Utilize Process Capacity and Controller Tuning to Attenuate Process Variability and Improve Process Performance

Surge tanks are often used to provide a buffer between unit operations to help isolate process upsets and reduce flow variability passed between the units. However, other process capacities such as column base volume, column overhead receiver tanks and even reactor vessels can be used to attenuate process variability. When a PID controller is used to control the vessel level, the tuning of the controller has a direct impact on ability of the “capacity” in the vessel to attenuate variability. Specifically, the tuning can make a 10,000 gallon tank act like a 100 gallon tank (or vice versa!) from a variability attenuation aspect. This presentation will discuss PID control techniques to provide maximum attenuation of flow variability and still provide good load regulation to keep the level within allowable limits. Plant examples will be used to illustrate the concepts and results.