04 fuels & combustion calculation09
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This document discusses different types of fuels and their properties. It covers solid, liquid, and gaseous fuels. For each fuel type, it lists relevant properties like heating value, composition, viscosity, etc. It also discusses concepts like stoichiometry, excess air, flue gas composition and volume, heating values and calculations to determine air required and flue gas produced when combusting different fuels.
![BASIS OF ANALYSIS
AS RECEIVED
Ultimate C +H +O +N +S +A +M =100
Proximate VM +FC +M +A = 100
AIR DRY [100C/(100-Ma)]
DRY ASH FREE [100C/(100-M-A)]](https://image.slidesharecdn.com/04fuelscombustioncalculation09-140331080648-phpapp01/85/04-fuels-combustion-calculation09-8-320.jpg)
![II-1 CHEMICAL REACTIONS
Combustion
C + O2 = CO2 + 32,790 kJ/kg of carbon,
Heat of formation at 25C is 393.7 kJ/mol [Perry p-2-188]
mCn Hm + (n +m/4)O2 = nCO2 + m/2 H2O + Q
S + O2 = SO2 + 9260 kJ/kg of sulfur
Calcination
CaCO3 = CaO + CO2 – 1830 kJ/kg of CaCO3gCO3
= MgO + CO2 – 1183 kJ/kg of MgCO3.
Sulfation
CaO + SO2 + 1/2 O2 = CaSO4 + 15141 kJ/kg S.](https://image.slidesharecdn.com/04fuelscombustioncalculation09-140331080648-phpapp01/85/04-fuels-combustion-calculation09-10-320.jpg)
![Limestone required for S capture
Limestone required for
unit mass of fuel
[R = Calcium to Sulfur molar
ratio]
If appreciable amount
of CaO is present in
coal ash replace R
with R’
R
X
S
Lq
caco332
100
S
X
RR cao
56
32
'](https://image.slidesharecdn.com/04fuelscombustioncalculation09-140331080648-phpapp01/85/04-fuels-combustion-calculation09-13-320.jpg)
![AIR REQUIRED/mass fuel burnt
Theoretical dry air requirement
Mda= [11.53 C + 34.34 (H – O/8) + 4.34 S+ A.S]
kg/kg coal
where A = 2.38 for S-capture;
= 0 for no S-capture
Actual dry air required
Tda = Excess air Coeff. X Mda kg/kg
Actual wet air required
Mwa = Tda (1 + Xm).](https://image.slidesharecdn.com/04fuelscombustioncalculation09-140331080648-phpapp01/85/04-fuels-combustion-calculation09-15-320.jpg)
![SOLID WASTE PRODUCED
Solid residues = Ash + Spent sorbents
Spent sorbents = CaSO4+CaO+MgO+inert
Wa = [Lw + ASH + (1 – Ec) – Xcao],
Gas product = CO2+H2O+N2+O2+SO2+Fly ash
inert
mgcosorcaco
sor LqX
LqXSELqX
E
S
Lw
84
40
32100
56
32
136
33](https://image.slidesharecdn.com/04fuelscombustioncalculation09-140331080648-phpapp01/85/04-fuels-combustion-calculation09-17-320.jpg)
04 fuels & combustion calculation09
- 1. Prabir Basu FUELS & COMBUSTION CALCULATIONS Unit 5
- 2. TYPES OF FUELS FOSSIL FUELS Solid fuels (COAL) Liquid fuels (OIL) Gaseous fuels (NATURAL GAS) NUCLEAR FUELS RENEWABLE FUELS (BIOMASS) WASTE FUELS (MUNICIPAL WASTES)
- 3. SOLID FUELS PROPERTIES HEATING VALUE ULTIMATE ANALYSIS PROXIMATE ANALYSIS ASH DEFORMATION POINTS Initial deformation temp. Softening temp. Hemispherical temp Fluid temp.
- 4. LIQUID FUELS PROPERTIES HEATING VALUE FLASH POINT IGNITION POINT (SELF, FORCED) VISCOSITY POUR POINT SULFUR ASH
- 6. Distillation
- 7. GASEOUS FUEL PROPERTIES HEATING VALUE COMPOSITION DENSITY
- 8. BASIS OF ANALYSIS AS RECEIVED Ultimate C +H +O +N +S +A +M =100 Proximate VM +FC +M +A = 100 AIR DRY [100C/(100-Ma)] DRY ASH FREE [100C/(100-M-A)]
- 9. HEATING VALUE HIGHER HEATING VALUE (GROSS) LOWER HEATING VALUE (NET) LHV = HHV – LH of steam (9H/100+M/100)
- 10. II-1 CHEMICAL REACTIONS Combustion C + O2 = CO2 + 32,790 kJ/kg of carbon, Heat of formation at 25C is 393.7 kJ/mol [Perry p-2-188] mCn Hm + (n +m/4)O2 = nCO2 + m/2 H2O + Q S + O2 = SO2 + 9260 kJ/kg of sulfur Calcination CaCO3 = CaO + CO2 – 1830 kJ/kg of CaCO3gCO3 = MgO + CO2 – 1183 kJ/kg of MgCO3. Sulfation CaO + SO2 + 1/2 O2 = CaSO4 + 15141 kJ/kg S.
