PREDICTION OF FLOW-RATES AND STABILITY IN LARGE-SCALE AIRLIFT REACTORS

Large-scale High Recirculation Airlift Reactors have been used to trea t biodegradable waste waters since the mid nineteen seventies. The sys tem is particularly attractive for situations where the land to locate wastewater works is restricted. Little is known, however, about the f luid dynamics of the gas-liquid mixture flowing around the reactor. Th is makes the determination of air injection rates difficult if effluen t quality and dynamic stability are to be maintained. When the air inj ected is not sufficient to maintain stable operation the reactor conte nts may reverse violently resulting in down time, failure to achieve t arget discharge quality and possible damage to the reactor itself. As a result many reactor installations operate at air injection rates abo ve those necessary for the biological processes. The extra air injecte d results in higher capital and process costs. This paper considers th e effect of air injection rates on the hydrodynamic stability of Airli ft Reactors and a two-phase model is proposed to predict stable operat ion at a reduced air injection rate. Results are presented which show the effect of reactor design on stability. Copyright (C) 1996 IAWQ.