(144f) Are Stacked Packings Structured Packings? Fluid Dynamics and Their Separation Efficiency for Gas-Liquid Systems

Random packing elements can be regularly arranged inside the column to form a regular structure as so-called stacked packings. This filling method of random packings is not new, it is known for quite some time in the separation techniques. For instance, hydraulics and mass transfer of stacked 50-150 mm ceramic Raschig rings have been investigated from 1960-1975 in the context of absorption processes for sulphuric acid processing [1-3].

For stacked packings consisting of Pall rings, Bia³ecki-rings or even modern lattice type packings such as Hiflow-ring and Nor-Pac no systematic investigations and no general approach for designing mass transfer processes for gas-liquid systems with stacked packings are present in literature.

Very good results were obtained for stacked 25-50 mm metallic Bialecki-rings in the liquid-liquid extraction processes, which werde presented in the literature [4].

Generally it is known, that stacked packings have a bigger operating range compared to random packings and a much lower pressure drop on one hand, but lower separation efficiency on the other.

Thus, which advantages have stacked packings? Can they be used as an alternative to random or to structured packings? And finally: Should stacked packings be regarded as structured packings or rather as random packings?

The main goal of this work is to provide the answers for the questions raised above based on detailed and systematic investigations. Another aim is to present their range of application for which they can be recommended as an alternative column filling to random and structured packings.

In this paper , a generally valid model for description of fluid dynamics [5] and mass transfer in the gas- and liquid phase of different stacked packing types such as 50 mm Raschig rings, 50 mm Pall rings, 25-50 mm Bialecki rings, 50 mm Nor Pac and 50 mm Hiflow rings made of ceramics, metal and plastics will be presented. The model is based on experimental data for different absorption and distillation systems such as NH3-air/water, NH3-water/air, CO2- water/air under normal pressure, chlorobenzene-ethylbenzene, ethanol-water in the pressure range from 13 mbar to 1000 mbar. Experiments have been carried out in columns with diameters ds= 0,15 – 0,6 m and bed heights up to 2m.

After that a comparison of stacked packing and structured packing and random packing is carried out and the obtained results are discussed.

As main results of this work it can be concluded, that the behaviour of stacked packing is similar to that of structured packing and processes are discussed in which this type of packed column can be applied successfully.

Literature

[1] W.M. Ramm

Absorption of gases (orig. Russian ), Moscow (1966)

[2] Z. Zio³kowski, J. Maækowiak, J. Kowalski

Liquid phase mass transfer in packed column filled with stacked Bia³ecki rings (orig. polish)

Inz. Chem. (1975), No 3, p.631- 640

[3] J. Maækowiak, S. Suder

Hydraulics and mass transfer behaviour in packed column filled with stacked Bia³ecki-Rings for gas/liquid-systems (orig. polish) Inz. Chem. (1977) Vol. VII, No.3, p.651 – 664

[4] J. Maækowiak, R.Billet

New Method for Design of Packed Columns with Random and Stacked Packings for Liquid-Liquid-Extraction (orig. englisch)

Ger. Chem. Eng Vol.1 (1986), p.48 - 64

[5] J. Maækowiak

Fluid Dynamics of Packed Columns

Springer-Heidelberg , London, New York 2010