Class 8 Science Coal-Petroleum
Natural Resources (mines of coal)
Natural resources are useful raw materials that we get from the earth. They occur naturally, which means that humans cannot make natural resources. Instead, we use and modify natural resources in ways that are beneficial to us. The materials present in nature are used to meet our basic needs. These are called natural resources. Earth’s natural resources include light, air, water, plants, animals, soil and mountains etc. Some other examples of natural sources and the ways we can use them are:
Depending upon the availability of various natural resources, they can be classified into two kinds:
1. Exhaustible natural resources –
These resources are present in limited quantity in nature. e.g. forests, wildlife etc.
2. Inexhaustible natural resources –
These resources are present in unlimited quantity in nature. e.g. water, sunlight.
Renewable Resources :
The resources that can be regenerated or renewed naturally are called renewable resources. For example sunlight, air, wind etc.
Non-Renewable Resources :
The resources that cannot be renewed or regenerated naturally are called non-renewable resources. e.g. coal, petrol, and natural gas are in this category because their rate of formation is extremely slow (at least millions of year). They are considered as non-renewable resources. Now, we study about some of the nonrenewable
The remains of dead plants and animals buried under the earth are called fossils. Fuels like coal, petroleum, natural gas are formed from the dead remains of plants and animals buried under the earth millions of years ago,
so these are known as fossil fuels.
Coal is a form of carbon, It is black in colour and it is a hard fossil fuel. Coal is found in deep coal mines under the
surface of the earth. In India, coal is mainly found in Bihar, Jharkhand, West Bengal, Odisha and Madhya Pradesh. The slow chemical process of the conversion of the dead plants into coal is called carbonisation.
How is coal formed?
1. Huge forest growing around 300 million years ago, covered most of the earth.
2. Due to natural calamities like earthquakes and volcanoes, these forests got buried under the soil.
3. The remains of dead plants got converted into Peat coal which contains 60% carbon.
4. The peat compressed between sediment layers to form lignite coal which contains 70% carbon.
5. Further compression resulted in the formation of bituminous coal which contains 80% carbon.
6. Finally, anthracite coal was formed which contained 90% carbon. Anthracite coal is considered as the best coal
due to more carbon content in it.
How is coal converted to Electricity?
Steam Coal, also known as thermal coal, it is used in power stations to generate electricity. Coal is first milled to a fine powder, which increases the surface area and allows it to burn more quickly. In this pulverised coal
combustion (PCC) systems, the powdered coal is blown into the combustion chamber of a boiler where it is burnt at high temperature (see in the diagram). The hot gases and heat energy produced converts water into steam.
The high-pressure steam is passed into a turbine containing thousands of propeller-like blades. The steam pushes these blades causing the turbine shaft to rotate at a high speed. A generator is mounted at one end of the turbine
shaft and consists of carefully wounded wire coils. Electricity is generated when these are rapidly rotated in a strong magnetic field. After passing through the turbine, the steam is condensed and returned to the boiler to be
heated once again. The electricity generated is transformed into the higher voltages (up to 4,00,000 volts) used for
economic, efficient transmission via power line grids. When it is near the point of consumption, such as our homes, the electricity is transformed down to the safer 100-250 voltage system used in the domestic market.