Form combustion

Page 1

Full combustion (solid fuel) MA yi Xi C 12 kgC/kmolC C kgC/kgFuel O2 0,21 kmolO2/kmolAir H 1 kgH/kmolH H kgH/kgFuel N2 0,79 kmolN2/kmolAir O 16 kgO/kmolO O kgO/kgFuel S 32 kgS/kmolS S kgS/kgFuel MMair 28,84 kgAir/kmolAir N 14 kgN/kmolN N kgN/kgFuel This form is valid for exercises that assume simplified composition of air Moisture kgH2O/kgFuel If other species are present (e.g. nitrogen, argon, water…) the above written Ash kgAsh/kgFuel general reaction is not correct ni C kmolC/kgFuel ε - Excess of air H kmolH/kgFuel βst,O2 kmolO2/kgFuel Stoichiometric O2/Fuel ratio O kmolO/kgFuel βst,Air kmolAir/kgFuel Stoichiometric Air/Fuel ratio S kmolS/kgFuel βAir kmolAir/kgFuel Air/Fuel ratio (molar basis) N kmolN/kgFuel α kgAir/kgFuel Air/Fuel ratio (mass basis) Moisture kmolH2O/kgFuel φ - Equivalence ratio Ash kmolAsh/kgFuel a kmolCO2/kgFuel XCO2 b kmolH2O/kgFuel XH2O c kmolSO2/kgFuel XSO2 d kmolN2/kgFuel XN2 e kmolO2/kgFuel XO2 n°molgas kmolFG/kgFuel MMgas kgFG/kgFuel Coal mass comp. Air compositionElement Coal molar comp. Flue gases composition CnCHnHOnOSnSNnN + nH2O H2O + βair st XO2O2 + XN2N2 → a CO2 + b H2O + c SO2 + d N2 + e O2 βO2 st = nC+ nH 4 + nS− nO 2 βair st = βO2 st XO2 βair = βair st ∙ 1 + ϵ α = βair ∙ MMair ni = yi MAi ϕ = 1 1 + ϵ = αst α a = nC b = nH 2 + nH2O c = nS d = nN 2 + βairXN2 e = nO 2 + βairXO2 − nC− nH 4 − nS n°molgas = a + b + c + d + e XCO2 = a n°molgas XH2O = b n°molgas XSO2 = c n°molgas XN2 = d n°molgas XO2 = e n°molgas MMgas = i=CO2 O2 Xi ∙ MMi Energy balance of the boiler: Data Value Unit Tin air C° Tin fuel C° Tstack C° Tash C° ξ*100 - LHV kJ/kgFuel η - First form: Q kWth α kgAir/kgFuel mair kg/s mfuel kg/s yash kgAsh/kgFuel cpair kJ/kgK Second form: cpfuel kJ/kgK cpflue gas kJ/kgK cpash kJ/kgK Adiabatic flame temperature: TAD C° Under the…