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Fuels and combustion (2014)
 

Fuels and combustion (2014)

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  • THEORETICAL AIR and EXCESS AIR
  • THEORETICAL AIR and EXCESS AIR

Fuels and combustion (2014) Fuels and combustion (2014) Presentation Transcript

  • FUELSandCOMBUSTIONBy. Engr. Yuri G. Melliza
  • 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.
  • TYPES OF FUELS Solid Fuelsex: Wood, coal, charcoal Liquid Fuelsex: gasoline, diesel, kerosene Gaseous Fuelsex: LPG, Natural Gas, Methane Nuclear Fuelsex: UraniumCombustible Elements1.Carbon (C) 3. Sulfur (S)2.Hydrogen (H2)
  • 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
  • Common Combustion GasesGAS MOLECULARWeight (M)C 12H 1H2 2O 16O2 32N 14N2 28S 32
  • HE COMBUSTION CHEMISTRYOxidation of Carbon118344361232)1(121(16)1(12)BasisMass111BasisMoleCOOC 2→+→++→+→+→+ 2
  • Oxidation of Hydrogen981181622)1(16(32)1(2)BasisMass11BasisMoleOHOH21212→+→++→+→+→+ 22 21
  • Oxidation of Sulfur21164323232)1(32(32)1(32)BasisMass111BasisMoleOSOS→+→++→+→+→+122
  • Composition of AIRa. Percentages by Volume (bymole)O2 = 21%N2 = 79%b. Percentages by MassO2 = 23%N2 = 77%7632179.==22OofMoleNofMoles
  • Combustion with AirA. Combustion of Carbon with airC + O2 + 3.76N2 → CO2 + 3.76N2Mole Basis:1 + 1 + 3.76 → 1+ 3.76Mass Basis:1(12) + 1(32) + 3.76(28) → 1(44) +3.76(28)12 + 32 + 3.76(28) → 44 + 3.76(28)3 + 8 + 3.76(7) → 11+ 3.76(7)
  • kg of air per kg of Carbon:Cofkgairofkg11.44=33.76(7)+8=Cofkgairofkg
  • B. Combustion of Hydrogen with airH2 + ½ O2 + ½ (3.76)N2 → H2O +½(3.76)N2Mole Basis:1 + ½ + ½(3.76) → 1 + ½(3.76)Mass Basis:1(2) + ½ (32) + ½(3.76)(28) → 1(18) +½ (3.76)(28)2 + 16 + 3.76(14) → 18 + 3.76(14)1 + 8 + 3.76(7) → 9 + 3.76(7)
  • kg of air per kg of Hydrogen:22 Hofkgairofkg34.32=13.76(7)+8=Hofkgairofkg
  • C. Combustion of Sulfur with airS + O2 + 3.76N2 → SO2 + 3.76N2Mole Basis:1 + 1 + 3.76 → 1 + 3.76Mass Basis:1(32) + 1(32) + 3.76(28) → 1(64) +3.76(28)32 + 32 + 105.28 → 64 + 105.28
  • 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 CH   H H H HChain structure SaturatedH H| |HC 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++=
  • Combustion of Hydrocarbon FuelFormula: (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
  • fuelkgairkg18f32e28d32c2b12a3.76(28)g32gFAt ++++++=Theoretical air-fuel ratio:Actual air-fuel ratio:[ ]fuelkgairkg18f32e28d32c2b12a3.76(28)g32gx)(1aFA+++++++=
  • 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