New technologies are enabling power plants that burn high-moisture coal to operate more cleanly and efficiently, a Lehigh energy researcher reported recently at a major international coal conference.
These technologies include the low-temperature drying of coals and the recovery and reuse of heat generated in the power plant, Nenad Sarunac said at the 33rd International Technical Conference on Coal Utilization and Fuel Systems in Clearwater, Fla.
Sarunac, associate director of Lehigh’s Energy Research Center
(ERC), said that improving plant efficiency along with the quality of the coals burned in U.S. power plants could significantly reduce the electric utility industry’s “carbon footprint.”
He and his collaborators presented four technical papers at the conference, which assembles utility officials and researchers studying coal utilization, environmental regulation and energy economics. This year’s conference drew about 300 experts from the U.S. and two dozen other countries.
The moisture content in so-called low-rank coals can exceed 40 percent, said Sarunac, compared to a moisture level of 6 to 8 percent in high-rank coals. This adversely affects a power plant’s performance and emissions.
One paper presented by Sarunac’s group discussed a study showing that a low-temperature, air/nitrogen lignite-drying system compared favorably in performance to a steam dryer. The paper was coauthored with researchers at Vattenfall of Sweden, a world leader in oxygen-combustion (oxyfuel) and one of Europe’s largest utilities.
The drying system was developed by engineers at ERC and at Great River Energy (GRE), a utility cooperative in Minnesota. In tests at a 1,000-megawatt oxyfuel power cycle developed by Vattenfall, it compared favorably with a steam dryer developed in Germany, Sarunac said.
A second paper, co-authored with ERC director Edward K. Levy and with Charles Bullinger and Mark Ness of GRE, described other applications of low-temperature coal drying, including a coal-to-liquids (CTL) plant where drying enabled low-rank coals to be gasified. The CTL conversion produces a synthetic gas, or syngas, that is used to produce gasoline, propane and other fuels. This work was conducted with GRE and Aker Solutions, an international engineering company based in Norway.
A third presentation discussed approaches for improving the efficiency of existing power plants. A fourth paper, “On-Site Coal Beneficiation for Off-Site Use,” was coauthored with Ness, discussed some of the potential benefits of cleaning and drying coal with recycled heat from the power plant process. These benefits include a reduction in the cost of transporting coal (due to its decreased weight), as well as the possible use of this so-called beneficiated coal at small plants that lack facilities for cleaning and drying coal.
If a significant amount of the low-rank coals that are currently transported on U.S. railroads were first cleaned and dried, said Sarunac, it would relieve the impact of coal shipments on the capacity of the country’s rail system.
The annual Clearwater Conference is sponsored by ASME (the American Society of Mechanical Engineers), the U.S. Department of Energy (DOE), the Coal Technology Association and DOE’s National Energy Technology Laboratory (NETL).
Sarunac also taught tutorials and chaired a technical session at the conference.
Posted on Tuesday, September 30, 2008