Flood point, random packing

Sepn. Purif., 3, 19 (1989)] takes holdup into account and applies to random as well as structured packings. It is somewhat cumbersome to use and requires three constants for each packing type and size. Such constants have been evaluated, however, For a number of commonly used packings. A more recent pressure drop and holdup model, suitable for extension to the flood point, has been pubhshed by Rocha et al. [Jnd. Eng. Chem. Research, 35, 1660 (1996)]. This model takes into account variations in surface texturing of the different brands of packing. 

Liquid and vapor loadings have little effect on HETP for random packing up to the point between loading and flooding. 

AP = Air pressure loss, in. of water APflood = Pressure drop at flood point for all random packings, in. of water/ft of packing height APd = Dry bed pressure drop, in. water/ft packed height... 

H.Z. Kister and D.R. Gill, Predict flood point and pressure drop for modem random packings, Chem. Engng. Progress, 87(2) (1991) 32-42. 

Kiarwe. H.Z. and D.R Gill Predict Flood Point and Pressure Drop for Modern Random Packings. Chem. Eng. Progress. 32 (February 1991). 

A packing pressure drop of 1.5 in/ft is approximately 95% of column packing flood. At 2.0 in/ft of pressure drop DP, most random packed towers are at the flood point. It is thus prudent and good practice to keep the limiting D, at 1.5 in/ft or less. 

Belles and Fair (55) compared flood-point predictions from the Eckert correlation to published experimental data for random packings. Their massive data bank consisted mainly of data for first-generation packings, but also included some data for second-generation packings. For the data compared, Bolles and Fair showed that Eckert s correlation gave reasonable flood-point prediction. Statistically, they showed that if a safety factor of 1.3 was applied to the correlation flood-point predictions, the designer will have 95 percent confidence that the column will not flood. 

Kister and Gill compared flood-point predictions from Eq. (8.1) to their massive data banks for second and third-generation random packings (60) and for structured packing (60a). Pressure drops were calculated using the Kister and Gill GPDC interpolation charts (Sec. 8.2.9). They showed that Eq. (8.1) predicted all the flood points in their data bank to within 15 percent and most to within 10 percent. 

Chapter 10 presents a compendium of GPDC data interpolation charts for flood, MOC, and pressure drop prediction, both for random and structured packings. When flood data are absent, pressure drop data can be used for approximating the flood point using Eq. (8.1). 

Regions below the loading point as well as the loading region itself are apparent from liquid holdup and interfacial area data as shown in Figure 12.52. At low rates, there is little influence of vapor rate on holdup and interfacial area. This behavior is typical of random as well as structured packings. In the latter, the effects of the rates on interfacial area seem to be less pronounced than for random packings. The appearance of the flood point in the holdup and area plots will undoubtedly match the flood point in the pressure drop. 

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