(343f) Effective Mass Transfer Areas in Packed Absorbers

High efficiency packings can be classified as random or structured. Random packings are discrete pieces of packing of a specific geometrical shape which are “dumped” or randomly-packed into the column shell. Structured packings are composed of ordered, crimped layers of corrugated sheets or wire mesh that are stacked in the column The unique designs of these types of packing promote liquid spreading and gas/liquid contact area while minimizing wasteful pressure drop.

In carbon dioxide absorption, the rate of mass transfer primarily depends on the gas/liquid contact area. High efficiency packings are designed to maximize this area. Random packings generally provide an irregular and open geometry that promotes surface wetting and rivulet formation. The surface of structured packing is treated to enhance liquid spreading; the treatments include perforating, embossing, and use of expanded metal. Perforations are used to divert the flowing liquid. While perforations enhance spreading, some packing area is naturally lost because of the perforations.

A number of models have been developed for the prediction of gas/liquid contact area. A widely used correlation assumes the contact area cannot exceed the available packing surface area. Others have proposed models for the prediction of gas/liquid contact areas. Unfortunately, these models have been based on back-calculated areas assuming models for gas and liquid mass transfer coefficients.

In this paper, measured effective mass transfer areas for a wide range of high performance packings will be presented. A detailed analysis of these data will be provided. A preliminary evaluation of the published models will also be presented.