Lehigh’s Energy Research Center (ERC) is co-recipient of an international award from a leading energy journal for developing a new technology that enables power plants to burn high-moisture coals more cleanly, efficiently and cheaply.
The 2010 award for Best Coal-Fired Project from Power Engineering magazine was presented last month at PowerGen 2010 International in Orlando, Fla. The conference was attended by more than 19,000 people representing 1,200 companies. The award honors technologies that “usher in breakthrough solutions” in four categories: coal- and gas-fired power plants, nuclear energy and renewable energy.
ERC associate director Nenad Sarunac and director Edward Levy were the lead Lehigh investigators in a 13-year collaboration with Great River Energy (GRE), a Minnesota-based utility company. The project also involved the Electric Power Research Institute; WorleyParsons, an Australia-based energy company; and Heyl and Patterson Inc., a Pittsburgh manufacturer.
The researchers developed a coal-drying and cleaning technology called DryFining ™ and implemented it in two 600-megawatt units of GRE’s Coal Creek Station in North Dakota. A full-scale coal-drying system designed to handle 1,100 tons per hour of wet lignite coal has been in commercial operation at Coal Creek since December 2009.
A significant reduction in harmful emissions
“DryFining ™ is a more affordable way to control emissions while improving fuel quality,” said an announcement by the U.S. Department of Energy, which provided funding for the project over the past decade.
DryFining ™ “simultaneously dries and refines coal and reduces potentially harmful emissions,” said DOE. “The process not only uses power plant waste heat to reduce moisture, but also generates more energy from less coal.”
In the Coal Creek Station test, DryFining ™ reduced mercury and sulfur dioxide (SO2) emissions by 40 percent, nitrogen oxides (NOx) by 30 percent and carbon dioxide (CO2) by 4 percent. Mercury, a neurotoxin, usually affects humans through fish consumption. Coal-fired power plants emit about 40 percent of the mercury discharged into the air in the United States. SO2 and NOx are acid-rain gases. CO2 is a greenhouse gas.
GRE estimated DryFining ™ would reduce Coal Creek’s annual operating expenses by $20 million while improving overall plant performance by almost 4 percent.
Prevalent but not optimal
Coal generates about half the electricity consumed in the U.S. and a larger portion worldwide. More than half the world’s coals, says Levy, are high-moisture coals like lignite, which contains 30 to 40 percent moisture. By contrast, bituminous contains 6 percent moisture and anthracite somewhat more.
“You get a very poor efficiency when you burn these coals because much of the coal’s fuel value is spent to evaporate fuel moisture,” says Levy. “The moisture causes problems with stable combustion and makes the coals harder to pulverize; it requires more energy and more grinding equipment.”
DryFining ™ utilizes waste heat to reduce coal moisture. ERC researchers also helped design a dryer that separates out heavy particles, mostly ash, pyrites and small rocks, that contain sulfur and mercury, which under normal circumstances would result in SO2 and mercury emissions.
“This is good for the environment,” says Sarunac, “and good for the utility, which doesn’t have to spend as much money to get rid of pollutants and greenhouse gases.”