Coal is an extremely important energy source, providing 39% of the world’s electricity. But the burning of coal also has a huge impact on the environment—it releases about 9 billion tons of harmful carbon dioxide into the atmosphere every year, contributing to global warming. The coal industry is developing new “clean coal” technologies that aim to cut down on these emissions while maintaining coal’s low cost.
Some clean coal technologies purify the coal before it burns. One type of coal preparation, coal washing, removes unwanted minerals by mixing crushed coal with a liquid and allowing the impurities to separate and settle.
Other systems control the coal burn to minimize emissions of sulfur dioxide, nitrogen oxides and small particles. Wet scrubbers remove sulfur dioxide, a major cause of acid rain, by spraying gas with limestone and water. The mixture reacts with the sulfur dioxide to form synthetic gypsum, a component of drywall.
Low-NOx (nitrogen oxide) burners reduce the creation of nitrogen oxides, a cause of ground-level ozone, by restricting oxygen and manipulating the combustion process. Filtration devices remove small particles that aggravate asthma and cause respiratory ailments by charging particles with an electrical field and then capturing them on collection plates.
Another technology that can help lower emissions is coal gasification – a process that converts the carbon in the coal into energy without burning it. The emissions from this process are easier to capture than with combustion. A side benefit of the process is that it produces hydrogen – which could be used as an energy source for future cars or power-generating fuel cells.
This gasification process uses steam and oxygen to turn coal into carbon monoxide and hydrogen. Other “clean coal” technologies have been used for several years and have improved as the world’s environmental concerns became more pronounced. Many coal plants use electrostatic precipitators (filtration devices that remove particles from flowing gas) and fabric filters to remove ash from the gases that are released by coal plants’ flues.