MODELING AND SIMULATION OF CATALYTIC REACTORS FOR PETROLEUM REFINING

MODELING AND SIMULATION OF CATALYTIC REACTORS FOR PETROLEUM REFINING

JORGE ANCHEYTA

A JOHN WILEY & SONS, INC., PUBLICATION

Copyright © 2011 by John Wiley & Sons, Inc. All rights reserved

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Library of Congress Cataloging-in-Publication Data:

Ancheyta, Jorge. Modeling and simulation of catalytic reactors for petroleum refi ning / Jorge Ancheyta. p. cm. Includes bibliographical references and index. ISBN 978-0-470-18530-8 (cloth)1. Catalytic reforming–Simulation methods. I. Title. TP690.45.A534 2011 665.5′3–dc22 2010030993

Printed in the United States of America

oBook ISBN: 9780470933565ePDF ISBN: 9780470933558ePub ISBN: 9781118002162

10 9 8 7 6 5 4 3 2 1

CONTENTS

v

PREFACE ix

ABOUT THE AUTHOR xii

1 PETROLEUM REFINING 1

1.1 Properties of Petroleum, 11.2 Assay of Crude Oils, 41.3 Separation Processes, 10

1.3.1 Crude Oil Pretreatment: Desalting, 101.3.2 Atmospheric Distillation, 121.3.3 Vacuum Distillation, 131.3.4 Solvent Extraction and Dewaxing, 131.3.5 Deasphalting, 141.3.6 Other Separation Processes, 15

1.4 Upgrading of Distillates, 171.4.1 Catalytic Reforming, 181.4.2 Isomerization, 181.4.3 Alkylation, 211.4.4 Polymerization, 231.4.5 Catalytic Hydrotreating, 251.4.6 Fluid Catalytic Cracking, 27

1.5 Upgrading of Heavy Feeds, 291.5.1 Properties of Heavy Oils, 291.5.2 Process Options for Upgrading Heavy Feeds, 31

2 REACTOR MODELING IN THE PETROLEUM REFINING INDUSTRY 53

2.1 Description of Reactors, 532.1.1 Fixed-Bed Reactors, 562.1.2 Slurry-Bed Reactors, 62

vi CONTENTS

2.2 Deviation from an Ideal Flow Pattern, 632.2.1 Ideal Flow Reactors, 632.2.2 Intrareactor Temperature Gradients, 662.2.3 Intrareactor Mass Gradients, 692.2.4 Wetting Effects, 772.2.5 Wall Effects, 81

2.3 Kinetic Modeling Approaches, 862.3.1 Traditional Lumping, 862.3.2 Models Based on Continuous Mixtures, 992.3.3 Structure-Oriented Lumping and Single-Event

Models, 1012.4 Reactor Modeling, 102

2.4.1 Classifi cation and Selection of Reactor Models, 1022.4.2 Description of Reactor Models, 1062.4.3 Generalized Reactor Model, 1552.4.4 Estimation of Model Parameters, 176

References, 188 Nomenclature, 203

3 MODELING OF CATALYTIC HYDROTREATING 211

3.1 The Hydrotreating Process, 2113.1.1 Characteristics of HDT Reactors, 2133.1.2 Process Variables, 2203.1.3 Other Process Aspects, 229

3.2 Fundamentals of Hydrotreating, 2413.2.1 Chemistry, 2413.2.2 Thermodynamics, 2433.2.3 Kinetics, 2463.2.4 Catalysts, 258

3.3 Reactor Modeling, 2613.3.1 Effect of Catalyst Particle Shape, 2613.3.2 Steady-State Simulation, 2693.3.3 Simulation of a Commercial HDT Reactor with

Quenching, 2733.3.4 Dynamic Simulation, 2833.3.5 Simulation of Countercurrent Operation, 293

References, 304 Nomenclature, 308

4 MODELING OF CATALYTIC REFORMING 313

4.1 The Catalytic Reforming Process, 3134.1.1 Description, 3134.1.2 Types of Catalytic Reforming Processes, 3164.1.3 Process Variables, 318

CONTENTS vii

4.2 Fundamentals of Catalytic Reforming, 3194.2.1 Chemistry, 3194.2.2 Thermodynamics, 3214.2.3 Kinetics, 3224.2.4 Catalysts, 330

