Computer Aided Simulation and Process Design of a Hydrogenation Plant Using Aspen HYSYS ...

158 Pages·2009·3.28 MB·English

Computer Aided Simulation and Process Design of a
Hydrogenation Plant Using Aspen HYSYS 2006

By
Mohammad Hossein Ordouei

A thesis
presented to the University of Waterloo
in fulfillment of the
thesis requirement for the degree of
Master of Applied Science
in
Chemical Engineering

Waterloo, Ontario, Canada, 2009

© Mohammad Hossein Ordouei 2009
Author’s Declaration

I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis,
including any required final revisions, as accepted by my examiners.

I understand that my thesis may be made electronically available to the public.

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ABSTRACT

Nowadays, computers are extensively used in engineering modeling and simulation fields in
many different ways, one of which is in chemical engineering. Simulation and modeling of a
chemical process plant and the sizing of the equipment with the assistance of computers, is of
special interests to process engineers and investors. This is due to the ability of high speed
computers, which make millions of mathematical calculations in less than a second associated
with the new powerful software that make the engineering calculations more reliable and precise
by making very fast iterations in thermodynamics, heat and mass transfer calculations. This
combination of new technological hardware and developed software enables process engineers
to deal with simulation, design, optimization, control, analysis etc. of complex plants, e.g.
refinery and petrochemical plants, reliably and satisfactorily.
The main chemical process simulators used for static and dynamic simulations are ASPEN
PLUS, ASPEN HYSYS, PRO II, and CHEMCAD. The basic design concepts of all simulators
are the same and one can fairly use all simulators if one is expert in any of them.
Hydrogenation process is an example of the complex plants, to which a special attention is made
by process designers and manufacturers. This process is used for upgrading of hydrocarbon
feeds containing sulfur, nitrogen and/or other unsaturated hydrocarbon compounds. In oil and
gas refineries, the product of steam cracking cuts, which is valuable, may be contaminated by
these unwanted components and thus there is a need to remove those pollutants in downstream
of the process. Hydrogenation is also used to increase the octane number of gasoline and gas oil.
Sulfur, nitrogen and oxygen compounds and other unsaturated hydrocarbons are undesired
components causing environmental issues, production of by-products, poisoning the catalysts
and corrosion of the equipment. The unsaturated C=C double bonds in dioleffinic and alkenyl
aromatics compounds, on the other hand, cause unwanted polymerization reactions due to
having the functionality equal to or greater than 2.
Hydrogenation process of the undesired components will remove those impurities and/or
increase the octane number of aforementioned hydrocarbons. This process is sometimes referred
to as “hydrotreating”; however, “upgrader” is a general word and is, of course, of more interest.
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In this thesis, a hydrogenation process plant was designed on the basis of the chemistry of
hydrocarbons, hydrogenation reaction mechanism, detailed study of thermodynamics and
kinetics and then a steady-state simulation and design of the process is carried out by ASPEN
HYSYS 2006 followed by design evaluation and some modifications and conclusions.
Hydrogenation reaction has a complicated mechanism. It has been subjected to hot and
controversial debates over decades. Many kinetic data are available, which contradict one
another. Among them, some of the experimental researches utilize good assumptions in order to
simplify the mechanism so that a “Kinetic Reaction” modeling can be employed. This thesis
takes the benefit of such research works and applies some conditions to approve the validity of
those assumptions. Meanwhile, some other papers from reputed companies such as IFP are used
in order to make sure that the present simulation and design is a practical one and applicable in
real world.
On the basis of this detailed study of reaction modeling and kinetic data, a hydrogenation plant
was designed to produce and purify over 98 million kilograms of different products; e.g.
Benzene, Toluene, Iso-octane etc. with fairly high purity.

iv
Acknowledgements

The author wishes to acknowledge and thank his supervisors, Dr. Ali Elkamel and Dr. Mazda
Biglari, for their guidance and support throughout the thesis.
The author also wishes to thank the readers of my thesis, Dr. Leonardo Simon and Dr. Luis
Ricardez for their valuable advice on this research.
And finally, thanks to my loving mother, my family and friends for their inspiration and
encouragement during the working on my thesis.
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Dedication

I would like to dedicate the present work to my parents and my sisters, who have been
supporting me in all steps of my life.

