Comparison of Feedback and Feedforward Control Systems for a Counter-Current Heat Exchanger

Aim of this study is to provide a simplified approach of a process modeling and control framework applied in a shell-and-tube heat exchanger. Initially, 1st order differential equations (ODEs) are developed in order to analyze the dynamic behavior and interactions of cold (coolant water) and hot (industrial flue gases) streams. After performing open-loop simulations that are required in order to verify the linear equivalence and the extraction of process transfer functions, a series of P/PI/PID controllers tuned via known methodologies (Ziegler–Nichols and Tyreus-Luyben) are compared under different scenarios: i) a constant set-point signal, ii) a variable set-point signal and iii) a constant set-point along with the effect of disturbances (temperature of the inlet hot and cold streams and hot stream flowrate). Based on performance criteria (ISE, IAE, ITAE, ITE) and control features, the best controllers are identified and proceed for a further comparison with i) an internal model-based feedback and ii) an internal model-based feedforward controller. The results drawn from the simulations conclude that the most suitable controller for the heat exchanger is the feedforward as it provides a fast response, zero overshoot and reduced effort from the manipulated variable, followed by a similar performance from the Tyreus-Luyben tuned controllers.