Can Captured Carbon Save Coal-Fired Power?

Like all big coal-fired power plants, the 1,600-mega-watt-capacity Schwarze Pumpe plant in Spremberg, Germany, is undeniably dirty. Yet a small addition to the facility—a tiny boiler that pipes 30 MW worth of steam to local industrial customers—represents a hope for salvation from the global climate-changing consequences of burning fossil fuels.

To heat that boiler, the damp, crumbly brown coal known as lignite—which is even more polluting than the harder black ­anthracite variety—burns in the presence of pure oxygen, releasing as waste both water vapor and that more notorious greenhouse gas, carbon dioxide (CO₂). By condensing the water in a simple pipe, Vattenfall, the Swedish utility that owns the power plant, captures and isolates nearly 95 percent of the CO₂ in a 99.7 percent pure form.

That CO₂ is then compressed into a liquid and given to another company, Linde, for sale; potential users range from the makers of carbonated beverages, such as Coca-Cola, to oil firms that use it to flush more petroleum out of declining deposits. In principle, however, the CO₂ could also be pumped deep underground and locked safely away in specific rock formations for millennia.

From the International Energy Agency to the United Nations–sanctioned Intergovernmental Panel on Climate Change (IPCC), such carbon capture and storage (CCS), particularly for coal-fired power plants, has been identified as a technology critical to enabling deep, rapid cuts in greenhouse gas emissions. After all, coal burning is responsible for 40 percent of the 30 billion metric tons of CO₂ emitted by human activity every year. “There is the potential for the U.S. and other countries to continue to rely on coal as a source of energy while at the same time protecting the climate from the massive greenhouse gas emissions associated with coal,” says Steve Caldwell, coordinator for regional climate change policy at the Pew Center on Global Climate Change, an Arlington, Va., think tank.

Even President Barack Obama has labeled the technology as important for “energy independence” and included $3.4 billion in the economic stimulus package for “clean coal” power plants. But although multiple projects around the world examine or test aspects of CCS, few of them have been connected to a full-size power plant: one producing on average 500 MW and upward of 10,000 metric tons of carbon dioxide a day—the core of the emissions problem.

“It makes nine metric tons of CO₂ per hour at full load,” says Staffan Görtz, Vattenfall’s CCS spokesperson, of the $100-million CCS demonstration boiler at Schwarze Pumpe. But he acknowledges that “we don’t have a storage site yet.”

Buried at Sea
Storage may be the simplest part of the CCS challenge. After all, since 1996, the Norwegian oil company StatoilHydro has been stripping CO₂ out of natural gas from the Sleipner field in the North Sea and rather than venting it to the atmosphere has been ­pumping it back into the field 1,000 meters deep for permanent storage.

The basics of carbon dioxide storage are simple: the same Utsira sandstone formation that has stored the natural gas for millions of years can serve to trap the CO₂, explains Olav Kaarstad, CCS adviser at Statoil. The 250-meter-thick band of sandstone—porous, crumbly rock that traps the gas in the minute spaces between its particles—is topped by a relatively impermeable 200-meter-thick layer of shale and mudstone (think hardened clay). “We aren’t really much worried about the integrity of the seal and whether the CO₂ will stay down there over many hundreds of years,” Kaarstad says.

More than 12 million metric tons of CO₂ have been injected into the formation, he notes. Statoil monitors its storage through periodic seismic testing, a process that is not unlike a sonogram through the earth, according to hydrologist Sally Benson, director of the global climate and energy project at Stanford University. That monitoring indicates that between 1996 and this past March, the liquid CO₂ has spread out as a thin layer permeating a three-square-kilometer expanse of porous sandstone—just 0.0001 percent of the area available for such storage.

“We’re not going into a salt cavern; we’re not going into an underground river. We’re going into microscopic holes,” explains geologist Susan D. Hovorka of the University of Texas at Austin, who has worked on pilot projects in the U.S. “Add it up, and it’s a large volume” of storage space.

Indeed, the Department of Energy estimates that the U.S. alone has storage available for 3,911 billion metric tons of CO₂, in the form of geologic reservoirs of permeable sandstone or deep saline aquifers, according to a 2008 atlas. These reservoirs are more than enough for the 3.2 billion metric tons of CO₂ emitted every year by the roughly 4,600 large industrial sources in the country. Most of that storage is near where the majority of coal in the U.S. is burned: the Midwest, Southeast and West. “There are at least 100 years of CO₂ sequestration capacity and probably significantly more,” Benson says.

The storage seems to be long term as well; the sequestered gas doesn’t just sit in the rock waiting for a chance to escape. Over decades it dissolves into the brine that shares the pore space or, over longer time spans, forms carbonate minerals with the surrounding rock, Hovorka notes. In fact, when she tried to pump CO₂ out of her test site ­using natural gas extraction techniques, the attempts failed completely.

