Slag Viscosity Assessment and Modification of P2O5-rich Biomass and Refuse-Derived Fuels for their Use in Entrained-Flow Gasification

• Fuel blending (SiO 2 enrichment) is necessary for biogenic residues. • Influence of P 2 O 5 on slag viscosity and structure compensated. • ANNliq model performs best for P 2 O 5 -containing slags. • Slag viscosity at laboratory and pilot scale is in good agreement. Slagging entrained-flow gasification is gaining attention due to its potential to produce CO 2 -neutral (net-zero) chemicals and liquid fuels from waste. This study evaluated the slagging behavior of phosphorus-rich biogenic residues such as solid digestate, pine wood, sewage sludge, and refuse-derived fuels from food packaging, mixed plastic, and automotive tire waste. Thermodynamic phase modeling by FactSage indicated that phosphorus-rich digestate and refuse-derived fuels from mixed plastic waste are promising feedstocks for entrained-flow gasification when enriched with SiO 2 . Experimental studies at the laboratory scale focused on the model validation and the effect of SiO 2 and P 2 O 5 on crystal formation and viscosity. This included the preparation of synthetic slags, respective viscosity measurements, as well as structural analysis by EPMA, SEM and XRD. This work highlights the key role of P 2 O 5 at concentrations up to 15 wt% and its interplay with K 2 O. A compensated impact of P 2 O 5 on the slag viscosity is concluded. The results were compared to viscosity models, where an artificial neural network model (ANNliq) showed the best overall performance for predicting phosphorus-rich slags. To validate the laboratory results and to cover refractory interactions, digestate slags were prepared under relevant entrained-flow gasification/combustion conditions. The results reveal the influence of oxidizing and reducing atmospheres on slag structure and emerging crystal formation.