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Clean Coal’s Dirty Secret – When ‘Clean’ Isn’t Clean


by Bill Chameides | February 4th, 2009
posted by Erica Rowell (Editor)

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In a bit of bitter irony “cleaning up” coal has increased coal waste. (Photo: Edbrown05/Wiki Commons)

Coal is the dirtiest fossil fuel. Burning it produces a myriad of noxious air pollutants. That’s a problem. Clean coal technology supposedly scrubs those pollutants before they get into the atmosphere. Problem gone, right? Not quite. Guess where those pollutants end up.

It has always amazed me that the best we’ve been able to do with waste from nuclear power plants is let it pile up at the plant itself – just not a sustainable solution. Little did I know that the same short-sighted model is being adopted at our nation’s coal-fired power plants.

When coal, a complex mixture of hydrocarbons and minerals, is burned, it generates not just electricity but byproducts in the form of air pollutants and solid waste including fly ash. I remember years ago asking someone who should know, what happens to the waste; he said it was recycled, put into construction materials and the like.

Another Turn of the Screw in the Story of Coal

That turns out to be only a small part of the story. And as a result of the coal ash spill at the Tennessee Valley Authority’s Kingston coal-fired power plant in Tennessee, the whole story of coal waste is beginning to see the light of day.

Since 2002 coal-fired power plants in the United States have produced an average of more than 120 million short tons of coal waste each year. In 2007 the United States produced more than 131 million short tons of coal waste. Only about 40 percent of that is recycled, and the rest is dumped into landfills and containment ponds like the one that gave way in Kingston. Every year we burn more coal, more of the stuff ends up in these ponds. Talk about toxic waste dumps.

But there’s more to this story than the leftover ash. There is also the serious problem of air pollutants: these include sulfur oxides (SOX), nitrogen oxides (NOX) and particulate matter (PM), which contribute to acid rain and smog, and a plethora of toxic metals such as mercury, which, among other things, renders fish caught from our lakes and streams unsafe for us to eat.

How to Deal With Pollution

There are two ways to deal with pollution:

  1. Pollution prevention means taking steps like enhancing energy-efficiency to produce less of the stuff in the first place.
  2. Pollution clean-up amounts to getting rid of whatever pollution is produced – and that often really means “storing” (or dumping) it, which isn’t the same as getting rid of it.

In the case of air pollution from coal-fired power plants, we have chosen the latter method for the most part – we’ve developed and implemented technologies that remove the air pollutants from the flue gas and convert them into solid materials.

‘Scrubbing’ the Flue

Cleaning NOX – Selective catalytic reduction (SCR) converts NOx pollutants into harmless nitrogen gas (N2) and water. Although using SCR may cause other toxic compounds to be concentrated in coal waste, this scrubbing method tends to have a better outcome than those that follow.

Cleaning SOX – The Clean Air Act’s requirements to remove SOX from coal-fired power plant emissions are typically met by using flue-gas desulfurization (FGD, in the alphabet soup of environmental terms). The process converts gaseous sulfur oxides into calcium sulfate, commonly referred to as gypsum, and/or calcium sulfite, a salt.

Cleaning PM – Power plants remove particulate matter through various collecting filters.

Once all these solid products are “caught,” they are thrown into the solid waste stream building up around the country in containment ponds and landfills. How much?

Some Staggering Statistics on Coal Waste

  • In the last two decades the volume of coal combustion waste has doubled: from about 65 to the more than 130 million short tons per year I mentioned above.
  • Incredibly, about 50 percent of that growth comes from flue-gas desulfurization [pdf] – our “fix” to clean up sulfate air pollution has actually significantly increased our coal waste problem. 
  • About 31 percent of this increased waste is recycled [pdf] into other uses; the rest is thrown into the coal waste stream.
  • So … “cleaning up” sulfate pollution has increased coal waste by almost 23 million short tons per year.

What’s perhaps worse is that this number is going to grow for two reasons:

  1. The primary market for gypsum (the main constituent of FGD waste that is reused) is near saturation and isn’t expected to be able to absorb much more coal waste; and
  2. Only about 30 percent of our coal-fired capacity have installed controls to limit sulfate pollution.

A New Waste Stream

The country is now getting ready to require coal-fired power plants to curb mercury emissions. Without question this is needed. Coal-fired plants are the single largest source of mercury in the United States, emitting about 48 tons annually.

When coal is burned, some of the impurities like mercury, lead, and arsenic that are concentrated in the fly ash, are removed as particulate matter. But about two-thirds of them are vaporized and thus currently uncontrolled.

The Bush administration’s Clean Air Mercury Rule (CAMR) established caps on mercury emissions, but the D.C. Court of Appeals negated the rule on on February 8, 2008 (see analysis of ruling [pdf]). (This is actually a good thing because mercury is a concentrated toxin that does not lend itself well to a cap-and-trade system. It would end up allowing some places to have elevated levels of mercury while others were cleaned up.) The Obama administration will likely develop new rules that pass judicial muster to regulate mercury emissions. This would be great for air quality, but it will cause another problem: it will move mercury into a different waste stream.

Cleaning up air pollution from coal is badly needed. But trading one form of pollution for another does not a clean technology make.

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1 Comment

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  1. clean burning coal
    Feb 23, 2009

    energy source would provide the US, both practically and economically. Geothermal energy is already less expensive to produce in terms of kilowatt-hours than the coal that the US keeps mining.

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