LAUSR

Abstract Agricultural residual biomass has great potential as an energy source, but is used only to a limited extent mainly because of the characteristics of its ash (quantity and composition), which can lead to problematic phenomena during combustion, among them fly ash deposition, the focus of this study. A previous work presented the results of laboratory experiments carried out using a fixed-grate reactor and involving four different agropellets under different operating conditions; the variables tested were deposition rate, bottom ash proportion and sintering degree during combustion. Based on these results, the analysis has been taken further and the fly ash deposits collected during these tests have been characterized by SEM-EDS and XRD. A methodology to differentiate between deposits caused by condensation (including thermophoresis and turbulent diffusion) and by inertial impact of coarse fly ash entrained from the bed has been proposed. Deposition by condensation has been found to decrease for higher values of excess air ratio in all cases. Conversely, deposition by inertial impact does not show a common behavior, due to the influence of bottom ash sintering degree and fuel composition. The ultimate aim of this study is to gain a better understanding of fly ash deposition, in order to develop better fuel blends, boiler design and operating parameters, enhancing the market penetration of agricultural residual biomass.