It is a substance which releases heat energy on combustion. The principal combustible elements of each fuel are carbon and hydrogen.
Primary Fuels: These fuels directly available in nature, Ex: Wood, Peat, Lignite coal, Petroleum and Natural gas.
Secondary Fuel: These are prepared fuels, Ex: Coke, Charcoal, Briquettes, Kerosene, fuel oil, petroleum gas, producer gas etc.
Fuels are also classified as Solid fuels, liquid fuel and Gaseous fuel.
Different types of coals: Peat, Lignite, Bituminous coal, Anthracite coal and Coke.
Gaseous fuels:Natural gas, Coal gas, Coke oven gas, Blast furnace gas, producer gas, Water gas and Sewer gas.
Energy producing elements in fuel: Carbon, oxygen, hydrogen and Sulphur.
Formation of Charcoal & Coke:
Charcoal:It is obtained by destructive distillation of wood.
Coke is formed by destructive distillation of certain types of coal.
Calorific value of fuel: Calorific value (GCV) is the amount of heat released on complete combustion of unit quantity of fuel.It is measured in kcal/kg.
GCV is also known as Higher Calorific Value (HCV),it is given by following formula
GCV or HCV = (8084 X C% + 28922 X (H2%–O2%/8) + 2224 X S%)/100…kcal/kg
Where C, H2, O2 and S are percentage of Carbon, hydrogen, oxygen and Sulphur respectively in fuel.
Net Calorific Value (NCV) or Lower Calorific Value (LCV):
LCV = HCV – (9 X H2% X 586), Where H2 = Hydrogen% in fuel and 586 is latent heat of steam
Useful heat Value (UHV) of coal:
NCV = GCV - 10.02 X Percentage of total moisture.
Ultimate analysis:Ultimate analysis indicates the various elemental chemical constituents such as Carbon, Hydrogen, Oxygen, Sulphur etc.
Proximate analysis of coal:Proximate analysis determines fixed carbon, Volatile matter, moisture and percentages of ash.
Volatile Matter (VM) & is its significance:
VM is generally a composition of methane, hydrocarbons, hydrogen and carbon monoxide and other incombustible gases like CO2 and Nitrogen. It is the indication of presence of gaseous fuel in the fuel.
- Helps in easy ignition of coal by increasing the flame length
- Sets minimum limit on the furnace height and volume.
- Silica (SiO2)
- Aluminum oxide (AlO3)
- Iron Oxide (Fe2O3)
- Sodium Oxide (Na2O)
- Potassium Oxide (K2O)
- Calcium Oxide (CaO)
- Magnesium Oxide or Magnesia (MgO)
- Temperature: High enough to maintain the ignition of the fuel.
- Turbulence: Is the mixing of fuel and air.
- Time: Sufficient enough for combustion.