‘Carbon Trees’ Would Suck CO2 Out of Air and Into Your Soda
Carbon dioxide is one of the most plentiful gases in the atmosphere, but when soda makers want to inject the fizz into their sweet-tasting drinks, they often have to pay through the nose for it. Many bottlers buy CO2 that was created as a byproduct of industrial processes, paying up to $300 per ton for the gas. So what if instead of relying on CO2 shipped via tanker trucks, soda makers could snare the gas right out of the air with a forest of roof-mounted synthetic "trees" — cutting their costs and helping reduce greenhouse gas pollution at the same time? That’s the vision of Billy Gridley, CEO of Global Research Technologies (GRT), a New York-based startup that is working to make prototypes of these high-tech devices commercially viable. Not long ago, few scientists believed it was possible to extract CO2 out of the atmosphere in a way that could be profitable. The barrier? Most methods of CO2 extraction consume enormous amounts of energy and require trucks or pipelines to ship the CO2 where it’s needed, which gets prohibitively expensive. GRT sees a way around those problems: create a device to capture the CO2 where it’s needed. The company has devised a lower-energy approach that Gridley says can capture CO2 cheaply enough to supply commercial buyers of the gas. The devices are called "carbon trees" because they mimic the carbon dioxide-absorbing abilities of real trees. In time, Gridley believes, GRT’s technology will be ready to help meet the huge challenge if Congress or the Environmental Protection Agency dictate that CO2 emissions must be captured and stored permanently as a potential solution to climate change. For now, GRT’s breakthrough looks less like a tall tree than a single fuzzy branch, one that’s connected to hodgepodge of tubes, compressors and other gizmos. GRT unveiled a working demonstration setup at last December’s meeting of the American Geophysical Union in San Francisco. By proving the viability of its technology, GRT created hope in climate science circles that "air capture" could yet emerge as a viable economic option to reduce global warming pollution. Above: GRT demonstrated its air capture technology at the American Geophysical Union conference last December. Photo: Molly Samuel, KQED.org Their prototype stands out because today no other system is being commercialized to capture CO2 out of ambient air. Others are focusing instead on industrial emissions. Backed by billions in public subsidies, engineering leaders such as Alstom, GE, and Siemens are racing to standardize systems that can snare the greenhouse gas exhaust from cement kilns, steel mills, and power plants, where CO2 levels are much higher than in the atmosphere. More than half of global greenhouse gas emissions come from such "stationary" sources. Utility executives describe the challenge of developing these systems as something like retrofitting a chemical plant on the back of a power plant. And once captured from power plants and factories, the CO2 will have to be trucked or piped away, either to markets where it can be sold, or to geological formations where it can be buried. Creating such a CO2 network, critics argue, will be on par with replicating the nation’s natural gas pipeline system — a 213,000-mile-long network that was built more than a century ago. GRT’s approach promises to eliminate much of this costly distribution infrastructure. Consider a McDonald’s today. "To carbonate beverages at the soda fountain, every week or so a truck rolls up to refill their CO2 supply," says Gridley. "A GRT unit (on the roof of the restaurant) could eliminate all those trucks, and all the fuel needed to deliver the CO2." The seed of GRT’s project to build synthetic trees took root in 2004, as a breakthrough made by Klaus Lackner, a geophysicist at Columbia University. Conventional CO2-capturing approaches rely on some combination of chemical additives, heat, and pressure to process CO2. But Lackner began toying with a class of materials that he knew had a chemical propensity to lock up CO2 on their surface. Lackner’s insight was part luck, part hunch. The twist was realizing that an increase in humidity — rather than energy-hogging shifts in heat or pressure — could get the material to exhale its captured CO2. "I didn’t quite believe it when I got it to work the first time," he says. Another cost-savings plus: the material Lackner identified is commonly available as a resin, or plastic, that can perform thousands of