The document discusses fuels and combustion. It begins by listing recommended books on fuels and fuel technology. It then defines a fuel as a substance that produces heat through combustion or nuclear processes. Fuels are classified as solid, liquid, or gaseous. Primary fuels occur naturally while secondary fuels are derived from primary fuels. Combustion and the combustion process are then defined. Different types of coal and methods of coal analysis and classification are outlined. Pyrolysis, the thermal decomposition of organic material at elevated temperatures in an inert atmosphere, is also discussed.

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Fuels and Combustion

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Recommended Books
1. Fuels and Combustion; M.L. Smith & K.W. Stinson
2. Fuels and Fuel Technology ; W. Francis & M.C. Peters
3. Fuel – Solid , Liquid and Gaseous; J.S.S. Brame & J.G.
King
4. Hydrocarbon Fuels; E.M. Goodger
5. Coal Conversion Processes; Stanley & Lee
6. Fuel Testing: Laboratory Methods in Fuel
Technology; G.W. Himus
7. Methods of Analysis of Fuels and Oils; J.R.
Campbell
8. Element of fuel , furnaces and combustion
9. O.P Gupta.

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Fuel
 A substance which produce heat
either by combustion or by nuclear
fission / fusion

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Classification of Fuels
 Fuels can be classified as solid, liquid
and gaseous fuels.
 Solid fuels : wood, coal, charcoal (50% to 95%
carbon) and coke
Liquid fuels : petrol, kerosene,
diesel, alcohol etc
Gaseous fuels : methane, propane,
butane, hydrogen, coal gas, gobar gas
etc

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Classification of Fuels
 Primary Fuels: Naturally occurring
e.g. coal, wood, natural gas
 Secondary Fuels: Which are derived from
primary fuels e.g. kerosene, coke etc
 Naturally occurring
 Artificially prepared

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Combustion
 Combustion is the conversion of a
substance (called a fuel) into chemical
compounds known as products of
combustion by combination with an
oxidizer.
 The combustion process is an exothermic
chemical reaction, i.e., a reaction that
releases energy.

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Combustion
 Combustion or burning is a complex
sequence of exothermic chemical
reactions between a fuel (usually a
hydrocarbon) and an oxidant
accompanied by the production of heat
or both heat and light

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Combustion
 Fuel + Oxidizer => Products of combustion + Energy
Fuel ?
Oxidizer ?
Products of Combustion ?
Incomplete Combustion ?

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Fundamental Definitions
 Calorific value
Amount of heat librated by the combustion of unit
quantity of fuel. kcal/ kg , kcal / m3
 Gross Calorific Value (G.C.V) or HCV
heating value measurement in which the product
water vapour is allowed to condense
 Net Calorific Value (N.C.V) or LCV
heating value in which the water remains a vapor
and does not yield its heat of vaporization
 HHV = LHV + (mwater /mfuel)ʎwater

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 Flash Point
The lowest temperature at which a liquid fuel
gives enough vapours in air which produce a
momentary flash when exposed to a flame
 Firepoint
The lowest temperature at which a liquid fuel
vapours in air produces a continuous flame
when exposed to a flame
Fundamental Definitions

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 Density
 Specific gravity
 Viscosity
 Pour Point
 Carbon Residue
Fundamental Definitions

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Coal
 Origin of Coal
Coal has been formed by the partial
decay of plant materials accumulated
million of years ago and further altered
by the action of heat and pressure
 In situ Theory: coal occupies the same
site where the orignal palnts grew
 Drift Theory: plants were uprooted and
drifted by rivers to get deposited

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Coal classification
• Peat :
• Lignite: soft coal and the youngest
• sub-bituminous
• Bituminous:
• Anthracite: hard and geologically the
oldest composed mainly of carbon

