OXYFUEL: In September 2007 the oxyfuel combustion chamber is lifted into place at the Schwarze Pumpe power plant in Germany--one of the first power plants in the world to capture carbon dioxide. Image: Courtesy of Vattenfall
Editor's Note: This is the first in a series of five features on carbon capture and storage, running daily from April 6 to April 10, 2009.
Like all big coal-fired power plants, the 1,600-megawatt-capacity Schwarze Pumpe plant in Spremberg, Germany, is undeniably dirty. Yet a small addition to the facility—a tiny boiler that pipes 30 MW worth of steam to local industrial customers—represents a hope for salvation from the global climate-changing consequences of burning fossil fuel.
To heat that boiler, the damp, crumbly brown coal known as lignite—which is even more polluting than the harder black anthracite variety—burns in the presence of pure oxygen, a process known as oxyfuel, releasing as waste both water vapor and that more notorious greenhouse gas, carbon dioxide (CO2). By condensing the water in a simple pipe, Vattenfall, the Swedish utility that owns the power plant, captures and isolates nearly 95 percent of the CO2 in a 99.7 percent pure form.
That CO2 is then compressed into a liquid and given to another company, Linde, for sale; potential users range from the makers of carbonated beverages, such as Coca-Cola, to oil firms that use it to squeeze more petroleum out of declining deposits. In principle, however, the CO2 could also be pumped deep underground and locked safely away in specific rock formations for millennia.
From the International Energy Agency to the United Nations–sanctioned Intergovernmental Panel on Climate Change (IPCC), such carbon capture and storage (CCS), particularly for coal-fired power plants, has been identified as a technology critical to enabling deep, rapid cuts in greenhouse gas emissions. After all, coal burning is responsible for 40 percent of the 30 billion metric tons of CO2 emitted by human activity every year.
"There is the potential for the U.S. and other countries to continue to rely on coal as a source of energy while at the same time protecting the climate from the massive greenhouse gas emissions associated with coal," says Steve Caldwell, coordinator for regional climate change policy at the Pew Center on Global Climate Change, a Washington, D.C. think tank.
Even President Barack Obama has labeled the technology as important for "energy independence" and included $3.4 billion in the $787 billion American Recovery and Reinvestment Act for "clean coal" power.
Today three types of technology can capture CO2 at a power plant. One, as at Schwarze Pumpe, involves the oxyfuel process: burning coal in pure oxygen to produce a stream of CO2-rich emissions. The second uses various forms of chemistry—in the form of amine scrubbers, special membranes or ionic liquids—to pull carbon dioxide out of a more mixed set of exhaust gases. The third is gasification, in which liquid or solid fuels are first turned into synthetic natural gas; CO2 from the conversion of the gas can be siphoned off.
Some U.S. utilities have already built or upgraded plants to capture CO2, which they either store or sell. The 180-MW Warrior Run coal-fired power plant in Cumberland, Md., already captures 96 percent of its CO2 emissions to sell for use as a fire extinguisher or dry ice. The Kingsport power plant in Kingsport, Tenn., has been capturing CO2 since 1984 to sell to carbonated beverage makers.
The U.S. Department of Energy (DoE) has invested more than $3 billion since 2001 to fund multiple CCS projects being conducted by seven regional partnerships, including demonstrations of ammonia capture technology at the massive coal-fired Pleasant Prairie power plant in Kenosha County, Wisc., and the R. E. Burger plant in Shadyside, Ohio. The Obama administration may even resurrect the FutureGen project—a 275-MW IGCC power plant that would capture 90 percent of its emissions; the Bush administration had canceled it because of spiraling costs (which may have been miscalculated). And the DoE has offered at least $8 billion in loan guarantees for coal-fired power plants with CCS.
Australia and China have demonstrated that postcombustion capture is possible in pilot plants. At Loy Yang Power Station in Victoria, a pilot plant run by Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) will capture 1,000 metric tons of CO2 a year; the Australian research organization has also collaborated with China's Huaneng Group to use an amine scrubber to capture CO2 from a co-generation power plant in Beijing and then sell it.
But although multiple projects around the world examine or test aspects of CCS, few of them have been connected to a full-size power plant: one producing on average 500 MW and upward of 10,000 metric tons of carbon dioxide a day—the core of the emissions problem. And the few that have been are either venting the CO2 after capturing it or selling it, instead of taking the next step and storing the greenhouse gas underground.
"It makes nine metric tons of CO2 per hour at full load," says Staffan Gortz, Vattenfall's CCS spokesman, of the $100-million CCS demonstration boiler at Schwarze Pumpe. But he acknowledges that "we don't have a storage site yet."