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LIVE GRAPH Click here to view updates in Kister, Lason, and Gill, Paper presented at the AIChE Spring National Meeting, Houston, Tex., March 19–23, 1995; and in Kister, Scherffius, Afshar, and Abkar, in Distillation 2007: Topical Conference Proceedings, 2007 AIChE Spring National Meeting, Houston, Texas. The latter reference also discusses correct and incorrect applications of those interpolation charts. There are many alternative methods for flood and pressure drop prediction. The Billet and Schultes [IChemE Symp. Ser. 104, pp. A171 and B255 (1987)] and the Maćkowiak (“Fluiddynamik von Kolonnen mit Modernen Füllkorpern und Packungen für Gas/Flussigkeitssysteme,” Otto Salle Verlag, Frankfurt am Main und Verlag Sauerländer Aarau, Frankfurt am Main, 1991) correlations are versions of the GPDC that take the liquid holdup into account. The Eiden and Bechtel correlation [IChemE Symp. Ser. 142, p. 757 (1997)] is a version of the GPDC in which accuracy is improved by using constants representative of packing shape instead of packing factors. The Lockett and Billingham correlation (IChemE Symp. Ser. 152, p. 400, London, 2006) uses a Wallis correlation EQUIPMENT FOR DISTILLATION AND GAS ABSORPTION: PACKED COLUMNS 14-59 FIG. 14-56 The Kister and Gill GPDC (SP) chart for structured packings only. Abscissa and ordinate same as in Fig. 14-55. (From Kister, H. Z., and D. R. Gill, IChemE Symp. Ser. 128, p. A109, 1992. Reprinted courtesy of IChemE.) C G 0.5 + mCL 0.5 = CLG (14-143) where C L = uL[ρL/(ρL −ρG)] 0.5 (14-144) and was shown to work well for high-surface-area (>400 m 2 /m 3 ) structured packings. Here CG is the gas C-factor, Eq. (14-77), based on the tower superficial cross-sectional area, and m and CLG are constants, available from the cited reference for some packing. A drawback of most of these correlations (except that of Eiden and Bechtel) is the unavailability of constants for many, often most, of the modern popular packings. The above methods apply to nonfoaming systems. Foaming systems can be handled either by applying additional derating (system) factors to the flood correlation (see Table 14-9) or by limiting the calculated pressure drop to 0.25 in of water per foot of packing (Hausch, “Distillation Tools for the Practicing Engineer,” Topical Conference Proceedings, p. 119, AIChE Spring Meeting, New Orleans, March 10–14, 2002). Pressure Drop The GPDC discussed above (Figs. 14-55 and 14-56) and the Kister and Gill interpolation charts provide popular methods for calculating packing pressure drops. An alternative popular method that is particularly suitable for lower liquid loads was presented by Robbins (below). For gas flow through dry packings, pressure drop may be estimated by use of an orifice equation. For irrigated packings, pressure drop increases because of the presence of liquid, which effectively decreases the available cross section for gas flow (Fig. 14-53). In principle, there should be a method for correcting the dry pressure drop for the presence of liquid. This approach was used by Leva [Chem. Eng. Progr. Symp. Ser. No. 10, 50, 51 (1954)]. A more recent method by Robbins [Chem. Eng. Progr., p. 87 (May 1991)] utilizes the same approach and is described here. The total pressure drop is ∆P t =∆P d +∆P L (14-145) where ∆P t = total pressure drop, inches H 2O per foot of packing ∆P d = dry pressure drop = C 3G f 2 10 (C4Lf) (14-146) ∆P