Experimental investigation of hydrodynamics in SiSiC foam packed reactors
Being one of seven project partners, the group at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) studied the multiphase hydrodynamics in solid foam packed trickle-bed reactors. The open-cell solid foams, consisting of a continuous network of solid material and hydraulic open void cavities, are characterized by comparable small pressure drops, high specific surfaces and improved thermal conductivity. Compared to conventional reactor internals, such as packings of spheres or extrudates, significant improvements of flow and temperature field homogeneity as well as improved catalyst exploitation. At HZDR, the studies covered the investigation of flow regimes, liquid distribution and liquid holdup which were studied by fast electron beam X-ray computed tomography. The fast X-ray tomography enables insights of the dynamic flow behavior in the reactor cross section with spatially and temporally high resolved tomographic images.
At the gas and liquid throughputs studied at HZDR, the trickle flow as well as the pulse flow were encountered as flow regimes at cocurrent downflow of water and air [4, 7]. The highly dynamic pulse flow is characterized by continuous alternation of gas- and liquid-rich periods in the cross-section which are driven through the reactor by the succeeding gas and liquid. The high input of shear stress and the continuous exchange liquid are key mechanisms which especially contribute to an improved reaction control of highly exothermal reactions. For the investigation of pulse dynamics, water and air throughputs, axial position and solid foam pore density were varied [5, 6, 8].
|The investigations of hydrodynamics in foam packed columns were carried out with the ultrafast electron beam X-ray computed tomography system ROFEX III. The measurements were carried out with a temporal resolution of 1 ms and a spatial resolution of 1 mm. Having two measurement planes with an axial distance of about 14 mm, the system provides a detailed insight in the morphology and statistical key parameters of the liquid pulses.
|Micro-CT images of the applied foams with pore densities of 20 ppi, 30 ppi and 45 ppi (from left to right)||Schematical drawing of the ultrafast X-Ray scanner ROFEX III|
Comparison pulse flow regime
Depending on operation conditions, partially and fully developed pulse flow ocurrs in solid foam packed reactors. Within the investigated measurement range pulse flow has been found at three gas/liquid velocity combinations (A, B, C) corresponding to gas and liquid superficial velocities uG and uL, respectively, of:
- A: uL=0.03 m s-1 | uG=1.0 m s-1
- B: uL=0.04 m s-1 | uG=0.8 m s-1
- C: uL=0.04 m s-1 | uG=1.0 m s-1.
Varying operation conditions, the trend of cross sectional liquid saturation measured within solid foams can be seen in the following table.
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-  Fischer, F.; Hoppe, D.; Schleicher, E.; Mattausch, G.; Flaske, H.; Bartel, R.; Hampel, U., An ultra fast electron beam x-ray scanner, Meas. Sci. Technol., 2008, 19(9), DOI:10.1088/0957-0233/19/9/094002
-  Fischer, F.; Hampel, U., Ultra fast electron beam X-ray computed tomography for two-phase flow measurement, Nuclear Engineering and Design, 2010, 9, DOI:10.1016/j.nucengdes.2009.11.016
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-  Zalucky, J.; Möller, F.; Schubert, M.; Hampel, U., Flow Regime Transition in Open-Cell Solid Foam Packed Reactors: Adaption of the Releative Permeability Concept and Experimental Validation, Ind. Eng. Chem. Res., 2015, 54(40), pp 9708-9721, DOI:10.1021/acs.iecr.5b02233
-  Zalucky, J.; Claußnitzer, T.; Schubert, M.; Hampel, U., Pulse flow in solid foam packed reactors: Analysis of morphology and key characteristics, AIChe J., 2016, submitted.
-  Zalucky, J.; Rabha, S.S.; Schubert, M.; Hampel, U.; Pulse dynamic visualization in foam packed reactors- flow path evolution, ProcessNet-Jahrestagung 2014, 30th September-2nd October 2014, Aachen,Germany [PDF (1,6 Mb)]
-  Zalucky, J.; Möller, F.; Schubert, M.; Hampel, U.; Co-currently downward flow regime transition in solid SiSiC foams: Flow regime prediction and measurement, Jahrestreffen der Fachgruppen CFD und MPS, 19th-20th March 2015, Lüneburg, Germany [PDF (1.2 Mb)]
-  Zalucky, J.; Claußnitzer, T.; Schubert, M.; Hampel, U.; Qualitative and quantitative analysis of liquid flow distribution in SiSiC foams using ultrafast X-ray computed tomography, ESCRE 2015, 27th-30th October 2015, Fürstenfeldbruck, Germany [PDF (0.6 Mb)]
-  T. Claußnitzer, Experimental investigation of cocurrent water/air downflow in SiSiC solid foam packed reactors, Diploma thesis, Technische Universität Dresden, 2015 (121.2 MB)