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Fuels and Combustion
8/3/2019 Lect 1intro to Fuel Engg
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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 FuelTechnology; 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
l A substance which produce heat
either by combustion or by nuclear
fission / fusion
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Classification of Fuels
l Fuels can be classified as solid, liquidand gaseous fuels.
l Solid fuels : wood, coal, charcoal (50% to 95%
carbon) and cokeLiquid fuels : petrol, kerosene,diesel, alcohol etcGaseous fuels : methane, propane,
butane, hydrogen, coal gas, gobar gasetc
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Classification of Fuels
l Primary Fuels: Naturally occurring
e.g. coal, wood, natural gas
l Secondary Fuels: Which are derivedfrom primary fuels e.g. kerosene, coke etc
l Naturally occurring
l Artificially prepared
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Combustion
l Combustion is the conversion of asubstance (called a fuel) into chemicalcompounds known as products of
combustion by combination with anoxidizer .
l The combustion process is an exothermic
chemical reaction, i.e., a reaction thatreleases energy.
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Combustion
l Combustion or burning is a complex
sequence of exothermic chemical
reactions between a fuel (usually ahydrocarbon) and an oxidant
accompanied by the production of heat
or both heat and light
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Combustion
l Fuel + Oxidizer => Products of combustion + Energy
l Fuel ?
l Oxidizer ?
l Products of Combustion ?
l Incomplete Combustion ?
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Fundamental Definitions
l Calorific value
Amount of heat librated by the combustion of unitquantity of fuel. kcal/ kg , kcal / m3
l Gross Calorific Value (G.C.V) or HCV
heating value measurement in which the productwater vapour is allowed to condense
l 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
l HHV = LHV + (mwater /mfuel ) water ʎ
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l Flash Point
The lowest temperature at which a liquid fuelgives enough vapours in air which produce a
momentary flash when exposed to a flame l Firepoint
The lowest temperature at which a liquid fuelvapours in air produces a continuous flame when
exposed to a flame
Fundamental Definitions
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l Density
l Specific gravity
l Viscosity
l Pour Point
l Carbon Residue
Fundamental Definitions
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Theoretical Flame Temperature:
It is the temperature attained by theproducts of combustion of fuel whenthere is no loss of heat to thesurroundings
Flue Gas: It is the gaseous product of combustion of fuel
Fundamental Definitions
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Coal
l Origin of Coal
Coal has been formed by the partialdecay of plant materials accumulated
million of years ago and further altered bythe action of heat and pressurel In situ Theory: coal occupies the same
site where the orignal palnts grewl 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 theoldest composed mainly of carbon
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Types
l As geological processes apply pressure to deadbiotic material over time, under suitable conditions it istransformed successively into
l 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 spillson land and water
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Lignite, also referred to as brown coal, is the lowestrank of coal and used almost exclusively as fuel for electric power generation.
l Jet is a compact form of lignite that is sometimes polished andhas been used as an ornamental stone since the Iron Age
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Jet
l Jet is a geological material and isconsidered to be a minor gemstone. Jetis not considered a true mineral, but
rather a mineraloid as it has an organicorigin, being derived from decayingwood under extreme pressure.
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Sub-bituminous coal
l Sub-bituminous coal, whose properties range fromthose of lignite to those of bituminous coal are usedprimarily as fuel for steam-electric power generation. Additionally, it is an important source of light
aromatic hydrocarbons for the chemical synthesis industry.
l Bituminous coal, dense mineral, black but sometimesdark brown, often with well-defined bands of bright anddull material, used primarily as fuel in steam-electricpower generation, with substantial quantities also usedfor heat and power applications in manufacturing and tomake coke
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l Anthracite, the highest rank; a harder, glossy, black coalused primarily for residential and commercialspace heating.
l Graphite, technically the highest rank, but difficult to
ignite and is not so commonly used as fuel: it is mostlyused 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
l Moisture Content :
Ø Moisture in coal must be transported,handled and stored
Ø Since it replaces combustible matter, itdecreases the heat content per kg of coal
Ø Aids radiation heat transfer
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Proximate analysis
l Volatile Matter:
Ø Consist of CH4, hydrocarbons, H2 and CO,and incombustible gases like CO2 and N2
Ø Proportionately increases flame length, andhelps in easier ignition of coal
Ø 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
l Fixed carbon:
Ø Solid fuel left in the furnace after volatilematter is removed
Ø consists mostly of carbon
Ø may contains some H2, O2, S and N2
Ø gives a rough estimate of heating value
of coal
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l Pyrolysis is usually the first chemical reaction that occurs in theburning of many solid organic fuels, like wood, cloth, and paper,and also of some kinds of plastic.
l In a wood fire, the visible flames are not due to combustion of thewood itself, but rather of the gases released by its pyrolysis;
l whereas the flame-less burning of embers is the combustion of the solid residue (charcoal) left behind by it.
l Thus, the pyrolysis of common materials like wood, plastic, andclothing is extremely important for fire safety and fire-fighting.
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l In practice it is not possible to achieve acompletely oxygen-free atmosphere. Becausesome oxygen is present in any pyrolysissystem, a small amount of oxidation occurs.The word is coined from the Greek-derivedelements pyr "fire" and lysis "separating".
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l Pyrolysis has been used since ancient times for turning wood intocharcoal in an industrial scale. Besides wood, the process canalso use sawdust and other wood waste products.
l Charcoal is obtained by heating wood until its complete pyrolysis(carbonization) occurs, leaving only carbon and inorganic ash.
l In many parts of the world, charcoal is still produced semi-industrially, by burning a pile of wood that has been mostlycovered with mud or bricks.
l The heat generated by burning part of the wood and the volatileby products pyrolyzes the rest of the pile. The limited supply of
oxygen prevents the charcoal from burning too.l A more modern alternative is to heat the wood in an airtight metal
vessel, which is much less polluting and allows the volatileproducts to be condensed.
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