High-potassium biomass ash readily undergoes low-temperature melting, particle agglomeration, and slagging during thermochemical conversion, undermining stable operation. Additive performance is often evaluated from potassium-capture capacity, but the subsequent high-temperature transformation of captured potassium and its relationship with ash melting remain unclear. In this study, SiO₂-Al₂O₃ additives with different Si/Al ratios were added to high-potassium peanut shell ash. Ash fusion tests, ICP-OES, XRD, SEM-EDS, and FactSage equilibrium calculations were used to clarify the effects of silicon and aluminum components on potassium speciation transformation and ash melting. All additives raised the deformation temperature from 1067 °C to 1166-1194 °C, but their effects on softening and flow differed markedly. The flow temperature of PH-Si fell from 1258 °C to 1210 °C, whereas that of PH-Al increased to 1388 °C. After treatment at 1200 °C, PH-SA2 and PH-SA3 had nearly identical residual potassium contents (18.45 and 18.46 wt.%, respectively), but their flow temperatures were 1249 and 1314 °C, showing that residual potassium alone does not determine melting resistance. FactSage predicted rapid equilibrium liquid-phase growth in PH-Si at relatively low temperature; liquid formation in PH-Al was delayed and its equilibrium liquid fraction remained lowest at 1200 °C. XRD and SEM-EDS showed that the additives altered crystalline phases, local potassium associations, and residual solid-framework morphology. Clear K-Si co-enrichment occurred in PH-Si and PH-SA2, whereas K and Al coexisted locally in PH-Al, which retained a more intact solid-particle framework. Overall, melting resistance depends mainly on the subsequent potassium transformation pathway, rather than initial capture or total residual potassium. The competing pathways of potassium entering K-Si-rich liquid phases or participating in Al-containing structures and refractory solid frameworks control softening and flow behavior.
 

high-potassium biomass ash,silicon-aluminum additives,potassium speciation transformation,ash melting,solid-phase framework