Bubble disintegration and dispersion by eccentric mechanical stirring in gas injection refining for iron and steel making

摘要

In gas injection refining processes,a great amount of gas is injected into molteniron in short time,so that very large bubbles are inevitably formed.Wide dispersion of small bubbles in the bath is indispensable for high refining efficiency.In a previous study[1],it is shown that mechanical stirring with forward-reverse and forward-interrupt rotation is very effective for bubble disintegration and wide dispersion in the bath.The bubble disintegration takes place owing to the strong turbulence or high shear stress field created by the impeller rotation.However these types of rotation require large stirring power and high mechanical strength of the impeller.In this study,eccentric mechanical stirring with unidirectional rotation is tested using water model for pursuing better bubble disintegration and dispersion.The impeller shaft was located distant from the container center.Effects of various factors on bubble disintegration and dispersion are investigated.These factors are stiffing mode (location of the impeller shaft in the bath),nozzle structure,blade size of impeller,immersion depth of the nozzle,and so on.In addition to gas injection from the end of the impeller shaft,gas injection from an immersed lance was studied.It is demonstrated that eccentric stirring with unidirectional rotation is very effective for bubble disintegration and dispersion in liquid.The bubble disintegration is more notable with larger blade length of the impeller.The deeper the nozzle immersion depth is,the wider is the bubble dispersion in the bath.It is shown that the interaction between the injected bubbles and the impeller is important for the bubble disintegration and dispersion.