A process called “gasification” allows many of the impurities in coal to be removed before it is combusted to generate electricity
Instead of directly burning coal, like traditional plants, the coal is gasified. As a gas, almost all pollutant-forming impurities can be removed. The coal gas can be made clean and burned in a gas turbine-generator. The turbine exhaust is then used to power a steam turbine-generator. This combination allows coal to be used more efficiently than ever before.
Source: Department of Energy

Gasification allows the coal to burn more efficiently and obtain more energy than traditional plants when using the same amount of coal
Gasification plants built near Tampa, Florida, and West Terre Haute, Indiana, are the cleanest, most efficient coal plants in the world.
Source: Department of Energy

Our overall air quality is better now than it was 30 years ago.
Part of this success is due to efforts by the coal-based electricity industry to reduce emissions.
Source: Coalition for Affordable and Reliable Energy

Coal is increasingly less polluting
Coal consumption trends to lower sulfur coal and sulfur dioxide emissions from U.S. coal-fired power plants have declined by more than 20% since 1970. This comes as a result of improved technology even as coal consumption for domestic electric power has almost tripled.
Source: Coalition for Affordable and Reliable Electricity

Clean coal technologies represent a new class of pollution control and power generating processes
These processes reduce air emissions and lower greenhouse gases to a fraction of the levels of conventional coal-burning plants. They also boost power plant efficiencies and release carbon gases in a form that can be prevented from entering the atmosphere.
Source: Department of Energy