Random packings ceramic

Table 7 Packing factors random packing, ceramic...

Fig. 21. Random packing elements for distillation columns (a), Raschig ring (metal) (b). Bed saddle (ceramic) (c), Intalox saddle (ceramic) (d), PaH ring...

Corrosivity. Corrosivity is an important factor in the economics of distillation. Corrosion rates increase rapidly with temperature, and in distillation the separation is made at boiling temperatures. The boiling temperatures may require distillation equipment of expensive materials of constmction however, some of these corrosion-resistant materials are difficult to fabricate. For some materials, eg, ceramics (qv), random packings may be specified, and this has been a classical appHcation of packings for highly corrosive services. On the other hand, the extensive surface areas of metal packings may make these more susceptible to corrosion than plates. Again, cost may be the final arbiter (see Corrosion and corrosion control). 

FIG. 14-58 Typical holdup data for random packings and the air-water system. The raschig rings are of ceramic material. To convert pounds per hour per fr to Idlograms per second per m , multiply hy 0.001.356 to convert inches to millimeters, miinltiplyhy 25.4. [Shulman etal., AIChE J. i, 247 (I.9.5.5).]... 

In comparison with tray towers, packed towers are suited to small diameters (24 in. or less), whenever low pressure is desirable, whenever low holdup is necessary, and whenever plastic or ceramic construction is required. Applications unfavorable to packings are large diameter towers, especially those with low liquid and high vapor rates, because of problems with liquid distribution, and whenever high turndown is required. In large towers, random packing may cost more than twice as much as sieve or valve trays. 

As an alternative to trays, especially at low volumetric liquid-to-vapor ratios, packing can be used to promote vapor-liquid contact. One approach is to dump specially shaped pieces of metal, glass, or ceramic material into the column, wherein they are supported on a grid. An example of dumped or random packing is shown in Fig. 7. 

Figure B.1 First-generation random packings, (a) Raschig ring, metal (6) Lessing ring, metal (c) Berl saddle, ceramic.

Figure 8.2 Second-generation random packings, (a) Intalox saddle, ceramic (6) Super Intalox saddle, ceramic (Courtesy of Norton Company.)...

It is seen that the pressure drop across the BSR is close to that across the monolithic reactor, and both are about two orders of magnitude lower than that across the randomly packed-bed reactor. Obviously, for a washcoated monolithic reactor the pressure drop will be slightly higher than for the incorporated monolith used in this comparison, depending on the ratio between the thickness of the washcoat and the ceramic or metal support. 

The first of the widely used random packings were Raschig rings which are hollow cylinders of ceramics, plastics, or metal. They were an economical replacement for the crushed rock often used then. Because of their simplicity and their early introduction, Raschig rings have been investigated thoroughly and many data of their performance have been obtained which are still useful, for... 

Metallic or ceramic foams exhibit several advantages over randomly packed beds in microreactors [55]. Open cell foams consist of a network of interconnected rods, which delineate cavities (called cells). Metallic foams have porosities of up to 95%, ceramic foams of 75-85%. Examples are shown in Figure 6. 

Random packings are fabricated from a wide variety of materials. Originally, most were made of ceramic and were popular for corrosive services despite their friability. Today, polypropylene is widely used to provide a bed that offers light weight, reasonable resistance to corrosion by many fluids, and low cost. Plastic random packings are often suitable where dissolved volatile organic componnds (VOCs) are to be removed from groundwaters. 

This model has been applied successfully to random packings of the ring and saddle type, in ceramic, steel, or plastic materials. A parity plot for tests of air-stripping of VOCs from water with air is shown in Figure 13.19, taken from reference 30. Several plastic packings were used. For details of the experiments, as well as use of the original Onda equations, see reference 31. 

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