15. Types
 As geological processes apply pressure to dead biotic
material over time, under suitable conditions it is
transformed successively into
 Peat, considered to be a precursor of coal, has
industrial importance as a fuel in some regions, for
example, Ireland and Finland. In its dehydrated form,
peat is a highly effective absorbent for fuel and oil
spills on land and water
 Lignite, also referred to as brown coal, is the lowest
rank of coal and used almost exclusively as fuel for
electric power generation.
 Jet is a compact form of lignite that is sometimes polished and
has been used as an ornamental stone since the Iron Age
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16. Jet
 Jet is a geological material and is
considered to be a minor gemstone. Jet
is not considered a true mineral, but
rather a mineraloid as it has an organic
origin, being derived from decaying wood
under extreme pressure.
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17. Sub-bituminous coal
 Sub-bituminous coal, whose properties range from
those of lignite to those of bituminous coal are used
primarily as fuel for steam-electric power generation.
Additionally, it is an important source of light aromatic
hydrocarbons for the chemical synthesis industry.
 Bituminous coal, dense mineral, black but sometimes
dark brown, often with well-defined bands of bright and
dull material, used primarily as fuel in steam-electric
power generation, with substantial quantities also used
for heat and power applications in manufacturing and
to make coke
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18.  Anthracite, the highest rank; a harder, glossy, black
coal used primarily for residential and commercial
space heating.
 Graphite, technically the highest rank, but difficult to
ignite and is not so commonly used as fuel: it is mostly
used in pencils and, when powdered, as a lubricant.
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Coal Analysis
Proximate analysis of coal
• Determines only fixed carbon, volatile matter,
moisture and ash
• Useful to find out heating value (GCV)
• Simple analysis equipment
Ultimate analysis of coal
• Determines all coal component elements: carbon,
hydrogen, oxygen, sulphur, etc
• Useful for furnace design (e.g flame temperature,
flue duct design)
• Laboratory analysis

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Proximate analysis
 Moisture Content :
 Moisture in coal must be transported,
handled and stored
 Since it replaces combustible matter, it
decreases the heat content per kg of coal
 Aids radiation heat transfer

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Proximate analysis
 Volatile Matter:
 Consist of CH4, hydrocarbons, H2 and CO,
and incombustible gases like CO2 and N2
 Proportionately increases flame length, and
helps in easier ignition of coal
 Sets minimum limit on the furnace height
and volume

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Proximate analysis
Ash Content :
• Ash is an impurity that will not burn
• Reduces handling and burning capacity.
• Increases handling costs.
• Affects combustion efficiency and boiler
efficiency
• Causes clinkering

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Proximate analysis
 Fixed carbon:
 Solid fuel left in the furnace after volatile
matter is removed
 consists mostly of carbon
 may contains some H2, O2, S and N2
 gives a rough estimate of heating value
of coal

24.  Pyrolysis is usually the first chemical reaction that occurs in the
burning of many solid organic fuels, like wood, cloth, and paper,
and also of some kinds of plastic.
 In a wood fire, the visible flames are not due to combustion of the
wood itself, but rather of the gases released by its pyrolysis;
 whereas the flame-less burning of embers is the combustion of
the solid residue (charcoal) left behind by it.
 Thus, the pyrolysis of common materials like wood, plastic, and
clothing is extremely important for fire safety and fire-fighting.
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25.  In practice it is not possible to achieve a
completely oxygen-free atmosphere. Because
some oxygen is present in any pyrolysis
system, a small amount of oxidation occurs.
The word is coined from the Greek-derived
elements pyr "fire" and lysis "separating".
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26.  Pyrolysis has been used since ancient times for turning wood into
charcoal in an industrial scale. Besides wood, the process can
also use sawdust and other wood waste products.
 Charcoal is obtained by heating wood until its complete pyrolysis
(carbonization) occurs, leaving only carbon and inorganic ash.
 In many parts of the world, charcoal is still produced semi-
industrially, by burning a pile of wood that has been mostly
covered with mud or bricks.
 The heat generated by burning part of the wood and the volatile
by products pyrolyzes the rest of the pile. The limited supply of
oxygen prevents the charcoal from burning too.
 A more modern alternative is to heat the wood in an airtight metal
vessel, which is much less polluting and allows the volatile
products to be condensed.
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