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Show combustion at this temperattrre and 884 K/s quench rate. When 2800 ppm S02 was doped to the fuel (bar B), the percentage of NO conversion was dropped to 80%. Injection of ash decreased conversion by about 4% (bar C). Total influence of S02 and ash (bar D) resulted in 69% NO conversion, however, injection of methanol into coal flue gas could convert only 61 % NO to N02 (bar E). Thus, even when both S02 and ash were added, natural gas still gave a little better results than coal. This can be attributed to a loss in ash reactivity during the collection process. It is believed that while held for a certain time in the baghouse the ash sulfated and then during collection it hydrated, changing its characteristics. Reactivity loss is also attributed to agglomeration of submicron ash particles dUling baghouse collection, making it difficult to resuspend the ash after rein jectio n. To evaluate the effect of ash on reconversion, results of two tests were compared: NO/NOx measurements with a clean fliter in the sampling probe and with a fliter fed with coal ash. The measurements were performed before and after methanol injection. The results of these tests indicated that the presence of ash reconverted about 50% of the existing N02 to NO. To obtain reproducible results, filters in the sampling system were cleaned and sample lines were purged with nitrogen prior to rreasurerrents. Thus, the results indicate that S02 decreases initial NO conversion and ash decreases initial conversion and increases reconversion. Several sets of experiments were also conducted during Illinois coal firing with injection of methanol at 866 K and with variation of quenching rates by addition of various heat exchangers. Sampling was performed at various locations allowing to check the effect of quench rate on NO control perfonnance and reconversion. Figure 3d demonstrates the effect of the quench rate on NO concentrations measured at different locations of sampling probe One can see that reaction time between 0.5 and 1 s is needed for efficient NO removal from coal flue gas. In these tests, a lower 9 - |
