The addition of Nigerian Kankara kaolin improves the ash properties of empty fruit bunches during combustion

Empty fruit bunch (EFB) can be used as a solid fuel for heat and power generation. However, the high potassium content in EFB ash can cause slagging and fouling which negatively affects thermal conversion systems. In this study, Kankara kaolin (mined from Katsina State in Nigeria) was used as an additive to improve the ash characteristics of EFB at high temperatures, thus simulating conditions in a typical biomass boiler. To achieve this, three cases of EFB composition was prepared and combusted in a furnace at temperatures of 700 °C, 800 °C and 900 °C. From the results, increased potassium concentration in EFB ash is observed with increasing temperature for pure EFB samples, while kaolin addition is associated with a decrease in the potassium concentration of EFB ash at all temperature regimes. For instance, at 700 °C, potassium concentration in ash reduced from 57.33 wt% (EFB only) to 45.69 wt% (EFB + kaolin 10 wt%) and 44.06 wt% (EFB + kaolin 15 wt%). The highest potassium reduction in EFB ash was recorded at 900 °C, with a decrease in potassium concentration of 65.32 wt% (EFB only) to 41.09 wt% (EFB + kaolin 10 wt%), and 30.89 wt% (EFB + kaolin 15 wt%). This shows a 52.71% potassium reduction for EFB + 15 wt% kaolin at the highest temperature considered in this study (900 °C). We further establish that the alkali metal (potassium) adsorption efficiency of Kankara kaolin is relatively significant during the high temperature regime where meta-kaolinite is formed. Furthermore, slagging and fouling indices showed kaolin addition to be associated with better ash properties. Graphical abstract: [Figure not available: see fulltext.].