Downcomer trays

Tower Internals and Equipment Modification. Tower capacity expansion can be achieved through the use of random or stmctured packing, or through the use of higher capacity trays such as the UOP multiple downcomer tray. Packing has been used in the gasoline fractionator, water quench tower, caustic and amine towers, demethanizer, the upper zone of the deethanizer, debutanizer, and condensate strippers. Packing reduces the pressure drop and increases the capacity. 

Installing the standard antijump baffles for certain inboard downcomer trays to keep droplets (produced by tray blowing ) from entering the downcomer. 

Figure 8-67C. Linde multiple-downcomer tray. Used by permission. Union Carbide Corp., Linde Division.

Downcomer backup Assume 114-in. clearance between bottom edge of downcomer and tray floor (or equivalent depending on design of downcomer-tray relationship.) See Figure 8-63. 

The very first continuous distillation column was the patent still used to produce Scotch whiskey in the 1830s. It had 12 bubble-cap trays with weirs, downcomers, tray decks, and bubble caps with internal risers. Current trayed towers are quite similar. As most distillation towers have always been trayed rather than packed, one would have to conclude that trayed towers must have some sort of inherent advantage over packed towers. And this is indeed true, in a practical sense even though, in theory, a packed tower has greater capacity and superior separation efficiency than a trayed column. 

Approximate number of units 12 in and larger 610 90 woven-wire fabric 500 with spacers 43 downcomer trays on close tray spacing 120... 

All trays must have a balance of downcomer areas. Notice that the areas of the two side downcomers on any tray (straight downcomers, not sloped) are nearly equal area to that of the center downcomer. In other words, the area of the center downcomer tray approximately equals the area of two side downcomers. The logic here is that the liquid backup height in all downcomers must be equal, or otherwise the choked downcomer (the one having a lesser area) will flood, causing tray failure. 

Figure 6-119. Sieve tray with downcomers, tray components. Used by permission, Hendrick Mfg. Co.

Fig. 1 Packed tower system. (Modified from Binkley, M.J. Thorngren, J.T. Gage, G.W. Bonilla, J.A. Beckman, D.H. Method of Downcomer-Tray Vapor Venting. U.S. Patent 5,106,556, Apr 21, 1992.)...

Tray contacting devices include both downcomer trays and downcomer-less trays. Trays with downcomers constitute the vast majority of tray installations. Fig. 1 shows a typical downcomer tray. 

FIGURE 12.38 Hanging downcomer tray. Note that the part of the tray floor normally used as the bottom of the downcomer is converted to bubbling (active) area. 

Installed and fixed Baffles Overflows Weirs Downcomers Trays Chimneys Internal distribution systems Dip pipes Vortex breakers ... 

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