FUELS AND COMBUSTION Fuels and Combustion Types of Fuels Complete/Incomplete Combustion Oxidation of Carbon Oxidation of Hydrogen Oxidation of Sulfur Air composition Combustion with Air Theoretical Air Hydrocarbon fuels Combustion of Hydrocarbon Fuel
Fuels and CombustionFuel: Substance composed ofchemical elements which in rapidchemical union with oxygenproduced combustion.
Combustion:Is that rapid chemical union withoxygen of an element, whoseexothermic heat of reaction issufficiently great and whose rateof reaction is suffi-ciently fastwhereby useful quantities of heatare liberated at elevatedtemperature.
Complete Combustion: Occurs when allthe combustible elements has been fullyoxidized.Ex:C + O2 → CO2Incomplete Combustion: Occurs whensome of the combustible elements has notbeen fully oxidized.Ex:C + O2 → CO
kg of air per kg of Sulfur:Sofkgairofkg4.29=32105.2832=Sofkgairofkg +
Theoretical AirIt is the minimum amount of air required tooxidize the reactants or the combustibleelements found in the fuel. With theoreticalair no O2 is found in products.
Excess AirIt is an amount of air in excess of theTheoretical requirements in order toinfluence complete combustion. Withexcess air O2 is present in theproducts.
HYDROCARBON FUELSFuels containing the element s Carbonand Hydrogen.Chemical Formula: CnHm
Family Formula Structure SaturatedParaffin CnH2n+2 Chain YesOlefin CnH2n Chain NoDiolefin CnH2n-2 Chain NoNaphthene CnH2n Ring YesAromaticBenzene CnH2n-6 Ring NoNaphthalene CnH2n-12 Ring NoAlcohols Note: Alcohols are not purehydrocarbon, because one of itshydrogen atom is replace by anOH radical. Sometimes it is usedas fuel in an ICE.Methanol CH3OHEthanol C2H5OH
Saturated Hydrocarbon: All the carbon atoms arejoined by a single bond.Unsaturated Hydrocarbon: It has two or moreadjacent Carbon atoms joined by a double ortriple bond.Isomers: Two hydrocarbons with the samenumber of carbon and hydrogen atoms but atdifferent structures.
H H H H H C C C CH H H H HChain structure SaturatedH H| |HC C=C C H| | | |H H H HChain Structure UnsaturatedRing structure SaturatedH HH C HC CH C HH H
Theoretical Air: It is the minimum or theoretical amountof air required to oxidized the reactants. With theoreticalair no O2 is found in the products.Excess Air: It is an amount of air in excess of the theo-retical air required to influence complete combustion.With excess air O2 is found in the products.Combustion of HydrocarbonFuel(CnHm)A. Combustion with 100% theoretical airCnHm + aO2 + a(3.76)N2 → bCO2 + cH2O +a(3.76)N2fuelairt kgkgm12n)a(3.76)(28a(32)FA++=
fuelaira kgkgm12n)a(3.76)(28a(32)e)(1FA+++=B. Combustion with excess air eCnHm +(1+e) aO2 + (1+e)a(3.76)N2 → bCO2+ cH2O + dO2 + (1+e)a(3.76)N2Actual Air – Fuel Ratiofuelairta kgkgFAe)(1FA+=Where: e – excess air in decimalNote: Sometimes excess air is expressible in terms oftheoretical air.Example: 25% excess air = 125% theoretical air
Orsat Analysis: Orsat analysis gives thevolumetric or molal analysis of thePRODUCTS on a DRY BASIS, (no amount ofH2O given).Proximate Analysis: Proximate analysisgives the amount of Fixed Carbon,Volatiles, Ash and Moisture, in percent bymass. Volatiles are those compoundsthat evaporates at low temperature whenthe solid fuel is heated.
ULTIMATE ANALYSIS: Ultimate analysisgives the amount of C, H, O, N, S inpercentages by mass, and sometimes theamount of moisture and ash are given.