capture-and-release cycles. GRT’s first commercial version will look more like a merry-go-round than a tree. The entire device is designed to be packed into a standard shipping container, making it easy to transport. When set up, door-sized panels made of Lackner’s special resin are hung on a carousel that will rotate slowly, exposing them to CO2 as they go round. Upon completing a revolution, a panel is automatically retrieved from the carousel and pulled into a chamber where it is wetted to release the stored CO2. The filter is then returned to the carousel for another rotation. Above: Artist’s rendering of commercial air capture system. Courtesy GRT The process generates a stream of "dilute CO2," as much as 250 times more concentrated than in the atmosphere, at concentrations of about 5 to 10 percent. To generate pure CO2, the panels can be wetted in a vacuum — a step that can double or triple adds costs. Someday, Lackner imagines, this extraction step could be performed inside tree-like towers designed to automatically seal, extract the CO2, and then reopen once the gas is piped away. "The taller the structures are, and the more surface area they have, the more CO2 they’ll capture," says Lackner. First on GRT’s hit list of potential customers are those with an appetite for dilute CO2: agricultural and biofuel players such as greenhouses and algae farms, which need large volumes of dilute CO2 to feed to their plants. Algae farms are emerging as a source of renewable biofuels, such as bio-diesel or "green gasoline." In these markets, GRT anticipates selling dilute CO2 at $50 to $75 per ton. (In December, as part of $564 million grant for biofuels development, the U.S. Energy Department directed $125 million to five algal-fuel projects). GRT’s other early-stage target includes the $1-2 billion market for pure CO2, such as producers of carbonated drinks and dry ice. Trucking costs can drive up prices for pure CO2 to $300 per ton for customers the farthest away from the source. In both these arenas, GRT plans to deliver cost-competitive CO2 by 2012. GRT’s next step would be to sell to very-high volume buyers. Today’s biggest market for CO2 is in the United States’ "oil patch," where drillers pump liquefied CO2 under high pressure into aging wells to drive more oil out of them. In Texas and the Southwest, the center of this "enhanced oil recovery" industry, drillers tap into natural reservoirs of CO2 in the earth and ship them to oil fields via pipeline. It’s roughly a $10 billion market today, where some 40 million tons of pure CO2 is bought annually. As the price of oil goes up, the thirst for CO2 rises; even at current prices, today’s CO2 supplies can’t meet demand. Gridley figures that if GRT can drive down its costs to $50 per ton of pure CO2, demand from oil drillers could be worth tens of billions of dollars annually. All this depends, of course, on whether GRT can successfully drive down the price of its systems. Standardizing the design is the key to reducing costs. "It’s like manufacturing cars," says Lackner. "Build one by hand, and it’s expensive. But build thousands on an assembly line, and the per-unit cost falls dramatically." Today, as GRT debugs its prototype to launch one-off mobile units next year, Lackner estimates the price for a single rig would be around $200,000. If GRT can scale up to supply the oil patch markets, he predicts large-scale manufacturing would drive the price down to a car-like $20,000 per unit. Farther out, the biggest opportunity of all for carbon capture players could be U.S. or global carbon markets. By 2020, if Kyoto-style regulations to control greenhouse gas pollution are adopted in the United States, Gridley estimates that some 2,000 million tons of CO2 would have to be captured and sequestered annually — potentially a $40 billion business. By that time, Gridley hopes GRT’s air capture technology will be among the lowest-cost options for companies looking to meet the new rules. But the company must first prove that it can supply today’s soda makers with something closer to one ton per day. In the past year, GRT relocated from Arizona to New York City, where Lackner is building a research team at Columbia University to advance the basic science of air-capture technology. Gridley, meanwhile, is focusing on developing and contracting out the company’s first fully-integrated prototype. He’s also hunting for venture capital to fund commercial development of the company’s first round of commercial units, scheduled to roll out in 2011.
