(94g) Experimental Investigations on the Fluid-Dynamic Design of High-Performance Separating Trays Based on a Miniaturized Measuring Cell

The characterization of fluid dynamics behavior is a central issue in the design of tray columns. For the design of energy-efficient columns and production plants the knowledge of operating window for optimal flow conditions are indispensable. Even for trays with high-performance valves there is a lack of reliable design tools and experimental data to determine or predict fluid dynamic variables. In particular for the prediction of organic systems new test setup and thus experimental data are required. Phenomena such as entrainment, weeping and the flow pattern on the tray must be sufficiently known for a characterization especially near the load limits. For conventional sieve trays, such information concerning fluid dynamics and operation window constraints already exist on the basis of numerous experimental investigations. For high-performance trays, such as valve trays, such procedures and experimentally supported data bases do not yet exist.

Funded by the German Federal Ministry for Economic Affairs and Climate Action, precisely these tools and methods are currently being developed. The approach hereby is carried out on three different research fields. At three different research institutes, one topic area each is being investigated more intensively. In close cooperation, the institutes coordinate their results in order to provide reliable tools.

• The Helmholtz-Zentrum Dresden Rossendorf (HZDR) places a special focus on single-valve simulation and measurement techniques to determine a CFD simulation tool that can accurately predict the behavior of industrial-scale separation trays. All investigations are focused on the water/air system.
• At the Technical University of Munich (TUM), a variety of high performance separation trays are being investigated under different flow conditions in an industrial scale column for the water/air system. With regard to the operating field, special attention is paid to the behavior at the capacity limits.
• At the Ruhr University Bochum (RUB) the interface between the aforementioned approaches is investigated. On the one hand, there is a need to investigate the interaction between the valves and incorporate it into the CFD modelling. The calculations set up on findings of single valves are validated by measurements on valve groups representing real behavior on commercial trays. On the other hand, detailed investigations of bubble patterns can lead to conclusions about the behavior of columns – e.g. weeping – on an industrial scale. Another much more important aspect is also being addressed at the Ruhr University Bochum. In addition to the scaling factor, it is feasible to analyze organic material on a miniaturized scale. Investigations of organic test systems will provide previous unknown insights into the operation behavior of such material systems.

Our contribution deals with the experimental studies and results at Ruhr University Bochum. Motivated by the aforementioned requirements a miniaturized measuring cell (MC) was designed. To prevent expansion and constriction of the liquid flow at the outlet downcomer and the exit weir, the measuring cell was designed in a rectangular shape (0.2 x 0.6 m). In addition, this design allows the investigation of the fluid dynamics with a high-speed camera system without significant distortion. To investigate the fluid dynamics and to be able to draw conclusions for scale-up processes and differences in material systems, various operating parameters have to be measured. There is a need to capture gas and liquid loadings, pressure drop, gas/liquid inlet/outlet temperatures, weeping, entrainment and liquid hold-up. To ensure that the designed cell can react flexibly to changing requirements from the other fields of the project, it has a modular design. There are options to replace active areas, change weir heights and tray spacing and adapt innovative entrainment and weeping collector systems. In order to investigate the weeping in a locally resolved manner, the weeping collector can also be divided into several chambers. In addition, the insight of the column is visible to determine flow patterns with a high-speed camera system. Due to the large number of correlations and measurements available for comparison, the column is initially started up with sieve trays and the water/air system. After successful validation, the active area of the trays is replaced with high-performance valves like those used by project partners. At first, gas and liquid rates as well as dry and wet pressure drop are recorded.

In this paper, the concept of the measuring cell and initial test results are presented and discussed with regard to the resulting requirements. The fluid dynamics of the newly designed test setup are compared and analyzed with existing technical installations. During start up, a considerable influence of the rectangular geometry compared to industrially applied round columns could be determined for the substance system water/air. This will be discussed and examined in more detail. In addition, detailed considerations of the interactions between valves and the resulting bubble formation mechanisms will be presented. Furthermore, a first outlook on the investigation of substitute material systems will be given.

The project is supported by the Federal Ministry for Economic Affairs and Energy, the AiF (IGF project: 20835 BG2) and IGF. Special thanks to all of them.