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Feb
12
2019

About This Word: clean coal

Posted in About This Word, Wordsmyth Blog by Andrea Hazard

Welcome to About This Word, where Wordsmyth showcases commentary about relevant words in the news and media our users and staff find interesting. Today’s word: “clean coal,” written by Wordsmyth science writer Andrea Hazard.

Is It Coal?

Clean coal is not a type of coal. It is, however, technology that removes pollutants, including carbon dioxide, from coal emissions. This technology is also called coal pollution mitigation. Coal pollution mitigation is important because coal contains a lot of contaminants and produces more carbon dioxide than any other fossil fuel. Fortunately, unlike other fossil fuels primarily used by consumers, power plants that integrate large-scale clean coal technology primarily use coal.

How It Works

Diagram shows a coal-fired power plant. A conveyor belt brings pulverized coal into the plant, where it is burned in a boiler, or furnace. Smoke escapes through a chimney. Water from a nearby river is piped into the boiler, which heats it into steam that turns a turbine. A generator attached to the turbine produces electricity, which is transmitted by power lines. A condenser cools the heated steam, which is returned to the river.

A typical coal-fired power plant. Credit: US government

Most coal-fired power plants use coal combustion to produce steam that turns a turbine. In these power plants, some clean coal technology reduces pollutants in the steam, including sulfur oxides, nitrogen oxides, particulates, and trace heavy metals. Other clean coal technology improves efficiency, which reduces carbon emissions. Therefore, increasing the temperature and pressure of steam improves efficiency.

Emission Issues

Unfortunately, high-temperature, high-pressure steam is corrosive. Modern super-alloys can better withstand corrosion, but cost more. For this reason, many plants still operate under sub-optimal conditions. Carbon capture technology can also mitigate carbon dioxide emissions, but carbon capture can reduce the power generated by as much as 42%

Some coal-fired power plants use coal to produce syngas (synthetic gas). The syngas, in turn, makes steam. This two-step process qualifies as clean coal technology. It makes controlling carbon dioxide emissions and other pollutants easier. The primary component of syngas is hydrogen, which, with further purification, can power fuel cells.

What are your thoughts on clean coal? Let us know on our Facebook, Twitter, or feedback page. In the meantime, check out this week’s Valentine’s Day crossword puzzle.

Until next time, Happy Wordsmything!

Reference

Li, F., & Fan, L. S. (2008). Clean coal conversion processes–progress and challenges. Energy & Environmental Science1(2), 248-267.