7.1.2: Mining, Processing, and Generating Electricity

Coal

Coal Mining

Coal is extracted using two general methods: surface mining and subsurface mining.

Surface mining is used when coal deposits are located near the Earth's surface. Large machines remove soil and rock, known as overburden, to expose coal seams (figure \(\PageIndex{a}\)).

Two common forms of surface mining are:

• Strip mining, in which overburden is removed in successive strips to expose and extract coal.
• Mountaintop removal, in which explosives are used to remove the top of a mountain and expose the entire coal seam at once.Much of the removed overburden is deposited in nearby valleys, creating valley fills that can bury streams and alter watershed drainage patterns (figure \(\PageIndex{b}\)).

Surface mining is generally less expensive than underground mining but can dramatically alter landscapes, destroy habitat, and increase erosion.

Subsurface mining (deep mining) is used when coal deposits are buried deeper underground. Miners access coal through tunnels and shafts that may extend hundreds or thousands of meters below the surface.

Although subsurface mining disturbs less land at the surface, it presents safety risks for miners and can cause land subsidence when underground tunnels collapse (figure \(\PageIndex{c}\)). 

Coal Processing and Transportation

After mining, coal is cleaned and processed to remove rock, sulfur, and other impurities. This improves its heating value and reduces some emissions during combustion.

Coal is then transported to power plants, primarily by rail but also by truck, barge, or ship (figure \(\PageIndex{e}\)). Because transportation can be costly, many coal-fired power plants are located near major coal-producing regions.

Generating Electricity from Coal

Most coal is used to generate electricity. At a coal-fired power plant, coal is pulverized into a fine powder and burned in a furnace (figure \(\PageIndex{f}\)).  The heat converts water into high-pressure steam, which spins a turbine connected to an electrical generator.

This process converts:

Chemical Energy → Thermal Energy → Mechanical Energy → Electrical Energy

After passing through the turbine, the steam is cooled, condensed back into water, and reused. Cooling water is commonly withdrawn from nearby rivers, lakes, or oceans.

The cooling water is generally returned to its source at a higher temperature than when it was withdrawn, a form of thermal pollution that can affect aquatic ecosystems.

As of 2026, there is only 1 coal power plant in California, the Argus Cogeneration Plant that is capable of generating 63 MW. It is located northeast of Los Angeles. 

This video shows how heat energy can be used to generate electricity. 

Conventional Oil and Natural Gas Extraction

Conventional oil and natural gas are extracted by drilling wells into underground reservoirs where fossil fuels have accumulated beneath a trap.

 In many conventional reservoirs, natural gas accumulates above oil because it is less dense. However, some reservoirs contain mainly oil or mainly natural gas.

When a new well is drilled, natural underground pressure may initially force oil and gas to the surface. As pressure declines, water or gas may be injected into the reservoir to increase recovery. Additional techniques, such as steam or carbon dioxide injection, can further improve extraction from older wells.

Oil and natural gas are produced from both:

• Onshore wells located on land  (figure \(\PageIndex{g}\))
• Offshore wells located beneath the ocean floor (figure \(\PageIndex{h}\))

Modern offshore drilling platforms can operate in water more than a mile deep.

Hydraulic Fracturing (Fracking)

Some fossil fuels occur in dense rock formations that do not allow oil or natural gas to flow easily. These resources can be extracted using hydraulic fracturing, commonly called fracking (figure \(\PageIndex{i}\)). 

Fracking involves several steps:

1. A well is drilled vertically and then horizontally through the oil- or gas-bearing rock layer.
2. Steel casing and cement are installed to help isolate the well from surrounding rock layers and groundwater.
3. Small perforating charges create openings in the casing.
4. A mixture of water, sand, and chemical additives is injected into the well at very high pressure.
5. The pressure fractures the rock, creating pathways for oil and natural gas to move through the formation.
6. Sand, called proppant, helps keep the fractures open after the pressure is released.
7. Oil and natural gas flow through the fractures and into the well, where they are brought to the surface.

Fracking has greatly increased oil and natural gas production, particularly from shale formations. However, the process requires large amounts of water and generates wastewater that must be managed carefully. Environmental concerns include habitat disturbance, methane leakage, groundwater contamination from improperly constructed wells or wastewater handling, and induced earthquakes associated primarily with deep wastewater injection.

Unconventional Oil Resources

Other unconventional fossil fuel resources require additional processing before use.

• Oil sands (also called tar sands) contain bitumen, a dense and highly viscous form of petroleum that must be heated or processed before it can be used.
• Oil shale contains kerogen, an organic material that can be combusted directly for energy or heated to convert kerogen into liquid and gaseous hydrocarbons.
   (figure \(\PageIndex{j}\)). 
• Coal-bed methane is natural gas trapped within coal deposits.

Because these resources require more intensive extraction and processing, they generally have larger environmental footprints than conventional oil and natural gas.