(271a) Mass Transfer Correlations for Structured Packings: Disorder in Order

Present paper addresses mass transfer related features of three well established models for predicting the efficiency (HETP, i.e. the height equivalent to a theoretical plate) of conventional corrugated sheet structured packings, i.e. Billet and Schultes (BS), Rocha, Bravo and Fair (RBF), and ?Delft model? developed by Olujiæ and co-workers at Delft University of Technology. These as well as other similar models generate HETP by balancing in specific way relative contributions of resistances at vapour and liquid side, as well as the effective area as main model parameters. Strikingly these methods differ significantly in the relative magnitude of individual contributions of liquid and vapour side mass transfer coefficients and the effective (interfacial) area, indicating that there are still uncertainties regarding the proper nature of mass transfer process as encountered in distillation utilising structured packings. Specific features of these models are addressed, using experimental evidence obtained in total reflux distillation tests performed recently at VSCHT at ambient conditions with Mellapak 250.Y packing in a column with internal diameter of 0.15 m, using methanol/ethanol, methanol/propanol, and ethanol/propanol as tests systems. Moreover, it is shown that ?profile method? developed at VSCHT can easily be used to adjust mass transfer correlations of published methods, which in case of Delft model leads to an increase in gas-side and a corresponding decrease in liquid-side volumetric mass transfer coefficient, respectively, resulting in much better agreement with experimentally measured packing efficiency, which however is accompanied by an increase of liquid side-resistance beyond that adopted according to the original method. This and other peculiarities as well as insufficiencies in related knowledge around the modeling and quantification of mass transfer coefficients and effective area are discussed.