Comparison of process identification and physical modelling for falling-film evaporators

Abstract Multiple-effect evaporators are widely used in dairies and other food industries. Because of the requirements for product quality a tight control of the evaporator is necessary. NIZO and SETPOINT-IPCOS have carried out a project on multivariable control of evaporators; the NIZO four-effect evaporator served as a case. In this first part of the project a dynamic model has been derived of the NIZO evaporator: (a) by application of the NIZO-STREAM program which is a simulation program based on physicomathematical modelling using first principles; and (b) by performing dedicated experiments on the process and using identification techniques, which results in an identified model. These models were compared in the context of using them in controller design. Both models appeared to be suitable to design well performing controllers.