Coal is the energy source used to produce most of the electricity in this country. When power-generating plants burn coal, their smoke stacks release particulates and gases into the atmosphere. These emissions include carbon dioxide (CO₂), sulfur dioxide (SO₂), nitrogen oxides (NOx), and mercury, by-products of combustion that contribute to acid rain, smog, air and water pollution, asthma and other respiratory diseases, and the greenhouse effect. Clean coal technology is a new generation of energy-generating processes that seek to reduce coal's negative environmental impact. It comprises multiple strategies to clean coal prior to combustion and reduce hazardous emissions. Some of these strategies include coal preparation, pollutant removal, carbon capture and storage, and gasification.

The coal industry has found several ways to prepare coal before it is burned. For example, coal washing removes unwanted minerals by mixing crushed coal with a liquid and allowing impurities to separate and settle. When coal enters the combustion chamber, the focus turns to removing pollutants so they do not leave the plant. One removal device, called a "scrubber," is installed inside a smokestack, where it captures exhaust gases, including sulfur dioxide. Carbon capture and storage is a carbon dioxide management strategy that has not yet been put into practice. In theory, it involves capturing CO₂ produced when coal burns and then storing it where it cannot later escape into the environment or pollute drinking water, such as in deep underground saltwater formations. While various capture and storage solutions have been proposed and tested on a very limited basis, they all have their drawbacks, not the least of which is the cost of implementation.

Coal gasification represents a promising new way to convert coal into energy. Gasification exposes coal to steam and controlled amounts of air or oxygen at a high temperature and under great pressure. Rather than burning the coal, these conditions break it up into its basic chemical components. These components then initiate chemical reactions that typically produce a mixture of carbon monoxide (CO), hydrogen, and other compounds. When carbon dioxide and mineral components are separated from the CO and hydrogen, what remains is "syngas" fuel, a clean-burning fuel that can generate electricity and produce steam to power a steam turbine.

Apart from CO₂, which would have to be safely captured and stored for this process to be truly clean and safe, most of the mineral remains from the coal end up either as an inert "slag" that is safe to dispose of or in a solid or liquid form that has commercial value and can be sold. As attractive as this seems in concept, gasification technology has yet to be widely implemented in power-generating facilities. The cost of installing gasification equipment in existing plants across the country—or building new plants from scratch—and the sheer scale of CO₂ that would need to be safely stored remain two of the biggest obstacles.

The U.S. has the world's largest known coal reserves—enough coal to last approximately 225 years at today's level of use. With coal likely to remain one of the nation's lowest-cost electric power sources for the foreseeable future, some argue that exploring technological solutions that will reduce its environmental impact seems appropriate. But others argue that because all fossil fuels are finite resources that will one day be used up, it makes even more sense to concentrate on developing renewable energy sources such as wind, solar, and geothermal power, and reducing our energy consumption.

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