Sieve tray design

This specialized Sieve Tray design is of high efficiency and operates with exceptional short tray spacings, sometimes as low as 6 in. between trays. 

Example 8-38 Sieve Tray Design (Perforated) with Downcomer... 

E-Z Stacker and E-Z Tray are commercially available modular air strippers for the ex situ removal of volatile organic compounds (VOCs) from groundwater. E-Z Stacker consists of 4 or 6 stacking units E-Z Tray units are arranged in pull-out drawers. The multiple sieve tray design of the E-Z Stacker uses forced-draft air bubble generation to provide VOC removal. All information is from the vendor and has not been independently verified. 

To this point we have covered general tray design for any type of tray— valve, bubble cap, or sieve type. Beginning here, we will review the design and rating of valve-type trays, followed by bubble cap and sieve tray design and rating. 

The jet flood equation is also based on the work of Souders and Brown [12]. This equation computes the ratio of the square power of the vapor load (noted in this chapter as Vload) to a constant, 8.75, to derive the tray flood. It has been used for over three decades by tray vendors (Koch and F.W. Glitsch [3]) to design and rate sieve-type trays. In many cases, especially for sieve-type tray design, jet flood governs tray flood and thus is the primary sieve tray design and rating equation. In contrast, Eqs. (3.88) through (3.90) are the principal equations for flood determination for both valve- and bubble cap-type trays. 

For sieve trays, the number of kinetic heads equivalent to the total pressure drop through the plate itself is a function of the ratio of the sieve-hole diameter to the tray thickness and the ratio of the hole area per tray to the active area per tray as shown in Fig. 16-5. This pressure drop for a reasonable sieve-tray design is generally in the range of 1 to 3 kinetic heads, and Fig. 16-12 can be used to choose the most reasonable number to use in preliminary designs Designating the number of kinetic heads obtained from Fig. 16-12 as K.H., the pressure drop due to gas flow through the holes for a sieve tray expressed as liquid head is... 

Because of their proprietary nature, valve trays are usually designed by their respective vendors based on process specifications supplied by the customer. However, most fabricators publish technical manuals that make it possible to estimate some of the design parameters. The procedure for calculating valve-tray pressure drop outlined here has been adapted from the Koch Design Manual. As for the other column specifications required, they can be obtained via the same calculation procedures outlined above for the sieve-tray design. 

Development in Palm Oil Deodorization. The main operation in the deodorizer is the stripping of volatile materials and thermal action due to the combined effects of superheated steam, high temperature, and efficient vacuum. The older deodorizers (prior to 1985) use bubble caps or sieve-tray designs to effect the... 

Sieve Tray Design Perforations usually are in the range of 0.125 to 0.25 in (0.32 to 0.64 cm) in diameter, set 0.5 to 0.75 in (1.27 to 1.81 cm) apart, on square or triangular pitch. There appears to be relatively little effect of hole size on the mass-transfer rate, except that with systems of high interfacial tension, smaller holes will produce somewhat better mass transfer. The entire hole area is normally set at 15 to 25 percent of the column cross section, although adjustments may be needed. The velocity through the holes should be such that drops do not form slowly at the holes, but rather the... 

Summarizing, the details of the sieve-tray design are as follows ... 

Next, enter the data presented above into the Mathcad sieve-tray design computer program of Appendix E. Since the dimensions of the tray are known, the fractional approach to flooding is adjusted until the tray design coincides with the tray dimensions determined in part (a) of this example. Convergence is achieved at a value of/= 0.431. This means that at the bottom of the distillation column the gas velocity is only 43.1% of the flooding velocity. Other important results obtained from the program are as follows ... 

Run the sieve-tray design program of Appendix E using these data. The program converges to a tower diameter D = 1.036 m and a tray spacing t = 0.6 m. When convergence is achieved, the results at the bottom of the tower are ... 

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