Efficiencies of Trays and Packings

The numbers of theoretical or equihbrium stages needed for a given vapor-hquid separation process can be evaluated quite pre- 

System Dia. m Packing Type Size, m Bed Depth m HETP, m HTU, m System press., kPa 

Polar hydrocarbons Methyl furan/methyl tetra-hydrofuran 0.61 Intalox 0.038 14.63 0.53 101 

Monochloro acetic acld/acetic anhydride 0.25 Intalox 0.025 2.74 — 0.86 8.0 

DMPC/DMPC cresols/DBOC batch 0.46 Pall rings 0.038 9.14 0.49 — 2.67 

The amount of liquid holdup in the packing is of interest when the liquid is unstable or when a desirable reaction is to be carried out in the vessel. A conelation for Raschig rings, Bed saddles, and intalox saddles is due to Leva (Tower Packings and Packed Tower Design, U.S. Stoneware Co., Akron, OH, (1953)  

In spite of all the effort that has been expended on this topic, the prediction of mass transfer efficiency still is not on a satisfactory basis. The relatively elaborate method of the AIChE Bubble-Tray Manual (AIChE, New York, 1958) is based on the two-film theory but has not had a distinguished career. A number of simpler correlations have been proposed and have some value as general guidance. That literature has been surveyed recently by Vital, Grossel, and Olsen [Hyd. Proc., S5-56 (Oct. 1984) 147-153 (Nov. 1984) 75-78 (Dec. 1984)]. 

Efficiency of mass transfer is expressed as the ratio of the actual change in mol fraction to the change that could occur if equihbrium were attained 

Because of concentration gradients along the tray, primarily in the hquid phase, the overall efficiency is different from a point efficiency. Since the hydrauhcs of the tray usually cannot be known accurately, point and overall efficiencies are difficult to relate. In Table 13.15, for instance, three kinds of efficiencies are shown  

Eqq is an overall efficiency based on average changes in the vapor phase mol fraction. 

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EFFICIENCES OF TRAYS AND PACKINGS 479 TABLE 13.18. Values of Parameters for Equations 13.259-13.261... 

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