Fuel is a substance which, when burnt, i.e. on coming in contact
and reacting with
oxygen or air, produces heat. Thus, the substances classified as
fuel must necessarily
contain one or several of the combustible elements : carbon,
hydrogen, sulphur, etc. In
the process of combustion, the chemical energy of fuel is
converted into heat energy.
To utilize the energy of fuel in most usable form, it is
required to transform the fuel from
its one state to another, i.e. from solid to liquid or gaseous
state, liquid to gaseous state,
or from its chemical energy to some other form of energy via
single or many stages. In
this way, the energy of fuels can be utilized more effectively and
efficiently for various
purposes.
Fuels may broadly be
classified in two ways, i.e.
(a) according to the
physical state in which they exist in nature – solid, liquid
and gaseous, and
(b) according to the
mode of their procurement – natural and manufactured
solid fuels and
thir characterstics:
Solid fuels are mainly classified into two categories, i.e. natural fuels, such as wood,
coal, etc. and manufactured fuels, such as charcoal, coke, briquettes, etc. (Table 3.1).
The various advantages and disadvantages of solid fuels are given below :
Advantages
(a) They are easy to transport.
(b) They are convenient to store without any risk of spontaneous explosion.
(c) Their cost of production is low.
(d) They posses moderate ignition temperature.
Disadvantages
(a) Their ash content is high.
(b) Their large proportion of heat is wasted.
(c) They burn with clinker formation.
(d) Their combustion operation cannot be controlled easily.
(e) Their cost of handling is high.
Charcoal and its Characteristics
Out of the mentioned various manufactured fuels, the charcoal occupies the first
place in India. In some parts of the country, for example, Mysore, huge quantities
of charcoal are being used till today in blast furnaces for reducing iron ores, etc.
and in many homes charcoal is used for cooking purposes. Charcoal is a produce
derived from destructive distillation of wood, being left in the shape of solid
residue. Charcoal burns rapidly with a clear flame, producing no smoke and
developing heat of about 6,050 cal/kg.
Coke and its Characteristics
It is obtained from destructive distillation of coal, being left in the shape of solid
residue. Coke can be classified into two categories : soft coke and hard coke. Soft
coke is obtained as the solid residue from the destructive distillation of coal in the
temperature range of 600-650oC. It contains 5 to 10% volatile matter. It burns
without smoke. It is extensively used as domestic fuel. Hard coke is obtained as
solid residue from the destructive distillation of coal in the temperature range of
1200-1400oC. It burns with smoke and is a useful fuel for metallurgical process.
3.4 LIQUID FUELS AND THEIR
CHARACTERISTICS
The liquid fuels can be classified as follows :
(a) Natural or crude oil, and
(b) Artificial or manufactured oils.
The advantages and disadvantages of liquid fuels can be summarized as follows :
Advantages
(a) They posses higher calorific value per unit mass than solid fuels.
(b) They burn without dust, ash, clinkers, etc.
(c) Their firing is easier and also fire can be extinguished easily by stopping
liquid fuel supply.
(d) They are easy to transport through pipes.
(e) They can be stored indefinitely without any loss.
(f) They are clean in use and economic to handle.
(g) Loss of heat in chimney is very low due to greater cleanliness.
(h) They require less excess air for complete combustion.
(i) They require less furnace space for combustion.
Disadvantages
(a) The cost of liquid fuel is relatively much higher as compared to solid fuel.
(b) Costly special storage tanks are required for storing liquid fuels.
(c) There is a greater risk of five hazards, particularly, in case of highly
inflammable and volatile liquid fuels.
(d) They give bad odour.
(e) For efficient burning of liquid fuels, specially constructed burners and
spraying apparatus are required
Diesel Fuel and its Characteristics
The diesel fuel or gas oil is obtained between 250-320oC during the fractional
distillation of crude petroleum. This oil generally contains 85% C. 12% H. Its
calorific value is about 11,000 kcal/kg.
