Types of Trays

FIGURE 14.4 Types of tray openings (a) bubble cap, (b) sieve, (c) valve. 

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Figure 8-28 presents the usual determination of optimum or near optimum theoretical trays at actual reflux based on performance. It is not necessarily the point of least cost for all operating costs, febrication costs or types of trays. A cost study should be made to determine the merits of moving to one side or other of the so-called optimum point From the Figure 8-28 ...

In addition nearly all of the major tray manufacturers can and do design bubble cap trays as well as the other t)pes on request for comparison with competitive types of trays. 

The type tray guide proposed by Huang and Hudson [30] serves to identify the m or breaks in type of tray design (Figure 8-120). In the region between types, the selection is not sharp and the design should be evaluated based on other criteria. 

The action on this type of tray seems to produce fewer jets of liquid froth than a bubble cap tray. The entrainment from the surface of the bubbling liquid-froth mixture is less (about K) than a bubble cap tray for the same superficial tower velocity and tray spacing. Generally the trays will flood before capacity reaches a limitation set by entrainment. 

Figure 8-150. Valve trays have the lowest liquid pressure drop of all three types of trays employed (also see Ref. 88,183,193 for additional interpretation). Used by permission, Klein, G. F Chem. Eng. V. 89, No. 9 (1992), p. 81 all rights reserved.

Fig. 2.14. Type of tray for freeze drying small cubes or granules of food.

Rolfgaard [2.2] compares the types of trays and heating systems The ribbed trays are said to have an uneven temperature distribution, because the distances between shelf and tray vary between 0.1 mm and 1 mm. The ribs could compensate this only partially. The variation in distances is correct, but Rolfgaard overlooks that the thermal conductivity in the bottom of the tray is so effective that practically no temperature differences are established in the bottom. Even with an evaporation of 3 kg ice/m2 h and the assumption that all heat is Transmitted only in the center of the tray (8 cm from the border of the tray), the temperature difference between border and center is approx. 5 °C. During the drying under actual conditions, no measurable temperature differences can exist. 

Fig. 2.16.2. Ice sublimation rate (kg/m2 h) for five different types of tray.

These three types of trays have a common feature in that they all have separate downcomers for the passage of liquid from each tray to the one below. There is another class of tray which has no separate downcomers and yet it still employs a tray type of construction giving a hydrodynamic performance between that of a packed and a plate column. Two examples of this type of device are the Kittel plate and a Turbogrid tray(53). Design data for these trays are sparse in the literature and the manufacturer s recommendations should be sought. 

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... 

Figure 13.41. Efficiencies of some fractionations with several types of trays as a function of vapor factor F = u fp or linear velocity, (a) Data of methanol/water in a column 3.2 ft dia [data of Kastanek, Huml, and Braun, Inst. Chem. Eng. Symp. Ser. 32(5), 100 (1969)]. (b) System cyclohexane/w-heptane in a 4 ft dia sieve column [Sakata and Yanagi, Inst. Chem. Eng. Symp. Ser. 56, 3.2/21 (1979)] valve tray data (Bulletin 160, Glitsch Inc., 1967). (c) Methanol/water [Standart et al., Br. Chem. Eng. 11, 1370 (1966) Sep. Sci. 2, 439 (1967). (d) Styrene/ethylbenzene at lOOTorr [Billet and Raichle, Chem. Ing. Tech. 38, 825 (1966) 40, 377 (1968)]. (e) Ethanol/water (Kirschbaum, Destillier und Rektifiziertechnik, Springer, Berlin, 1969). (f) Methanol/water [Kastanek, Huml, and Braun, Inst. Chem. Eng. Symp. Ser. 32, 5.100, (1969)].

TYPE OF TRAY INSTALLATION REMOVABLE WELDED BOLTED ... 

Specifying the need for a tray-type column, the type of tray must be determined. Sieve trays are considered most appropriate for this application. They offer a simple and inexpensive construction with low pressure drop (if the hydraulic design is adequate). Bubble cap and valve-type trays offer advantages in controlling liquid droplet entrainment, but pose significant difficulties for installation of cooling coils. 

Fig. 2.16.2. Ice sublimation rate (kg/m2 h) for five different types of tray. 1, Flat tray as in Figure 2.14(a), with 20 mm filling height 2, flat tray with one rib of 20 mm height 3, ribbed tray as in Fig. 2.15 4, ribbed tray as in Fig.

W. L. Gore Associates (Figure 2.17) has developed a type of tray from which product particles cannot escape during the drying process - the Lyoguard tray. When handling cytostatic products, persons, the environment and the freeze-dryer are protected from contamination. 

Campbell s series [5] states that many authors recommend, as do I, the O Connell method for hydrocarbons. You may select the two-film method by entering T. The Fractionation Research Institute (FRI) has for more than 30 years used and proven a much more thorough method called the two-film method, which is equally applicable to both fractionators and absorbers [6], The FRI method accounts for the actual tray internal configuration and fluid dynamics, making it far superior to the O Connell method. I have therefore produced a type of two-film method for determining tray efficiency that has been checked to be within 3% accuracy of hundreds of answers calculated with the FRI method. Called the Erwin two-film method, it is recommended for all types of trays and will also calculate the liquid tray residence time in seconds. This method is included in the three tray computer program executable files in the CD accompanying this book. 

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. 

Two types of trays are most common sieve trays and valve trays. A sieve tray is a simple perforated plate. Gas issues from the perforations to give a multiorifice effect liquid is prevented from descending the perforations or weeping by the upward motion of the gas. At low gas flow rates, the upward gas motion may be insufficient to prevent weeping. 

A third type of tray, once commonly employed but currently used only for special applications, is the bubble-cap tray. Its design and operation are discussed by Bolles (1963). 

The height of a distillation column depends on the feed conditions, the product purity specifications and the extent of separation through the vapour-liquid equilibrium relationship, but also on the type of tray or packing used in the column as this affects the rate of separation. Column vendors will normally provide information on tray or packing efficiencies.9,10... 

The hardware design proceeds In two phases primary (basic) and secondary (detailed layout). The primary phase sets column diameter, type of tray, and split of tray area Into bubbling and downcomer areas. This phase also provides a preliminary (and usually close) estimate of tray spacing, number of passes, and other features of tray and downcomer layout such as weir height, fractional hole area, hole diameter, and clearance under the downcomer. These estimates are later firmed up in the secondary phase. 

The discussions in this chapter emphasize sieve and valve trays, as these trays Eire 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 modern distillation practice argnes against a detailed discus-... 

Type of tray Hole diameter, in Tray thickness Number of passes... 

Connection. Always place your pumps in some type of tray so that any leaks will be contained and will not create slick spots. This placement is especially important if the pump is positioned on the floor. By placing the pump on the floor (and in a tray), any vibration effects from the pump on instruments sitting on lab benches will be limited. 

The fractionating unit is a sieve-tray column with a standard type of tray design. The vapor velocity through the tower is about 90 percent of the maximum allowable value. 

The trays of the DT are designed with an upper plate, lower plate, and structural members between designed-to-hold pressurized steam. The DT has three different types of trays predesolventizing trays, countercurrent trays, and a sparge tray. 

DCs are vertical, cylindrical vessels with a multitude of horizontal trays. The desolventized material enters at the top and is supported by the tray. The material is mixed above each tray and conveyed downward from tray to tray by agitating sweeps anchored to a central rotating shaft. The DC has three different types of trays steam drying trays, air drying trays, and air cooling trays. 

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