Slag crust solidification in copper–steel composite cooling staves for blast furnaces

Intensified blast furnace ironmaking has aggravated refractory erosion and cooling component failure, making the formation of a stable slag crust increasingly important for long campaign life. In this study, a three-dimensional transient model coupling molten slag flow, heat transfer, and phase change was developed to quantify slag crust formation on a copper–steel composite cooling stave. The enthalpy–porosity method and temperature-dependent thermophysical properties were employed to describe the evolution of the liquid fraction, mushy zone, and effective slag crust thickness. The model was validated using in-plant thermocouple measurements from the furnace belly. The results show that a continuous solidified band forms within 10–15 s, and complete coverage of the hot face is achieved after approximately 60 s. The effective slag crust thickness increases from approximately 5–6 to 23 mm during 30–600 s and reaches approximately 43 mm at 2400 s. The safety threshold of 30 mm is first reached at approximately 1170 s. In addition, the predicted peak thermocouple temperature of approximately 228 °C and recovery time of approximately 32 min agree well with the measured response during severe spalling events. These results demonstrate that the proposed model can quantitatively describe the transient formation and re-formation of the slag crust and the corresponding thermal response of the cooling stave, providing a basis for slag crust evaluation and cooling strategy optimization.