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MME 241 Fuels and Combustion

Date: 08 October 2011 Lecture: 10

August 2011 Term

Topic: Liquid Fuels (Types; Petroleum; Products of

Dr. H. M. Mamun Al RashedDepartment of MME

Web: http://teacher.buet.ac.bd/hrashed/

Bangladesh University of Engineering and Technology, Dhaka - 1000

Topic: Liquid Fuels (Types; Petroleum; Products of

Petroleum; Origin, Storage and Handling)

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Liquid Fuel

• Definition � Obvious!

• Almost all internal combustion engines depend on them.

• Type

– Petroleum� major stake

– Coal tar and crude benzol

– Synthetic fuel from coal, shale oil and alcohol

– Oil from tar sand– Oil from tar sand

• Origin of Petroleum

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• Different theories

– Inorganic Origin

– Organic Origin

• Carbide theory (OPG)

– CH present in petroleum formed by action of water on

inorganic carbidesinorganic carbides

– Inorganic carbides are formed by the reaction of metal and

carbon under high temperature and pressure inside earth.

Ca + 2C � Cac2 (under high T and P)

4Al + 3C � Al4C3

Cac2 + 2H2O � Ca(OH)2 +C2H2 (Acetylene)

Al4C3 + 12 H2O � 4Al(OH)3 + 3CH3 (methane)

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• These lower CHs then undergo hydrogenation and polymerisation to yieldmore CHs.

C2H2 + H2 � C2H4 (ethylene)

C2H4 + H2 � C2H6 (ethane)

3C2H2 � C6H6 (benzene)

3C2H4 � C6H12 (cyclohexane)

• Problem of this theory– Presence of N and S compounds

– Presence of chlorophyll and haemin

– Presence of optically active compounds

Polymerisation

– Presence of optically active compounds

• This theory is also known as Deep seated terrestrial hypothesis.

• From as early as 1877, Dmitri Mendele'ev, a Russian who developed theperiodic table, postulated an inorganic origin when it became apparent thatthere were widespread deposits of petroleum throughout the world. Hereasoned that metallic carbides deep within Earth reacted with water at hightemperatures to form acetylene (C2H2). This acetylene condensed to formheavier hydrocarbons.

• According to the theory, the mantle of the earth contained iron carbide whichwould react with percolating water to form methane.

• The problem with this theory is the lack of evidence for the existence of ironcarbide in the mantle.

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• Engler theory (1900) (OPG)– Animal origin

– SO2 gas from volcanoes near sea-side kills fishes and other sea animals.• They get stacked pile by pile near sea-side.

– After many years, petroleum formed by decay and decomposition andmarine animals under high pressure and temperature.

– This theory is favoured for:• Presence of brine in petroleum• Presence of brine in petroleum

• Presence of N and S compounds

• Presence of optically active compounds

• Presence of fossils

• Experiments on decomposition of fish oil and animal fats under high pressure andtemperature gives quite similar products.

– Problem• Cannot explain presence of chlorophyll

• Cannot explain presence of coal deposits near oil fields

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• Modern Theory– Decay and decomposition of both marine animals and plants

– They might get buried due to some disruptions such as earthquakes

– There are four phases of in oil formation• Embedment of organic matter in source beds

• Conversion to fluid

• Migration of oil into the reservoir rock

• Secondary transformation of oil in the reservoir rock

– (i) The source of oil is: plankton, marine algae, sear grass and larger marineanimalsanimals

– Fish may be absent since oil contains low amount of P.

– The dead matters settle down in the bottom of sea or lagoons.

– The process is accelerated by the presence of mineral compoundstransported by the current of water.

– The deposits are attacked by anaerobic (can live in the absence ofatmospheric oxygen) bacteria.

– Most of the organic compounds are destroyed and lost.

– Unsaturated fatty oils and fatty acids, surviving the bacterial attack, undergopolymerisation � to give insoluble solids.

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– They are getting continuously buried and compacted.

– During compaction, water content is reduced to 10% or less.

– Under the reducing condition, decarboxylation and other reductionprocesses occur and composition becomes more like petroleum.

– (ii) the compacted bed of organic matters form fluid throughconsiderable amount of degradation.

– Presence of optically active matters (porphyrines) hints that hightemp (>200C) may not be involved, since porphyrines arePresence of optically active matters (porphyrines) hints that hightemp (>200C) may not be involved, since porphyrines aredestroyed above this temperature.

– The degradation occurs by• Anaerobic bacterial action

• Low temp cracking in presence of clay and mineral catalysts � this is themajor process for oil formation from compacted layers

• Irradiation by radioactive materials

– (iii) With time, the liquids migrate to different areas of suitablerocks.

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– During migration, composition of oil may change by filtration,solution or absorption.

– Oil reservoirs are built by migration of oils from several compactedbeds.

