Packed towers extraction rates

Mass Transfer Extraction rates for packed towers are usually excellently correlated for a given situation on the coordinate system of Fig. 15-35. Treybal [Chem. Eng. Prog., 62(9), 67 (1966)] nas suggested means whereby overall Hto s may be resolved into constituent... 

The number of variables that are known to influence the rate of extraction is exceedingly large, and includes at least the following Size, shape, and material of packing Tower diameter Packing depth... 

The problems relating to mass transfer may be elucidated out by two clear-cut yet different methods one using the concept of equilibrium stages, and the other built on diffusional rate processes. The selection of a method depends on the type of device in which the operation is performed. Distillation (and sometimes also liquid extraction) are carried out in equipment such as mixer settler trains, diffusion batteries, or plate towers which contain a series of discrete processing units, and problems in these spheres are usually solved by equilibrium-stage calculation. Gas absorption and other operations which are performed in packed towers and similar devices are usually dealt with utilizing the concept of a diffusional process. All mass transfer calculations, however, involve a knowledge of the equilibrium relationships between phases. 

Packed Towers. The introduction of packing into a tower may influence the rate of extraction in several ways. The packing particles hinder the rising droplets consequently the hold-up of dispersed-phase and inter-... 

FIG. 14-61 Liq uid distribution in a 6-in column packed with 1/4-in broken-stone packing. Increments of radius represent equal-annual-area segments of tower cross section. Central-point inlet. Water rate = 500 lb/(b-fr). Air rate = 810 lb/(b-ft ). To convert pounds per bour-square foot to kilograms per second-square meter, multiply by 0.00L356 to convert inches to centimeters, multiply by 2.54. (Data from Baker, Chilton, and Vernon, in Shetxuood and Pigford, Absorption and Extraction, 2d ed., McGraw-Hill, New York, 1952. )... 

Trial Estimates and Converged Flow Rates and Compositions in aU Stages of an Extraction Battery for a Four-Component Mixture 476 Sizing of Spray, Packed, or Sieve Tray Towers 486 Design of a Rotating Disk Contactor 488 Application of Ion Exchange Selectivity Data 503... 

Sieve-tray towers are very effective, both with respect to liquid-handling capacity and extraction efficiency, particularly for systems of low interfacial tension which do not require mechanical agitation for good dispersion. The general assembly of plates and downspouts is much the same as for gas-liquid contact except that a weir is not required. Towers packed with the same random packing used for gas-liquid contact have also been used for liquid extractors however, mass-transfer rates are poor. It is recommended instead that sieve-tray towers be used for systems of low interfacial tension and mechanically agitated extractors for those of high interfacial tension (Treybal, 1980). 

Illustration 2. A solution of acetic acid in water containing 10% acid is to be c.x-tracted with methyl isobutyl ketone to reduce the concentration to 0.1%. A tower packed with J -in. carbon Raschig rings is to be used, with the solvent dispersed. The extract is to contain 6.5% acetic acid, and the rate of flow of aqueous solution is to be 30 cu. ft./hr. sq. ft. tower cross section. Mass-transfer rates and equilibrium data are provided by Sherwood, Evans, and Longcor [Ind, Eng, Chem. 31, 1144 (1939)]. Calculate the height of tower required. 

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