Development of a Standardized Method for Mass Transfer Measurements in Absorption and Desorption

Development of a standardized method for mass transfer measurements in absorption and desorption

A. Kunze¹, P. Lutze¹, M. Kopatschek², S. Müller², M. Grünewald², A. Górak¹

¹ TU Dortmund University, Laboratory of Fluid Separations

Emil-Figge-Strasse 70, D-44227 Dortmund, Germany

Phone: +49 (0) 231 755-3034, E-Mail: anna-katharina.kunze@bci.tu-dortmund.de

² University of Bochum, Chair of Fluid Separations

Universitaetsstrasse 150, D-44780 Bochum, Germany

Due to the rising use of rigorous models for designing absorption and desorption processes a coherent method for mass transfer parameter determination must be developed. Currently, a comparability of mass transfer parameters investigated experimentally at different sights or different columns is not existent. Additionally, there is hardly one method to evaluate mass transfer parameters determined in the past, because often important information about the measurements and calculation is missing. That leads to the effort of a standardized experimental and calculation method for determination of mass transfer parameters in absorption and desorption. The main focus is to increase transparency and comparability for mass transfer parameters on gas and liquid side β_G und β_L and the effective interfacial area a_eff from different authors ^[1,2]. This will lead to a decrease in necessary safety factors resulting in a cost and resource optimized column design.

A consortium of 14 industrial partners, including manufacturers and users of packings, as well as two academic partners are working on this standard method in Europe. The first step of the standard method is to figure out an experimental method to achieve coherent results on pilot plant scale. Therefore, concentration measurements on different plants are carried out to calculate the volumetric mass transfer parameters (β_G^.a_eff) and (β_L^.a_eff). The method is developed for structured and random packings. During the development of an experimental method the main focus is on the configuration of the setup. Detailed investigations concerning the influence of e.g. gas and liquid distributors, packing height, and taking samples is carried out. The experiments for the experimental method are carried out in two columns with a diameter of 288 mm, which have exactly the same configuration. The experimental method will then be adapted additionally to a column with a higher diameter to carry out further experiments.

In addition a mathematical tool is necessary, which guarantees a consistent calculation of mass transfer parameters for rigorous modeling. The stepwise data processing from the experimental data to gain parameters for rigorous modeling is described in Figure 1.

Figure 1: Pathway for the determination of model parameters of rigorous absorption models.

Based on the experimental data the first step is to define the volumetric mass transfer parameters (β_G^.a_eff) and (β_L^.a_eff). To take temperature and concentration dependence of the chemical system data into account, a detailed analysis of possible calculation methods is carried out. To define the temperature and concentration dependence of the phase equilibrium, at least seven basic system data (such as vapor pressure as well as density, viscosity and diffusion coefficients in gas and liquid phase) have to be calculated. To minimize the calculation effort, a global sensitivity analysis is carried out. For the most sensitive parameters, different calculation methods are compared. In addition, also the experimental data are implemented in the sensitivity analysis to determine the influence of deviations in each measured value.

A combination of three chemical systems is necessary to determine β_L, β_G and a_eff, one of the following properties has to be fulfilled by one of the systems:

-       mass transfer resistance on liquid side for β_L

-       mass transfer resistance on gas side for β_G

-       fast reaction pseudo first order for interfacial area a_eff

Via correlation of interfacial area between the three different chemical systems the phase specific mass transfer parameters can be determined.

Within this presentation, the detailed results of the analysis of equipment parameters, the method in general as well as the mathematical tool will be shown.

This work is part of GVT funded project „Standardization of mass transfer measurements in absorption and desorption“.

Literature

[1]    A. Hoffmann et al., “Standardization of mass transfer measurements: A basis for the description of absorption processes“, Chemical Engineering Research and Design 2007, 85 (1), 40-49.

[2]   J.F. Rejl et al., “Methods standardization in the measurement of mass-transfer characteristics in packed absorption columns“, Chemical Engineering Research and Design 2009, 87 (5), 695-704.