Can Carbon Capture Technology Save America's Coal Power?

September 26, 2013

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CCS--Carbon-Capture--CO2--008The Wall Street Journal reported recently that the Obama administration’s new Environmental Protection Agency (EPA) rules on carbon emissions threaten to “block the construction of new coal-fired power plants unless they are built with novel and expensive technology to capture greenhouse-gas emissions.”

One might add “unproven” technology as well, which we’ll get into later.

EPA released new rules “that would set the first national limits on heat-trapping carbon pollution from existing power plants," writes The Christian Science Monitor. "To meet the new standards, coal-fired plants would have to install expensive new technology to capture a portion of their carbon dioxide emissions and bury them underground. Experts say new gas-fired plants could meet the proposed standards without new technology.” 

Many have speculated that the rules seem designed to eliminate coal-fired power plants. As WSJ noted, “The only way coal plants could comply is to capture carbon-dioxide emissions and stick them underground -- a costly process that hasn't been demonstrated at commercial scale before.” Technology that sounds great in theory, but has been tested only at a few sites.

Leaving aside the question of whether this was a move by the Obama Administration for the express purpose of scuttling the coal industry in America in the name of global warming, the question is whether the technology in question can work on the level it would need to.

Carbon Capture And Storage.

“It’s called carbon capture and storage (CCS),” writes Sarah Gardner, an industry observer reporting for Marketplace. “Rather than letting the CO2 go up the stack and into the air, the coal plant would capture it, put it under high pressure and then inject it into the ground, where it can’t fuel global warming.”

Gardner quotes Lisa Camooso Miller of the American Coalition for Clean Coal Electricity as saying that while the technology is being used, it’s “still not a technology that is in full deployment at a commercial scale.”

Something will have to be done, however, if the new rules stick. Science Insider reports that under the new rules, “coal plants would have to limit their carbon dioxide pollution to about  500 kilograms per megawatt hour of producing power,” which would be a “30 percent to 50 percent greater reduction than required by existing rules.”

Grab It, Store It, Bury It.

The idea behind carbon capture and storage (CCS) technology is to essentially grab the CO2 at the source of emission, store it, and go bury it. The carbon dioxide is separated from other gases, compressed and purified, and transported.

GreenFacts explains that there are three basic approaches to capturing the CO2:

A post-combustion system. With this approach, the flue gas produced by combustion of the fuel with air “only contains a small fraction of CO2,” which is captured “by injecting the flue gases in a liquid that selectively absorbs the CO2 (such as a cooled or compressed organic solvent).” At this point you’re left with “nearly pure CO2" which you can then separate out. “Similar separation processes are already used on a large scale to remove CO2 from natural gas.”

Image from www.rsc.org

Image from www.rsc.org

A pre-combustion system. This is used when the primary fuel “is first converted into gas by heating it with steam and air or oxygen,” resulting in a conversion which “produces a gas containing mainly hydrogen and CO2, which can be quite easily separated out.”

Oxyfuel combustion. This uses pure oxygen, not air, to burn the fuel, since air only contains 20 percent of oxygen and “a lot of nitrogen.” It’s pretty hard to separate oxygen from the air, but it results in “a gas mixture containing mainly water vapour and CO2.” The water vapour is taken out of the CO2 by cooling and compressing the gas stream.

Industry observer Damian Carrington notes that the post-combustion approach is the most common technology chosen for power plants. "Post-combustion has the advantage that it can be retrofitted to some existing power stations, which will generate much of the world's CO2 for decades to come,” he writes. It’s expensive, though, so older coal plants probably wouldn’t find it economically feasible.

Of the pre-combustion system, Carrington notes that the “advantage here is that the energy penalty -- the power used for separating out the CO2 – is much lower, perhaps just 11 percent and has no thermodynamic minimum, unlike post-combustion CCS. The downside is that it cannot be retrofitted.” If you’re building a new plant it’s a good choice, however.

Carrington points out that oxyfuel combustion “can only be used in new plants and an air-separation unit has to be built to provide the oxygen.” In other words, it’s expensive, too.

Statoil Tried It.

Proponents of CCS say that the Norwegian state energy company, Statoil, has used the technology to capture CO2 on its natural gas wells in the North Sea. Its incentive to do so -- the technology isn’t cheap -- is that Norway taxes carbon emissions.

But Statoil recently canceled the flagship CSS project. The Wall Street Journal reported that Norway was shutting down the Statoil ASA-operated Mongstad full-scale CO2 capture project, which was “meant to capture CO2 from the nearby gas-fired power plant and refinery… The project has been both challenging and costly, and the risks are now seen as too big to go through with it, the government said.”

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There are some promising projects in operation, however. Industry journal PlantEngineer reported in early September that the carbon capture and storage project at Yorkshire’s Ferrybridge coal-fired power station “has taken delivery of a steam-driven heat exchange system, from Spirax Sarco.”

The project will capture carbon dioxide from the flue gas of “major emitters, such as power stations,” and possibly bury it “in exhausted oil and gas reservoirs or saline aquifers.” It’s a relatively large capture process, using “an amine-based solvent to absorb up to 100 tonnes of carbon dioxide per day.”

The way PlantEngineer describes it, Spirax Sarco's steam system “is used to re-boil and regenerate the CO2 saturated solvent, for reuse, by stripping the carbon dioxide out under controlled high-temperature and pressure conditions.”

Carbon Into Bricks? Maybe.

One of the more intriguing technologies for dealing with captured carbon, which could be a far sight more useful than simply burying it, is turning the captured carbon into bricks, which can then be used to build homes and buildings.

Gizmodo Australia reported in August that a team from the University of Newcastle “is perfecting a method of capturing carbon emissions and transforming them into carbonate rock bricks.” The process is based on the fact that “the mineral carbonation technology replicates the Earth’s carbon sink mechanism by combining CO2 with low-grade minerals such as magnesium and calcium silicate rock to make inert carbonates.”

It might all be a moot point anyway, at least as far as coal is concerned. Science Insider writes that “the power industry is turning to natural gas for generating electricity, suggesting that the market for building coal-fired power plants with carbon capture equipment could be decades off.”

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