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Show responsible. Fieldner, Hall, and Field summarized their findings and the findings of 182 other investigators of the fusibility and clinkering of coal ash in their publication in 1918. In 1932 Nicholls, Selvig, and Ricketts 7 proposed a simple ratio of the major acidic (Ti02 + A1203) to basic (Fe203 + CaO + MgO + Na20 + K20) constituents as an index for predicting the softening temperature of bituminous coals. No attempt was made to weigh the individual constituents or their combination. In 1933 Schaefer modified the simple acid-basic ratio concept to allow for combining A1203 and Si02 when SiO? occurs in a fixed ratio to the A1203, as in a clay. When Si02 is present as quartz, the value of the index is reduced. Iron oxide was also weighed more heavily than other basic constituents. Babcock and Wilcox published, "The Initial Deformation and Softening Temperatures of Bituminous Coals as They Relate to the Percentage of Iron in the Ash for Reducing and Oxidizing Conditions." The curves presented show dramatically the impact of iron as a fluxing agent for alumina and silica in Eastern coals, particularly under reducing conditions. Since these earlier correlations, at least 13 other correlations for ash fusibility have been presented. Their results are summarized in Table Bryers and Taylor 10 performed a step-wise, second-order, multiple regression analysis on Eastern and Western coals, using individual basic constituents as the independent variable. The program was designed to examine one variable at a time. It can select the most important variable first, develop a suitable expression, and then modify the expression to include the additional variables in a descending order of their significance. The resultant expression provides a very good fit to the data. However, the expression becomes too cumbersome to handle. Rather than fit the data with a good deal of precision, they decided to sacrifice accuracy and return to a single-variable, second-order regression analysis using the percentage of basic constituents as the independent variable. Each rank coal was treated separately. Figure 1 shows several curves for different coal ranks relating ash-softening temperature to the percent of basic constituents. Bryers and Taylor were the first to treat coal as a nonhomogeneous substance by examining the individual size and gravity fractions comprising the coal. Except for a few cases, the mineral matter in coal is not a homogeneous, uniformly distributed mixture. The mineral matter exists in coal as 4 |
