Unit 6 · Topic 6.3 Beta

Fuel Types and Uses

The main fuels differ in energy per kilogram, carbon dioxide per unit of energy and use.

Practice 1: Concept Explanation

Part 1 · Hook

Why this matters

A truck runs on diesel, a furnace burns natural gas, a steel mill uses coal and a family cooks over charcoal. Each fuel is stored solar energy from ancient or recent plants, but they differ in how much energy they pack per kilogram, how much carbon dioxide they release and what they are good for.

Part 2 · Before you start

What this builds on

Part 3 · Prerequisite check

Quick check before you start

1. What gas is released when fossil fuels burn?

  1. Carbon dioxide
  2. Oxygen
  3. Nitrogen
  4. Helium
Show the answer

Combustion combines the fuel's carbon with oxygen, making carbon dioxide.

  • Correct: Carbon dioxide:
  • Oxygen:
  • Nitrogen:
  • Helium:

2. Why is coal nonrenewable?

  1. It forms over millions of years, far slower than we use it
  2. It releases carbon dioxide
  3. It is mined
  4. It is black
Show the answer

The rate of formation, not pollution, makes a fuel nonrenewable.

  • Correct: It forms over millions of years, far slower than we use it:
  • It releases carbon dioxide:
  • It is mined:
  • It is black:

Part 4 · See it

See it first

Four boxes in a row: peat, partly decayed plant material; lignite, soft brown moist coal; bituminous, hard black coal widely burned for electricity; anthracite, hardest and highest in carbon. An arrow underneath reads more heat, pressure, depth of burial and time. Bars show carbon content and energy per kilogram rising from peat to anthracite and moisture falling.
Coal ranks from peat to lignite, bituminous and anthracite; carbon and energy per kilogram rise with rank. LevlPrep original diagram.

Part 5 · Step by step

How it works, step by step

  1. Plants are buried in swamps without oxygenthey do not fully decay and form peat
  2. More heat, pressure and time act on the buried peatit becomes lignite, then bituminous coal, then anthracite
  3. Each step drives off water and concentrates carbonenergy per kilogram rises, so less fuel is needed for the same energy
  4. A fuel's energy comes more from hydrogen than carbon (natural gas)it releases less carbon dioxide per unit of energy, though not zero

Part 6 · Key ideas

Key ideas

  • Coal ranks by energy content: peat (not yet coal), lignite, bituminous, anthracite. Coal is used mainly for electricity and steel making.
  • Petroleum (crude oil) is refined by boiling point into gasoline, diesel, jet fuel, heating oil and asphalt. Tar sands hold bitumen, a heavy oil that takes much energy and water to extract.
  • Natural gas is mostly methane. It releases about half the carbon dioxide of coal per unit of energy: cleaner, but not zero emissions.
  • Wood and charcoal are the main fuels for many poorer households. Cogeneration captures waste heat from making electricity and uses it to heat buildings or water.

Part 7 · Misconception

A common mistake

The wrong idea: Natural gas is a clean fuel, so switching to it means zero carbon dioxide emissions.

What actually happens: Burning methane makes carbon dioxide and water. Natural gas releases about half as much carbon dioxide as coal per unit of energy, so it is cleaner than coal but not zero emissions, and leaked methane is itself a heat-trapping gas.

Part 8 · Check yourself

Check yourself

Exam-style questions. Anything you miss goes into your review queue.

1. Why does burning natural gas release less carbon dioxide per unit of energy than burning coal?

  1. Natural gas burns at a lower temperature, so less carbon dioxide forms
  2. Natural gas is renewable, so its carbon dioxide does not count
  3. Its energy comes partly from hydrogen, which burns to water, not carbon dioxide
  4. Natural gas contains no carbon atoms, so it makes no carbon dioxide
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Methane has four hydrogen atoms for each carbon atom. Burning hydrogen releases energy and makes water, so natural gas gives more energy for each unit of carbon dioxide; it releases roughly half the carbon dioxide of coal per unit of energy. It is not zero emissions.

  • Natural gas burns at a lower temperature, so less carbon dioxide forms: The flame temperature is not the reason for the difference.
  • Natural gas is renewable, so its carbon dioxide does not count: Natural gas is a nonrenewable fossil fuel.
  • Correct: Its energy comes partly from hydrogen, which burns to water, not carbon dioxide: Right: much of the energy comes from hydrogen, which forms water.
  • Natural gas contains no carbon atoms, so it makes no carbon dioxide: Methane has a carbon atom, so burning it does make carbon dioxide.

