Prediction of ash fusion temperature from ash composition for some New Zealand coals

Three improved techniques are presented for predicting the fusibility temperatures of coal ash from ash composition for particular coalfields. The first uses ternary equilibrium phase diagrams where the vertices are percent base, percent fluxing acidic oxides and percent non-fluxing acidic oxides. For reducing conditions FeO is a base, but for oxidizing conditions Fe₂O₃ is a non-fluxing acid. Plots of ash fusibility results on these diagrams show the range of behaviour of a particular coal and where low temperatures occur. They can be used to predict behaviour of fresh samples. The second method uses multiple regression equations above and below the minimum in the ash fusion temperature-percent base plot (usually 38% base), using as predictors, percent base (B), B², and acid flux and base flux factors F_A, F_B (or their logarithms). The third technique, the most accurate, uses stepwise regression, again on split observations above and below the minimum in the ash fusion temperature-percent base plot. With 40 parameters it is possible to identify the significant ash fusion parameters present for each ash fusion measurement in each coalfield. Two sets of observations which included measurements of borate (B₂O₃) showed that it caused a significant but negligible reduction in ash fusion temperature.