L = pressure drop due to liquid presence = 0.4[L f/20,000] 0.1 [C 3G f 2 10 (C4Lf) ] 4 (14-147) G f = gas loading factor = 986F s(F pd/20) 0.5 (14-148) L f = liquid loading factor = L(62.4/ρ L)(F pd/20) 0.5 µ L 0.1 (14-149) The term F pd is a dry packing factor, specific for a given packing type and size. Values of F pd are given in Tables 14-13 and 14-14. For operating pressures above atmospheric, and for certain packing sizes, L f and G f are calculated differently: Gf = 986F s(F pd/20) 0.5 10 0.3ρ G (14-150) L f = L(62.4/ρ L)(F pd/20) 0.5 µ L 0.2 F pd > 200 (14-151a) L f = L(62.4/ρ L)(20/F pd) 0.5 µ L 0.1 F pd < 15 (14-151b) The Robbins equations require careful attention to dimensions. However, use of the equations has been simplified through the introduction of Fig. 14-58. The terms L f and G f are evaluated, and the ∆P L is obtained directly from the chart. Basic nomenclature for the Robbins method follows: C3 = 7.4(10) −8 C 4 = 2.7(10) −5 F pd = dry packing factor, ft −1 F s = superficial F-factor for gas, U tρ g 0.5 , ft/s(lb/ft 3 ) 0.5 G = gas mass velocity, lb/hr⋅ft 2 G f = gas loading factor, lb/hr⋅ft 2 L = liquid mass velocity, lb/hr⋅ft 2 L f = liquid loading factor, lb/hr⋅ft 2 ∆P = pressure drop, inches H2O/ft packing (× 83.3 = mm H2O/m packing)
14-60 TABLE 14-13 Characteristics of Random Packings Packing factor, m−1 Size, <strong>Bed</strong> mm, or density,* Area, % Normal Dry Name no. (#) kg/m3 m2 /m3 voids † Fp ‡ Fpd Vendor Metals Pall rings 16 510 360 92 256 262 Various (also Flexi-rings, 25 325 205 94 183 174 Ballast rings, P-rings) 38 208 130 95 131 91 50 198 105 96 89 79 90 135 66 97 59 46 Metal Intalox (IMTP) 25 224 207 97 134 141 Koch-Glitsch [also I-rings, AHPP, 40 153 151 97 79 85 [Sulzer, Amistco, RSMR, MSR] § 50 166 98 98 59 56 Rauschert, Montz] § 70 141 60 98 39 –– Nutter rings #0.7 177 226 98 — 128 Sulzer #1 179 168 98 98 89 #1.5 181 124 98 79 66 #2 144 96 98 59 56 #2.5 121 83 98 52 49 #3.0 133 66 98 43 36 Raschig Super-ring #0.5 275 250 98 –– –– Raschig #0.7 185 175 98 –– –– #1 220 160 98 82 –– #1.5 170 115 98 59 –– #2 155 98 99 49 –– #3 150 80 98 36 –– Cascade mini-rings #1 389 250 96 131 102 Koch-Glitsch (CMR) #1.5 285 190 96 95 — #2 234 151 97 72 79 #2.5 195 121 97 62 –– #3 160 103 98 46 43 #4 125 71 98 33 32 #5 108 50 98 26 ¶ –– Fleximax #300 –– 141 98 85 –– Koch-Glitsch #400 –– 85 98 56 — Jaeger Tripacks #1 223 118 96 85 –– Raschig (Top-Pak) #2 170 75 98 46 — VSP 25 352 206 98 105 ¶ –– Raschig 50 296 112 96 69 –– Ralu-rings 25 310 215 98 157 ¶ –– Raschig 38 260 135 97 92 ¶ –– 50 200 105 98 66 ¶ –– Hiflow 25 298 203 96 –– –– Rauschert 50 175 92 98 52 — Hy-Pak, K-Pak, #1 262 174 97 148 –– Koch-Glitsch, AIPR #1.5 180 118 98 95 –– Amistco #2 161 92 98 85 –– #3 181 69 98 52 — Raschig rings 19 1500 245 80 722 –– Various ( 1 ⁄16 in wall) 25 1140 185 86 472 492 50 590 95 92 187 223 75 400 66 Ceramics 95 105 –– Berl saddles 6 900 900 60 — 2950 Various 13 865 465 62 790 900 25 720 250 68 360 308 38 640 150 71 215 154 50 625 105 72 150 102 Intalox, Flexi-saddles, 6 864 984 65 — 2720 Various Torus-saddles, Novalox 13 736 623 71 660 613 25 672 256 73 302 308 50 608 118 76 131 121 75 576 92 79 72 66 Raschig rings 6 960 710 62 –– 5250 Various 13 880 370 64 1900 1705 25 670 190 74 587 492 50 660 92 74 213 230 75 590 62 75 121 –– Pall ring 25 620 220 75 350 — Raschig 38 540 164 78 180 — 50 550 121 78 142 –– 80 520 82 78 85 ¶ —
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