2. Which list puts coal types in order from lowest to highest energy content?

  1. Lignite, anthracite, bituminous
  2. Lignite, bituminous, anthracite
  3. Anthracite, bituminous, lignite
  4. Bituminous, lignite, anthracite
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With more heat and pressure over time, lignite becomes bituminous coal and then anthracite, gaining carbon and energy per kilogram.

  • Lignite, anthracite, bituminous: Anthracite is the highest rank.
  • Correct: Lignite, bituminous, anthracite: Right: energy content rises from lignite to bituminous to anthracite.
  • Anthracite, bituminous, lignite: This is the order from highest to lowest.
  • Bituminous, lignite, anthracite: Lignite is the lowest rank of coal.

3. Which describes cogeneration?

  1. Making electricity in two generating stations that share one fuel supply
  2. Mixing coal and natural gas before they are burned
  3. Using the waste heat from making electricity to heat buildings or water
  4. Burning two fuels at once in a single furnace to make more heat
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In cogeneration (combined heat and power), the heat that would be lost from making electricity is captured and used, so more of the fuel's energy does useful work.

  • Making electricity in two generating stations that share one fuel supply: Sharing a fuel supply does not capture any waste heat.
  • Mixing coal and natural gas before they are burned: Mixing fuels does not reuse waste heat.
  • Correct: Using the waste heat from making electricity to heat buildings or water: Right: electricity and useful heat from the same fuel.
  • Burning two fuels at once in a single furnace to make more heat: Burning two fuels is co-firing, not cogeneration.

Data

Energy content and carbon dioxide of five fuels

1 GJ = 1,000 MJ.
Energy released per kilogram burned, and carbon dioxide released per gigajoule (GJ) of energy (invented data for practice, near typical values)
FuelEnergy content (MJ per kg)Carbon dioxide (kg per GJ)
Lignite1595
Bituminous coal2790
Anthracite3098
Gasoline4667
Natural gas5050

4. How much energy, in MJ, do 40 kg of anthracite release when burned?

Type a number, then its unit (MJ). Scale words (2.5 million) and powers of ten (2.5 × 10^6) are read.

Show the answer

40kg×30MJ1kg40\,\text{kg} \times \frac{30\,\text{MJ}}{1\,\text{kg}}=1,200MJ= 1{,}200\,\text{MJ}.

  • Answer: 1200 MJ

5. A factory uses 2,000 GJ of energy a year. Write the setup for the carbon dioxide it would avoid each year by switching from bituminous coal to natural gas, then give the answer in kg.

Type the setup as on the exam, with brackets and units, then the answer.

Show the answer

Each GJ saves 90−50=4090 - 50 = 40 kg. Setup: 2,000GJ×(90−50)kg1GJ2{,}000\,\text{GJ} \times \frac{(90 - 50)\,\text{kg}}{1\,\text{GJ}}=80,000kg= 80{,}000\,\text{kg}.

  • Setup: 2000GJ(90−50)kgGJ2000\,\text{GJ}\,\frac{(90 - 50)\,\text{kg}}{\text{GJ}}; answer 80,000 kg

6. Which conclusion about coal is best supported by the table?

  1. Higher-rank coal holds more energy per kilogram
  2. Lignite releases the least carbon dioxide of the three coals
  3. The three coals hold the same energy per kilogram
  4. Coal releases less carbon dioxide per GJ than gasoline
Show the answer

Energy content rises from lignite (15 MJ/kg) to bituminous (27) to anthracite (30).

  • Correct: Higher-rank coal holds more energy per kilogram: Right: 15, 27 and 30 MJ per kg rise with rank.
  • Lignite releases the least carbon dioxide of the three coals: Bituminous coal (90 kg per GJ) releases less than lignite (95).
  • The three coals hold the same energy per kilogram: The three values are 15, 27 and 30 MJ per kg.
  • Coal releases less carbon dioxide per GJ than gasoline: Each coal releases more carbon dioxide per GJ (90 to 98) than gasoline (67).

Part 9 · Summary

Summary

The main fuels differ in energy per kilogram, carbon dioxide per unit of energy and use. Coal ranks from lignite to bituminous to anthracite as heat and pressure raise its carbon and energy content. Crude oil is refined into transportation fuels; natural gas, mostly methane, releases about half the carbon dioxide of coal for the same energy but is not zero emissions. Cogeneration puts waste heat to use.

Part 10 · Up next

What comes next

Part 11 · Connections

Connections

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