Notes Petro Refine 1 120701082001 Phpapp02

8/13/2019 Notes Petro Refine 1 120701082001 Phpapp02

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PETROLEUM REFINERY ENGINEERING

Petroleum is a combustible oily liquid of reddish brown to almost black colour, produced from oil

wells. It is a comp lex mixture of hy drocarbons and thei r derivat ives containing oxygen, sulphur,

nitrogen and minor quantities of some other materials. The importance of petroleum crude oil and natural

gas has been realized with the development of its numerous applications as fuel and feedstoc k. The

invention of the in ternal com bust ion engines in the last quarter of the nineteenth century gave an

impetus to the development of petroleum processing. The most basic refining process is aimed at

separating the crude oil into its various components. Crude oil is heated and put into a still -- a distillation

column -- and different hydrocarbon components boil off and can be recovered as they condense at

different temperatures. Additional processing follows crude distillation, changing the molecular structure

of the input with chemical reactions, some through variations in heat and pressure, and some in the

presence of a catalyst.

The main constituents of petroleum _hydrocarbons _ may differ in the number of carbon and

hydrogen atoms in the molecular structure. The hydrocarbons are present in the following groups or

homologous series: paraffins (saturated st. chain hydrocarbons, alkanes), naphthenes (cycloalkanes),

and benzene hydrocarbons (aromatics). In most grades of petroleum, paraffins and naphthenes prevail

mostly.

Based on the chemical composition of the crude

(1) Paraffin-Base Crude Oils These contain higher molecular weight paraffins which are solid at

room temperature, but little or no asphaltic (bituminous) matter. They can produce high-grade lubricatingoils.

(2) Asphaltic-Base Crude Oils Contain large proportions of asphaltic matter, and little or no

paraffin. Some are predominantly naphthenes so yield lubricating oil that is more sensitive to temperature

changes than the paraffin-base crudes.

(3) Mixed-Base Crude Oils The "gray area" between the two types above. Both paraffins and

naphthenes are present, as well as aromatic hydrocarbons. Most crude fit this category.

CRUDE OIL PHYSICAL PROPERTIES

The physicalproperties of crude are as follows

Specific Gravity: 0.669 to 0.99

API Gravity: 1050


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Viscosity: 14 centipoises

The American Petroleum Institute (API) has developed the term Degrees

API Gravity (API) which is widely used as another general characterization of

the density of crude oils. The relationship is as follows:

API = (141.5/Specific Gravity at 60 degrees Fahrenheit) - 131.5

Specific Gravity at 60 degrees Fahrenheit is the density of the crude oil

measured at 60F divided by the density of water at 60F.

Therefore, when comparing two crude oils, the higher density crude (i.e., the one

with the highest specific gravity) will have a correspondingly lower API. For

example, the 34.5API West African crude oil Bonny Light is heavier than the

40.4API North Sea crude oil Forties.

Chemical composition

On an average crude oil is [ultimate analysis] made up of the following components:

Carbon - 84%

Hydrogen - 14%

Sulphur - 1 to 3% (hydrogen sulfide, sulfides, disulfides, elemental sulfur)

Nitrogen - less than 1% (basic compounds with amine groups)

Oxygen - less than 1% (found in organic compounds such as carbon dioxide, phenols, ketones,

carboxylic acids)

Metals - less than 1% (nickel, iron, vanadium, copper, arsenic)

Salts - less than 1% (sodium chloride, magnesium chloride, calcium chloride)

Crude oils are complex mixtures containing many different Hydrocarbons compounds that vary in

appearance and composition from one oil field to another. Crude oils are generally classified as

paraffinic, napthenic or aromatic based on the predominant proportion of similar Hydrocarbons.


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Hydrocarbons found in crude may be of the following types

1. Paraffins (Alkanes)

General formula: CnH2n+2 (n is a whole number, usually from 1 to 20)

These compounds are saturated hydrocarbons with all carbon bonds satisfied, that is, the

hydrocarbon chain carries the full complement of hydrogen atoms.

