om_04_fuels-2_refining & liquid fuels.pdf

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Department of Maritime Studies

Dr.-Ing.

Wolfgang Busse

E-Mail: [email protected]

www.sf.hs-wismar.de

Operating Media and Dangerous Materials

Chapter 2: Fuels

Lesson 4 :

- Crude Oil Processing

- Liquid Fuels


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Operating Media & Dangerous Materials

Chapter 2: Fuels

Lesson 4: Refining & Liquid Fuels

18-Oct-13

2

Dr.-Ing. Wolfgang Busse 2013

Refining & Liquid Fuels

Content

Crude Oil Processing

o Pre-treatment, Fractional distillation, Conversion,

Removing impurities, Blending

Properties of Liquid Fuels, Fuel oil performance & Test

methods

o Physical properties

(density, viscosity, )

o Ignition & combustion properties

(cetane number, calorific value, )

o Chemical properties

(sulphur content, ash content, )


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Each crude-oil field has a different composition.

The composition be determined by a combination of gas-chromatography,

fluorescence-spectroscopy and infrared-spectroscopy techniques.

That may be used, for instance, in forensic analysis of oil spills at sea; Even

after refining, crude-oil derivatives may be associated to their source field.

Crude OilComposition & Properties


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Crude Oil Components:

Alkanes = Paraffins

Alkene = Olefins

Cycloalkane = Naphtenes Aromatics

Crude Oil Classification:

Paraffin based crudes (a waxy residue)

Asphalt based crudes (an asphalt type residue)

Mixed type-based crudes (a combination residue)



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Properties of Crude Oil:

Crude Oil is a mixture, the properties therefor vary in a wider range:

Density: from 700 kg/m3to 1000 kg/m3at 20 C

Freezing and boiling points: solid-liquid equilibrium may exist in the range210 K to 280 K, and liquid-vapour above 280 K (at 100kPa); vapours start to

decompose at about 900 K

Pour point: 5..15 C

Viscosity: 5 20 10-6 m2/s at 20 C

Vapour pressure: 5..20 kPa at 20 C / 40..80 kPa at 38 C; vapours are

heavier than air (2 to 3 times).



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Crude Oil = Petroleum that has been separated from natural gas;

Complex mixture of alkanes, and small amounts of alkenes,

alkynes, cycloalkanes, aromaticand inorganiccompounds

Types:

Light crude oil:

low sulphur and metal content, brightly colored, low

viscosity

Heavy crude oil:

high sulphur and metal content, dark, high viscosity

The different boiling points of the various components enables

their separation by fractional distillation.

Crude Oil Processing


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Dehydration & Desalting Plant

Removing natural gas, water, salt and sludge are removed from the wet oil

Crude Oil Pre-Treatment


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Refinery Process Steps

1. Fractional Distillation

Crude Oil is physically separated into product groups (fractions) with

different boiling range (different molecule range). The hydrocarbons

within a fraction have similar properties.

2. Conversion

chemically converting the separated hydrocarbons into more desirable

reaction products by changing the size and/or the structure of the

molecules

3. Removing Impurities / Treatment

Removing unwanted ingredients such as sulphur

4. Blending

Improving the product qualities by mixing compositions

Crude Oil Refining


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Car fuel

Jet fuel

Road tar

Step 1: Fractional Distillation

Hydrocarbons are separated in a

distillation plant, which produces

different fractions of oil and gas.

Fractionsare groups within a

certain range of boiling points.

MarineFuelOil (MFO)

LPG


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Crude oil can be separated by physical methods, in this case by fractional distillation,

because the many hydrocarbons have different boiling and condensation points.

The crude oil is vaporised by heating and the vapour passed into the fractionating

column- a large construction of many levels and pipes.

This is a continuous process (not a batch process). The fractionating column works

continuously with heated-vaporised crude oil piped in at the bottom and the variousfractions condensed and constantly tapped off from various levels, each with a different

condensation temperature range.

The most volatile fraction, i.e. the molecules with the lowest boiling points, go higher up

the column and condense at the higher levels in the column at the lowest temperatures.

The rest separate out according to their boiling/condensation point so that the highest

boiling fraction, i.e. the less volatile molecules with higher boiling points, tend to

condense more easily lower down the column, albeit at the higher temperatures.

