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Residue Hydrotreating

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modelling of residue hydrotreater
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  • Modeling of vacuum residue hydrotreatment Impact of the feedstock description on model output

    Pedro Manuel Mendes Rivotti

    Dissertao para obteno do Grau de Mestre em Engenharia Qumica

    Jri Presidente: Prof. Joo Carlos Moura Bordado Orientadores: Prof. Fernando Manuel Rama Cardoso Ribeiro

    Dr. Vitor Raul Lameiras Franco da Costa Vogal: Prof. Francisco Manuel da Silva Lemos

    Setembro de 2009

  • i

    Resumo

    Neste trabalho apresentado o estudo de um modelo de hidrotratamento de resduos de vcuo desenvolvido no IFP.

    O modelo em estudo simula a operao de um reactor de hidrodesmetalizao e de uma unidade completa, envolvendo as seces de hidrodesmetalizao e hidrodessulfurao. A difuso no interior do catalisador descrita pelas equaes de Stefan-Maxwell adaptadas a um sistema com molculas com grande diferena de dimenses. O elevado nmero de compostos considerados e as equaes utilizadas para descrever a difuso no interior do catalisador levam a que uma rotina de estimao de parmetros possa convergir para um mnimo local sem significado fsico, se os parmetros iniciais forem introduzidos aleatoriamente.

    Neste estudo apresentada a metologia utilizada para obter estimativas iniciais dos parmetros do modelo, nomeadamente das constantes cinticas e de adsoro. A obteno das estimativas iniciais foi feita utilizando como base um resduo do Mdio Oriente (Buzurgan). Com os parmetros obtidos, a resposta do modelo foi simulada para outros resduos, com diferentes origens geogrficas (Arabian Light, Djeno e Oural). O estudo consistiu igualmente numa anlise de sensibilidade aos diferentes valores a introduzir no modelo.

    A resposta do modelo a variaes nos seus parmetros e valores de entrada pde ser explicada, na maioria dos casos, utilizando argumentos baseados nos fenmenos fsicos e qumicos envolvidos no processo cataltico. As simulaes efectuadas para resduos com diferentes origens geogrficas apenas evidenciaram pequenos desvios em relao aos dados experimentais.

    Palavras-chave: resduos, hidrotratamento, modelizao, difuso, Stefan-Maxwell

  • ii

    Abstract

    This work comprises the study of a vacuum residue hydrotreatment model developed in IFP. The model in study simulates the operation of a hydrodemetallization reactor and of a complete

    unit, including the hydrodemetallization and hydrodesulfurization sections. The diffusion inside the catalyst is described by the Stefan-Maxwell equations extended for starkly different sized molecules. The large number of compounds considered and the equations used to describe the diffusion inside the catalyst may cause a parameter estimation routine to converge to a local minimum without physical significance, if randomly chosen parameters are used as initial estimates.

    This study presents the methodology used to obtain initial estimates for the model parameters, namely for the kinetic and adsorption constants. The initial estimates for the model parameters were obtained using a Middle East residue (Buzurgan) as a reference. With the obtained parameters, the model output was simulated for other residues, with different geographical origins (Arabian Light, Djeno and Oural). The study also included a sensitivity analysis to the required model inputs.

    The model sensitivity to variations in its parameters and inputs could be explained, in most cases, using arguments based on the physical and chemical phenomena involved in a catalytic process. The simulations for residues with different geographical origins only evidenced slight deviations to the experimental data.

    Keywords: residues, hydrotreatment, modeling, diffusion, Stefan-Maxwell

  • iii

    Acknowledgments

    The first acknowledgment must go to Prof. Rama Ribeiro, without whom this journey at IFP would not be possible. I express my deepest appreciation for the friendship and support over the last years.

    I am also thankful to Cristina and Victor for the support and guidance during the internship and for their precious help with the thesis writing.

    I feel lucky to be given the opportunity of sharing a six months adventure with some of my best friends. For this, I should thank my fellow Portuguese comrades: Akira, Alberto, Bela, Boubou, Clara, Ins, Leonor, Lus and Susana.

    My experience at IFP was certainly improved by the constant mutual aid and cultural exchange with the best bureau mates: Caio, Mathhias, Sebastien and Tarek. Ill surely miss you all.

    I also express my gratitude to the family and friends in Portugal, for the long distance support and for constantly asking me when I would return home.

  • iv

    Table of contents

    1 Introduction ................................................................................................................................... 1 2 Bibliographic study ...................................................................................................................... 2

    2.1 Introduction .......................................................................................................................... 2 2.2 Residue feedstocks ............................................................................................................. 2

    2.2.1 Introduction .................................................................................................................. 2 2.2.2 Fractioning methods ................................................................................................... 3 2.2.3 Asphaltenes ................................................................................................................. 4 2.2.4 Resins ........................................................................................................................... 5 2.2.5 Metals ........................................................................................................................... 5 2.2.6 Sulfur and nitrogen ..................................................................................................... 6

    2.3 Residue hydrotreatment units ............................................................................................ 7 2.3.1 Introduction .................................................................................................................. 7 2.3.2 Hydrotreatment applications ...................................................................................... 7 2.3.3 Hydrotreatment catalysts ........................................................................................... 8 2.3.4 Hydrotreatment reactions ........................................................................................... 9

    2.3.4.1 HDS ......................................................................................................................... 10 2.3.4.2 HDM ........................................................................................................................ 10 2.3.4.3 HDN......................................................................................................................... 11 2.3.4.4 Cracking reactions .................................................................................................. 11 2.3.4.5 Condensation reactions and coke formation........................................................... 12

    2.3.5 Hydrotreatment technology ..................................................................................... 12 2.3.5.1 Fix-bed reactor ........................................................................................................ 13 2.3.5.2 Other types of reactors............................................................................................ 14 2.3.5.3 Operating conditions ............................................................................................... 15

    2.4 Conclusions ........................................................................................................................ 15 2.5 Modeling.............................................................................................................................. 16

    2.5.1 Introduction ................................................................................................................ 16 2.5.2 Hydrodynamics .......................................................................................................... 17 2.5.3 Intragranular diffusion .............................................................................................. 17

    2.5.3.1 Fick's first law .......................................................................................................... 19 2.5.3.2 Stefan-Maxwell equations ....................................................................................... 19

    2.5.4 Adsorption ................................................................................................................. 21 2.5.5 Deactivation ............................................................................................................... 22 2.5.6 Kinetics and feedstock description ......................................................................... 23 2.5.7 IFP models ................................................................................................................. 24

    2.5.7.1 THERMIDOR .......................................................................................................... 24 2.5.7.2 Model for the HDM section ..................................................................................... 24

  • v

    2.5.7.3 Model for the HDS section ...................................................................................... 25 2.6 Conclusions ..........................................................................................................

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