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Coal Basics

Coal takes millions of years to form

Coal is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is classified as a nonrenewable energy source because it takes millions of years to form. Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests.

The plants were covered by layers of dirt and rock over millions of years. The resulting pressure and heat turned the plants into a substance now known as coal.

Three images showing how coal was formed. The first image is of a swamp, 300 million years ago. Before the dinosaurs, many giant plants died in swamps.

The second image is of water, 100 million years ago. Over millions of years, these plants were buried under water and dirt.

The third image is of rocks and dirt over the coal. Heat and pressure turned the dead plants into coal.
Click to enlarge »

Source: National Energy Education Development Project (public domain)

Types of coal

Coal is classified into four main types, or ranks: anthracite, bituminous, subbituminous, and lignite. The ranking depends on the types and amounts of carbon the coal contains and on the amount of heat energy the coal can produce. The rank of a coal deposit is determined by the amount of pressure and heat that acted on the plants over time.

Anthracite contains 86%–97% carbon, and generally has the highest heating value of all ranks of coal. Anthracite accounted for less than 1% of the coal mined in the United States in 2014. All of the anthracite mines in the United States are located in northeastern Pennsylvania. Anthracite is mainly used by the metals industry.

Bituminous coal contains 45%–86% carbon. Bituminous coal in the United States is between 100 and 300 million years old. Bituminous coal is the most abundant rank of coal found in the United States, and it accounted for 48% of total U.S. coal production in 2014. Bituminous coal is used to generate electricity, and it is an important fuel and raw material for making iron and steel. West Virginia, Kentucky, Pennsylvania, Illinois, and Indiana were the five main bituminous coal-producing states in 2014, accounting for 70% of total bituminous production.

Subbituminous coal typically contains 35%–45% carbon, and it has a lower heating value than bituminous coal. Most subbituminous coal in the United States is at least 100 million years old. About 44% of total U.S. coal production in 2014 was subbituminous, and nearly 90% was produced in Wyoming.

Lignite contains 25%–35% carbon and has the lowest energy content of all coal ranks. Lignite coal deposits tend to be relatively young and were not subjected to extreme heat or pressure. Lignite is crumbly and has high moisture content, which contributes to its low heating value. Lignite accounted for 8% of total U.S. coal production in 2014. About 92% of total lignite production is mined in Texas and North Dakota, where it is burned at power plants to generate electricity. A facility in North Dakota also converts lignite to synthetic natural gas and pipes it to natural gas consumers in the eastern United States.

File Scrub L3 ::::: EE ... coal_home-basics ... coal_mining-basics

Mining and Transporting Coal

Mining coal

Diagram of surface mining. A huge backhoe digs through the top soil, the overburden and then into a shallow coal seam.

Source: Adapted from National Energy Education Development Project (public domain)

Artist's rendering of a typical deep mine.

Source: Adapted from National Energy Education Development Project (public domain)

Coal being transported by rail
Picture of coal being transported by rail.

Source: Stock photography (copyrighted)

Coal miners use large machines to remove coal from the ground. Many U.S. coal beds are near the surface, and about two-thirds of U.S. coal production comes from surface mines. Modern mining methods allow coal miners to easily reach most of the nation's coal reserves. Advances in mining technology enable today's coal miners to produce about three times the amount of coal in one hour than they produced in 1978.

Coal miners use two primary methods to remove coal:

Surface mining is used to produce most of the coal in the United States because the method is less expensive than underground mining. Surface mining can be used when the coal is less than 200 feet underground. In surface mining, large machines remove the top soil and layers of rock known as overburden to expose the coal seam. Mountaintop removal is a form of surface mining where the tops of mountains are dynamited and removed to access coal seams. After the mining is finished, the disturbed area is covered with topsoil, and the area is replanted.

Underground mining, sometimes called deep mining, is used when the coal is several hundred feet below the surface. Some underground mines are 1,000 feet deep, and extend for miles. Miners ride elevators down deep mine shafts and travel on small trains in long tunnels to get to the coal. The miners use large machines that dig out the coal.

Processing coal

After coal is removed from the ground, it may go to a preparation plant located near the mining site. The plant cleans and processes coal to remove rocks and dirt, ash, sulfur, and other unwanted materials. This process increases the heating value of the coal.

Transporting coal

After coal is mined and processed, it is transported to market, which can be more expensive than the cost of mining it.

