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Show 6/15 2. EXPERIMENTAL RESULTS AND DISCUSSION 2. 1 Formation Characteristics of Nitrogen Compounds under low Temperature Pulverized Coal Combustion Condition TH and NL coals which evolve different nitrogen compounds as the volatile matter are burned in the experiments. Figures 2 and 3 show the results of (a) the change of gas species concentration in the combustion gas, (b) the residual fraction of both volatile matter and fixed carbon contents in the burning particles and (c) the residual fraction of carbon, hydrogen and nitrogen contents in the char along the furnace. ax is incase of TH and NL coa 1, respecti ve 1 y. From Fig.2(a) NH3 concentration becomes much higher than HCN especially just after the injector. When NH3 concentration decreases in the ignition region, N20 concentration increases once. As seen from Fig.2(b), this increase is caused by the volatile matter combustion. After that, N20 concentration decreases with decreasing . CO concentration since N20 is decomposed by H radicals by way of the following reactions as CO + OH ~ CO2 + H N20 + H ~ N2 + OH In the downstream beyond about 300 mm N20 concentration increases again in accordance with the decrease of NO concentration. As shown in Fig.2(c), there appea rs no change of the res i dua 1 fraction of nitrogen element conta i ned i n the char particles in this region. This result suggests that the increase of N20 concentration may be caused by the reaction from NO to N20 as described the details later. In case of NL coal, on the other hand, only HeN is evolved as the nitric constituent from volatile matter as shown in Fig.3(a). This can be said as one of the most different points from that of TH coal. HeN is rapidly formed in the ignition region. After that, NO and N20 are produced at the same time as HeN reduces its concentration. I n the downstream N20 concentration increases with decreasing NO concentration. The tendency of NL coal there is similar to that of TH coal. As shown in Fig.3(c), the mass fraction of residual nitrogen in the char particles is much hi gher than that of TH coal, and still decreases |