Turn-around energy losses in an external-loop airlift reactor

Abstract

Gas holdups, liquid circulation rate and pressure distributions are measured in an external-loop airlift bubble column, which consists of elbow joints at the bottom and a gas—liquid separator at the top. Four different liquids are used for studying the effects of liquid viscosity (1–266 mPa s) and surface tension (28–73 mNm −1) on the above three parameters. Energy balances are applied for evaluating the energy losses in the bottom and top turn-around sections of the column. The energy loss coefficients, defined based on the superficial liquid velocity and directly estimated from the energy loss terms, are correlated in terms of the gas holdup and liquid circulation velocity as well as the liquid properties. The results indicate that while the effect of surface tension on the coefficients is minimal, that of viscosity is noticeable. The correlation are found to represent the present experimental trends reasonably well and can be combined with the energy balances to predict the liquid circulation rate in this type of external-loop airlift reactors.