Coal is a nonrenewable energy source because it takes millions of years to create. It is a combustible black or brownish-black sedimentary rock composed mostly of carbon and hydrocarbons—molecules containing hydrogen and carbon. The energy in coal comes from the remains of prehistoric plants and animals, making it part of the fossil fuels family.
How is Coal Formed?
Coal formation began during the Carboniferous period (280 to 345 million years ago). Much of the earth was covered with swamp during this time, and large amounts of plants and other organic matter grew. As the plants and other life forms died, they sank to the bottom of the swampy areas. They slowly decomposed, and formed peat—a soggy, dense, sponge-like material. Over time, the peat was buried and compressed under the earth’s surface. As the earth’s surface changed over millions of years, sand, clay and other minerals accumulated, burying the peat. Layer upon layer created heat and pressure, which compressed the peat into a hard substance we call coal.
Types of Coal
Coal is classified in four main categories based on the amounts of carbon it contains and the heat energy it can produce. The higher ranks of coal typically contain more heat-producing energy.
Lignite – Over time, heat and burial pressure turn peat into lignite. Lignite is somewhat light in color, soft and crumbly. It is considered an “immature” coal with only 25-35% carbon. It is mainly used at power plants to generate electricity.
Sub-bituminous – Lignite that becomes darker and harder over time is called sub-bituminous coal. Sub-bituminous coal contains 35-44% carbon.
Bituminous – More chemical and physical changes to sub-bituminous develop the coal into bituminous coal. Bituminous coal is dark and hard. It contains 45-86% carbon. It is used to generate electricity.
Anthracite – Mature coal is call anthracite. Anthracite coal is very hard and shiny. It contains 86-97% carbon and has a heating value slightly higher than bituminous coal.
Where is Coal Found?
Some coal beds lie within 200 feet of the earth’s surface. These beds are mined by stripping the top soil off the coal. Then the coal is dug out. This is called surface mining. Deeper coal beds can be found up to 1,000 feet/305 meters below the earth. Miners tunnel underground to get this coal. This is called underground mining or deep mining.
Coal reserves can be found in about 70 countries worldwide, and, according to the World Coal Institute, more than 847 billion tons of proven coal reserves are available internationally. The largest proved coal reserves are available in:
- United States
- Russian Federation
The US is the international leader in coal reserves, with nearly 30% of the world’s supply, according to the BP Statistical Review of World Energy (June 2009).
How is Coal Extracted?
Coal is extracted from the ground by mining underground or at the surface. Coal mines are many miles wide. First, dirt above the coal deposit is removed. Coal is found in thick, flat layers. Explosives are then used to break the exposed coal into smaller pieces. The coal is then loaded into a wagon and lifted to the surface.
Finding coal reserves is a long process of exploring, mapping and drilling. It often starts with the creation of a geological map of an area that may contain coal reserves. Then, geochemical and geophysical surveys are carried out, as well as exploratory drilling. The area will become a mine if it’s proven to contain usable coal that can be recovered economically.
Coal is extracted by surface (or “opencast”) mining and underground (or “deep”) mining. The method used is determined by the geology of the area.
Underground mining accounts for about 60% of the world’s coal production.
Surface mining recovers a higher percentage of the coal deposit than underground mining, but it is only feasible when the coal deposit is near the surface.
Demand for Coal
Worldwide proven coal reserves are more than 847 billion tons—enough to last approximately 130 years at current consumption levels. The countries with the largest reserves of coal are the United States, Russia, China and India. Together they make up 67% of the world’s coal reserves.
Coal provides 26% of global primary energy needs and generates 41% of the world’s electricity, according to the World Coal Institute Coal Facts 2008. The US Energy Information Administration expects coal use to double by 2030 to meet rising world energy demand.
Uses for Coal
In some countries, coal may be burned directly for heat or cooking, but most coal is used in power plants to generate electricity. Coal has plenty of uses outside of electricity too. Materials that contain coal and coal coke (a concentrated form of coal that has been stripped of its volatile materials) are used in many products we use every day, including:
- Golf balls
- Paper clips
- Sugar substitute
History of Coal
Archaeological evidence indicates that the Romans in England used coal in the second and third centuries (A.D. 100-200). It was used in the 1300s by Native Americans for cooking, heating and baking pottery.
