Sparged Systems

The next choice concerns the intensity of mass transfer and turbulence required. For a first selection, three levels can be defined [see Middleton (1997, Sec. 15.1) for more detail, and also Section 11-6.3 for reacting systems]  

Moderate intensity kLa of order 0.05 s for fast reactions with other slower steps where particle suspension and/or heat transfer require enhancement. Agitated vessels are useful here, and indeed are often selected where the intensity needs are uncertain, or may vary widely (as in general-purpose reactors). The larger top surface area per unit volume than can be achieved with bubble columns allows higher exit gas flow rates without liquid entrainment and carryover. 

High intensity kLa of order 0.5 s for very fast reactions and short residence times Static mixers in turbulent flow offer plug flow in both phases. Thin-fllm contactors such as wiped-film columns or spinning disks offer large surface per unit volume, giving very rapid mass transfer and evaporative flux. 

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Sulfurchlorination of unsaturated compounds or mercaptans is normally carried out at atmospheric pressure in a glass-lined reaction vessel because of the potential to Hberate HCl during the reaction. The sulfurchlorination vessel is equipped with a cooling jacket or coils (very exothermic reaction), a nitrogen or dry air sparging system, an overhead condenser, and a caustic or bleach scmbber. If one of the reactants (olefin or mercaptan) is alow boiling material, ie, isobutylene, a glass-lined pressure vessel is recommended. 

Air sparging systems, involving the injection of air directly into the groundwater... 

In an air sparging system, the primary mechanism for contaminant removal is by the transfer of contaminants from the dissolved to the vapor phase. The extent to which this transfer can take place during air sparging depends on the Henry s law constant, which is an indication of the extent to which each will partition between the dissolved state and the vapor state under equilibrium conditions. A contaminant with a greater Henry s law constant is more readily stripped from groundwater by air sparging than one with a lower Henry s law constant. 

Design of an air sparging system requires a balanced airflow to maintain effectiveness and control of the migration of fluids and vapors. Because of the potential for loss of control, an air sparge system should not be designed or installed without a field pilot test. Design data from pilot tests include ... 

Site and Pilot Test Data Required for Air Sparging System Design... 

Designing an effective air sparging system is as much art as science. In its best form, it has the potential to provide an effective and efficient remedial alternative. If it is poorly designed and operated, air sparging can lead to adverse environmental consequences. 

Spartech is a mobile system designed for the removal of volatile contaminants from aquifers. It is a patented air sparging system that works by bubbling air through an aquifer and is essentially an in situ method of air stripping. The volatilized contaminants may be recovered by using a soil vapor extraction (SVE) system or similar device. 

The ORC system is designed to treat a plume with a peak BTEX concentration of 25 ppm and close the site in 1 year. The values for the air sparging system were derived independently by the site consultant and site closure is expected in 3 years (D138231). 

Mechanically agitated tanks and three-phase sparged reactors Design of the agitator and the sparging system for MSSR... 

The power required by an impeller in a gas sparged system Pm is usually less than the power required by the impeller operating at the same speed in a gas-free liquids Pmo. The Pm for the flat-blade disk turbine can be calculated from Pmo (Nagata, 1975), as follows ... 

Calculate Pm, the power required in the gas-sparged system. Pm is calculated from the following equation ... 

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