4.3 Reactor Modeling, 3314.3.1 Development of the Kinetic Model, 3314.3.2 Validation of the Kinetic Model with Bench-Scale Reactor

Experiments, 3454.3.3 Simulation of Commercial Semiregenerative Reforming

Reactors, 3504.3.4 Simulation of the Effect of Benzene Precursors in the

Feed, 3574.3.5 Use of the Model to Predict Other Process Parameters, 361

References, 364 Nomenclature, 366

5 MODELING AND SIMULATION OF FLUIDIZED-BED CATALYTIC CRACKING CONVERTERS 368

Rafael Maya-Yescas

5.1 Introduction, 3705.1.1 Description of the Process, 3705.1.2 Place of the FCC Unit Inside the Refi nery, 3715.1.3 Fractionation of Products and Gas Recovery, 3735.1.4 Common Yields and Product Quality, 373

5.2 Reaction Mechanism of Catalytic Cracking, 3745.2.1 Transport Phenomena, Thermodynamic Aspects, and

Reaction Patterns, 3745.2.2 Lumping of Feedstock and Products, 3765.2.3 More Detailed Mechanisms, 378

5.3 Simulation to Estimate Kinetic Parameters, 3785.3.1 Data from Laboratory Reactors, 3795.3.2 Data from Industrial Operation, 384

5.4 Simulation to Find Controlling Reaction Steps During Catalytic Cracking, 385

5.5 Simulation of Steady Operation of the Riser Reactor, 3875.6 Simulation to Scale Up Kinetic Factors, 3905.7 Simulation of the Regenerator Reactor, 393

5.7.1 Simulation of the Burning of Nonheterogeneous Coke, 393

5.7.2 Simulation of Side Reactions During the Burning of Heterogeneous Coke, 402

5.7.3 Simulation of the Energy Balance in the Regenerator, 4095.8 Modeling the Catalyst Stripper, 410

viii CONTENTS

5.9 Simulation of a Controlled FCC Unit, 4115.9.1 Mathematical Background, 4125.9.2 Controllability of the Regenerator, 4155.9.3 A Technique to Regulate Tregenerator in Partial Combustion

Mode, 4235.10 Technological Improvements and Modifi cations, 438

5.10.1 Effect of Feedstock Pretreatment, 4385.10.2 Pilot-Plant Emulation, 4535.10.3 The Sulfur Balance, 459

5.11 Conclusions, 466 References, 468 Nomenclature, 472

INDEX 475

PREFACE

ix

The reactor is the heart of a chemical process, and a thorough understanding of the phenomena occurring during the transformation of reactants into the desired products is of vital importance for the development and optimization of the process. Particularly in the petroleum refi ning industry, in which apart from the reactors, other operations (separations, heating, cooling, pumping, etc.) are carried out in series or in parallel and each plant is connected with others, improper design and operation of reactors can cause shutdown of a plant or, even worse, of the entire refi nery, with the consequent loss in produc-tion and income. It is thus essential to have a thorough knowledge of the fundamental equations critical to chemical reactor design, such as reactor sizing and optimal operating conditions.

The reactors used during petroleum refi ning are among the most complex and diffi cult to model and design. The composition and properties of the various petroleum fractions that are converted in reactors is such that the reaction system can involve various phases, catalysts, reactor confi guration, continuous catalyst addition, and so on, making the development of a model a challenging task. In addition, the presence of hundreds of components under-going different reaction pathways and competing for the active sites of cata-lysts, contributes to increasing the complexity of the formulation of the kinetics and reactor models.

Over the years, many excellent textbooks have been published dealing with various aspects of reactors: chemical reactor design, modeling of chemical reaction kinetics, reaction mechanisms, chemical reaction engineering, scale - up, and so on. The level of sophistication in each book varies from academic reactions (e.g., A → B), represented by simple kinetic models (e.g., the power - law model, − =r kCA A

n ) and using integrated equations for the design of ideal reactors (e.g., PFR, CSTR), to complex catalytic reaction systems employing a set of differential equations to solve for mass and energy balances. However,

x PREFACE

detailed descriptions of the various reactor models, reaction kinetics, and real examples of the application of these models for the simulation of experimental reaction units and commercial plants have not previously been treated in detail. Moreover, most books do not discuss the modeling of the reactors that are typically used during the conversion of oil distillates in the petroleum refi ning industry, and do not describe reactor models in an uncluttered or thorough manner.

