Ailer is fired using 200 kg hr of pure

Question

Combustion problem NO - 14

A boiler is fired using 200 kg /hr of pure saturated hydrocarbon gas ( Cn Hm ) at atmospheric pressure and 20 oc. The dry analysis of the flue gas which leaves the boiler at atmospheric pressure and 300 ^oc is CO₂ = 12%
CO₂ =12% , O₂ = 3% , N₂ =80 % ,

Estimate the formula of the fuel and total volumetric rate of the gas .

SOLUTION -

Basis - 100 kg mole of dry flue gas-
O₂ in flue gas = 85 kg mole
O₂ supplied by air = 85 *21/79 = 22.59 kg mole
O₂ reported in flue gas = O₂ as CO₂ + O₂ as O₂ = 12+3.0 =15 .0 kg mole
O₂ unaccounted = O₂ reacted with H₂ = 22.59 -15.0 =7.59 kg mole
H₂ REACTED =7.59*2 = 15.18 kg mole = 15.18 *2 =30.36 kg mole

Formula of the fuel ( hydrocarbon ) gas -
Atom of carbon = 12 kg atom
Amount of hydrogen = 30.36 atom
Atom of H /Atom of C = 30.36/12 = 2.53
As the ratio is more than 2.0 , hence it is paraffin of formula , C_nH_2n +2
Hence , n /2n+2 = ½.53
N = n =3.77 = 4.0

Hence the fuel is n- butane = C₄H₁₀
Volumetric flow rate --
Amount of fuel = 200/58 = 3.45 kg mole/hr
Assuming ideal gas , volume at 20^oc and 1 atomsphere . is-
V= n.R.T/P = 3.45 *0.082 *(273+20) /1.0 = 82.95 m3 /hr