Clean Coal Technology

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Coal is mostly carbon. When coal burns, it unavoidably creates the greenhouse gas carbon dioxide (CO2).

Coal also contains sulfur. When coal burns, the sulfur is converted into sulfur dioxide (SO2), an air pollutant.

When coal burns, nitrogen in the air and the coal are converted into oxides of nitrogen (NOx), an air pollutant.

Unburned coal contains impurities that are collectively referred to as particulate matter, which is also an air pollutant.

Coal contains trace amounts of mercury that are released when it burns.
Advanced NOx control technology
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NOx is combined with ammonia and a catalyst to form harmless nitrogen gas and water vapor.
Advanced mercury control technology
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Mercury can take different chemical forms, depending upon the coal source.

One means of reducing mercury involves injection of activated carbon into the flue gas stream.

The mercury "sticks" to the carbon that is removed by an electrostatic precipitator (ESP) or fabric filter (baghouse).

Some species of mercury can also be removed by the SO2 scrubbing process.
Typical particulate removal
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Particulates (fine dust) are removed from flue gas either using an electrostatic precipitator (ESP) or fabric filters sometimes referred to as a "baghouse".

Removing particulates using an ESP involves electrically charging the particles so the ESP can remove them.

Fabric filters are like gigantic (several stories tall) vacuum cleaner bags hung in a "baghouse" through which the flue gas passes. Particulates are trapped in the bags and removed.
Typical SO2 scrubbing
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SO2 in the flue gas reacts with limestone or, sometimes, other chemicals to create a solid material.

The solid material is collected for disposal or reuse. For example, sometimes the waste is converted into gypsum, which can be used to manufacture drywall.
CO2 reduction
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Power plant emissions are regulated by the Federal Environmental Protection Agency and by state and local authorities. Capture of CO2 becomes an additional step in the pollution control process.

With most of the pollutants removed, the flue gas is emitted from the power plant stack (chimney).

Congress first coined the term "clean coal technology" in the mid-1980s. Back then, the phrase meant technologies that reduce sulfur dioxide and nitrogen oxide emissions because Congress was considering ways to reduce those pollutants. Today, it obviously means a lot more. Read more +

Clean coal technology refers to technologies that improve the environmental performance of coal-based electricity plants. These technologies include devices that increase the operational efficiency of a power plant, as well as those technologies that reduce emissions. Early work to develop clean coal technologies focused on efforts to reduce traditional pollutant emissions like sulfur dioxide (SO2); nitrogen oxides (NOx), which are a precursor to smog; and particulate matter. Clean coal technology will continue to improve in response to environmental challenges.

According to U.S. Environmental Protection Agency figures, emissions of traditional pollutants regulated by the Clean Air Act, have dropped significantly - even as the use of coal to generate electricity has nearly tripled to meet growing energy demand. That’s proof of the success of clean coal technology. And the coal-based electricity sector’s work to develop and deploy new technologies to capture and safely store CO2 is also evidence of the industry’s commitment to expanding the use of advanced clean coal technologies.

Of course, these continued innovations require investment from both private industry and the American government.

These public/private partnerships have been an important driver for innovations that have allowed electricity providers to meet new environmental standards while holding down costs to the consumer. Bringing these types of new technologies to the marketplace often involves investments in first-of-their-kind and first-of-their-scale technologies.

Past investments in clean coal technology have provided demonstrable benefits in the form of reduced emissions and cleaner air. An ACCCE-funded study entitled DOE Clean Coal Technology Programs Offer Highest Return on Investment reports that, by 2020, American taxpayers will see a return of $13 for every dollar the government invests in these technologies. <<