– (IV) Further change in composition in reservoirs may occurdepending on history of oil and nature of reservoir rocks.

– This secondary transformation occurs by radioactivity, bacterialaction and catalytic influence of rocks.

– No direct ranking system• Coal from older era are lighter and more simple in structure.

– Yields more distillates

• Difference between origins of petroleum and coal– Oil � sea plants and animals decaying under strong reducing atm;

Coal � land plants decaying under mild reducing atm

– Oil migrates from their original sources;

Coal seams remain static where deposited/formed.

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Petroleum

• It means oil obtained from earth.

• Also known as mineral oil, crude petroleum, crude oil, crude or oil

• It may be straw-coloured, black or dark-coloured.

• It may contain gas and solid.

• Gas may be separated and form a separated reservoir of gas.

• When gas and liquid are removed, the solid left are exposed to surfaceand a natural deposit of asphalt occurs.

• Typically petroleum is found in reservoir rocks having fluid holding• Typically petroleum is found in reservoir rocks having fluid holdingcapacity, porosity and fluid transmitting capacity and permeability.

• The rocks are usually sedimentary rocks of coarse-grained minerals,such as sand, sandstone, grit, limestone and dolomite.

• Upward migration of fluid from the reservoir is prevented by “caprock” or sealing formation.– Cap rock has very fine pores and low permeability. � clays and shales

• Migration in other directions are prevented by cap rocks and geometryof reservoirs. � formation of oil trap

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Composition of Petroleum

• Unlike coal, ultimate analysis of crude petroleumvaries.

– C: 83-87%

– H: 11-14%

– S: 0.5-3%

– N: 0.1%

– O: 2-3%– O: 2-3%

• Ash content is typically <0.1%.

– Almost all metals are found in ash

• Si, Fe, Al, Ca, Mg, Ni and Na

• Crude petroleum is a mixture of CH

– Paraffins, naphthenes, aromatics, higher mol weight CH

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Classification of Petroleum

• Paraffin-base� residue (wax+ asphalt)

• Asphalt-base � residue (asphalt)

• Mixed-base � residue (wax+ asphalt) � 90% of

current oil production

Paraffin-based yields kerosene, diesel fuels,• Paraffin-based � yields kerosene, diesel fuels,

lubricants and waxes

• Asphalt-based � yields gasoline and asphalts

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Uses of Petroleum (OPG)

• LPG � Liquefied before use; Domestic and industrial fuel– Is a mixture of propane and butane

• Gasoline (Petrol) � Fuel for ignition of IC engines– Dry cleaning of clothes

• Naphtha � Solvent, paint thinner, H2 production in fertiliser factories,fuel gas in steel plants

• Jet Fuel � Fuel gas for aviation

• Kerosene � Domestic

• Diesel Fuel for diesel engines• Diesel � Fuel for diesel engines

• Gas Oil � Gasified oil, industrial furnace

• Lubricating Oil �

• Petrolatum � base material for grease production

• Light Fuel Oil � fuel in industrial furnaces

• Heavy Fuel Oil � furnace fuel; can be cracked to produce gasoline,diesel, light oils

• Bitumen/Tar � Binder in road making and coating

• Wax � candles, waxed papers, match coatings

• Residue Pitch � road making, industrial fuel 12

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Production of Petroleum• After scientific studies indicate the possible presence of oil,

– an oil company selects a well site and

installs a derrick—a tower-like steel

structure—to support the drilling equipment.

– A hole is drilled deep into the earth until oil

or gas is found, or the company abandons the

effort.

• In rotary drilling, a rotating bit attached

to a length of hollow drill pipe bores a holeto a length of hollow drill pipe bores a hole

in the ground by chipping and cutting rock.– As the bit cuts deeper, more pipe is added.

– A stream of drilling “mud”—a mixture of clay, chemicals, and water—iscontinuously pumped through the drill pipe and through holes in the drillbit.

– Its purpose is to cool the drill bit, plaster the walls of the hole to preventcave-ins, carry crushed rock to the surface, and prevent “blowouts” byequalizing pressure inside the hole.

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• When oil or gas is found,

– the drill pipe and bit are pulled from the well,

– and metal pipe (casing) is lowered into the hole and cemented in place.

– The casing’s upper end is fastened to a system of pipes and valves called awellhead, or “Christmas Tree,” through which natural pressure forces theoil or gas into separation and storage tanks.

– If natural pressure is not great enough to force the oil to the surface,pumps may be used.pumps may be used.

– In some cases, water, steam, or gas may be injected into the oil-producingformation to improve recovery.

• Most common practice of oil extraction � rotary drilling

– Derrick

– Drill Column

– Rotating Mechanism

– Mud Circulating System

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Must Read SS for details

Section 5.2.2 (p153-155)

Videos

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Storage and Handling

• Liquid fuels of low flash points are stored in tanks fitted withroofs floating on the liquid surface.– To reduce presence of air

• To prevent fire hazards and evaporation losses

– They are transferred by pipelines or tankers.

