Investigation of coal ash deposition under staged combustion in a pilot-scale facility.

摘要

Coal ash deposition during staged combustion was investigated using a pilot-scale combustor. Two coals, Pittsburgh #8 and Black Thunder, were used in this study. Staged combustion results in altered oxygen concentration profiles and lower flame temperatures. Therefore, deposit samples were collected under both staged and conventional combustion conditions at two heat rates. Furthermore, several samples were allowed to mature (cure) for several hours in a natural gas flame under either reducing or oxidizing conditions. The composition and morphology of the samples was determined through the scanning electron microscopy point count (SEMPC) technique.; A large amount of sintering was observed in the Pittsburgh #8 samples that were cured under reducing conditions, especially in the samples collected under reducing conditions. In these samples there was a complete lack of oxygen present near the probe while curing. Furthermore, the samples collected under reducing conditions were more sintered than the conventional samples. However, the extent of sintering in the reducing cured samples was significantly larger than observed in the uncured or oxidizing cured samples. Only a small quantity of gas phase oxygen was sufficient to prevent the large amount of sintering observed in the reducing cured samples. Increased sintering of the Black Thunder samples was also observed for the samples cured under reducing conditions. However, the extent of this increase was much smaller than that observed in the Pittsburgh #8 samples. The increased sintering observed under reducing conditions was attributed to the fluxing of the aluminosilicate glass by Fe 2+.; The heat rate, and therefore the heat flux, was also found to have a significant effect on the extent of sintering. Samples collected and cured under lower heat fluxes were found to have less compositional mixing. Therefore,the decreased temperatures observed in staged combustion tend to decrease the extent of sintering in deposits.