Coal is an abundant fuel source that is relatively inexpensive to produce and convert to useful energy. However, producing and using coal affects the environment.
Effects of coal mining
Surface mines (sometimes called strip mines) were the source of about 66% of the coal mined in the United States in 2015. These mining operations remove the soil and rock above coal deposits, or seams. The largest surface mines in the United States are in Wyoming's Powder River Basin, where coal deposits are close to the surface and are up to 70 feet thick.
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. This technique changes the landscape, and streams are sometimes 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 the area must be reclaimed close to its original condition.
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Underground mines generally have a lesser effect on the landscape compared to surface mines. However, the ground above mine tunnels can collapse, and acidic water can drain from abandoned underground mines.
Methane gas that occurs in coal beds (seams) can explode if it concentrates in underground mines. This coal bed methane must be vented out of mines to make mines safer places to work. In 2014, methane emissions from coal mining and abandoned coal mines accounted for about 10% 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 coal bed methane extracted from mines.
Emissions from burning coal
Several principal emissions result 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 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 and bottom ash are 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 effects 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 (put into storage, possibly underground) where it will remain permanently.
Reuse and recycling can also reduce the environmental effects of coal production and use. 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 such as cement and synthetic gypsum for wallboard.