Two-phase flow in ceramic monoliths
Monolithic structures operated in the Taylor flow regime are considered as highly promising for the intensification of heterogeneous catalytic reaction processes. The slug-bubble formation favors mass and heat transfer as well as catalyst utilization, if the flow conditions are properly matched with the requirements of the reaction. However, to fully benefit from the excellent gas-liquid mass transfer behavior and tunable residence time of the Taylor flow regime, homogeneous and well defined gas-liquid distribution patterns are required.
To reveal the maldistribution susceptibility of monolith reactors, the ultrafast electron beam X-ray modality was applied to test various distributor designs (e.g. needle distributors). To evaluate the impact of flow maldistribution from the targeted process configuration, a new methodology was proposed to measure the Taylor flow specific characteristics of every unit cell in each individual channel and to couple these data efficiently with a simulation framework originally developed for single channel studies.
Significant spatial and temporal deviations in the phase holdup as well as in the gas bubble and liquid slug lengths were found. To evaluate the impact of the Taylor flow maldistribution on the reactor performance, the data of more than 125,000 unit cells were used to simulate the reactor productivity. Therefore, the hydrogenation of glucose was exemplarily considered in a pseudo 2D reactor model for the Taylor flow configurations with bubble and slug length as well as two-phase flow velocity as inlet parameters. To efficiently calculate the sorbitol productivity for the huge number of unit cells, a grid interpolation schema was applied.
The results verify that a monolith reactor solely designed by using superficial velocities and empirical correlations for gas bubble and liquid slug lengths fails significantly in achieving high product selectivity and the desired conversion. The developed methods are a solid base to design and select proper distributors ensuring favorable flow configurations for specific chemical processes.
- TU Dresden,
- Åbo Akademi University
Helmholtz Association (Helmholtz Energy Alliance ‘Energy Efficient Chemical Multiphase Processes’ - HEA-E0004)
- M. Schubert, S. Kost, R. Lange, T. Salmi, S. Haase, U. Hampel (2016).
Maldistribution susceptibility of monolith reactors: Case study of glucose hydrogenation performance.
AIChE Journal 62, 4346-4364.
- T. Schäfer, C. Meitzner, R. Lange, U. Hampel (2016).
A study of two-phase flow in monoliths using ultrafast single-slice X-ray computed tomography.
International Journal of Multiphase Flow 86, 56-66.
- T. Schäfer, M. Wagner, U. Hampel, M. Weiß, C. Meitzner, R. Lange (2014).
Hydrodynamic characterization of transient multiphase flows in monolithic structures using ultrafast X-ray tomography.
7th World Congress in Industrial Process Tomography, 2.-5. September 2013 Krakow, Poland, pp. 624-631.
- C. Meitzner, G. Hilpmann, T. Schäfer, S. Haase, R. Lange, U. Hampel (2017).
Homogeneous gas-liquid distribution for monolithic structures via a needle distributor.
Submitted to Chemical Engineering & Technology.