Sieve tray design requirements

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. 

For tray columns, bubble caps, valves or sieve, the feed liquid usually enters the column either in between functioning trays or at the top (reflux). The liquid or liq-uid/vapor mixture for flashing liquids must be dispersed uniformly across the tray. Such an arrangement often requires a special tray designed for the purpose to allow... 

Sieve trays are used throughout the absorption column, however two distinct hydraulic designs are required. The first sieve plate design is required for trays below the weak-acid feed point. Above the weak-acid feed point, the downcoming liquid flowrate is diminished. The vapour flowrate essentially remains constant throughout the column. Different vapour to liquid ratios above and below the weak-add feed point require a second hydraulic design to be considered. 

Design the trays for a distillation column separating dichlorobenzene (DCB) from a high-boiling reaction product. Include designs for sieve trays and valve trays, and discuss the applications of each. The product is temperature-sensitive, so sump pressure should be held at about 100 mmHg (3.9 inHg or 0.13 bar). The separation requires 20 actual trays. 

Consider the absorber of Example 3.7. Assume that the wash oil is n-tetradecane (C14H30). The absorber will be a cross-flow sieve-tray tower with dg = 4.5 mm on an equilateral-triangular pitch 12 mm between hole centers, punched in stainless steel sheet metal 2 mm thick, with a weir height of 50 mm. Estimate the number of real trays required, the dimensions of the absorber, and the power required to pump the gas and the liquid through the tower. Design for a 65% approach to the flooding velocity. 

Design a suitable sieve tray for the absorber of Prob. 8.4 and compute its hydraulics (which may be considered constant for aU the trays) and the number of real trays required, graphically and through Eq. (8.16). Take the surface tension as 30 dyn/cm. 

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