Phosphorus-Related Ash Chemistry at High Temperatures: Role of Aluminum on Particle Adhesion

Phosphorus-containing ash generated from the thermochemical conversion of biomass is expected to be applied as a phosphorus resource. Handling of ash is important in biomass utilization. In this study, the effect of Al, a coexisting element in ash, on P-related particle adhesion at high temperatures was investigated using synthetic ashes, which are model compounds of ashes, to understand phosphorus-related ash chemistry. Synthetic ashes containing P, Al and Si (P-Al-Si) were prepared, and their adhesiveness was quantified as tensile strength at 500-900 degrees C. Below 20 wt % of P, tensile strength increased slightly with increasing P concentration. At P concentrations of 20 wt % or higher, the tensile strength increased rapidly with increasing P concentration. P easily reacted with Al derived from ash, resulting in the formation of P-Al or P-Al-Si compounds. Since the slag formation temperatures of these systems were higher than that of the P-Si system, Al in P-containing ash suppressed the increase in adhesion. On the other hand, excess P in P-Al-Si synthetic ashes increased particle adhesion due to the formation of P-Si compounds. Addition of Al2O3 nanoparticles showed the strongest effect for decreasing adhesion because the formation of a P-Al phase was promoted.