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.

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.

Methods and systems include, using a monitoring system, initiating a control logic configured to control a production control system pertaining to a refrigeration system connected to a plurality of production trains. The method may include obtaining a plurality of production parameters; calculating, using the plurality of production parameters, an isentropic efficiency value for the primary compressor if the production flow rate is less than a production threshold; comparing each of the plurality of isentropic efficiency values; determining from the comparing each of the plurality of isentropic efficiency values, a primary compressor having a lowest isentropic efficiency value; selecting the respective primary compressor having the lowest isentropic efficiency value. The method may include, using a production control system, shutting down the selected primary compressor.