1.2 Downcomer details

The liquid from the top tray is directed to the tray below through a downcomer or downspout. The downcomer liquid flow passage is normally formed by a vertical plate starting from the weir outlet, called an apron. The adequate residence time needs to be ensured in the downcomers for the disengagement of vapor/gas from liquid. The downcomer residence time of more than 3 s is desirable to get only clear liquid on the tray. The different types of segmental downcomers constructions are shown in Figure 8.3. The bottom downcomer area is normally more than 50% of the top downcomer area for sloped downcomers.

 

Figure 8.3. Design of segmental downcomers: (a) vertical apron, (b) inclined apron, (c) inlet weir and, (d) recessed well ( [1] page 563 ).