The entrained flow gasification is an essential technology for biomass energy conversion for syngas (CO+H₂) production, while the vaporization of alkali metals (e.g. K and Na) at high temperature causes the enrichments of silicon and aluminum in the ash and slag, forming high slag viscosity that impedes liquid slag discharge. This study focused on the flowability regulation and mechanism of corn straw ash (CSA) slag by introducing CaO for aluminosilicate network depolymerization via visualized high-temperature experiments. The macroscopic dynamics and microscopic network structure of the molten slag with CaO addition were quantified. Results showed that raising CaO/SiO₂ from 0.21 to 0.68 reduced the ash flow temperature from approximately 1415 to 1275 °C, a decrease of approximately 140 °C; further to 1.16 reduced viscosity by 30 Pa·s (1400 °C), enabled stable vertical dripping (1290–1330 °C), and boosted spreading velocity from 1.25 to 80 mm/min (1450 °C). Combined structural and rheological analyses indicated a composition-dependent relationship between Ca-induced aluminosilicate network depolymerization and macroscopic flow behavior. The microstructural disintegration diminished the internal yield stress of the aluminosilicate melt, enabling capillary surface tension to dominate the fluid detachment. This competitive shift triggered a kinetic transition of the dripping slag from yield-dominated to viscosity-tension-driven. However, increasing the CaO/SiO₂ mass ratio to 2.58 triggered premature crystallization, and a flow model was developed to define a flow behavior index (n), which linked slag viscosity and macroscopic flow behavior with aluminosilicate-network descriptors such as NBO/T, thereby providing a quantitative framework for evaluating Ca-induced slag modification and theoretical guidance for biomass entrained-flow gasification.

entrained-flow gasification; biomass ash;slag flowability;Ca-induced depolymerization;slag dynamics