Ash–Bed Material Interaction during the Combustion and Steam Gasification of Australian Agricultural Residues

The time-dependent layer-formation process of the agglomerates for three common agricultural residues in Australia with different ash-forming elements, together with quartz sand as the bed material, were investigated in a lab-scale, fixed-bed reactor under combustion (5% v/v O2) and steam-gasification (50% v/v steam) atmospheres at 900 °C. The impact of the atmosphere on the ash–bed material interaction was studied from the elemental composition and the morphology of the agglomerates, which were characterized with scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The ash–bed material interaction mechanisms for the three feedstock were identified as part of the alkali metals react to form ash particles, which, for wheat straw and cotton stalks, consist of Na, Mg, Si, P, K, and Ca and, for grape marc, is composed mostly of KCaPO4; the remaining alkali metals react with either Si from the quartz sand (for grape marc and cotton stalk) or reactive Si from the fuel (for whea...