Ethane recovery process

• US 5,953,935 A
• Filed: 11/04/1997
• Issued: 09/21/1999
• Est. Priority Date: 11/04/1997
• Status: Expired due to Fees

• Current Assignee: Mcdermott Engineers & Constructors Limited
• Original Assignee: Mcdermott Engineers & Constructors Limited
• Inventors: Sorensen, James N.
• Primary Examiner(s): Kilner, Christopher B.
• Application Number:
  US08/963,923
• Time in Patent Office: 686 Days
• Field of Search: 62/620, 62/621, 62/630
• US Class Current: 62/621
• CPC Class Codes: C10G 5/06 by cooling or compressing
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2200/78 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 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 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

Abstract

An improved ethane recovery system and process which increases the recovery of ethane up to about 99% with no increase in plant residue compression horsepower. The improved ethane recovery process employs an additional fractionation column which receives two vapor streams in different regions thereof which allows the fractionation column to produce the top reflux to the demethanizer column.

Claims

1. In an ethane recovery system, an apparatus comprising:

separating means constructed to receive a cooled natural feed gas stream, said separating means dividing the cooled natural feed gas stream into an upper vapor stream and a lower liquid stream;

dividing means connected to said separating means and receiving said upper vapor stream therefrom, said dividing means dividing the vapor stream into three streams, a first, a second, and a third vapor streams;

distilling means located downstream from said separating means and said dividing means, said distilling means providing a bottom ethane product stream and an upper methane residue gas stream, said distilling means being connected to said separating means and receiving said lower liquid stream in a middle region of said distilling means, said distilling means further receiving said first vapor stream from said separating means in an upper mid-section region thereof;

fractionating means connected to said separating means and to said distilling means , said fractionating means receiving said second and third vapor streams for separating methane therefrom and providing a bottom stream as a top reflux to said distilling means.

2. In an ethane recovery system as set forth in claim 1, wherein said second vapor stream enters said fractionating means in a bottom region.

3. In an ethane recovery system as set forth in claim 2, wherein said third vapor stream enters said fractionating means in a middle region of said fractionating means.

4. In an ethane recovery system as set forth in claim 3, the apparatus further comprising a heat exchanger connected to said separating means for cooling said third vapor stream prior to said fractionating means.

5. In an ethane recovery system as set forth in claim 1, the apparatus further comprising compression means located downstream from said distilling means for compressing the upper methane residue gas stream.

6. In an ethane recovery system as set forth in claim 1, wherein said distilling means comprises a demethanizer.

7. In an ethane recovery system as set forth in claim 1, wherein said fractionating means comprises an absorber.

8. In an ethane recovery system as set forth in claim 1, the apparatus further comprising a heat exchanger for cooling said natural gas feed stream and warming the upper methane residue gas stream.

9. In an ethane recovery system as set forth in claim 8, the apparatus further comprising a plurality of heat exchangers for warming the upper methane residue gas stream.

13. In an ethane recovery process as set forth in claim 1, wherein the overhead gas stream from the fractionating means is condensed and partly recycled to the top region of the fractionating means.

10. In an ethane recovery process, the method comprising the steps of:

locating a separator downstream from a heat exchanger for receiving a cooled natural feed gas stream;

separating the cooled natural feed gas stream into an upper vapor stream and a lower liquid stream;

dividing the upper vapor stream into a first, a second, and a third vapor streams;

delivering the lower liquid stream from the separator to a middle region of a demethanizer;

passing the first vapor stream through an expander and into an upper mid-section of the demethanizer;

passing the second vapor stream into a bottom region of fractionating means;

passing the third vapor stream into a middle region of the fractionating means;

sending a bottom stream from the fractionating means to an upper region of the demethanizer; and

producing an upper methane residue gas stream and a lower bottom natural gas liquids stream with the demethanizer.

11. In an ethane recovery process as set forth in claim 10, the method further comprising the step of passing a portion of the upper methane residue gas stream into the fractionating means.

12. In an ethane recovery process as set forth in claim 11, the method further comprising the steps of producing a bottom stream with the fractionating means and sending it to an upper region of the demethanizer.