Sieve Tray Towers

Mameter of the Tower. The cross section of the tower must be made large enough to accommodate the downcomer and the perforated zone. Diameters of 12 ft or more are common. 

Tray spacing is from 6-24 in., the larger dimension to facilitate servicing the trays in place when necessary. Both the downcomer cross section and the depth of coalesced layer are factors related to the spacing, and so is the efficierrcy. The depth of coalesced layer at each tray must be sufficierrt to force the liquid through the holes. In 

A correction also can be applied for the ratio of perforated and total tray areas. For the case of Example 14.10, the depth of coalesced layer is 1.6 in. according to this equation. 

Tray Efficiency. A rough correlation for tray efficiency is due to Treybal (1963) as mortified by Krishnamurly and Rao [Ind. Eng. Chem. Process. Des. Dev. 7 166 (1968)] it has the form 

Application of the rules given here for sizing extraction towers without mechanical agitation is made in Example 14.10. The results probably are valid within only about 25%. The need for some pilot plant information of the particular system is essential. 

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FIG. 23"37 Equipment for liquid/liquid reactions, a) Batch stirred sulfonator. (h) Raining bucket (RTL S A, London), (c) Spray tower with Loth phases dispersed. (d) Two-section packed tower with light phase dispersed, (e) Sieve tray tower with light phase dispersed, (f ) Rotating disk contactor (RDC) (Escher B V, Holland). (g) Oldshue-Rushton extractor (Mixing Equipment Co. ). 

Sieve tray towers have holes of only 3-8 mm dia. Velocities through the holes are kept below 0.8 ft/sec to avoid formation of small drops. Redispersion of either phase at each tray can be designed for. Tray spacings are 6-24 in. Tray efficiencies are in the range of 20-30%. 

Pulsed packed and sieve tray towers may operate at frequencies of 90 cycles/min and amplitudes of 6-25 mm. In large diameter towers, NETS of about 1 m has been observed. Surface tensions as high as 30-40 dyn/cm have no adverse effect. 

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. 

Figure 13.31. Assembled sieve tray towers, (a) Flowsketch sieve tray tower in small diameters (Pfaudler Co.).

Figure 14.13. Towers with reciprocating trays or with pulsing action, (a) Assembly of a 36 in. Karr reciprocating tray column (Chem. Pro. Co.), (b) Sieve trays used in reciprocating trays columns (left) large opening trays for the Karr column (middle) countermotion trays with cutouts (right) countermotion trays with downpipes for heavy phase, (c) Rotary valve pulsator, consisting of a variable speed pump and a rotary valve that alternately links the column with pairs of suction and discharge vessels, (d) Sieve tray tower with a pneumatic pulser [Proc. Int. Solv. Extr. Conf. 2, 1571 (1974)]. (e) A pulser with a cam-operated bellows.

Sieve tray tower Take 1.5 ft tray spacing, 0.25 in. holes on 0.75 in. triangular spacing. The downcomer area is found with Eq. (14.36) ... 

Sizing of Spray, Packed, or Sieve Tray Towers 486... 

Cross-sectional view of sieve-tray tower showing flow and nomenclature for pressure-drop calculations. (Units of all symbols are feet of liquid.)... 

Because liquid gradient is very small in most sieve tray towers, the last term in Eq. (16) is often dropped. 

A sieve-tray tower has an ID of 5 ft, and the combined cross-sectional area of the holes on one tray is 10 percent of the total cross-sectional area of the tower. The height of the weir is 1.5 in. The head of liquid over the top of the weir is 1 in. Liquid gradient is negligible. The diameter of the perforations is in., and the superficial vapor velocity (based on the cross-sectional area of the empty tower) is 3.4 ft/s. The pressure drop due to passage of gas through the holes may be assumed to be equivalent to 1.4 kinetic heads (based on gas velocity through holes). (Tray thickness = hole diameter and active area = 90 percent of total area-see Fig. 16-12). If the liquid density is 50 lb/ft3 and the gas density is 0.10 lb/ft3, estimate the pressure drop per tray as pounds force per square inch. 

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... 

Customarily the phase with the highest volumetric rate is dispersed since a larger interfacial area results in this way with a given droplet size. In equipment that is subject to backmixing, such as spray and packed towers but not sieve tray towers, the disperse phase is made the one with the smaller volumetric rate. When a substantial... 

Sieve tray tower Design is based on a coalesced layer of 1 inch h = 2.54 cm) with 50% of pressure drop through perforations and 50% through downcomer. An 18-inch tray spacing is used. 

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