What’s the Real Story With Clean Coal?
The goal of the Sierra Club’s Beyond Coal campaign is to retire one-third of the nation’s over 500 coal plants by 2020; so far 147 have retired. Burning coal, the dirtiest fossil fuel, still produces about 40 percent of the electricity in the U.S., although this figure has been declining because of the natural gas boom. Coal mining destroys mountaintops and dumps rubble and toxic waste into streams. Burning coal is responsible for soot and smog that result in over $100 billion in health costs each year. Coal plants release toxic mercury into the air and leave behind dangerous coal ash pollution.
Moreover, coal-fired power plants are responsible for one third of all U.S. carbon dioxide emissions each year. Carbon dioxide, a powerful greenhouse gas, traps heat and warms the planet. In May, carbon emissions in the atmosphere topped 400 parts per million for the first time in over 2.5 million years. Humans have now put enough carbon dioxide into the atmosphere to change life on Earth as we know it; and we are already feeling the effects of climate change in more extreme weather and rising seas.
On June 25, President Obama made good on his promise to deal with climate change by proposing a multi-pronged approach to reduce U.S. greenhouse gas emissions. His plan includes boosting clean energy production, providing global leadership to address climate change, and preparing the nation for the impacts of climate change. The most significant measure will regulate emissions from new and existing coal-fired power plants under the authority of the Clean Air Act. In 2012, the U.S. Environmental Protection Agency set limits on the amount of carbon dioxide new power plants can emit, but this standard has not yet been finalized. New and existing power plants will likely only be able to meet these new standards by using clean coal technology.
Clean coal technology used to refer to any technology that reduced the environmental impact of coal burning for electricity. “When the coal industry claims it already has clean coal,” said Mary Anne Hitt, director of the Beyond Coal campaign, “They are talking about strategies for removing sulfur dioxide, nitrogen oxide and mercury, but they don’t do anything about CO2 because it’s too expensive. When the president talks about clean coal technology, he is referring to carbon capture and storage….the two are not even having the same conversation.”
Carbon capture and storage involves capturing waste carbon dioxide from power plants, transporting it and storing it where it theoretically will not leak, usually underground. Capturing carbon from power plants can be accomplished in a variety of ways. Flue gas (the combustion exhaust) separation involves removing CO2 with a solvent, separating it out with steam and then condensing it into a liquid. Oxy-fuel combustion burns the coal in pure oxygen, which produces a gas mix of mostly steam and CO2; the two elements are then separated through cooling and condensing the gas stream. Pre-combustion capture removes CO2 before the coal is burned through a gasification process using amine, a derivative of ammonia. Post-combustion capture separates CO2 from flue gas with a filter made from a solvent that absorbs CO2; the solvent is later heated, which releases steam and concentrated CO2.
After CO2 is captured, it is compressed and transported via pipes to a storage site. Currently, underground storage, or geological sequestration, is practiced mainly by oil and gas companies. CO2 is injected into depleted oil or gas reserves to drive the remaining oil to the drilling site or improve its flow. However, according to Juerg Matter, an associate research professor at Lamont-Doherty Earth Observatory working on carbon storage in Iceland and Oman, much of the millions of tons of CO2 currently used in the U.S. for enhanced oil recovery come from natural gas reserves naturally occurring in Colorado, Wyoming and Montana.
Only a handful of commercial industrial carbon capture and storage projects are in operation anywhere in the world. The first was established at the Sleipner gas field in Norway, where one million tons of compressed liquid CO2 are injected into saline aquifers deep under the seabed each year. Other carbon capture and storage commercial ventures are found in Algeria and Australia. To date, there are no commercial ventures in the United States that capture, transport, and inject large quantities of CO2 (1 million tons or more per year) to sequester carbon.
The main reason for this is that carbon capture and storage is very expensive. For example, it’s estimated that requiring new plants to implement post-combustion capture would require 20 to 25 percent of their energy output due to reduced energy output and the energy requirements of using the technology. Moreover, the public is concerned about the safety of carbon storage. Carbon sequestration on land raises questions about groundwater safety, access to land, storage permanence, and long-term monitoring and liability. Scientists still don’t know if CO2 stored underground can remain secure permanently or if CO2 might eventually leak into the atmosphere or groundwater. Ocean storage could increase the acidity of ocean waters and harm marine life.
Congress has funded carbon capture and storage research and development since 1997, including allotting $3.4 billion in the 2009 stimulus for research programs at the Department of Energy. Its goal is to achieve large-scale implementation of the technology by 2020. The range of carbon capture and storage research includes techniques for capturing carbon at smoke stacks, storage options, technology needed for long-term monitoring, impacts on natural systems if leaks occur, risks of polluting groundwater or the atmosphere, how to create legislation, as well as the legal and environmental implications of carbon capture and storage. About 5 percent of it is cutting edge research into unconventional carbon storage solutions.
