NEWS SEQUESTRATION FEATURE
NATURE|Vol 442|10 August 2006
PUTTING THE CARBON BACK
One way to keep carbon dioxide out of the atmosphere is to put it back in the ground. In the first of two News Features on carbon sequestration, Quirin Schiermeier asks when the world's coal-fired power plants will start storing away their carbon. In the second, Emma Marris joins the enthusiasts who think that enriching Earth's soils with charcoal can help avert global warming, reduce the need for fertilizers, and greatly increase the size of turnips.
The hundred billion tonne challenge
etzin, a dozy village of 4,000 people west of Berlin, hardly looks like a vision of the future. Nestled in the Havel countryside -- an idyllic mix of rivers and forests -- it has a small tourist industry and, as is typical for such parts of eastern Germany, a not-so-small unemployment problem. "There's no news at the moment", says the community's website. But there could be news soon. In 2004, Ketzin was chosen as the site of mainland Europe's first large-scale carbon storage demonstration project. By the end of the year, drilling will start at a former gas storage facility on the edge of town. In the next two years, some 60,000 tonnes of carbon dioxide (roughly the annual carbon dioxide output of 40,000 cars) will be injected into an aquifer of salty water 700 metres beneath the surface. The Ketzin project will test the `storage' part of carbon capture and storage (CCS), a strategy designed to allow energy to be generated from fossil fuels without the carbon dioxide produced in the process ending up in the atmosphere. Little more than a fringe idea five years ago,
K
CCS was singled out at the 2005 G8 summit as a technology that could make a difference to climate change. Experts see it as a central part of any strategy for maintaining the generation of energy at today's levels: as Vassilios Kougionas, a European Commission officer in charge of clean-coal initiatives and international energy relations, puts it, "Without CCS there is no point in continuing with fossil fuels." And yet, for all this enthusiasm, there is a distinct lack of urgency in government approaches. The countries most interested in CCS have, at best, preliminary plans for it; most haven't even got that far. Meanwhile, the number of power stations whose carbon dioxide is neither captured nor stored is rising inexorably, as is the atmospheric level of the gas. To some observers, this represents a failure not of science or technology, but of will. "It does require quite substantial research and technology efforts to make CCS better and more efficient -- but we could still start today if desired," says Hans Ziock, a physicist at Los Alamos National Laboratory in New Mexico, who has worked on carbon dioxide capture
2006 Nature Publishing Group
technologies for more than a decade. David Hawkins, director of the National Resources Defense Council's Climate Center in Washington DC, goes further: "Global efforts are completely out of scale with what is needed."
Act now or pay later
The International Energy Agency (IEA) predicts that by 2030, global energy demand will grow by 1.7% a year. Although contributions from nuclear and renewable sources may increase, the IEA predicts that 85% of the rise in demand will be met by greater use of fossil fuels. This means the overall capacity of coal-fired power plants will have to double in that time, from 1,100 gigawatts to 2,200 gigawatts1. Taking into account the existing plants that will be shut down, the world is looking at 1,400 gigawatts' worth of new coal plants (see graphic on page 623). This doubling of capacity is the greatest expansion of power generation in the planet's history. Since 1750, humanity's burning of coal has released about 150 billion tonnes (gigatonnes) of carbon into the atmosphere. During their lifetimes, the new generation of plants will
620
G. BAKER/AP
NATURE|Vol 442|10 August 2006
SEQUESTRATION NEWS FEATURE
release 140 gigatonnes. Meanwhile, climate cal characteristics that will need to be assessed scientists are arguing that carbon dioxide levels in situ. He also points out that even if some should not be allowed to get much higher than reservoirs leak, it still makes more sense to use 550 parts per million (p.p.m.); the current level them, and thus spread out emissions over time is 380 p.p.m., which compares with 280 p.p.m. rather than do nothing. in the eighteenth century. Some argue that the Everyone agrees that large-scale carbon ceiling needs to be a lot lower. dioxide storage would be a gargantuan techRobert Socolow is a physicist and co-princi- nical feat. Locking away 250 million tonnes of pal investigator of the Carbon Mitigation Ini- carbon per year -- equivalent to 4% of annual tiative at Princeton University in New Jersey. global emissions -- would require an injecHe calculates that if carbon dioxide levels are tion of 25 million to 