Effect of Sodium Oxides in Ash Composition on Ash Fusibility

Ash fusibility is closely associated with ash slagging, which has great significance on efficiency and cleanliness of thermal conversion and coal utilization. Not being a dominant component of coal ash, Na2O is believed to be an inducement for slagging problems. In this study, for the realization of better understanding of the underlying mechanisms, the influence of Na2O on the ash fusibility was investigated from the perspectives of content variation and temperature rising. Experimental approaches, such as ash fusion temperature (AFT) test, X-ray diffraction (XRD), and scanning electronic microscope (SEM), were applied to quantify the ash fusibility and detect minerals' transformation and surface morphology in ash melting. The ash melting process was simulated by a multicomponent system based on the FactSage database, which includes SiO2-Al2O3-Fe2O3-CaO-Na2O. This study also used Gibbs free energy theory to analyze the chemical reactions, mineral behaviors, and phase diagram and record the sodium migration in the melting process. In general, Na2O reduces the fusion temperatures of ash samples, which can be related to the performances of minerals albite, nepheline, and anorthite, as well as the eutectics they form.