Report 1 (10-2011) 2003

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Refinery Overview

Report No.1 (11-2011)

Dalia Mamoun Beshir Mohamed

Page 1 of 8

1. Introduction

Oil refining is one of the most complex chemical industries, which involves many different

aspects and complicated processes with various possible connections. The objective in refinery

operations is to generate as much profit as possible by converting crude oils into valuable

products such as gasoline, jet fuel, diesel, and so on [James et al., 2001; Zhang et al., 2000].

In recent years the requirements for large quantities of liquid hydrocarbons, particularly gasoline

and diesel fuels, have increased and will continue to escalate, which will necessarily cause the

steady rise in production volume of the refining industry. The International Energy Agency in its

World Energy Outlook 2008 is predicting the increase in yearly oil use to be 1.3% until 2020 and

1.0% from 2020 to 2030 [Muzic et al., 2010].

2. Refinery

The typical fuels refinery has as a goal the conversion of as much of the barrel of crude oil into

transportation fuels as is economically practical. These transportation fuels have boiling points

between 0 and 345°C (30 to 650°F). The greater the densities will mean more of the crude oil

will boil above 566°C (1050°F). Historically this high-boiling material or residua has been used

as heavy fuel oil but the demand for these heavy fuel oils has been decreasing because of stricter

environmental requirements. This will require refineries to process the entire barrel of crude

rather than just the material boiling below 566°C (1050°F) [James et al., 2001].

In refineries some processes will take place depending on the complexity of the refinery (may be

all) such as crude desalting and atmospheric and vacuum distillation; gasoline manufacturing

processes, such as catalytic reforming, catalytic cracking, alkylation, and isomerization;

hydrodesulfurization processes for naphtha, kerosene, diesel, and reduced crude; conversion

processes such as distillate and resid hydrocracking; resid conversion processes such as delayed

coking, visbreaking, solvent deasphalting, and bitumen manufacture; pollution control processes

such as sulfur manufacture, sulfur plant tail gas treatment, and stack gas desulfurization.

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2.1. Crude desalting

Crude desalting is the first processing step in a refinery. The objectives of crude desalting are the

removal of salts and solids and the formation water from unrefined crude oil before the crude is

introduced in the crude distillation unit of the refinery.

2.2. Refinery distillation

Crude oil as produced in the oil field is a complex mixture of hydrocarbons ranging from

methane to asphalt, with varying proportions of paraffins, naphthenes, and aromatics. The

objective of crude distillation is to fractionate crude oil into light-end hydrocarbons (C1-C4),

naphtha/gasoline, kerosene, diesel, and atmospheric resid. Some of these broad cuts can be

marketed directly, while others require further processing in refinery downstream units to make

them saleable.

2.3. Hydrotreating

Hydrotreating processes aim at the removal of impurities such as sulfur and nitrogen from

distillate fuels (naphtha, kerosene, and diesel) by treating the feed with hydrogen at elevated

temperature and pressure in the presence of a catalyst.

2.4. Hydrocracking

Distillate hydrocracking is a refining process for conversion of heavy gas oils and heavy diesels

or similar boiling-range heavy distillates into light distillates (naphtha, kerosene, diesel, etc.) or

base stocks for lubricating oil manufacture. The process consists of causing feed to react with

hydrogen in the presence of a catalyst under specified operating conditions: temperature,

pressure, and space velocity.

2.5. Thermal processes

2.5.1. Visbreaking

Visbreaking is a mild thermal cracking process. The function of a visbreaking unit is to produce

lower viscosity and low-pour resid for blending to fuel oil. In this cracking process, cracked gas,

gasoline/ naphtha, gas oil, and thermal tar are produced. The gas oil is blended back into the

thermal tar to yield fuel oil. Thermal cracking reduces the viscosity and pour point of the resid

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and hence the cutter stock requirement for blending this resid to fuel oil. Thus, the overall

production of fuel oil is reduced. A second consideration is the removal of some feed sulfur.

Although visbreaking is an inefficient process in this respect, sulfur removal does occur to some

extent.

