FUELS

Dr. SURENDRAN PARAMBADATH (M.Sc, M.Phil, M.Tech)

Formerly: Post Doctoral Research Associate,Nano-Information Materials Research Laboratory,

Pusan National University, Busan-South Korea

Currently: Assistant ProfessorGovt. Polytechnic College, Perinthalmanna

Any substance which on proper burning in air gives amount of heat, that can be used economically for domestic and industrial purposes.

Classification of fuels:

A. Based upon their occurrence or preparation (i) Natural or primary fuels-which occur in nature ie available in

nature and can be used directly.

Eg: Wood, charcoal, Peat, Lignite, bituminous coal, anthracite coal, petroleum and natural gas.

(ii) Artificial or secondary fuels which are manufactured artificially, generally from primary fuels.

Eg: Coke, kerosene oil, Petrol, Diesel oil, Coal gas, water gas,etc…

B. Based upon their physical state, there are (i) Solid fuels (ii) Liquid fuels and (III) Gaseous fuels.

Classification of fuelsType of Fuel Primary (Natural) Secondary

(Artificial) 1) Solid Wood, Wood,

charcoal, Peat, Lignite, bituminous coal etc.

Charcoal, Coke, Charred peat, Coal briquette.

2) Liquid Crude Petroleum Various fractions of petroleum.

3) Gaseous Natural gas Coal gas, Oil gas, Water gas, Producer gas, Gobar gas etc.

The calorific value of a fuel is defined as the quantity of heat liberated by the complete combustion of a unit mass of the fuel in air or oxygen with the subsequent cooling of the products of combustion to the initial temperature of the fuel.

The presence of moisture in the fuel will reduce its calorific value.

Calorific Value

Characteristics of a good fuel1 High calorific value which determines the amount of heat

produced and temperature attained.

2 Moderate ignition temperature.

3 Moderate velocity of combustion for continuous supply of heat.

4 Low moisture content. Velocity of combustion in presence of moisture leads to low temperature.

5 Low non-combustible matter content, as their presence lead to formation of ash, decreases in calorific value of fuel, additional cost of storage handling of disposal of waste products etc.

Liquid Fuels

The main source of liquid fuel is petroleum, which on distillation gives important liquid fuels petrol, diesel and kerosene oil.

Petra = rock, oleum = oil.

Treatment of Petroleum

Remove dirt, water sulphur etc.

Fractional distillation

Heating up to 400oC in an iron retort, whereby all volatile constituents except the residue are evaporated, and fractionally separated during condensation.

Crude Oil

Super Unleaded

Petrol

Unleaded Petrol

Leaded Petrol

Diesel

1. Gasoline or Petrol or Motor Spirit.

It is a mixture of low boiling (40-120oC) hydrocarbons such as pentane, hexane, heptane and octane. Petrol and alcohol in the ratio o 4:1 gives Power alcohol.

CH3-CH2-CH2-CH2-CH3

PentaneCH3-CH2-CH2-CH2-CH2-CH3

HexaneCH3-CH2-CH2-CH2-CH2-CH2-CH3

HeptaneCH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Octane

2. Kerosene oil

It is a mixture of higher hydrocarbons such decane to hexadecane.

It is used as a domestic fuel in stoves, as jet engine oil and for making oil gas.

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Decane

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Dodecane

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Didecane

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Tridecane

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Tetradecane

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Pentadecane

CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Hexadecane

3. Diesel oil

It is a mixture of hydrocarbons with boiling range (250-320oC).

KnockingThe metallic sound produced during irregular burning of the fuel is termed as knocking.

Straight chain alkane> branched chain alkane> Olefines> Cycloalkane> Aromatic hydrocarbons

Octane Number

The octane number of a fuel is a measure of its tendency to knock; when burnt in a spark-ignition engine.

n-hptane ----------Maximum knocking Octane number 0

Iso-octane -----------Minimum knocking Octane number 100

Tetraethy lead or Diethyl telluride: Anti knocking agents.

