CHARACTERISTIC EVALUATIONS OF ICI AIR-LIFT TYPE DEEP SHAFT AERATOR.

An aeration system employing a long vertical shaft of 100 m or more depth has recently been developed by ICI. The interior of the shaft is divided into two parts. Air bubbles sparged in one side of the interior flow down to the bottom and then flow up through the other side of the shaft to the surface, as liquid circulates through both sides. This liquid circulation is maintained by the gas lift action of the sparged air. In this aeration system, the flow path of the air bubbles introduced is long enough to yield high oxygen utilization. In the present paper, the authors discuss operating problems of ICI''s deep shaft aerator. The airlift type deep shaft was simulated by a mathematical model. The momentum balance equation for the fluid flow, the theoretical and empirical relations between gas velocity, liquid velocity, gas slip velocity and gas holdup, and the mass balance equation for oxygen transferred through the gasliquid interface, were all simultaneously solved to obtain the distributions of gas holdup and oxygen utilization along the shaft length. The calculated results give valuable information, such as the relations between the gas velocity, liquid circulation velocity, depth of air introduced and oxygen utilization. The power economy of the deep shaft is discussed in connection with its design and operating problems.