Engineering Case Studies
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Carbon Capture and Storage for Climate Management
| posted 10-30-2009 |
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 In the global fight against climate change, one of the key strategies is switching to renewable energy. Fossil fuels are finite and running out, the argument goes, and they emit too much carbon dioxide and other greenhouse gasses into the atmosphere, contributing to climate change. Renewable energy sources like wind and solar do not emit greenhouse gasses. There's just one problem. Or perhaps several. Right now, there is almost no infrastructure set up to produce the amount of electricity the world needs through renewable means. And the cost of the technology, as it now stands, is prohibitive. That's today's reality, says Ruben Juanes, a professor of energy studies at the Massachusetts Institute of Technology, even if we don't like it. “We're not going to convert our energy systems, which are fundamentally fossil fuel-based, to solar or wind or biofuel-based in the next few years,” he says. “That's not to say we shouldn't work on it, because we should. But because these energy systems are so large, it creates lots of inertia before there can be a change. In the meantime, he says, “Every year we keep dumping into the atmosphere 25 gigatons of carbon dioxide, so maybe we should start doing something about it now, before the next energy system is put in place.” The solution that a lot of scientists are working on is to stop pumping all that carbon dioxide into the atmosphere, and start pumping it somewhere else—underground. Carbon capture: the details The process is called carbon capture and storage, and it involves using technology at the source of some of the major carbon emitters—like coal power plants and oil and gas fields—to collect the carbon dioxide before it gets dispersed into the air, and then store it, either deep underwater or in geologic formations underground. It's a process that has occurred naturally for millions of years. Stuart Gilfillan, a researcher at the University of Edinburgh School of Geosciences, says there are fields of carbon dioxide deep underground and underwater just as there are deposits of oil and gas. The carbon dioxide tends to be dissolved in water, he says, in underground reservoirs, called aquifers. Because carbon dioxide-enriched water is denser than regular water, it sinks. He says when engineers inject carbon dioxide underground, it tends to collect in a large cloud. Although carbon dioxide-infused water is denser than water without carbon dioxide, the carbon dioxide itself is less dense than water. It's also less viscous, he says, which means it's thinner and moves more easily through the aquifer's porous rock layers. As the cloud passes through the aquifer, it disintegrates. Bit by bit the carbon dioxide stays behind in tiny globules in the water. The key is to send down a cloud just small enough so that by the time the cloud gets to the end of the aquifer, it has disintegrated entirely. Juanes says his work shows that, in the U.S. at least, we have enough underground space to hold at least the next 100 years of carbon dioxide emissions. Putting carbon capture to the test There are a few major pilot projects already testing these technologies around the world. In North Dakota, the Dakota Gasification Company has built a small coal power plant that captures carbon by taking solid coal and heating it until it becomes a gas mixture consisting of methane, hydrogen, and carbon dioxide. Then they use a chemical process to convert the mixture to hydrogen and carbon dioxide. The hydrogen is burned as a clean fuel whose only byproduct is water, and the carbon dioxide gets stored. Although this process sounds very complex, Stuart Haszeldine, of the Scottish Center for Carbon Storage, says it's very efficient and can produce a wide range of useful byproducts. “If you build a new coal-burning plant, that's what you'd build,” he says. But the downside is that it can't be used to modify existing power plants. For that you'd have to use the one of two other methods. In one, currently in use in Norway at the Sleipner project, the exhaust from a power plant passes through a chemical solution that acts like a filter. The chemical attracts carbon dioxide and binds it there, and then a second stage process separates and liquefies the carbon dioxide for storage. One challenge of this method, says Haszeldine, is that the equipment needed to achieve it is very large, at least as big as the power plant itself. But it does have advantages: unlike gasification, this method can be retrofitted onto an existing plant, and it is already pretty far along in its development. At Sleipner, Statoil gas company has been separating carbon dioxide from their gas production and injecting it into an aquifer under the North Sea for the past 10 years. The third method that is also currently in use is the least tested. The first major pilot project just began in eastern Germany, by a Swedish company called Vattenfall. Rather than burning coal in regular air, which mostly consists of nitrogen, the project burns coal in pure oxygen. When you do that, the only byproducts are water and carbon dioxide—and it's fairly simple to separate the carbon dioxide out, pressurize it, and then store it underground. Haszeldine says an advantage of this method is that techniques to isolate oxygen from air are well established and proven. But the downside is that the process uses a lot of energy—which means it can significantly reduce the efficiency of a coal power plant. Another challenge the Vattenfall project has faced has little to with technology, and everything to do with politics. So far they haven't been allowed to inject any carbon dioxide into their proposed underground storage site. The local community has been fighting them, because they question what the consequences of that storage might mean for