FOSSIL FUELS - Energy Source

 CONVENTIONAL SOURCES OF ENERGY:

• The fuels derived from wood , coal and petroleum such as charcoal , coke , coal gas , Petrol , diesel , kerosene , fuel oil and liquefied petroleum gas ( LPG ) are  known as conventional sources of energy ( or conventional fuels )

 

 FOSSIL FUELS :

• The  fuels which are present  under the earth crust over a very , very long time are called fossil fuels.

• Fossil fules cannot be prepared  again when exhausted.

• Coal , petroleum and natural gas are fossil fuels .

• Fossil fuels are the major source of energy for generating electricity in power plants 

How Fossil Fuels Were Formed :

• The plants and animals which died millions of years ago , were gradually buried deep in  the earth and got covered with sediments like mud and sand.,

• In the absence of oxygen,  bacteria  converted the buried remains of plants and animals into fossil fuels under high  pressure and heat.

• Buried remains of large plants were converted into coal.

• Small plants and animals were converted into petroleum and natural gas .

 Is sun the Ultimate Source of Fossil Fuels :

• Fossil fuels are energy-rich compounds of carbon which were originally made by the plants with the help of sun's energy (solar energy). Without sunlight, there could have been no coal, petroleum natural gas.

• The green plants need sunlight energy to grow. They get this energy from sunlight, and store it in the form of carbon compounds. So, every leaf and every bit of wood in the plant was made with the energy of sunlight.

COAL:

• Buried remains of large plants were converted into coal. 

• Coal is a complex mixture of compounds of carbon , hydrogen and oxygen , and some free carbon .

• Small amounts of nitrogen and sulphur compounds are also present in coal.

• When coal is burnt , the carbon present in coal reacts with the oxygen of air to form carbon dioxide .

•  A lot of heat is produced during the burning of coal which makes it a good fuel . The burning of coal produces a lot of smoke which pollutes the air .

Uses of Coal:

• Coal is used as a fuel for heating purposes in homes and in industry .

• Coal is used as a fuel in thermal power plants for generating electricity .

• Coal is used to make coke .

• Coal is used in the manufacture of fuel gases like coal gas .

• Coal is used in the manufacture of  synthetic natural gas .

 Coke :

• When coal is heated  strongly in the absence of air, then all the volatile materials are removed from coal and hence  coke is formed .

• Coke consists 98 %  of carbon .

• Coke is a better fuel than coal because it produces more heat  than an equal mass of coal .

• It does not produce smoke while burning . Thus , burning of coke does not cause air pollution .

• Coke is is  used as a reducing agent in the extraction of metals from their ores .

 Petroleum:

• The name petroleum means rock oil (petra = rock;  oleum =oil).

• So It is called petroleum because it is found under the  earth crust trapped in rocks.

• Petroleum is a dark coloured, viscous, and foul smelling crude oil.

• The crude oil petroleum is a complex mixture of several solid, liquid and gaseous hydrocarbons mixed with water, salt and earth particles.

• Petroleum is lighter than water and insoluble in it.

• Petroleum is obtained by drilling holes (called oil wells) into the earth's crust. When a well is drilled through the rocks, natural gas comes out first , the crude oil comes out by itself due to gas pressure.

• Before petroleum can be used as a fuel for specific purposes, it has to be purified or refined by the fractional distillation.

• The fractional distillation of petroleum gives the  fractions  such as  Petroleum gas , Petrol (or Gasoline), Diesel, Kerosene and Fuel oil, lubricating oil.

 Uses of fractions of petroleum  :

• Petroleum gas is used as a fuel for domestic heating purposes in the form of liquefied petroleum gas (LPG).

• Petrol is used as fuel in motor cars, scooters, motor-cycles, and other light vehicles.

• Diesel is used as a fuel for heavy vehicles like buses, trucks, tractors and railway engines. Diesel is also used as a fuel to run water-pumps for irrigation purposes and in diesel generators to produce electricity on a small scale.

• Kerosene oil is used as a household fuel. For example, kerosene is used in wick stoves or pressure stoves to cook food. Kerosene is also used as an illuminant (for lighting purposes) in hurricane lamps.

• A special grade of kerosene oil is used as 'aviation fuel' in jet aeroplanes.

• Fuel oil is used in industries to heat boilers and in furnaces.

• Fuel oil also used in thermal power plants for generating electricity.

• Fuel oil is a better fuel than coal because fuel oil burns completely and does not leave any residue.

 Petroleum gas:

• Petroleum gas is a mixture of three hydrocarbons : butane, propane and ethane. But main constituent of petroleum gas is butane.

• Butane, propane and ethane, all burn readily to produce lot of heat. This makes petroleum gas a very good fuel.

• Petroleum gas is obtained from the fractional distillation of petroleum. It is also produced by the cracking of petrol.

 Liquefied Petroleum Gas (LPG) :

• When petroleum gas is  subjected to high  pressure then  Liquefied Petroleum Gas (LPG) is formed.

