Packing spray nozzle distributor

Figure 9-8K. Spray nozzle distributor using full-cone wide-angle spray nozzles (depends on tower diameter). Not recommended for distillation applications, where the point-type distributors provide higher packing efficiency. Used by permission of Nutter Engineering, Harsco Corp., Bull. TI-1.

In addition, spray-nozzle distributors have been used to irrigate packed beds (Figure 10-14). Spray nozzles for distributing liquid usually are not used in fractionating columns or absorbers. Their use is limited to heat transfer operations where liquid entrainment from the bed top is not... 

Another type of distributor, not shown in Fig. 14-64, is the spray nozzle. It is usually not recommended for hquid distribution for two reasons. First, except for small columns, it is difficult to obtain a uniform spray pattern for the packing. The fuU-cone nozzle type is usually used, with the need for a bank of nozzles in larger columns. When there is more than one nozzle, the problem of overlap or underlap arises. A second reason for not using spray nozzles is their tendency toward entrainment by the gas, especially the smaller droplets in the spray size distribution. However, some mass transfer in the spray can be expected. 

End Effects Analysis of the mass-transfer efficiency of a packed cohimn should take into account that transfer which takes place outside the bed, i.e., at the ends of the packed sections. Inlet gas may veiy weU contact exit liquid below the bottom support plate, and exit gas can contact liquid from some types of distributors (e.g., spray nozzles). The bottom of the cohimn is the more hkely place for transfer, and SU-vey and KeUer [Chem. Eng. Prog., 62(1), 68 (1966)] found that the... 

Losses of amine up the stack are undetectable in the CANSOLV SO2 Scrubbing System. Losses from evaporation do not occur because the amine is in salt form in solution, and losses from entrainment are avoided by using trough type distributors instead of spray nozzles to distribute the amine over the packing. In extreme cases where upsets in gas flow are anticipated, a demister may also be used. 

The liquid distributors were replaced with carefully positioned spray nozzles, and the packing was removed. HCl in the vent was removed to a level one-fortieth of the original design. 

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). 

Distributors and collectors of liquid provide uniform wetting of the packings area and the withdrawal of phases from the packing. The best-known distributor types are orifice-riser, perforated-pipe, spray-nozzles, and through distributors. 

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. 

In spray-header distributors (Fig. 10), a main header with a collection of spray nozzles is used to distribute liquid to the packed bed. Spray header distributors are well suited to liquid distribution at low liquid rates, of moderately fouling fluids, and for... 

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. 

Spray distributors should never be embedded in the packing, because this is likely to cause premature flooding (237). For good distribution, a spray distributor containing more than a single spray nozzle should be placed at least 18 in, and preferably more than 24 in, above the bed. 

The liquid reflux distributors above each packed zone are often arrays of solid-cone sprays preferably the nozzles should be V4 iiich or larger in orifice, free passage, and pipe sizes. The spray liquid needs to be screened at all times. The sprays are not as good distributors as the drip-pan type, but they are economical and contribute to heat transfer without adding substantial pressure drop. The nozzles should be designed to operate at a flow rate that gives a good spray pattern without excessively small droplet sizes. 

In order to achieve perfect function, a spray distributor with several nozzles must be arranged so that the spray cones overlap, when they fall on the packings. It is only in this way that it can be ensured that liquid reach each sections of the column. 

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