2.5.2. Delayed coking

Delayed coking is a thermal process in which the vacuum residue from crude distillation is

heated in a furnace then confined in a reaction zone or coke drum under proper operating

conditions of temperature and pressure until the unvaporized portion of the furnace effluent is

converted to vapor and coke. Delayed coking is an endothermic reaction, with the furnace

supplying the necessary heat for the coking reactions. The reactions in the delayed coking are

complex. In the initial phase, the feed is partially vaporized and cracked as it passes through the

furnace. In the next step, cracking of the vapor occurs as it passes through the drum. In the final

step, successive cracking and polymerization of the liquid confined in the drum takes place at

high temperatures, until the liquid is converted into vapor and coke. The coke produced in the

delayed coker is almost pure carbon containing some of the impurities of the feed, such as sulfur

and metals.

2.6. Gasoline manufacturing processes

2.6.1. Catalytic reforming

Catalytic reforming of heavy naphtha is a key process in the production of gasoline. The aim of

catalytic reforming is to transform, as much as possible, hydrocarbons with low octane to

hydrocarbons with high octane. The chemical reactions that lead to these changes are guided by a

catalyst under well-defined operating conditions.

2.6.2. Fluid catalytic cracking

Fluid catalytic cracking (FCC) is an effective refinery process for conversion of heavy gas oils

into gasoline blend components. Cracking is achieved at high temperatures in contact with

powdered catalyst without the use of hydrogen. After separation of the catalyst, the hydrocarbons

are separated into the desired products by fractionation. The main products of the FCC process

are gasoline, distillate fuel oil, and olefinic C3/C4 liquefied petroleum gas (LPG). By-product

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coke, which is deposited on the catalyst during the reaction, is burned off in the regenerator. The

heat liberated during the combustion of coke supplies the heat required to vaporize the feedstock

and heat of reaction.

2.6.3. Alkylation

Alkylation is important refining processes for the production of alkylate a high-octane gasoline

blending component. Alkylate product is a mixture of branched hydrocarbons of gasoline boiling

range.

2.6.4. Isomerization

Most gasoline formulations require inclusion of some light naphtha to meet the front-end

distillation and octane specs. However, C5/C6 normal paraffins in this boiling range have low

octane, which make them very difficult to include in the gasoline formulation. Branched chain

C5 and C6 hydrocarbons have higher octane, making them more suitable for inclusion in

gasoline. The isomerization process is designed for continuous catalytic isomerization of

pentanes, hexanes, and their mixtures. The process is conducted in an atmosphere of hydrogen

over a fixed bed of catalyst and at operating conditions that promote isomerization and minimize

hydrocracking.

3. General properties of petroleum fractions

Most petroleum distillates, especially those from the atmospheric distillation, are usually defined

in term of their ASTM boiling ranges. The following general class of distillates is obtained from

petroleum: liquefied petroleum gas, naphtha, kerosene, diesel, vacuum gas oil, and residual fuel

oil.

3.1. Distillates

3.1.1. Liquefied Petroleum Gas

The gases obtained from crude oil distillation are ethane, propane, and n-butane isobutene. These

products cannot be produced directly from the crude distillation and require high-pressure

distillation of overhead gases from the crude column. C3 and C4 particularly are recovered and

sold as liquefied petroleum gas (LPG), while C1 and C2 are generally used as refinery fuel.

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3.1.2. Naphtha

C5-400°F ASTM cut is generally termed naphtha. There are many grades and boiling ranges of

naphtha. Many refineries produce 400 °F end-point naphtha as an overhead distillate from the

crude column, then fractionate it as required in separate facilities. Naphtha is used as feedstock

for petrochemicals either by thermal cracking to olefins or by reforming and extraction of

aromatics. Also some naphtha is used in the manufacture of gasoline by a catalytic reforming

process.

3.1.3. Kerosene

The most important use of kerosene is as aviation turbine fuel. This product has the most

stringent specifications, which must be met to ensure the safety standards of the various

categories of aircraft. The most important specifications are the flash and freeze points of this

fuel. The initial boiling point (IBP) is adjusted to meet the minimum flash requirements of

approximately 100°F. The final boiling point (FBP) is adjusted to meet the maximum freeze

point requirement of the jet fuel grade, approximately -52°F. Full-range kerosene may have an

ASTM boiling range between 310 and 550°F Basic civil jet fuels are

1. Jet A, a kerosene-type fuel having a maximum freeze point of -40°F Jet A-type fuel is used

by mainly domestic airlines of various countries, where a higher freeze point imposes no

operating limitations.

