Fuels and Combustion
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Transcript of Fuels and Combustion
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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
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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 and cokeLiquid fuels : petrol, kerosene, diesel, alcohol etcGaseous fuels : methane, propane, butane, hydrogen, coal gas, gobar gas etc
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Classification of Fuels
Primary Fuels: Naturally occuing 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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Basic Flame types
Premixed: Fuel and oxidizer are mixed first and burned later
Non-premixed: Combustion and mixing occur simultaneously
Fundamental Definitions
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Combustion
Air-Fuel Ratio; A/FOxygen-Fuel Ratio; O/FStoichiometric or Theoretical A/F Excess Air % excess air = 100[(A/F)actual - (A/F)theo ]/(A/F)theo
120% of theoretical air ?Fuel- Rich flame: If there is an excess of fuel
Fuel - lean flame : if there is an excess of oxygen
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Combustion
1 kg of C needs ? kg of O2
1 kg of H2 needs ? Kg of O2
1 kg of Sulphur needs ? kg of O2
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Combustion
Problem:
A fuel contains by mass 88 % carbon, 8 %
H2, 1% S and 3% ash. Calculate the
stoichiometric air/fuel ratio.
Ans: ?
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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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DensitySpecific gravityViscosityPour PointCarbon Residue
Fundamental Definitions
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Theoretical Flame Temperature:
It is the temperature attained by the products of combustion of fuel when there is no loss of heat to the surroundings
Flue Gas: It is the gaseous product of combustion of fuel
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:
• semi-bituminous:
• Anthracite: hard and geologically the oldest composed mainly of carbon
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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 1-2 gm 72 mesh coal at 105-110 C till
constant weight
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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
72 mesh coal 900-950 C for 7 minutes
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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• 1-2 gm 72 mesh 800 C (burned)
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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