Nearly 70% of coal delivered in the United States is transported, for at least part of its trip to market, by train. Coal can also be transported by barge, ship, truck, and even by pipeline.

It is often cheaper to transport coal on river barges, but barges are unable to take coal everywhere it's needed. If the coal is used near the coal mine, it can be moved by trucks and conveyors. Coal can also be crushed, mixed with water, and sent through a slurry pipeline. Sometimes, coal-fired electric power plants are built near coal mines to lower transportation costs.

File Scrub L3 ::::: EE ... coal_home-basics ... coal_where-basics

Getting (Producing) Coal

Where the United States gets its coal

Did you know?

The Black Thunder mine and the North Antelope Rochelle mine in Wyoming each produce almost as much coal as West Virginia, the nation's second-largest coal-producing state. Together, the two mines produced 22% of total U.S. coal production in 2013.

In 2013, 985 million short tons of coal were mined in 25 states. Surface mines were the source of 65% of total U.S. coal production and accounted for 60% of the total number of mines.

Five states accounted for approximately 69% of total U.S. coal production in 2013:

  • Wyoming (39%)
  • West Virginia (12%)
  • Kentucky (8%)
  • Illinois (5%)
  • Pennsylvania (5%)

Coal is mainly found in three regions, the Appalachian coal region, the Interior coal region, and the Western coal region (includes the Powder River Basin).

Facts and data for each coal-producing region for 2013.1

Appalachian coal region

  • The Appalachian region includes Alabama, Eastern Kentucky, Maryland, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia.
  • Almost 27% of the coal produced in the United States came from the Appalachian coal region.
  • West Virginia is the largest coal-producing state in the region, and the second-largest coal-producing state in the United States.
  • Underground mines supplied 70% of the coal produced in the Appalachian coal region.

Interior coal region 

  • The Interior coal region includes Arkansas, Illinois, Indiana, Kansas, Louisiana, Mississippi, Missouri, Oklahoma, Texas, and Western Kentucky.
  • About 19% of total U.S. coal was mined in the Interior coal region.
  • Illinois was the largest coal producer in the Interior coal region, accounting for 28% of the region's coal production, and 5% of total U.S. coal production.
  • Underground mines supplied 54% of the region's coal production, and surface mines supplied 46%.

Western coal region

  • The Western coal region includes Alaska, Arizona, Colorado, Montana, New Mexico, North Dakota, Utah, Washington, and Wyoming.
  • Of the coal produced in the United States, 54% was produced in the Western coal region.
  • Wyoming produced 73% of the coal mined in the Western coal region, and it is the largest coal-producing state in the United States. Nine of the top-10 producing coal mines in the United States are located in Wyoming, and all of those mines are surface mines.
  • Surface mines produced 90% of the Western coal region's total coal production.

1Year for which final annual data were available at the time of update.

File Scrub L3 ::::: EE ... coal_home-basics ... coal_use-basics

Uses of Coal

Did you know?

A pound of coal supplies enough electricity to power ten 100-watt light bulbs for about an hour.

Coal was the source of about 18% of U.S. total primary energy consumption in 2014. About 93% of the coal consumed in the United States is used to generate electricity by the electric power sector. The remaining 7% of coal is used as an energy source in many industries like the steel, cement, and paper industries.

Electric power

Coal is used to produce about 39% of all the electricity generated in the United States. Power plants can make steam by burning coal. The steam then turns turbines (machines for generating rotary mechanical power) to generate electricity.

Many industries and businesses have their own power plants, and some use coal to generate electricity, mostly in combined heat and power plants.


Blast furnace in a modern steel works
Blast furnace in a modern steel works

Source: BBC (copyrighted)

Many industries use coal and coal byproducts. The concrete and paper industries burn large amounts of coal to produce heat. The steel industry uses coal indirectly to make steel. First, coal is baked in furnaces to make coal coke, and then the coke is used to smelt iron ore into iron to make steel. The high temperatures created by burning coke give steel the strength and flexibility needed for bridges, buildings, and automobiles.

Converting coal into gas and liquids

Coal can be turned into gases and liquids, which can be used as fuels or processed into chemicals to make other products. These gases or liquids are sometimes called synthetic fuels or synfuels. Synthetic fuels are made by heating coal in large vessels. These fuels produce fewer air pollutants when burned than burning coal directly.

