Packed towers construction materials

The construction of packed towers is relatively straightforward. The shell of the column may be constructed from metal, ceramics, glass, or plastics material, or from metal with a... 

Figure 13.15. Mechanism, nomenclature, and constructions for absorption, stripping and distillation in packed towers, (a) Two-film mechanism with equilibrium at the interface, (b) Sketch and nomenclature for countercurrent absorption or stripping in a packed tower, (c) Equilibrium and material balance lines in absorption, showing how interfacial concentrations are found, (d) Equilibrium and material balance lines in stripping, showing how interfacial concentrations are found, (e) Equilibrium and material balance lines in distillation, showing how interfacial concentrations are found.

When column diameters are less than 0.6 m (2.0 ft) packed towers can be considerably cheaper. However, if alloy metals are necessary, plate towers may result in less cost. Using ceramic or other similar resistant materials for packing and materials of construction, packed towers can serve to handle corrosive materials and acids. Because the gas flow in packed towers may offer less degree of agitation, packed tower operation may be better for liquids that tend to foam. When liquids are thermally sensitive, packed columns may offer less holdup and thus prevent changes taking place in the liquids due to thermal reaction. 

Industrial nitric acid processes are basically of three types (1) ambient, (2) medium, and (3) high pressure. For the 1 ambient pressure variety, a low pressure drop contactor like packed tower is desired. The other two types can be handled by a relatively high pressure drop contactor like plate column. It may be noted here that the NO absorption train constitutes a major portion of the nitric acid plant cost since the material of construction (SS-304 ELC) is relatively expensive. Table 3.2 compares packed and plate columns for NO absorption. 

Materials of construction must he corrosion resistant. Steel should he hot galvanized, although some resin coatings may suffice. GRP casings are used hy some manufacturers. The water-dispersal packing of a cooling tower is made of treated timber or corrugated plastic sheet. 

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