Simultaneous Removal of SOx and Halogens under Combustion of Coal Water Mixture Added Fine Limestone

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This report mainly focuses on SOx and halogen removal ability of limestone in the pulverized coal combustion. Effects of reactions between internal minerals in the coal with limestone on SO_2 capture are discussed. Three Chinese coals (YZHS coal (Sulfur content=5.7wt%), DT coal (S=1.7wt%), VZLS coal (S=0.6wt%)) used in this study have significant mineralogical composition and particle size distribution of minerals. The combustion experiment was conducted about the fuels that mixed coal and limestone (sulfur to calcium molar ratio is 1 to 3). The reactions of the added limestone with sulfur and minerals were evaluated by CCSEM analysis of fly ashes. YZHS coal has lower kaolinite content and bigger sized minerals than that of DT and YZLS coals. De-S and De-Cl ability of limestone depends strongly on the coal type. The higher desulfurization efficiency was achieved in combustion of impregnated coals, which is in part due to the intimate contact between sorbent and coal matrix, portion of added calcium adhered to coal surface, as a result, could adsorb sulfur readily, the reaction of calcium and inherent minerals was inhibited to larger extent. In addition, impregnation of calcium acetate into coal was developed, which made calcium acetate disperse well on the surface of coal particles. The high decomposition rate of calcium acetate decreased its sintering degree in the furnace. Both factors contributed to the higher desulfurization efficiency in DT combustion. In DTF having upside of 1200℃ and downside of 900℃, using calcium acetate as sorbent obtained the desulfurization efficiency more than 80%, compared to only 55% was obtained using limestone. The greater sulfation rate of calcium acetate led to much gypsum and gypsum/aluminosilicate formed in the ash.