2 Recommended Books Fuels and Combustion; M.L. Smith & K.W. Stinson Fuels and Fuel Technology ; W. Francis & M.C. PetersFuel – Solid , Liquid and Gaseous; J.S.S. Brame & J.G. KingHydrocarbon Fuels; E.M. GoodgerCoal Conversion Processes; Stanley & LeeFuel Testing: Laboratory Methods in Fuel Technology; G.W. HimusMethods of Analysis of Fuels and Oils; J.R. Campbell
3 FuelA substance which produce heat either by combustion or by nuclear fission / fusion
4 Classification of Fuels Fuels can be classified as solid, liquid and gaseous fuels.Solid fuels : wood, coal, charcoal and coke Liquid fuels : petrol, kerosene, diesel, alcohol etc Gaseous fuels : methane, propane, butane, hydrogen, coal gas, gobar gas etc
5 Classification of Fuels Primary Fuels: Naturally occuing e.g. coal, wood, natural gasSecondary Fuels: Which are derived from primary fuels e.g. kerosene, coke etcNaturally occurringArtificially prepared
6 CombustionCombustion 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 ???
7 CombustionCombustion 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
8 Combustion Fuel ? Oxidizer ? Products of Combustion ? Fuel + Oxidizer => Products of combustion + EnergyFuel ?Oxidizer ?Products of Combustion ?Incomplete Combustion ?
9 Fundamental Definitions Basic Flame typesPremixed: Fuel and oxidizer are mixed first and burned laterNon-premixed: Combustion and mixing occur simultaneously
10 Combustion Air-Fuel Ratio; A/F Oxygen-Fuel Ratio; O/F Stoichiometric or Theoretical A/FExcess Air% excess air = 100[(A/F)actual - (A/F)theo ]/(A/F)theo120% of theoretical air ?Fuel- Rich flame: If there is an excess of fuelFuel - lean flame : if there is an excess of oxygen
11 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
12 CombustionProblem:A fuel contains by mass 88 % carbon, 8 % H2, 1% S and 3% ash. Calculate the stoichiometric air/fuel ratio.Ans: ?
13 Fundamental Definitions Calorific valueAmount of heat librated by the combustion of unit quantity of fuel. kcal/ kg , kcal / m3Gross Calorific Value (G.C.V) or HCVheating value measurement in which the product water vapour is allowed to condenseNet Calorific Value (N.C.V) or LCVheating value in which the water remains a vapor and does not yield its heat of vaporizationHHV = LHV + (mwater /mfuel)ʎwater
14 Fundamental Definitions Flash PointThe lowest temperature at which a liquid fuel gives enough vapours in air which produce a momentary flash when exposed to a flameFirepointThe lowest temperature at which a liquid fuel vapours in air produces a continuous flame when exposed to a flame
15 Fundamental Definitions DensitySpecific gravityViscosityPour PointCarbon Residue
16 Fundamental Definitions Theoretical Flame Temperature:It is the temperature attained by the products of combustion of fuel when there is no loss of heat to the surroundingsFlue Gas: It is the gaseous product of combustion of fuel
17 CoalOrigin of CoalCoal has been formed by the partial decay of plant materials accumulated million of years ago and further altered by the action of heat and pressureIn situ Theory: coal occupies the same site where the orignal palnts grewDrift Theory: plants were uprooted and drifted by rivers to get deposited
18 Coal classification Peat : Lignite: soft coal and the youngest sub-bituminousBituminous:semi-bituminous:Anthracite: hard and geologically the oldest composed mainly of carbon
19 Coal Analysis Proximate analysis of coal Ultimate analysis of coal Determines only fixed carbon, volatile matter, moisture and ashUseful to find out heating value (GCV)Simple analysis equipmentUltimate analysis of coalDetermines all coal component elements: carbon, hydrogen, oxygen, sulphur, etcUseful for furnace design (e.g flame temperature, flue duct design)Laboratory analysis
20 Proximate analysis Moisture Content : Moisture in coal must be transported, handled and storedSince it replaces combustible matter, it decreases the heat content per kg of coalAids radiation heat transfer1-2 gm 72 mesh coal at C till constant weight
21 Proximate analysis Volatile Matter: Consist of CH4, hydrocarbons, H2 and CO, and incombustible gases like CO2 and N2Proportionately increases flame length, and helps in easier ignition of coalSets minimum limit on the furnace height and volume72 mesh coal C for 7 minutes
22 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 efficiencyCauses clinkering1-2 gm 72 mesh 800 C (burned)
23 Proximate analysis Fixed carbon: Solid fuel left in the furnace after volatile matter is removedconsists mostly of carbonmay contains some H2, O2, S and N2gives a rough estimate of heating value of coal