97/03485 Coal characterization and high gradient magnetic separation studies of coal fines from Paradise Kentucky

Abstract

Five coal slurry ponds at the TVA Paradise facility in Western Kentucky were characterized and high gradient magnetic separation (HGMS) studies were conducted on selected samples. The objective was to determine whether or not HGMS is an effective technique to remove pyritic sulfur and ash from coal fines. Lateral changes in particle size distribution within individual ponds reflect temporal changes in the hydrology within the ponds. Where material was dredged and stacked at the side of the pond, the particle size was coarser and the material was more acidic, due to oxidation of pyrite. Wet HGMS studies were conducted over a range of concentrations, and at different field strengths of up to 2 Tesla (20,000 gauss). Various matrices were used in the magnet including relatively coarse screens and fine particle size magnetic stainless steel wool. Grinding to finer particle sizes liberates the pyrite and ash-forming minerals, enhancing their separation in the magnet. At particle sizes greater than 200 mesh ( 75 micrometers) clogging occurred within the magnet when the finer wool matrix was used. Tests are currently underway at higher field strengths of 6 Tesla. By a single pass through the magnet the sulfur content of the coal fines wasmore » reduced by between 1.5 and 2% while the ash content also reduced by several percent. Additional sulfur removal could be achieved by second and third passes but the sulfur reductions were less. Excessive abundances of ash - forming minerals (above 40% ) limited the effectiveness of the magnet. A front end process (such as flotation) to remove the majority of the ash-forming minerals and provide a fine (<200 mesh) feed for the magnet, would likely enhance the effectiveness of HGMS. In this respect, HGMS may be more effective as a polishing step following more conventional coal cleaning technologies.« less