Gas sparging devices

Previous to our work, no Kj a data in HRS-agitated systems were available, and scepticism about the use of helical impellers in gas-liquid systems was only supported by the argument of their limited capacity of gas dispersion. We have shown, quantitatively, that provided this drawback is compensated with a suitable device, the aeration performance of the HRS is comparable to that observed in remote impellers. Currently, we are continuing oxygen transfer studies in non-Newtonian fluids in vessels equipped with helical ribbon impellers used together with more efficient gas sparging devices. 

It is recognized that filtration is operational, that colloidal-bound PCB congeners are not retained by the filter, and that operational dissolved measurements may be biased positively by colloidal material. Techniques to measure truly dissolved PCBs include gas sparging, differential diffusion into membrane-bound lipids (e.g., semipermeable membrane devices, [230]), and selective adsorption (e.g. non-equilibrium solid phase microextraction [231, 232]). Unfortunately, none of these techniques has sufficient sensitivity to reliably and unambiguously measure truly dissolved PCB congeners at the levels present in the Great Lakes. 

Basically, no special devices have been developed to handle mobile phases in nano-HPLC. However, our experience dictates that reservoirs small in volume and of high quality glass are preferred for this purpose. Solvent containers should be air tight and free from any contamination. The use of helium gas, through a sparging device, may be beneficial for degasification of solvents in nano-HPLC, which can improve check valve reliabilities, especially at nano flow, and diminish baseline noise in UV detection. Besides, each reservoir should be equipped with a shutoff valve for efficient helium consumption [9]. 

Purge and trap injectors are equipped with a sparging device by which volatile compounds in solution are carried into a low-temperature trap. When sparging is complete, trapped compounds are thermally desorbed into the carrier gas by rapid heating of the temperature-programmable trap. 

In airlift bioreactors the fluid volume of the vessel is divided into two interconnected zones by means of a baffle or draft-tube (Fig. 5). Only one of these zones is sparged with air or other gas. The sparged zone is known as the riser the zone that receives no gas is the downcomer (Fig. 5a-c). The bulk density of the gas-liquid dispersion in the gas-sparged riser tends to be less than the bulk density in the downcomer consequently, the dispersion flows up in the riser zone and downflow occurs in the downcomer. Sometimes the riser and the downcomer are two separate vertical pipes that are interconnected at the top and the bottom to form an external circulation loop (Fig. 5c). External-loop airlift reactors are less common in commercial processes compared to the internal-loop designs (Fig. 5a, b). The internal-loop configuration may be either a concentric draft-tube device or an split-cylinder (Fig. 5a, b). Airlift reactors have been successfully employed in nearly every kind of bioprocess—bacterial and yeast culture, fermentations of mycelial fungi, animal and plant cell culture, immobilized enzyme and cell biocatalysis, culture of microalgae, and wastewater treatment. 

In this group are included those devices, such as sparged and agitated ves -sets and various types of tray towers, in which the gas phase is dispersed into bubbles or foams. Tray towers are the most important of the group, since they produce countercurrent, multistage contact, but the simple vessel contactors have many applications (Treybal, 1980). 

The previous sections dealt with gas-liquid contacting without mechanical agitation in such devices as bubble-columns and airlift towers. To obtain better gas-liquid contacting, mechanical agitation is often required. The discussion is confined to baffled sparged stirred-tanks with impellers. Aeration by surfaction impellers are sometimes used in one wastewater treatment facilities (Zlokarnik. 1978). 

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