Fossil fuels like coal, crude oil, and natural gas are classified as primary or natural fuels that occur underground. They were formed over millions of years from the remains of ancient plants and animals. Coal is a solid fossil fuel that was formed from plant matter during the Carboniferous period 300 million years ago. Crude oil is a liquid fossil fuel formed from decayed marine organisms and methane is a gas fossil fuel. Fossil fuels are non-renewable resources that are being depleted through human usage.

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CLASSIFICATION OF FUEL
FUEL
OCCURENCE
PHYSICAL
STATE
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On the basis of occurrence
FUEL
PRIMARY OR
NATURAL FUEL
SECONDARY OR
ARTIFICIAL FUEL
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CLASSIFICATION OF FUEL
Fuels are classified as
• Primary fuels – Fuels which occur naturally
such as coal, crude petroleum and natural
gas. Coal and crude petroleum, formed from
organic matter many millions of years ago,
are referred to as fossil fuels.
• Secondary fuels – Fuels which are derived
from naturally occurring ones by a
treatment process such as coke, gasoline,
coal gas etc.
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On basis of physical state
FUEL
SOLID LIQUID GAS
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FUEL
Primary Fuels
Solid
Eg. Wood,peat
Liquid
Eg.crude oil
Gas
Eg.Natural gas
Secondary fuels
Solid
EgCoke,charcoal
Liquid
Eg. Petrol ,LPG
Gas
Eg.coal gas
,water gas
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7. What are fossil fuels?
Solid = _________
Liquid = ___________
Gas = _____________
Fossil fuels took millions of years to form. Once they are used, we cannot replace
them. Therefore, we call them _________________ _____________
________________.
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8. Most coal was formed from plants which grew 300 million years ago.
The time period is called CARBONIFEROUS ERA
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• The ranking sequence is:
Wood
Peat
Lignite (brown coal)
Bituminous Coal
Anthracite
• In general, deposits close to the surface which
can be worked by strip mining produce a more
economical fuel than deep mined coal.
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12. OIL (PETROLEUM)
Buried organic matter
rich in hydrocarbons
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13. How oil and gas were formed
1. In the ocean - Plants use sun’s energy to survive and
animals get their energy by eating plants
2. Plants and animals in ocean die. The one’s that are not
eaten fall to the bottom of the sea.
3. A few millions of years later - layers of mud forms on top of
the dead animals and plants
4. Another few millions of years later - layers of sand builds up
on top of the mud
5. Pressure of all these layers of mud and sand squashes and
turns in to mud stone
6. Pressure of all these layers of mud and sand squashes and
turns plants and animals to oil and natural gas
7. Now, scientist burn oil and gas in power stations but this
releases harmful gases
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14. FOSSIL FUELS
85% of the world’s
commercial energy
COAL
OILNATURAL GAS 14Archana Singh

15. OIL and NATURAL GAS (Methane)
Even though it was not made from dead plants or animals, nuclear fuel is considered
to be a fossil fuel because it comes from the ground and is running out.
Made from the decayed remains of sea creatures which died
millions of years ago
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18. NATURAL GAS
Methane, other
Gases in bedrock
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20. Advantages of natural gas
• Cleaner to burn
– Half as much CO2 as coal
• More efficient
– 10% energy lost
• 60-year supply at current rates
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21. Disadvantages of natural gas
• Difficult to transport
– Pipelines
– Liquified Natural Gas (LNG) tankers
• Can be polluting, dangerous when
extracted
• Methane bed drilling pollutes
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