Apparatus for contacting a liquid with a gas

Apparatus for contacting a liquid, in a tank containing a body of same, with a gas from a gas space overlying said body of liquid, comprising:

• (a) a generally tubular draft member oriented with its central axis aligned vertically, having a cylindrical main body portion and an outwardly flared conical upper section positioned in said tank with the upper end of said conical inlet section forming a liquid inlet positioned proximate to but beneath normal liquid level in said tank and with the lower end of said draft member vertically spaced from the bottom of said tank to form a liquid outlet, wherein enclosing walls of said conical inlet section form an angle with the draft member central axis of from 5.degree. to 35.degree. and said conical inlet section has a vertical height of from 0.25 to 1.25 times the diameter of said draft member;
• (b) a rotatable axial pumping impeller having a diameter which is smaller than but at least 90% of the diameter of said draft member, positioned in said draft member proximate to the juncture of said conical inlet section and the cylindrical main body portion of said draft member, for axial downflow pumping of liquid through said draft member and inducement of circulation of liquid discharged from said draft member liquid outlet through said body of liquid in said tank to said draft member liquid inlet;
• (c) means for rotating said impeller at a speed above about 200 rpm so as to create a plurality of gas vortices within said conical inlet section of said draft member for vortex entrainment of gas in the downwardly flowing liquid pumped through said draft member;
• and
• (d) baffle means positioned in said conical inlet section of said draft member above said impeller to prevent bulk rotation of said body of liquid in said tank during rotation of said impeller while permitting the formation of a liquid vortex extending downwardly towards said impeller for said vortex entrainment of gas, to effect said gas-liquid contacting.