INFLUENCE OF FLUE-GAS DESULFURIZATION SYSTEMS ON COAL COMBUSTION BY-PRODUCT QUALITY AT KENTUCKY POWER-STATIONS BURNING HIGH-SULFUR COAL

Two Kentucky power plants burning similar blends of high-sulfur wester n Kentucky and southern Indiana coal provide a unique opportunity to e xamine the variations in coal combustion by-products due to difference s in the method of wet flue-gas desulfurization (FGD). One plant emplo yed carbide lime-based scrubbing for two units and a dual-alkali proce ss for the third unit. The second plant employed a Mississippian limes tone from Kentucky for all four units. This study provides an example of optical and SEM petrographic techniques, supplemented by chemical a nalyses, applied to the study of, at least from the geologic perspecti ve, non-traditional materials. The coal sources comprise a blend of hi gh volatile C and B bituminous, high vitrinite (85-90%, mmf), high-sul fur (>3%, dry) coals. The fly ash is dominated by glassy phases (70-80 %) with about 5-10% spinel (predominately magnetite), 3-10% quartz, an d 4-10% isotropic coke comprising the remaining portion of the ash. SE M observations indicate that the glassy particles exhibit a bimodal si ze distribution with sub-micron glass spheres and a population of larg er (several 10s of microns) spheres. The bottom ash has higher proport ions of spinels and mullite, with negligible carbon forms, compared to the fly ash from the same units. Fly ashes were observed to be lower in Fe and higher in Al, Si, and S compared to the bottom ashes. Carbid e lime, a by-product of acetylene manufacture, soda ash, and limestone were the reagents used in the flue-gas desulfurization processes. The primary FGD by-product is a calcium sulfite slurry which is vacuum fi ltered and mixed with fly ash and, usually, lime, to form a stable pro duct for disposal. The FGD by-products have some potential, as yet unr ealized, for utilization. (C) 1998 Elsevier Science Ltd. All rights re served.