By John P. Roche
Teams of scientists around the world are investigating potential ways to reduce the amount of carbon dioxide (CO2) in the atmosphere. This can be done in two ways: (1) by reducing the release of new CO2, via energy efficiency and use of non-carbon-based energy sources, or (2) by removing CO2 that is in the atmosphere or about to be released to the atmosphere, via sequestering carbon in plants, in soil, or in underground geological formations.
A team of researchers in Iceland, in a program called CarbFix, recently had success in injecting CO2 and water into basaltic rock 400 to 800 meters underground. They found that more than 95% of the injected CO2 turned to minerals in less than two years, which was far faster than expected. Basalt is attractive for this purpose because it contains calcium, and when CO2 is added to basalt, it reacts with the calcium to form calcium carbonate (CaCO3). (Basalt also contains magnesium, which can combine with CO2 to produce magnesium oxide [MgO]). The results of the CarbFix study, which was published in Science by Juerg Matter and colleagues, suggests that capture and storage of carbon in the ground can be feasible from a geological standpoint. But hurdles remain, including the high cost of the process.
In terms of cost, ameliorating atmospheric CO2 increase by reducing the release of new CO2, via energy efficiency and non-carbon energy sources, is the most economical. But energy efficiency can only do so much, and non-carbon energy sources, although attractive in terms of net cost and expanding in use, still produce only a fraction of our energy. This is where capture and storage of carbon underground could potentially serve as a useful interim measure. The process requires two steps: capturing the carbon dioxide and then storing the carbon. Capture and storage of carbon from small scale energy sources, like vehicles, might be impractical, but capturing carbon dioxide from larger sources, like fossil-fuel-based power plants, and then sequestering that captured carbon underground, might be achievable. A one thousand megawatt coal power plant releases millions of tons of CO2 each year. Capturing and storing that carbon would be beneficial environmentally if it could be made to work economically.
Basalt formations, which were used for carbon storage in the CarbFix study, are attractive because injected carbon can be incorporated into minerals quickly, locking up the carbon in a safe and long-term manner. Another option being studied is injecting CO2 into porous formations of sedimentary rock where CO2 can displace salty water in the pores of the rock. Scientists are also investigating injecting CO2 into rock formations under the ocean. David Goldberg and colleagues of the Lamont–Doherty Earth Observatory in New York State estimate that CO2 injection into basaltic formations in the deep ocean offers several advantages, including immense reservoir capacity, location of suitable reservoirs near population centers, and a reduced probability of leakage following injection. Goldberg and colleagues estimate that such deep-sea basaltic reservoirs could accommodate centuries of fossil-fuel generated CO2 from the United States.
Sequestering carbon under the ground or under the deep sea offers promise, but cost remains an issue. Eli Kintisch, in his news summary in Science magazine of Juerg Matter and colleagues CarbFix study in Iceland, wrote that the cost of sequestering a ton of carbon dioxide is estimated at from $50 to $100. Robert Socolow, in his analysis of carbon capture and storage options in Scientific American, wrote that experts estimate that capturing and storing a ton of CO2 from a type of coal plant called a coal gasification plant would cost only about $25. As technology improves, Socolow noted, this cost could be reduced even more.
One way to make the carbon capture-and-storage process more economical would be to sequester the carbon in concert with oil drilling operations. This would have three economic advantages. First, large oil drilling projects have infrastructure in place that could help lower the costs of injecting CO2 into the ground. Second, they have huge potential storage reservoirs on site—the formations that yielded the crude oil. Third, the injection of CO2 could be used to squeeze out oil reserves that the initial steps of the drilling process could not extract, helping to get this difficult to obtain oil and in turn helping to offset the cost of the carbon sequestration.
As complicated and costly as the process of capturing and storing carbon generated from fossil fuel combustion might be, it does offer considerable promise as one component of an atmospheric carbon-management strategy. Such a process could be implemented in concert with other measures, such as an increase in the use of biofuels for power generation plants. Biofuel plants would be carbon neutral because the carbon released via combustion would be taken up again in the growth of more biofuels. If used with carbon-capture technology, biofuel plants would act on a net basis to scrub carbon out of the atmosphere—a profound advantage. And as the search for reducing energy costs continues, non-carbon-based energy sources such as solar power may continue to be explored, given their simplicity and potential low net cost.
Matter, J.M., Stute, M., Snæbjörnsdottir, S.Ó., Oelkers, E.H., Gislason, S.R., Aradottir, E.S., Sigfusson, B., Gunnarsson, I., Sigurdardottir, H., Gunnlaugsson, E. and Axelsson, G. 2016. Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions. Science, 352(6291): 1312–1314. Read more.
Kintisch, E., 2016. New solution to carbon pollution? Science, 352(6291), pp.1262-1263. Read more.
Goldberg, D.S., Takahashi, T., Slagle, A.L. 2008. Carbon dioxide sequestration in deep-sea basalt. PNAS 105(29): 9920–9925. Read more.
Socolow, R. 2005. Can we bury global warming? Scientific American 293(1): 49–55. Read more.
Coninck, H.D., Loos, M.A., Metz, B., Davidson, O. Meyer, L.A. 2005. IPCC special report on carbon dioxide capture and storage. Intergovernmental Panel on Climate Change. Read more.
Vishal, V., Singh, T.N. 2016. Geologic Carbon Sequestration. Springer.
Lovins, A.B., 2005. More profit with less carbon. Scientific American, 293(3): 74–83. Read more.
Wilson, E. Gerard, D. 2007. Carbon Capture and Sequestration: Integrating Technology, Monitoring, Regulation. Blackwell.