Coal and Petroleum

What you'll learn

• What are fossil fuels and how they formed.
• Coal: types, products and uses.
• Petroleum: extraction, refining and products.
• Natural gas and its uses.
• Why we must conserve fossil fuels.

Key concepts

What are fossil fuels?

• Fossil fuels: coal, petroleum and natural gas — formed from the remains of dead plants and animals over millions of years under high pressure and temperature.
• They are non-renewable — once used, cannot be replaced on human timescales (take millions of years to form).
• Inexhaustible natural resources: sunlight, wind, water — will not run out.
• Exhaustible natural resources: coal, petroleum, natural gas — will eventually run out.

Coal

Formation (coalification):

1. Dead plants and trees fell into swamps hundreds of millions of years ago.
2. Covered by layers of earth and rock — buried.
3. Over millions of years, heat and pressure converted plant matter into coal.
4. This process is called carbonisation (slow process — more carbon over time).

Types of coal (in order of carbon content and quality):

Products from coal:

• Coke: coal heated without air (destructive distillation) → coke (mainly carbon).
  • Used in metallurgy (making steel/iron in blast furnaces).
• Coal tar: thick, black liquid obtained when coal is heated without air.
  • Source of many useful chemicals: dyes, medicines, explosives, paints, perfumes, plastics.
  • Used to surface roads.
• Coal gas: flammable gas obtained from coal; used as fuel in older times.
• Ammoniacal liquor: used as fertiliser.

Petroleum

Formation:

1. Tiny marine organisms (algae, zooplankton) died and settled on the sea floor.
2. Covered by layers of sand and rock → buried.
3. Over millions of years, heat and pressure → petroleum (crude oil) and natural gas.
4. Oil and gas trapped in porous rock formations capped by non-porous rock.

Extraction:

• Drilled from underground or under the sea using oil rigs/drilling platforms.
• Crude oil is a mixture of hydrocarbons (compounds of hydrogen and carbon).

Petroleum refining — Fractional distillation:

• Crude oil is heated in a distillation tower → different fractions collected at different heights (different boiling points).

CNG (Compressed Natural Gas):

• Natural gas: mainly methane (CH₄); found above crude oil deposits.
• Compressed → CNG (Compressed Natural Gas).
• Cleaner fuel than petrol/diesel; used in buses, auto-rickshaws, domestic cooking (piped PNG).
• LPG (Liquefied Petroleum Gas): propane + butane; stored in cylinders under pressure; household cooking.

Why conserve fossil fuels?

• Non-renewable — will run out in the future (crude oil estimated to last ~50 years at current use; coal ~100–200 years).
• Pollution: burning produces CO₂ (greenhouse gas → climate change), SO₂ and NOₓ (acid rain), particulate matter (smog).
• Oil spills: catastrophic for marine ecosystems.

Conservation measures:

• Use renewable energy (solar, wind, hydroelectric, geothermal).
• Energy efficiency: LED bulbs, efficient engines, better insulation.
• Public transport and carpooling reduce vehicle fuel use.
• Electric vehicles (EVs): shift away from petrol/diesel.
• Reduce, Reuse, Recycle — less energy needed for new products.

Quick check

• What are fossil fuels? Why are they called non-renewable?
• How is coal formed? Name the four types in order of carbon content.
• What is coke? How is it obtained? What is it used for?
• List three useful products obtained from petroleum refining and their uses.
• Why must we conserve fossil fuels? Name two conservation measures.

Open the Practice tab for graded questions on Coal and Petroleum.