Classification of fuels
1. Solid fuels
Natural solid fuels are readily available in nature. Example wood, peat, lignite, bituminous coal, anthracite coal etc.
Wood is used in places where waste wood is available in large quantity. Peat is not widely used because it has lower heating value. Lignite is an intermediate product between peat and bituminous coal. It has more moisture content and lower heating value. Bituminous coal contains very little moisture and high carbon. This is mostly used for power generation in thermal power plants. Anthracite coal is the final stage of coal formation. It is used for domestic purposes because of its smokeless combustion. It has higher heating value. It is also used for thermal power plants.
Artificial solid fuels are prepared fuels. Examples: Charcoal, coke, briquetted coal, pulverized coal etc.
Charcoal is prepared by the dry distillation of wood. It is the best fuel since it has no sulphur content. But it is costly Coke is obtained by destructive distillation of soft coals in closed retorts. Briquetted coal is obtained by briquetting the dried coal by applying pressure alone. Pulverised coal is obtained by pulverized the low grade fuels.
2. Liquid Fuels
Liquid fuels are obtained from natural petroleum. They are used in internal combustion engines and also for steam raising purposes. Gasoline, paraffin, diesel oil, crude oil are the examples of liquid fuels.
Advantages of liquid fuels
1. They have a higher calorific value.
2. They require less space than solid fuels.
3. Consumption is easily controlled.
3. Gaseous fuels
Fixed composition gases are acetylene, methane, ethylene and ethane. Composite industrial gases are blast furnace gas, coke over gas, producer gas, illuminating gas, blue water gas, carbureted water gas etc.
Blast furnace gas is a by-product in the production of pig iron in the blast furnace. It is used for power generation or steam raising in boilers or for preheating the blast furnace. Coke oven gas is obtained by destructive distillation of coal in closed retorts. It is used for industrial heating and power generation. Producer gas is obtained from the incomplete combustion of coke or charcoal. It has a lower calorific value. Its major constituent is nitrogen, as inert gas. Illuminating gas is also prepared as coke even gas. It is also used for industrial heating and power generation. Blue water gas is produced in a generator by passing steam through red hot coke. Carburetted water gas is obtained by blowing steam through incandescent bed of fuel containing carbon. By adding unsaturated hydrocarbons, this gas is used for domestic purposes.
Advantages of gaseous fuels
1. Physical handling of gaseous fuel is not required. It may be easily piped into the furnace.
2. It is free from ashes and other foreign matters.
3. It burns completely.
4. It produces less smoke with a low percentage of excess air.
5. In high temperature work, it is economical than coal or oil.