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Fueling the Mix: Coal and U.S Electric Power Generation
An image of a coal mine in the Powder River Basin

An image of a coal mine in the Powder River Basin of Wyoming and Montana

Coal is an important fuel source in the United States today. Responsible for approximately 39 percent of the country’s electrical generation, coal is vital to the day-to-day operation of people’s lives.

The United States is rich in coal deposits, with large resources.  One of the most important and largest of those deposits is found in the Powder River Basin (PRB) of Wyoming and Montana, which, in 2012, produced more than 42 percent of the Nation’s coal.

On February 26, USGS released its new assessment of in-place resources, recoverable resources, and economic reserves of coal in the Powder River Basin, the first of a new generation of coal assessments from the USGS. Estimates of total in-place coal resources in the PRB are 1.07 trillion short tons, while recoverable coal resources are 162 billion short tons, and coal reserves are 25 billion short tons.

What Do All these Numbers Mean?

Previous assessments focused only on total in-place and recoverable coal resources, but this assessment includes in-place resources and a regional assessment of recoverable coal resources and economic coal reserves.

A map showing the four assessment units for the Powder River Basin

A map showing the four USGS assessment units for the Powder River Basin

In-place coal resources include in-place tonnage estimates of total coal volumes.  In-place resources are those quantities that are estimated, as of a given date, to be contained in known deposits prior to production. The quantity which can be technically produced or mined, may be significantly less than the volumes estimated to be in place.

Recoverable resources are calculated using those coal beds from the total in-place resources that are deemed both shallow and thick enough to be recoverable using current surface mining technology.

Coal reserves are a subset of coal resources. To be classified as reserves, the coal must be considered economically producible at the time of classification, but facilities for extraction need not be installed and operative.

Current reserves does not mean that is all that remains mineable. The size of reserves changes because mining costs and coal sales prices are subject to fluctuation based on market conditions – recoverable resources become reserves with favorable changes in costs, demand, and prices.

What is Coal?

Coal is a sedimentary rock made predominantly of carbon that can be burned for fuel. Coal formed when prehistoric forests and marshes were buried and compressed over hundreds of millions of years.  After deposition and subsequent burial, some contents of the rock, such as moisture, are squeezed out due to the pressure leading to higher and higher concentration of carbon, though other elements (such as sulfur, oxygen, nitrogen) remain in the coal.  This process resulted in the various types of coal seen today, which are ranked according to their moisture content and concentration of carbon.

USGS and Coal

USGS has studied coal for more than 100 years. In addition to its own research, USGS works with others, predominantly state geological surveys, to provide the basic geologic information to assess the Nation’s coal resources. The largest and most well-known areas of coal the USGS has assessed are the Appalachian Basin and Illinois Basin in the eastern U.S. and the Williston Basin, Colorado Plateau,  and the Powder River Basin in the western U.S.

Coal is loaded on to a truck in the Powder River Basin

Coal is loaded on to a truck in the Powder River Basin. The Powder River Basin contains the largest deposits of low-sulfur subbituminous coal in the world.

USGS also studies the environmental effects of developing and using coal, such as greenhouse gas emissions from underground coal fires, air quality impacts from coal utilization, and studying coal quality for fuel use optimization.

Optimizing fuel use and minimizing its impact on the environment are necessary components of 21st century strategies for meeting society’s energy needs. One critical aspect of fuel use optimization is an understanding of the geologic factors that affect fuel quality. For example, the composition of coal critically influences power generation efficiency, the impact of coal use on the environment, and the composition and usefulness of combustion products.

Coalbed Gas

There is another important resource directly related to the Nation’s coal: coalbed gas. Generated in and produced from coal seams, coalbed gas, often called coalbed methane, accounts for approximately eight percent of the U.S. natural gas production and has many of the same uses as coal, such as production of electricity and fuel for our home furnaces during the winter. In addition, it can be used in fertilizers, or for transportation in place of gasoline, which is derived from oil.

In addition to its uses, coalbed gas can be a hazard as it could lead to suffocation and explosions (it is extremely flammable in combination with coal dust). Miners would bring canaries into the mines to help them know when large concentrations of methane were in the area.  In modern times, mine ventilation techniques and methane detection equipment has reduced the methane hazard for miners.

Coal is an important part of the U.S. energy mix, and the United States is richly endowed with coal. After all, the Powder River Basin is the largest deposit of low-sulfur subbituminous coal in the world. However, as the latest assessment of the Powder River Basin also shows, there is a significant difference between the in-place resources and the recoverable resources, let alone the economic resources. USGS’ coal research provides critical information for government and private managers to know just how much coal really is present, what is usable, and its quality.

Types of Coal
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An Introduction to the Ranks of Coal Read More

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The highest rank of coal. It has the highest level of carbon and lowest level of volatiles. Read More

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It is hard, brittle, and quite lustrous (shiny). Read More

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Bituminous coal is a middle rank coal with a high heating value. Read More

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It is the most common type of coal used in electricity generation in the United States. Read More

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Lignite is the lowest grade coal with the least concentration of carbon. Read More

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Lignite is also referred to as "Brown Coal." Read More

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Peat is not actually coal, but rather the precursor to coal. Read More

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Peat is a soft organic material that, when placed under high pressure and heat, will become coal. Read More

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Page Last Modified: February 12, 2014