Consist of straight chain (normal)- or branched-chain ( isomers) atoms

The lighter straight chain molecules are found in gases and heavier in paraffin waxes.

The branched chain (isomer) parrafins are usually found in heavier fractions of crude oil and

have higher octane numbers than normal parrafins.

examples: methane, ethane, propane, butane, isobutane, pentane, hexane

2. Aromatics

General formula: C6H5- Y (Y is a longer, straight molecule that connects to the benzene ring)

They are unsaturated ring type (cyclic) compounds which react because they have carbon

atoms that are deficient in hydrogen.

ringed structures with one or more rings. They have at least one benzene ring.


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rings contain six carbon atoms, with alternating double and single bonds between the carbons

typically liquids and are found in heavier fractions of crude oil.

examples: benzene, naphthalene

3. Napthenesor Cycloalkanes

General formula: CnH2n(n is a whole number usually from 1 to 20)

ringed structures with closed rings (cyclic)

Found in all fractions of crude except the very lightest.

rings contain only single bonds between the carbon atoms

typically liquids at room temperature

examples: cyclohexane, methyl cyclopentane


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Nonhydrocarbons.

1. Sulfur Compounds. Sulfur may be present in crude oil as hydrogen sulfide (H 2S), as

compounds (e.g. mercaptans, sulfides, disulfides, thiophenes, etc.) or as elemental sulfur. Each crude oil

has different amounts and types of sulfur compounds, but as a rule the proportion, stability, and

complexity of the compounds are greater in heavier crude-oil fractions. Hydrogen sulfide is a primary

contributor to corrosion in refinery processing units. Other corrosive substances are elemental sulfur and

mercaptans.

Moreover, the corrosive sulfur compounds have an obnoxious odor.

2. Oxygen Compounds. Oxygen compounds such as phenols, ketones, and carboxylic acids

occur in crude oils in varying amounts.

3. Nitrogen Compounds. Nitrogen is found in lighter fractions of crude oil as basic compounds,

and more often in heavier fractions of crude oil as non basic compounds that may also include trace

metals such as copper, vanadium, and/or nickel. Nitrogen oxides can form in process furnaces. The

decomposition of nitrogen compounds in catalytic cracking and hydrocracking processes forms ammonia

and cyanides that can cause corrosion.

4. Trace Metals. Metals, including nickel, iron, and vanadium are often found in crude oils in small

quantities and are removed during the refining process. Burning heavy fuel oils in refinery

furnaces and boilers can leave deposits of vanadium oxide and nickel oxide in furnace boxes,

ducts, and tubes. It is also desirable to remove trace amounts of arsenic, vanadium, and nickel

prior to processing as they can poison certain catalysts.

Fractionation Processes:

Process name Action Method Purpose feedstocks products

Atmospheric

distillation

separation thermal Separate

fractions

Desalted

Crude oil

Gas, Gas oil,

distillate,

residue

Vacuum

distillation

separation thermal Separate w/o

cracking

Atm. tower

residue

Gas oil, lube

stock, residue


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An oil refinery is an industrial process plant where crude oil is processed and

refined into more useful products. Oil refineries are quite large industrial complexes with

extensive pipelines carrying streams of fluids between large chemical (thermal and

catalytic) processes.


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Temperature increases down the column

(PetroleumGas)

Petrol

Naphtha

Kerosene

Diesel

Lubricants

Bitumen


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Catalytic ReformingAlthough motor gasolines have numerous specifications that must be

satisfied to provide the performance demanded by our high-performance motor

vehicles, the most widely recognized gasoline specification is the octane number.

Gasolines are typically retailed in grades of regular, mid-grade and premium,

which are differentiated by the posted octane number.

