Proprietary trays

Adjustable weirs (Fig. 14-22 ) are used to provide additional flexibility. They are uncommon with conventional trays, but are used with some proprietary trays. Swept-back weirs (Fig. 14-22b) are used to extend the effective length of side weirs, either to help balance liquid flows to nonsymmetric tray passes or/and to reduce the tray liquid loads. Picket fence weirs (Fig. 14-22c) are used to shorten the effective length of a weir, either to help balance multipass trays liquid flows (they are used in center and off-center weirs) or to raise tray liquid load and prevent drying in low-liquid-load services. To be effective, the pickets need to be tall, typically around 300 to 400 mm (12 to 16 in) above the top of the weir. An excellent discussion of weir picketing practices was provided by Summers and Sloley (Hydroc. Proc., p. 67, January 2007). 

Antijump baffles (Fig. 14-24) are sometimes installed just above center and off-center downcomers of multipass trays to prevent liquid from one pass skipping across the downcomer onto the next pass. Such liquid jump adds to the liquid load on each pass, leading to premature flooding. These baffles are essential with proprietary trays that induce forward push (see below). 

In most cases the design of proprietary trays is best left to the supplier. 

The determination of tray column diameters is also discussed in ChaptO 1 and covned in detail in standard chemical engineering texts such as Perry s Chemical Engineer s Handbook (1963) and the Handbook of Separation Process Technology (Fair, 1987). Data on proprietary tray designs are normally supplied by the manufacturers. 

The design of a distillation column is based on information derived from the VLE diagram describing the mixtures to be separated. The vapor-liquid equilibrium characteristics are indicated by the characteristic shapes of the equilibrium curves. This is what determines the number of stages, and hence the number of trays needed for a separation. Although column designs are often proprietary, the classical method of McCabe-Thiele for binary columns is instructive on the principles of design. 

High capacity/high efficiency trays have valves or sieve holes oi bodi They typically achieve higher efficiencies and capacities by taking advantage of the active area under the downcomer. At this time, each ot the major vendors has its own version of these trays, and the designs arc proprietary. 

Valve trays, because of their proprietary nature, are usually designed by manufacturers, although it is possible to obtain an estimate of design and performance from published literature 63 and from the methods summarised in Volume 6. 

The outflow end of the pump tubing is connected directly to the components of the chemistry module. This module consists mainly of connectors and glass mixing coils. Proprietary modules are available, of course, but it is perfectly feasible to assemble the necessary components on a plastic tray fitted with four legs. Pump tubing and connectors are available from many suppliers. Apart from the OEMs, sources include ... 

Trays from this family are proprietary, and have been extensively used in the last two to three decades with great success. Compared to equivalent conventional trays, the truncated downcomer/forward push trays give about 8 to 12 percent more gas-handling capacity at much the same efficiency. 

In general, gas and liquid flows pulsate, with a particular perforation passing both gas and liquid intermittently, but seldom simultaneously. In large-diameter (>2.5-m, or 8-ft) dual-flow trays, the pulsations sometimes develop into sloshing, instability, and vibrations. The Ripple Tray is a proprietary variation in which the tray floor is corrugated to minimize this instability. 

Weep rste prediction. Lockett and Banik (56) and Hsieh and McNulty (63) proposed correlations for predicting weep rates from sieve trays. Both correlations are based on pilot scale deta, mainly with the air-water system. The Hsieh and McNulty correlation is based on a broader data bank, which includes the experimental data by Lockett and Banik. Hsieh and McNulty used an even wider, non-air-water, proprietary deta bank for testing some of their predicted trende. 

Apack meat trays have a base similar to that of the produce tray. It is mated to a clear, heat sealable PLA lidstock. PLA is an inherently poor oxygen barrier, but use of a proprietary post-extrusion step reportedly extends shelf life by 50% to 6-9 days. 

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. 

Due to the need to use case-by-case analysis the Kister studies [136, 137] focused on item 1. The data evaluated came from published reports by Fractionation Research (FRI) and Separation Research Program (SRP) at the University of Texas, taken from commercial size equipment rather than laboratory research columns. The FRI data includes No. 2 and No. 2.5 Nutter random rings packing, aind Norton s Intalox 2T structured packing, each considered currently state-of-the-art or close to it, while the sieve and valve trays were of FRI s latest designs, plus Nutter s proprietary valve trays, all using 24-in. tray spacing. 

---