2. Jet A-1, a kerosene-type fuel identical with Jet A but with a maximum freeze point of -47°F.

This type of fuel is used by most international airlines. Jet A and Jet A-1 generally have a

flash point of 38°F.

3. Jet B is a wide-cut gasoline-type fuel with a maximum freeze point of -50 to -58°F. The fuel

is of a wider cut, comprising heavy naphtha and kerosene, and is meant mainly for military

aircraft.

3.1.4. Diesel

Diesel grades have an ASTM end point of 650-700°F Diesel fuel is a blend of light and heavy

distillates and has an ASTM boiling range of approximately 350-675°F Marine diesels are a little

heavier, having an ASTM boiling end point approximately 775°F. The most important

specifications of diesel fuels are cetane number, sulfur, and pour or cloud point. Cetane number

is related to the burning quality of the fuel in an engine. The permissible sulfur content of diesel

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is being lowered worldwide due to the environmental pollution concerns resulting from

combustion of this fuel. Pour point or cloud point of diesel is related to the storage and handling

properties of diesel and depends on the climatic conditions in which the fuel is being used.

3.1.5. Vacuum Gas Oil

Vacuum gas oil is the distillate boiling between 700 and 1000°F. This is not a saleable product

and is used as feed to secondary processing units, such as fluid catalytic cracking units, and

hydrocrackers, for conversion to light and middle distillates.

3.1.6. Residual Fuel Oil

Hydrocarbon material boiling above I000 °F is not distillable and consists mostly of resins and

asphaltenes. This is blended with cutter stock, usually kerosene and diesel, to meet the viscosity

and sulfur specifications of various fuel oil grades.

3.2. Vacuum distillation products

In an atmospheric distillation tower, the maximum flash zone temperature without cracking is

700-800°F. The atmospheric residuum, commonly known as reduced crude, contains a large

volume of distillable oils that can be recovered by vacuum distillation at the maximum

permissible flash zone temperature. The TBP cut point between vacuum gas oil and vacuum

resid is approximately 1075-1125°F. The cut point is generally optimized, depending on the

objectives of the vacuum distillation, into asphalt operation and pitch operation.

3.2.1. Asphalt Operation

Given the specification of the asphalt (penetration) to be produced, the corresponding residuum

yield can be determined from the crude assay data. In case a number of lubricating oil distillates

is to be produced, the distillation range of each has to be specified, and the corresponding yields

can be determined from the crude assay data. Lube cuts are produced as sidestreams from the

vacuum column.

In asphalt operation, some gas oil must remain in the pitch to provide the proper degree of

plasticity. The gravity of an asphalt stream is usually between 5 and 8 oF API. Not all crudes can

be used to make asphalt.

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Experimental data for asphalt operation are necessary to relate asphalt penetration to residual

volume. The penetration range between 85 and 10, are possible and the units are generally

designed to produce more than one grade of asphalt.

The principal criteria for producing lube oil fractions are viscosity, color, and rejection to

residuum the heavy impurities and metals. These oils are further refined by solvent extraction,

dewaxing, and other types of finishing treatment, such as hydrotreating.

References

James H. Gary and Glenn E. Handwerk, Petroleum Refining Technology and Economics, 4th

edition, Marcel Dekker Inc., ISBN: 0-8247-0482-7, 2001.

Muzic M., K. Sertic-Bionda, T. Adzamic, “The Application of Theoretical Solutions to the

Differential Mass Balance Equation for Modelling of Adsorptive Desulfurization in a

Packed Bed Adsorber,” Chemical Engineering and Processing , doi:10.1016/j.cep.2011.

02 .009, 2010.

Refinery process handbook

Rober A. Meyers, Handbook of petroleum refining processes, 3

rd

edition, McGraw-Hillhandbooks.

Zhang N., Zhu X.X., “A novel modelling and decomposition strategy for overall refinery

optimization,” Computers and Chemical Engineering , vol. 24, pp. 1543- 1548, 2000.

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Appendix A

A typical diagram of oil refinery

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Report 1 (10-2011) 2003