CO2 Emissions

Published on March 20th, 2012 | by Zachary Shahan


Storing CO2 Underground (New MIT Study)

March 20th, 2012 by  

Some interesting news from MIT this week on storing CO2 underground. Check out this MIT News Office repost by David Chandler:

Using tiny glass beads, the researchers simulated the way liquified carbon dioxide would spread through salty water in the pores of deep rock formations. Image: Michael Szulczewski, of the Juanes Research Group, MIT

A new study by researchers at MIT shows that there is enough capacity in deep saline aquifers in the United States to store at least a century’s worth of carbon dioxide emissions from the nation’s coal-fired powerplants. Though questions remain about the economics of systems to capture and store such gases, this study addresses a major issue that has overshadowed such proposals.

The MIT team’s analysis — led by Ruben Juanes, the ARCO Associate Professor in Energy Studies in the Department of Civil and Environmental Engineering, and part of the doctoral thesis work of graduate students Christopher MacMinn PhD ’12 and Michael Szulczewski — is published this week in the Proceedings of the National Academy of Sciences.

Coal-burning powerplants account for about 40 percent of worldwide carbon emissions, so climate change “will not be addressed unless we address carbon dioxide emissions from coal plants,” Juanes says. “We should do many different things” such as developing new, cleaner alternatives, he says, “but one thing that’s not going away is coal,” because it’s such a cheap and widely available source of power.

Efforts to curb greenhouse gases have largely focused on the search for practical, economical sources of clean energy, such as wind or solar power. But human emissions are now so vast that many analysts think it’s unlikely that these technologies alone can solve the problem. Some have proposed systems for capturing emissions — mostly carbon dioxide from the burning of fossil fuels — then compressing and storing the waste in deep geological formations. This approach is known as carbon capture and storage, or CCS.

One of the most promising places to store the gas is in deep saline aquifers: those more than half a mile below the surface, far below the freshwater sources used for human consumption and agriculture. But estimates of the capacity of such formations in the United States have ranged from enough to store just a few years’ worth of coal-plant emissions up to many thousands of years’ worth.

The reason for the huge disparity in estimates is twofold. First, because deep saline aquifers have no commercial value, there has been little exploration to determine their extent. Second, the fluid dynamics of how concentrated, liquefied carbon dioxide would spread through such formations is very complex and hard to model. Most analyses have simply estimated the overall volume of the formations, without considering the dynamics of how the CO2 would infiltrate them.

The MIT team modeled how the carbon dioxide would percolate through the rock, accounting not only for the ultimate capacity of the formations but the rate of injection that could be sustained over time. “The key is capturing the essential physics of the problem,” Szulczewski says, “but simplifying it enough so it could be applied to the entire country.” That meant looking at the details of trapping mechanisms in the porous rock at a scale of microns, then applying that understanding to formations that span hundreds of miles.

“We started with the full complicated set of equations for the fluid flow, and then simplified it,” MacMinn says. Other estimates have tended to oversimplify the problem, “missing some of the nuances of the physics,” he says. While this analysis focused on the United States, MacMinn says similar storage capacities likely exist around the world.

Howard Herzog, a senior research engineer with the MIT Energy Initiative and a co-author of the PNAS paper, says this study “demonstrates that the rate of injection of CO2 into a reservoir is a critical parameter in making storage estimates.”

When liquefied carbon dioxide is dissolved in salty water, the resulting fluid is denser than either of the constituents, so it naturally sinks. It’s a slow process, but “once the carbon dioxide is dissolved, you’ve won the game,” Juanes says, because the dense, heavy mixture would almost certainly never escape back to the atmosphere.

While this study did not address the cost of CCS systems, many analysts have concluded that they could add 15 to 30 percent to the cost of coal-generated electricity, and would not be viable unless a carbon tax or a limit on carbon emissions were put in place.

Franklin Orr Jr., a professor of earth sciences and director of the Precourt Institute for Energy at Stanford University, says, “The important contribution of this work is that it adds consideration of the rate of injection of CO2, because that can be constrained by pressure rise in the deep saline aquifers. This paper provides evidence that even when those constraints are considered there is lots of capacity for storage. That is a very useful contribution.”

James J. Dooley, a senior staff scientist at the Pacific Northwest National Laboratory who was not involved in the MIT study, calls it “a very sound analysis that demonstrates that given the appropriate regulatory and economic conditions, carbon dioxide capture and storage technologies can be the basis for deep and sustained greenhouse gas reductions in the U.S. and around the world.”

While uncertainties remain, “I really think CCS has a role to play,” Juanes says. “It’s not an ultimate salvation, it’s a bridge, but it may be essential because it can really address the emissions from coal and natural gas.”

The research was supported by grants from the U.S. Department of Energy, the MIT Energy Initiative, the Reed Research Fund, the Martin Family Society of Fellows for Sustainability and the ARCO Chair in Energy Studies.

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is tryin' to help society help itself (and other species) with the power of the typed word. He spends most of his time here on CleanTechnica as its director and chief editor, but he's also the president of Important Media and the director/founder of EV Obsession, Solar Love, and Bikocity. Zach is recognized globally as a solar energy, electric car, and energy storage expert. Zach has long-term investments in TSLA, FSLR, SPWR, SEDG, & ABB — after years of covering solar and EVs, he simply has a lot of faith in these particular companies and feels like they are good cleantech companies to invest in.

  • I think this entire CCS / clean coal stuff is a ruse to legitimate new Coal Power plants.
    They will build a few trial systems, encounter problems implementing it, the cost will rise and then they say it’s not worth it… but now we got these new coal power stations and they work for at least another 40 years…
    At least they are more efficent! (30% -> 40%)

    • Bob_Wallace

      Or at least a ruse to delay the closing of existing coal plants.

      We just aren’t building new coal plants in the US. There are a small number that were started some years ago and are yet to be finished and their is, I think, one new coal plant approved. But overall we’ve quit building coal plants.

      The coal industry is fighting a rear guard action in the US, holding off their eventual defeat.

      • I think the US will come to renewables in quite a different way, than places like Germany.

        The sad & rather disgusting, yet very effective extraction of unconventional natural gas reserves (fracking), will tranform the US energy sector, away from centralized power stations towards more decentralized gas fired power stations.

        Once the system becomes more and more decentralized, people & buisnesses will realize that combining it with local wind & solar makes it even cheaper for them.

        It’s the dirty road to a renewable future… but at least it’s a road. 😉

        • You might be spot on.

        • Bob_Wallace

          Agreed. We’re moving to a clean grid via a clean/dirty natural gas phase.

          Nice thing is, gas turbines are very dispatchable and they have a fuel price. If there’s wind or solar available those NG plants will be turned off.

          Then, my guess, battery storage will be cheaper than NG plants and the plants will rot away….

  • And what is the plan for the highly saline brine that must be extracted from the deep saline formations to make way for the CO2? It’s not empty space down there. Saline brine can’t be dumped on the surface. And what about the possibility of injection pushing brine into the drinking water?

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