Juerg Matter is involved in one of these cutting-edge strategies: sequestering carbon in basalt rocks. The CarbFix project is a collaboration between the Earth Institute, Reykjavik Energy, the University of Iceland and several others. More than 90 percent of Iceland is made of basalt, a highly reactive and porous type of rock created from ancient lava flows. CO2 from a geothermal power plant is being injected 1,600 feet underground into basalt. After interacting with the calcium in the basalt, the seltzer-like CO2 turns into calcite, a major component of limestone. Once it becomes solid and stable rock, it cannot leak. CarbFix is essentially speeding up a natural process called weathering.
“In the lab,” said Matter, “this mineralization process takes from weeks to a month. Our initial data suggests that in the field, the reaction could take decades to one hundred years. If it’s decades, that would be good because it could be monitored.” By the end of the year, the project will have injected 2,000 tons of CO2; the stored CO2 will be carefully monitored to study how it spreads; see if there are any leaks; track chemical reactions between CO2, groundwater and rocks; and ensure that the storage is permanent. Basalt is one of the most common rocks in Earth’s crust. The whole ocean bottom below the sediment in the Pacific, Atlantic and Indian Oceans is comprised of basalt. According to CarbFix, there is enough storage capacity in the basalt formations on land and under the sea to sequester all human produced CO2 for the foreseeable future.
Peridotite, another rock common in the Earth’s mantle, when pushed to the surface by geological forces over time and exposed to air, reacts with CO2 to form solid rock like limestone or marble. In Oman, peridotite commonly occurs at or near the surface. Matter and his Lamont-Doherty colleague Peter Kelemen estimated that the peridotite is naturally absorbing 10,000 to 100,000 tons of carbon a year from CO2 in the air or water. If heated water containing pressurized CO2 were injected down into the peridotite, the reaction could be sped up 100,000 times or more. (Read about the Oman research here.)
The scientists estimate that Oman could potentially sequester 4 billion tons of CO2 a year, about 13 percent of the carbon emissions humans generate each year. They are mapping sites where these natural reactions occur and studying if they can be sped up to sequester CO2. Large expanses of peridotite are also found on Papua New Guinea and Caledonia, along the coasts of Greece and the former Yugoslavia, and in smaller deposits in the western United States.
Lamont-Doherty scientists are also looking into storing CO2 in deep marine sediments. Under the pressure and low temperatures of marine sediments deeper than two miles, liquid CO2 is denser than the water that fills the spaces between grains of sediment and so will sink. It will then be trapped by gravity, with the deep ocean sediments providing a physical barrier to prevent leakage.
The Newark Basin, a geologic formation under New Jersey and New York, could be porous and permeable enough to sequester CO2. Composed mostly of porous sandstone with layers of clay on top, which could serve as a barrier to leakage, the geology looks promising.
Lamont scientists are drilling a 2,000-foot borehole at the Earth Observatory in Palisades, NY, to examine the Newark Basin’s makeup. They have also injected small amounts of CO2-containing water into another area to study what effect CO2 leaks might have on surrounding rocks and microbe communities. The U.S. Department of Energy estimates that the potential CO2 storage capacity of the Newark Basin is 10 billion metric tons—equal to about 40 years of CO2 emissions from NY, NJ and PA.
Even if it were possible to capture and store the CO2 from all power plants, however, 30 to 50 percent of the global emissions derived from transportation would still persist in the atmosphere. Technology to capture CO2 from the air could help solve this problem as well as deal with potential CO2 leaks from sequestered carbon.
Klaus Lackner, director of the Earth Institute’s Lenfest Center for Sustainable Energy, and his colleague Allen Wright have been working on artificial trees that use an absorbent resin to pull CO2 from the air much faster than photosynthesis does. Lackner envisions forests of these car-sized artificial trees, speculating that 10 million of them could capture 12 percent of annual CO2 emissions from humans.
So, is carbon capture and storage technology ready for the new regulations on carbon emissions that Obama is proposing? “The technology is ready to be applied on a large scale,” said Matter. ”But it’s not yet economically viable. Because there is no policy on carbon emissions and no market, people can’t make money on CO2.”
The reason that Norway, Algeria and Australia have commercial industrial carbon capture and storage is that these countries have a tax on carbon emissions. It is more expensive for the companies to release CO2 into the atmosphere than to capture and store it. Besides establishing emissions limits, said Matter, the government also needs to put a price on carbon through a carbon tax or cap and trade—or it may prove too expensive for coal plants to be retrofitted to capture carbon and they may be forced to close.
“The critical questions are policy and economics. The legislation has to get the economics right. The U.S. should go forward with legislation and emissions limits,” said Matter. “That will be a really good example for the world.”