Enhancement of mass transfer rate of elements in molten steel bath via bottom-blowing gas stirring in converter

To reveal the removal mechanism of impurity elements in molten steel by bottom-blowing stirring in converters, industrial tests were carried out to investigate the effects of bottom-blowing gas stirring on the removal of phosphorus, sulfur and oxygen in molten steel in converter baths, based on numerical simulations and cold-state simulation tests. Numerical simulation results showed that the enhancement of bottom-blowing intensity could significantly optimize the kinetic conditions of molten steel baths. When the bottom-blowing intensity reached 0.107 m³/(t·min), the volume proportion of liquid dead zones decreased by 7.2% and 10.5%, respectively, compared with the operating conditions of 0.089 and 0.053 m³/(t·min). Cold-state simulation tests confirmed that the enhancement of stirring effect could effectively shorten the homogenization time of molten steel baths. The volumetric mass transfer coefficient of molten steel baths reached the peak value when the bottom-blowing intensity was 0.107 m³/(t·min), on the basis of which a correlation model between converter bottom-blowing flow rate and volumetric mass transfer coefficient was established. Further industrial tests on 150 t converters indicated that in the post-stirring stage with no oxygen involvement at the end point, the mass transfer rates of phosphorus, manganese and sulfur in molten steel were significantly higher than those in the stage from temperature measurement, sampling and carbon determination to temperature measurement, sampling and oxygen determination. These results demonstrated that the bottom-blowing post-stirring after lance lifting at the end point played a crucial regulatory role in the mass transfer process of elements in molten steel baths.