Cetane Number

It a measure of the ignition quality ie the antikonocking character of a diesel oil.

CrackingIt is the process of breaking up of less volatile bigger molecule of hydrocarbons from petroleum into more volatile lower molecules of hydrocarbons.

1. Thermal cracking

Fuel oil and lubricant oil are subjected to high temperature pyrolysis at about 770K and high pressure, when random cleavage of carbon-carbon bonds takes place and lower alkanes result.

A-A-A-A-A-A-A- A-A-A A-A-A A-A-A-A A-A-A-A-A-A-A+ +

2. Catalytic cracking

In this process heating is done at a lower temperature in presence of catalysts silica and alumina mixture to produce gasoline.

Gaseous Fuels

1. Natural GasIt is formed by the decomposition of organic matter under the earth and is almost always present in petroleum wells.Composition:

CH4 = 71%, C2H6 = 5-10% , H2 = 3%, CO + CO2 = restIt is a cheap convenient fuel and burns with a hot blue flame.

Uses: 1.It is an excellent fuel for

domestic and industrial purpose.

2.Manufacture of a number of chemicals by synthetic process.

3.As a raw material for the manufacture of carbon black.

4.In preparation of synthetic proteins by microbiological fermentation of methane (CH4)

2. Water GasIt is a mixture of combustible gases CO and H2 with small amounts of non-combustible CO2 and N2.

Water gas can be made by passing steam and a little air alternatively through a bed of red hot coal or coke maintained at a temperature of about 900-1000oC in a reactor.

C + O2 CO2

2C + O2 2CO

Uses: 1.As a fuel gas2.As an illuminating gas3.As a source of hydrogen gas

4.In manufacture of ammonia gas. Combination of water gas:

CO = 41%, H2 = 51%, CO2 = 4.2%, N2 = 3%, CH4 = 0.8%

3. Producer Gas

It is a mixture of CO and N2 and is prepared by blowing controlled amount of air through a deep bed of red hot coke or coal, maintained at about 1100oC in a special reactor. Composition:

CO = 30%, N2 = 52%, H2 = 13%, CH4 = 3% and CO2 = 2%

Uses: 1.For running gas engines.2.For heating open-hearth furnace

muffle furnace, retorts etc. 3.As a reducing agent in metallurgical

operations.

4. Gobar Gas (Dung Gas)Degradation of biological matter by the bacterial action in the absence of free oxygen produces, biogas.

Combination of water gas:

CH4 = 50-60%, H2 = 5-10%, CO2 = 30-40%, N2 = 2%

Uses: 1.It is mainly used as domestic cooking

gas.2.As an illuminant in villages3.As a fuel to run engines.

5. LPG (Liquefied Petroleum Gas)It is obtained as a by product, during the cracking of heavy oils and from natural gas.

The main constituents of LPG are n-butane, iso-butane, propane and butene with little or no propene and ethane.

Uses: 1.Mainly as a domestic fuel for

burning gas stove in houses.2.As a fuel in some of the

industries.3.As motor fuel.4.In laboratories in gas burners

for heating purpose.

Advantages of LPG

1.Easy to operate, to control and easy to store.

2.Higher efficiency and heating rate.3.No smoke and hence neat, clean and no

pollution.4.Easy to transport, undergoes complete

combustion.5.Cheaper than gasoline, as a motor fuel.

6. CNG (Compressed Natural Gas)It is highly compressed form of natural gas. It consists of methane and may contain small amounts of ethane and propane.

Uses: 1. In commercial vehicles such as taxis, truck, buses. Disadvantage: 2. Mainly maintaining at high pressure.3. The release of methane gas through pipe line

during transport and from vehicles due to its incomplete combustion.

Solid Fuels

1. Wood2. Charcoal Charcoal is a black porous brittle solid which can burn in air

to give CO2 and traces of CO. It is the most active form of carbon and a good adsorbent.

3. Peat The progressive transformation of wood to anthracite under

the earth, due to excessive pressure, high temperature, absence of oxygen, presence of bacteria and time.