According to the IPCC, which issued a special report on CCS in 2005, a properly selected site should securely store at least 99 percent of the sequestered CO₂ for more than 1,000 years. James Dooley, a senior research scientist at Pacific Northwest National Laboratory and an IPCC lead author, considers that to be a reachable goal. “If it took all that energy to shove [the CO₂] into that sandstone, it’s going to take a lot of energy to get it out,” he notes. “Like an oil field, where we get out half or less of the original oil in place, a lot of the CO₂ gets stuck in there. It’s immobilized in the rock.”

Encouraged by the success of the Sleipner project, Statoil recently began another CO₂ injection program at the Snøhvit natural gas field in the Barents Sea, despite the requirement that a 150-kilometer pipeline be built on the seabed to pump the CO₂ to where it can be sequestered.

And since 2004 oil giant BP and its partners (including Statoil) in the In Salah gas field in Algeria have been stripping the nine billion cubic meters of natural gas produced there annually of the 10 percent carbon dioxide it contains and pumping a million metric tons of liquid CO₂ back into the underlying saline aquifer through three additional wells.

BP uses a variety of techniques, among them satellite monitoring, to observe the impact of the CO₂ storage (and natural gas removal) on the land. Whereas some areas sank by roughly six millimeters as natural gas was extracted, near the CO₂ injection wells the land rose by some 10 millimeters, says Gardiner Hill, manager of technology and engineering for CCS at BP’s alternative energy arm. The U.S. National Energy Technology Laboratory is also working on developing appropriate monitoring, verification and accounting technologies.

BP and Statoil are not doing these CCS projects for charity, of course. Norwegian government tax on carbon of roughly $50 a metric ton inspired the CO₂ sequestration at Sleipner and Snøhvit. “It costs a fraction of the tax,” Kaarstad says. “We are actually making money out of this.”

Both Statoil and BP foresee a bonanza of moneymaking CO₂ storage opportunities. Hill notes that if CCS is deployed on a very large scale, society will need the expertise of the oil industry—its “100 years of understanding the subsurface,” he says. “We would expect the experience we are building through this to position BP to take advantage of any future business.”

Money Today
Pumping CO₂ into the ground already makes some people money through enhanced oil recovery (EOR). For 35 years oil services companies such as Denbury Resources and Kinder Morgan have piped carbon dioxide from naturally occurring reservoirs in Colorado to the declining oil fields of the Permian Basin in West Texas.

The U.S. has at least 100 such projects and 6,000 kilometers of CO₂ pipelines. All told, they have injected some 300 billion cubic meters of the gas since the 1970s, according to R. Tim Bradley, Kinder Morgan’s president of CO₂, to raise the yield from oil fields by some 650,000 extra barrels a day—more than 10 percent of daily U.S. total production.

Most important with respect to CCS, the Great Plains Synfuels Plant in North Dakota has pumped as much as two million metric tons of carbon dioxide a year to the Weyburn oil field in Saskatchewan since 2000. The CO₂ basically scours more hydrocarbons out of the oil field. “The Dakota gasification project is creating synthetic gas and taking the CO₂ from that process,” then piping it to the Weyburn oil field, observes Kurt Waltzer, carbon storage development coordinator at the Clean Air Task Force, an environmental group based in Boston. “In effect, you have demonstrated all the components of doing a CCS project.”

Using carbon dioxide to pump out more fossil fuels—and permanently storing the gas in the process—might sound counterproductive to limiting climate change because those fuels, when burned, put more CO₂ into the atmosphere. But it does reduce overall emissions by at least 24 percent, calculates Ronald Evans, Denbury’s senior vice president of reservoir engineering: every recovered barrel of oil eventually puts 0.42 metric ton of CO₂ into the atmosphere, but 0.52 to 0.64 metric ton is injected underground in recovering it. In fact, Bradley estimates that enhanced oil recovery in the U.S. could reduce CO₂ emissions by 4 percent, if done correctly.

The great fear commonly associated with carbon sequestration is that trapped CO₂ might suddenly escape to the surface with deadly consequences, as happened in 1986 at Lake Nyos in Cameroon. That volcanic lake had naturally accumulated two million metric tons of carbon dioxide in its cold depths; one night it spontaneously vented, displacing the oxygenated air, and suffocated more than 1,000 nearby villagers.

Yet in all the decades of commercial CO₂ injection for EOR, there have been no dangerous leaks. CO₂ from leaks and ruptured injection wells has always dispersed too quickly to pose a threat.

For example, prospectors in Utah drilling for natural gas in 1936 accidentally created a CO₂ geyser. It still erupts a few times a day as pressure builds but is “so unhazardous that it’s a tourist attraction, not a risk,” says Stanford’s Benson. In fact, air concentrations of carbon dioxide have to build up to more than 10 percent to be hazardous, which is difficult to achieve, according to modeling at Lawrence Livermore National Laboratory.

