Ethane recovery system

• US 4,851,020 A
• Filed: 11/21/1988
• Issued: 07/25/1989
• Est. Priority Date: 11/21/1988
• Status: Expired due to Fees

• Current Assignee: Mcdermott International Incorporated New Orleans La
• Original Assignee: Mcdermott International Incorporated
• Inventors: Montgomery, George J. IV
• Primary Examiner(s): Capossela, Ronald C.
• Application Number:
  US07/274,243
• Time in Patent Office: 246 Days
• Field of Search: 62/24, 62/54
• US Class Current: 62/621
• CPC Class Codes: B01D 1/2806 The vapour is divided in at least two streams and only a part of the vapour is compressed
• CPC Class Codes: C07C 7/04 by distillation
• CPC Class Codes: C07C 9/06 Ethane
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/72 Refluxing the column with at least a part of the totally condensed overhead gas
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• 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 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

A method of recycling a portion of the overhead vapor stream to enhance ethane recovery from a demethanizer. After the overhead vapor stream is discharged from the demethanizer, a portion of it, reflux, is compressed in a cyrogenic compressor to a pressure greater than that of the demethanizer. Afterwards the pressurized reflux is chilled in a heat exchanger causing at least a portion of it, and preferably all of it, to condense to a liquid. The pressure of this condensed reflux is then equalized to that of the demethanizer across a recycle valve so that a liquid reflux can be fed back to the top of the demethanizer. This recycling of a liquid reflux enhances ethane recovery as a column bottoms product from the demethanizer.

Claims

1. A method of improving ethane recovery from natural gas wherein condensed liquid is returned to a demethanizer as reflux comprising the steps of:

(a) removing overhead vapor from a demethanizer,

(b) compressing a portion of said overhead vapor, now reflux, to a pressure greater than that of said demethanizer,

(c) reducing the temperature of said compressed relux thereby causing at least a portion of it to condense, the temperature of said compressed reflux being reduced by cross-exchanging it with an uncompressed portion of said overhead vapor in a heat exchanger;

(d) equalizing the pressure of said reflux to that of said demethanizer; and

(e) feeding said reflux back to said demethanizer.

2. The method as set forth in claim 1 wherein said reflux is totally condensed before being fed to said demethanizer.

3. The method as set forth in claim 2 wherein said reflux is compressed in a cyrogenic compressor.

4. The method as set forth in claim 3 wherein the pressure of said reflux is equalized to that of said demethanizer across a recycle valve.