STUDY ON BEHAVIORS OF COAL NITROGEN CONVERTED TO TAR

To develop a new method for reducing the NOx emissions in coal combustion processes, the possibility of removing the nitrogen with coal tar was confirmed by the experimental study of the formation behaviors of the tar and coal-N. Six different coals were pyrolyzed by using a free-fall pyrolyzer in an atmosphere of Ar gas at various heating temperatures. It is explained that (1) both the tar yield and the conversions of coal-N to tar-N increase with increasing pyrolyzing temperature until about 873 K and then decreases as the temperature continuously increases; (2) the contents of nitrogen compounds such as carbazole, naphthoquinoline, and isoquinoline in the tar are larger at 973 K than that at 1173 K. On the basis of the experimental results presented here, the NOx reduction effects in the combustion of the coal preremoved tar-N were estimated in both cases of high-temperature coal combustion as pulverized coal-fire combustion and low-temperature coal combustion as fluidized bed combustion. It is found that the conversion of coal-N to NOx in the case of high-temperature coal combustion can be reduced by about 20%, and it can be reduced by about 40% in the case of low-temperature coal combustion.