Advanced gas control in gas-liquid mixing systems

An improved system for the mixing of a gas with a body of liquid without appreciable loss of gas into an overhead gas phase comprising:

• (a) a mixing vessel for a body of liquid into which a gas is to be mixed, a portion of said body of liquid to be maintained in a recirculating flow condition, said portion having no gas-liquid interface with an overhead gas phase;
• (b) impeller means positioned essentially in the center of the mixing vessel and having an upwardly extending drive shaft, said impeller means being adapted to establish a recirculating flow condition within said recirculating portion of the body of liquid, with liquid flow being downward in the inner region thereof and upward in the outer region thereof;
• (c) conduit means for introducing a feed gas stream directly into the recirculating portion of the body of liquid;
• and
• (d) baffle means separating said recirculating portion of the body of liquid from a relatively quiescent portion thereof, while maintaining fluid communication therebetween, said quiescent portion of the body of liquid having a gas-liquid interface and an overhead gas phase, and being adapted to accommodate a change in liquid level in response to a change in volume of said body of liquid between the condition in which no gas bubbles are in the body of liquid and the condition that exists when a desired gas bubble concentration is developed therein, said baffle means comprising (a) an outer conical baffle that slopes upward and inward so as to direct the upward flow of liquid, and the accompanying gas, from the outer region of the body of liquid toward the downward suction of the impeller means, the slope of said outer conical baffle precluding the accumulation of gas in dead zones thereunder, and (b) an inner conical baffle that slopes downward and inward toward the drive shaft of said impeller means so as to direct the flow of liquid, and the accompanying gas, into the downward suction of the impeller means, the slope of said inner conical baffle effectively precluding the accumulation of gas in dead zones in the center of said body of liquid, said inner conical baffle being positioned so that its upper, outermost end is above and spaced apart from the uppermost end of the outer conical baffle so as to establish a vent opening therebetween for communication between the recirculating portion of the body of liquid and the quiescent zone, said vent opening being positioned apart from the upward and inward flow path established by said outer conical baffle, whereby the desired gas and liquid mixing are effectively achieved, the inner and outer conical baffles eliminating dead zones near the impeller drive shaft and under the baffle means, minimizing gas velocity during normal operations and facilitating venting of gas during upset conditions.