(271b) Billet-Schultes Model - A Design Tool for Packed Columns

This paper discusses major features and demonstrates the usability of Billet-Schultes method as a tool for design of packed columns for absorption and distillation.Packed columns employing gas-liquid counter-current flow are widely used across a wide range of industries. Many correlations and models were developed to estimate the packing characteristics and process performance. After the first recognition of relation between hydrodynamics and mass transfer process proposed by Kirschbaum in the 1930s, suspended bed of droplet model (SBD), particle model and Channel model are the most well-known basis in packed columns. In particular the channel model elaborated by Billet and Schultes, was widely employed in separation industry. Our contribution will give a detailed introduction to the model equation and its application to the characterization of packings. However, conventional models described merely the ideal and simple physical conditions, deviation from the models were summarized usually as constants in modeling equations. Our experimental investigations have confirmed that a large amount of liquid flows on the column wall and the quantitative fraction depends on packing geometry, packing size and column diameter. On-wall flow which was considered as source of maldistribution in packing columns can not be neglected. So far, using experimental data for scale-up to predict the optimal height of packing columns often failed, especially for large column with high capacity in the rectification processes. Therefore a modified model was established by dividing the holdup into effective core-flows and shortcut flows based on measurements using wire mesh sensor (WMS) which brings almost no mechanical influence in the performance. It links the distribution and modeling process and could be applied for comparison of packing characteristics (pressure drop resistance, mass transfer coefficients) in different column diameters based on effective holdups. Consequently, it should result in a more accurate prediction of the optimal column height using the HTU-HTU model for the column designs.