Evaluation of control algorithms for three-phase hydrogenation catalytic reactor

The present work deals with the proposition and evaluation of easy to implement control structures for a hydrogenation industrial size reactor. The used mathematical model formulation is a detailed deterministic and previously validated one, which was made focusing on the hydrogenation reaction of o-cresol to obtain the 2-methyl-cyclohexanol, in the presence of a Ni/SiO2 catalyst. A simplified model, generated through factorial design statistical tool, is also used for stationary states predictions, providing very quick solution, suitable for on-line applications. Five different control structures, based on the feedback and feedforward classic structures and on combinations of them, are evaluated both concerning to the ability of the controller to maintain (regulatory control) or to change the controlled variable to the new set-point (servo control) in a reasonable action time. The study shows that, in the analyzed operation range, the combined structure is the best one to be used for this reactor, both for the servo and regulatory control problems. The calculation of control actions is significantly reduced by the use of simplified models. However, since an offset is present in the regulatory problem when the simplified model is used, this model is not suggested to be used in the regulatory problem. (C) 2008 Elsevier B.V.. All rights reserved.