Spray-type distributor

Graf states For spray type distributors in vacuum towers the main header of the distributor will be 18-36 in. above the top of the packing. ... 

When a high liquid flow rate is required, notched-trough, orifice-type, or spray-type distributors are the best selections. 

Spray-type distributor. It can be designed using the following criteria ... 

Spray-type distributor can also be used for some cases. 

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.

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 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. 

The perforated-pipe distributor is best suited where vapor mass velocities are high and where an open area in excess of 70 percent is needed to avoid localized flooding (305). Together with the spray type, the perforated-pipe distributor offers the highest vapor flow area. However, the maximum liquid flow recommended for this type of distributor is relatively low and should not exceed 10 gpm/ft of column area (305) with standard designs. 

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). 

Orifice distributors with bottom perforations should be avoided in plugging services, even when filters are installed there have been cases where small solid particles passed through the filter, agglomerated in the pan or troughs, and blocked perforations. In pressure distributors, particularly the spray type, a filter is often [but not always (297)] sufficient. 

Unfortunately, the heat transfer coefficient is not completely independent of the packed depth. This occurs because the spray-type liquid distributor typically used in these towers also provides some amount of heat transfer. This results in proportionally better performance from short packed beds than from deeper beds. By correlating operating data from such towers, Graf reports that vapor-to-liquid temperature differences of 50T are typical [13]. A deep packed bed is required to obtain a 20 F temperature difference between vapor and liquid streams. Figure 6-4 shows the efiective packed depth as compared to an actual packed depth if each foot of bed depth greater than 4 ft were equally efficient. 

An overview of the application ar of the spray liquid distributors is presented in Table 5 togedier with other types of distributors considered in this book. 

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... 

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. 

It is difficult to compare the performance of various spray towers since the type of spray distributor used influences the results. Data from Hixson and Scott 33 and others show that KGa varies as G70-8, and is also affected by the liquid rate. More reliable data with spray columns might be expected if the liquid were introduced in the form of individual drops through a single jet into a tube full of gas. Unfortunately the drops tend to alter in size and shape and it is not possible to get the true interfacial area very accurately. This has been investigated by Whitman et a/. 34 , who found that kG for the absorption of ammonia in water was about 0.035 kmol/s m2 (N/m2), compared with 0.00025 for the absorption of carbon dioxide in water. 

There are three types of nonproprietary nonagitated types of extraction columns (see Figure 12). The spray columns are the simplest type of extractors, containing only distributors for the feed (often through perforated pipes). This... 

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. 

Pressurized liquid distributors use pressure drop across an orifice to deliver a smooth liquid distribution to a packed bed. Two main types exist, pipe-orifice distributors and spray distributors. Of the two, spray distributors are the most common. In specifying either type, the main criteria to be set are the pressure drop available for use and the minimum orifice size. These... 

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. 

The operating conditions for solid-state fermentation for cellulase production are dependent on the strain to be used, the reactor type and the medium composition, but the basic operating procedure remains the same as shown in Fig. 2. The final product can be obtained as crude solid cellulase, liquid cellulase or powder cellulase according to the application. Figure 3 shows a process flowsheet for cellulase production [25]. In the process, wheat bran is used as substrate. Seeds are prepared in a stirred-tank fermentor and then sprayed into the medium by a spray distributor. The fermentation is performed in a shallow-tray fermentor. The temperature and humidity in the fermentor are automatically regulated. After fermentation, cellulase is recovered by water extraction and purified by salt precipitation and ion exchange. The final product is concentrat-... 

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. 

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