Conversion of Sulfur during Pulverized Oxy-coal Combustion

On the basis of experiments in the Chalmers 100 kW(th) oxy-fuel test facility, this study presents an analysis of sulfur chemistry of pulverized lignite combustion, comparing oxy-fuel and air-fired conditions. Four test cases were investigated: an air-fired case, two oxy-fuel cases with dry recycling (30 and 35 vol % O-2), and one oxy-fuel case with wet recycling (43 vol % O-2 on a dry basis). The amounts of sulfur in the flue-gas, ashes, and condensed water from the condenser were quantified, and a sulfur mass balance was established. The composition of the ashes and the ash-forming matter in the fuel was analyzed. The ashes were investigated by X-ray diffraction, while the size of fuel and ash particles was determined by laser diffraction. In general, the results show that the lignite has a high sulfur self-retention by ash, especially in oxy-fuel combustion. The experiments also show that the conversion of fuel S to SO2 from oxy-fuel combustion is around 35% lower compared to air-fired conditions, whereas the flue-gas concentration of SO2 is higher in oxy-fuel combustion because of the absence of air-borne nitrogen.