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Table of Contents
LIST OF FIGURES ................................................................................................................................... X
LIST OF TABLES ................................................................................................................................. XIV
CHAPTER 1: INTRODUCTION ............................................................................................................ 1
1.1 The advantages of computer simulators ......................................................................................................... 1
1.2 Process simulators .......................................................................................................................................... 1
1.3 Hydrocarbons characteristics .......................................................................................................................... 3
1.4 The objectives of hydrogenation reactions in industries ................................................................................. 6
1.5 Hydrogenation Process ................................................................................................................................... 7
1.6 Designing levels and modeling steps ............................................................................................................... 9
1.7 The levels of process simulation ................................................................................................................... 11
1.8 The objective of the thesis ............................................................................................................................ 11
1.9 Applications of the thesis.............................................................................................................................. 13
1.10 Organization of this work............................................................................................................................ 14
CHAPTER 2: LITERATURE REVIEW .............................................................................................. 15
2.1 Chemistry of hydrocarbons ........................................................................................................................... 15
A. Carbon:............................................................................................................................................................... 15
B. Sulfur: ................................................................................................................................................................. 16
C. Nitrogen: ............................................................................................................................................................ 17
2.2 Reactions, kinetics and thermodynamics of hydrogenation .......................................................................... 17
A. Desulfurization .............................................................................................................................................. 17
B. Denitrification ................................................................................................................................................ 18
C. Hydrogenation of olefinic, diolefinic and alkenyl aromatics ......................................................................... 18
2.3 The Le Chatelier’s principle ........................................................................................................................... 20
2.4 Catalyst selection .......................................................................................................................................... 22
2.5 Typical hydrogenation plant ......................................................................................................................... 23
2.6 Review on simulation on hydrogenation plants ............................................................................................ 26
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CHAPTER 3: MODELING OF A HYDROGENATION PLANT ..................................................... 28
3.1 Starting the modeling ................................................................................................................................... 28
3.2 Feed streams ................................................................................................................................................ 28
3.3 Reaction modeling by HYSYS ........................................................................................................................ 30
3.4 Reaction section of hydrogenation plant ...................................................................................................... 31
A. The reaction rate model: ................................................................................................................................... 31
B. Chemical reactions in PFR: ................................................................................................................................. 32
C. Catalyst specifications ........................................................................................................................................ 32
D. Reaction parameters ......................................................................................................................................... 33
E. Reactor modeling ............................................................................................................................................... 34
F. Tubular reactor (PFR) sizing ................................................................................................................................ 36
G. PFR modeling results and analyses .................................................................................................................... 38
3.5 Cooling and separation section of hydrogenation plant ................................................................................ 44
A. The modeling of cooling heat exchangers ......................................................................................................... 44
B. Two-phase separator modeling ......................................................................................................................... 49
C. Sizing of vertical drum separator and analyses .................................................................................................. 51
3.6 Purification section ....................................................................................................................................... 57
A. Mass transfer operation .................................................................................................................................... 57
B. Modeling of distillation columns........................................................................................................................ 58
C. Comparison with other possible arrangement .................................................................................................. 62
3.7 Annual capacity ............................................................................................................................................ 64
CHAPTER 4: MODIFICATIONS ........................................................................................................ 67
4.1 Reaction section ........................................................................................................................................... 67
A. Re-sizing the tubular reactors ............................................................................................................................ 68
B. Comparison the new design with old design ..................................................................................................... 70
4.2 Cooling and phase separation section ........................................................................................................... 71
A. New arrangement .............................................................................................................................................. 72
B. Comparison the new arrangement with the old one ......................................................................................... 74
4.3 Purification section ....................................................................................................................................... 75
A. New arrangement .............................................................................................................................................. 75
B. Column design properties .................................................................................................................................. 78
C. The result of new arrangements ........................................................................................................................ 80
D. Comparison of two arrangements ..................................................................................................................... 81
CHAPTER 5: PROCESS DESCRIPTION .......................................................................................... 83
5.1 General process descriptions ........................................................................................................................ 83
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5.2 Energy streams ............................................................................................................................................. 85
CHAPTER 6: CONCLUSIONS AND OTHER APPROACH ............................................................ 88
6.1 Conclusions ................................................................................................................................................... 88
6.2 Other approaches: ........................................................................................................................................ 91
REFERENCES ........................................................................................................................................ 92
Appendices ......................................................................................................................................................... 96
APPENDIX A: The mechanism of ethylene hydrogenation .................................................................................. 96
APPENDIX B: Catalyst Effect, Catalyst Selection and Related Kinetic Data .......................................................... 97
APPENDIX C: Simulation and Optimization by ASPEN HYSYS 2006 .....................................................................107
APPENDIX D: Modeling and simulation of a plug flow reactor for hydrogenation reaction ...............................137

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List of Figures

Figure 1.1. Simplified flow chart of an “upgrader unit”………………………………………………6
Figure 2.1. Energy diagram for the hydrogenation of benzene………………………………………20
Figure 2.2. Effect of hydrogen purity and pressure on benzene hydrogenation ……………………..21
Figure 2.3. Flow diagram of an Exxon hydrotreating unit……………………………………………23
Figure 2.4. The block flow diagram of an upgrader gas hydrotreater…………………….…………..25
Figure 2.5. Block flow diagram of the selective hydrogenation of pyrolysis gasoline………….…....25
Figure 3.1. The Block flow diagram (BDF) of the present hydrogenation process……………….….28
Figure 3.2. The mixed stream resulted from HC and H feed streams….…………………………….35
2
Figure 3.3. The feed streams and PFR arrangement for the Hydrogenation plan…………………….37
Figure 3.4. Multi-bed catalytic reactors…………….………………………………………………...38
Figure 3.5. The 1st Hydrogenation Reactor outlet stream……………………………………….……39
Figure 3.6. The two-phase outlet stream from the 2nd Hydrogenation Reactor………………………40
Figure 3.7. Reaction Overall Information page of the 1st Hydrogenation Reactor…………………...41
Figure 3.8. Sizing the 1st and the 2nd Hydrogenation Reactors………………………………….……42
Figure 3.9. Changes in the Molar Flow rate of Iso-octane and Ethyl Benzene……………………...43
Figure 3.10. Changes in the Molar Flow rate of n-Butane and Iso-Butane……………………….….44
Figure 3.11. Duty of the First Step Pre-Cooler…………………………………………………….…45
Figure 3.12. Design parameters and the Duty of the air-cooler………………………………………47
Figure 3.13. Duty of the After Cooler………………………………………………………………...48
Figure 3.14. Forces on liquid in gas stream …….......…………………………………………….….49
Figure 3.15. Designing the gas velocity factor for vertical gas-liquid drum .………………………..50
Figure 3.16. Key dimensions for knock-out drum ………………………...…………………………51
Figure 3.17. The properties of the stream “To FirstSep”….………………………………...……..…51
Figure 3.18. Modeling and the arrangement of a vertical drum ……………………………………..53
Figure 3.19. Compositions and flow rates of gas outlet from the FirstSep drum ……………………54
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