Column Pall rings

FIG. 14-72 HETP values for four sizes of metal pall rings, vacuum operation. Cyclobexane/n-beptane system, total reflux,. 35 kPa (5.0 psia). Column diameter = 1.2 m (4.0 ft). Bed height = 3.7 m (12 ft). Distributor = tubed drip pan, 100 streams/nv. [Adapted from Shafiat and Kunesh, Ind. Eng. Cbem. Res., 34,1273 (1.9.9.5),] Reproduced with permission. Copyright 1995 American Chemical Society. 

Figure 9-26. SLE Data Chart for 1-in. metal Pall rings, aqueous systems, pressure drop only. Data from 15-84 in. dia. test columns with packed heights of 2-10 ft. Reproduced with permission of the American Institute of Chemical Engineers, Kister, H. Z. and Gill, D. R., Chemical Engineering Progress, V. 87, No. 2 (1991) p. 32 all rights reserved.

HETP Use HETP = 18 in. based on on-site column data and manufacturer s confirmation that for in. Pall rings in this system, the 18 in. HETP should perform satisfactorily. Note For each design verify expected HETP through the manufacturer. 

Lower pressure drop and greater usable capacity allow use of smaller diameter columns. Pressure drop per stage is 30-50% less than either size Pall ring. 

Extraction column packed column, diameter 0.5 m, height 4 m, packed height 3 m, packing 25 mm stainless steel pall rings, design pressure 2 bar, material carbon steel. 

Raschig rings are cheaper per unit volume than Pall rings or saddles but are less efficient, and the total cost of the column will usually be higher if Raschig rings are specified. For new columns, the choice will normally be between Pall rings and Berl or Intalox saddles. 

For packed column separations using Pall rings, the height of a transfer unit (HTU) may be estimated as follows ... 

Mozenski and Kucharski [2] examined the pressure-drop, overload limit, and flooding limit of a column (0.5 m diameter) packed with Pall rings (35 mm diameter) and Bialecki rings (35 mm and 50 mm diameter) sprayed with propylene carbonate up to 15 bar. Some specific correlations have been proposed and compared with literature data for atmospheric pressure, particularly with the use of the Sherwood diagram for loading-and flooding capacities. 

Figure 13.45. Number of stages per meter (reciprocal of HETP), pressure loss per meter and pressure loss per theoretical stage in a 500 mm dia column filled with metal pall rings. Other charts in the original show the effects of packing height and column diameter, as well as similar data for Raschig rings (Billet, 1979). (a) Methanol/ethanol at 760Torr and total reflux in a column 500 mm dia. (b) Ethylbenzene/styrene at 100 Torr and total reflux in a column 500 mm dia.

Yin et al. [15] investigated liquid distribution in a column of 60 cm in diameter containing pall rings. The authors found that the distributor type had a significant effect on the distribution, which was verified using computational fluid dynamics (CFD). 

Figure 9.3 Liquid spread profile in a packed column (20-in-lD column, packed with 6 ft of 2-in Pall rings, water study. Data from P. J, Hoek, Ph.D. thesis. University of Delft, The Netherlands, 1983.)...

Figure 9.7 shows HETPs measured in teBts that simulate various types of maldistribution in a 4-ft column containing a 12-ft bed of 1-in Pall rings (181,160). The y-axis is the ratio of measured HETP in the maldistribution tests to the HETP obtained with an excellent distributor. 

For random packings there are many reports (3,56,98,136,140a, 162-167) of an increase in HETP with column diameter, fewer in which column diameter hed little effect on HETP (3,56,162,163), and an odd case in which increasing column diameter led to a decrease in HETP (56). Billet and Mackowiak s (3,62,166) scaleup chart for Pall rings implies that efficiency decreases as column diameter increases. 

Example 9 HETP of a Packed Absorber McDaniel, Bassyoni, and Holland [Chem. Engng. Sci., 25, 633 (1970)] presented the results of field tests on a packed absorber in a gas plant. The packed section was 23 ft in height, and the column was 3 ft in diameter and filled with 2-in metallic Pall rings. The measured feeds are summarized in the table below. 

Estimate the mass-transfer coefficients at the top of the packed gas absorber in Example 9. The column has 23 ft of 2-in metallic Pall rings and is 3 ft in diameter. The specific surface area of this packing is 112 mVm. The flows and physical properties are estimated to be as summarized below. 

Example 13 Packed Column Pressure Drop Air and water are flowing countercurrently through a bed of 2-inch metal Pall rings. The air mass velocity is 2.03 kg/s m (1500 Ibs/hrTF), and the liquid mass velocity is 12.20 kg/s m (9000 Ibs/hrTf). Calculate the pressure drop by the generalized pres-... 

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