Sulfur trioxide formation during oxy-coal combustion

Abstract

The purpose of this study was to investigate the effects of increased oxygen and carbon dioxide concentration on the formation of sulfur trioxide during oxy-coal combustion in two different types of pilot-scale furnaces: a pulverized-coal and a circulating-fluidized-bed-fired system. For pulverized-coal (PC) testing, concentrations of SO 3 and SO 2 were significantly higher for oxy-fired conditions as compared to air-fired conditions. For a high-sulfur Illinois bituminous coal, SO 3 concentrations were 4–6 times greater on average. When firing a low-sulfur Utah Bituminous coal, SO 3 concentrations were similar for oxy-firing vs. air-firing, and the overall levels were very low compared to the Illinois coal, consistent with differences in the fuel sulfur contents. PC-fired emissions on a normalized mass basis (mass SO 3 per unit energy input) indicated higher SO 3 emissions under air-fired conditions vs. oxy-firing, for both the Illinois and Utah coals. Circulating fluidized bed testing was also carried out using the low-sulfur Utah coal, and SO 3 concentrations were notably higher for oxy-firing vs. air-firing, in contrast to the similar concentration levels observed for PC-firing. When compared on a normalized mass basis, the emissions were similar for both air- and oxy-firing, which is also in contrast to the PC-fired results for this coal.