Wood Peat Lignite

Bituminous CoalAnthracite Coal

4. Lignite It is soft, dark brown colored variety, representing second stage in the conversion of vegetable matter into coal. C= 67%, H = 6%, O = 35% and Ash = 2.5%

Uses: i) Lignites are usually dried, powdered and pressed into small briquettes and burnt as house hold fuels and for steam raising boiler fuel, ii) Most important use is in manufacture of producer gas.

5. Bituminous CoalIt is the third stage of conversion of vegetable matter into coal.

C= 75-88%, H = 5%, O = 2 % and Ash = 10%

Uses: 1.Widely used as a domestic fuel.’2.In several industries for making

metallurgical coke, coal gas and for steam raising.

6. Anthracite CoalIt is a class of highest rank coal, the last one in theformation of coal from vegetable matter. It is the hardest of all kind of coal. It is dense, black and brittle.

C= 90%, H = 3%, O = 2 % and Ash = 5%

Uses: 1. As a fuel for house hold purposes2. For steam raising3. In metallurgical purposes, where high local heat

and no smoke are desirable.

Nuclear Fuels

Otto Han discovered the fission of Uranium opened the prospects of using the vast energy stored in the atomic nucleus for the production of electric power.

1 Kg of Uranium = 3x106 Kg of high grade coal.

Mass Defect and Nuclear Energy

A B + CHigh Mass Low mass Difference is called Mass defect. That

difference is the loss of mass during the formation of the nucleus of the isotope or the actual loss of mass equivalent to the energy released during the formation of the given nucleus from individual nucleons.

Main Parts of a Typical Nuclear Reactor1. Reactor core: Consists of an assemblage of fuel elements, control rods,

coolant and moderator. The fission chain reaction takes place in this part of the

reactor and heat energy is liberates.2. Reflector: To reflect back some of the leaking neutrons. 3. Pressure Vessel: Which encloses the core and reflector.4. Shielding: To weaken the Y-rays and radiations coming out from the

reactor.5. Heat Exchanger: To transfer the heat liberated from the reactor core to

boil water and get steam.6. Turbine: To operate utilizing the steam from the heat exchanger, and to

drive a generator to produce electricity.7. Moderators: Used are graphite or beryllium or heavy water. Reduce the

KE of fast fission neutrons. 8. Control roads: Boron, steel or cadmium to absorb some neutrons.9. Coolants: Used ordinary water, heavy water, liquid metal like sodium,

organic liquids and gases. They remove heat from the reactor.

Nuclear Fusion

Nuclear fusion is the process of combination of light weight nuclei to form heavier nucleus, with the simultaneous release of energy.

Advantageous Over Fission Reaction

1.Much greater amount of energy.2.Products of fusion are non

radioactive while fission products are unstable and radioactive and hence fission products pose a waste-disposal problem.

Rocket Propellant

Fuels used in rockets for their propulsion are called propellant.

1.Solid Propellant2.Liquid Propellant3.Hybrid propellant

Solid PropellantThe first mankind Propellant.

Modern Solid Propellants are divided in to two classes.

A. Composite propellant Consists of a blend of polyurethane or

polybutadiene as fuel and ammonium perchlorate as oxidizer. Along with some finely divided Al or Mg.

B. Double base propellant Consists of nitroglycerine and

nitrocellulose, both containing the oxidizer and fuel element in the same molecule.

Liquid Propellant

A. Monoliquid propellant: Consists of a single of a single liquid chemical compound, which on decomposition or ignition gives out a large volume of hot gases. Eg: Hydrazine, Methyl nitrate, nitro methane and hydrogen peroxide.

B. Biliquid propellant: Consists of a combination of liquid fuels like kerosene, alcohol, liquid H2 or hydrazine and liquid oxidizer like liquid oxygen, dinitrogen tetroxide or nitric acid.

Hybrid Propellant

It consists of a solid fuel and a liquid oxidizer. Eg: A mixture of acrylic rubber and liquid N2O4

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