Gas-liquid Transfer Research Articles

Hydrodynamics and Oxygen Transfer Characteristics in Activated Sludge Aeration Tanks

Spiral liquid circulation rate in the conventional aeration tank was investigated based upon the theoretical development of the hydrodynamics and the experimental observation. The effect of liquid circulation rate on the gas-liquid oxygen transfer and the oxygen exchange between the bubbling zone and the bubble-free zone in the aeration tank were clarified. The spiral liquid circulation rate at the liquid surface in the aeration tank was correlated as functions of the superficial gas feed rate, the diffuser depth and the bubble diameter generated from the air diffusers. The oxygen exchange resistance between the bubbling zone and the bubble-free zone was 3 - 5 % compared to the overall oxygen transfer resistance from the atmosphere to the bubble-free zone, while that in the deep aeration tank was significant. It was also clarified that the higher spiral liquid circulation rate increases the bubble ascending velocity and thus hinders the gas-liquid oxygen transfer.

Influence of the surface deformability on marangoni instability in a liquid layer with surface chemical reaction: I. Stationary convection

A stationary instability due to chemical absorption for an infinite liquid layer placed at a horizontal rigid wall and opened to the ambient gas is studied. A pseudo-first order chemical reaction on the deformable free surface is assumed. A bulk diffusion controlled and adsorption—desorption controlled gas—liquid transfer mechanism is supposed. A linear stability theory is developed. The surface deformability reduces the stability and this result fits better to the experimental data. Depending on the type of the surface chemical reaction the system stability is influenced in two different ways. While the accumulation of the solute by an autocatalytic reaction destabilizes the layer, the surfactant decrease due to a chemical change stabilizes the system. The solute convection along the surface is a profound stabilizing factor. The effects of the liquid phase mass transfer resistance and the surface diffusion on the stability are also considered.

Coupling of microbial kinetics and oxygen transfer for analysis and optimization of gluconic acid production with Aspergillus niger

Gluconic acid fermentation has been widely used for the analysis of various aspects of kinetics and gas liquid transfer of oxygen. Most of these studies are, however, restricted to processes with bacteria. Mathematical models for industrially important productions with fungi have not been elaborated. In the experimental part of this work computer coupled fermentations of gluconic acid production with Aspergillus niger NRRL 3 have been performed. Knowledge of the stoichiometric relationship in the key reaction (glucose oxidase) provides an excellent opportunity for on-line estimation of glucose, biomass and product gluconate from oxygen uptake and carbon dioxide evolution rates. Starting then from experimental observations on the pH-depending oxygen kinetics of gluconic acid formation and influences of product concentrations on the growth of Aspergillus niger a mathematical framework is developed in which the kinetics of growth and production are coupled with gas liquid oxygen transfer. The model can be successfully applied to simulations of the experimental results of gluconic acid fermentations with cyclic addition of glucose. An important aspect in the coupling of transport and microbial reaction in this model is the incorporation of the influence of sugar and gluconate on the solubility of oxygen and k La via changes of viscosities and molecular diffusivities. With the development of such a comprehensive model, it appears feasible to investigate the influence of various process conditions (sugar feeding, pressure, optimal pH profiles) and to study their possible impacts on the productivity of the overall process.

Air Stripping of Chloroform from Water

The Environmental Protection Agency recently promulgated interim regulations requiring the reduction of trihalomethane compounds to 100 μg/I as chloroform or below in many public drinking water supplies. Such substances generally exhibit a significant vapor pressure in the warmer areas of the United States, suggesting the use of liquid-gas transfer processes for their removal.

Oxygen permeability in ultrathin and microporous membranes during gas-liquid transfer.

The apparatus described here offers a useful system for measuring membrane oxygen permeabilities with the membrane in contact with liquid on one side. Results using this system indicate that liquid migration into the pores of microporous membranes can play a significant role in reducing their permeability to oxygen.

MODEL COMPARISONS FOR DYNAMIC k L a MEASUREMENTS WITH INCOMPLETELY MIXED PHASES

Oxygen transfer coefficients for gas-liquid systems can be determined by dynamic response experiments. Calculation of the unknown k L a parameter involves analysing the step response data with a model which suitably describes the gas and liquid phase mixing phenomena as well as the electrode dynamics. Various combinations of plug-flow, disperion-flow and well-mixed models are proposed to describe particular gas-liquid systems. Through Laplace transformation, the first moments are calculated in terms of the model parameters. From experimental step response data, the first moment is obtained as the area above the response curve. Using the tabulated relations, dynamic k L a response data can be analysed for many particular gas-liquid oxygen transfer situations. Comparisons between the moment relationships serve for the calculation of the errors in k L a which would be incurred when using an incorrect two-phase model. In general, approximate models may lead to large errors.

Experimental study of Gas—liquid transfer rates using an inclined perforated tray without downcomer

Gas—liquid interfacial area, liquid phase and gas phase mass transfer coefficients are measured for an inclined perforated plate without downcomer. The influence of geometric and hydrodynamic parameters is investigated experimentally. The existence of optimal geometries and hydrodynamic conditions which yield maximal mass transfer rates is shown. A techno—economic study is carried out which compares usual equipment with the present technique. Possible applications are suggested.