Packing trough-orifice distributor

The five primary designs used for water distributors are orifice plate, trough-type distributor, orifice headers, combination of trough and orifices, and spray nozzles (see Fig. 2). These distributors equally dispense the water over the packing causing the water to break into tiny droplets, which increases the air-to-water contact. 

For single- or multiple-bed columns, a distributor is needed for each bed. A center-fed packed distillation column, for example, requires at least two beds. In some cases, the cost of the distrib-utor(s) can approach that of the packing. One can select from several different types of liquid distributors, including trough, orifice/riser, perforated pipe, and spray nozzle. These are illustrated in Figure 12.55 and described below. 

Several distributor types are available trough, orifice-rise, and perforated pipe. Examples of these types are shown in Fig. 14-64. The trough distributor provides good distribution under widely varying flow rates of gas and liquid. The liquid may flow through simple V-notch weirs, or it may flow throu tubes that extend from the troughs to near the upper level of the packing. Some deposition of solids can be accommodated. 

Orifice redistributors (Fig. 3.8a) These are identical to orifice distributors, either the pan or the trough type, except that hats, caps, or strips are usually installed above the risers to prevent liquid from the packed hed above from entering the vapor risers, and also to promote lateral mixing of vapor. 

With a trough distributor it is often more difficult to obtain uniform distribution next to the tower wall than with a PAN or orifice pipe distributor. Bonilla [131] recommends the rule of thumb Any 10% of the outer surface area of packing in the tower should not receive more or less liquid than the average 10% of the surface area. 

Packed-tower efficiency and turndown are strongly dependent on the quality of initial liquid distribution. Uneven distribution may cause local variations in the liquid/gas ratio, localized pinch conditions, and reduced vapor-liquid contact. Figure 14 shows two common liquid distributor types, the ladder type (shown as the top distributor) and the orifice type (shown as the redistributor). The ladder type is a horizontal header of pipes, which are perforated on the underside. The orifice type is a flat perforated plate equipped with round or rectangular risers for gas passage. Other common types of distributors are a header equipped with spray nozzles (spray distributor) and a header of horizontal channels, with V notches cut in the vertical walls of the channels (notched-trough distributor). 

In all single streams distributors the liquid phase is distributed over the cross-sectioii of the apparatus fixtm orifices bored in the bottom of troughs, pan formed distributors c r pipes, or in the walls of pipes and troughs. The points, at which the liquid is entering the packing, are uniformly distributed over the column cross-section. The diameters of all orifices of a given distributor, respectively their cross-sections, are equal. Their calculation is discussed in point 7.3.1.12. 

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