In North Dakota, the Great Plains Synfuels Plant converts coal into synthetic natural gas. Syngas produced from coal can also be used to produce electricity and hydrogen. There are currently no commercially operating facilities in the United States that produce liquids from coal, but coal has been converted to liquids in South Africa for decades.

File Scrub L3 ::::: EE ... coal_home-basics ... coal_environment-basics

Coal & the Environment

Coal is an abundant fuel source that is relatively inexpensive to produce and convert to useful energy. However, producing and using coal impacts the environment.

Impacts of coal mining

Surface mines (sometimes called strip mines) are the source of about 65% of the coal that is mined in the United States. These mining operations remove the soil and rock above coal deposits, or seams.

Mountaintop removal and valley fill mining has affected large areas of the Appalachian Mountains in West Virginia and Kentucky. In this form of coal extraction, the tops of mountains are removed using explosives. As a result of this technique, the landscape is changed, and streams may be covered with rock and dirt. The water draining from these filled valleys may contain pollutants that can harm aquatic wildlife downstream. Although mountaintop mining has existed since the 1970s, its use became more widespread and controversial beginning in the 1990s.

U.S. laws require that dust and water runoff from areas affected by coal mining operations must be controlled, and laws require that the area has to be reclaimed close to its original condition.

Did you know?

Some electric power plants use scrubbers (flue gas desulfurization equipment) to reduce the amount of sulfur exiting their smokestacks. The power plants use electrostatic precipitators or baghouses to remove particulates and heavy metals from the smoke.

Underground mines have less of an impact on the environment compared to surface mines. The largest impact of underground mining may be the methane gas that must be vented out of mines to make the mines a safe place to work. Methane is a strong greenhouse gas. In 2013, methane emissions from underground coal mining accounted for about 9% of total U.S. methane emissions and 1% of total U.S. greenhouse gas emissions (based on global warming potential). Some mines capture and use or sell the methane extracted from mines. Surface mines contributed about 2% of total U.S. methane emissions. Learn more about greenhouse gas emissions.

The ground above mine tunnels can also collapse, and acidic water can drain from abandoned underground mines.

Emissions from burning coal

In the United States, most of the coal consumed is used as a fuel to generate electricity. Burning coal produces emissions that adversely affect the environment and human health.

There are several principal emissions resulting from coal combustion:

  • Sulfur dioxide (SO2), which contributes to acid rain and respiratory illnesses
  • Nitrogen oxides (NOx), which contribute to smog and respiratory illnesses
  • Particulates, which contribute to smog, haze, and respiratory illnesses and lung disease
  • Carbon dioxide (CO2), which is the primary greenhouse gas emission produced from the burning of fossil fuels (coal, oil, and natural gas)
  • Mercury and other heavy metals, which have been linked to both neurological and developmental damage in humans and other animals
  • Fly ash and bottom ash, which are residues created when coal is burned at power plants. In the past, fly ash was released into the air through the smokestack, but laws now require that most emissions of fly ash be captured by pollution control devices. In the United States, fly ash is generally stored near power plants or placed in landfills. Pollution leaching from ash storage and landfills into groundwater and the rupture of several large impoundments of ash are environmental concerns.

Reducing the environmental impacts of coal use

The Clean Air Act and the Clean Water Act require industries to reduce pollutants released into the air and water.

Industry has found several ways to reduce sulfur, NOx, and other impurities from coal. Industry has also found more effective ways of cleaning coal after it is mined, and coal consumers have shifted toward greater use of low sulfur coal.

Power plants use flue gas desulfurization equipment, also known as scrubbers, to clean sulfur from the smoke before it leaves their smokestacks. In addition, industry and the U.S. government have cooperated to develop technologies that can remove impurities from coal or that can make coal more energy-efficient so less needs to be burned.

Equipment intended mainly to reduce SO2, NOx, and particulate matter can also be used to reduce mercury emissions from some types of coal. Scientists are also working on new ways to reduce mercury emissions from coal-burning power plants.

Research is underway to address emissions of carbon dioxide from coal combustion. Carbon capture separates CO2 from emissions sources and recovers it in a concentrated stream. The CO2 can then be sequestered, which puts CO2 into storage, possibly underground, where it will remain permanently.

Reuse and recycling can also reduce coal’s environmental impact. Land that was previously used for coal mining can be reclaimed and used for airports, landfills, and golf courses. Waste products captured by scrubbers can be used to produce products like cement and synthetic gypsum for wallboard.