OCR Text |
Show thirteen units predicted to have only rare slagging are predicted correctly.. One should notice that, using this conservative procedure, only one unit experiences a slagging frequency greater than that predicted. The predictors of fouling problems were not as good as slagging predictors for classifying the units by their plant experience. For the fouling parameters, sodium in ash had the highest percentage of "correct" categorizations, but the B&W fouling factor had the smallest error with regard to missing by two categories. Table 4 gives numerical results for the two best fouling predictors, and Table 5 gives results by classifying units by the "worst" fouling case as determined by sodium in ash and B&W fouling factor. Using the "worst" predictor method, actual fouling is worse than predicted fouling in only 9 percent of the cases. CONCLUSION The collection and on-going analysis of slagging and fouling experience at 131 power plants provides a unique opportunity to evaluate existing slagging and fouling parameters. The analysis to date suggests that several slagging parameters probably are useful, and that two (the silica percentage and ash softening temperature) appear to be better than others. The use of the "worst case" prediction based on several slagging parameters minimizes the chance of underestimating expected slagging problems. Fouling parameters do not appear to be as good as slagging parameters for predicting plant experience, although the B&W fouling factor appears the best at this time. REFERENCES (1) Attig, R. C, and Duzy, A. F., "Coal Ash Deposition Studies and Application to Boiler Design", Proceedings of the American Power Conference, Vol. 31, 1969, pp. 290. (2) Reid, W. T., and Cohen, P., "The Flow Characteristics of Coal-Ash Slags in the Solidification Range", ASME Transaction, Vol. 66, Special Section, 1944, pp. 83-97. (3) Standard Test Method for Fusibility of Coal and Coke Ash, ASTM Standard D1957. 1-13 |