Fahim M.A., Sahhaf T.A., Elkilani A.S. Fundamentals of Petroleum Refining

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PREFACE

Fundamentals of Petroleum Refining provides a thorough and balanced intro-

duction to refinery engineering topics from basic concepts and unit opera-

tions to overall refinery economics. Based on the fundamentals of

thermodynamics and kinetics, the text develops the scientific background

needed for an understanding of refinery operations. It also provides an in-

depth description of major refinery processes and then assimilates an

integrated refinery by focusing on the economic and operational aspects

necessary for enhancing performance and profitability.

The authors have over two decades of experience teaching and consult-

ing in the field of petroleum refining. Although there are a number of books

on petroleum refining, very few of them can be considered suitable for

teaching the subject in a manner that integrates engineering fundamentals

and petroleum refining technology. Our book has more in-depth coverage

and more examples on using computational tools.

Fundamentals of Petroleum Refining serves both professionals and aca-

demics. It is mainly directed towards undergraduate and graduate students

in Chemical and Petroleum Engineering, Chemistry and Chemical Tech-

nology. College graduates new to the field of engineering, who may just be

starting their careers in the oil and gas industry, will also find the text useful.

Professionals and academics will also benefit from this book. For experi-

enced engineers and managers, Fundamentals of Petroleum Refining is ideal for

acquiring the necessary background in the field and understanding new

applications in the refining industry.

The book includes important subjects which are not commonly consid-

ered in refinery textbooks. Topics include clean fuels, gasification, biofuels

and the environmental impact of refining. Throughout the book, numerous

problem sets and examples are given in order to put the fundamental

principles of refining into practice. Many worked examples offer clear

understanding of the covered subjects. Excel spreadsheets for property and

material balance calculations help in performing detailed and repetitive

calculations and these are to be found at http://www.elsevierdirect.com/

companions/9780444527851. Examples on using process simulators (UNI-

SIM) are also presented. The text begins with an introduction to the

petroleum refining industry then focuses on feedstocks and products in

Chapters 1 and 2. Chapter 3 covers the subject of calculating the thermo-

physical properties of crude oils and petroleum fractions. Atmospheric and

vacuum distillations are covered in Chapter 4. Major conversion processes

are described in Chapters 5–8. These chapters cover the subjects of catalytic

reforming and isomerization, coking, hydroconversion (hydrotreating and

hydrocracking) and fluid catalytic cracking. Product blending is covered in

Chapter 9, and alkylation is explained in Chapter 10. The subject of

hydrogen production, which is of principal importance in a modern refin-

ery, is covered in Chapter 11. Due to the changing energy outlook in terms

of pollution regulations on burning fuels, clean fuel production is discussed

in Chapter 12.

A great deal of attention has been given in the last few years to residue

upgrading in order to improve the economics of refining. Chapter 13

discusses this issue in detail. Refinery safety is also an important topic and

is thoroughly reviewed in Chapter 14. Acid gas treatment and removal are

discussed in Chapter 15. The factors related to refinery economics are

reviewed in Chapter 16. Environmental and effluent treatment methods

are discussed in Chapter 17. An overall case study is given in Chapter 18.

Chapters 1–10 can be used as core materials for teaching an undergrad-

uate course in petroleum refining. If time allows, parts of other chapters can

also be used. The book also covers more advanced topics, which might be

used for an introductory graduate course. Throughout the book, empirical

correlations are used to calculate product yields and perform material

balances. These correlations are mainly based on regression of published

pilot plant data.

The authors would like to thank Dr Souad Al-Radwan and Engineer

Hussein Said of Kuwait National Petroleum Company (KNPC) for their

valuable comments on some technical issues. We would also like to thank

Engineers Mohamed Hamed and Khalid Damiyar for their technical help

during the production of this book. Many thanks go to Ms Jennifer Baran

for her excellent proofreading and language editing of the book.

xvi Preface

CHAPTER ONE

Introduction

1.1. Introduction

Petroleum refining plays an important role in our lives. Most trans-

portation vehicles are powered by refined products such as gasoline, diesel,

aviation turbine kerosene (ATK) and fuel oil. The recent price rise of crude

oil from $50 to $150 per bbl over the last 2 years has affected the refining

industry in three ways: First is an increased search for fuel products from

non-fossil sources such as biodiesel and alcohols from vegetable sources,

second is the development of better methods to process tar sand, coal

gasification and synthesis of fuels by Fischer–Tropsch (FT) technology and

third is the initiation of long-term plans to look for renewable energy

sources. However, crude oil prices are still a cheap source for transportation

fuels and petrochemicals.

On the other hand, stricter environment regulations have raised the cost of

producing clean fuels. This motivated the search for producing clean fuels by

non-conventional methods, such as by ambient desulphurization by liquid

oxidants. Olefin alkylation and Fischer–Tropsch are other possible methods

for producing clean fuels. New technology and better design of refinery equip-

ment are also being developed in order to produce clean and less expense fuels.

