[Editors] MIT: A more eco-friendly option for coal power plants

[Elizabeth Thomson]

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MIT: A quicker, easier way to make coal cleaner
--‘Partial capture’ of emissions could be near-term move
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For Immediate Release
MONDAY, NOV. 17, 2008

Contact: Elizabeth A. Thomson, MIT News Office
E: thomson at mit.edu, T: 617-258-5402

Photo Available

***EDITORS, PLEASE NOTE: The following release is one of two you will  
be receiving about MIT research to be presented tomorrow, Nov. 18, at  
the 9th International Conference on Greenhouse Gas Control  
Technologies***




WASHINGTON, DC--Construction of new coal-fired power plants in the  
United States is in danger of coming to a standstill, partly due to  
the high cost of the requirement — whether existing or anticipated —  
to capture all emissions of carbon dioxide, an important greenhouse  
gas. But an MIT analysis suggests an intermediate step that could get  
construction moving again, allowing the nation to fend off growing  
electricity shortages using our most-abundant, least-expensive fuel  
while also reducing emissions.

Instead of capturing all of its CO2 emissions, plants could capture a  
significant fraction of those emissions with less costly changes in  
plant design and operation, the MIT analysis shows.

“Our approach — ‘partial capture’ — can get CO2 emissions from coal- 
burning plants down to emissions levels of natural gas power plants,”  
said Ashleigh Hildebrand, a graduate student in chemical engineering  
and the Technology and Policy Program. “Policies such as California’s  
Emissions Performance Standards could be met by coal plants using  
partial capture rather than having to rely solely on natural gas,  
which is increasingly imported and subject to high and volatile prices.”

Hildebrand will present her findings on Nov. 18 at the 9th  
International Conference on Greenhouse Gas Control Technologies in  
Washington, DC. Her co-author is Howard J. Herzog, principal research  
engineer at the MIT Energy Initiative and chair of the conference  
organizing committee.

The United States is facing a pressing need for more power plants that  
run essentially all the time. Renewable sources aren’t suited to the  
task, nuclear plants can’t be built quickly enough, and expanded  
reliance on natural gas raises price and energy-security concerns.  
Coal, which now supplies more than half of all U.S. electricity, seems  
the best option.

But as several states have started to regulate CO2 emissions, and  
others are expected to follow suit, some of the luster has come off  
coal. Amid the uncertainty, no one wants to be the “first mover” on  
building a new coal plant incorporating carbon capture and storage  
(CCS). Depending on the type of plant, carbon capture alone can  
increase the initial capital cost by 30 to 60 percent and decrease  
plant efficiency so that the cost per kilowatt-hour rises. That high  
cost would reduce — or possibly eliminate — the hours the plant will  
be called on to run. Plus, CCS hasn’t been proved at full scale, so no  
one knows exactly what to expect.

In Herzog’s view, the call for full carbon capture is “a policy of  
inaction, a policy that won’t move forward either new coal plants or  
the CCS technology.” Partial capture could be a viable intermediate  
step.

The push for full capture (defined as 90 percent of the total) is in  
part economic: everyone assumed that 90 percent capture would — due to  
economies of scale — yield the lowest cost per ton of CO2 removed.  
Anything less than 90 percent would mean a higher per-ton cost.

To investigate that assumption, Hildebrand and Herzog modeled the  
technological changes and costs involved in capturing fractions  
ranging from zero to 90 percent. The model takes into account  
technological breakpoints. For example, carbon capture is achieved by  
a series of devices that absorb CO2, release it and compress it. Full  
capture may require two or more parallel series.

The model confirms that the cost per ton of CO2 removed declines as  
the number of captured tons increases. Not surprisingly, when the  
second series is added, cost per ton goes up, but it then quickly  
levels off. Cost per ton is thus roughly the same at, say, 60 percent  
capture as it is at 90 percent capture. Since there are no economies  
of scale to be gained by going to 90 percent, companies can remove  
less — and significantly reduce their initial capital investment as  
well as the drop in efficiency once the plant is running.

The researchers conclude that as a near-term measure, partial capture  
looks promising. New coal plants with lower CO2 emissions would  
generate much-needed electricity while also demonstrating carbon  
capture and providing a setting for testing CO2 storage — steps that  
will accelerate the large-scale deployment of full capture in the  
future.

This research was supported by the MIT Carbon Sequestration Initiative  
and the National Science Foundation.

The GHGT-9 conference is organized by MIT in collaboration with the  
IEA Greenhouse Gas R&D Programme (IEA GHG), with sponsorship from the  
U.S. Department of Energy.

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Written by Nancy Stauffer, MIT Energy Initiative
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