Making the Ash Fusion Temperature Test Useful

This project addressed uncertainties related to ash fusion temperature (AFT) measurements for the prediction of ash deposition in utility boilers. The approach to elucidate areas of concern included:

• correlation of the melting characteristics of a range of coal ashes with their AFTs.
• Establishing the feasibility of applying digital imaging techniques to the AFT measurement.

A database containing the ash analyses and AFTs of 250 coal ashes was used for correlating their melting characteristics. Evgueni Jak from the University of Queensland provided the theoretical melting characteristics from calculations using the Chemical Thermodynamic Model (FACT). From these calculations, the calculated proportion of liquid at the various AFTs and the liquidus temperature were correlated with the AFTs. These correlations demonstrated that:

• there was a definite correlation between the proportion of liquid and the AFTs. The correlation was different for the main primary melt phases, mullite and anorthite.
• There was also a correlation between the liquidus temperature and the AFTs. This will provide the means to evaluate the AFTs of different coals and coal blends using ternary phase diagrams or FACT predictions.

Due to the current development of FACT to only consider major ash elements (Si, Al, Fe and Ca), the approach appears limited in its present application to coals from a particular area or mine when the effect of minor elements is consistent.

The investigations into the feasibility of using digital imaging techniques were entirely successful and it was shown that these techniques could be applied to the AFT measurement and provide automatic interpretation of the ash fusion test and remove the human error in this procedure. A plan for implementation of the hardware and software necessary for development of these techniques was developed and presented for further development of a commercial prototype.

In addition, it was demonstrated that by continuous monitoring of the test, additional information, similar to that obtained from thermo-mechanical analysis (TMA) could be derived from the data provided by the digital imaging procedures.