Ethane extraction process for a hydrocarbon gas stream

• US 6,755,965 B2
• Filed: 04/20/2001
• Issued: 06/29/2004
• Est. Priority Date: 05/08/2000
• Status: Expired due to Term

• Current Assignee: Inelectra S.A.
• Original Assignee: Inelectra S.A.
• Inventors: Pironti, Filippo, Vincentelli, Jorge
• Primary Examiner(s): Griffin, Walter D.
• Assistant Examiner(s): Nguyen, Tam M.
• Application Number:
  US09/839,759
• Publication Number:
  US 20020042550A1
• Time in Patent Office: 1,166 Days
• Field of Search: 208/347, 208/350, 208/351, 208/353, 585/802, 626/22, 62/482, 626/31
• US Class Current: 208/347
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: C07C 7/09 by fractional condensation
• CPC Class Codes: C07C 9/02 with one to four carbon atoms liquefied petroleum gas C10L3/12
• CPC Class Codes: C07C 9/06 Ethane
• 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 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• 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 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2215/64 Propane or propylene
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• 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 2270/02 Internal refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/04 Internal refrigeration with work-producing gas expansion loop
• 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: Y02P 20/151 : Reduction of greenhouse gas [GHG] emissions, e.g. CO2

Abstract

A process for ethane extraction from a gas stream based on turboexpansion and fractionation with no mechanical refrigeration is provided. The feed gas is sweetened and dehydrated by a conventional amine process and by a molecular sieve unit, to remove carbon dioxide and water. After this pretreatment, the feed gas undergoes to a series of cooling steps through a cryogenic brazed aluminum heat exchanger and fed to a demethanizer column. A stream rich in methane is recovered from the top of this column and fed to a centrifugal compressor and subsequently routed to a booster/turboexpander. The temperature of the methane gas is greatly reduced by the expansion allowing the cooled methane stream to be a cooling source for cryogenic heat exchanger. Feed for a de-ethanizer column comes from the bottom liquids of the de-methanizer column. Ethane is recovered overhead at the de-ethanizer column.

Claims

1. A process for recovering ethane from a methane, ethane and propane containing gas stream comprising:

(a) providing the hydrocarbon gas stream comprising from about 50% to about 75% by mole methane, from about 15% to about 40% by mole ethane and from about 1% to about 4% by mole propane;

(b) cooling the hydrocarbon gas stream to provide a partially condensed feed stream;

(c) separating said partially condensed feed stream into a vapor hydrocarbon feed stream and a condensed liquid hydrocarbon feed stream;

(d) providing a cryogenic heat exchanger;

(e) cooling the vapor hydrocarbon feed stream in a the cryogenic heat exchanger by heat exchange with a first cooling source, a second cooling source and a third cooling source to form a cooled and substantially condensed hydrocarbon feed stream, wherein said first cooling source is said condensed liquid hydrocarbon feed stream;

(f) distilling said cooled and substantially condensed hydrocarbon feed stream and said condensed liquid hydrocarbon feed stream in a demethanizer column to form a methane-rich stream and an ethane/propane-rich stream, wherein said methane-rich stream is said second cooling source;

(g) compressing said methane-rich stream to form a compressed methane-rich stream;

(h) cooling said compressed methane-rich stream to form a compressed methane-rich stream;

(i) turboexpanding said compressed methane-rich stream to a lower pressure to provide said third cooling source for said cryogenic heat exchanger;

(j) distilling said ethane/propane-rich stream in a de-ethanizer column to form an ethane-rich stream and a propane-rich stream; and

(k) recovering said ethane-rich stream.

2. The process of claim 1 wherein said ethane-rich stream contains at least 90% by mole ethane.

3. The process of claim 1 wherein said ethane-rich stream contains less than about 0.5% by mole methane and less than about 3% by mole propane.

4. The process of claim 1 wherein said methane-rich stream contains at least 95% by mole methane.

5. The process of claim 1 wherein said ethane-rich stream contains at least 96.5% by mole ethane.