Ethane recovery and ethane rejection methods and configurations

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.