The reason is that CO₂ belching from a volcanic lake creates conditions very different from those of the gas escaping from a wellhead or seeping into a basement, explains Julio Friedmann, leader of the carbon management program at Lawrence Livermore. At Lake Nyos, an abrupt release of the CO₂ allowed dangerous concentrations to pool in low-lying surrounding areas. Pressurized gas escaping from a wellhead or crack simply mixes rapidly with the atmosphere, presenting no danger, much as the use of a fire extinguisher is not hazardous. In situations where atmospheric mixing is minimal, such as for a slow leak into a basement, the problem can be eliminated by simply installing a sensor and a fan, as in apartment buildings today near natural CO₂ seepages in Italy and Hungary.

At a demonstration project in Japan, even a magnitude 6.8 earthquake didn’t shake injected CO₂ loose from a deep saline aquifer; the wellheads did not so much as leak. Big earthquakes might cause leakage, but in many cases, they will not, Friedmann says.

Nevertheless, “the first CCS project that is done badly is the last CCS project that will be done,” warns Mark Brownstein, New York City–based managing director of business partnerships in the climate and air program at the Environmental Defense Fund (EDF). “In this respect, it is very similar to nuclear power.”

So storage may work, but can the carbon dioxide from power plants be captured? After all, as Statoil’s Kaarstad says, “power plants are an order of magnitude more difficult with regard to capturing CO₂.”

Capturing CO₂
Today three types of technology can capture CO₂ at a power plant. One, as at the Schwarze Pumpe, involves the oxyfuel process: burning coal in pure oxygen to produce a stream of CO₂-rich emissions. The second uses various forms of chemistry—in the form of amine or ammonia scrubbers, special membranes or ionic liquids—to pull carbon dioxide out of a more mixed set of exhaust gases. The third is gasification, in which liquid or solid fuels are first turned into synthetic natural gas; CO₂ from the conversion of the gas can be siphoned off.

The primary problem with all of them is cost. Simply put, it costs money—and energy—to capture the CO₂, ranging from as little as $5 a metric ton at natural gas projects such as In Salah to more than $90 a metric ton for certain gasification technologies.

The Department of Energy estimated in May 2007 that a new power plant burning pulverized coal and equipped with amine scrubbers to capture 90 percent of the CO₂ would make electricity at a cost of more than $114 per megawatt-hour (compared with just $63 per MWh without CO₂ capture). A similar integrated gasification combined cycle (IGCC) plant—in which coal is turned to gas before being burned—capturing the same amount would produce electricity for roughly $103 per MWh. For the consumer, the extra cost of carbon capture would therefore amount to about $0.04 per kilowatt-hour.

The DOE, for its part, hopes to bring that price down. “In terms of total cost, they want to shoot for $10 per metric ton of CO₂,” says CO₂ sequestration project leader Rajesh Pawar of Los Alamos National Laboratory. “We are closer to the $50 per ton range right now.”

Nevertheless, even the currently high costs have not stopped utilities and governments from building some carbon capture plants and planning for more. The 180-MW Warrior Run power plant in Maryland already captures 96 percent of its CO₂ emissions to sell in fire extinguishers. The Kingsport power plant in Tennessee has been capturing CO₂ since 1984 to sell to carbonated beverage makers. Abroad, Vattenfall will expand the Schwarze Pumpe operation and convert several commercial boilers in power plants, such as Janschwalde in Germany and Nordjylland in Denmark, for CCS by 2015, according to Vattenfall’s Görtz. Australia and China are both building what will become zero-emissions coal-fired power plants using IGCC technology, dubbed ZeroGen and GreenGen, respectively.

The Obama administration may even resurrect the FutureGen project—a 275-MW IGCC power plant that would capture 90 percent of its emissions; the Bush administration had canceled it because of spiraling costs (which may have been miscalculated). And the DOE has offered at least $8 billion in loan guarantees for coal-fired power plants with CCS.

Duke Energy is spending $2.35 billion to build a 630-MW IGCC power plant in Edwardsport, Ind., that may become the first commercial CCS project in the country—although as designed (and pending approval), it would capture only about 18 percent of the CO₂ it will generate in 2013. “It is our goal to make this one of the first demonstrations of CCS at a working power plant,” says Angeline Protogere, a Duke spokesperson. “Coal powers about half the nation’s electricity, and we have to find ways to burn it cleanly.”

Of course, such a demonstration plant will not address some of the other issues vilifying coal use, such as mountaintop-removal mining to get at coal seams or the toxic coal ash left over afterward. And all (or nearly all) of the greenhouse gas would need to be captured for a coal-fired power plant to be climate-friendly. But IGCC is capable of removing 90 percent or more of the CO₂. “Our request is to look at 18 percent capture and sequestration,” Protogere says. “That doesn’t preclude going back and asking for a higher level later on.”

