- Calorific Value Definition: The calorific value is defined as the amount of heat produced by the complete combustion of one unit of fuel.
- Units for Solid Fuels: The calorific value of coal is measured in calories per gram or kilocalories per kilogram.
- Units for Liquid Fuels: Liquid fuels, such as diesel, have their calorific value measured in calories per litre or kilocalories per litre.
- Units for Gaseous Fuels: Gaseous fuels have their calorific value measured in calories per cubic metre.
- Examples of Calorific Values: Lignite (5000 kcal/kg), Diesel (11,000 kcal/litre), and Natural gas (560 kcal/m³).
Steam plants burn coal, oil or gas to raise steam and generate electricity. In thermal power generating plants the calorific value of a fuel is the heat released when one unit of that fuel burns completely. Solids are quoted per kilogram. Liquids are quoted per kilogram or per litre. Gases are quoted per cubic metre. Gross (higher) value includes the heat in the water vapour. Net (lower) value subtracts that latent heat.
For coal, 1 cal/g is the same number as 1 kcal/kg. Oil is often given in kcal/kg as well as kcal/litre, because a litre of oil weighs less than a kilogram. Plant gas figures use cubic metres at a stated temperature and pressure. A single textbook number is only a typical grade. Moisture, ash and gas mix move the result.
The list below repeats common teaching figures. Treat them as order-of-magnitude values, not a certificate for a named cargo.
- Lignite is often listed near 5000 kcal/kg in notes. UN energy definitions put moist lignite below about 4165 kcal/kg, so 5000 kcal/kg is high for true lignite and closer to sub-bituminous coal.
- Bituminous coal is often listed near 7600 kcal/kg. Measured gross values commonly sit around 5700 to 8000 kcal/kg.
- Anthracite is often listed near 8500 kcal/kg. A typical gross value is closer to 7500 to 8000 kcal/kg.
- Heavy fuel oil is often listed near 11,000 kcal/kg. Residual oil is usually closer to 10,000 kcal/kg on a gross basis.
- Diesel oil is often listed near 11,000 kcal/kg. The figure matches a typical gross value of about 45 MJ/kg.
- Petrol is often listed near 11,110 kcal/kg. Treat that as a rounded typical gross value, not a laboratory result to four figures.
- Natural gas is listed here as 560 kcal per cubic metre. Pipeline natural gas is far hotter, about 8400 to 9600 kcal/m³ (about 35 to 40 MJ/m³). 560 kcal/m³ is in the range of weak manufactured gases, not sales gas.
- Coal gas (town gas) is listed here as 7600 kcal per cubic metre. Historic town gas was usually nearer 4000 to 5000 kcal/m³. 7600 kcal/m³ is closer to rich gas or natural gas.