The bigger the molecule, the greater the intermolecular attractive forces between the

molecules, so the higher the boiling or condensation point (see lesson hydrocarbons).

Note: Covalent chemical bonds like C-C or C-H are not broken in the process, only the

intermolecular force of attraction is weakened to allow the initial evaporation or boiling

and this.


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Crude oil is heated in a boiler using high-

pressure steam up to ~600C. The crude

oil vapor is passed to the bottom of the

distillation tower.

In the distillation tower, the vapor movesup along the trays, passing holes equipped

with bubble caps.

On its upward movement, the vapor cools

down. In every tray, a certain fraction of

the vapor falls below its boiling point and

condensates. The condensate falls and

gathers on the tray under the bubble cap

from where it is flowing out of the tower bubble cap trays


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..

Section of an industrial distillation tower showing detail of trays with bubble caps


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Schematic flow diagram of an atmospheric and vacuum distillation plant


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Properties of the various fractions

The physical properties of different fractions which vary with molecular size. The

longer the carbon chain, the bigger the molecule gets ...

1. the more viscous the molecule as the intermolecular attractive forces between

molecules increases the bigger the molecule in a series of molecules of similar

structure.

2. the molecule has a higher melting point as more vibrational kinetic energy is

needed to overcome the intermolecular attractive forces holding the molecules

together

3. the molecule has a higher boiling point as more particle kinetic energy is

needed to overcome the increasing intermolecular forces between the liquid

molecules.

4. the molecule is less flammable as they become less volatile, again due to

increasing intermolecular forces with increasing size of molecule so for example,

petrol (small molecules) is much more flammable than lubricating oil (much bigger

molecules).


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Step 2: Conversion

From the distillation tower the fractions are passed to various

conversion processes - to get qualities and quantities suited to the

market demands:

Cracking

Reforming

Alkylation

Coking

Breakdown of large molecules into small molecules,

e.g. cracking light oil fractions into gas, heavy oil fractionsinto diesel oil etc.

Change of straight chains into branched chains / alicyclics /aromatics, e.g. n-octane to isooctane for gasoline (=> higherknocking resistance)

Merging of small molecules into big molecules, e.g. thecombination of propene and butene into compounds forgasoline

Cracking of residue fractions into heavy oil and hydrocarbonintermediates. In this process, coke is produced.


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Step 2: Conversion

Cracking (to crack = to break-down)

= splitting of hydrocarbon molecules (molecule decomposition) into smaller

hydrocarbon molecules (less C-atoms)

The molecules increasingly vibrate when heating. At temperatures higher then

360C the bonds between the C-atoms loosen, and shorter hydrocarbon

chains are formed.

The splitting also produces coke forming a deposit in the pipes of the cracking

furnace or on the catalyst. It must be removed (burned) periodically.


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Step 2: Conversion

Cracking - Processes

Thermal Cracking

From the residue of atmospheric or vacuum distillation a light heating oil (middle distillate)

is extracted. Visbreaking is only a mild cracking, Target is saving gas oil for the viscosity

adjustment of the heating oil, not the production of gasoline or diesel fuel.

Steam Cracking

Saturated hydrocarbons are broken down into smaller, often unsaturated, hydrocarbons.

A gaseous or liquid hydrocarbon feed like naphtha, LPG or ethane is diluted with steam

and briefly heated in a furnace without the presence of oxygen.

Catalytic CrackingOnly for high-boiling distillates, the high sulphur amounts in the residue would poison the

catalyst. The process is better controllable and as about 10% higher yield.

Hydrocracking

At pressure of 15 to 17 MPa and temperature of 480C with the help of an hydrogenating

catalyst a high cracking yield is achieved. The process requires high effort.


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Step 2: Conversion

Catalytic

Cracking

Reaction

Feedstock reacts with

catalyst and cracks intodifferent hydrocarbons

Regeneration

Catalyst is reactivated

by burning off coke

Fractionation

Cracked hydrocarbon

stream is separated

into various products.

O ti M di & D M t i l


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Step 2: Conversion

Reforming

Catalytic reforming = removing hydrogen from hydrocarbons producing

compounds with higher octane ratings such as aromatics.

Catalytic reformer unit is used to convert the naphtha-boiling range molecules

into higher octane reformate (reformer product). The reformate has higher

content of aromatics and cyclic hydrocarbons. An important by-product of areformer is hydrogen released during the catalyst reaction. The hydrogen is

used either in the hydrotreaters (uses hydrogen to desulfurize distillates after

atmospheric distillation) or in the hydrocracker.

Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker.

O ti M di & D M t i l


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Step 2: Conversion

Alkylation

= assembly of hydrocarbon molecules (the opposite of cracking)

Catalytic high-pressure hydrogenetion

Production of gasoline (petrol) from distillation residue (low hydrogen content)by adding hydrogen under pressure and temperature. Analogous to the

process of producing gasoline from coal.

Hydrogeneting refining under pressure

Production of fuel from unsaturated hydrocarbons by attaching hydrogen, afterremoving S, N, O, H2S, NH3und H2O at pressures of 1 to 10 MPa and

temperatures of 300 to 400C. These fuels have a good storage stability and

dont cause corrosion


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Step 3: Removing Impurities

Fractions contain impurities such as S, N, O, water, metals, inorganic

salts. They are removed by:

Sulfuric acid tower

Absorption tower

Scrubber

Separates unsaturated hydrocarbons, nitrogen,

oxygen, and solid residues such as asphalt

Separates water using a drying agent

Separates sulphur & sulphur compounds



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Step 3: Removing Impurities

Desulphurization

Hydrofiner and Claus-Unit

Sulphur is natural component of crude oil. Depending on the deposit, the

sulphur content is between some tenth percent (North Sea, North-Africa)

and several percent (Arabia, Russia, South-America)

The quality standards for distillate products from crude oil such as liquefied

gas, gasoline/petrol, diesel fuel, and heating oil EL can only be met by

desulphurization.

This is done in the Hydrofiner(hydro-desulfurization): The sulphur

compounds in the distillate react at a catalyst with hydrogen, forminggaseous hydrogen sulfide H2S.

The hydrogen sulfide gas is separated and then in the Claus-Unitprocessed

to sulphur. Overall main reaction equation: 2 H2S + O2 S2+ 2 H2O (The

real process runs in several steps, with SO2 as intermediate product.)



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Step 4: Blending

Blending is done to obtain the specific characteristics of the end

products, for example:

Blending gasoline fraction with branched chains / alicyclics /

aromatics and various additives to obtain a certain gasoline grade(octane number)

Blending lubricating oil fraction with various hydrocarbons and

additives

Blending of naphtha fraction to obtain various grades for

petrochemical industries



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Utilization of the Petroleum Fractions



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Fraction C-

atoms

Boiling

point [C]

Utilization

Gas 1 - 4 < 20 LPG liquefied petroleum gas, as fuel and as

raw material for synthesizing organic compounds

Gasoline 5 - 10 40180 Fuel for vehicles

Naphtha 6 - 10 70180 Synthesizing organic compounds for plastic,synthetic rubber, detergent, medicine, paint,

Kerosene 11 - 14 180250 Fuel for airplane, paraffin stove,

Diesel oil 15 - 17 250300 Fuel for diesel engines, and for industries

Lubricating oil 18 - 20 300350 Lubricant (high viscosity)

Wax > 20 > 350 Paraffin wax for candles, matches, shoe polish, ...

Heavy oil > 20 > 350 Fuel for ships, boiler plants, power plants

Bitumen > 40 > 350 Materials for asphalts, roofing, anticorrosion

coating, electric isolator,



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Deepen your knowledge:

Select some typical marine engineering applications of

petroleum products. What are important quality requirements for these products?

Which petroleum fractions are used?

How are the petroleum fractions processed to achieve the

quality requirements on the products?



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Tks



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Questions ?



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Literature

1. OSHA_Petroleum Refining Process.docx



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Web links

1. http://www.en.wikipedia.org/wiki/Cracking_(chemistry)

2. http://www.world-petroleum.org/index.php?/Technology/petroleum-refining-

courtesy-of-aip.html

3. https://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.html
http://www.en.wikipedia.org/wiki/Cracking_(chemistry)http://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttps://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.htmlhttps://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.htmlhttps://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.world-petroleum.org/index.php?/Technology/petroleum-refining-courtesy-of-aip.htmlhttp://www.en.wikipedia.org/wiki/Cracking_(chemistry)http://www.en.wikipedia.org/wiki/Cracking_(chemistry)http://www.en.wikipedia.org/wiki/Cracking_(chemistry)

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