An innovative coal-drying technology that will extract more energy from high moisture coal at less cost and simultaneously reduce potentially harmful emissions is ready for commercial use after successful testing at a Minnesota electric utility. The DryFining technology was developed with funding from the first round of the U.S. Department of Energy’s Clean Coal Power Initiative (CCPI).
Great River Energy of Maple Grove, Minn., has selected the WorleyParsons Group to exclusively distribute licenses for the technology, which essentially uses waste heat from a power plant to reduce moisture content in lignite coal. Great American Energy, a 50-50 joint venture of Great River Energy and the North American Coal Corporation, will also market the technology, whose first user will be the utility’s Spiritwood Station under construction near Jamestown, N.D.
In addition to using power plant waste heat to reduce moisture, DryFining also segregates particles by density. This means a significant amount of higher density compounds containing sulfur and mercury can be sorted out and returned to the mine rather than oxidized in the boiler. The end result is more energy can be extracted from the coal while simultaneously reducing emissions of mercury, sulfur dioxide, and nitrogen oxides, major potential pollutants that result from coal-based combustion.
As part its CCPI-funded project, Great River Energy tested a 115-ton prototype dryer in the company’s 546-megawatt Coal Creek Station Unit 2 in Underwood N.D. Following a successful increase in boiler efficiency and reduction of emissions, Great River Energy expanded the project by building full-scale dryer modules for the entire Coal Creek Station. The Office of Fossil Energy’s National Energy Technology Laboratory manages the CCPI program.
Lignite is one of four major coal types produced in the United States, accounting for about 7 percent of annual production, and is an important energy source for electricity generation. In general, lignite has a higher moisture and ash content, resulting in a lower power efficiency and higher rate of emissions than coals with less moisture. Great River Energy’s innovative technology reduces the cost of drying coal by using the waste heat and segregating particles by density, thereby generating energy with less coal while reducing emissions and emission-control costs.
At the Coal Creek Station, the technology increased the energy content of the lignite from 6,200 to 7,100 Btus per pound, thereby reducing fuel input into the boilers by 14 percent. At the same time, sulfur dioxide and mercury emissions were reduced by more than 40 percent, nitrogen oxide by more than 20 percent, and carbon dioxide by 4 percent.
These results are important to energy consumers because the United States has about 280 power stations burning high-moisture coal, generating more than 100 gigawatts of electricity, which equates to about one-third of the electric power generated by coal in the country.
