Systems and Methods for Enhanced Recovery of NGL Hydrocarbons

• US 20140260421A1
• Filed: 03/14/2013
• Published: 09/18/2014
• Est. Priority Date: 03/14/2013
• Status: Abandoned Application

• Current Assignee: IPSI, LLC (Bechtel Group Incorporated)
• Original Assignee: IPSI, LLC (Bechtel Group Incorporated)
• Inventors: Elliot, Douglas, Lee, Guang Chung, Yu, Ji, Yao, Jame, Golikeri, Sudhir
• Application Number:
  US13/827,147
• Publication Number:
  US 20140260421A1
• Time in Patent Office: Days
• US Class Current: 62/636
• 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 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• 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 2205/30 using a washing, e.g. "scrubbing" or bubble column for purification purposes
• 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 2210/04 Mixing or blending of fluids with the feed stream
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2210/62 Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• CPC Class Codes: F25J 2230/30 Compression of the feed stream
• 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 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• 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

Systems and methods for the enhanced recovery of ethane and heavier hydrocarbons using an absorbing agent. Typical absorbing agents include one or more C3+ alkanes. The systems and methods separate components of a feed gas containing methane and heavier hydrocarbons, which maximizes ethane recovery, without requiring appreciable increases in capital and operating costs, and improves the safety margin with respect to the risk of CO₂ freeze-out.

Claims

1. A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:

cooling an absorbing agent and an inlet stream comprising the feed gas in a heat exchanger to produce a cooled absorbing agent and a chilled inlet stream;

separating the chilled inlet stream in a separator to produce a liquid hydrocarbon stream and an overhead vapor stream;

combining the cooled absorbing agent with a portion of the overhead vapor stream to form a combined stream;

cooling the combined stream into a reflux exchanger to produce a subcooled liquid stream;

expanding another portion of the overhead vapor stream in an expander to produce a demethanizer feed stream; and

introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.

2. The method of claim 1, wherein the absorbing agent comprises one or more C3+ alkanes.

3. The method of claim 1, wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons.

4. The method of claim 1, wherein the absorbing agent and the inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream.

5. The method of claim 1, further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream.

6. A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:

combining a residue gas recycle stream and an absorbing agent to form an enriched residue gas recycle stream;

cooling the enriched residue gas recycle stream and an inlet stream comprising the feed gas in a heat exchanger to produce a chilled enriched residue gas recycle stream and a chilled inlet stream;

separating the chilled inlet stream in a separator to produce a liquid hydrocarbon stream and an overhead vapor stream;

cooling the chilled enriched residue gas recycle stream in a reflux exchanger to produce a subcooled liquid stream;

expanding the overhead vapor stream in an expander to produce a demethanizer feed stream; and

introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.

7. The method of claim 6, wherein the absorbing agent comprises one or more C3+ alkanes.

8. The method of claim 6, wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons.

9. The method of claim 6, wherein the enriched residue gas recycle stream and the inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream.

10. The method of claim 6, further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream.

11. The method of claim 10, wherein a portion of the residue gas stream is used to form the residue gas recycle stream.

12. The method of claim 6, further comprising processing the ethane and heavier hydrocarbons in a demethanizer column, wherein an ethane-rich stream is recovered as another top product in the deethanizer column and another stream comprising propane and heavier components is recovered as another bottom product in the deethanizer column.

13. The method of claim 12, wherein a portion of the another stream is recycled to form the absorbing agent.

14. A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:

combining a portion of an inlet stream comprising the feed gas and an absorbing agent to form an enriched split feed stream;

cooling another portion of the inlet stream comprising the feed gas and the enriched split feed stream in a heat exchanger to produce a chilled enriched split feed stream and a chilled inlet stream or cooling the another portion of the inlet stream comprising the feed gas and an enriched inlet stream in the heat exchanger to produce the chilled enriched split feed stream and the chilled inlet stream;

separating the chilled inlet stream in a separator to produce a liquid hydrocarbon stream and an overhead vapor stream;

cooling the chilled enriched split feed stream in a reflux exchanger to produce a subcooled liquid stream or cooling an overhead vapor separator stream in the reflux exchanger to produce the subcooled liquid stream;

expanding the overhead vapor stream in an expander to produce a demethanizer feed stream; and

introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.

15. The method of claim 14, wherein the absorbing agent comprises one or more C3+ alkanes.

16. The method of claim 14, wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons.

17. The method of claim 14, wherein the another portion of the inlet stream and the enriched split feed stream or the enriched inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream.

18. The method of claim 14, further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream.

19. The method of claim 14, further comprising compressing and cooling the enriched split feed stream to produce the enriched inlet stream.

20. The method of claim 14, further comprising:

separating the chilled enriched split feed stream in another separator to produce the overhead vapor separator stream and a bottom liquid separator stream; and

combining the bottom liquid separator stream and the liquid hydrocarbon stream.

21. A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:

cooling an absorbing agent and an inlet stream comprising the feed gas in a heat exchanger to produce a cooled absorbing agent and a chilled inlet stream;

contracting the chilled inlet stream with the cooled absorbing agent in an absorber to produce a liquid hydrocarbon stream and an enriched overhead vapor stream;

cooling a portion of the enriched overhead vapor stream in a reflux exchanger to produce a subcooled liquid stream;

expanding another portion of the enriched overhead vapor stream in an expander to produce a demethanizer feed stream; and

introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.

22. The method of claim 21, wherein the absorbing agent comprises one or more C3+ alkanes.

23. The method of claim 21, wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons.

24. The method of claim 21, wherein the absorbing agent and the inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream.

25. The method of claim 21, further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream.