Ash Fusion Quantification by Means of Thermal Analysis

Conclusions

A new experimental method for quantification of ash melting has been developed. Using the new method, a conventional STA apparatus is employed, and the melting is detected as endothermic reactions involving no change in mass. The DSC signal is transferred into a melting curve (showing the melt fraction in the ash as a function of temperature) either by simple comparison of the areas below the melting curve or by accounting for the relevant melting enthalpies. The execution of the measurement is simple and the repeatability of the results is very good. The subsequent conversion of the STA curves to a melting curve requires knowledge of the identity of chemical species in the ash and the involved chemistry.

The method has so far been tested on a number of simple salt mixtures, for which the measured melting behaviour agrees with the predictions from phase diagrams, and a number of ashes collected during combustion of pure straw, co-combustion of straw and coal, and coal combustion, for which melt was detected between 40 °C and 110°C below the corresponding IDT. Characterising the fusion by STA provides a more detailed description of the ash fusion as compared to conventional methods, and the onset of ash fusion is precisely determined. Furthermore, the method typically enables identification of the chemical species melting in different temperature ranges. As ash melting has a major impact on the deposit formation tendency, the presented detailed ash fusion determination improves the prediction of ash deposition propensities.