Question 1.1.3: A sample of coal was found to have the following composition......
A sample of coal was found to have the following composition by weight
C = 75%; H = 5.2%; O = 12.1%; N = 3.2% and ash = 4.5%
Calculate (i) minimum amount of O_2 and air necessary for complete combustion of 1 kg of coal; (ii) weight of air required if 40% excess air is supplied.
Step-by-Step
\begin{aligned}O_2 \text{required from air} &= \text{Total} O_2 \text{required} – O_2 \text{in fuel}\\ & = 2.416 ~kg – 0.121 ~kg = 2.295 ~kg\end{aligned}
Minimum weight of air required = 2.295 × \frac{100}{ 23} = 9.978 ~kg.
Weight of excess air = 9.978 × \frac{40}{100} = 3.9912 ~kg
Total air supplied = 9.978 + 3.9912 = 13.969 kg.\quad \quad \quad [Ans = 13.969 ~kg]
| Constituent | Amount per kg of the coal sample | Combustion reaction |
Weight of \bf O_2 required
|
| C | 0.75 kg | C +O_2 \rightarrow CO_2 |
0.75 × \frac{32}{12} = 2 ~kg
|
| H | 0.052 kg | H_2 +\frac{1}{2} O_2 \rightarrow H_2O |
0.052 × \frac{16}{2} = 0.416 ~kg
|
| O | 0.121 kg | – | – |
| N | 0.032 kg | – | – |
| Ash | 0.045 kg | – | – |
| – |
\text{Total} O_2 \text{required} = 2.416 ~kg
|
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