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Cooler coal plants could cut emissions

U. OREGON (US) — Refrigerating coal-plant emissions would reduce carbon dioxide emissions by more than 90 percent—at a cost of 25 percent efficiency.

Based on computations done on a spreadsheet and published in the journal Physical Review E, scientists project a dramatic reduction in levels of carbon dioxide and other dangerous chemicals coming from coal-fueled electricity-generation plants.

Such an “energy penalty” possibly would raise electricity costs by about a quarter—according to the scientists’ separate, unpublished economic analysis—but reap huge societal benefits through reductions of health-care and climate-change costs associated with burning coal.

An energy penalty is the reduction of electricity available for sale to consumers if plants used the same amounts of coal to maintain electrical output while using a cryogenic cleanup.

“The cryogenic treatment of flue gasses from pulverized coal plant is possible, and I think affordable, especially with respect to the total societal costs of burning coal,” says University of Oregon physicist Russell J. Donnelly, whose research team was funded by the US Department of Energy for the work detailed in the published journal article.

According to the journal paper, carbon dioxide would be captured in its solid phase, then warmed and compressed into a gas that could be moved by pipeline at near ambient temperatures to dedicated storage facilities that could be hundreds of miles away. Other chemicals such as sulfur dioxide, some nitrogen oxides, and mercury also would be condensed and safely removed from the exhaust stream of the plants.

“In the US, we have about 1,400 electric-generating unit powered by coal, operated at about 600 power plants,” Donnelly says. That energy, he adds, is sold at about 5.6 cents per kilowatt-hour, according to a 2006 Congressional Budget Office estimate.

“The estimated health costs of burning coal in the US are in the range of $150 billion to $380 billion, including 18,000-46,000 premature deaths, 540,000 asthma attacks, 13,000 emergency room visits, and two million missed work or school days each year.”

Costs to society

In their economic analysis, Donnelly and research assistant Robert E. Hershberger, also a co-author on the journal paper, estimate that implementing large-scale cryogenic systems into coal-fired plants would reduce overall costs to society by 38 percent through the sharp reduction of associated health-care and climate-change costs.

Donnelly experimented with such cooling in the 1960s with a paper mill in Springfield, Oregon, to successfully remove odor-causing gasses. Subsequently the National Science Foundation funded a study to capture sulfur dioxide emissions—a contributor to acid rain—from coal burning plants. The grant included a detailed engineering study by the Bechtel Corp. of San Francisco.

The Bechtel study showed that the cryogenic process would work very well, but noted that large quantities of carbon dioxide also would be condensed, a consequence that raised no concerns in 1978. “Today we recognize that carbon dioxide emissions are a leading contributor to climate-warming factors attributed to humans,” Donnelly says.

Calling upon that earlier work, Donnelly pursued a two-year project to update his thermodynamic calculations and create “a spreadsheet-accessible” formula for potential use by industry.

While the required cooling machinery might be the size of a football stadium, the cost for construction or retrofitting, he says, would not be dramatically larger than building present systems that include scrubbers, which would no longer be necessary.

The US Environmental Protection Agency in December issued new mercury and air toxic standards (MATS), calling for the trapping of 41 percent of sulfur dioxide and 90 percent of mercury emissions. A cryogenic system, Donnelly says, would capture at least 98 percent of sulfur dioxide and virtually 100 percent of mercury in addition to the 90 percent of carbon dioxide.

Co-authors with Donnelly and Hershberger on the journal article are: Charles E. Swanson, who earned his doctorate in physics from the University of Oregon and served as postdoctoral researcher under Donnelly; John W. Elzey, a former research associate in Donnelly’s Cryogenic Helium Turbulence Lab and now a scientist at GoNano Technologies in Moscow, Idaho; and John Pfotenhauer, who earned his doctorate at the University of Oregon and now is in the mechanical engineering department at the University of Wisconsin, Madison.

Source: University of Oregon

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