A multiphase fluid mechanics approach to gas holdup in bath smelting processes

In slag-based, smelting-reduction processes, the overflow of slag from the vessel is considered a major limitation to productivity; this phenomenon is commonly called slag foaming. While much has been learned from laboratory-scale studies of foaming, the superficial gas velocities are well below those encountered in production (centimeters per second compared to meters per second). A multiphase fluid dynamic model was developed to determine the relationship between gas velocity and void fraction (holdup) at industrial production rates. In the model, the drag between the gas and slag is balanced against the weight of the slag. Within the framework of the model, the only unknown quantity is a drag factor which can be extracted from experimental data. Values of this factor from water models, smelting-reduction converters, and other slag systems fall in a narrow range. The model can be used to estimate slag height in smelting-reduction vessels. The behavior of slags at high rates of gas injection is markedly different from foaming observed at low flow rates.