Trace Element Reductions in Fine Coal Using Advanced Physical Cleaning

Abstract

Abstract Studies show that pre-combustion physical cleaning can substantially reduce the trace element contents of a given coal. Using an advanced fine coal cleaning circuit comprised of an enhanced gravity separator (EGS) and a flotation column, over 80% of the Hg and Se contents of a −250 μm Illinois No. 6 coal sample were rejected while achieving an energy recovery of 80%. According to a statistical correlation evaluation, this performance was achieved due to a strong affinity of the Hg and Se with the ash forming and coal pyrite particles, which were rejected at rates of 84 and 83%, respectively. However, Cr was found to have a moderate affinity with the organic material, which limited its rejection to 62%. Treatment of a pre-cleaned pulverized coal combustion boiler feed sample originating from the same Illinois No. 6 coal seam provided an additional reduction in total sulfur and trace element contents. Overall, the EGS-Column circuit was found to be effective in reducing the amounts of three trace elements found in coal that have been identified as potential air toxics, which are emitted into the air during the coal combustion process. Keywords: Trace elementair toxicenhanced gravity separatorcolumn flotationcorrelation coefficientsulfur emission