The Effect of Column Diameter and Packing Height on the Pressure Drop and on the HETP of Structured Packings

Abstract

The standardization of the measuring method for the determination of packing separation efficiency should start with a full understanding of all the conditions that affect its measurements in order to maintain them at the identical level during the measurement of different packings with the aim of comparing or evaluating the effects of the geometric modification of newly developed/designed packings. The effect of the column diameter, the bottom concentration of the distillation mixture, and the packing height on the HETP and the pressure drop are evaluated on the basis of the data measured in columns with diameters of 0.15, 0.43, and 1.22 m packed with RSP 250, Mellapak 250Y, or Montz BSH 250 structured packing, and utilizing the cyclohexane/n-heptane distillation system. It was found that below the loading point, the pressure drop was only slightly affected by the column diameter. The difference between the pressure drops of the 0.15 and 1.22 m diameter columns was within the experimental data scatter. The effect of the concentration range of distillation mixture on the separation efficiency is more pronounced than is the effect of the column diameter. HETP increases with increasing bottom concentration and packing height, and the increase found in this paper reached 50%. The effect of the column diameter onto the packing separation efficiency is not significant. The HETP, measured in columns with widely different diameters using a distillation mixture of approximately the same concentration range, did not demonstrate any significant effect of the diameter. The presented data do not support the recommendation of Ottenbacher et al. (Chem. Eng. Res. Des., 2011, 8, 1427) to consider as relevant only the packing efficiencies measured on columns with a diameter of at least 0.4 m because the data from the smaller diameter columns are dominated by the wall effects.