Modern tools of process control : The case of black, gray & white models

The use of models in modern process control is examined both with respect to the continuous and the batch chemical industries. Models are distinguished in two ways: knowledge-driven (fundamental or white) and data-driven (black box), depending on the type of information used in their development. Gray models are defined as the ones with some combination of these two characteristics. The type of models used in the Model Predictive Control (MPC) algorithm for continuous processes and in the optimization of batch processes is then examined separately. It is argued that the linear MPC algorithm utilizes data-driven models, but its use in nonlinear processes will require the use of gray models. This is postulated as the Gray Model Conjecture. In batch processes it is argued that the needed models are gray. These types of models, the Tendency models, are briefly described through their successful in the optimization of batch reactors. The models needed for the study of the interrelationship between process design and control is also discussed L'utilisation des modeles dans la theorie moderne de la commande des procedes est examinee a la fois dans le cas des processus chimiques continus et dans le cas de ceux discontinus. On distingue deux types de modeles: les modeles de connaissance (fondamentaux ou boite blanche) ou ceux etablis a partir de mesures (boite noires). Les modeles boite grise sont definis comme etant des combinaisons de ces deux extremes. On examine ensuite separement les types de modele utilises dans les algorithmes de commande predictive (MPC) pour les procedes continus et dans l'optimisation des procedes discontinus. L'algorithme MPC lineaire utilise des modeles pilotes par les donnees mais son emploi sur des procedes non lineaires necessite des modeles boite grise. Cela conduit au Postulat du Modele Gris. Dans les procedes discontinus on a besoin de modeles gris. Ces types de modele, dits de tendance, sont brievement decrits a travers leur utilisation reussie pour l'optimisation des reacteurs discontinus. On discute enfin des modeles qu'il est necessaire d'utiliser pour l'etude des relations entre conception et commande des procedes.