Extreme weather events, like Superstorm Sandy that just drenched the northeastern coast of the United States, often refocus the public's attention on climate change. With Sandy, there were no straightforward connections, partly because it’s hard to connect climate change to a single weather event. Nevertheless, the storm may leave the US public more willing to tackle some of the challenges of climate change.
One of these big challenges is mitigating carbon emissions. Industrial development, power plants, and transportation integral to our modern society all release greenhouse gases that capture heat from the sun and warm the planet. The production and consumption of energy accounts for the majority of the greenhouse gas emissions in the United States, 91 percent of which is made of carbon dioxide (CO2) from burning fossil fuels.
In a world dependent on oil, coal, and natural gas, global emissions of CO2 will continue unless we improve energy efficiency and continue replacing some of those fossil fuels with some combination of nuclear power and renewable energy like solar and wind power. Another option for emission reductions involves preventing coal-fired power plants, cement plants, and steel mills from emitting carbon dioxide in the first place. Carbon capture systems grab carbon dioxide from the flue gas and concentrate the pure CO2. Pumping that gas underground could permanently store the carbon in places other than our planet’s atmosphere.
Carbon capture and storage (CCS) technologies could be part of our low-carbon energy future. Calculations from the International Energy Agency estimate that the cheapest suite of emissions reductions technologies operating by 2050 includes a 14 percent contribution from CCS. If that scenario played out as imagined, CCS would capture about 123 gigatonnes of CO2 by 2050. Currently, 16 operating or planned large-scale CCS projects will collectively capture about 0.03 percent of that CO2 yearly by 2015 (36 million metric tons). Most of that gas comes from natural sources or existing industrial processing streams. Only a few projects, like Boundary Dam in Canada and Kemper County in Mississippi, apply CCS to power plants.
Taken together, current CCS projects may not look like they’re on track to help reduce global carbon emissions as there are so few industrial-scale capture projects—particularly on power plants. But these projects are necessary baby steps for scaling up CCS technologies. Every capture plant and storage project is an opportunity to improve and develop the technology for the future while curbing CO2 emissions today, says Charles Freeman, a researcher at the Pacific Northwest National Laboratory in Washington state.
Why aren’t carbon capture technologies able to make a dent in our global CO2 emissions yet? Capturing carbon requires energy, so a power plant equipped with a carbon capture system must burn more coal. Walking capture technologies through incremental scale-ups to maximize energy efficiency takes money as well. Without regulations that either require carbon capture technologies or tax carbon emissions there’s little economic incentive for carbon-emitting industries to capture their carbon right now.
As it stands, some funding for operating and planned CCS projects comes from federal governments in the US, Canada, Norway and the European Union. But that money is becoming hard to find in some parts of the world, particularly Europe. In June, developers in Scotland scrapped plans to build a 1852 MW coal-fired power plant outfitted with carbon capture over concerns about acquiring government funding. That plant would have been six times larger than the average power plant in the US in 2011.
But as government money is drying up, other sources are emerging. Increasingly, the oil industry is stepping in to fund CCS projects because captured CO2 can help them retrieve more oil from drained fields through a process called enhanced oil recovery (explained on page 2 of this article). They’re also supporting projects that hope to offset CCS installation and operating costs by turning captured CO2 into a sellable product, like baking soda. The X-Prize Foundation, known for funding spacecraft competitions, is also developing a challenge to turn carbon dioxide into useful materials.
With the right economic drivers, be it policy or CO2 utilization, some capture technologies are very close to being developed and available at the scales necessary, Freeman says. And those technologies could help mitigate climate change. Recent models predict that outfitting US coal-fired power plants with current CCS technology, despite the energy penalties, could reduce greenhouse gas emissions by about 50 percent by 2100 (Environ. Sci. Technol., DOI: 10.1021/es3006332).
A large carbon capture facility opened in Mongstad, Norway last May. It’s a test bed for capture technologies attached to either a gas power plant or an oil refinery. But the testing phase is just that—a test. All captured CO2—initially up to 100,000 metric tons a year—will be released to the atmosphere. Transporting and storing that small amount of captured carbon dioxide would be too expensive, according to Vegar Stokeset, spokesman for the facility in Mongstad. However, storage will be necessary once a capture plant is built to process the entire emissions from the power plant.
The carbon capture technology deployed at this test site is time- and industry-tested. Trapping carbon dioxide in a solution of amines (nitrogen-containing molecules where the nitrogen atom sports a free pair of electrons) was first patented in 1930, and natural gas refineries still use this trick today to remove CO2 mixed with the crude methane (Science, 2009, DOI: 10.1126/science.1176731). Workers bubble the CO2-containing natural gas through an amine solution, commonly monoethanolamine. Carbon dioxide binds to the nitrogen atom of the amines, while the rest of the gas passes through. Boiling the amine solution releases the carbon dioxide gas, which can be compressed and transported through pipelines.
Heating and cooling the amine solution for each round of carbon capture requires energy. Add in more electricity to power pumps that compress the captured CO2, and carbon capture equipment sucks about 20 to 30 percent of a power plant’s capacity, says Gary Rochelle, a chemical engineer at the University of Texas, in Austin. This parasitic energy load, combined with the upfront costs of building a capture plant near a power plant, tip the balance sheet away from installing such facilities without a regulatory mandate. But once operating, amine scrubbers could capture 75 to 90 percent of the CO2 in flue gas.
Moving amine scrubbing from pilot projects to full-sized power plants requires testing the process on increasingly larger scales. Without large-scale commercial installations of the amine scrubbing technology, it’s hard to improve the energy efficiency of the process. And without big capture plants operating, some argue that the government can’t mandate the technology yet. "It’s a chicken and egg problem—though mostly chicken problem, taken quite literally," Rochelle says. "[The legislature] is too chicken to make the tough decisions that need to be made on this issue."
In the US, regulations might be in the works, but not without political complications. The Environmental Protection Agency recently proposed the first regulations limiting carbon emissions from future coal-burning power plants. In its last vote of the session in September, the House of Representatives passed a bill to prevent those restrictions, though the bill will die in the Senate. But a question remains unanswered: if carbon emissions limits are eventually enacted, how can power plants comply without passing the cost on to their customers via higher electricity bills?