Control advanced

B. Stancato and co-workers, "Advanced Control/Optimi2ation for Mitsubishi Kashima Ethylene Plant," paper presented atMIChE Spring Meeting, Houston, April 7—11,1991. 

Thomas F. Edgar/ Ph D / Professor of Chemical Engineering, University of Texas, Austin, TX. Advanced Control Systems, Process Measurements, Section Editor)... 

Dale E Seborg/ Ph D / Profe.s.sor of Chemical Engineering, University of California, Santa Barbara, CA. (Advanced Control Sy.stems)... 

The immediate objective of an advanced control effort is to reduce the variance in an important controlled variable. However, this effort must be coupled with a commitment to adjust the target for this controlled variable so that the process is operated closer to the constraint. In large throughput (commodity) processes, very small shifts in operating targets can lead to large economic returns. 

While the single-loop PID controller is satisfactoiy in many process apphcations, it does not perform well for processes with slow dynamics, time delays, frequent disturbances, or multivariable interactions. We discuss several advanced control methods hereafter that can be implemented via computer control, namely feedforward control, cascade control, time-delay compensation, selective and override control, adaptive control, fuzzy logic control, and statistical process control. 

Regulatory Control For most batch processes, the discrete logic reqmrements overshadow the continuous control requirements. For many batch processes, the continuous control can be provided by simple loops for flow, pressure, level, and temperature. However, very sophisticated advanced control techniques are occasionally apphed. As temperature control is especially critical in reactors, the simple feedback approach is replaced by model-based strategies that rival if not exceed the sophistication of advanced control loops in continuous plants. 

Host computers. These are the most powerful computers in the system, capable of performing func tions not normally available in other units. They act as the arbitrator unit to route internodal communications. An operator interface is supported and various peripheral devices are coordinated. Computationally intensive tasks, such as optimization or advanced control strategies, are processed here. 

---