The control of the evaporating process is of the highest importance in the sugar industry, on one hand because of the influence of its behaviour on the regularity of the sugar quality and on the other hand because of the large energy involvement, The highly nonlinear behaviour of the process leads in practice to the establishment of a nonlinear structure based on a knowledge model. This paper presents a model of the evaporators, based on balance equations and also representations of phenomena. The model is validated, using a study of parameter sensitivities, with data collected on the industrial plant. Finally, the validated model is included in a nonlinear predictive control structure, and the results are promising enough to think next about the validation of this control scheme on the industrial plant.