and a deethanizer in a two-column or single column configuration that can be used for ethane recovery and ethane rejection. During ethane recovery, 95% ethane recovery and 99% propane recovery are achieved, while during ethane rejection the sales gas Wobbe Index requirement is maintained while maintaining 95% propane recovery. A residue gas recycle exchanger is most preferably configured to use the demethanizer overhead product to either cool a portion of the residue gas and a portion of the feed gas during ethane recovery, or to cool a portion of the feed gas using two distinct heat transfer areas to produce a feed gas reflux at significantly lower temperature.

Claims

1. A method of flexible ethane recovery, comprising:

feeding a first portion of a feed gas to a demethanizer as a first reflux and a second portion of the feed gas after cooling and expansion to the demethanizer as a demethanizer feed;

using a demethanizer overhead product in a residue gas recycle exchanger to cool a portion of compressed residue gas and the first portion of the feed gas to thereby produce the first reflux and a second reflux for the demethanizer during ethane recovery, wherein first and second reflux are fed to the demethanizer at different first and second reflux locations;

or

using the demethanizer overhead product in the residue gas recycle exchanger to cool the first portion of the feed gas in two separate heat transfer areas to thereby produce the first and second reflux to the demethanizer during ethane rejection, and feeding the first and second reflux to the demethanizer at the different first and second reflux locations; and

using a demethanizer bottom to cool the second portion of the feed gas and feeding the demethanizer bottom after the cooling step to a deethanizer or deethanizer section of the demethanizer.

2. The method of claim 1 further comprising using a plurality of switch valves to control switchover from ethane rejection to ethane recovery.

3. The method of claim 1 wherein the second portion of the feed gas is cooled to −

38°

to −

45°

F. to partially condense the second portion of the feed gas, separating the partially condensed feed gas into a liquid fraction and a vapor fraction, and feeding the liquid and vapor fraction to the demethanizer at separate locations.

4. The method of claim 3 further comprising a step of expanding the vapor fraction in a turbo expander and reducing pressure of the liquid fraction before feeding the liquid and vapor fraction to the demethanizer.

5. The method of claim 1 further comprising a step of withdrawing an ethane stream as a deethanizer overhead product or deethanizer section overhead product.

6. The method of claim 1 further comprising a step of compressing a deethanizer overhead product or deethanizer section overhead product and combining the compressed overhead product with the demethanizer overhead product during ethane rejection.

7. A residue gas recycle exchanger for flexible ethane recovery in an NGL recovery plant, comprising:

piping and conduits configured for coupling the residue gas recycle exchanger to a demethanizer such that a demethanizer overhead product provides refrigeration to a portion of compressed residue gas and a portion of a feed gas to thereby produce a first and a second reflux stream to different first and second reflux locations on the demethanizer during ethane recovery; and

wherein the piping and conduits are further configured for coupling the residue gas recycle exchanger to the demethanizer such that the demethanizer overhead product provides refrigeration to the portion of the feed gas to thereby produce a first and a second feed gas reflux stream to the different first and second reflux locations on the demethanizer during ethane rejection.

8. The residue gas recycle exchanger of claim 7, wherein the recycle exchanger is fluidly coupled to a plurality of switch valves that are configured to control switchover from ethane rejection to ethane recovery.

9. A gas processing plant for flexible ethane recovery, comprising:

a feed gas source configured to provide a feed gas;

a demethanizer configured to receive a demethanizer feed, and a first and a second reflux stream at different first and second reflux locations, and also configured to produce a demethanizer overhead product and a demethanizer bottom product;

a deethanizer or deethanizer section fluidly coupled to the demethanizer such that the demethanizer bottom product is fed to the deethanizer or deethanizer section, and wherein the deethanizer or deethanizer section is configured to produce a C3+ bottom product and a C2 enriched overhead product;

a residue gas recycle exchanger fluidly coupled to the demethanizer such that the demethanizer overhead product cools

(a) a portion of compressed residue gas and a first portion of the feed gas to thereby produce the first reflux and a second reflux for the demethanizer during ethane recovery, and such that the first and second reflux are fed to the demethanizer at the different first and second reflux locations;

or

(b) the first portion of the feed gas in two separate heat transfer areas of the residue gas recycle exchanger to thereby produce the first and second reflux to the demethanizer during ethane rejection, and such that the first and second reflux are fed to the demethanizer at the different first and second reflux locations.

10. The gas processing plant of claim 9 further comprising using a plurality of switch valves that are configured to allow for switchover from ethane rejection to ethane recovery.

11. The gas processing plant of claim 9 further comprising a feed gas separator that is configured to receive a partially condensed second portion of the feed gas, to separate the partially condensed second portion of the feed gas into a liquid fraction and a vapor fraction, wherein the feed gas separator is fluidly coupled to the demethanizer to allow feeding the liquid and vapor fraction to the demethanizer at separate locations.

12. The gas processing plant of claim 11 further comprising a turbo expander fluidly coupled between the feed gas separator and the demethanizer to expand the vapor fraction, and a JT valve fluidly coupled between the feed gas separator and the demethanizer to reduce pressure of the liquid fraction.

13. The gas processing plant of claim 9 further comprising a conduit that is configured to allow withdrawal of the C2 enriched overhead product from the plant.

14. The gas processing plant of claim 9 further comprising a compressor configured to compress the C2 enriched overhead product for combination with the demethanizer overhead product during ethane rejection.