More sulfur dioxide and other acid gasses could be scrubbed from power plant emissions with a new technology developed by the Department of Energy’s Pacific Northwest National Laboratory. The new method, Reversible Acid Gas Capture, is a sustainable twofer: it doubles the amount of pollutants currently captured by the leading water-based scrubber, and it is far more energy-efficient. David Heldebrant, the scientist who headed the PNNL research team, points out that the technology easily lends itself to a retrofit for existing power plants. That’s good news for reducing pollution from coal-fired power plants, but it would be a mistake to call it a win for “clean coal.”
Sulfur Dioxide and Power Plant Emissions
Sulfur dioxide is one of the gasses emitted by burning coal or oil, typically to generate electricity or in smelting and other industrial processes. According to the U.S. EPA, aside from the documented effects on human health, the environmental effects of high concentrations of sulfur dioxide include acidic deposition, haze, stunted plant growth, species decline, and corrosion of the national heritage – in other words, damage to concrete and limestone buildings, statues, monuments, and other historic structures.
Reversible Acid Gas Capture and Sulfur Dioxide
The Reversible Acid Gas Capture process uses oil-like organic liquids that contain no water to bind with the acid gasses in power plant emissions. The liquid is then heated to recover the gasses for proper disposal. In comparison, the other leading method uses monoethanolamine, which captures only half the amount of gasses by weight, and must be mixed with water to dilute its corrosive properties. The excess water requires more energy to pump and heat to a point where the captured gasses are released. Monoethanolamine, also called ethanolamine, is toxic and flammable in addition to being a corrosive.
PNNL and Acid Gas Capture
Before turning to sulfur dioxide capture, PNNL researchers developed a similar process for capturing carbon dioxide, resulting in a liquid salt. After the captured carbon is stripped out, the liquid reverts to its original state and can be reused. Heldebrant presented the team’s work with the acid gasses sulfur dioxide, carbonyl sulfide and carbon disulfide at a meeting of the American Chemical Society in mid-August.
Acid Gas Capture and “Clean Coal”
Reversible Acid Gas Capture has great promise as a transitional technology that would provide a relatively quick and inexpensive way to reduce emissions from coal-fired power plants. Over the long run, though, coal itself will have to go. Cleaning up emissions from power plants does not make coal any less “dirty” in terms of environmental damage. For starters, pollution related to coal transportation is a problem, with marine traffic in particular being identified as a significant source of sulfur emissions. The transportation issue is growing, too. China, which has vast coal resources of its own, is reported to have become a net importer of coal from Russia and Australia. Asia, Europe and South America have also become important overseas importers of coal from the Appalachian region of the U.S., where mountaintop coal mining has literally blown up and buried hundreds of pristine mountains and streams in one of America’s richest ecosystems. This practice gives the lie to “clean coal,” regardless of any improvements in tailpipe emissions from power plants and industrial processes.
Image: Clem Rutter on wikimediacommons, tugs berthing coal carrier at power station.