Perforated trays

Formex pro-cess, Snam-progetti /V-formyl-morph o-line (FM) water is added to the FM to increase its se-lectivity and also to avoid high reboiler temperatures during solvent recovery by distillation 40 perforated-tray ex-tractor, FM density at 1.15 aids phase separation low corrosion allows use of carbon steel equipment... 

FIG. 12-85 Perforated-tray type of reactor-discharge control. 

FIG. 15-37 Portion of a perforated-tray tower, arranged for light liquid dispersed. 

TABLE 15-8 Mass-Transfer Data for Perforated-Tray Towers... 

An impingement scrubber is designed to make the dust particles impinge and adhere to water droplets. Gas is introduced at the bottom and passes up through water-covered perforated trays, where dust is removed by the scrubbing liquid. 

Data from bubble cap and perforated tray columns for the Murphree vapor plate efficiencies are correlated [86] ... 

Sieve Tray or Perforated Tray With Downcomers... 

Figure 8-67A. Sieve or perforated tray with downcomers.

Figure 8-68A. Perforated tray without downcomer. Used by permis Sion, Hendrick Mfg. Co., Carbondale, Pa.

Figure 8-120. Selection guide, perforated trays with downcomers. Used by permission, Chen-Jung and Hodson, J. R. Petroleum Refiner, V. 37 (1958) p. 104, Gulf Publishing Co., all rights reserved.

Vq = vapor velocity through perforated holes, ft/sec p = fraction perforated hole area in perforated tray area only... 

Figure 8-128. Orifice coefficient for perforated trays. Used by permission, Hughmark, G. A., and O Connell, H. E., The Americsn Institute of Chemical Engineers, Chem. Eng. Prog., V. 53, (1957), p. 127M, all rights reserved.

This is the case with diameter determination. The relation of Equation 8-250 for the perforated tray or sieve tray with downcomers can be used for the plate without downcomers. Generally, the liquid level and foam-froth height will be higher on this tray, hence the ralue of h., clear liquid on the tray, may range from 1-in. to 6-in. depending on the service. 

Data are not available to distinguish between the entrainment of sieve and perforated trays without downcomers. The relation of Himt et al. [33] given for sieve trays is recommended, and should apply quite well. 

Figure 8-147. Veipor and liquid rates for tray activation perforated trays, no downcomers. Compiled from data of Sutherland [69] and Myers [47].

At the flood point, liquid continues to flow down the column, but builds up at a greater rate from tray to tray. Sutherland [69] demonstrated that flooding moves up the column from the point of origin. For this reason it is important to design perforated trays without downcomers with extra care, as changing internal rates are quickly reflected in performance if the proper hole requirements are not met. They are a usefiil tray for steady state operations. 

For new towers, the designs will usually develop to utilize the entire tower cross-section. However, for existing towers with perforated trays being installed to replace bubble caps or packing, the optimum active tray area may not utilize the entire cross-section. If the number of holes required is small compared to available area, it is better to group the holes on 2.5 dg to 3.5 do than to exceed these limits. Holes separated by more than 3 in. are not considered effective in tray action so necessary for good efficiency. Blanking strips may be used to cover some holes when more than required have been perforated in the tray. 

Example 8-40 Design of Perforated Trays Without Downcomers... 

Because it is known that the entrainment from perforated trays is considerably less than for bubble caps, the 2-ft, 8-in. diameter would be very conservative and perhaps excessively large. 

Fair, J. R., Tray Hydraulics-Perforated Trays, Chap. 15 in... 

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. 

Sonication using ultrasonic cleaner baths remains a popular extraction approach particularly for controlled-release products. In sonication, an ultrasonic wave of 20-40 kHz generated by a piezoelectric transducer is used to produce the formation and collapse of thousands of microscopic bubbles (cavitations) in the water bath to facilitate the break up of the solid particles and the subsequent dissolution of the API. Note that parameters such as the wattage power of the sonicator, presence of the perforated tray, depth of the water level, bath temperature and the number of sample flasks sonicated might all affect the extraction rate. For... 

There are two types of tray decks perforated trays and bubble-cap trays. In this chapter, we describe only perforated trays, examples of which are... 

Possibly 90 percent of the trays seen in the plant are of these types. Perforated tray decks all have one feature in common they depend on the flow of vapor through the tray deck perforations, to prevent liquid from leaking through the tray deck. As we will see later, if liquid bypasses the outlet weir, and leaks through the tray deck onto the tray below, tray separation efficiency will suffer. 

On the other hand, bubble caps (or even the more ancient tunnel cap trays) are different, in that they do not depend on the vapor flow to retain the liquid level on the tray deck. More on this later. For now, just recall that we are dealing only with perforated tray decks. 

This concept is the basis for tray design for perforated tray decks. While various valve tray vendors maintain that this rule does not hold for their equipment, it is the author s industrial experience that valve trays leak just as badly as do sieve trays, at low vapor hole velocities. To summarize ... 

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