Design of PI/PID Control Algorithm for a Benchmark Heat Exchanger System using Frequency Domain Specifications

This paper presents the design of a proportionalintegral (PI)/proportional-integral-derivative (PID) controller for a shell and tube heat exchanger (STHE) system. In a heat exchanger system, the transfer of heat from a hot fluid to a colder one is maintained by adopting a cascade control structure. The main objective of this work is to maintain the temperature of the shell outlet. The cascade control structure is designed for controlling the temperature in which the inner loop contains a flow controller that controls the flow rate of the tube outlet. STHE system is modeled to a first order plus dead time (FOPDT) system for the inner loop (controlling the flow rate) as well as for the outer loop (controlling the temperature). The inner loop is controlled by a PI controller while the outer loop is controlled by a PID controller. The controllers are designed based on the frequency domain specifications such as gain margin and phase margin to attain the desired control output. The proposed controller can achieve the desired values of temperature irrespective of external disturbances and parameter uncertainties.