Effect of the draft tube on mixing in the reactor with internal circulation loop – CFD simulation

conference paper

English

Reactors with internal circulation loop are nowadays widely spread (extensively applied) in chemical industry, biochemical fermentation or biological wastewater treatment processes. Internal loop reactors consist of concentric draft tube, in which a gas bubbles rising up, and the downcomer in which the liquid is flowing downward. Size and diameter of the draft tube is of crucial importance reactor geometry parameters and together with number of the draft tubes has big effect on two phase hydrodynamics and mixing processes (mass transfer) inside the reactor. Present paper is divided onto the two parts. In the first part, the validation of selected mathematical model (mixed flow) is carried out. Results of experimental measurements (liquid velocity and gas hold-up) obtained on the laboratory scale reactor with internal circulation loop are compared with the CFD simulations. The CFD simulation (bubbly flow and mass transfer models) was made by COMSOL Multiphysics version 3.5a. The obtained results of numerical simulation are in good agreement with experimental data. In the second part, the study of mixing in the reactor with new geometry of the draft tube is described. The standard experimental techniques for testing of mixing processes are quite problematic, because common tracers (soluble salts) have significant influence on the two phase hydrodynamics inside the reactor. So the alternative nontrivial method should be used. The CFD simulation is used for study of mixing in the reactor with the draft tube. Concept of three or two zones draft tube was applied for numerical investigation of mixing processes. This approach was simpler than experimental study with nontrivial methods. The point of interest was a mixing time. The virtual tracer was injected into the reactor and it was measured concentration on several points in the reactor. In the moment, when concentration on all points into the reactor was constant, the mixing time was reached. The split of the draft tube onto two or three zones has big effect onto mixing (mass transfer) in the reactor. The mixing time was decreased with increase of number of draft tube into the reactor. On the other hand the two phase hydrodynamics was not significantly affected.

CFD, bubble column, airlift, mass trasfer, mixing

LEŠTINSKÝ, P.; VEČEŘ, M.

2014

23. 8. 2014

Praha

978-80-02-02555-9

21st International Congress of Chemical and Process Engineering CHISA 2014 and 17th Conference PRES 2014, Authors of papers

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