Define calorific value and write the significance of proximate analysis of coal.

Calorific value is the total quantity of heat liberated when a unit mass (or unit volume) of a fuel is burnt completely in air or oxygen. Units: kcal/kg, cal/g, kJ/kg; kcal/m³ for gaseous fuels. HCV (gross) includes the latent heat of the steam formed; LCV (net) = HCV − latent heat of steam.

Significance of proximate analysis

• Moisture: it lowers the calorific value and wastes heat in evaporation, so it should be low.
• Volatile matter: high volatile matter gives a long, smoky flame and lowers the calorific value. Such coal suits gas manufacture. Low volatile matter suits coke making.
• Ash: it lowers the calorific value, forms clinkers that block air supply, and adds handling and disposal cost, so it should be low.
• Fixed carbon: the higher the fixed carbon, the higher the calorific value and the better the coal. It also gives an idea of the rank of the coal.