O’Connel correlation

FIG. 14-7 O Connell correlation for overall column efficiency for absorption. To convert ffP/ i in pound-moles per cubic foot-centipoise to Idlogram-moles per cubic meter-pascal-second, multiply by 1.60 X 10 . [O Connell, Trans. Am. Inst. Chem. Eng., 42, 741 (1946).]... 

Eduljee (1958) has expressed the O Connell correlation in the form of an equation ... 

Viscosity, Relative Volatility Efficiency increases as liquid viscosity and relative volatility diminish. These effects are reflected in the O Connell correlation (below). 

The O Connell correlation was based on data for bubble-cap trays. For sieve and valve trays, its predictions are likely to be slightly conservative. 

The prime variables affecting the orifice coefficient, Cv, are the fractional hole area and the ratio of tray thickness to hole diameter. More than 20 published correlations are available for evaluating Cv (12). Fair et al. (18) and Van Winkle (5) recommend the correlation by Liebson et al. (48 Fig. 6.21a). The Hughmark and O Connell correlation (66) is preferred by Ludwig (4) and Chase (30),... 

For valve trays, the hydraulic gradient is somewhat larger than that of sieve trays, probably not by much (13). In a similar manner to sieve trays, it is often neglected in the pressure drop calculation (7-9,71,80). In cases of a long flow path of liquid, it should be checked using the Hughmark and O Connell correlation above. 

Several empirical tray efficiency correlations are available in the literature. Of these, the O Connell correlation has been the standard of the industry for several decades. 

The O Connell correlation (149, Fig. 7.5a). This correlation is based on test data from 31 plant columns, including hydrocarbon, chlorinated hydrocarbon, and alcohol separation columns. It evolved from an earlier correlation by Drickamer and Bradford (150), which empirically correlated efficiency test data for 54 refinery columns, The earlier correlation was modified by O Connell to include nonhydrocarbon and high-relative-volatility systems. 

Figure 7.5 The O Connell correlation for overall column efficiency, (a) Plot for distillation (b) plot for absorbers. (Prom H. E, O Connell, Trane. AlChE, 42. p. 741, 1946, Reprinted courtesy of the American Institute of Chemical Engineers.)...

The O Connell correlation was based on data for bubble-cap trays, and it was stated (131) to predict 90 percent of the efficiency data within 10 percent, both for distillation and absorption. For sieve and valve trays, its predictions are likely to be slightly conservative (151). Ludwig (4) warns that O Connell s absorber correlation (Fig. 7.55, sometimes predicts efficiencies that are too high He believes that it can be used for stripping of gases from rich oils and for absorbers provided care is exercised not to accept too high values. 

One type of system scaleup which can be done with confidence is extending efficiency data from one pressure to another. The small increase of efficiency with pressure (Sec. 7.3.4) can be allowed for using the O Connell correlation (Sec. 7.2.2). Caution is required when going to high pressures (> 150 psi), as vapor recycle may reduce efficiency, and this effect is difficult to predict. 

The actual number of stages is equal to the number of equilibrium stages divided by the fractionator efficiency(overall column efficiency). Although the tray efficiency will vary, we will use the fractionator efficiency. The fractionator efficiency is obtained from the O Connel correlation given in Figure 6.17. Vital et al. [46] have reviewed and tabulated fractionator and absorber efficiencies for many systems. These data may help to arrive at a reasonable fractionator efficiency. 

The O Connell correlation relates tray efficiency to liquid viscosity and system relative volatility ... 

The most widely used empirical approach to estimating E0 is the O Connell correlation, although it has been pointed out that it usually underpredicts the overall efficiency in the distillation of water solutions (Wankat, 1988 Kister, 1992) ... 

Table VI. Component Critical Volumes (Vc) from Reference 23 and Root Mean Square Deviations (s) between the Brelvi—O Connell Correlation (12) and Component Isothermal Compressibilities from Reference 11, pp. 124—128...

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