Modeling and Simulation of Catalytic Reactors for Petroleum Refi ning is designed to give an up - to - date treatment of all the important aspects of reactor modeling, with particular emphasis on reactors employed in the petroleum refi ning industry. We explain and analyze approaches to modeling catalytic reactors for steady - state and dynamic simulations and discuss such aspects as thermodynamics, reaction kinetics, process variables, process schemes, and reactor design. To validate the models developed, experimental data obtained directly from laboratory and commercial plants are used. Our goal is that the book will become an essential reference for chemical and process engineers, computational chemists and modelers, catalysis researchers, and professionals in the petroleum industry, as well for use as a textbook either for full courses in chemical reaction engineering or as a supplement to related courses.

The book is organized in fi ve chapters, each with individual reference and nomenclature sections. About 500 references are cited and discussed, covering most of the published literature regarding the modeling of reactors used in the petroleum refi nery industry. Chapter 1 provides an in - depth introduction to topics related to petroleum refi ning, such as petroleum properties, separa-tion processes, upgrading of distillates, and upgrading of heavy feeds. A brief description of all the conversion and separation processes is given in this chapter. Detailed experimental data on light, medium, and heavy crude oil assays are also provided.

General aspects of reactor modeling in the petroleum refi ning industry are treated in Chapter 2 . The emphasis is on reactors, deviations from ideal fl ow patterns, kinetic modeling approaches, estimation of model parameters, and classifi cation and description of reactor models. The fundamental equations are given for each reactor model, together with their advantages and disad-vantages. A generalized reactor model is proposed from which each previously reported reactor model can easily be derived.

Chapter 3 is devoted to the modeling of catalytic hydrotreating reactors. The most important features of this type of reactor are highlighted in the fi rst sections, such as the characteristics and classifi cation of hydrotreating reactors, process variables, other process aspects (quench systems, reactor internals), and fundamentals of hydrotreating (chemistry, thermodynamics, kinetics, and catalysts). The fi nal section covers hydrotreating reactor modeling, with exam-ples of the modeling and simulation of reactors operating with catalysts of different particle shapes, steady - state operation, hydrotreating reactors with quenching, dynamic simulation, and co - current and countercurrent operations for both laboratory and commercial reactors.

PREFACE xi

The modeling of catalytic reforming reactors is the subject of Chapter 4 . The description and types of processes, process variables, and fundamentals of catalytic reforming are described at the beginning of the chapter, followed by a section on reactor modeling in which the development of a kinetic reforming model is reported. Validation of the model developed, with bench - scale iso-thermal reactor experiments and simulation of commercial semiregenerative reforming reactors, is discussed. The effect of benzene precursors in the feed in both laboratory and commercial reactors is also simulated, and use of the reactor model to predict other process parameters is highlighted.

In Chapter 5 , Dr. Maya - Yescas describes the modeling and simulation of the fl uid catalytic cracking reactor. Descriptions of the process, reaction mech-anism, transport phenomena, thermodynamics, and kinetics are provided in the initial sections. Simulations used to estimate kinetic parameters from labo-ratory and commercial reactors, to determine the controlling reaction steps, of steady - state operation, of scale - up kinetic factors, of the regenerator reactor, of burning nonheterogeneous coke, of side reactions during the burning of heterogeneous coke, and of the energy balance in the regenerator are dis-cussed in detail. Other sections deal with modeling a catalyst stripper, simula-tion of the controlled unit, pilot - plant emulation, and industrial plant emulation.

Detailed experimental data and comparisons with reactor model predic-tions are provided in each chapter. Also, all data and parameters required to build up each reactor and kinetic model are detailed, so that readers can adapt their own computer programs for use in reactor simulation, optimization, and design purposes.

