Question

suppose use air( 79 % mole N2 and 21 % mole O2, molecular weight of 29) in place of O2 in the process. Why would we choose to use air instead of O2?. How many kg/hr of air are required to deliver the 3200 kg/hr of O2 to the process?

Answer 1

Most easy answer would be that air is cheaper than O2. Using air also allows us to have a better control over the combustion process and the amount of products and side products If any be formed.

If we use air instead of O2

We know air has,

0.21 mol of O2 and 0.79 mol of N2

Converting to mass fraction,

0.21 moles of O2 = 0.21 x 32 = 6.72

0.79 moles of N2 = 0.767

So, for 3200 kg of O2 we would have = 3200 x 0.767/0.233 = 10534 kg of N2

So total air requirement would be = 10534 + 3200 = 13734 kg/hr

thus we would require, 13734 kg/hr of air for required 3200 kg/hr of O2 for the process