(139f) A Creative Solution to a Splitter with Multiple Constraints Using APC

A splitter overhead condenser system in one of our Olefin plants has unique heat integration with the feed propane vaporization system and cooling water system.  Similar to other olefins plants, the reboiler has heat integration with the quench system.  The complex heat integration results in several challenging constraints that must be managed.  In addition, the active constraint set changes often depending on ambient and unit conditions.  These challenging constraints were not well handled in the existing Advanced Process Control (APC).  To address this problem, the APC was revamped using a creative design to robustly handle these constraints.  In addition, several advanced techniques and unique solutions were used throughout the design, modeling, and implementation of this revamp.  A unique aspect about this revamp is the APC uses a very long time-to-steady-state model (30 hours) while using a steady state model for the product composition, whereas, most APC models are significantly shorter (about 2 hours) with ramp models for the product composition