– Storage tankers are underground.

• Liquid fuels with higher flash points (kerosene, diesels) arestored in tanks with fixed roofs.– Heating coils are sometimes added for heavier grades of oils for easy– Heating coils are sometimes added for heavier grades of oils for easy

pumping.

• Fuel oils contain some water which is deposited at the bottomand is collected through a drain cock.

• Lighter oils are pumped to burners without preheating.

• Heavier oils are preheated twice � in store and during delivery– Heating in the tank is achieved by low pressure steam coils placed at the

bottom of tanks.

– Temperature should be fixed based on viscosity.

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• Liquid fuels are supplied to the furnaces by

– Gravity feed system

• Overhead feed tank or ground level feed tank with a pump fitted in the

delivery system

• Used for few burners only

• Light oils are favoured.

– Ring main system

• Medium and heavy oils

• Batteries of oil burners

• Helps to reduce temperature and pressure differences between burners

• Working Principle

• Oil is circulated through a ring main round mains at a speed 2/3 times the

actual burner feed speed.

• Branch lines are used fir feeding burners.

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– There are oil filters both at suction ad discharge sides of

pump filter.

– There is a oil heater in the mains.

– Figure 5.11 SS

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Properties and Testing of Petroleum

• Viscosity– Performance of diesel fuels depend on viscosity.

– Low viscosity causes excessive leakage at the injection pistons andhigher viscosity causes coarse droplets of oils which results inengine deposits due to incomplete combustion.

– Performance of lubricating oils also depend on viscosity.

– If the lubricant is subjected to different temperature beyondtolerance limit, performance of lubricant is reduced.

Paraffin-based has low dependence on temp and naphthenic-based– Paraffin-based has low dependence on temp and naphthenic-basedhas higher dependency on temperature.

– Viscosity-Temperature relationship can be expressed by viscosityindex (VI).

– Highly paraffinic Pennsylvania oil has 100VI and naphthenic Gulf oilhas 0VI.

– VI of an oil at 100F = [(L-U)/(L-H)] *100

– Higher VI oil is preferred when temperature variation is greater.

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• Flash Point and Fire Point– Which one is higher?

– Gasolines � <23C � highly flammable

– Kerosenes � 23-66C

– Fuel Oils and Gas Oils � >66C

• Pour Point and Cloud Point– Pour point is the temperature 2.8C higher than the temp at which oil ceases

to flow in cold atmto flow in cold atm

– Flow is ceased due to increase in viscosity or crystallisation of wax from oil.

– Heavy fuels have higher pour temp and heating measures are sometimesnecessary.

– Asphaltic materials � pour point depressants � prevent crystallisation andgrowth of crystals

– By increasing proportion of lighter CH � pour point can be reduced

– 5/6C + Pour Point � Cloud Point

– Cloudy because of crystallisation of wax

– Cloud point is important for diesels since crystals may block the filters of fuelinjection systems and hampers flow.

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• S– Even after purification � some S remain

– Kerosine � 0.05-0.2%

– Diesel � 0.3-1.5%

• Moisture– Max 1%.

– Separated by preheating

• AshAsh– Very low

– <0.1%

• Octane Number– Fuel gives maximum power when it burns silently and slowly.

– Under certain condition, whole unburnt fuel may burn quickly with formationof pressure waves.

– This leads to knocking of engine (is a sound that is made when the fuel ignitestoo early).

• Power is wasted and engine life is reduced.

• Severe knock causes severe engine damage, such as broken connecting rods, meltedpistons, melted or broken valves and other components. 21

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– Anti-knocking quality of fuel is measured in a standard engine interms of relative performance of two standard fuels � expressedas Octane Number

– Octane number of gasoline is equal to the percentage by volume ofiso-octane in a mixture of n-heptane and iso-octane.

• n-heptane has poor anti-knocking quality ((easily ignites under pressure)and is 0 octane number.

• iso-octane has excellent anti-knocking quality (minimal ignition underpressure) and is 100 octane number.

• If a gasoline matches with 80/20 mixture of above, its octane number is80.

• Anti-knocking quality depends on type of CH. � Aromatics good ones.• Anti-knocking quality depends on type of CH. � Aromatics good ones.

• During refining, one aim is to conversion of CH to aromatics.

• Octane number can be increased by additives � tetraethyl lead (TEL)with halides

– Halides are added to prevent lead deposition.

– Octane rating decreases with an increase in the carbon chainlength.

– Octane ratings increase with carbon chain branching.

– Octane ratings increase in aromatics with same number of carbons.• Aviation gasoline has octane number >100.

– The higher the number, the less likely an engine is to pre-ignite andsuffer damage. 22