Contacting gas-liquid

The target quantity of the gassing process is the absorption rate in the gas/liquid (G/L) system. It is directly proportional to the interfacial area between the gas phase and the liquid phase. The limiting factor is the diffusion of the dissolved gas through the liquid-side of the boundary layer, which can only be affected by its thickness to a limited extent. A substantial intensification of mass transfer is only possible by increasing the G/L interfacial area gas sparging by means of stirrers, nozzles, sintered or perforated plates etc. should therefore effect a dispersion of the gas into fine bubbles. 

Unlike the heat exchange, the G/L interfacial area is not constant, but depends in addition to the process parameters also on specific physical properties, which significantly contribute to the size of the gas bubbles (see Section 4.10). 

The interfacial surface area made available for a gas and liquid to contact largely establishes the thermal efficiency of the contact device. That is, the gas-liquid interface is also the heat transfer surface. Consequently, the greater 

It is important that no bypassing of the two phases occurs in the tower. A uniform liquid distribution across the tower s cross section is essential. This is accomplished by spraying the water over the top of the tower. Spray nozzles also help to create droplet surface and increase contact time. 

This is an important system in chemical processing. The effect of apparent density (liquid plus gas) as the fluid mixture enters the impeller is quite pronounced on the system horsepower. The horsepower falls off with increased gas flow which may lead to the danger of underpowering the unit. The absorption coefficient is a func- 

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The liquid-piston type of compressor has been of particular advantage when hazardous gases are being handled. Because of the gas-liquid contact and because of the much greater liquid specific heat, the gas-temperature rise is veiy small. 

James R. Fair/ Ph D / P.E., Professor of Chemical Engineering, University of Texas Eel-low, Amencan Institute of Chemical Engineers Member, Amencan Chemical Society, American Society for Engineenng Education, National Society of Professional Engineers. (Section Editor, Absorption, Gas-Liquid Contacting)... 

Introduction Packed columns for gas-liquid contacting are used extensively for absorption, stripping, and distillation operations. Usually the columns are filled with a randomly oriented packing material, but for an increasing number of applications the packing is very care-... 

Objectives of Gas Dispersion The dispersion of gas as bubbles in a liquid or in a plastic mass is effected for one of the following purposes (1) gas-liquid contacting (to promote absorption or stripping,... 

Contac ting power is defined as the power per unit of volumetric gas flow rate that is dissipated in gas-liquid contacting and is ultimately converted to heat. In the simplest case, in which all the energy is... 

Plate Towers Plate (tray) towers are countercurrent gas-atomized spray scrubbers using one or more plates for gas-liquid contacting. They are essentially the same as, if not identical to, the devices used for gas absorption and are frequently employed in apphcations in which gases are to be absorbed simultaneously with the removal of dust. Except possibly in cases in which condensation effects are involved, countercurrent operation is not significantly beneficial in dust collection. 

Ah.soi ption. Sec. 4, Thermodynamics and Sec. 18, Liquid Gas Systems. For plate columns, see Sec. 18, Gas-Liquid Contacting Plate Columns. For packed columns, see Sec. 18, Gas-Liquid Contacting Packed Columns. ... 

Several manual and continuous analytical techniques are used to measure SO2 in the atmosphere. The manual techniques involve two-stage sample collection and measurement. Samples are collected by bubbling a known volume of gas through a liquid collection medium. Collection efficiency is dependent on the gas-liquid contact time, bubble size, SO2 concentration, and SO2 solubility in the collection medium. The liquid medium contains chemicals which stabilize SO2 in solution by either complexation or oxidation to a more stable form. Field samples must be handled carefully to prevent losses from exposure to high temperatures. Samples are analyzed at a central laboratory by an appropriate method. 

A venturi scrubber aeeelerates the waste gas stream to atomize the scrubbing liquid and to improve gas-liquid contact. In a venturi scrubber, a "throat" section is built into the duet that forces the gas stream to accelerate as the duct narrows and then expands (refer to Figure 14). As the gas enters the venturi throat, both gas velocity and turbulence increase. 

Contactor design is important in order to maximize the ozone-transfer efficiency and to minimize the net cost for treatment. The three major obstacles to efficient ozone utilization are ozone s relatively low solubility in water, the low concentrations and amounts of ozone produced from ozone generators, and the instability of ozone. Several contacting devices are currently in use including positive-pressure injectors, diffusers, and venturi units. Specific contact systems must be designed for each different application of ozone to wastewater. Further development in this area of gas-liquid contacting needs to be done despite its importance in waste treatment applications. In order to define the appropriate contactor, the following should be specified ... 

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

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