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

Abstract

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 °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.