| OCR Text |
Show Emissivity; We anticipated that the deposits will have a high reflectivity based on the relatively high deposition rates of calcium and the low leposition rates of iron. This is consistent with the observations during the test bum. During the test burn, the furnace exit gas temperature was about 100°C above its typical value when burning bituminous coals, indicating higher ash reflectivity in the radiant section of the boiler. Quantitative Predictions and Experimental Results Figure 7 illustrates predicted and measured ash deposit elemental composi tion as a function of particle residence time (li). These data were collected in the MFC with particle temperature histories that are representative of a commercial boiler and where particle velocities are measured. Replicate experiments indicate that the coefficient of variation (standard deviation divided by the mean) for these data is 6-7 %. For a typical pulverized coal boiler operating at maximum continuous rating (MCR), the data would represent conditions near the burners at 0 .15 s and near the furnace arch at 1.1 s residence time. As indicated in the figure, the ash chemistry changes rapidly early in particle residence time. Later in residence time, changes in ash chemistry become less pronounced. These data are in qualitative and, in many cases, quantitative agreement with the predictions, including those elements in less than 2 % concentration in the ash (Figure 7b). They are also in agreement with general utility experience in that iron is both predicted and measured to be enriched in 0.50 c 0 0.40 • 8102 .. Co) CID ~ LL 0.30 CI) CI) CID ~ 0.20 4) •• ••• •• AFeI220033 •••••• • CaO ..-..-..-..-. ..... .-..-..-. ------------- --- --- .....••....•. . , 'A ••••••••••••••••••• 1:) ~ >C 0 0.10 .... '----.. _-............................... .. e .. --....-................... _- " .......................... ... 0.00 ......................................................... ..&...I. .................................................................. .I....A.. .......... ........ 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0.02 ---..----......... .----......--......... ~ ........ -..---......... ~ ........ -- c 0 ;; (.) f! • K20 • • Ti02 LL • MgO CI) 0.01 CI) = ~ 4) 1:) >C , •• , • Na20 .-- . .............. - ~ ....•.......... .•.•.•.•.......•..•....•...•...•.. ~ ..... ~ 0 ----- ----------------.-- ------ A 0.00 ...-. ....... -......--.... ................................. ...-. ............................................. ...... 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Residence TIme (s) Figure 7. Comparison of sensitivity of data (symbols) and predictions (lines) to particle residence time for a Pittsburgh #8 coal. The dominant dependence in this particular case is the iron concentration. Predictions were performed prior to experiments. 11 |
