M8.7 Summary

Exothermic CSTRs can exhibit interesting, and challenging, nonlinear behavior. Even a simple two-state model, with jacket temperature manipulated and the reactor temperature as the (controlled) output variable, can have multiple steady-state behavior. For reactors with three steady states, the intermediate steady-state is unstable, requiring a feedback controller for stable operation.

CSTRs often have recirculating jacket fluid heat-transfer systems to improve the heat removal capability. For tighter control, and particularly for start-up and transition control, it is important to incorporate a split-range strategy; here, the jacket temperature controller output manipulates either a hot fluid valve or a cold fluid valve, depending on the range of the controller output. For most reactors it is desirable for the cold valve to fail open and the hot valve to fail closed.