Ethane recovery and ethane rejection methods and configurations

• US 10,451,344 B2
• Filed: 09/08/2016
• Issued: 10/22/2019
• Est. Priority Date: 12/23/2010
• Status: Active Grant

• Current Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Original Assignee: Fluor Technologies Corporation (Fluor Corporation)
• Inventors: Mak, John
• Primary Examiner(s): Raymond, Keith M
• Application Number:
  US15/259,354
• Publication Number:
  US 20170051970A1
• Time in Patent Office: 1,139 Days
• 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 2200/40 Features relating to the provision of boil-up in the bottom of a column
• 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 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/02 using simple phase separation in a vessel or drum
• 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 2210/60 Natural gas or synthetic natural gas [SNG]
• CPC Class Codes: F25J 2215/60 Methane
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2215/64 Propane or propylene
• CPC Class Codes: F25J 2215/66 Butane or mixed butanes
• CPC Class Codes: F25J 2230/20 Integrated compressor and process expander; Gear box arrangement; Multiple compressors on a common shaft
• CPC Class Codes: F25J 2230/24 Multiple compressors or compressor stages in parallel
• CPC Class Codes: F25J 2230/32 Compression of the product stream
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• 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 2240/40 : Expansion without extracting work, i.e. isenthalpic throttling, e.g. JT valve, regulating valve or venturi, or isentropic nozzle, e.g. Laval
• CPC Class Codes: F25J 2245/02 : Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2270/20 : Quasi-closed internal or closed external hydrogen refrigeration cycle
• 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 2290/02 : Comparison of processes or apparatuses
• CPC Class Codes: F25J 2290/12 : Particular process parameters like pressure, temperature, ratios
• 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
• CPC Class Codes: F25J 3/0247 : separation of CnHm with 4 carbon atoms or more

Abstract

Contemplated plants for flexible ethane recovery and rejection by allowing to switch the top reflux to the demethanizer from residue gas to the deethanizer overhead product and by controlling the flow ratio of feed gas to two different feed gas exchangers. Moreover, the pressure of the demethanizer is adjusted relative to the deethanizer pressure for control of the ethane recovery and rejection.

Claims

1. A method of changing ethane recovery to ethane rejection operation in an NGL plant, comprising:

changing a top reflux of a demethanizer from a demethanizer overhead product to a deethanizer overhead product for ethane rejection;

reducing a demethanizer pressure to a pressure that is lower than a deethanizer pressure for ethane rejection; and

increasing flow of a first portion of a feed gas relative to flow of a second portion of the feed gas for ethane rejection;

wherein the demethanizer is configured to receive a second reflux below the top reflux, wherein the second reflux is the first portion of the feed gas, wherein the second portion of the feed gas is cooled in a demethanizer side reboiler heat exchanger and then combined with a third portion of the feed gas to form a partially condensed feed stream, wherein the partially condensed feed stream is separated into a liquid stream and a vapor stream, wherein the demethanizer is configured to receive the liquid stream and the vapor stream.

2. The method of claim 1, wherein the demethanizer is configured to produce a demethanizer bottom product that is fed to a deethanizer that is configured to produce the deethanizer overhead product.

3. The method of claim 1, wherein the feed gas is cooled before the step of sub-cooling by expanding the feed gas in a turbo expander.

4. The method of claim 1, wherein the first portion of the feed gas is cooled in a feed gas heat exchanger.

5. The method of claim 4, wherein the demethanizer overhead product is heated in the feed gas heat exchanger.

6. The method of claim 1, wherein the demethanizer pressure is between 445 psig and 475 psig or at least 475 psig, and wherein the deethanizer pressure is between 319 psig and 450 psig.

7. The method of claim 1, wherein the demethanizer produces a demethanizer bottom product that is fed to a deethanizer.

8. The method of claim 1, wherein an operating pressure in the demethanizer is between 445 psig and 475 psig or at least 475 psig, and wherein an operating pressure in a deethanizer is between 319 psig and 450 psig.

9. The method of claim 1, wherein a deethanizer produces a deethanizer bottom product, the method further comprising feeding the deethanizer bottom product into a depropanizer.

10. The method of claim 1, wherein the feed gas has a pressure of at least 1000 psig.

11. The method of claim 1, further comprising expanding the feed gas in a turbo expander prior to subcooling the first portion of the feed gas.

12. The method of claim 11, wherein the feed gas is expanded in the turbo expander prior to cooling the second portion of the feed gas.

13. The method of claim 1, wherein a propane recovery of at least 99% is achieved during ethane rejection.

14. The method of claim 1, where the first portion and the third portion of the feed gas are cooled by the demethanizer overhead product in a feed gas heat exchanger.

15. The method of claim 14, wherein the deethanizer overhead product is cooled by the demethanizer overhead product in the feed gas heat exchanger.

16. The method of claim 1, wherein each of the vapor stream and the liquid stream are expanded before feeding to the demethanizer.

17. The method of claim 16, wherein the vapor stream is expanded using a turbo expander.

18. The method of claim 16, wherein the liquid stream is expanded using a JT valve.

19. The method of claim 1, wherein the demethanizer is configured to receive the liquid stream below the vapor stream.

20. The method of claim 1, wherein the demethanizer is configured to produce a demethanizer bottom product, the method further comprising lowering a temperature of the demethanizer bottom product for ethane rejection.