Variable liquid level eductor/impeller gas-liquid mixing apparatus and process

A process for mixing a gas and a liquid, which is subject to change in liquid levels during the mixing operation, in a mixing vessel having a hollow draft tube with an axial flow, down-pumping impeller means positioned therein for vortex development and the ingestion of gas from an overhead gas space within the mixing vessel into the body of liquid therein, comprising:

• (a) rotating said impeller means to create a liquid recirculation flow pattern within the mixing vessel, with liquid passing downward inside the draft tube and upward in the annular space between said draft tube and the walls of the mixing vessel, so as to develop a vortex and to draw gas from the overhead gas space by gas ingestion at an operating liquid level within the mixing vessel;
• and
• (b) recirculating liquid from said mixing vessel through an eductor having a vacuum chamber and a discharge nozzle;
• (c) communicating said vacuum chamber with said overhead gas space, and communicating said discharge nozzle with the entrance of said draft tube, said liquid recirculation creating a vacuum which draws gas from said overhead gas space into said eductor, mixes it with the recirculating liquid and discharges the mixture into the entrance of the draft tube, whereby said gas is mixed with said liquid independently of the liquid level and of the speed of the impeller, and the liquid level is maintained at an operating level of the impeller means.

An apparatus for dissolving a gas in a liquid, comprising a closed container for receiving a liquid to a predetermined level to leave an overhead gas space;

• means for adding and mixing a gas supply with said liquid to produce a predetermined gas liquid interaction, a portion of said added gas escaping from the liquid into the overhead gas space;
• impeller means having a suction inlet for drawing gas down from the overhead gas space and mixing it with the liquid provided that the liquid level is within an operating range;
• means for recirculating a portion of the liquid through a liquid-operated eductor having a vacuum chamber and a discharge nozzle which exits below the liquid level;
• a suction tube communicating between the vacuum chamber of the eductor and the overhead gas space, for drawing gas from the gas space into the eductor under the influence of the recirculation flow through the eductor, to produce a gas/liquid mixture and discharge it into the liquid independently of the level of the liquid within the container and means for regulating the rate of recirculation of the liquid through the eductor and the rate at which gas is drawn from the overhead gas space.

An apparatus for mixing a gas and a liquid which is subject to change in liquid levels during the mixing operation comprising:

• (a) a mixing vessel having a hollow draft tube with an axial flow, down-pumping impeller means positioned therein and capable of creating a circulation flow pattern within the mixing vessel, with liquid being passed downward inside the draft tube and upward in the annular space between the draft tube and the walls of the mixing vessel, thereby developing a vortex and drawing gas from the overhead gas space within the mixing vessel provided that the liquid is at an operating liquid level within said mixing vessel, and
• (b) a liquid recirculation system comprising a conduit having an outlet section withdrawing liquid from a lower area of said vessel and an inlet section for reintroducing said liquid at an upper area of said vessel, pump means for pumping the liquid through said conduit, and an eductor connected to the inlet section of said conduit, said eductor having an inlet for receiving a continuous supply of said recirculating liquid, a converging-diverging nozzle having a restricted throat for increasing the velocity of said liquid, a vacuum chamber associated with said restricted throat, and a discharge nozzle below the liquid level in the vessel and opening into the entrance of the impeller draft tube, and a suction tube communicating between the vacuum chamber of the eductor and the overhead gas space, whereby vacuum in the vacuum chamber of the eductor draws gas from the overhead gas space through the suction tube, for mixing with the recirculating liquid in the eductor and for discharge into the entrance of the impeller draft tube.