At coal-fired power plants, scientists and engineers are seeking ways to cleanse coal exhaust of sulfur, mercury, arsenic, and other impurities. Clean coal technologies refer to an array of techniques, equipment, and approaches that aim to remove chemical contaminants during the generation of electricity from coal. Among these technologies are various types of scrubbers, devices that chemically convert or physically remove pollutants. Some scrubbers use minerals such as magnesium, sodium, or calcium in reactions to remove sulfur dioxide (SO2) from smokestack emissions.

 

Others use chemical reactions to strip away nitrogen oxides (NOX), breaking them down into elemental nitrogen and water. Multilayered filtering devices are used to capture tiny ash particles. Another “clean coal” approach is to dry coal that has high water content to make it cleaner-burning. We can also gain more power from coal with less pollution through gasification, in which coal is converted into a cleaner synthesis gas (called syngas) by reacting it with oxygen and steam at a high temperature. Syngas from coal can be used to turn a gas turbine and also to heat water to turn a steam turbine.

 

The U.S. government and the coal industry have each invested billions of dollars in clean coal technologies for new power plants. These efforts have helped to reduce air pollution from sulfates, nitrogen oxides, mercury, and particulate matter. If the many older plants that still pollute our air were retrofitted with these technologies, pollution could be reduced even more. This is a goal of the Obama administration’s Clean Power Plan, launched in 2015.