35 million barrels per to be kept in the desired range, then humanity day, depending on compression density. That's needs to avoid about a third of the emissions equivalent to about a third of the flow of oil expected in the next 50 years. That means find- currently coming from reservoirs. ing a way to not release 175 gigatonnes of carAccording to Orr, if the infrastructure used bon. "If we get going now," he says, "the job will to pump carbon dioxide into the ground was be less than half as difficult. If we don't it means roughly the same size as the infrastructure curwe're running a very costly strategy." rently deployed to bring oil to the surface, it The good news is that, in principle, such could deal with about a seventh of the world's vast amounts of gas could indeed be tackled by production of fossil-fuel-generated carbon. CCS. Deep aquifers in the world's sedimentary That is less than half the amount produced basins have a total storage capacity estimated at at power stations and large factories -- the between 1,000 and 10,000 gigatonnes2. Pump- sources for which CCS is best suited. ing carbon dioxide into them is a straightforward matter. Oil companies already pump Ground work carbon dioxide into petroleum reservoirs on a "It's a big enterprise," says Socolow. But piperoutine basis as a way of flushing out the hydro- line building and well-drilling are mature and carbons. And experience with oil shows that remarkably inexpensive technologies, and such reservoirs can keep their contents stored running costs would be extremely low. Experts away for geological lengths of time, points out calculate that setting up storage facilities, each Gnter Borm, director of geo-engineering at capturing several million tonnes of carbon per Germany's National Research Centre for Geo- year, for the carbon dioxide produced from sciences in Potsdam and coordinator for the hundreds or thousands of plants, might cost as European Union-funded Ketzin project. much as $80 billion. In a world set to invest $16 Not all reservoirs are as well adapted to CCS trillion in energy by 2030, $80 billion is not an as a 100-million-year-old oilfield might be. unthinkable amount; the cost of deep disposal Some may leak, and in some there might be for Britain's nuclear waste has recently been a risk of sudden, catastrophic releases of gas. estimated as 11.3 billion ($21 billion). What's In low-lying land, such leakages could suffo- more, the figure might come down as the techcate people because carbon dioxide is heavier nology matures and economies of scale cut in. than air, so will fill up valleys and basins. Under As yet, industrial-scale CCS activities the sea, gas-filled reservoirs could potentially are limited to just three sites -- in Norway, Canada and Algeria -- and to trigger landslides and thus tsumegatonnes rather than giganamis. But provided storage sites "If we get going are chosen carefully, designed tonnes of carbon. Since it began for safe operation, and properly in 1996, the Norwegian project now, the job will monitored, the risks are managehas pumped around 10 million be less than half tonnes of carbon dioxide 1,000 able, says Lynn Orr, director of as difficult." -- the Global Climate and Energy metres beneath the North Sea bed into the Utsira Sand forProject at Stanford University in Robert Socolow mation; the carbon dioxide is California. a contaminant in natural gas At Ketzin, scientists will keep track of any undesired chemical interactions from the Sleipner West field. In the Canadian between carbon dioxide and minerals, which and Algerian projects, the gas being stored could in principle dissolve the `cap-rock' that away is also being used to enhance the proseals a storage site, or contaminate drink- ductivity of oilfields, which covers some of able ground water. Scientists monitoring a the costs. All these sites have been continusmaller storage project, the Frio Brine Pilot ously monitored for possible leakages, but Experiment in Texas, recently reported that none seems to have occurred. the injection of carbon dioxide had made the In total, 11 or so full-scale CCS projects are brine 1,500 metres down substantially more planned, or have been proposed, in the United acid3; such acidic brine could potentially eat States, Canada, Britain, Norway Germany, and through the surrounding rock and escape into Australia. But given present trends, experts think it unlikely that CCS will be employed higher aquifers. But Hawkins counsels against too much at any substantial level before 2030, by which pilot-project research of this type. He thinks time the 1,400-gigawatts' worth of power stathat each reservoir will have unique geologi- tions will already have been built. For CCS to
2006 Nature Publishing Group
DATA LINK GAS AG LEIPZIG
621
W. FERNANDES
SEQUESTRATION NEWS FEATURE
NATURE|Vol 442|10 August 2006