Duke is not alone. American Electric Power will begin ­capturing at best just over 3 percent of the 8.5 million metric tons of carbon dioxide emitted by its 1,300-MW Mountaineer Power Plant in West Virginia later this year and injecting the CO₂ more than three kilometers underground. The Erora Group plans to build a 630-MW IGCC plant with CCS dubbed Cash Creek in Henderson County, Kentucky. Summit Power proposes to build a 170-MW IGCC plant in West Texas that would capture 80 percent of its CO₂ emissions. BP and Southern Company have projects as well.

But previous plants, such as two proposed by the utility NRG in New York State and Delaware, have fallen by the wayside. They were killed by the high cost of the technology and a lack of federal policy—a cap-and-trade program, a carbon tax or some other mechanism effectively setting a price on CO₂ pollution—to make them economically feasible, notes Caroline Angoorly, head of environmental markets at JPMorgan Chase, who formerly led development of these projects while at NPG.

Nevertheless, Oklahoma-based Tenaska is planning for two plants. One $3.5-billion plant in Taylorville, Ill., would gasify the high-sulfur local coals before capturing at least 50 percent of the CO₂. Another $3.5-billion plant planned for Sweetwater, Tex., would burn pulverized coal to generate 600 MW of electricity while capturing its 5.75 million metric tons of emissions postcombustion with amine or ammonia scrubbers or, possibly, with advanced membranes that separate CO₂ from other flue gases.

Already Australia and China have demonstrated that such postcombustion capture is possible in pilot plants. At Loy Yang Power Station in Victoria, a pilot plant run by CSIRO will capture 1,000 metric tons of CO₂ a year; the Australian research organization has collaborated with China’s Huaneng Group to use an amine scrubber to capture CO₂ from a co-generation power plant in Beijing and then sell it. And Statoil is building a CCS research site at its Mongstad refinery in Norway.

If postcombustion capture can be demonstrated commercially, “then the market for those existing coal-fired power plants is very large. There are at least two billion tons of domestic emissions from pulverized coal power plants,” says Greg Kunkel, Tenaska’s vice president for environmental affairs. “You can’t tackle the larger problem [of climate change] unless you deal with those plants in some way.”

And that consideration has brought even environmental groups such as the Natural Resources Defense Council (NRDC) and the EDF to support carbon capture and storage. By their estimations, coal-fired power plants coming online since the turn of the millennium will emit more CO₂ than all other human coal burning has since the dawn of the industrial age: 660 billion metric tons over their 50-year lifetime versus 524 billion metric tons between 1751 and 2000. “The next 25 years of investment would produce 34 percent more emissions than all previous human use of coal,” says engineer and scientist George Peridas of NRDC’s climate center. “This is a massive legacy, and we cannot afford to let that happen.”

Not all environmentalists agree, of course. Both the Sierra Club and Greenpeace have objected to CCS, although all environmentalists seem to agree that global greenhouse gas emissions must be reduced by at least 80 percent below 1990 levels by midcentury, a goal also shared by the Obama administration.

“Environmentalists are talking about coal not because we love coal,” adds Brownstein of the EDF. “It’s because we have to deal with coal to achieve the kind of CO₂ reductions we need to make in the timeframe we need to make them.” As a result, the NRDC, the EDF, the Clean Air Task Force and other groups support both a cap-and-trade scheme to limit CO₂ emissions as well as subsidies for the first CCS coal-fired power plants to be built. “If we don’t address the problem of coal, it’s game over for climate change,” says John Thompson, director of the coal transition project for the Clean Air Task Force.

And CCS can be equally well applied to other CO₂-intensive industries: cement production, steel making and aluminum smelting, among others. They can even be combined with the burning of plant matter to create a “carbon negative” fuel that when burned removes more CO₂ from the air than it puts in. But it is going to take time: research engineer Howard Herzog of the Massachusetts Institute of Technology estimates that the first new CCS coal plant in the U.S. won’t be completed before 2015. “We may have by 2020 a handful, maybe even close to 10,” he says. “If your goal is 80 percent cuts [in CO₂ emissions] by 2050, then it’s not big enough.”

But “every five years of inaction ... requires an extra gigaton of reductions,” notes BP’s Hill. “Unless we get started now, we don’t get the advantage of CCS and the emissions reductions we need.” And action is going to take money: the IEA estimates at least $20 billion over the next decade, whereas the industry group American Coalition for Clean Coal Electricity says it will cost $17 billion for CCS to be available by 2025.

“We’re going to have to do it, the same as adding wind, solar, nuclear power and conservation,” says Friedmann of Lawrence Livermore. “It’s a climate imperative, so let’s get on with it.”

Note: This article was originally printed with the title, "Can Captured Carbon Save Coal?"