Spray nozzle liquid distributor

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... 

The term mist generally refers to liquid droplets from submicron size to about 10 /xm. If the diameter exceeds 10 /xm, the aerosol is usually referred to as a spray or simply as droplets. Mists tend to be spherical because of their surface tension and are usually formed by nucleation and the condensation of vapors (6). Larger droplets are formed by bursting of bubbles, by entrainment from surfaces, by spray nozzles, or by splash-type liquid distributors. The large droplets tend to be elongated relative to their direchon of mohon because of the action of drag forces on the drops. 

Figure 9. Spray nozzle liquid distributor. (Courtesy of Norton Chemical Process Products Corporation.

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. 

Liquid to grids is usually supplied by spray nozzles, and thess may plug. As with other distributors, adequate measures are required to prevent plugging, and the grid manufacturer must be supplied with good data on the fouling potential of the service. 

Another type of distributor, not shown in Fig. 14-64, is the spray nozzle. It is usually not recommended for liquid distribution for two reasons. First, except for small columns, it is difficult to obtain a uniform spray pattern for the packing. The full-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 fiieir tendency toward entrainment by the gas, especi ly the smaller droplets in the spray size distribution. However, some mass transfer in the spray can be expected. 

Liquid Fat Application to Mixed Feeds. The typical operation consists of a horizontal batch dry feed mixer, equipped with fat addition ports. Hot fat is added to the batch after the dry ingredients have been mixed to minimize segregation of ingredients into fat balls. Some operators spray the fat, and others prefer to let it mn into the mixer through small distributor fines or horizontal pipes with diagonal cuts. Much can be said in favor of the distributor line approach. Spray nozzles clog, even if equipped with screens. A spray fan pattern, that doesn t deposit fat on the sides of... 

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. 

The spray nozzle is not widely used. If more than one nozzle is used, it is difficult to obtain a uniform spray pattern because of overlap and underlap of the patterns. Also, liquid entrainment from the sprays is a problem. Spray distributors are sometimes used in petroleum refinery vacuum columns. The full cone nozzle is normally used, singly or in banks. 

FIGURE 5.8-5 Types of liquid distributors (a) orifice/riser (6) perforated pipe (c) trough and (d) spray nozzle. 

The chief problem in a falling-film evaporator is that of distributing the liquid uniformly as a film inside the tubes. This is done by a set of perforated metal plates above a carefully leveled tube sheet, by inserts in the tube ends to cause the liquid to flow evenly into each tube, or by spider distributors with radial arms from which the feed is sprayed at a steady rate on the inside surface of each tube. Still another way is to use an individual spray nozzle inside each tube. 

Like perforated-pipe distributors, the spray distributor turndown ratio is about 2 1 (111). Excessive liquid flow rates may create a mist problem, while low liquid flow rates reduce the cone diameter and may create poorly irrigated areas. For this reason, oversized spray nozzles must be avoided (237). As with perforated pipe distributors, a dual liquid distributor can be used to enhance turndown (Sec. 3.8). 

If the service contains solids, or the liquid is close to its freezing point, a weir-type distributor is the best choice. If it is still desired to use a perforated-pipe, spray, or orifice distributor, a filter should be installed upstream to remove particles that can block the perforations or spray nozzles (237,305). Successful applications of this technique have been reported (237,346). 

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... 

The liquid is injected with a bottom-spray nozzle, which is situated in the center inside the Wurster tube. In the Wurster coater, air enters the equipment through the bottom via a segmented distributor plate that consists of a perforated plate, as illustrated in Fig. 16. 

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