The suitability of a diesel fuel is determined by its cetane value.
Diesel fuels :
consist of longer hydrocarbons and have low values of ash, sediment, water and
sulphalt contents.
The main characteristics of a diesel fuel is that it should easily ignite below
compression temperature. The hydrocarbon molecules in a diesel fuel should be,
as far as possible, the straight-chain ones, with a minimum admixture of aromatic
and side-chain hydrocarbon molecules.
It is used in diesel engines as heating oil and for cracking to get gasoline.
Kerosene Oil and its Characteristics:
Kerosene oil is obtained between 180-250oC during fractional distillation of crude
petroleum. It is used as an illuminant, jet engine fuel, tractor fuel, and for preparing laboratory gas. With the development of jet engine, kerosene has
become a material of far greater importance than it is used to be. When kerosene is
used in domestic appliances, it is always vaporized before combustion. By using a
fair excess of air it burns with a smokeless blue flame.
Heavy Oil and its Characteristics
It is a fraction obtained between 320-400oC during fractional distillation of crude
petroleum. This oil on refractionation gives :
(a) Lubricating oils which are used as lubricants.
(b) Petroleum-jelly (Vaseline) which is used as lubricants in medicines
and in cosmetics.
(c) Greases which are used as lubricants.
(d) Paraffin wax which is used in candles, boot polishes, wax paper,
tarpolin cloth and for electrical insulation purposes.
Gaseous fuels occur in nature, besides being manufactured from solid and liquid fuels.
The advantages and disadvantages of gaseous fuels are given below :
Advantages
Gaseous fuels due to erase and flexibility of their applications, possess the
following advantages over solid or liquid fuels :
(a) They can be conveyed easily through pipelines to the actual place of
need, thereby eliminating manual labour in transportation.
(b) They can be lighted at ease.
(c) They have high heat contents and hence help us in having higher
temperatures.
(d) They can be pre-heated by the heat of hot waste gases, thereby
affecting economy in heat.
(e) Their combustion can readily by controlled for change in demand like
oxidizing or reducing atmosphere, length flame, temperature, etc.
(f) They are clean in use.
(g) They do not require any special burner.
(h) They burn without any shoot, or smoke and ashes.
(i) They are free from impurities found in solid and liquid fuels.
Disadvantages
(a) Very large storage tanks are needed.
(b) They are highly inflammable, so chances of fire hazards in their use is high
Solid fuels are mainly classified into two categories, i.e. natural fuels, such as wood,
coal, etc. and manufactured fuels, such as charcoal, coke, briquettes, etc. (Table 3.1).
The various advantages and disadvantages of solid fuels are given below :
Advantages
(a) They are easy to transport.
(b) They are convenient to store without any risk of spontaneous explosion.
(c) Their cost of production is low.
(d) They posses moderate ignition temperature.
Disadvantages
(a) Their ash content is high.
(b) Their large proportion of heat is wasted.
(c) They burn with clinker formation.
(d) Their combustion operation cannot be controlled easily.
(e) Their cost of handling is high.
Charcoal and its Characteristics
Out of the mentioned various manufactured fuels, the charcoal occupies the first
place in India. In some parts of the country, for example, Mysore, huge quantities
of charcoal are being used till today in blast furnaces for reducing iron ores, etc.
and in many homes charcoal is used for cooking purposes. Charcoal is a produce
derived from destructive distillation of wood, being left in the shape of solid
residue. Charcoal burns rapidly with a clear flame, producing no smoke and
developing heat of about 6,050 cal/kg.
Coke and its Characteristics
It is obtained from destructive distillation of coal, being left in the shape of solid
residue. Coke can be classified into two categories : soft coke and hard coke. Soft
coke is obtained as the solid residue from the destructive distillation of coal in the
temperature range of 600-650oC. It contains 5 to 10% volatile matter. It burns
without smoke. It is extensively used as domestic fuel. Hard coke is obtained as
solid residue from the destructive distillation of coal in the temperature range of
1200-1400oC. It burns with smoke and is a useful fuel for metallurgical process.
