It has been nearly a decade since the Instrumentation, Systems and Automation Society (ISA) introduced S88, its first standard for batch control systems. Its still integral in optimizing operations today.
Install a flow meter in the recycle, cascade the flow set point with a pressure control loop. With proper tuning, the valve characteristics are lost in the flow control loop, which should be tuned fast with PI.
DuPont Polyester Technologies (DPT) realizes the benefit of CFX computational fluid dynamics (CFD) modeling software, which provides a multi-size bubble model and manages the complexities involved with modeling a rotating agitator.