Identification and Observability of Lumped Kinetic Models for Vacuum Gas Oil Hydrocracking
Résumé
The so-called “lumping approach” is widely used to study complex processes such as hydrocracking of vacuum residue. In order to describe the composition changes in such systems, not only must the kinetic parameters be determined, but the lumped reactions that occur should also be identified. In this study, the modeling of catalytic hydrocracking of vacuum gas oil has been carried out using six component lumps. Three different identification strategies have been developed to determine the reaction subnetwork containing a given number of reaction pathways that provides the data fit. The strategies were compared according to their tendency to provide increasingly better results, as a function of the number of reactions present. Although, in this way, 40% of the original reaction superstructure was eliminated from the system, the kinetic parameters of the remaining reactions still could not be identified with complete certainty. Hence, the linearized state-space model representations of the reaction networks have been further analyzed with the objective of identifying observable subsystems. The results show that there exists a five-reaction network that is observable and can be determined using the finally proposed identification strategy, while its curve fitting is also satisfactory. It has also been shown that it gives the best results from all possible five-reaction subsystems.
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