Separators knockout drums

Design methods are discussed elsewhere (417) and are based on limiting the maximum diameter of droplets entrained in the vapor stream. Maximum droplet diameter can be reduced by supplying a knockout facility upstream of the compressor. This can be either an enlargement of the vapor space above the top tray, an in-line liquid separator, or a separate knockout drum. Mist eliminators are effective and can be installed above the top tray or in the drum. If the vapor temperature is higher than the worst ambient conditions, the lines from the knockout facility to the compressor should either be kept short and insulated or be provided with liquid-removal facilities. 

Types of Equipment The three most commonly used types of equipment for handling emergency relief device effluents are blowdown drums (also called knockout drums or catch tanks), cyclone vapor-liquid separators, and quench tanks (also called passive scruh-hers). These are described as follows. 

Cyclone Separator with Separate Catch Tank This type of blowdown system, shown in Fig. 26-17 and 26-18, is frequently used in chemical plants where plot pan space is hmited. The cyclone performs the vapor-liquid separation, while the catch tank accumulates the hquid from the cyclone. This arrangement allows location of the cyclone knockout drum close to the reactor so that the length of the relief device discharge hne can be minimized. The cyclone nas internals, vital to its proper operation, which will be discussed in the following sections. 

Cyclone Separator with Integral Catch Tank This type of containment system, depicted in Fig. 26-19, is similar to the ore-mentioned type, except that the knockout drum and catch tank are combined in one vessel shell. This design is used when the vapor rate is quite high so that the knockout drum diameter is large. 

They have higher separation efficiency than a horizontal knockout drum. 

The author states that this equation is vahd for the design of knockout drums which can separate liquid droplets of 400 [Lm and larger. 

Cyclone Separator with Separate Catch Tank (See Figs. 26-17 and 26-18.) The sizing of a cyclone knockout drum for emergency relief systems is somewhat different from sizing a cyclone separator for normal process sei vice for the following reasons ... 

Cyclone Separator with Integral Catch Tank (See Fig. 26-19.) The diameter of the knockout drum is calculated by the criteria given in the preceding section and Fig. 26-18. Since the liquid is also to be retained in the vessel, extend the shell height below the normal bottom tangent line to increase the total volume by an amount equal to the volume of the hquid carried over. 

A vessel handling large amounts of liquid or a large liquid surge volume will usually be horizontal. Also, where water must be separated from hydrocarbon liquid, the vessel will be horizontal. A vessel with small surge volume such as a compressor knockout drum will usually be vertical. 

Figure 12-38. Tangential inlet knockout drum with separate liquid catchtank.

Knockout drums are sometimes called catch tanks or blowdown drums. As illustrated in Figure 8-12, this horizontal knockout drum system serves as a vapor-liquid separator as well as... 

Any stream containing liquid or solid or both should not be vented directly to the environment, which means essentially any relief vent stream since it is unusual that the stream would be fully as a gas. The liquid and/or solid should be collected and contained for later treatment. Typical collection and separation methods include knockout drums and cyclones. If the remaining gas stream contains toxic or flammable substances, it should also be treated or flared. 

Gravity Separators Three types of gravity separators are commonly used in the chemical process industries (CPI) horizontal blowdown drum/catch tank, vertical blowdown drum/catch tank, and multireactor knockout drum/catch tank. 

Figure 12-38. Tangential inlet knockout drum with separate liquid catchtank. (Source Grossel [39].)...

Efficiencies of 95% for collection of 5 m droplets can be achieved by proper design of cyclone separators. For applications such as knockout drums on the suction of compressors, however, it is sufficient to remove only droplets greater than 40-50 m. 

Liquid Knockout Drum (Empty) 618 Knockout Drum with Wire Mesh Deentrainer 620 Size and Capacity of Cyclone Separators 621 Dimensions and Weight of a Horizontal Pressure Drum 628... 

---