OCR Text |
Show flows having distributed excess air are compared with the size distribution for the uniform excess air case, and the measurements, in Figure 9. Distributing excess air broadly enough that some portions of the postflame gas are rich has a marked effect on the size distribution, including significant contributions to carbon loss from particles smaller than 90 Jim. CONCLUSION Air leaking into the furnace and convection sections was proposed as an explanation for carbon loss in the presence of 25 to 30% excess air in the flue gas from a pulverized coalfired boiler. The measurements of amount and size distribution of unburned char could not be explained solely by an average excess air in the furnace lower than indicated by the flue gas analysis, but were consistent with lower-than-expected excess air combined with excursions to extremely low or negative excess air due to fluctuations in feed rates, random variation in fuel-air mixing at the burners, and poor mixing of air leaking into the furnace. ACKNOWLEDGMENTS The experimental data and samples from the field tests at the Seward Electric Generating Station were provided by Joseph J. Battista (Pennsylvania Electric Co.), Robert E. Douglas (CONSOL, Inc.), and Edward A. Zawadzki (Management and Technical Systems). The size distribution of unburned carbon was determined by Jianyang Xie (Pennsylvania State University). Seward Station Manager Dick Imler and John Kline (Pennsylvania Electic Co.) assisted with the oxygen measurements in boiler no. 12. All were essential contributions to the work. SYMBOLS de size of char particle, m EA <EA> Inc Incoal excess air, dimensionless average excess air, dimensionless mass of carbon (char), kg mass of coal, kg standard deviation of excess air, dimensionless 18 |