Mass Transfer Analysis of Spinning Cone Columns Using CFD

The mechanisms of liquid–-gas mass transfer in spinning cone distillation columns (SCC) have been investigated in a pilot-scale SCC with an inner diameter for the column shell of 0.148 m, a rotational speed of 500 rpm, and gas and liquid flow rates of up to 500 and 0.3 Lmin –1 , respectively. The actual three-phase flow system (the continuous liquid film, the dispersed liquid droplets, and the gas) has been modelled using an Eulerian two-phase (the dispersed liquid and the gas) CFD model of the column with the geometry and the boundary conditions based on consideration of all three phases. The analysis is directed towards the comparative evaluation of the film and the spray-related mass-transfer coefficients and the comparison of these with the measured values. The results show that the film mass-transfer coefficient is nearly constant over the whole practical range of fluid flow rates and that it is clearly insufficient to explain the experimental data. In contrast, the spray mass transfer coefficient rises steadily and, at the onset of the loading regime, it exceeds its film-related counterpart by an order of magnitude. Both the trend and the absolute value of the spray mass transfer coefficient match the observed values very well. Implications of these findings for the possible optimization of SCC design and operation are discussed.

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