It is our intention that Modeling and Simulation of Catalytic Reactors for Petroleum Refi ning will quickly become a leading book in this fi eld through its emphasis on detailed descriptions of catalytic reactor modeling used in the petroleum refi ning industry, its use of laboratory and commercial data for model validations, the details provided of results of simulations in steady - state and dynamic operations, and in general its focus on more practical issues regarding reactor modeling than have been available in previous textbooks on chemical reactor engineering.

ACKNOWLEDGMENTS

I would like especially to acknowledge Dr. Rafael Maya - Yescas, Professor of Chemical Reaction Engineering. Universidad Michoacana de Nicol á s de Hidalgo, Morelia, Michoac á n, M é xico, who kindly agreed to write Chapter 5 . I also thank all the M.Sc., Ph.D., and postdoctoral students who over a period of many years have contributed enormously to the preparation of this book.

JORGE ANCHEYTA

ABOUT THE AUTHOR

xii

Jorge Ancheyta, holds a bachelor ’ s degree in petrochemical engineering (1989), a master ’ s degree in chemical engineering (1993), and a master ’ s degree in administration, planning, and economics of hydrocarbons (1997) from the National Polytechnic Institute of Mexico. He split his Ph.D. between the Metropolitan Autonomous University of Mexico and the Imperial College London (1998), and was awarded a postdoctoral fellowship in the Laboratory of Catalytic Process Engineering of the CPE - CNRS in Lyon, France (1999). He has also been a visiting professor at the Laboratoire de Catalyse et Spectrochimie, Universit é de Caen, France (2008, 2009, 2010), and Imperial College London (2009).

Dr. Ancheyta has worked for the Mexican Institute of Petroleum (IMP) since 1989, where his present position is project leader of research and development. He has also worked as a professor on the undergraduate and postgraduate levels at the School of Chemical Engineering and Extractive Industries at the National Polytechnic Institute of Mexico since 1992 and for the IMP postgradu-ate program since 2003. He has supervised about 100 B.Sc., M.Sc., and Ph.D. theses as well as a number of postdoctoral and sabbatical - year professors.

Dr. Ancheyta has worked on the development and application of petroleum refi ning catalysts, kinetic and reactor models, and process technologies, primar-ily in catalytic cracking, catalytic reforming, middle distillate hydrotreating, and heavy oils upgrading. He is the author or co - author of a number of patents, books, and about 200 scientifi c papers, and has been awarded the highest dis-tinction (level III) as a national researcher by the Mexican government and is a member of the Mexican Academy of Science. He has also been guest editor of various international journals: Catalysis Today , Petroleum Science and Technology , Industrial Engineering Chemistry Research , Energy and Fuels , Chemical Engineering Communications , and Fuel . Dr. Ancheyta has also chaired numerous international conferences and is a member of the scientifi c boards of various prestigious journals.

1

1 PETROLEUM REFINING

Modeling and Simulation of Catalytic Reactors for Petroleum Refi ning, First Edition. Jorge Ancheyta.© 2011 John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc.

1.1 PROPERTIES OF PETROLEUM

Petroleum is the most important substance consumed in modern society. It provides not only fuel and energy for transportation but is also used in plastics, paint, fertilizer, insecticide, medicine, and elsewhere. The exact composition of petroleum varies widely from source to source, but the percentage of chemical elements changes over fairly narrow limits. Hydrogen and carbon are the major components, and sulfur, nitrogen, oxygen, and metals are present in relatively lower quantities (Table 1.1 ). Usually, petroleum or crude oil comes from deep underground, where the vestiges of plants and animals from mil-lions of years ago have been heated and pressurized over time. It is blackish in color and has a characteristic odor that comes from the presence of small amounts of chemical compounds containing sulfur, nitrogen, and metals.

The change in crude oil quality around the world (e.g., heavy petroleum production has been increased in recent years) has obliged crude oil refi ners to reconfi gure current refi neries and to design new refi neries specifi cally to process heavier feedstocks (i.e., blends of various crude oils with elevated amount of heavy petroleum). These new feeds are characterized by high amounts of impurities (sulfur, metals, nitrogen, asphaltenes) and low distillate yields, which make them more diffi cult than light crude oils to process.

Comparisons of some properties of various crude oils are presented in Tables 1.2 and 1.3 . It is clear that light and heavy crude oils have remarkable