Transient models for oxygen mass transfer in airlift contactors

Abstract

The mathematical model was developed and tested for the prediction of gas-liquid oxygen mass transfer behavior in the ALC. Many types of unsteady state models were formulated, i.e. CSTR, CSTRs-in-series, PFR and dispersion models. Comparison between simulation results and experimental data concluded that the dispersion model was most suitable for the prediction of gas-liquid oxygen mass transfer in the ALC. In the dispersion model, both riser and downcomer were considered as a plug flow region with dispersion, whereas the gas separator was modeled as a region of completely mixed. The model predictions were satisfactory not only for their numerical accuracy, but also for their ability to agree well with the actual reported experimental data. The effect of the overall mas stransfer coefficient (KLa) and gas phase dispersion coefficient (DG,r) on the modeling results were inverstigated. The results showed that increasing either KLa and DG,r would result in a faster rate of mass transfer from gas bubble to liquid. In addition, the model was successfully tested over a range of operating parameters e.g. the ratio between downcomer and riser cross sectional areas (Ad/Ar) and the inlet gas flowrate (QG,in). The model was then used to predict the performance of the ALC with a constant liquid feed flowrate (QL,F). Lastly, it was found that the model was not able to correctly predict the behavior of the high draft tube ALC. The reason for this inaccuracy was still unknown