Improved temperature control of a batch reactor with actuation constraints

In some industrial batch reactors the accuracy in tracking desired temperature profiles is significantly influenced by the characteristics of the actuation system that regulates the thermal exchange. In these plants it may not be structurally possible to switch promptly between the heating and the cooling configurations; this implies that, for long time periods, the sign of the actuating signal is constrained to be either positive or negative. This fact, as long as spontaneous evaporation of the coolant, limits the possibility of tracking the desired temperature profile. Under the constraints that the actuation system can only subtract heat from the reactor, a new scheme is proposed to improve the controllability of the reactor temperature. The strategy alternates phases of coolant injection and phases of forced draining of the jacket. The proposed scheme has been worked out on the basis of the numerical analysis of a detailed thermodynamic model of an industrial reactor. The scheme has been extensively tested with remarkable results and is now in use in some industrial reactors of the CIBA Specialty Chemicals at Pontecchio Marconi, Italy.