Packing Material—Random Packings

Packing material selection is primarily based on the corrosion resistance. The factors below are also important. Reference 16 has an excellent detailed discussion. 

Metals. Carbon steel packings are usually the first choice for noncorrosive services. Compared to ceramic and plastic, they normally 

Plastics. Polypropylene is inexpensive and is most popular when temperatures do not exceed 250°F. Caution is required where hot spots are likely, e.g., due to heat of solution. Other plastics may be better for higher temperatures, but these tend to be more expensive. Generally, plastic Pall rings are stiffer and resist softening more than other shapes because of their internal arms.  

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Fig. 2. Packing materials for packed columns, (a)—(f) Typical packing elements generally used for random packing (g) example of stmctured packing.

There are two basic types of packing materials random and structured packings. Random packings are commonly formed from different shapes such as rings, shown in Figure 9.19, or saddles, shown in Figure 9.20. They are constructed out of ceramic, metal, plastics, or coke with the most popular metal application being... 

Packing material Random, ceramic Raschig ring, 2 in. 

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). 

Introduction Packed columns for gas-liquid contacting are used extensively for absorption, stripping, and distillation operations. Usually the columns are filled with a randomly oriented packing material, but for an increasing number of applications the packing is very care-... 

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).]... 

The term porosity refers to the fraction of the medium that contains the voids. When a fluid is passed over the medium, the fraction of the medium (i.e., the pores) that contributes to the flow is referred to as the effective porosity of the media. In a general sense, porous media are classified as either unconsolidated and consolidated and/or as ordered and random. Examples of unconsolidated media are sand, glass beads, catalyst pellets, column packing materials, soil, gravel and packing such as charcoal. 

Wetting For operation at low liquid loads, the onset of minimum wetting can adversely affect scale-up, particularly with random packings and aqueous systems. Scale-up reliability at low liquid loads can be improved by pilot-testing at the composition range expected in the prototype, and by using identical packing materials and surface treatment in the pilot tests and in the prototype. 

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