- 11. Basic Stoichiometry C + O2 = CO2 + q 1 kmol of carbon combines with 1 kmol of oxygen to produce 1 kmol of carbon dioxide and release q amount of heat. 1 kmol of reactant = M kg of the reactant when M is the molecular weight of the reactant. So mass of one kmol of oxygen (O2) is 2x16 = 32 kg 1 kmol of a gas occupies 22.4 nm3 at 00C 1 atm
- 12. BASIC EQUATION 1. C + O2 = CO2 kJ/kg carbon 2. H2 + ½ O2 = H2O 3. S + O2 = SO2 4. Adding oxygen requirements of above eqns and subtracting the oxygen in fuel we get the total oxygen required VO2= (1.866C + 5.56H + 0.7S - 0.7O) Nm3/kg 5. Since air contains 21% oxygen by volume, the air required is VAir = VO2/0.21 = 8.89 (C + 0.375S) + 26.5 H - 3.3O Nm3/kgf
- 13. Limestone required for S capture Limestone required for unit mass of fuel [R = Calcium to Sulfur molar ratio] If appreciable amount of CaO is present in coal ash replace R with R’ R X S Lq caco332 100 S X RR cao 56 32 '
- 14. EXCESS AIR •Owing to imperfect mixing combustion always needs a little extra oxygen. It is known as excess air. •Excess air coefficient = Actual air/ Theoretical air •Total excess air at exit = excess air at entry + leakage (negative draft) •Flue gas volume VG = Vg + (exair-1)Vair(1+Xm) Nm3/kgFuel
- 15. AIR REQUIRED/mass fuel burnt Theoretical dry air requirement Mda= [11.53 C + 34.34 (H – O/8) + 4.34 S+ A.S] kg/kg coal where A = 2.38 for S-capture; = 0 for no S-capture Actual dry air required Tda = Excess air Coeff. X Mda kg/kg Actual wet air required Mwa = Tda (1 + Xm).
- 16. TYPICAL EXCESS AIR COEFFICIENT PF Slag tap Bubbling CFB Oil & Gas Oil & Gas Anthracite Bituminus All fuels All fuel Negative pressure Positive pressure 1.2-1.25 1.15-1.2 1.3-1.5 1.2 1.08-1.07 1.05-1.07
- 17. SOLID WASTE PRODUCED Solid residues = Ash + Spent sorbents Spent sorbents = CaSO4+CaO+MgO+inert Wa = [Lw + ASH + (1 – Ec) – Xcao], Gas product = CO2+H2O+N2+O2+SO2+Fly ash inert mgcosorcaco sor LqX LqXSELqX E S Lw 84 40 32100 56 32 136 33
- 18. Flue gas volume per kg fuel VCo2= 1.866C+0.7 RS Nm3/kgFuel VSO2 = 0.7S (1-Esor) Nm3/kgFuel VN2=0.79 VAIR+ 0.8 N Nm3/kgFuel where Vair is the volume of air required per kg fuel VH2O= 11.1H+1.24W+1.6Xm .VAIRNm3/kgFuel Flue gas volume, Vg = Vco2+Vso2+VN2+ VH2O Nm3/kgFuel
- 19. Mass of gaseous products/kg fuel Carbon dioxide produced per kg fuel N2 = N + 0.768Mda.EAC Oxygen = O + 0.231Mda(EAC - 1) + (1 - Esor)S/2 In case of no sulfur capture last term is zero Sulfur-dioxide = 2S(1- Esor) Fly ash = ac x ASH; where ac = fraction of ash as fly ash 3 3 2 84 100 1 32 44 66.3 caco mgco CO X XSR CW
- 20. Mass of flue gas Total mass of flue gas per unit mass of fuel burnt where Mwa is the weight of wet air per unit fuel. For no sulfur capture Esor = 0 = R = Lq , and 2.5S should be 2.0S Wc Mwa 0.231Mda 3.66C 9H Mf Lq Xml N O 2.5S(1 Esor) ac ASH 1.375SR 1 1.19 XMgCO3 XCaCO3
- 21. Heating Value (approximate) Higher heating value = 33,823 C+144249(H-O/8)+9418S kJ/kg Lower heating value LHV = HHV – 22604H -2581M kJ/kg
- 22. Problem Composition of #2 heating oil is given as: C- 86.4%, H-13.33%, S – 0.15%; O – 0.04%, N – 0.06%, Ash – 0.02%. Find A) Composition of the fuel on) Dry ash free basis B) Higher heating value C) Lower heating value D) amount of dry air required to burn 1 kg fuel E) If the amount of air in flue gas is 5% what was the amount of air used /kg fuel