Catch Tank Design Knockout Drums

The relieved vent stream enters the catch tank at one end, the gas phase is separated from the liquid phase, the liquid phase remains in the catch tank and the gas leaves it at the other end. Such catch tanks working accordii to the gravity separator principle are widely used in industry, because they are applicable for many substances. Another advantage is the capacity to contain large volumes and the fact that they may be placed quite a distance away from the reaction vessel. 

Their design can be performed according to technical regulation API 521 [103]. The aim of the assessment regarding the design is a comparison of the length of the tank and the necessary distance the droplets need to settle. 

In a first step the settling of the droplets in the tank is calculated. 

If the boundary condition is made that only those droplets may leave the catch tank again which are smaller in diameter than ddropiet 150 pm, then this equation becomes simplified to  

C is a dimensionless factor representing a drag coefficient, which may be calculated by the following approximation 

---

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. 

Multireactor Knockout Drum/Catch Tank This interesting system, depic ted in Fig. 26-22, is sometimes used as the containment vessel for a series of closely spaced reac tors (Speechly et al., Trinci-ples of Total Containment System Design, presented at I. Chem. E Noith West Branch Meeting, 1979). By locating the drum as shown in Fig. 26-22, minimum-length vent lines can be routed direc tly to the vessel without any bends. 

---