Of tray towers

Packings of random and structured character are suited especially to towers under 3 ft dia and where low pressure drop is desirable. With proper initiai distribution and periodic redistribution, voiumetric efficiencies can be made greater than those of tray towers. Packed internals are used as replacements for achieving greater throughput or separation in existing tower shells. 

Possible restriction of tray towers to nonfouling materials that are free of suspended solids. 

Figure 7.11 Packing is often used in pumparound sections of trayed towers.

Flooding, holdup, and mass transfer rates are highly interdependent and are not simply related. Reissinger and Schroter (1978) state that tray towers in comparison with other types have good efficiencies at 60 nr /m2 hr at frequencies of 60-90/min and amplitudes of 10 mm. Packed towers have about 2/3 the capacities of tray towers. Also in comparison with unagitated towers, which are limited to interfacial tensions below lOdyn/cm, pulsed towers are not limited by interfacial tension up to 30-40 dyn/cm. Some... 

Numerous attempts have been mnds to develop useful correlations for pradicting the efficieocy of tray towers. The most comprehensive study was carried ont under sponsorship of the American Institute of Chemical Engineers (AJChE) and resulted in the publication of the AlChE bubble tray design manoal.21 The AlChE prediction method, which is aimed primarily at bubble-cap trays, involves first estimating the number or gas-phase and liquid-phme transfer units, Nc and Nt, for the specific conditions on the miy, combining there to obtain the number of overall gas transfer units Noc, and predicting the point efficiency by the relationship... 

In this group are included those devices, such as sparged and agitated ves -sets and various types of tray towers, in which the gas phase is dispersed into bubbles or foams. Tray towers are the most important of the group, since they produce countercurrent, multistage contact, but the simple vessel contactors have many applications (Treybal, 1980). 

Passage of liquid from the top to the bottom of trayed towers occurs primarily via downcomers. Downcomers are conduits having circular, segmental, or rectangular cross sections that convey liquid from an upper tray to a lower tray in distillation columns. Different types of downcomers are shown in Fig. 6.14. The major differences are in the cross-sectional areas and in the slopes of the lengthwise extension. 

Although for many decades the basic design of tray-tower internals remained relatively static, recent years have seen a great many innovations, only a few of which can be mentioned here. 

Figure 7-4. Schematic of tray tower absorber. Babcock and Wilcox, 1992A)...

Process flow sheet and stream summary of tray towers. 

---