COAL: Ancient Gift Serving Modern Man
American Coal Foundation
What is Coal's Future?
With a 250- to 300-year supply of coal under our feet, the picture of coal's role in the future is bright. However, coal has a reputation to overcome: the idea that it is a dirty fuel. Modern coal combustion facilities, such as those found at many of the nation's electric power plants, use equipment to remove most of the polluting elements from coal smoke. In fact, so much is removed that one can hardly see any smoke at all coming from these "smokestacks." Most of what shows is steam.
The dark, sooty material called fly ash that once went up the stack is now removed by filters or by devices called precipitators. With precipitators, the flue gas is passed through an electric field. The ash particles become negatively charged and are attracted to positively charged collecting plates and later removed for disposal. This method eliminates 99.5 percent of the offending material.
Coal contains sulfur, which combines with oxygen when the coal is burned to produce sulfur oxides. The effect of sulfur oxides on the environment has been the topic of significant debate for a number of years. Beginning in the 1970s, coal producers and major coal consumer initiated a number of efforts to reduce the amount of sulfur compounds emitted into the environment.
One was the use of "flue gas scrubbers," which can remove up to 95 percent of the sulfur oxides from the stream of gases produced by coal combustion before they go up the smokestack. In one process, sulfur dioxide in the flue gas reacts with a lime or limestone water slurry to form calcium sulfite or calcium sulfate (gypsum) sludge. In another, sulfur and sulfuric acid are produced as by-products. Still others can produce a dry by-product.
Sulfur emissions (SO2 -- sulfur dioxide) also are being reduced by greater use of inherently low-sulfur coals. Less than two decades after the Clean Air Act was passed, the sulfur content of coal purchased and burned by electric utilities had decreased 37 percent. Physically washing coal after it is mined and before it is burned is another way to reduce sulfur compound emissions. This process can remove sulfur-iron compounds (pyritic sulfur) from raw coal, but cannot remove organic sulfur, which is part of coal's molecular structure.
All these techniques represent a significant investment in maintaining clean air. A single scrubber, for example, can cost more than $100 million to construct, and many millions of dollars a year to operate. There are more than 140 scrubbers installed and operating at U.S. utilities, and about 50 more planned.
Electric utilities have already spent $60 billion to control sulfur emissions, and the investment, which continues every year, has paid off. According to the U.S. Environmental Protection Agency, sulfur dioxide emissions from electric utilities have gone down 18 percent from their 1973 peak. Taking into account that coal use by utilities has gone up dramatically during the period makes the accomplishment all the more impressive. As new, technologically advanced power plants replace older, less efficient ones, the trend toward lower sulfur dioxide emissions is expected to be enhanced.
As a fossil fuel, coal also contains carbon, which combines with oxygen to form carbon dioxide (CO2) during the combustion process. CO2 is one of five major so-called "greenhouse" gases, which help trap radiated heat back to the earth's surface.
This "greenhouse effect" is a natural process which maintains the earth's temperature at a level sufficient to support life. However, recent scientific and political debate has intensified over whether human activity -- such as fossil fuel use and deforestation -- has caused an acceleration of the natural greenhouse effect.
While most scientists agree that global atmospheric CO2 and other greenhouse gases have risen in quantity over the past century, great disagreement remains over whether these increases have already -- or will ever -- affect the earth's climate.
Given coal's vital present and future role in meeting the world's energy needs, solutions to concerns over possible climate change will have to be global in nature and carefully balance environmental objectives with viable options for continuing to fully utilize fossil fuels.