The water-modelling of the ejection rate of overflow generated by air-lift pump has been studied under various operating conditions, namely, top pressure, gas flow rate, nozzle submergence, riser diameter and lift ratio. The decrease of top pressure and the increase of nozzle submergence have the same effect as the increase of gas flow rate on the ejection rate of overflow. The ejection rate of overflow increased as top pressure decreased, nozzle submergence increased, gas flow rate increased, lift ratio decreased and/or riser diameter decreased.
Air-lift pumps (Clark and Dabolt, 1986; Nicklin, 1963; Stenning and Manin, 1968) are finding increasing use where pump reliability and low maintenance are required. They have been studying for lifting manganese nodule from deep seabed (Shimizu et al., 1992; Shimizu et al, 1984), since air-lift pumping system is safe and convenient compared to the submerged pumping system because it requires virtually no maintenance and various components of the system are set on the mining ship. Air is injected at the bottom of riser and the levels in the riser then rises because the average density of a gas-liquid mixture is less than that of liquid in the riser. When gas flows greater than certain minimum, liquid can be pumped to a considerable height and flown from the top of the riser, and a pumping action results. When the gas-liquid mixture flows in the riser, a variety of flow-patterns (Taitel et al., 1980) are possible depending on the gas flow rate. The gas can be distributed as small bubble (bubbly flow); as long round- nosed bubble (slug flow): as distorted bullet-shaped bubble churn turbulent flow); as a central core surrounded by a liquid annulus (annular flow); or finally at very high gas-flows as continuous medium supporting droplets of liquid (mist flow).
