Integral control of heat-exchanger-plus-bypass systems

This paper shows that integral control delivers high quality temperature control in heat-exchanger-plus-bypass (HEPB) systems, when the bypass is placed on the stream whose temperature is to be controlled. A tuning formula, for the integral controller, that depends only on the process time delay and the initial jump of the step response of the HEPB system is given. This formula guarantees closed-loop stability for a wide range of operating conditions, and it minimizes the integral of the square of the tracking error and control action under certain conditions. The control quality that results from colocating the bypass on the controlled stream and using integral control is demonstrated with nonlinear simulations.