Liquid Mixing in a Bubble Column

In most of the bubble column design, it is assumed that liquid phase is well mixed and spatial distributions of molar concentrations for all components are uniform. However, there is liquid mixing in actual bubble column reactors. The performance of a bubble column strongly depends on the liquid mixing induced by bubbles in the column. Those assumptions therefore cause some errors in column optimum design. Only a few quantitative investigations have been carried out on two-phase turbulence and liquid mixing. In this study, numerical simulations for liquid mixing in a bubble column have been carried out and compared with experiments. The transient behavior of tracer concentration was measured for test columns of 0.3 m in diameter. The height of the columns was 1 m. Bubbles were supplied by using two types of spargers: ring spargers and a perforated plate. A hybrid method, NP2-3D, which is based on the combination of multi-fluid and interface tracking methods, was used to simulate the flow. In a two-phase turbulence model, linear superposition of bubble-induced turbulence and shear-induced turbulence was assumed. Numerical prediction could qualitatively describe the effects of column diameter and gas inlet on the liquid mixing in a column.