The Impact of Aluminosilicate-based Additives upon the Sintering and Melting Behaviour of Biomass Ash

Biomass ash typically contains higher concentrations of alkali-based compounds, with lower eutectic temperatures when compared with coal ash, which can become sticky and even molten at combustion temperatures. One approach to mitigate the consequent fouling risk is to use an additive to increase the concentration of higher melting-point compounds within the ash, which produces weaker deposits. The aim of this study is to determine the effect of two additives, waste coal pulverised fuel ash (PFA) and kaolin, upon the melting behaviour of biomass ashes. Sinter strength testing has been conducted upon these samples at various sintering temperatures, as well as a range of blends of the ashes and additive, in order to determine the strength of the resulting deposit and the impact of increased additive concentration. Ash fusion testing results indicate changes in flow temperatures with increasing additive concentration, with SEM and XRD results highlighting associated phase changes. Results show that, while both additives reduce KCl release and increase flow temperatures, coal PFA initiates sintering at 900°C, due to iron fluxing in the presence of silica and alumina. Kaolin is shown to be the more effective additive. This indicates that iron content is crucial in the effectiveness of Al-Si additives.