In a process in which both a turbine or motor and an expander are utilized to drive a compressor, the use of the expander is substantially maximized while still insuring that the driving force applied to the turbine or motor does not go below a low limit. A variable limit is also utilized to prevent...http://www.google.es/patents/US4360882?utm_source=gb-gplus-sharePatente US4360882 - Process control system
