Patent ID: 7240897

Claim:
A mixing apparatus comprising an elongate draft tube to be supported upright in a body of liquid, the draft tube having an upper exit end and a lower intake end, and a gas injector arrangement for injecting gas into liquid so that in use gasified liquid will rise buoyantly in the draft tube to issue from its exit end with rotational swirling of the liquid around the draft tube's axial direction, and drawing further liquid in at the intake end; wherein the apparatus comprises an angled vane arrangement adjacent the intake end of the draft tube which comprises a set of vanes, angled from a radial direction and distributed around a circumferential liquid intake area at the intake end of the draft tube, and acts in use in concert with the intake flow caused by the gasification of the liquid to induce said rotational swirling of the liquid, the radial extent of said vanes lying at least partly outside the diameter of the draft tube, and the intake end of the draft tube connecting to an outward radial projection in the form of an outwardly-flaring wall portion beneath which said vanes are disposed, and wherein an axially-extending inner wall surface of the draft tube meets said outwardly-flaring wall portion via an outwardly-flaring transitional wall portion, gradually curved in axial cross-section, to promote smooth attached flow of indrawn liquid adjacent the draft tube wall at the intake end in use; the interior of the draft tube being open above the vane arrangement such that an open run of draft tube interior, unobstructed by traversing vanes, extends above the vane arrangement for at least 80% of the length of the draft tube.