Synergistic effects of biomass and composite fluxes on melting behavior and gasification reactivity of high-ash-fusion coal

High-ash melting-point coal poses challenges in entrained-flow gasification, including slag blockage and low reactivity. Adding fluxes is necessary. This study investigates flux regulation mechanisms in the co-gasification of coal and rice husk using hot-stage microscopy, x-ray diffraction, Fourier transform infrared, and thermodynamic simulation. Orthogonal and mixture designs show that flux dosage (P = 0.047) and biomass blending ratio (P = 0.080) dominate ash-fusion temperature (AFT). A 40% rice husk blend improves adaptability. Iron and magnesium-based fluxes significantly lower AFT; magnesium-based flux generates the most oligomers, while iron-based flux is most effective in reducing AFT. Composite fluxes show synergistic effects by lowering sintering temperature, dissolving refractory minerals (e.g., mullite, quartz), and disrupting aluminosilicate networks, with no high-melting-point crystals formed. They depolymerize [AlO4]5, [AlO6]9, and silicate networks, increasing the liquid phase by 30%–50%. Composite fluxes optimize gasification mainly by improving melt fluidity rather than altering activation energy.