System for mixing high viscous liquids with gas

Abstract

A system and method for mixing high viscous liquids with gas is provided. The disclosed embodiments include a reactor or mixing vessel having a draft tube disposed therein, a gas injection subsystem adapted to inject gas into the reactor or mixing vessel proximate the entrance of the draft tube. The embodiments also include an agitator disposed within the draft tube which makes the draft tube the primary site for the gas-liquid mixing. In particular, the agitator is adapted to create gas bubbles having an average diameter between about 0.3 mm and 3.0 mm which are then ejected into the reactor or mixing vessel. The mass transfer efficiency associated with the present system and method is enhanced from the combined effect of gas dissolution into the high viscous liquid within the draft tube and greater bubble residence time within the high viscous liquid.

1 . A system for mixing a high viscous liquid with a gas comprising:
 a reactor adapted for containing a high viscous liquid;   a draft tube disposed therein, the draft tube having an entrance, an exit and a passageway where an agitator is disposed and through which the high-solids content liquid flows in a downward orientation;   a gas injection subsystem disposed in operative association with the reactor and adapted to inject a source of gas into the reactor at a location proximate the entrance of the draft tube;   an agitator disposed within the draft tube, the agitator adapted for creating gas bubbles having an average diameter of between about 0.3 mm and 3.0 mm and the agitator is further adapted for dispersing the high viscous liquid and gas bubbles from the exit of the draft tube into the reactor and increase residency time of the gas bubbles within the reactor.   
     
     
         2 . The system of  claim 1  wherein the agitator further comprises a radial impeller having a diameter and the impeller further defining a radial clearance between a tip of the impeller and the draft tube of between about 0.05 to 0.5 times the diameter of the impeller. 
     
     
         3 . The system of  claim 1  wherein the entrance of the draft tube is located below a surface of the high viscous liquid in the reactor and the high viscous liquid in the reactor is continuously recirculated through the draft tube. 
     
     
         4 . The system of  claim 1  wherein the reactor is an aeration basin of a wastewater treatment system, the gas is oxygen, and the high viscous liquid has a solids loading of greater than about 10 grams per liter. 
     
     
         5 . The system of  claim 1  wherein the reactor is fermentation vessel, the gas is oxygen, and the high viscous liquid has a solids loading of between about greater than about 5 grams per liter and about 70 grams per liter.