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

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, 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

• 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 steel making 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

• 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)

• 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

Awaiting image

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