Packing support plate

As indicated above, packed column internals include hqiiid distributors, packing support plates, redistributors (as needed), and holddown plates (to prevent movement of packing under flow conditions). Costs of these internals for columns with random packing are given in Fig. 14-80, based on early 1976 prices, and a Marshall and Swift cost index of 460. 

Figure 2. Multibeam packing support plate. (Courtesy of Norton Chemical Process Products Corporation.)...

Figure 3. Trickle-bed reactor. Key A, gas b, liquid c, liquid distributor d, thermocouple e, alumina particles f, jacket g, catalyst h, glass beads i, gas distributor j, packing supporting plate K distributor plate.

The space between the bottom tray or packing support plate and the liquid level is a prime potential troublespot in distillation and absorption columns. Numerous mishaps originating in this section have been reported (12, 49, 71, 107, 203, 231, 238, 255, 296, 375, 440). It is estimated (143, 207) that 50 percent of the problems in the lower part of the column are initiated in this space. Many of these problems are associated with the reboiler return (or bottom feed) inlet. Therefore, it is important to follow these guidelines. 

The top of the reboiler return or bottom feed nozzle should be located at least 15 to 18 in below the tray (or packing support plate) above (143, 207, 211, 237, 307) (Fig. 4.16). Some designers (211, 237) recommend that the distance from the centerline of the nozzle... 

In large-diameter packed colxunns where I-beams support the packing support plate, a larger space between the reboiler return nozzle and the packing support plate may be required. The prime consideration here is allowing sufficient open area between the bottom of the beam and the high liquid level for adequate vapor distribution. Detailed discussion is in Sec. 8.2. 

Gravity cycles tend to be most severe in column bottom lines. These cycles can be quite violent, can dislodge and damage trays and packing support plates, and in some cases, even pull a vacuum deep enough to collapse a vessel (158). Gravity outlet lines should be surveyed with special care to ensure no gravity cycle can form. 

Formation of a continuous liquid phase above the packing support plate. 

The first packing support plates for random dumped packings were slotted or perforated, flat ceramic plates. The use of 1-in. to 2-in. size ceramic Raschig ring packings, common in those days, required small holes or narrow slots that gave the plate a low open area of only 15% to 25%. Even... 

In columns 72-in. or larger diameter, the packing support plates usually are clamped to the supporting ledge at both ends. This prevents movement of the individual beams during operating upsets that could allow some packing pieces to fall out of the packed bed. 

Because a packing support plate usually is located immediately above the gas inlet in an absorber or the reboiler return in a distillation column, this plate could be used to control vapor distribution. Obviously, vapor maldistribution can reduce column efficiency in the same way as liquid maldistribution although due to the turbulence in the vapor phase, its rate of radial cross-mixing is at least three times that of the liquid phase. The potential for vapor maldistribution increases as column diameters or operating pressures increase. Fortunately, the vapor phase tends to maintain a uniform distribution once it has been established. Thus, usually only the packing support plate immediately above the vapor inlet needs to act as a vapor distributor. This support plate should be located at least one vapor-inlet diameter plus 12-in. above the center-line of the vapor inlet nozzle. 

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