Gas-liquid-solid volumetric mass transfer coefficient and impeller power consumptions for industrial vessel design

Abstract

Waste-water treatment, fermentation, chlorination/de-chlorination and hydrogenation are processes often realized in mechanically agitated vessels. In many cases the gas-liquid mass transfer can be the limiting process in the utilization of mechanically agitated vessels. The parameter describing gas-liquid mass transfer intensity (volumetric mass transfer coefficient kLa) becomes than the key parameter. Because in fermentation processes as well as in hydrogenation ones solid particles are usually also present in gas-liquid system, we aim to study experimentally the effect of solid particles presence on kLa and power input values using reliable measuring methods. This study broadens the results on transport characteristics published in IJHMT recently (Petříček et al., 2017) [1].Measurements were conducted in a three phase multiple-impeller fermenter of i.d. 29 cm containing microparticles of the diameter 137 ± 30 μm. To cover the effect of impeller type in our results, we gradually used Rushton turbine, Pitched-blade pumping down and Techmix pumping down impellers of the diameter of 1/3 of the vessel diameter. To measure kLa using dissolved oxygen (DO) polarographic probes the Dynamic pressure method (DPM) has been chosen. We present our results in the form of dependencies of kLa on process parameters as impeller power, gas superficial velocity, impeller blade speed, etc. We used several mathematical shapes of the dependencies to find which ones will describe the kLa dependency accurately well, to be used in agitated vessels industrial design, when gas-liquid-solid system should be treated.Usually, kLa correlations are based on gassed power input and superficial gas velocity. We tested several correlation types, evaluated their empirical parameters and proposed the correlation shapes suitable for fermenter design, operating and scale-up under the conditions, where solid particles affect the interfacial mass transfer.