Types of Towers

Towers are named for the service or type of unit they are associated with. For example, a stripper is used to strip lighter material from the bottoms of a main tower or a vacuum tower. It is generally used in a vacuum/ crude unit for distilling crude bottoms residue under 

From the outside, tower configurations are similar in appearance, varying only in dimension some towers have swaged top and bottom sections. The principal difference among towers is the type and layout of the internal components that control the vapor-liquid contact. 

This chapter describes the internal and external plant layout requirements for the two mo.st common types of tower the trayed and packed arrangements. Exhibit 10-8 depicts a typical trayed tower with some 

Within the conventional inline process unit, towers 

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This type of tower uses fans at the base to force air through the tower fill or packing (Figure 9-102). Due to the relatively low oudet air velocity, there is a tendency for discharged hot air to recirculate into the fan intake and reduce tower performance. The fan handles only atmospheric air thereby reducing its corrosion problem when compared to the fan on an induced draft tower. The tower size for the forced as well as the induced draft unit is considerably less than for an atmospheric or natural draft unit due to the higher heat transfer rates. 

The siting, as well as the selection of type of tower, can be critical. Rotating the tower, shielding the motor, use of baffles can all help in meeting environmental noise requirements. If in doubt, consult your cooling tower designer. 

As its name implies, a tower reactor typically has a height-to-diameter (h/D) ratio considerably greater than 1. Types of tower or column reactors (the words tower and column may be used interchangeably) go by descriptive names, each of which indicates a particular feature, such as the means of creating gas-liquid contact or the way in which one phase is introduced or distributed. The flow pattern for one phase or for both phases may be close to ideal (PF or BMF), or may be highly nonideal. 

In the quantitative development in Section 24.4 below, we assume the flow to be ideal, but more elaborate models are available for nonideal flow (Chapter 19 see also Kastanek et al., 1993, Chapter 5). Examples of types of tower reactors are illustrated schematically in Figure 24.1, and are discussed more fully below. An important consideration for the efficiency of gas-liquid contact is whether one phase (gas or liquid) is dispersed in the other as a continuous phase, or whether both phases are continuous. This is related to, and may be determined by, features of the overall reaction kinetics, such as rate-determining characteristics of mass transfer and intrinsic reaction. 

Figure 24.1 Types of tower or column reactors for gas-liquid reactions (a) packed tower, (b) plate tower, (c) spray tower, (d) falling-film tower, (e) bubble column...

Absorption Towers or Columns are tall cylindrical structures designed for absorption(qv) of gases by liquids. There are several types of towers, such as ... 

Tower diameter selection is usually made with the maximum expected gas and liquid flow rates and depends on the size and type of tower packing The portion of Fig. 3 with solid lines illustrates the pressure-drop relationship for 1.5-m. [3.81 -cm] Pull rings supplied by the manufacturer for typical superficial gas and liquid flow rates used in the chemical processing industry.1 This relationship is usually available in graphical form from any manufacturer of packed-tower packing elements. While these... 

It should be clear that major differences exist between mechanical- and natural-draft systems. Table 4.1 summarizes our discussion by comparing the two types of towers. 

Windage losses or drift vary with the type of tower and local conditions. Average estimates for normal tower operations are 0.3-1% of circulation for natural-draft towers and 0.1-0.3% of circulation for mechanical-draft towers. 

The paper considers the state-of-the-art in cooling towers, covering various types of towers in use. It discusses how they respond to the present and the future needs of the industry. A trend toward the counterflow design in the heat exchanger is indicated, and a forced draft counterflow tower is described. The design of the fan-assisted tower using both mechanical and natural draft is briefly dealt with. 1 ref. cited. 

Although there is a wide variety of cooling tower manufacturers, designs, and structural materials used, particular types of tower are often associated with specific industries. This may further concentrate the focus of survey questioning to center around potential problem areas specific to the industry in question. For example ... 

Also, high levels of bacteria/biomass can significantly interfere with the efficiency of the various types of tower film-fill. Typically, the film-fill and tower manufacturers propose a maximum TAB of 1 x 105 cfu/ml. This level should be reduced to 1 x 104 cfu/ml if the TSS >25 ppm or if the film-type is a particularly high-efficiency design. 

The total weight of a dry plate tower is usually less than that of a packed tower designed for the same duty. However, if liquid holdup during operation is taken into account, both types of towers have about the same weight. 

The complete installed cost of various types of towers is given in Fig. 16-28. This cost includes all the components normally associated with a tower as outlined above. 

Of the above parameters, the ability to increase gas/liquid contact will always result in higher absorption efficiency in a wet scrubber. If temperature can be reduced and the liquid-to-air ratio increased, then the absorption efficiency will also be improved in the scrubber. The actual design of the tower (diameter, height, depth of packed bed, etc.) will also depend on the given vapor/liquid equilibrium for the specific pollutant/scrubbing liquor. Additionally, the type of tower (packed vs tray, and so on) used will affect this equilibrium. The design of wet scrubbers is not covered in this chapter, but design examples can be found elsewhere in the literature (14). 

Smith (15) has presented a practical ammonia-stripping tower design based on the concept of the height of transfer unit vs the gas/liquid ratio for a given type of tower packing. He has provided a sample design problem. 

The design of an air stripping tower is essentially similar to that of the conventional cooling tower (12). There are two basic types of tower configuration crosscurrent and countercurrent, with the former being more common at the present time. 

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