(71a) Novel Techniques to Improve Polymer Reactor Temperature Controller Tuning

Good control of polymer loop reactor temperature improves product quality, reduces product transition time and increases production rate. However, due to the sensitive nature of the exothermic process, and an operating philosophy that is sensitive to any potential process disturbances during loop testing, it is difficult to make improvements to the tuning of the control loops.

Measuring process dynamics on a polymer loop reactor and related cooling loops can be difficult due to the highly exothermic reaction and different operating conditions for the many products. Combine these factors with an operating philosophy that is sensitive to any potential process disturbances during loop testing and it is difficult to measure process dynamics and improve loop tuning. Even minor deviations from the reactor temperature set point can result in a deactivation of the reactor by the safety system.

In this case. a combination of technologies was used to improve reactor and reactor coolant temperature loops. First, the process dynamics were approximated from closed loop response of the coolant loop and reactor temperature during normal operation. The coolant and reactor temperature processes were simulated within native control system. The simulation was used to evaluate the improvement from improved loop tuning and to develop an open loop step test plan that would satisfy the concerns of the operation department. Then, open loop step tests were performed to obtain more accurate process dynamics which were used to improve the accuracy of the simulation. The improved simulation was used to further improve the reactor tuning and control performance.

The improved tuning and control scheme changes reduced the reactor temperature variability, reduced the impact of heat exchanger swaps, reduced product transition time and reactor startup time. These changes resulted significant increase in production capacity.