Print this pageStratigraphic and Geographic Distribution of Coal Quality Characteristics in Lignites of Northeast Texas
CROWLEY, SHARON S., U.S. Geological Survey, Reston, VA; PETER D. WARWICK, U.S. Geological Survey, Reston, VA; and WILLIAM H. MASON
The distribution of coal quality characteristics was examined for lignites of the Wilcox Group (Paleocene-Eocene) from three mine areas (Thermo, Winfield South, and Winfield North) in northeast Texas. Ash yield, sulfur forms, moisture, calorific value, and selected potentially hazardous trace elements were plotted on cross sections of lignite beds and on isoline maps to determine their stratigraphic and geographic distribution. This study has been undertaken as a part of the U.S. Geological Survey's National Coal Resource Assessment (NCRA) program in the Gulf Coast Region. The distribution in coal of Hazardous Air Pollutant elements (HAPs), as defined in the Clean Air Act Amendments of 1990, are an important focus of the NCRA program.
Preliminary results indicate that the distribution of ash yield and calorific value is related to the stratigraphic and geographic position of the lignite beds in the study area. In the following discussion, coal quality data for 712 samples (88 cores) have been normalized to the average moisture content of feed coal to the power plant (32.5 percent). Based on these data, ash yields for lignite samples in the Thermo mine area (mean ash yield of 15.5 percent) are generally less than those for the other mine areas, and mean calorific values in the Thermo mine area (6438 Btu/lb) are generally higher than those for the other mines. Based on a subset of coal quality data (138 samples, 64 cores), two lignite beds that are stratigraphically the highest and lowest coal beds in the Winfield South and Winfield North mine areas contain samples having higher ash yields (mean ash yield of 25.3 percent) and lower calorific values (mean values of 5157 Btu/lb) than other coal beds. In contrast, the distribution of the HAPs elements and sulfur forms does not appear to be stratigraphically or geographically controlled.