Tuesday, August 28, 2012

New Proposal for Clean Coal: Deep Freeze

A new way to treat the gaseous waste from coal fired power plants is being proposed by a scientist from the University of Oregon, freezing out the toxic nitrogen and sulfur gases and a large fraction of the carbon dioxide.
Refrigerating coal-plant emissions would reduce levels of dangerous chemicals that pour into the air — including carbon dioxide by more than 90 percent — at a cost of 25 percent efficiency, according to a simple math-driven formula designed by a team of University of Oregon physicists.

The computations for such a system, prepared on an electronic spreadsheet, appeared in Physical Review E, a journal of the American Physical Society.

In a separate, unpublished and preliminary economic analysis, the scientists argue that the "energy penalty" would raise electricity costs by about a quarter but also reap huge societal benefits through subsequent 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," said UO physicist Russell J. Donnelly, whose research team was funded by the U.S. Department of Energy for the work detailed in the published journal article
While the required cooling machinery would be large — potentially the size of a football stadium — the cost for construction or retrofitting likely would not be dramatically larger than present systems that include scrubbers, which would no longer be necessary, Donnelly said. The new journal article does not address construction costs or the disposal of the captured pollutants, the latter of which would be dependent on engineering and perhaps geological considerations.
Last December the U.S. Environmental Protection Agency 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 would do better based on the conservatively produced computations by Donnelly's team — capturing at least 98 percent of sulfur dioxide, virtually 100 percent of mercury and, in addition, 90 percent of carbon dioxide.
The energy costs of the system are pretty obvious; it takes a lot of refrigeration to reduce the temperature of the flue gases in a coal fired power plant below the temperature needed to freeze out the gases, essentially making dry ice out of the CO2.  But those costs are well known; apparently they would cost on the order of 25 percent of the energy produced by the plant.

However, it offers other benefits as well. Current flue gas discharge (FGD) treatment techniques are massive scale chemical neutralization in the scrubbers, (barge loads of lime or limestone), massive post capture treatment treatment system, and resulting large scale water pollution hazards.  Does the 25% efficiency loss include replacing the existing treatment systems?  Could it be even more economical in the long run?  It's certainly worth consideration.

Found at Watts Up With That.

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