In coke-making, it is often required to calculate the amount of coke, coke oven gas and tar produced per ton of coal. This can be done by performing elemental balance. For this purpose ash, C, N, H and O balance can be done to obtain the required information. This is illustrated by the following problem

1) By product coke ovens are surrounded by air. There may occur leakage of air in the oven. Consider a coke- oven surrounded by moist air, (The air is at 750 mm Hg pressure and  temperature) . The relative humidity of air is 40%. It carbonizes coal of the composition (Wt%)  C 76.1, H 4.6, N 2.3, S 1.9,O 2.5,  6.3 and ash 6.3. The following product and by products are produced:

Product:

By –product: (a)

and  C₆H₆ 1.1, C₂H₄ 2.7, CH₄ 4.4, CO 1.7, CO₂ 1.3, H₂ 36.5, N₂ 6.9, O₂ 2, H₂S 2.1 and NH₃ 1.3

(b)

,   and rest incombustibles .