Effects of Gas Redispersion and Liquid Height on Gas–Liquid Hydrodynamics in a Multistage Bubble Column

Abstract

The influence of staging, superficial gas velocity, u g, and clear liquid height, h, on the values of volumetric mass transfer co-efficient, k L a, gas hold-up, ɛ g and liquid phase axial dispersion co-efficient, D L, of a 14 cm diameter and 98 cm tall bubble column were studied. The mass transfer parameter, k L a, was estimated by using the electrical conductivity method of Panja and Rao (1991) which consists of measuring the changes in electrical conductivity of water as a function of time obtained by absorbing pure carbon dioxide in water and using the measured data to infer the value of the mass transfer parameter with the help of a mathematical model. The parameter, D L, was determined by conducting tracer mixing experiments and fitting the dispersion model. From the results of the present work, the staging of the column was found to cause an increase in the value of k L a by about 60%, an increase in the value of ɛ g by about 5–10%. and a decrease in the value of D L by about 68–78, while the increase in the power input due to staging was found to be only 2.5% over the range of u g equal to 0.3–4.5 cm s −1 It was also found that in the absence of a gas redistributor, the values of k L a and D L decreased with increase in h. For identical values of gas flow rates and h, the values of k L a obtained under desorption conditions were found to be much higher than the values obtained under absorption conditions. Also, experiments were carried out on absorption of pure CO 2 into an aqueous solution of NaOH under batch and continuous co-current up-flow conditions with CO 2 as limiting reactant, and a preliminary mathematical model was proposed to explain the experimental results.