Expanded metal packing

Column packing is also especially susceptible to SCC. Expanded metal packing or mesh contain a great deal of cold-work and very high stress levels, rendering it particularly susceptible to SCC. Although both types of packing can be stress-relieved, alone or with the column itself, a preferred method is to manufacture them from crack resistant alloys. 

Figure 9-6MM. Nutter BHS structured packing with expanded metal texture, which maintains high mass transfer efficiency across all operating conditions. Nutter Engineering designs and manufactures BSH in North America under exclusive license from Julius Montz GmbH of Germany. Used by permission of Nutter Engineering, Harsco Corp.

The broad classes of packings for vapor-liquid contacting are either random or structured. The former are small, hollow structures with large surface per unit volumes that are usually randomly dumped into the tower. Structured packings are normally layers of elements fabricated form expanded metal, woven wire screen, or sheet metal, and are stacked into the tower very carefully. 

Figure 13.50. Effect of surface design on the total reflux performance of a 400 m /m packing. B1-400 is made from sheet metal BSH-400 is made from expanded metal. Pressure = 1.03 bar, column diameter = 0.43 m. (Olujic et ah, 2000).

The form and shape of the electrodes are tailored for the specific reactor configuration. Typical shapes include flat metal sheets, perforated or expanded metal grids, metal foams and meshes, and three-dimensional packed bed electrodes formed by stacking metal meshes, pressing catalyst powders, or by use of microporous carbon felts and cloths (three-dimensional electrodes are particularly attractive for low-current density reactions because the electrode surface per unit reactor volume can be made very large) [28]. 

Packing is made from expanded metal with shaped perforated holes and arranged horizontally and vertically to provide changing direction of the holes... 

To increase the efficiency for the electrochemical treatment of effluents rotating three-dimensional electrodes were also tested. Thus, a rotating packed bed electrode [44] and a vertically moving particle bed electrode were proposed [45, 46]. Plater barrels were also adapted for the removal of metals [47,48]. Likewise, rotating cylinder electrodes made of reticulated vitreous carbon [49], expanded metal sheets [50], woven wire meshes [51] and wedge wire screens [52] were also examined. 

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