Analyzing Transient Response Characteristics of Glycerin Heating Process

The glycerin heating process system is an important performance characteristic that determines the correctness of a system that responds to the change in input temperature. Controlling the temperature of the glycerin purification process system was not an easy task, as an increase in operating temperature would significantly reduce the quality of the purified glycerin. This is because an unlimited increase in temperature beyond the set point and an excessive prolongation of the heating process would result in the formation of an excessive secondary oxidation product in the final purified glycerin. This paper discusses the transient response characteristics of the glycerin heating process using a parallel PID controller. The glycerin heating process behavior was determined experimentally using a step input test and modelled as the First Order plus Delay Time. PID controller is the essential element in the process control system used to regulate the measured variables to the desired value, existence of overshoot, and larger settling time even in disturbances or changes in the input signal. The controller parameters were adjusted using Ziegler- Nichols, Cohen-Coon, and Wang tuning methods, each of which was analyzed based on the corresponding integral error criterion value. The Integral Square Error, Integral Absolute Error and Integral Time-weighted Absolute Error criteria value were used to evaluate the efficiency of the glycerin heating process. The transient response performances in terms of overshoot, rise time and settling time were also evaluated. Simulation work has shown that the process has experienced high overshoots for Ziegler-Nichols and Cohen-Coon, and has taken a longer time to settle. Wang's method exhibits no overshoot but a slow response. The lower gain PID controller was found to improve the process response in terms of overshoot but increase the rise time and settling time. The results indicate that the desired process performance was more or less influenced by the interaction between the tuning parameters. The study concludes that the PID controller with lower gain improves the transient response of the glycerin heating process in terms of overshoot but takes a longer time to settle. The Ziegler-Nichols PID controller is not recommended for controlling the glycerin heating process due to process response oscillations that are difficult to eliminate without prolonging the heating cycle.