3.4 LIQUID FUELS AND THEIR
CHARACTERISTICS
The liquid fuels can be classified as follows :
(a) Natural or crude oil, and
(b) Artificial or manufactured oils.
The advantages and disadvantages of liquid fuels can be summarized as follows :
Advantages
(a) They posses higher calorific value per unit mass than solid fuels.
(b) They burn without dust, ash, clinkers, etc.
(c) Their firing is easier and also fire can be extinguished easily by stopping
liquid fuel supply.
(d) They are easy to transport through pipes.
(e) They can be stored indefinitely without any loss.
(f) They are clean in use and economic to handle.
(g) Loss of heat in chimney is very low due to greater cleanliness.
(h) They require less excess air for complete combustion.
(i) They require less furnace space for combustion.
Disadvantages
(a) The cost of liquid fuel is relatively much higher as compared to solid fuel.
(b) Costly special storage tanks are required for storing liquid fuels.
(c) There is a greater risk of five hazards, particularly, in case of highly
inflammable and volatile liquid fuels.
(d) They give bad odour.
(e) For efficient burning of liquid fuels, specially constructed burners and
spraying apparatus are required
Diesel Fuel and its Characteristics
The diesel fuel or gas oil is obtained between 250-320oC during the fractional
distillation of crude petroleum. This oil generally contains 85% C. 12% H. Its
calorific value is about 11,000 kcal/kg.
The suitability of a diesel fuel is determined by its cetane value.
Diesel fuels :
consist of longer hydrocarbons and have low values of ash, sediment, water and
sulphalt contents.
The main characteristics of a diesel fuel is that it should easily ignite below
compression temperature. The hydrocarbon molecules in a diesel fuel should be,
as far as possible, the straight-chain ones, with a minimum admixture of aromatic
and side-chain hydrocarbon molecules.
It is used in diesel engines as heating oil and for cracking to get gasoline.
Kerosene Oil and its Characteristics:
Kerosene oil is obtained between 180-250oC during fractional distillation of crude
petroleum. It is used as an illuminant, jet engine fuel, tractor fuel, and for preparing laboratory gas. With the development of jet engine, kerosene has
become a material of far greater importance than it is used to be. When kerosene is
used in domestic appliances, it is always vaporized before combustion. By using a
fair excess of air it burns with a smokeless blue flame.
Heavy Oil and its Characteristics
It is a fraction obtained between 320-400oC during fractional distillation of crude
petroleum. This oil on refractionation gives :
(a) Lubricating oils which are used as lubricants.
(b) Petroleum-jelly (Vaseline) which is used as lubricants in medicines
and in cosmetics.
(c) Greases which are used as lubricants.
(d) Paraffin wax which is used in candles, boot polishes, wax paper,
tarpolin cloth and for electrical insulation purposes.
Gaseous fuels occur in nature, besides being manufactured from solid and liquid fuels.
The advantages and disadvantages of gaseous fuels are given below :
Advantages
Gaseous fuels due to erase and flexibility of their applications, possess the
following advantages over solid or liquid fuels :
(a) They can be conveyed easily through pipelines to the actual place of
need, thereby eliminating manual labour in transportation.
(b) They can be lighted at ease.
(c) They have high heat contents and hence help us in having higher
temperatures.
(d) They can be pre-heated by the heat of hot waste gases, thereby
affecting economy in heat.
(e) Their combustion can readily by controlled for change in demand like
oxidizing or reducing atmosphere, length flame, temperature, etc.
(f) They are clean in use.
(g) They do not require any special burner.
(h) They burn without any shoot, or smoke and ashes.
(i) They are free from impurities found in solid and liquid fuels.
Disadvantages
(a) Very large storage tanks are needed.
(b) They are highly inflammable, so chances of fire hazards in their use is high
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