OCR Text |
Show en en o ..J I « W I a:: « I o Cl W z a:: :::> aJ Z :::> 4~~~--------------~--------~------~ I ~ 3 2 1 I , ~ I '\ • I '\ ~ I' ~ , , \ , ! ~ , ~\ \. \. ~ 0 "~ , ~ ~ ~~\~ 3.5 II ~., ...~. ~.,. " 7 ~ I '/. ./ I ~ ~ ~ /"\. /\\ ~ 14 I r · '. \. . o o o PENELEC, 1992 . e.\ '.~ ,--------------; o I , . . , ~, , '.' .. .. , \ \ ... .. ", \\ ..... . ,\ , •... \ '., ., . ' . ... .. .. " , , ... . '-. ". '-. '-. " ,--. , I • , ... ! -. .. \ \ ". '. . '. ". I'" ...... • ••••• -.-....... . .. .. .' .. .... " '. --..... . .......... ... ............... . ....... . ----------------- o~~~----~----~--~--------~--------~ o 10 20 EXCESS AIR 30 (0/0) 40 Figure 7. Calculated dependence of carbon heat loss on excess air for various widths of excess air distribution, and comparison with the Babcock & Wilcox (1963) correlation and Pennsylvania Electric Co. (1992) measurements. The calculations were made using the model described in the text. The curve for the standard deviation O'EA = 0 (uniform excess air), was fit to the B&W curve by adjustment of the carbon oxidation rate coefficient and the characteristic size of char particles used to generate the oxygen concentration history in the postflame region. The curves for O'EA = 3.5, 7, and 14% show the calculated effect on carbon loss due to increasing width of the distribution of excess air in the postflame region. The horizontal line was used to identify combinations of mean and standard deviation of excess air expected to produce the same level of unburned carbon as at the point from which the line originates (2.4% of the coal heat input lost as unburned char). The values for the average excess air at the intersections of the vertical lines with the excess air axis are, from left to right: 3.6, 5.3, and 15.4%. 14 |