Quicker, easier way to make coal cleaner found

November 17, 2008

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.

Source: Massachusetts Institute of Technology

Explore further: Carbon Capture: key green technology shackled by costs

Related Stories

Permafrost: hiding a climate time bomb?

November 20, 2015

On the front line of climate change in the Canadian Arctic, scientists hunt for clues to a potentially catastrophic global warming trend: melting permafrost.

Could companies someday make a profit off unwanted CO2?

November 18, 2015

The world has a carbon dioxide problem, and to fix it, much attention has been paid to renewable energy sources, which don't emit the greenhouse gas. But what if we could turn waste CO2 into marketable chemicals and fuels ...

Seagrass restoration paying off for eastern shore

October 30, 2015

Seagrasses are crucial to the health of shallow coastal marine environments, in Virginia and worldwide. Seagrass meadows provide habitat and serve as nursery and feeding grounds to a diverse range of sea creatures – crustaceans, ...

Peru creates huge national park in Amazon basin

November 7, 2015

Peru is creating a national park to protect a vast territory in the Amazon basin that is vulnerable to drug trafficking and illegal logging and mining, the country's environment minister said Saturday.

Recommended for you

The ethics of robot love

November 25, 2015

There was to have been a conference in Malaysia last week called Love and Sex with Robots but it was cancelled. Malaysian police branded it "illegal" and "ridiculous". "There is nothing scientific about sex with robots," ...

Glider pilots aim for the stratosphere

November 20, 2015

Talk about serendipity. Einar Enevoldson was strolling past a scientist's office in 1991 when he noticed a freshly printed image tacked to the wall. He was thunderstruck; it showed faint particles in the sky that proved something ...


Adjust slider to filter visible comments by rank

Display comments: newest first

3.7 / 5 (3) Nov 17, 2008
So how are they going to capture the carbon dioxide?
1 / 5 (4) Nov 17, 2008
I'm guessing, but if the astronauts are going to start recycling their body fluids for drinking water, someone could figure how to remove the CO2 from using coal.
5 / 5 (1) Nov 18, 2008
What the hell are you talking about? Do you even know what coal is?

...we're talking about cola, aren't we??? LMAO
5 / 5 (1) Nov 18, 2008
May I submit the following alternative?

4 / 5 (1) Nov 19, 2008
This is a model. Where is the field test to vallidate it? Computer models are not a primary source of data.
4 / 5 (1) Nov 24, 2008
Yeah, again back to coals. Why those people don't get it-there are so many alternatives, why should they use coal!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.