Inorganic elements removal from elephant grass via water leaching: Kinetic analysis and combustion-relevant ash characteristics

Elephant grass (EG), a high yield perennial energy crop, is increasingly cultivated for pellet-based heat and power generation, however, its high inorganic and ash contents pose challenges related to slagging and fouling tendency during combustion. This study investigates water pretreatment for leaching inorganic elements from EG. Batch water washing experiments were conducted at 25, 40, 60, and 80 °C for 5–180 min using a hotplate, while preliminary screening experiments under sealed hydrothermal conditions were performed at 80–200 °C using an autoclave to evaluate the effect of elevated temperature on alkali metal removal. Hotplate washing resulted in substantial inorganics removal, with leaching efficiencies in the order: K (97–98%) > Na (84–90%) > P (83–92%) > Mg (62–79%) > Mn (48–69%) > Ca (20–41%), and ash (38–51%). Hydrothermal pretreatment by autoclaving achieved near complete alkali metal removal, with over 99% K removal and Na below detection limits, however, the high energy demand renders this approach less suitable for large-scale application, therefore hotplate results were emphasized. Kinetic analysis showed that inorganics leaching followed second-order kinetics, with apparent activation energies of 2.90 kJ.mol −1 K −1 based on leachate analysis and 4.90 kJ.mol −1 K −1 for ash removal. After washing pretreatment, fouling and slagging tendency improved considerably, reflecting that lesser ash-fusion related issues can be expected from the treated feedstock. For practical applications, a pretreatment duration of 30 min at a temperature range of 40–60 °C is recommended, as it provides effective removal of inorganics while minimizing energy consumption.