Sieve-tray extraction tower

FIGURE 14 Sieve-tray extraction tower arranged for light liquid dispersed. Reprinted from Treybal5 with permission of The McGraw-Hill Companies. 

The GS enriching process is a counter-current gas-liquid extraction done at a pressure of 2000 kPa in a sieve tray tower with the upper half operating at 30 C and the lower at 130 C. ( 5) In the top half of the tower, feedwater extracts deuterium from the upflowing cold H2S, reaching a maximum at the centre of the tower. The recycled lean H2S entering the lower hot half of the tower strips deuterium from the water, which then leaves the system depleted in deuterium. A cascade of several stages is used to reach the desired feed concentration for the final water distillation or finishing unit. Transfer between cascades can be either by gas or liquid from the centre of the tower. 

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... 

This is the first of the coffee decaffeination patents that describe a continuous, counter-current liquid-liquid extraction. A brief description of the process is provided here. A water extract of roasted coffee beans, called coffee liquor, which contains aromas and caffeine and other water soluble components such as carbohydrate and protein materials is fed to a vacuum suipper. The extract is concentrated to about 30-50% in an evaporator-condenser and is fed to a sieve tray tower. The liquor passes across the hays in the tower downward through downspouts countercurrent to supercritical CO2 which enters the tower at the bottom and passes upward through the holes in the sieve trays. CO2 extracts caffeine from the liquor, and the decaffeinated liquor leaves the near the bottom of tower. The condensate water from the vacuum stripper prior to the tray tower is fed to the sieve trays in the top section of the tower. The water washes the caffeine from the supercritical CO2 passing upward. The caffeine-free CO2 is recycled to the bottom of the column. 

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). 

Stagewise contact with controlled coalescence redispersion cycles Tray column Pulsed sieve column. Pulsed Mixer-Settler-cascade, Extraction tower with controlled cycle Scheibel column, ARD-Extractor, Leisibach column, Mixer-Settler cascade ... 

Figure 12.6-2. Extraction towers (a) perforated-plate or sieve-tray tower, b) agitated extraction tower.

By repeating this process in successive stages, the deuterium oxide is increased to a concentration of 15%. The ten extraction towers of the plant contain sieve trays. Water flows downward across each tray in successirai. H2S gas is forced upward, bubbling through the sieve holes for contact with the water. This is shown in Fig. 7.9. 

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