In the modern refinery, the refining processes are classified as either

physical separation or chemical conversion ones. Examples for each class are

given in Table 1.1.

1.2. Refining Processes

1.2.1. Physical Separation Processes

1.2.1.1. Crude Distillation

Crude oils are first desalted and then introduced with steam to an atmo-

spheric distillation column. The atmospheric residue is then introduced to a

vacuum distillation tower operating at about 50 mmHg, where heavier

products are obtained. Typical products from both columns and their

boiling point ranges are listed in Table 1.2.

Fundamentals of Petroleum Refining

2010 Elsevier B.V.

1.2.1.2. Solvent Deasphalting

This is the only physical process where carbon is rejected from heavy

petroleum fraction such as vacuum residue. Propane in liquid form (at

moderate pressure) is usually used to dissolve the whole oil, leaving asphal-

tene to precipitate. The deasphalted oil (DAO) has low sulphur and metal

contents since these are removed with asphaltene. This oil is also called

‘‘Bright Stock’’ and is used as feedstock for lube oil plant. The DAO can also

be sent to cracking units to increase light oil production.

1.2.1.3. Solvent Extraction

In this process, lube oil stock is treated by a solvent, such as N-methyl

pyrrolidone (NMP), which can dissolve the aromatic components in one

phase (extract) and the rest of the oil in another phase (raffinate). The

solvent is removed from both phases and the raffinate is dewaxed.

Table 1.2 Crude distillation products (Gary and Handwerk, 2001)

Yield (wt%)* True boiling temperature (



Atmospheric distillation

Reﬁnery gases (C

 C

)0.10 –

Liquid petroleum gases (LPG) 0.69 –

Light straight run (LSR) 3.47 32–82 (90–180



Heavy straight run (HSR) 10.17 82–193 (180–380



Kerosene (Kero) 15.32 193–271 (380–520



Light gas oil (LGO) 12.21 271–321 (520–610



Heavy gas oil (HGO) 21.10 321–427 (610–800



Vacuum distillation

Vacuum gas oil (VGO) 16.80 427–566 (800–1050



Vacuum residue (VR) 20.30 þ566 (þ1050



* The yields quoted here depend on feed composition and properties. In this case feed API was 26.3.

Table 1.1 Major reﬁning processes in modern reﬁneries

Physical separation

Chemical conversion

Catalytic Thermal

Distillation Reforming Delayed coking

Solvent deasphalting Hydrotreating Flexicoking

Solvent extraction Hydrocracking Visbreaking

Solvent dewaxing Alkylation

Isomerization

2 Chapter 1

1.2.1.4. Solvent Dewaxing

The raffinate is dissolved in a solvent (methyl ethyl ketone, MEK) and the

solution is gradually chilled, during which high molecular weight paraffin

(wax) is crystallized, and the remaining solution is filtered. The extracted

and dewaxed resulting oil is called ‘‘lube oil’’. In some modern refineries

removal of aromatics and waxes is carried out by catalytic processes in ‘‘all

hydrogenation process’’.

1.2.2. Chemical Catalytic Conversion Processes

1.2.2.1. Catalytic Reforming

In this process a special catalyst (platinum metal supported on silica or silica

base alumina) is used to restructure naphtha fraction (C

–C

) into aromatics

and isoparaffins. The produced naphtha reformate has a much higher octane

number than the feed. This reformate is used in gasoline formulation and as a

feedstock for aromatic production (benzene–toluene–xylene, BTX).

1.2.2.2. Hydrotreating

This is one of the major processes for the cleaning of petroleum fractions

from impurities such as sulphur, nitrogen, oxy-compounds, chloro-

compounds, aromatics, waxes and metals using hydrogen. The catalyst is

selected to suit the degree of hydrotreating and type of impurity. Catalysts,

such as cobalt and molybdenum oxides on alumina matrix, are commonly

used.

1.2.2.3. Catalytic Hydrocracking

For higher molecular weight fractions such as atmospheric residues (AR)

and vacuum gas oils (VGOs), cracking in the presence of hydrogen is

required to get light products. In this case a dual function catalyst is used.

It is composed of a zeolite catalyst for the cracking function and rare earth

metals supported on alumina for the hydrogenation function. The main

products are kerosene, jet fuel, diesel and fuel oil.

1.2.2.4. Catalytic Cracking

Fluid catalytic cracking (FCC) is the main player for the production of

gasoline. The catalyst in this case is a zeolite base for the cracking function.

The main feed to FCC is VGO and the product is gasoline, but some gas oil

and refinery gases are also produced.

1.2.2.5. Alkylation

Alkylation is the process in which isobutane reacts with olefins such as

butylene (C

) to produce a gasoline range alkylate. The catalyst in this case

is either sulphuric acid or hydrofluoric acid. The hydrocarbons and acid

react in liquid phase. Isobutane and olefins are collected mainly from FCC

and delayed coker.

Introduction 3

1.2.2.6. Isomerization

Isomerization of light naphtha is the process in which low octane number

hydrocarbons (C

) are transformed to a branched product with the

same carbon number. This process produces high octane number products.

