Non-coalescent Batch Research Articles

Gas-Liquid Contactors' Aeration Capacities When Agitated by Rushton Turbines of Various Diameters.

Mass transfer processes are one of the most important operations in chemical, biochemical, and food industries worldwide. In the processes that are controlled by the gas–liquid mass transfer rate, the volumetric mass transfer coefficient kLa becomes a crucial quantity. The dataset was measured with the aim to create a correlation for kLa prediction in a non-coalescent batch under the wide range of experimental conditions. The dynamic pressure method, which was reported as physically correct in the past, was chosen to be the method for experimental determination of kLa. Our previous work targeted the kLa dependencies in viscous and coalescent batches resulting in correlations that are viable for the broad range of process conditions. We reported that the best-fit correlation is based on the hydrodynamic parameter circumferential velocity of impeller blades in the case of non-coalescent liquids in the vessel equipped by single or multiple impellers at a constant D/T ratio (diameter of the impeller to the inner diameter of the tank). Now, we focus on the influence of various impeller diameters on transport characteristics (mainly kLa) in a non-coalescent batch. The experiments are carried out in a multiple-impeller vessel equipped with Rushton turbines (of four diameters) and in both laboratory and pilot-plant scales. Various impeller frequencies and gas flow rates are used. We examine the suitability of the hydrodynamic description, which was reported in the past, to predict kLa also when the D/T ratio changes. We show that the correlation based on the energy dissipation rate better fits the experimental data and predicts kLa values more accurately in the case of varying D/T values. This correlation could be adopted in the design and scale-up of agitated devices operating with non-coalescent batches.

Heat Transfer Between Gas and Non-coalescent Liquid in a Bubble Column

Multiphase contactors, e.g. bubble columns, are often used in operations accompanied by heat transfer between the phases. The effect of multi-orifice aerator for the heat transfer between gas and the non-coalescent liquid was investigated for two different aerator patterns. This study was performed on the bubble column 0.15 m in diameter with various liquid levels and for various superficial gas velocities. The aqueous solution of 0.3 M Na2SO4 was used as a non-coalescent batch. The gas-to-liquid heat transfer measurements were performed by a non-steady state method based on measurements of the gas- and liquid- temperature in the time for an evaluation of the heat fluxes and heat transfer coefficient.

Volumetric mass transfer coefficient in multiple-impeller gas–liquid contactors. Scaling-up study for various impeller types

Focused on liquid film-controlled processes in mechanically agitated aerated vessels, an attempt is made to develop scale-up correlations based on isotropic turbulence theory. It is shown that including the impeller tip speed fD (impeller frequency*impeller diameter) in data treatment significantly improves the volumetric mass transfer coefficient (kLa) prediction abilities in scaling-up applications. Additionally, simplified correlation is developed, which evades the need of impeller power knowledge. Its good usability for kLa prediction is shown except for the case when common correlation is made together for axial and radial impellers. The study is based on measurements of volumetric mass transfer coefficient in a pilot scale multiple-impeller vessel with non-coalescent batch and six various impeller types, which expand previous data set from a laboratory scale tank.

Gas hold-up, mixing time and gas–liquid volumetric mass transfer coefficient of various multiple-impeller configurations: Rushton turbine, pitched blade and techmix impeller and their combinations

Gas hold-up, mixing intensity of dispersion characterised by exchange flows between adjacent impellers and a volumetric mass transfer coefficient are presented for 18 impeller configurations in triple-impeller vessel of inner diameter 0.29 m . Rushton Turbines, six Pitched Blade impellers pumping down and hydrofoil impellers Techmix 335 (Techmix co., Czech republic) pumping up or down and their combinations were used. 0.5 M Na 2 SO 4 aqueous solution was used as a liquid phase, which represents non-coalescent batches. Gas hold-ups and volumetric mass transfer coefficients are presented for individual configurations as functions of specific power dissipated and superficial gas velocity. The regression of the mass transfer coefficients shows large standard deviation (30%). The power number included to the regression to express the impeller configuration effect did not improve the standard deviation significantly (23%). The impeller configurations with low power number (less than unity) provide higher dispersion mixing intensities, while the impeller configurations with high power number provide better mass transfer performance.

Hydrodynamic and mass transfer characteristics of ejector loop reactors

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 2SO 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.

Critical assessment of the dynamic double-response method for measuring kLa: experimental elimination of dispersion effects

A survey of measuring techniques for k L a is presented which eliminate the dispersion effects in both phases in various equipments (agitated vessels, bubble and packed columns). The double-response method (DRM) attempts to overcome the lack of knowledge of the gas-phase mixing in agitated vessels by measuring the off-gas transient. However, the correctness of the method depends on the hardly acceptable assumption that the dispersion consists of a monosized bubbles. The correctness of the DRM is tested here experimentally by comparison of k L a measured by this method with those obtained by the dynamic pressure method and the steady-state sulphite feeding method using pure oxygen, the correctness of which was proven earlier. The measurements were done in water (coalescent batch), a 0.5 M Na 2SO 4 solution (non-coalescent batch), and in a solution of 1%wt carboxymethylcellulose in 0.5 M Na 2SO 4 (viscous non-coalescent batch). In non-coalescent and viscous batches, the DRM yields up to 94% lower k L a compared to the correct methods.

Critical assessment of gassing‐in methods for measuring kla in fermentors

The reliability of dynamic measurement methods of k(l)a in fermentors using a step oxygen concentration change in the feed gas was tested. The tests were performed both for the original variant using the nitrogen right harpoon over left harpoon air exchange and the newly presented variant using the oxygen-enriched air (27 vol % O(2)) --> air exchange. The testing consisted in comparing k(l)a values determined from these methods with values determined from the steady-state Na(2)SO(3) feeding method and the dynamic pressure method, the reliability of which was proven earlier. The measurements were done in water (coalescent batch) and in 0.5M Na(2)SO(4) solution with and without the addition of 1 wt % carboxymethylcellulose (noncoalescent batches). It was found that in noncoalescent liquids the methods tested give extremely low k(l)a values (as low as 15% of the correct value). The methods are defective in principle irrespective of the gases used for exchange.