Types of Fuels & Uses (College Board AP® Environmental Science): Study Guide

Jacque Cartwright

Written by: Jacque Cartwright

Reviewed by: Alistair Marjot

Updated on

Fuelwood

  • Fuelwood is the most common source of energy for people living in developing countries

  • Roughly 40% of the world's population rely on fuelwood

  • Wood is relatively accessible and cheap or free to cut down and use as fuel

  • Charcoal is made by burning wood in low-oxygen conditions for an extended time

  • The use of fuelwood contributes to deforestation, soil erosion and desertification in many countries

  • The amount of wood cut each year is greater than the rate of replanting and regrowth

    • In many areas, there is little wood left, and people have to walk further and further to collect it

  • Indoor pollution leads to health issues from exposure to smoke

  • It is estimated that it is responsible for 1.5 million deaths each year in developing countries

  • Burning fuelwood creates by-products, including:

    • carbon dioxide

    • heat

    • steam

    • water vapor

    • wood ash which can be used as a fertilizer

Peat as fuel

  • Peat is a soil-like, brown, partially decomposed organic material that can be cut, dried and burned for fuel

  • Peat forms over millions of years under waterlogged and acidic conditions

  • Dead plant matter accumulates and becomes compacted under its own weight

  • The place where peat accumulates is known as a peat bog, or peatland

  • When dried, peat is an alternative to firewood that burns easily with a distinct odor and smoky flame

  • Peat is a minor contributor to global energy supplies and is considered a slow renewable as it accumulates under 1 mm a year

  • Although not strictly a fossil fuel, the IPCC classifies peat as a 'solid fossil fuel,' as its greenhouse gas emissions are similar to other fossil fuels

  • Peat is an efficient carbon sink and deposits are found all over the world

  • Frozen peatlands in northern latitudes have begun to thaw, releasing methane gas into the atmosphere

    • Continued thawing has the potential to release billions of tons of methane gas

  • Peat is the first step in the formation of low-grade lignite coal over millions of years

Coal fuel

  • Peat transforms into coal in a process called 'coalification,' where buried plant matter becomes harder, denser, drier and carbon-enriched

Diagram showing coal formation: plants form peat in wetlands, buried under sediment, subjected to heat and pressure, transforming into coal over millions of years.
Formation of coal from peat
  • The categories or ranks of coal depend on heat, pressure, and time

  • The higher the pressure, time and heat, the better the quality of coal

Peat → lignite → bituminous → anthracite

  • Lignite (brown coal) is the lowest-grade coal with a low concentration of carbon

    • Lignite has a low heating value with a high moisture content and is mainly used to generate electricity

    • Most harmful to human health

  • Bituminous is a middle-rank coal between lignite and anthracite.

    • Bituminous coal usually has a high heating (Btu) value

    • Used for electricity generation and steelmaking in the United States

  • Anthracite coal is the highest ranking and is known as hard coal

    • Hard but brittle with a shine

    • Anthracite has a high percentage of fixed carbon with low volatile matter

    • Used mostly for residential and commercial space heating

  • The US has the largest recoverable coal reserves in the world but China is the largest producer of coal

Natural gas fuel

  • Natural gas is primarily methane (CH₄) with traces of carbon dioxide (CO₂) and water vapor (H₂O)

  • Considered non-renewable, it is formed as layers of buried plants and gases are exposed to intense heat and pressure over thousands of years

Diagram showing the formation of oil and natural gas. Left: Ancient sea with water, sand, and remains. Right: Modern oil rig over layers of rock and gas deposits.
Natural gas formation
  • Considered the cleanest of the fossil fuels when burned, as it releases the fewest pollutants, CO₂ and H₂O

  • Gas is found in the large cracks and spaces between layers of rock 

  • Alternatively, gas is found in the tiny pores within sedimentary rock

  • Russia, Iran and Qatar have the largest natural gas reserves

  • Shale gas, which is stored in the small pores of sedimentary rock, can be accessed through fracking

  • Used for generating electricity, powering vehicles, cooking, heating, or cooling homes and businesses

Crude oil as a fuel

  • Crude oil is a hydrocarbon fossil fuel formed over millions of years from dead and decomposed organic material under heat and pressure

  • Crude oil is the raw resource extracted from the earth and then refined (called feedstock) into gasoline, jet fuel and other petroleum goods

  • It is a thick, sticky, black liquid that is found in porous rock (under the ground and under the sea)

Diagram of an oil rig above the sea, showing layers: sea, rock with fossil, crude oil, and seabed. Labels indicate how crude oil forms.
Diagram showing crude oil under the sea
  • Crude oil can be recovered from tar sands, which are a combination of clay, sand, water, and bitumen

  • Bitumen is a semi-solid form of oil that is mined using strip mining techniques or heated in-situ with steam

  • About 66% of the world's oil reserves are in tar sand

  • Oil shale is a fine-grained sedimentary rock high in organic compounds called kerogen

  • Shale oil (a slow-flowing, dark brown, heavy oil) is derived when the kerogen is vaporized at high temperatures, condensed and then heavily refined

Specialized fuel

  • Fossil fuels can be made into specific fuel types for specialized uses (e.g., in motor vehicles)

  • Synfuel is a synthetic liquid fuel produced from the chemical conversion of coal, natural gas or biomass, such as ethanol from corn

  • Syngas is produced from coal through a chemical process called coal gasification

    • This produces a gas that is lower in particulates, mercury and sulfur dioxide when burned

  • There are enough raw materials in the world to meet demand for centuries, but making them takes a lot of energy and manufacturing plants are expensive to build

  • Coal reserves would drop significantly and the product is still a carbon-based fuel with global warming, acid rain and air pollution potential

  • The end product is more expensive and produces greenhouse emissions

Cogeneration

  • Cogeneration or combined heat and power (CHP), is a single power plant that creates electricity and usable heat

Diagram of a Combined Heat and Power (CHP) system showing water, air, and fuel supplies to a prime mover, heat exchanger, generator, and control panel.
Simplified diagram of CHP system
  • Heat from electricity generation is utilized for residential, commercial and industrial uses

  • Cogeneration captures and uses waste heat, making it more efficient than traditional power plants that generate electricity and heat separately

  • This saves energy and cuts greenhouse gas emissions

  • Cogeneration systems use natural gas, coal, and biomass

  • Denmark uses CHP networks to provide 60% of it’s space and water heating

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Jacque Cartwright

Author: Jacque Cartwright

Expertise: Geography Content Creator

Jacque graduated from the Open University with a BSc in Environmental Science and Geography before doing her PGCE with the University of St David’s, Swansea. Teaching is her passion and has taught across a wide range of specifications – GCSE/IGCSE and IB but particularly loves teaching the A-level Geography. For the past 5 years Jacque has been teaching online for international schools, and she knows what is needed to get the top scores on those pesky geography exams.

Alistair Marjot

Reviewer: Alistair Marjot

Expertise: Environmental Systems and Societies & Biology Content Creator

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

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