Application of Discrete Time Controllers to A Pilot Scale Packed Distillation Column

Abstract

The process involved is a pilot scale packed distillation column that separates a mixture of methanol and water. The performances of two discrete time controllers that different parameter tuning techniques were used for each of them were examined in the face of the set point tracking of the overhead product composition. The success of the discrete time controllers were assessed by means of the rise time and integral of the square error (ISE) criteria. A discrete time proportional integral controller with two terms was obtained by using the velocity form of controller law. For this controller, the proportional sensitivity term (Kc) and the other term were determined by creating root locus diagram and replacing the closed loop poles to the appropriate location in unit circle of z-plane. The most successful proposed controller action was obtained with Kc of 0.95 and integral time constant of 2.375 min according to rise time of 3.7 min and ISE criteria of 1.08. The discrete time proportional integral derivative (PID) controller with six parameters as P=0.009185, I=0.01835, D=0, N=100, b=1, c=1 that were tuned by using Simulink control design and 1 min sampling time was applied to the process. The same controller performance with six parameters of P=1.164, I=0.5319, D=-0.01481, N=3.783, b=0.1233, c=0.01017 was investigated by choosing 0.5 min sampling time. By comparing all the performances obtained, it can be said that the discrete time controller with two terms tuned by the suggested approach can easily be applied to obtain the most desired performance.

Keywords

• discrete time controller
• packed distillation column
• root locus
• closed loop pole placement