The Octane Number of a test fuel refers to the percentage by volume of


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isooctane in a mixture of isooctane and heptane in a reference fuel that when

tested in a laboratory engine, matches the antiknock quality, as measured by a

knockmeter, of the fuel being tested under the same conditions. The octane

number posted at the gasoline pump is actually the average of the Research

Octane Number (RON) and Motor Octane Number (MON), commonly referred to

as (R+M)/2. RON and MON are two different test methods that quantify the

antiknock qualities of a fuel. Since the MON is a test under more severe

conditions than the RON test, for any given fuel, the RON is always higher thanthe MON.Unfortunately, the desulfurized light and heavy naphtha fractions of crude

oils have very low octane numbers. The heavy naphtha fraction is roughly 50

(R+M)/2. Catalytic Reforming is the refinery process that reforms the molecular

structure of the heavy naphtha to increase the percentage of high-octane

components while reducing the percentage of low-octane components.

The hydrocarbon compounds that constitute heavy naphtha are classified

into four different categories: paraffins, olefins (a very low percentage of olefins

occur in the heavy naphthas from crude), naphthenes and aromatics. In lieu of a

complete course in organic chemistry, simplistically the paraffins and olefins are

compounds with straight or branched carbon chains, whereas the naphthenes

and aromatics are carbon rings. The paraffins and naphthenes are saturated

hydrocarbons. Saturated means that they have the maximum number of

hydrogen atoms attached to the carbon atoms. The olefins and aromatics,

however, are unsaturated hydrocarbons because the compounds contain carbon

atoms that are double bonded to other carbon atoms. The straight chain,

saturated compounds exhibit very low octane numbers, the branched, saturated

compounds exhibit progressively higher octane numbers, while the unsaturated

compounds exhibit very high octane numbers.

Catalytic Reforming uses a precious metal catalyst (platinum supported by

an alumina base) in conjunction with very high temperatures to reform the

paraffins and napthenes into high-octane components. Sulfur is a poison to the

Catalytic Reforming catalyst, which requires that virtually all the sulfur must be

removed from the heavy naphtha through Hydrotreating prior to Catalytic

Reforming. Several different types of chemical reactions occur in the Catalytic

Reforming reactors.olefins are converted to paraffins, paraffins are isomerizedto branched chains and to a lesser extent to naphthenes, and naphthenes are

converted to aromatics. Aromatic compounds are essentially unchanged. The

resulting reformate product stream from Catalytic Reforming has a RON from 96-

102 depending on the reactor severity and feedstock quality. The

dehydrogenation reactions which convert the saturated naphthenes into

unsaturated aromatics produce hydrogen. This hydrogen is available for


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distribution to other refinery processes which consume hydrogen.

The Catalytic Reforming process consists of a series of several spherical

reactors which operate at temperatures of approximately 900F. The reforming

reactions are .endothermic. meaning that the reactions cool the hydrocarbons.

The hydrocarbons are re-heated by direct-fired furnaces in between the

subsequent reforming reactors. As a result of the very high temperatures, the

catalyst becomes deactivated by the formation of .coke. (i.e., essentially pure

carbon) on the catalyst which reduces the surface area available to contact with

the hydrocarbons. A simplified process flow for the Catalytic Reforming process

is presented above.


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Fluidized Catalytic Cracking

The Fluidized Catalytic Cracking (FCC) process unit is considered by many refiners to be the heart of the

petroleum refinery. This derives from the fact that the FCC is a key tool to correct the imbalance reflected

by the markets demand for predominantly lighter, lower boiling petroleum products, whereas fractionated

crude oils typically provide an excess of heavy, high boiling range oils. The FCC process converts heavy

gas oils into lighter products which are then used as blend stocks for gasoline and diesel fuels. The

olefinic FCC catalytic naphtha product exhibits a very high-octane value for gasoline blending. The FCC

process cracks the heavy gas oils by breaking carbon-to-carbon bonds in the large molecules comprising

the gas oils and splitting them into multiple smaller molecules which boil at a much lower temperatures.

