Calculate the gross and net calorific value of coal having the following composition: carbon = 85%, hydrogen = 8%, sulphur = 1%, nitrogen = 2%, ash = 4%, and the latent heat of steam is 587 cal/g. (asked in MU Dec 2025)

Answer: GCV \(=9650.4\) kcal/kg; NCV \(=9227.8\) kcal/kg.

The composition adds up to 100% (85 + 8 + 1 + 2 + 4), so oxygen \(=0\%\).

Dulong's formula:

\[\text{GCV}=\frac{1}{100}\left[8080\,C+34500\left(H-\frac{O}{8}\right)+2240\,S\right]\ \text{kcal/kg}\]

\[\text{GCV}=\frac{1}{100}\left[8080\times85+34500\times(8-0)+2240\times1\right]=\frac{1}{100}\left[686800+276000+2240\right]\]

\[\text{GCV}=\frac{965040}{100}=9650.4\ \text{kcal/kg}\]

Net calorific value: 1 part of H gives 9 parts of water, so mass of water formed per gram of coal \(=0.09H\) g.

\[\text{NCV}=\text{GCV}-0.09\,H\times587=9650.4-0.09\times8\times587=9650.4-422.64\]

\[\text{NCV}=9227.76\ \text{kcal/kg}\]

(Nitrogen and ash do not contribute to the calorific value.)