Packing HETP

Practical packing HETP, HETPpacking. Practical = (m) (HETP) (Test packing)... 

Pressures above 1 to 2 psia have small effects on HETP for random and structured packing. For high vacuum the data are not totally firm as to the consistency of effects, generally HETP increases (efficienq becomes lower). At high pressure above 200-300 psia structured packing HETP increases (lower efficiency) [90]. 

The efficiency of a plate can be predicted with more certainty than the equivalent term for packing (HETP or HTU). 

M.J. Lockett, Easily predict structured packing HETP, Chem. Engng. Progress, January, (1998) 60-66. 

Rules of Thumb Since in most circumstances packing HETP is sensitive to only few variables, and due to the unreliability of even the best mass-transfer model, it has been the authors experience that rules of thumb for HETP are more accurate and more reliable than mass-transfer models. A similar conclusion was reached by Porter and Jenkins (IChemE Symp. Ser. 56, Summary paper, London, 1979). 

Physical Properties Data presented by a number of workers [e.g., Vital, Grossel, and Olsen, Hydroc. Proc. 63(12), 75 (1984)] suggest that, generally random packing HETP is relatively insensitive to system properties for nonaqueous systems. A survey of data in Chapter... 

Errors in VLE These affect packing HETP in the same way as they affect tray efficiency. The discussions and derivation earlier in this subsection apply equally to tray and packed towers. 

Figure 14-67a shows virtually no loss of efficiency when a distributor uniformly tilts, such that the ratio of highest to lowest flow is 1.25 (i.e., a "1.25 tilt ). In contrast, an 11 percent chordal blank of a level distributor causes packing HETP to rise by 50 percent. 

Liquid and vapor loads have little effect on random packings HETP. 

TABLE 9.2 Published Ruing erf Thumb lor Random-Packing HETP... 

Maldistribution in packed columns may cause a severe reduction in column efficiency. For 1-in packings, HETP may increase fay a factor as high as 2 or 3 due to maldistribution (116,131,132). 

Figure 0.7 Comparing the effects of "small-scale and large-scale" maldistribution on packing HETP. (a) Comparing the effect of a simulated continuous tUt (max/ min flow ratio = 125 ) to the simulated effect of blanking a chordal area equal ts 11 percent of the tower area, (b) Comparing the effects of simulated continuous tilts (max/min flow ratios 125 and 1.5) to the effects of a situation where one-half of the distributor passes 25 percent more liquid to the other hen. (c) Comparing the effects of random maldistribution to these of zonal maldistribution. (Ae-...

Loadings. For many random and corrugated-sheet structured packings, HETP is independent of vapor and liquid loadings (Fig. 6.16a). For wire-mesh and many corrugated-sheet structured packings, HETP increases with vapor and liqnid loeds (Fig. 8.16c). For some packings, HETP decreases as vapor and liquid loads increase (Fig. 8.16d). 

Pressure, peia Reflux Diam- Height, ft Packing HETP, in... 

Predict packing HETP using Eq. (9.34) and adjust its prediction using factors derived in steps 3 and 4 above. Examine the reliability of these factors. The larger the number of data points they are based on, the more reliable they are. Some judgment is required here the author advocates a conservative approach. 

Unlike random packings, structured-packing HETP often rises with loads (Fig. 8.16c). HETP is measured at a constant reflux ratio (L/V), usually at total reflux, so that vapor and liquid loads are raised and lowered simultaneously. It is therefore difficult to state whether HETP rises due to the increase in the vapor load or that in the liquid load (Sec. 8.2.1), but there are suggestions (Sec. 8.1.10) that the liquid load plays the prime role. 

Ponchon-Savarit diagram. 26 Ponter underwetting theory, 516, 517 Porter rivulet model. 542 Porter and Jenkins packing HETP, 532-534 regime transition. 332 Poynting factor. 7 Prado and Fair tray efficiancy, 375 PRO/II. 169, 170,180... 

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