Effect of Packed Height on Liquid Phase H.T.U. for Packed Columns

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Abstract
Since the publication of Sherwood and Holloway's paper, 5) it has been believed that the height of a packed column has no effect on the values of HL or kLa and the variation of these values with the packed height, observed in the experimental column, results from the end effects caused by the gas-liquid contact above and below the packing. On the other hand, van Krevelen and others7) state that kL is proportional to the -1/3 power of the packed height and a recent study by Fujita and others1) shows that kLa varies with the packed height to the -0.19 power. This work has been undertaken for the purpose of making sure whether packed height has any effects on the values of HL. Experiments on the absorption of pure carbon dioxide by water were performed in two columns, 6.6 and 12.5cm in inside diameters, respectively, packed with 15mm Raschig rings, with the packed height varying from 0.05 to 1.50m. Observed values of N.T.U. are shown in Figs. 2 and 3, plotted on logarith mic scales against the liquid mass flow rate, with the packed height as a parameter. To obtain the true values of N.T.U. from these data, it is necessary to make correction so as to eliminate the end effects, for which a new method is proposed and employed. In Figs. 5 and 8, the N.T.U. values corrected by the above method are plotted on logarithmic coordinates against water rate. Fig. 5 obtained with the 6.6cm column shows the presence of three regions, A, B and C, so classified according to the values of liquid rate and packed height. The N.T.U. values in regions A, B and C are proportional to the 1.0, 0.92 and 0.56 power of the packed height, respectively, as shown in Fig. 6. The values of HL in region A, therefore, are independent of the packed height, but the HL values in regions B and C vary at the rate of the 0.08 and 0.44 power of the height, respectively, as seen in Fig. 7 and Eqs. 3 to 5. The N.T.U. values with the 12.5cm column, shown in Fig. 8 are proportional to the 1.0 power of the packed height.The HL values, therefore, are independent of the height of the packing, as shown in Fig. 9, and can be represented by the same equation obtained for region A with the 6.6cm column. The variation of HL values in regions B and C with that of the packed height may be due to the non-uniformity of liquid distribution in the column.

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