Liquid backmixing and phase holdup in a gas-liquid multistage agitated contactor

Axial backmixing of the liquid phase in a multistage agitated contactor (MAC) is investigated through residence time distribution (RTD) experiments over a large range of variables such as gas velocity, liquid velocity, stirring speed, and the number of stages using an air-water system. The experimental RTD curves are satisfactorily compared with the cascade of stirred tanks with backflow (CTB) model. The backflow ratio of the liquid phase is evaluated. The effects of the operating variables on the backflow ratio are examined. The phase holdup in a MAC is also investigated. Based on the data from the present study and the literature, a correlation is developed to predict the backflow ratio in a MAC for an air-water system operated in co-current manner. It is also observed that low backmixing is achieved in the MAC.