Mechanical stirring for highly efficient gas injection refining

In gas injection refining processes, wide dispersion of small bubbles in the bath is indispensable for high refining efficiency. Eccentric mechanical stirring with unidirectional impeller rotation was tested using a water model for pursuing better bubble disintegration and dispersion. Effects of various factors on bubble disintegration and dispersion were investigated. These factors were stirring mode, eccentricity and rotation speed, nozzle structure, nozzle immersion depth, and gas flow rate. Gas injection from a nozzle at the end of the impeller shaft and from an immersed lance was studied. Under eccentric stirring, a vortex was formed away from the shaft. Small bubbles were produced in the strong turbulence or high shear stress field near the rotating impeller and moved in the direction to the vortex keeping up with the macroscopic flow induced by the mechanical stirring. Thus small bubbles could disperse widely in the bath under eccentric stirring with unidirectional rotation.