MERCURY REMOVAL IN ILLINOIS BASIN COALS BY COAL PREPARATION

The Illinois Basin is the third largest U.S. coal producing region, after the Powder River and Appalachian Basins. With increased adoption of scrubbers in U.S. coal-fired utilities, the high sulfur content of Illinois Basin coals is no longer an impediment, and this sulfur content allows scrubbers to operate efficiently. Nonetheless, Illinois Basin coals are commonly prepared prior to delivery, to reduce mineral matter and optimize heating value. As part of a larger collaborative study of element variation and its controls in Illinois Basin coals, we sampled thirteen coal cleaning operations preparing Illinois Basin coals in Illinois and Indiana. Samples include prepared coal, coal feeding the circuit, and refuse coal at various stages of the cleaning process. Some operations have mixed or multiple products, where more than one coal bed is mined. In addition to proximate and ultimate determinations, samples were analyzed for mercury, trace elements, sulfur forms, and organic petrology.

Results for cleaned coals show reduction of mercury and trace element contents together with reductions in ash yield and sulfur content, and increased heating values, parameters tracked by coal producers. For eight preparation circuits in Illinois, feed coals have mercury contents ranging from 0.05 to 0.48 ppm, whereas the cleaned product ranges from 0.04 to 0.09 ppm mercury. Each of these cleaned coals is below the world average for mercury in coal (0.10 ppm; [1]). Reduction of mercury for these eight circuits ranges from -26.9 to 82.5 percent on an as-received basis, with a mean reduction of 32 percent. As a result, coal preparation reduces the proportion of mercury and toxic trace elements that must be captured from the flue gas under the U.S. EPA Mercury and Air Toxics Standards [2]. Mercury and trace element reduction are generally correlated with pyritic sulfur reduction, suggesting a pyritic host for these constituents. Quantification of mercury and trace element distribution in pyrite by laser ablation ICP-MS is ongoing. Our results show benefits of coal preparation beyond improvements in overall coal quality.

[1] Yudovich, Ya. E., and Ketris, M.P., 2005, International Journal of Coal Geology 62, 107-134.

[2] U.S. Environmental Protection Agency [EPA], 2011, Mercury and air toxics standards (MATS), https://www.epa.gov/mats.