(43b) Will Laboratory and Pilot Plant Columns Soon be Superfluous?

Established methods for the design of packed columns for distillation, absorption and desorption are based on simplified and extensive model assumptions. Due to the high complexity of the phase distribution within the column and insufficient knowledge of the mass transfer behavior of real multicomponent systems, only limited predictions on the actual separation performance of industrial columns can thus be retrieved.

A widely used parameter for characterizing the mass transfer performance of structured packings is the HETP value, which, among other things, depends strongly on the physical properties of the components to be separated. Therefore, in many cases tests in calibrated lab columns are required for an unknown non-ideal system to separate. Scale-up of the plant to production scale is then done using the HETP value determined with standard test systems that are usually chosen from the list of recommended test systems for distillation columns compiled by Onken and Arlt[1].

The disadvantage of this column-based methodology is the comparatively large amount of investigated system required, which often cannot be provided and the high costs for conducting the experiments. For a fast and cost-efficient determination of the HETP value, respectively a weakening factor, which translates the HETP from an ideal to a real system, an apparatus as small as possible while maintaining scale-up capabilities is therefore desirable. The idea here for a new measuring cell is, to focus on the channel between two packing sheets, while at the same time minimizing wall effects that small columns show, compared to industrial scale columns. The obtained results of the measuring cell can then be used in an improved method for the design of columns with structured packings.

To examine the basic feasibility and resilience of this new approach, the separation performance as well as the fluid dynamics need to be considered. Therefore, separation performance measurements and both the single-phase and the two-phase pressure drop will be presented. With short separation zones it has to be ensured, to stay above the detection limit of the change in concentration. Therefore cyclohexane / n-heptane was identified as a suitable test system and a packing with a surface area of 500 m²/m³ was chosen.

Furthermore, the experimental results of the measuring cell are directly compared with results from conventional lab (DN50, DN80) and pilot-plant (DN250) columns. This comparison is necessary to investigate the transferability and informative value of the new measuring cell in comparison to conventional lab columns, to be able to further develop the scale-up method. The aim of this contribution is to present these basic experimental considerations.

The authors gratefully acknowledge financial support from the German Federal Ministry of Education and Research (BMBF) and project supervision by the DLR Project Management Agency for Environment and Sustainability for the project "ReProvAP" (Reduzierung der klimarelevanten Prozessemissionen durch die verbesserte Auslegung von strukturierten Packungskolonnen) with the funding codes 01LJ2002F

[1] Onken, U., Arlt, W., 1990. Recommended Test Mixtures for Distillation Columns. The Institution of Chemical Engineers