Hydrodynamic and mass transfer characteristics of ejector loop reactors

Autor: M. Fialová, P. Havelka, Václav Linek, J. Sinkule, J. Zahradník
Rok vydání: 2000
Předmět:
Zdroj: Chemical Engineering Science. 55:535-549
ISSN: 0009-2509
Popis: Volumetric liquid-side mass transfer coefficient k L a was measured in the upflow ejector (with and without swirl) and in the cocurrent ejector–distributor bubble column as well as gas and liquid phase backmixing in the column. Water and 0.3 M aqueous solution of Na 2 SO 4 were used to simulate coalescent and non-coalescent batches. Different methods were used to measure k L a : dynamic pressure-step (DPM), steady-state physical (SPM), classic sulfite (CSM) and steady-state sulfite method (SSM). Pure oxygen and air were used as the gas phase. Large intensity of liquid mixing in the column caused by the jet with high kinetic energy was confirmed. Gas backmixing in the coalescent batch was well described by the axial dispersion model while gas backmixing in the non-coalescent batch was successfully described by the model of two parallel series of four perfect mixers with backflow, where the respective branches corresponded to the small and large bubbles present in the dispersion, was therefore proposed. Experimental data indicated lower extent of mixing in large bubbles as compared with the smaller ones. Installation of a swirl significantly influenced bubble sizes in the non-coalescent batch. Values of k L a ej in the ejector with a swirl were lower than those for the ejector without a swirl, both in the coalescent and non-coalescent batches. The coefficient k L a col in the column was well correlated with gas holdup for the coalescent batch. A good agreement was observed between the data obtained by DPM and SPM methods. In the non-coalescent batch the chemical methods were used as the DPM method failed being limited by the response rate of oxygen probes used. Both the methods (CSM and SSF) yielded similar values of k L a col in the case of oxygen absorption. Absorption of air yielded significantly lower values k L a col (by factor of two) when a model of a single series of four perfect mixers was used for description of the gas flow in the reactor. The model of two parallel series of four perfect mixers with backflow was therefore used, taking into account particular contributions of small and large bubbles to the overall mass transfer in the column. It has been shown that decisive part of oxygen has been absorbed from the small bubbles.
Databáze: OpenAIRE
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