• Thus, liquefied petroleum gas (or LPG) consists mainly of butane alongwith smaller amounts of propane and ethane which has been liquefied by applying pressure.

• Domestic gas cylinders contain a mixture of  liquefied butane, propane and ethane hydrocarbons under pressure. When knob of the gas cylinder is turned , the pressure is released and the highly volatile LPG gets converted into gas. This gas goes into the burner of our cooking stove. When matchstick is applied to the burner, the gas burns with a blue flame producing a lot of heat. This heat is used for cooking .
• foul smelling substance called ethyl mercaptan (CHSH) is added to LPG cylinders to know  the detection of gas leakage.

 Advantağes of LPG :

•  LPG has a high calorific value  50 kJ/g . So, it is a good fuel.

•  IPG burns with a smokeless flame.

•  LPG does not produce any poisonous gases on burning

•  LPG is easy to handle and convenient to store.

•  LPG is a very neat and clean domestic fuel.

Dangers of LPG :

• LPG is an extremely good domestic fuel but it can be dangerous too.

• LPG is a highly inflammable gas . it catches fire easily.

• In case of leakage of LPG from the gas cylinder an explosion  can take place.

 Natural Gas :

• Natural gas is formed under the earth crust  by the decomposition of vegetable matter lying under water. This decomposition is carried out by anaerobic bacteria in the absence of oxygen.

• Natural gas is present  under the crust of the earth either alone or alongwith above the petroleum oil trapped under the rocks  .

• Natural gas burns easily and produces a lot of heat.

• Natural gas consists about 95% methane (CH₄ ) , with small quantities of ethane and propane.

Natural gas as a fuel :

• Natural gas is used as a domestic and industrial fuel.

• Natural gas burns readily to produce a lot of heat. So, in many areas natural gas is used as the main fuel for domestic and industrial heating purposes.

• Natural gas is used as a fuel in thermal power plants for generating electricity .

Compressed Natural Gas (CNG):

• Compressed Natural Gas (CNG) is used as a fuel in transport vehicles (like cars, buses and trucks) .

• It is a good alternative to petrol and diesel because it does not cause any air pollution.

 Advantages of Natural Gas:

• Natural gas is used as a  fuel for heating purposes in homes and industries.

• Natural gas is a good fuel because it has a high calorific value of up to 50 kJ/g. Natural gas burns with a smokeless flame and causes no air pollution.

• It does not produce any poisonous gases on burning.

• Natural gas is an environment friendly fuel as compared to other fossil fuels.

• A great advantage of natural gas is that it can be supplied directly from the gas wells to the homes and factories for burning through a net-work underground pipelines, and this eliminates the need for additional storage and transport.

 Disadvantage Of Using Fossil Fuels:

• The main disadvantage of using fossil fuels is that the burning of fossils fuels causes a lot of pollution in the environment.

• The burning of fossil fuels produces acidic gases such as sulphur dioxide and nitrogen oxides. These acidic gases cause acid rain. The acid rain damages trees and plants (crops, etc.), reduces fertility of soil by making it acidic.

• Acid rain damages buildings by corroding them slowly. The monuments made of marble stone and statues are also damaged by acid rain.

• The burning of fossil fuels produces a poisonous gas, carbon monoxide  into air.

• The burning of fossil fuels produces large amount of carbon dioxide which goes into air. Though carbon dioxide gas is not harmful immediately, it damages the environment in the long .The presence of increasing amounts of carbon dioxide gas in the atmosphere is causing increased greenhouse effect leading to excessive heating of the earth. This is harmful for all the life on earth.

• The burning of fossil fuels (especially coal) produces smoke which pollutes the air.

• The burning of coal leaves behind a lot of ash. It also puts tiny particles of ash (called fly-ash) into the air causing air pollution.

 Control of pollution:

• The pollution of air caused by burning petroleum fuels (like petrol and diesel) in vehicles can be controlled by fitting the vehicles with catalytic converters. 
• The catalytic converter is a device which changes the harmful gases coming from the engine of a car into harmless gases before releasing them into air. 
• For example, the catalytic converter brings about the complete combustion of the poisonous gas carbon monoxide to form carbon dioxide which is not poisonous at all. It also changes harmful nitrogen oxides into harmless nitrogen gas.

• The catalytic converter is fitted in the exhaust system of a vehicle (like a car).

• The pollution of air caused by burning coal in thermal power plants and factories can be controlled by washing down the smoke and acidic gases by water in a scrubber. 
• Scrubbers are tanks where the smoke and waste gases produced by thermal power plants and factories, etc., are sprayed by jets of water before they reach chimney. Water dissolves most of the harmful acidic gases like sulphur dioxide and nitrogen oxides.

• The pollution of air caused by burning coal in thermal power plants and factories can also be controlled by installing electrostatic precipitators in their chimneys. When an electrostatic precipitator is installed in the chimney, then the unburnt carbon partieles and fly-ash particles present in smoke keep on depositing on the inner walls of the chimney and do not go into air. The 'deposit' of carbon and fly-ash particles can be removed by sweeping the chimney from time to time.