make a difference, the mechanisms it requires must be available to a substantial fraction of those plants after they have been built. Conventional coal-burning technology, which will probably be used to produce 1,200 of the 1,400 gigawatts, produces flue gases that are about 14% carbon dioxide. If the carbon dioxide is to be captured and stored it must first be `scrubbed' from the gas stream, typically by running the gases through an amine solution. This takes up the carbon dioxide and then, when heated, releases it in pure form. The problem with using this technique is that the equipment needed not only costs money -- it also takes up a lot of space. Fitting such equipment into a plant not designed for it is expensive. The main alternative to the conventional plant is the integrated gasification combined cycle (IGCC). The capital costs for IGCC plants are 20% greater than for conventional plants. But they have environmental benefits -- among which is being cheaper to kit out for CCS. In IGCC plants, the fuel -- coal, fuel oil or biomass -- is introduced into a hot gasifier along with oxygen and steam. This produces a fuel gas consisting mainly of carbon monoxide and hydrogen. The carbon monoxide then goes through a second `shift' reaction with steam, making carbon dioxide and more hydrogen. The carbon dioxide can be relatively easily separated at this point. Four IGCC plants are currently in operation -- two in the United States, one in the Netherlands and one in Spain. Although more expensive, and less profitable, than conventional plants, they have very low emissions of sulphur dioxide and other pollutants. Carbon dioxide capture from plants such as these would be significantly easier and cheaper than from conventional plants.
Making it pay
At the moment, the efficiency of IGCC plants is about 40%, which is roughly the same as that for good conventional plants. CCS would drop the efficiency of both sorts of plant to about 30%. But IGCC plants use two thermodynamic cycles; the hydrogen from the gasifier and the shift reaction drives a gas turbine while the heat from that turbine and the gasifier drives a separate steam turbine. Having more than one cycle means that, in principle, it should be possible to push the overall efficiency much higher, to the point where, even when paying the energy penalty associated with CCS, the plants would still be competitive. "First comes efficiency, then CCS," says Jacek Podkanski, a senior energy technology specialist with the IEA. The US `FutureGen' initiative, a $1-billion publicprivate partnership to design, build, and operate a coal-fuelled zero-emissions power plant by 2015, aims to prove the technical and economic feasibility of a commercialscale IGCC plant fitted with CCS. In Europe,
Flow reversal: Statoil has pumped around 10 million tonnes of carbon dioxide, separated from the Sleipner West natural gas field, beneath the North Sea bed.
622
2006 Nature Publishing Group
STATOIL
NATURE|Vol 442|10 August 2006
SEQUESTRATION NEWS FEATURE
per tonne of car- are capture-ready. The idea is also part of an bon dioxide tax on EUChinese `memorandum of understandemission-intensive ing' on near-zero-emissions power generation 1,600 industries. The cost technology, and was highlighted in the 2005 New coal of capturing, trans- G8 action plan. CCS coal (under current plans) porting and storing But some fear that capture-readiness will just 1,200 a tonne of carbon provide a cheap way of doing a small amount dioxide is estimated to cut emissions. "The term `capture-ready' 800 by the Intergovern- is pretty meaningless, because its definition mental Panel on includes subsequent installation of unidentiClimate Change to fied equipment," says Hawkins. 400 be between $20 and To him, it would make more sense for govConventional coal $70, which is why ernments to set up well-defined performance the Statoil seques- standards for power-generating facilities, such as 0 tering project makes a maximum carbon dioxide output allowed per 2003 2007 2011 2015 2019 2023 2027 Year sense. But emitting unit of electricity. Such standards could become a tonne of carbon gradually more strenuous as better technologies dioxide currently become available. Another possibility, Socolow the German energy company RWE Power has costs less than $20 on the European exchange, points out, would be simply to subsidize the recently announced that it will invest 1 bil- and analysts doubt that the price is likely to technology. He thinks 23 cents per kilowattlion (US$1.3 billion) in the construction of a increase much in the future. "The price of emit- hour would make CCS a profitable route for a 450-megawatt IGCC plant in Germany. The ting carbon dioxide must rise, otherwise it just new coal-fired plant using today's technologies. plant, fully equipped for CCS, could become won't work," says Borm. That is only a little more than the operational in 2014. Other companies, such "CCS is perfectly d...