280 to 345 million years ago – The “Carboniferous period,” fossil fuel formation begins.
1300s – The Hopi Indians in what is now the US southwest use coal for cooking, heating and to bake the pottery they made from clay.
1673 – Coal is rediscovered in the US by explorers.
1720 – The first commercial coal mine in North America begins production at Port Morien (Baie de Mordienne) in Canada.
1748 – The first documented mining of coal in the US 50 tons is dug.
The first US commercial coal production begins from mines around Richmond, VA. Coal was used to manufacture shot, shell, and other war material during the Revolutionary War.
1769 – Scottish engineer James Watt invents the steam engine. It used coal to make steam to run the engine.
1770s – The English find that coal could produce a fuel that burned cleaner and hotter than wood charcoal.
1800s – The Industrial Revolution spreads. People used coal to manufacture goods, and to power steamboats and railroad engines. Coal was used to fuel their boilers.
1882 – Thomas Edison builds the first practical coal-fired electric generating station, supplying electricity to some residents of New York City.
1961 – Coal becomes the major fuel used by electricity utilities to generate electricity, and becomes the largest source of electricity.
Today – Coal provides 41% of the world’s electricity, according to the World Coal Institute.
Coal to Liquids
Can coal be a liquid? Yes! Coal liquefaction, the process of converting coal to liquid, turns coal into an alternative for liquid fuels. South Africa has the only commercial coal liquefaction industry in the world, and it has been producing fuels this way since 1955. These fuels are used for cars and jets and have potential outside of transportation as well. Coal-derived dimethyl ether, for example, could be used in developing countries for heating and cooking as it is non-toxic and less harmful to the environment than traditional petroleum gas.
How Does Coal Mining Affect the Environment?
Coal mining and coal use has historically had a negative impact on the environment, particularly by creating harmful gases like carbon dioxide and methane. But the coal industry is working to improve these detrimental effects.
Coal companies reduce carbon dioxide emissions by capturing the gas and injecting it into deep geological formations for storage. Mining also produces methane gas, which has a much greater global warming potential than carbon dioxide. Using technological advances, the industry has been successful in recovering the methane and preventing it from being released into the atmosphere. According to the International Energy Agency, replacing older coal-fired power plants with more efficient plants could significantly reduce the industry’s greenhouse gas emissions.
Coal mining’s effect on the environment reaches beyond the atmosphere: the Earth also feels its effects.
Land – Coal mining can lead to soil erosion and dust, and it causes disturbance to large tracts of land.
Water – Acid mine drainage, a metal-containing water that is formed by the chemical reaction between water and rocks containing sulphur-bearing minerals, can pollute water around a coal mine with heavy metals like copper, lead and mercury. Methods coal companies can use to minimize water pollution include building specialized water treatment plants and recycling contaminated water.
Plants and animals – Coal mining, particularly surface mining, can disturb land that is used for grazing, animal habitats, forests, crops and more. But the coal-mining industry makes rehabilitating land once mining is complete a top priority. After mining is complete, companies reshape the area, replace top soil and replant vegetation, making the reclaimed land suitable for wildlife, agriculture and more.
What is ‘Clean Coal Technology’?
The coal industry is using new technology to reduce the impact of the burning and mining of coal on the environment. One of the most well known “clean coal technologies” is carbon capture and sequestration (CCS), which involves securing the carbon dioxide created by coal, converting it to a liquid-like state and then storing it permanently underground.
The FutureGen project, for example, includes plans for a near-zero-emissions coal plant in Illinois that will use coal gasification technology to generate electricity while capturing harmful CO2 emissions.
Scientists predict that the world must reduce its greenhouse gas emissions by as much as 80% in order to avoid serious complications from global climate change. CCS technology is an important part of meeting that goal. Coal is a huge supplier of power, but it is also a huge producer of CO2. Underground storage capacity is more than enough to take on coal’s carbon emissions. According to the World Resources Institute, large US coal sources emit 2-3 billion tons of CO2 per year, but the Department of Energy estimates that the US contains underground capacity for 1-4 trillion tons, making underground storage a viable option for years to come.
Integrated Gasification Combined Cycle (a process of turning coal into gas, then removing impurities from and combusting the gas) and Pressurized Fluidized Bed Combustion (which produces a high-pressure gas stream as well as steam that can power a turbine) are also promising technological advances in the quest for “clean” coal.