20.7: Coal Power

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Where does coal come from?

Would you go to a coal mine? It's not very attractive. We like the benefits of electricity, but coal must be mined. Coal mining can be done by tunneling into a mountain. But if the coal is near the surface, the whole mountaintop may be removed. That's what's been done in this photo.

Coal

Coal is a solid hydrocarbon. Coal is useful as a fuel, especially for generating electricity. Coal is relatively inexpensive and abundant. Many nations, like China and the U.S., rely heavily on coal. Around the world, coal is the largest source of energy for electricity.

How Coal Forms

Coal forms from dead plants that settled at the bottom of swamps millions of years ago (Figure below). Water and mud in the swamp kept oxygen away from the plant material. Sand and clay settled on top of the decaying plants. The weight of this material squeezed out the water and some other substances. Over time, the organic material became a carbon-rich rock. This rock is coal.

The plants in this tropical swamp could one day become coal

The plants in this tropical swamp could one day become coal.

Coal has different grades. Bituminous coal forms at lower temperatures. It contains a lot of sulfur. When it is burned, it causes a lot of pollution. Anthracite coal forms under higher temperatures. This drives off the sulfur, and the coal burns more cleanly.

What Is Coal?

Coal is a black or brownish-black rock that burns easily (Figure below). Most coal is sedimentary rock. The hardest type of coal, anthracite, is a metamorphic rock. That is because it is exposed to higher temperature and pressure as it forms. Coal is mostly carbon, but some other elements can be found in coal, including sulfur. The coal with the least sulfur is the cleanest coal. Anthracite has very little sulfur and thus is very desirable.

Chunks of coal, which is a solid hydrocarbon

Coal is a solid hydrocarbon formed from decaying plant material over millions of years.

Using Coal

To prepare coal for use, the coal is first crushed into powder and burned in a furnace. Like other fuels, coal releases most of its energy as heat when it burns. The heat from the burning coal is used to boil water. This makes steam. The steam spins turbines, which creates electricity.

Coal in the USA

The United States is rich in coal (Figure below). Many regions of the country have significant coal deposits.

US coal producing regions in 1996

United States coal-producing regions in 1996. Orange is highest grade anthracite; red is low volatile bituminous; gray and gray-green is medium to high-volatile bituminous; green is subbituminous; and yellow is the lowest grade lignite.

Summary

Coal is solid fossil fuels formed primarily from ancient swamp plants, especially during the Carboniferous.
Coal is the source of most electricity.
Coal that forms at higher temperatures burns more cleanly.

Review

How does coal form?
There are swamps today. Why is coal not considered a renewable resource?
Why are there different grades of coal? What is different about them?
How does burning coal make usable energy?