Bubble columns with internals
Most reactions carried out in bubbles columns are of exothermic nature (e.g. Fischer-Tropsch and methanol synthesis). To ensure stable reactor operation, the excess heat is removed from the system, for example via internally placed tube bundle heat exchangers transferring it directly from the source. Large specific surface areas of the tube bundles (between 25 and 45 m-1 depending on the operation and reaction carried out) are needed to remove the heat. Referring to the reactor’s cross-sectional area, between 20 and 40 % are commonly covered by the internals.
Figure 1: Experimental setup of the bubble column with internals equipped with wire-mesh sensor measurement technique.
Thus, the aim of this study is to reveal the influence of such tube bundles of various tube layouts and sizes on the hydrodynamics, i.e. bubble size distribution, interfacial area, velocity profiles and gas phase holdup as well as on the mass transfer behavior using ultrafast X-ray computed tomography, wire-mesh sensors and fast responding oxygen needle probes.
Smaller internal tubes were found to promote bubble breakup and increase gas holdup, which, in turn, leads to higher a interfacial area with a superior gas-liquid mass transfer characteristic. Tomographic analyses also revealed the formation of gas slugs in individual sub-channels of the tube bundles reducing the gas residence time and preventing intensive radial exchange of the gas phase.
Figure 2: Flow patterns and gas holdup distribution in the cross-sectional area of the column.
In addition, liquid mixing 1D cell models are developed accounting for the effect of the internals for scale-up purposes as well as for the prediction of flow patterns, hydrodynamic behavior and mass transfer performance.
Funding: European Research Council (ERC Starting Grant, Grant Agreement No. 307360)
References: F. Möller, U. Hampel, M. Schubert (2017). Sub-Channel Flow Behavior in Vertical Tube bundles in Bubble Columns. ProcessNet Fachgruppentagung Mehrphasenströmungen, Dresden, Germany
F. Möller, U. Hampel, M. Schubert (2016). Bubble Columns with Internals: liquid circulation and swarm dynamics. ProcessNet Fachgruppentagung Mehrphasenströmungen, Bingen, Germany