Behind the Grid: Coal Power

Coal Power

(Published, 06/01/2020, Ruralite)

Anthracite Coal used in a coal-fired power plant

Coal is among the oldest and most-used fuels known to civilization. It is found and mined in nearly every nation in the world and has long been coveted as a powerful source of heat and light. Beginning in the 1880s, coal became the fuel of choice for generating electricity. Its abundance and low cost have made it the most common resource for electricity generation for over 100 years. But those days have come to an end.

How is coal formed?
Coal formation begins with dead and decaying plants. Sometimes, that plant matter gets covered beneath water and mud. As the plant matter gets buried deeper and deeper, there is less and less oxygen and eventually the decay stops. This partially-decayed matter is called peat. The peat gets compressed by weight from above and heat from below which slowly pressure-cooks it into coal.

Why is coal so full of energy?
Plants store energy in chemical bonds called carbohydrates. Usually, that energy is released slowly as plants decay. But in the case of coal, that energy is trapped and compressed. Not all coal is the same. Some forms are far more energy-dense than others. Different types of coal are found in different places depending on their geologic history. Lignite has the least energy, bituminous is in the middle and anthracite coal is the most energy-dense.

How is coal used to make electricity?
In a modern power plant, processed coal is milled to a fine powder, which increases the surface area and allows it to burn more quickly. The powdered coal is blown into a chamber and burned at high temperatures. Water is stored in tubes above the chamber and the heat boils the water into steam.

This high-pressure steam goes into a turbine containing thousands of propeller-like blades. The steam pushes these blades causing the turbine shaft to rotate at high speed. A generator is mounted to the end of the turbine shaft. After passing through the turbine, the steam is condensed and returned to the boiler to be heated again.

What is the environmental impact of coal?
Coal is composed almost entirely of carbon. Burning it emits large amounts of carbon dioxide (a greenhouse gas) into the atmosphere. Burning coal also releases traces of sulfur, mercury, lead, arsenic, and other particulates into the air.

Surface mining of coal impacts the environment and ecosystem in many negative ways. And subsurface coal mining causes lung damage and is a dangerous environment for workers.

Is there a future for "Clean Coal"?
Clean coal usually means capturing carbon emissions from burning coal and injecting them into the earth. There is some merit to the concept but even the best system would still produce carbon and it is an expensive technology. It should also be noted that coal is a finite resource that will eventually be depleted.

Coal can be found in nearly every country in the world. Only about 70 countries have enough to be economically recovered. There are an estimated 1.1 trillion metric tons of proven coal reserves worldwide. The ample supply is one of the reasons it remains in such high use.

Top 12 Known Coal Reserves:

  • 22.3% — United States
  • 15.5% — Russia
  • 14.0% — Australia
  • 13.1% — China
  • 9.50% — India
  • 3.50% — Germany
  • 3.30% — Ukraine
  • 3.10% — South Africa
  • 2.50% — Poland
  • 2.50% — Kazakhstan
  • 2.20% — Indonesia
  • 1.10% — Turkey

Source: Worldometer