A prototype coal dryer demonstrated at Great River Energy’s Coal Creek Station in Underwood, S.D., has proven successful enough that the power company intends to install full-size dryers on the station’s 546-megawatt Unit 2 as part of the second phase of its cost-shared project with the U.S. Department of Energy. Plans to install the technology on the 546-megawatt Unit 1 -- at Great River Energy’s expense -- also are underway.
The project uses waste heat from the power plant to reduce moisture content in the lignite coal used. This makes it possible to extract more energy from the coal and, at the same time, reduces emissions of mercury, sulfur dioxide and nitrogen oxides.
Lignite coal, the feedstock fuel for the station’s two units, contains up to 40 percent water measured by weight. High-moisture coal typically yields lower power efficiency and higher emissions than drier coal. However, the high cost of drying the coal before use has been prohibitive until now.
The technology developed at Coal Creek economically captures and uses the waste heat already being produced by the plant to remove water from coal. By reducing moisture content, less coal is required to generate the same amount of electricity, which means fewer emissions and lower emission-control costs.
Great River Energy has designed a full-scale dryer system that includes four dryers, each capable of processing 35 tons of coal an hour, which will meet the complete fuel needs of Unit 2. The system, expected to be installed by March 2008, will process about 3.75 million tons of raw coal per year.
In the U.S., 279 power stations burn high-moisture coals and, combined, generate more than 100 GW of electricity ― nearly a third of the electric power generated by coal in this country. An additional 100 GW of power is expected to be produced by high-moisture coals over the next 20 years. If the new coal-drying technology were installed in power stations that produce just 10 GW of power, it would result in an annual emissions reduction of nearly 7,000 tons of nitrogen oxides, more than 18,000 tons of sulfur dioxide, more than 7 million tons of carbon dioxide, more than 9,000 tons of particulates and nearly 300 pounds of mercury, says the DOE.