A Computational Investigation of Transport Phenomena in Stirred Reactors and Catalyst Particles

Doctoral thesis, 1994

Transport phenomena in stirred vessels and catalyst particles have been studied with computational models. The turbulent flow in a cylindrical, baffled vessel stirred with a coaxially mounted Rushton turbine was represented with a numerical solution of the transport equations. The influence of turbulence was accounted for by the .kappa.-.epsilon. model. The influence of the modeling of the impeller was studied by comparing the swirling radial jet model and a model based on empirical data. Both models were found to give predictions in the range of available literature data. The prescribed length-scale in the impeller outflow influenced the predicted radial velocity and the turbulent quantities close to the impeller, while the flow in other regions was mainly unaffected. The influence of commonly used scale-up criteria on the model predictions was studied. Simulations with the swirling radial jet model predicts minor changes of the flow pattern when the Reynolds number is changed. The model was used to simulate the effects of the flow pattern on mixing time measurements and it gave reasonable agreement with experimental data. The influence of the position of injection and detectors was studied. The model could be used to predict suitable detector positions for the measurement of the inhomogeneity in the whole volume. A model of the influence of electrochemical phenomena on the simultaneous transport and reaction in a catalyst particle during liquid-phase hydrogenation was developed. This model can predict the conditions for which a high influence on the reaction rate can be expected. The model was also used to predict the influence on selectivity. The dynamic response of the catalyst particle to changes in the external hydrogen concentration was estimated as well.