Q1. Natural gas containing a mixture of methane, ethane, propane, and butane is burned in a furnace with excess air.

a. One hundred k mol of a gas containing 94.4 mole% methane, 3.40% ethane, 0.60% propane, and 0.50 percent butane is to be burned with 17% excess air. Calculate the required molar flow rate of the air.

b. Let

nt(kmol/h) = molar flow of the fuel gas

x1, x2, x3, X4, = mole fractions of methane, ethane,

propane, and butane, respectively, in the fuel

Pxs = percent excess air

na (kmol/h) = molar flow rate of the air fed to the furnace

Derive an expression for na in terms of the other variables. Check the formula with the results of part (a).