OLID FUELSomponents of Solid Fuels:1. Carbon (C)2. Hydrogen (H2)3. Oxygen (O2)4. Nitrogen (N2)5. Sulfur (S)6. Moisture (M)7. Ash (A)
A.Combustion with 100% theoretical airaC + bH2 + cO2 + dN2 + eS + fH2O + gO2 +g(3.76)N2 → hCO2 + iH2O + jSO2 + kN2B.Combustion with excess air x:aC + bH2 + cO2 + dN2 + eS + fH2O +(1+x)gO2 +(1+x)g(3.76)N2 → hCO2 +iH2O + jSO2 + lO2 + mN2WHERE: a, b, c, d, e, f, g, h, I, j, k, x are thenumber of moles of the elements.x – excess air in decimal
S FLOW RATE OF FLUE GAS (ProducAir+Fuel → ProductsWithout considering Ash loss+= 1FAmm FgConsidering Ash loss−+= lossAsh1FAmm Fg
HeatingValueHeating Value - is the energy releasedby fuel when it is completely burned andthe products of combustion are cooled tothe original fuel temperature.Higher Heating Value (HHV) - is theheating value obtained when the water inthe products is liquid.Lower Heating Value (LHV) - is theheating value obtained when the water inthe products is vapor.
For Solid Fuels with the presence ofFuel’s ULTIMATE ANALYSISkgKJS93048OH212,144C820,33HHV 22 +−+=where: C, H2, O2, and S are in decimals from theultimate analysis
HHV = 31 405C + 141 647H KJ/kgHHV = 43 385 + 93(Be - 10) KJ/kgFor Liquid Fuelswhere: Be - degrees Baume For Coal and Oils with the absence ofUltimate AnalysisfuelofkgairofKg3041HHVFAt=
For GasolinekgKJ)API(93639,38LHVkgKJ)API(93160,41HHV°+=°+=kgKJ)API(93035,39LHVkgKJ)API(93943,41HHV°+=°+=For Kerosene
For Fuel OilsInstitutePetroleumAmericanAPIkgKJ)API(6.139105,38LHVkgKJ)API(6.139130,41HHV−°+=°+=
For Fuel Oils (From Bureau of StandardFormula)).t(.St@S 561500070API131.5141.5S−−=°+=HHV = 51,716 – 8,793.8 (S)2KJ/kgLHV = HHV - QLKJ/kgQL= 2442.7(9H2) KJ/kgH2= 0.26 - 0.15(S) kg of H2/ kg of fuel
WhereS - specific gravity of fuel oil at 15.56 °CH2- hydrogen content of fuel oilQL- heat required to evaporate and superheat the watervapor formed bythe combustion of hydrogen in the fuelS @ t - specific gravity of fuel oil at any temperature tOxygen Bomb Calorimeter - instrument used in mea-suring heating value of solid and liquid fuels.Gas Calorimeter - instrument used for measuringheating value of gaseous fuels.
Properties of Fuels and Lubricantsa)Viscosity - a measure of the resistance to flow that alubricant offers when it is subjected to shear stress.b) Absolute Viscosity - viscosity which is determined bydirect measurement of shear resistance.c) Kinematics Viscosity - the ratio of the absolute viscosto the densityd) Viscosity Index - the rate at which viscosity changes wtemperature.e) Flash Point - the temperature at which the vapor abovea volatile liquid forms a combustible mixture with air.) Fire Point - The temperature at which oil gives off vaporthat burns continuously when ignited.
g) Pour Point - the temperature at which oil will nolonger pour freely.h) Dropping Point - the temperature at which greasemelts.i) Condradson Number(carbon residue) - thepercentage amount by mass of the carbonaceousresidue remaining after destructive distillation.j) Octane Number - a number that provides ameasure of the ability of a fuel to resist knockingwhen it is burnt in a gasoline engine. It is thepercentage by volume of iso-octane in a blend withnormal heptane that matches the knocking behavior ofthe fuel.
k) Cetane Number - a number that provides ameasure of the ignition characteristics of a dieselfuel when it is burnt in a standard diesel engine. It isthe percentage of cetane in the standard fuel.Prepared By: ENGR YURI G. MELLIZA, RMEXAVIER UNIVERSITYCoralles St. Cagayan De Oro City