Abstract: Mixing apparatus includes a tank having an upright draft tube extending from above an operating level of liquid contained in the tank to a level near the bottom of the tank, the draft tube being in fluid communication with the tank at a level near the bottom of the tank below the operating level of the liquid. A nozzle is disposed within the draft tube for directing a stream of liquid downwardly against an impingement surface transverse to the draft tube at the level of fluid communication to entrain gas drawn down the draft tube and create a pattern of bubbles flowing radially outwardly from the draft tube. The impingement surface is close to, or is a portion of, the tank bottom so that the radially flowing bubbles sweep across at least a portion of the bottom of the tank.

Abstract: Mixing apparatus includes a tank having an upright draft tube extending down below an operating level of liquid contained in the tank. An upright rotary shaft extending through the draft tube rotates an impeller below the draft tube for pulling gas and water into a submerged mixing zone. A propeller at the bottom of the shaft rotates in the bottom of a tubular upright still-well below the draft tube for pulling liquid upwardly from the bottom of the tank toward the impeller. A perforated, conical shaped shroud extends downwardly and outwardly from the bottom of the draft tube around the top of the impeller blades. Gas bubbles generated by the rotating impeller flow upwardly through the holes in the shroud. A plurality of spaced apart and radially extending vanes on top of the shroud constantly direct the flow pattern of the bubbles in a radial direction away from the mixing unit toward the edges of the tank.