Ethane recovery and ethane rejection methods and configurations

• US 9,557,103 B2
• Filed: 12/15/2011
• Issued: 01/31/2017
• 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
• Application Number:
  US13/996,805
• Publication Number:
  US 20140007616A1
• Time in Patent Office: 1,874 Days
• US Class Current: 1/1
• 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 2200/72 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 2205/04 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 2215/60 Methane
• CPC Class Codes: F25J 2215/62 Ethane or ethylene
• CPC Class Codes: F25J 2215/64 Propane or propylene
• CPC Class Codes: F25J 2230/30 Compression of the feed stream
• 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 2240/04 Multiple expansion turbines in parallel
• CPC Class Codes: F25J 2245/02 Recycle of a stream in general, e.g. a by-pass stream
• CPC Class Codes: F25J 2280/02 Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0228 characterised by the separated product stream
• 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 flexibly recovering ethane from a feed gas, comprising:

expanding the feed gas in a turbo expander to produce a partially expanded feed gas;

cooling and additionally expanding a first portion of the partially expanded feed gas to produce a second reflux;

cooling a second portion of the partially expanded feed gas to produce a partially condensed feed stream;

separating the partially condensed feed stream into a vapor stream and a liquid stream;

expanding the vapor stream and the liquid stream prior to feeding into a demethanizer;

using a demethanizer side reboiler in cooling a third portion of the partially expanded feed gas to produce a cooled feed stream;

combining the cooled feed stream with the partially condensed feed stream;

feeding into the demethanizer a top reflux and the second reflux below the top reflux, wherein the demethanizer produces a demethanizer bottom product and a demethanizer overhead product;

feeding at least part of the demethanizer bottom product to a demethanizer to produce a demethanizer bottom product and a demethanizer overhead product; and

feeding a portion of the demethanizer overhead product back to the demethanizer as the top reflux during ethane recovery, and feeding a portion of the demethanizer overhead product back to the demethanizer as the top reflux during ethane rejection;

wherein flow of the third portion of the partially expanded feed gas to the demethanizer side reboiler is decreased relative to flow of the first portion and the second portion of the partially expanded feed gas during ethane rejection.

2. The method of claim 1, wherein the demethanizer is operated at a higher pressure than the deethanizer during ethane recovery, and wherein the demethanizer is operated at a lower pressure than the demethanizer during ethane rejection.

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

4. The method of claim 1, wherein an ethane recovery of at least 95% is achieved during ethane recovery.