A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butane (C4H8) by volume. It is to be fed to the combustion chamber in 10% excess air at 25°C, where it is completely burnt to carbon dioxide and water. The flue gases produced are to be used to generate 5 bar steam from water at 90°C.

A: Determine the actual fuel:air ratio by mass

B: Calculate

(i)               The net calorific value per m3 of the fuel/air mix at 25°C

(ii)             The net CV per kmol of the fuel/air mix at 25°C

Data:

Net calorific value (MJm-3) at 25°C of;

Butane = 111.7 MJm-3

Butane = 105.2 MJm-3

Propane = 85.8 MJm-3

Air is 21% oxygen, 79% nitrogen by volume and 23.3% oxygen and 76.7% nitrogen by mass

Atomic mass; C=12, O=16, N=14, H=1