Study of axial dispersion on several modern structured and random packings

Abstract

The study investigates the phenomenon of axial dispersion in a packed absorption column, which is known to reduce the efficiency of separation equipment by reducing the mass transfer driving force. The aim of the study is to determine the Bodenstein number, which represents axial dispersion, for five types of modern packings used in the column. The packings used in the study were random packings (NeXRing0.7 and NeXRing1.2) and structured packings (MellaPak350Y, 452Y, and 500Y). The data obtained from dynamic experiments in the form of a response to a step change in tracer substance concentration were compared to a diffusion-type differential equation, which was solved with boundary conditions for a closed system. By measuring the responses at two different packed bed heights and using convolution, the influence of the end effects was eliminated. The lowest axial dispersion was obtained for M452Y, and it is almost twice as low as for M250Y. It was found that the values of the Bodenstein number for standard series of Mellapak type packing (M250Y, M350Y and M500Y) have comparable axial dispersion, especially at low liquid rates. The axial dispersion obtained for random packings is generally higher compared to structured packings. However, compared to other random packings such as Pall rings (25 mm) and Intalox saddles (25 mm), NXR0.7 and NXR1.2 exhibit up to a two-fold reduction in axial dispersion.