Improvement of Impeller Blade Structure for Gas Injection Refining under Mechanical Stirring Original Research Article

The impeller blade structure for gas injection refining under mechanical stirring has been explored by water model experiments. A sloped swept-back blade impeller is proposed for the purpose. The central part of the impeller is disk- or plate-shaped, and the blades are fitted to the side of the disk or plate. In addition, a disk is put on the top side of the impeller blades. The impeller can strengthen the radial and downward flow between the blades and weaken the swirl flow in the zone above the impeller. These effects on flow phenomena are favorable for disintegration and wide dispersion of bubbles which are injected from a nozzle attached to the center of the underside of the impeller. In addition, the sloped swept-back impeller requires less power consumption. The impeller shaft should be placed away from the vessel center so as to disperse the injected bubbles widely in the bath under mechanical stirring even with unidirectional impeller rotation and without installing baffles. The number of gas holes in the nozzle and the direction of gas injection have a little effect on the bubble disintegration and dispersion in the bath. Highly efficient gas injection refining can be established under the conditions of proper impeller size, larger nozzle immersion depth, larger eccentricity and rotation speed of the impeller. The sloped swept-back blade impeller can decrease the power consumption and yet improve the bubble disintegration and wide dispersion in the bath.