Question

a fuel gas containing 95% methane 5% N2 is burnt in a boiler furnace with 150% excess air. 86% of the methane goes to formation of CO2. 10% to CO and 4% remains unburnt. Calculate the composition of stack gas

Answer 1

$CH_4+ 2O_2 \rightarrow CO_2 +2 H_2O$

$2CH_4+3O_2 \rightarrow 2CO +4H_2O$

Let it be 1 mole of methan. Then 0.86 mole goes to formation of CO₂. As we can see from reaction it form 0.86 mole of CO₂.

0.1 mole goes to formation of CO. As we can see from reaction we get 0.1 mole CO.

And 0.04 mole of CH₄ remained.

Also in fuel gas was N₂ $\frac{1x5}{95}=0.05 mole$

So composition of stack gas is $CO_2:CO:NH_4:N_2 = 0.86:0.1:0.04:0.05=21.5:2.5:1:1.25$