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Show - 7 - Existing Slagging Predictors Figure 7 shows the low accountability of several existing slagging predictors in explaining the variability in heat flux reduction. The figure also reveals the potential impact of including operating conditions and additional coal characteristic terms in empirically explaining this particular slagging qualifier. Deposit cleanability, in addition to maintainable heat flux (MHF), must obviously be considered in a complete evaluation of slagging behavior. Studies utilizing simulated wallblowing are already underway. FOULING DEPOSIT DIFFICULTIES Linear discriminant analysis (LDA) was used to investigate the potential for using operating conditions and coal characteristics to classify fouling behavior in the pilot-scale combustor. LOA provides a method for evaluating the ability of a quantitative parameter to discriminate between groupings of a qualitative variable. The fouling qualifiers used in this study were the deposit tenacity and deposit-induced convective section pressure drop difficulties (plugging). The most successful combinations of variables for predicting deposit removal difficulties and plugging problems were found to be exit gas temperature, ASTM softening temperature, ash loading, and fly ash median particle size. Figure 8 displays the exit gas temperature dependency. Table 4 is a compilation of the ranges of the parameters and Tables 5 and 6 are summaries of the classifications. Fairly significant success rates (80.4% and 81.5%) were achieved. The linear discriminant functions were also used to predict fouling behavior for two recent fuel evaluation programs (40 combustion tests using 10 additional coals). Table 7 is a compilation of the ranges of input parameters and Tables 8 and 9 are the classification summaries for deposit tenacity and plugging problems, respectively. The models di scrimi na ted between groups qu i te accurate 1 y but tended to be overly conservative. The firing mode was also found to discriminate quite well between the observed fouling classifications. The opposed-wall mode exhibited the highest frequency of fouling difficulties but an examination of the base data revealed little imbalance in the independent variables with respect to firing mode. Furthermore, the bias that was found would contradict the trends observed from a theoretical standpoint. For instance, the average exit gas temperatures and ash loadings were slightly lower for the opposed-wa 11 mode than for the other two fi ri ng confi gu rat ions. Potential links between fouling behavior and firing mode are possible in the form of differing deposit compositional shifts and fly ash/bottom ash ratios. Firing-configuration-induced differences (flow pattern effects) have been shown to playa role in determining the composition of the fouling deposits in the Consol combustor as discussed in the next section. The link between firing mode and fouling behavior warrants further investigation. |