A fuel is analyzed and found to contain; 75.0 wt% methane, 10.0% ethane, 5.0% ethylene and the balance water. The flowrate of the fuel is 102.7 kg/h. Calculate the molar composition of this gas on both a wet and a dry basis and the ratio(mol H2O/ mol dry gas). If tgis fuel is to be burned with 28% excess air, what is the required air feed rate (kmol/h)? How would the answer change if the combustion were only 40% complete?
Assuming 100 g of gas, calculate the moles of each component and their mole fractions with a wet basis (with water) and a dry basis (without water) :
n(CH4) = 4.67 mol
n(C2H6) = 0.332 mol
n(C2H4) = 0.178 mol
n(H2O) = 0.544 mol
n(wet) = 5.724 mol
n(dry) = 5.724 - 0.544 = 5.18
Ratio = n(H2O)/n(dry) = 0.544/5.18 = 0.105
To find the ratio of water to dry moles of gas we write the balanced equations for the combustion occuring:
CH4 + 2O2 = CO2 + 2H2O
C2H6 + 3.5O2 = 2CO2 + 3H2O
C2H4 + 3O2 = 2CO2 + 2H2O
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