Multistage tray towers

MULTISTAGE (TRAY) TOWERS—THE METHOD OF PONCHON AND SAVARIT... 

MULTISTAGE TRAY TOWERS—METHOD OF McCABE AND THIELE... 

As the potentialities of liquid extraction as a separation method were developed, the need for efficient, continuously operated, multistage equipment became apparent. It was natural therefore to turn to devices which had been so successful in other similar fluid-contacting operations, such as the bubble-tray tower and the packed tower of distillation. These devices have proved to be disappointing in liquid-extraction service, however for example, bubble-tray towers provide tray efficiencies in liquid-extraction operations of less than 5% (S7), and conventional packed towers show heights of transfer units of 10 to 20 ft. or more (T3). 

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). 

In this chapter we have presented multistage systems with special emphasis on absorption processes. We have studied multitray countercurrent absorption towers with equilibrium trays for both cases when the equilibrium relation is linear and when it is nonlinear. This study was accompanied by MATLAB codes that can solve either of the cases numerically. We have also introduced cases where the trays are not efficient enough to be treated as equilibrium stages. Using the rate of mass transfer RMT in this case, we have shown how the equilibrium case is the limit of the nonequilibrium cases when the rate of mass transfer becomes high. Both the linear and the nonlinear equilibrium relation were used to investigate the nonequi-librium case. We have developed MATLAB programs for the nonequilibrium cases as well. 

Efficiencies In actual operation the trays of a distillation column rarely, if ever, operate at equilibrium despite attempts to approach this condition by proper design and choice of operating conditions. The usual way of dealing with departures from equilibrium in multistage towers is through the use of stage and/or overall efficiencies. 

The fine dispersion is carried out with a secondary gas dispersing facility (impeller). In a multistage tower reactor,the primary gas dispersion is usually carried out with a perforated plate or porous plate, the secondary gas dispersion facilities (stage separating trays) redisperse the large bubbles formed by coalescence from... 

Trays Multistage Performance predictable Intermediate pressure drop More expensive tower Plugging possible Trays must be filled Intermediate pressure drop... 

Stage-type equipment of two major types is used (1) single-stage mixer-settlers and multistage cascades constructed from them and (2) sieve-tray, multistage towers. 

---