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The Rock That Ate CO2
When Peter Kelemen started his fieldwork in the Omani desert several years ago, he wasn’t looking for a solution to global warming. His research, which concerned the geology of the earth’s mantle-the 1,800-mile-thick layer beneath the crust-was something only his rock-obsessed colleagues could appreciate. To study ancient volcanism, Kelemen frequently collected a common mantle rock called peridotite, large tracts of which can be found in Oman, forced to the surface over many ages by tectonic collisions. When peridotite is exposed to the air, it reacts with carbon dioxide, and its outer layers are transformed into carbonate rock. For Kelemen, a geologist at Columbia University, this seemed to be bad news. "When the rock is all weathered and turned into carbonate, that obscures the high-temperature history," he says. "So my main response over the years when I would see these carbonate deposits was to run the other way." Recently his response has undergone a metamorphosis. Kelemen now thinks that with some modest technical investment, peridotite formations-which also exist on or near the surface in California and New Guinea, on the Aegean coast, and on some Pacific islands-could be used to slow global warming by absorbing billions of tons of carbon dioxide from the atmosphere every year. Kelemen’s epiphany came about a year ago, when he and a Columbia colleague, Juerg Matter, decided to date Oman’s carbonate rocks. Geologists knew that the chemical reaction between the surface layers of peridotite and carbon dioxide occurs rapidly. "If a leaf or a pebble falls on these rocks and you come back a few days later, it’s all covered up with carbonate," Kelemen says. But underground veins of carbonate were thought to take millions of years to form. Kelemen and Matter found otherwise. "We took a bunch of samples and sent them to Woods Hole for carbon-14 dating," Kelemen says, referring to the oceanographic institute in Massachusetts. "When all the dates came back, every single sample was less than 45,000 years old, and I really started to get excited." The rocks’ young age meant that they were still forming, probably fed by carbon dioxide dissolved in groundwater. Kelemen and Matter calculated that Oman’s peridotite deposits naturally soak up about 100,000 tons of carbon annually. Although that is only a small fraction of the 30 billion tons of CO2 we throw into the atmosphere every year, it still dwarfed previous estimates of peridotite’s appetite for carbon. More important, Kelemen and Matter realized that the carbon-storing potential of peridotite beneath the earth’s surface remained largely untapped. In a paper published last November in Proceedings of the National Academy of Sciences , Kelemen and Matter proposed that peridotite’s CO2 absorption rate could be ramped up by a factor of 100,000 using conventional oil-drilling technology. Pressurized CO2 and hot water could be pumped into peridotite formations. Heat from the water would accelerate the reaction that forms carbonate rock. After this kick-start, the reaction, which releases its own heat, would become self-sustaining. The formation of new carbonate would cause rocks to buckle and shift imperceptibly. "Not really earthquakes," Kelemen says. "Just little stress releases in the subsurface, but nothing serious. "In principle-and when a scientist says that, you’re going to hear some science fiction," Kelemen warns-"if human output remains the same, and the Omanis could somehow convert every single kilogram of peridotite in that country into solid carbonate, they could take up all the human output for a thousand years. Rocks are very dense; the air is not." Realistically, Kelemen estimates that the peridotite in Oman could be used to lock up roughly one-eighth of the CO2 produced every year by the burning of fossil fuels. He and Matter envision two complementary strategies for storing CO2 in the world’s peridotite formations. The most straightforward approach would be to build power plants near peridotite beds, where carbon emissions could be captured on-site and pumped directly into the rocks. But that wouldn’t make a real dent in global emissions. The second approach would take advantage of an enormous, natural carbon-capture system: the oceans. Surface ocean water absorbs carbon dioxide from the air, so the CO2 content of the surface water is in equilibrium with the atmosphere. Kelemen and Matter propose that the seawater overlying shallow peridotite formations off the coast of Oman, the western United States, and elsewhere could be heated and injected beneath the seabed. The peridotite would react with the seawater, removing carbon dioxide to form carbonate rock. The CO2-depleted seawater would be returned to the surface to absorb more of the gas from the air, and the cycle would start again. Given the right combination of peridotite and shallow seafloor, this could work anywhere. "Seawater is free," Kelemen says, "and the air transports CO2 all over the world for nothing." Kelemen and Matter are now looking for a site in Oman for a pilot project, which they hope to launch within five years, probably by capturing carbon dioxide from the flue gases of a power plant and pumping it into peridotite formations on land. Their idea seems sound, says Wally Broecker, a geophysicist at Columbia and one of the world’s leading advocates of harnessing natural processes to reduce greenhouse gases. "When we’ve done everything we can with the other stuff, with alternative energy and carbon taxes, we’re going to find that we’re still dumping CO2 into the air at an alarming rate," Broecker says. "It’s a desperate situation, and we’ve got to push everything we can."
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The Rock That Ate CO2