Researchers at the Massachusetts Institute of Technology say a shorter-term solution, with cheaper start-up costs, could help spread the use of carbon capture and storage at coal plants and still clean up a large amount of carbon dioxide.
Although CCS has been touted as the answer to the problem of cleaning up coal, there are still no full-scale commercial plants using the system, in part because it carries a hefty price tag for power companies. Carbon capture alone, not including transporting and storing the CO2, can boost the cost of a power plant by 30 to 60 percent, depending on the type of plant. It can also decrease plant efficiency, according to the study, raising the cost per kilowatt-hour.
The researchers said partial capture, for both pulverized coal and integrated gasification combined cycle plant (aka “clean coal”), represents a smaller capital investment, because smaller or fewer pieces of equipment are necessary. Full capture, defined as 90 percent of emissions captured, is often accomplished with two trains of carbon dioxide absorbers and strippers, while a single train can be used for partial capture up to a certain level, according to the study. It won’t help with operating costs, though. Once the plant is up and running, the MIT study showed that the cost per ton for operating a power plant with CCS is about the same at 60 percent capture as at 90 percent.
Ashleigh Hildebrand, a graduate student in chemical engineering at MIT and co-author of the study, said in a statement that a system using partial capture could get CO2 emissions from coal-fired plants down to the emissions levels of natural gas plants. She said policies such as California’s Emissions Performance Standards could be met by coal plants using partial capture instead of relying solely on natural gas, which Hildebrand said is increasingly imported and subject to volatile prices.
Although a move to partial capture by power companies isn’t likely to satisfy the most staunch environmentalists, the researchers said it could be a viable intermediate step. The study points out that coal currently supplies more than half of all U.S. electricity, so it isn’t likely to disappear anytime soon.
In these tough economic times, such intermediate, and less expensive, steps may be becoming a trend. Last week, California’s Electric Power Research Institute announced that it would study a potential system that could combine solar thermal with fossil fuel. The nonprofit group plans to examine whether adding steam from solar thermal projects to conventional fossil fuel power plants can help reduce fuel costs and plant emissions.
As for carbon capture and storage, the technology took a big step forward in September when Sweden’s Vattenfall started operating a coal-fired power plant equipped with CCS technology in Germany. The company said the 30-megawatt Schwarze Pumpe pilot plant can produce 10 tons of highly concentrated CO2 per hour. The CO2 is then loaded into tankers and shipped to a nearby gas field for sequestration. However, the technology stumbled in the U.S. earlier this year when plans for a big carbon capture and storage project were dropped by the Department of Energy due to rising costs. The DOE now plans to dole out its cash to a number of smaller test projects around the country.
Hildebrand will present her findings from the MIT study tomorrow at the 9th International Conference on Greenhouse Gas Control Technologies in Washington, D.C. Her co-author is Howard Herzog, principal research engineer at the MIT Energy Initiative and chair of the conference organizing committee.