I have an assignment where i need to calculate how much air is needed to completely combust 100kg of a dry fuel with the masspercentages:

C 75%

H 6.2%

S 2.8%

O 12%

and some minerals that do not react.

it is specified that the combustion of the fuel only creates CO

_{2}, H

_{2}O and SO

_{2}we consider the air to be made of 21% O and 79% N.

the answer is to be multiplied with an excess air coefficient of λ=1.8.

I have tried some different calculation methods but none of them give me the solution stated in the book.

The book has 62.4 Kmol air as the solution.

I hope someone is able to help me as i am quite stuck with the assigenment.