The FCC may achieve conversions of 70-80% of the feed hydrocarbons boiling above the gasoline range

(i.e., 430F) to products boiling below 430F. The lower density of the FCC products relative to the gas oil

feedstocks has the added benefit of producing a volume gain in which the combined volume of the liquid

product streams is greater than the volume of the unit feed stream. Since most petroleum products are

bought and sold on a volume basis, the volume gain aspect of the FCC process is a key aspect in how it

enhances refinery profitability. The resulting FCC product hydrocarbons are highly olefinic (i.e.,

unsaturated). Virgin is a term used to distinguish straight-run (i.e., crude distillation and possibly

hydrotreated only) hydrocarbons stocks from those that are products of conversion units such as the

FCC.

The FCC cracking reactions are catalytically promoted at very high temperatures of 950-1,020F. At these

temperatures, coke (i.e., essentially pure carbon) formation deactivates the catalyst by blocking catalyst

surface area which prevents intimate contact between the catalyst and the hydrocarbons. To retain

catalyst activity, the FCC utilizes a very fine powdery, zeolite catalyst that behaves like a fluid (i.e., is able

to flow). The fluidized catalyst is continuously circulated in the FCC from the reactor to a regenerator

vessel and then returned to the reactor. Coke is removed from the catalyst in the regenerator vessel

through the controlled incomplete combustion of the carbon with oxygen to form carbon monoxide and

carbon dioxide.


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PETROLEUM REFINERY ENGINEERING

Books for Reference:

1. Petroleum Refinery Engineering, 4th

Ed., 1958, W.L. Nelson, McGraw-Hill Book

Company

2. Handbook of Petroleum Processes, 3rd Edition, R. A. Meyers McGraw-Hill

3. Fundamentals of Petroleum and Petrochemical Engineering.Uttam Ray

Chaudhuri, CRC Press, 2010

4. Mcketta S. (Ed), PetroleumProcessing Hbk, Marcell Dekker Inc.1992.

5. Gary J., Handework G., Petroleum Refining Technology and Economics,

Marcell Dekker Inc. 1984.

6.B. K. Bhaskara Rao, "Modern Petroleum Refining Processes",2ndEdn., Oxford and

IBH Publishing Company, New Delhi, 1990.

7. G. D. Hobson and W. Pohl., ModernPetroleum Technology", Gulf Publishers, 2nd

Ed., 1990

8. An Introduction to Industrial Organic Chemistry, 2nded., P. Wiseman, (1979), Applied

Science Publishers, London.


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About Fundamentalsof Petroleum and Petrochemical Engineering.

BY Uttam Ray Chaudhuri, CRC Press, 2010:

The supply of petroleum continues to dwindle at an alarming rate, yet it is the source of a range of

products - from gasoline and diesel to plastic, rubber, and synthetic fiber. Critical to the future of this

commodity is that we learn to use it more judiciously and efficiently.

Fundamentals of Petroleum and Petrochemical Engineering provides a holistic understanding of

petroleum and petrochemical products manufacturing, presented in a step-by-step sequence of the entire

supply chain. Filled with crucial information relevant to a range of applications, the book covers topics

such as:

The essential preliminaries for the exploration and production of crude petroleum oil and gas

Analysis of crude oil and its petroleum products The processing of petroleum in refineries

The fundamentals of lubricating oil and grease Petrochemicals - their raw materials and end

products, and

manufacturing principles of industrially important products

Theories and problems of unit operations and the processes involved in refineries and

petrochemical plants

Automatic operations in plants Start up, shutdown, maintenance, fire, and safety operations

Commercial and managerial activities are necessary for the ultimate success of a refining ormanufacturing business. Due to the advancement of technology, new petrochemicals are being invented

and will continue to be relevant to the petroleum industry in the near future.


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Notes Petro Refine 1 120701082001 Phpapp02