Determination and modeling of the influence of the fluid-dynamics in hydrotreating bench scale plants (1999)

Public ISBD Titre : Determination and modeling of the influence of the fluid-dynamics in hydrotreating bench scale plants Type de document : texte imprimé Auteurs : Christophe Guéret, Directeur de thèse Année de publication : 1999 Importance : 175 f. Présentation : ill. Format : 30 cm. Note générale : Thèse de Doctorat : Génie Chimique : Berlin, Technische Universität Berlin : 1999 Bibliogr. f. 176 - 188 . - Annexe f. 189 - 231 Langues : Anglais (eng) Mots-clés : Hydrotreating Three-phase reactors Axial dispersion Mass transfer Residence time distribution Upflow Downflow Index. décimale : D001299 Résumé : At an industrial scale, the hydrotreating of oil fractions is carried out in multiphase fixed bed reactors. The oil fraction and hydrogen cross the catalyst bed, usually in cocurrent downflow. Since the product specifications are steadily becoming more severe, the testing of new catalysts and of modified operating conditions in pilot plants becomes increasingly important. Although these pilot plants are frequently by a factor of 100 000 smaller than the industrial units, they still have to allow the upscaling to industrial units. In the literature, relatively low conversion degrees in pilot plants are frequently reported, especially in downflow. The significantly lower fluid velocities in pilot plants seem to be responsible for such differences, as the influence of fluid-dynamic non-idealities and of the extraparticle mass transfer phenomena increases with a decrease of the fluid velocities. In the present work, the influence of important fluid-dynamic non-idealities on the hydrotreating of gas oil fractions in pilot plants was examined. This was done on the one hand in experiments with different pilot plants and the other hand by simulations with an especially developed multiphase model. The phenomena were considered as well in an isolated manner. In order to examine any interactions with the chemical reactions, they were also studied in a reactive system. This methodology was applied to the phenomena, "axial dispersion" and "gas-liquid mass transfert". The axial dispersion and the liquid holdup were determined in residence time distribution experiments. The residence time distribution experiments resulted in a significantly higher axial dispersion in downflow than in upflow. Subsequently, the desulfurization degrees in upflow and in downflow were determined, in order to measure the relative importance of the axial dispersion. In this context, the "wetting degree" of the catalyst was examined, too. However, no significant difference between the upflow and the diwnflow desulfurization performance was observed over a large range of operating conditions. The gas-liquid mass transfer was examined by taking samples of the gas phase at reaction conditions. The composition of the gas phase was compared with the results of flash calculations. The gas samples indicate no important gas-liquid mass transfer resistance. Subsequently, the influence of the gas-liquid mass transfer was examined in catalytic experiments by varying the gas velocity. The desulfurization experiments confirmed the absence of an important gas liquid mass transfer resistance. In the second part of the work, a simulation program was developed, which-contrary to the "pseudohomogeneous" models that are frequently used in industry-accounts for the presence of a gas and a liquid phase. In addition to the chemical reaction kinetics, axial disoersion and gas-liquid mass transfer were integrated into the model. The model reproduces the influence of the axial dispersion and of the gas-liquid mass transfer in a qualitative manner. The variation of the desulfurization degree after an increase of the gas velocity is correctly reproduced in a quantitative manner, too. Significant differences between the experiments and the simulation concerning the axial dispersion indicate, that the yet neglected intraparticle mass transfer should also be examined. Determination and modeling of the influence of the fluid-dynamics in hydrotreating bench scale plants [texte imprimé] / Christophe Guéret, Directeur de thèse . - 1999 . - 175 f. : ill. ; 30 cm. Thèse de Doctorat : Génie Chimique : Berlin, Technische Universität Berlin : 1999 Bibliogr. f. 176 - 188 . - Annexe f. 189 - 231 Langues : Anglais (eng) Mots-clés : Hydrotreating Three-phase reactors Axial dispersion Mass transfer Residence time distribution Upflow Downflow Index. décimale : D001299 Résumé : At an industrial scale, the hydrotreating of oil fractions is carried out in multiphase fixed bed reactors. The oil fraction and hydrogen cross the catalyst bed, usually in cocurrent downflow. Since the product specifications are steadily becoming more severe, the testing of new catalysts and of modified operating conditions in pilot plants becomes increasingly important. Although these pilot plants are frequently by a factor of 100 000 smaller than the industrial units, they still have to allow the upscaling to industrial units. In the literature, relatively low conversion degrees in pilot plants are frequently reported, especially in downflow. The significantly lower fluid velocities in pilot plants seem to be responsible for such differences, as the influence of fluid-dynamic non-idealities and of the extraparticle mass transfer phenomena increases with a decrease of the fluid velocities. In the present work, the influence of important fluid-dynamic non-idealities on the hydrotreating of gas oil fractions in pilot plants was examined. This was done on the one hand in experiments with different pilot plants and the other hand by simulations with an especially developed multiphase model. The phenomena were considered as well in an isolated manner. In order to examine any interactions with the chemical reactions, they were also studied in a reactive system. This methodology was applied to the phenomena, "axial dispersion" and "gas-liquid mass transfert". The axial dispersion and the liquid holdup were determined in residence time distribution experiments. The residence time distribution experiments resulted in a significantly higher axial dispersion in downflow than in upflow. Subsequently, the desulfurization degrees in upflow and in downflow were determined, in order to measure the relative importance of the axial dispersion. In this context, the "wetting degree" of the catalyst was examined, too. However, no significant difference between the upflow and the diwnflow desulfurization performance was observed over a large range of operating conditions. The gas-liquid mass transfer was examined by taking samples of the gas phase at reaction conditions. The composition of the gas phase was compared with the results of flash calculations. The gas samples indicate no important gas-liquid mass transfer resistance. Subsequently, the influence of the gas-liquid mass transfer was examined in catalytic experiments by varying the gas velocity. The desulfurization experiments confirmed the absence of an important gas liquid mass transfer resistance. In the second part of the work, a simulation program was developed, which-contrary to the "pseudohomogeneous" models that are frequently used in industry-accounts for the presence of a gas and a liquid phase. In addition to the chemical reaction kinetics, axial disoersion and gas-liquid mass transfer were integrated into the model. The model reproduces the influence of the axial dispersion and of the gas-liquid mass transfer in a qualitative manner. The variation of the desulfurization degree after an increase of the gas velocity is correctly reproduced in a quantitative manner, too. Significant differences between the experiments and the simulation concerning the axial dispersion indicate, that the yet neglected intraparticle mass transfer should also be examined.

Réservation

Réserver ce document

Exemplaires (1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité	Spécialité	Etat_Exemplaire
D001299	D001299	Papier	Bibliothèque Annexe	Thèse de Doctorat	Disponible	Genie_chimique	Consultation sur place