| OCR Text |
Show Sodium in Ash, Normalized In addition to using the raw sodium in ash value as a fouling parameter, the normalized sodium in ash value may be used. Figure 8 shows the plot of fouling data on a grid of sodium in ash, normalized, and unit area steam generation rate. The data are divided into three regions as shown. The sodium in ash, normalized, plot is similar to the sodium in ash plot -- the boundaries shown correctly classify 67 percent of the units, and 88 percent of the units with data in the safe region had no problems. Alkalies in Coal Another fouling parameter receiving some mention is alkalies in the coal on a molar basis, defined as: Alkalies in coal, molar basis = (Na20 + 0.659 KpO) • ygjj- . Suggested values are: < 0.30 = Low fouling 0.30 - 0.45 = Medium fouling 0.45 - 0.60 = High fouling > 0.60 = Severe fouling. Figure 9 shows a plot of fouling data for alkalies in coal and unit area steam generation rate. Only 55 percent of the units were correctly categorized by the boundaries shown in Figure 9. Still, 86 percent of the units plotted in the safe region had no fouling problems. DISCUSSION There are numerous criteria that have been suggested as parameters for categorizing the slagging and fouling tendencies of coals. Some of these have received wide use while others are more obscure. While various persons have used and/or recommended the use of various of these parameters, none of the existing parameters have received universal endorsement. One factor that complicates the adoption of slagging and fouling criteria based solely on coal properties is the fact that boiler design 1-11 |
