Numerical Investigation of Thermo-reactive Multiphase Flow in a Tuyere-Blown Slag-Fuming Furnace: Part I

Zinc recovery in a slag-fuming furnace (SFF) is a reduction-smelting process in which coal injected through submerged tuyeres undergoes partial combustion, supplying heat to the bath while generating CO for the reduction of dissolved ZnO and iron oxides. This study examines the metallurgical behavior of an industrial FeOx–SiO2–CaO–Al2O3–ZnO slag containing 38.5 wt% Fe2O3, 21.2 wt% SiO2, and 6.3 wt% ZnO using a transient two-dimensional Eulerian–Eulerian computational fluid dynamics (CFD) framework. The model couples multiphase flow, finite-rate coal combustion, gas-phase species transport, and slag-reduction reactions with a population balance model that accounts for bubble breakup, coalescence, and the resulting evolution of bubble size and gas–slag interfacial area. Reaction heat enters through a single unified source term. Radiative transfer near the free surface uses a gray-gas model. Slag density, viscosity, and surface tension follow the local temperature and the evolving composition; heat capacity and thermal conductivity follow temperature alone. The reaction mechanism couples the exothermic partial combustion of coal and oxidation of CO with the endothermic reduction of ZnO. Two supporting analyses are reported. In a property-level benchmark against published viscosity measurements for an industrial zinc–copper smelting slag, including the compositional dependence of the viscosity closure reduces the maximum absolute deviation from 47.1 to 22.2% and the mean absolute percentage error from 20.6 to 15.0%, used to select and adjust the closure, so the improvement is not cross-validated against a held-out slag. In a separate parametric sweep, in which the initial bath temperature was varied at fixed injection conditions, the normalized tuyere jet penetration increases from $$y/Y=0.15$$ y / Y = 0.15 to 0.53 ( y/dₜ=2.5 y / d t = 2.5 to 8.8 on the tuyere-diameter scale) through the temperature dependence of the viscosity closure. The transient calculation predicts a 32.7% concentration-based ZnO depletion over the cycle. The interval of fastest ZnO removal corresponds to the period of highest predicted reduction activity. Within the model, the zinc-fuming rate is therefore controlled by the coupled local availability of CO, gas–slag interfacial area, bubble dynamics, and slag-side mass transfer rather than by equilibrium thermodynamics alone.