Trays, sieve layout

Figure 8-67B. For sieve tray layout arrangements typical one-, two-, and four-pass tray flow patterns with clarifying flow markings by this author. Used by permission, Glitsch, Inc., Bui. 4900-5th Ed.

Sieve or perforated trays. These are much simpler in construction, with small holes in the tray. The liquid flows across the tray and down the segmental downcomer. Figure 11.52 indicates the general form of tray layout. 

Because of their simplicity and low cost, sieve (perforated) trays are now the most important of tray devices. In the design of sieve trays, the diameter of the tower must be chosen to accommodate the flow rates, the details of the tray layout must be selected, estimates must be made of the gas-pressure drop and approach to flooding, and assurance against excessive weeping and entrainment must be established. 

Tray layout discussions in this chapter emphasize sieve and valve trays, as these trays are most frequently encountered in industrial practice. Several of the considerations also apply to other tray types (e.g., bubble-cap trays). Considerations unique to bubble-cap trays were excluded from this chapter. The infrequent application of this type of tray in modem distillation practice argues against a detailed discussion here. A large amount of information on bubble-cap tray layout is available and is well documented in several texts (48, 257, 371, 409). 

Figure 6.3 Typical layout of the components for sieve trays, (a) Recommended, with equilateral triangular hole pitch (6) Square hole pitch (Part a Henry Z. Kister, excerpted by special permission from Chemical Engineering, September 8,1980, copyright fry McGraw-Hill, Inc., New York, NY 10020.)...

Now click on Tray Rating. In the Object Manager, click on New and call this section 1. In the Specs tab, input the stages for this section (2 to 15), pick Sieve from the Tray Type menu, and input the other variables as listed in item 1. In the Design/Pdrop tab, pick the Fair flooding calculation method and do NOT check Update section pressure drop. In the Layout tab, the tray type is sieve, and use the defaults for the other items. At this point do not put any numbers into the Downcomers tab (this means default values will be used). 

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