(223d) Looking inside Structured Packings: Numerical Investigations of Distillation Using Openfoam

Emissions from the process industry are a major contributor to global warming. A significant reduction in these emissions can be achieved with more efficient processes with properly designed structured packing columns. The benefits range from lower pressure drop to the possibility of more sophisticated process integration [1]. Retrofitting existing columns with structured packings can lead to higher separation efficiencies as well as increased capacity.

A key disadvantage of using structured packings in distillation columns is the uncertainties in their design. Thus, either (semi-)empirical correlations to predict mass transfer in the packing or scale-up engineering experiments are necessary to determine the required packing height for a given separation task [1]. Therefore, the development of an improved design methodology for columns with structured packing is the main objective of the collaborative project ReProvAP, to which this work contributes.

The present work shows an alternative way to determine the separation efficiency in the design of packed columns. The goal is to reduce the dependence on pilot-scale experimental studies and to gain insight into small-scale phenomena. To this end, high-resolution simulations from the field of computational fluid dynamics (CFD) are applied. The computational domain covers a periodic element of the fluid between two corrugated sheets of a structured packing and is modeled to be from the center of a column. Effects from the column wall and packing edge are not considered. For the simulations in this work, the solver interGCSTFoam developed in OpenFOAM by Hill [2] is improved and utilized.

The simulations give quantitative insight into parameters such as the effective mass transfer area, mass transfer coefficients, and HETP values. By varying physical properties in the simulations, their influences on fluid dynamics and mass transfer can be visualized and quantified. The workflow of the simulation, starting from preprocessing, as well as selected results will be presented.

References:

[1] J. Stichlmair, H. Klein, S. Rehfeldt: Distillation: principles and practice, 2^nd edition. Wiley-VCH, 2021.

[2] S. Hill: Numerische Modellierung und Simulation der Fluiddynamik und des Stoffübergangs in strukturierten Packungen. Dissertation, Technical University of Munich, 2022.