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Coal — Affordable, Available and Clean? Maybe.
SciGuy, a science blog with Eric Berger

Saturday, June 17, 2006

If you're concerned about greenhouse gases, then burning coal is your worst nightmare. If you burn a ton of coal, you generate two tons of carbon dioxide. Yes, really -- the burnt carbon molecule attracts two heavier oxygen atoms, and presto, you've got carbon dioxide.

A large coal-fired plant, say a 1,000 MW-plant that can power up to 900,000 homes, will spew 6 million tons of carbon dioxide into the atmosphere per year. That's the equivalent of 2 million cars, and coal power plants account for at least one-quarter of the carbon dioxide humans pump into the atmosphere. Now consider this: 90 percent of China's power comes from coal, and will continue to do so as the country grows.

On the plus side, however, is coal's abundance, especially in the United States, which has about 26 percent of the world's coal reserves. There's probably enough coal in the world to keep the lights on and the air conditioners running for two centuries. Certainly that's long enough to master solar energy or fusion power, right?

So coal presents a best-case and worst-case scenario: it's cheap and abundant, and yet it's terrible for the environment. That's why I found this news of a new and cheaper method of capturing and sequestering carbon dioxide such a hopeful development:

Capture begins with a new technology from the New Hampshire company Powerspan. In a large industrial box, Powerspan passes the airy remnants of coal combustion through an ammonium carbonate solution. The carbon dioxide in this flue gas -- roughly 10 percent to 15 percent of it -- bonds with the solution to form ammonium bicarbonate, while the other elements pass through on their way to smokestack release. From a given stream of waste gas, the technology captures 90 percent of the CO2 or about 20 tons a day for every 24 megawatt-hours of electricity produced.

When heated, the ammonium bicarbonate releases a relatively pure stream of CO2. This CO2 can then be compressed by pressures of up to 2,000 pounds-per-square-inch, making it into a supercritical gas with the density of a liquid but the easy flow of its unpressurized state. It costs about 10 percent of the electricity generated by the coal burning to capture and compress the greenhouse gas, according to Frank Alix, Powerspan's chairman and CEO--far less than the 30 percent required for other proposed technologies.

Technologies to store compressed carbon dioxide have likewise advanced in recent years, with places like the salt domes beneath Texas and Louisiana being ideal repositories.

What kind of future could there be if clean coal became a reality? Electricity prices would probably stabilize. Electric cars suddenly become a lot more carbon neutral. And voila -- we reduce, by a great deal, our dependence upon unfriendly foreign governments for our energy.

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