them. Haszeldine says the evidence, from existing natural carbon dioxide fields and experience with underground oil and gas, shows “good reason to believe carbon dioxide will be safely stored for tens of thousands of years.” Plus he says, the geological formations where scientists intend to store carbon dioxide are “too deep for drinking water and too shallow for oil and gas,” which means putting carbon dioxide there won't affect other natural processes or the human population. The counter arguments But the residents near the Vattenfall project aren't the only people worried about carbon storage. Lorelei Scarboro is a community organizer for Coal River Mountain Watch, an anti-coal organization in West Virginia. She says this isn't the first time the coal industry has proposed injecting a byproduct of coal underground. She says the government already issues permits to coal companies to inject toxic sludge into geologic formations underground, and as a result, “a lot of people are very sick because of contaminated water.” “That's our main concern with carbon capture and storage,” Scarboro says. “When they take the waste and drill this really long hole, or they decide to put it in sediment under the ocean, someday, somehow that will come back up and come back to haunt us.” Michael Crocker, media director for Greenpeace, says that's not even half the problem. The most important issue, he says, is that carbon storage technology is not ready, and by the time it will be, it will be too late to use it to stop global warming. His organization advocates an immediate end to coal power and a switch to renewable technologies like solar and wind. Additionally, Crocker says, even if the technology does get developed and implemented, “It uses between 10 and 40 percent of the power from the power station, which would virtually erase all the efficiency measures gained in coal-powered power plants in the last 50 years.” Simon Shackley, a social policy researcher on carbon storage issues, says “The public does have the power to stop a lot of this happening and have been in opposition to this in a lot of countries.” Shackley says the question is “not just what's best for utility x, but also for the community.” He says governments would do better to include detractors and proponents in the initial discussion of carbon capture and storage to look for a compromise everyone can agree to. “What does Greenpeace need?” he asks, to accept carbon capture as part of a multi-faceted solution. “Will they accept it if we change something else, or modify the design somewhat, or include a provision for some measures on energy efficiency?” He says conversations like these have a positive impact on the overall outcome. “If you got Greenpeace involved,” he says, “they'd push that sort of line, and that would be quite helpful. It's a different way to think about energy.” Toward a global strategy Given that the U.S. relies on coal power for more than 50 percent of its electricity, and huge developing countries like India and China seem to be ramping up their own coal-power initiatives, scientists like Juanes argue it's not realistic to count solely on wind and solar energy, without looking at short-term strategies for lowering the climate impact of coal. But Haszeldine says it will be at least another 10 years or so before these technologies could be ready to be implemented on a worldwide scale. Right now, the pilot projects tend to be working with 30–40 megawatt power plants—but a typical power plant today generates 300–400 megawatts. Shackley says scientists learn more every time they test a new technology. This learning curve allows them to make the technology more efficient and less expensive—and, he says, better they should make those improvements at an early stage, before the world invests billions of dollars in a vast infrastructure that costs a lot more than it needs to. But as the counter-arguments show, technology is only part of the challenge. The main reason Statoil began storing carbon instead of venting it was not because the technology existed, but because the government created a tax on offshore carbon dioxide emissions. That meant that, although it cost them money to build the infrastructure and store the carbon dioxide, it cost significantly less than paying a carbon tax. “They were really trying to promote this technology within Norway and could afford to do it,” Shackley says. “I don't think that would be repeated anywhere else in the world.” But he says governments can encourage this technology in other ways, such as allowing energy companies that capture and store carbon dioxide to charge higher prices. Steve Caldwell, a policy analyst from the Pew Center on Global Climate Change, says the key is to put a price on carbon, such as through a cap and trade system. “Putting a price will make firms make different decisions,” he says, such as to “invest in carbon capture and storage, build nuclear plants, or run more energy efficiency programs.” Haszeldine says he believes it is crucial to include carbon capture in any short-term plans to fight global warming. In his opinion, the problem is, “There aren't enough plants on the starting blocks right now.” He says projects have been proposed around the world, but “very few have actual money behind them. And even fewer countries have created a market mechanism to sell fuel from those plants for more money.” “It's easy to delay,” Haszeldine says, but the world has reached the crunch time. “There’s no known alternative to doing this. The world's hooked on burning fossil fuel. You can wait, but you'll suffer the consequences.” ______________________________ Carbon capture and sequestration: a viable alternative Carbon capture: hype or hope? ______________________________  COMMENTSWhat's the best way to encourage utility and oil companies to invest in expensive technology to store carbon? How do we accurately put a price on our environment? Leave your response in the comments below. |
