Role of interfacial contact topology in reduction-dependent molten iron–slag dripping through coke-packed beds

Hydrogen-enriched blast furnace operations change the reduction state and composition of dripping slag; however, its effects on coupled iron–slag flow through coke-packed beds remain insufficiently quantified. Therefore, dynamic multiphase simulations were performed for molten iron and FeO–CaO–SiO 2 –Al 2 O 3 –MgO slag dripping in a three-dimensional coke-packed bed. Reduction- and temperature-dependent density, viscosity, surface tension, and iron–slag interfacial tension were estimated for degrees of reduction of 0.70–1.00 and 1300–1500 °C. The simulations quantified phase holdup, center-of-mass dripping velocities, apparent contact areas among iron, slag, coke and void, and iron–slag mixing. A regression model using only slag viscosity, iron–slag interfacial tension, and slag/iron volume ratio weakly reproduced the slag/iron velocity ratio; incorporating the slag–coke/iron–coke contact-area ratio captured the trend across cases. At full reduction, lower slag viscosity promoted rapid slag dripping; at 70% reduction, extensive slag–coke contact reduced the apparent slag velocity despite the low viscosity. Both iron-slag contact per liquid volume and the fraction of liquid interfaces occupied by iron–slag boundaries decreased with increasing reduction degree, indicating stronger phase-separated flow. These results demonstrate that melt dripping is not governed by slag viscosity alone but by the coupled effects of interfacial contact topology.