(167b) A Real-World Case Study: Distillation Tower Constraint Control

Distillation operations constitute a significant portion of energy usage and unit operations of every Hydrocarbon Processing Industry (HPI) facility. While the principles of thermodynamic and mechanical design of these unit operations are well understood, often times the design of the instrumentation and controls becomes the rate-limiting factor affecting their reliable performance. Further, as ultimately happens, economic drivers compel operators to maximize production from these units, thus requiring the controls to keep the units’ operations within mechanical limitations, which further complicates the controls’ design.

Historically, Model Predictive control (MPC) or “APC” was successfully implemented to ensure reliable and optimal operations at the mechanical limits of existing equipment. Sometimes, for a variety of reasons, however, MPC fails to generate the expected outcomes. A common observation made across multiple HPI sites and companies is that constraint-based regulatory controls are, poorly understood and, consequently, either not implemented at all or implemented with limited success.

This presentation uses a real-world example of a distillation tower that was subject to numerous operating constraints and illustrates the thought process behind designing the regulatory cont