One main advantage of this process is to separate hexane (C

) before it

enters the reformer, thus preventing the formation of benzene which

produces carcinogenic products on combustion with gasoline. The main

catalyst in this case is a Pt-zeolite base.

1.2.3. Thermal Chemical Conversion Processes

These processes are considered as upgrading processes for vacuum residue.

1.2.3.1. Delayed Coking

This process is based on the thermal cracking of vacuum residue by carbon

rejection forming coke and lighter products such as gases, gasoline and gas

oils. Three types of coke can be produced: sponge, shot and needle. The

vacuum residue is heated in a furnace and flashed into large drums where

coke is deposited on the walls of these drums, and the rest of the products

are separated by distillation.

1.2.3.2. Flexicoking

In this thermal process, most of the coke is gasified into fuel gas using steam

and air. The burning of coke by air will provide the heat required for

thermal cracking. The products are gases, gasoline and gas oils with very

little coke.

1.2.3.3. Visbreaking

This is a mild thermal cracking process used to break the high viscosity and

pour points of vacuum residue to the level which can be used in further

downstream processes. In this case, the residue is either broken in the

furnace coil (coil visbreaking) or soaked in a reactor for a few minutes

(soaker visbreaker). The products are gases, gasoline, gas oil and the

unconverted residue.

A schematic diagram of a modern refinery containing most of the pro-

cesses described above is given in Figure 1.1 (Gary and Handwerk, 2001).

1.3. Refinery Configuration

The refinery configuration can range from single topping for crude

distillation to high conversion refinery for petro-refinery. This will depend

on the factors indicated in the following sections ( Jones and Pufado, 2005):

4 Chapter 1

Atmospheric Distillation

Desalting

Crude Oil

Gas

LPG

Gas Plant

Gas

Separation

Catalytic

Cracking

Vacuum

Dist.

Solvent

Asphalt

Lube feedstock

Solvent

Extraction

Solvent

Dewaxing

Hydro-

treating &

Blending

Gasoline (Naphtha)

Sweetening & Blending

Distillate

Sweetening & Blending

Residual

Sweetening & Blending

Solvent

Deasphalting

Polymerization

Aviation

gasoline

Automotive

gasoline

Solvents

Jet fuel

Kerosene

Solvents

Distillate fuel oils

Diesel fuel oils

Distillate fuel oils

Catalytic

Isomerization

Hydrotreating

Catalytic

Hydrocracking

Coking

Coke

Visbreaking

Alkylation

Catalytic

Reforming

Hydro-

desulfurization

Atmospheric

Residue

Vacuum

Residue

Light SR Naphtha

Heavy SR Naphtha

Kerosene

Gas Oil

Middle Distillate

Lt Vacuum Distillate

Hvy Vacuum Distillate

Lubricants

Greases

Waxes

Deoiled wax

Dewaxed oil

Atmospheric Residue

Light crude oil

Distillate

n-Butane

Alkylate

Light SR Naphtha

Reformate

Vacuum Residue

Residue

Figure 1.1 The Modern refinery

Introduction 5

1.3.1. Type of Products

In this case, refining is carried out by increasing the hydrogen/carbon (H/C)

ratio. This can be achieved either by hydrogenation processes such as

hydrotreating, hydrocracking or by carbon rejection processes such as ther-

mal cracking (coking) and FCC. The products of such processes are shown in

Fig. 1.2 (Speight, 1999).

Some products can also be produced by special refining operations, like

in catalytic reforming, isomerization and alkylation. In Figure 1.2, the

products are classified in terms of average carbon number and H/C ratios.

1.3.2. Environmental Regulation

Modern regulations in many countries require a low level of contaminants

like sulphur. This requires the change of severity or design of hydroconver-

sion units which can produce ultra low sulphur products. Clean fuels are

gaining great interest, and completely new refinery configurations are now

being introduced to produce clean fuels from new refinery feeds and

configurations. Additional units have been added to existing refineries to

handle untreated gas emissions and refinery waste water due to changes in

environmental regulations.

1.3.3. Crude Assay and Quality

Crude quality is getting heavier worldwide. Existing refineries, which are

designed to handle normal crudes are being modified to handle heavy crude.

New technology for upgrading is used to obtain clean and light products

from lower cost feeds. The crude assay will determine the yields of different

cuts and consequently, the refinery configuration. A high conversion crack-

ing-coking refinery is shown in Figure 1.3 (Jones and Pufado, 2005).

LPG

Gaso

Cracking

Hydrogenation

Crude Oil

Average Carbon Number (Atoms per Molecule)

Hydrogen/Carbon Atom

Ratio

01020304050

C Refinery Coke

VR Vacuum Residue

AR Atmospheric Residue

CR Crude Oil

GO Gas Oil

JF Jet Fuel/Diesel

Gaso Gasoline

LPG Liquefied PG

Figure 1.2 Petroleum products (Speight,1999)

6 Chapter 1