Distillation trays

Distillation trays constiircted of porous catalyticaUy active material and reinforcing resins Method described for removing or replacing catalyst on trays as a hquid slurry Catalyst bed placed in downcomer, designed to prevent vapor None specified Wang et al., Chinese Patent 1,060,228 (1992) Jones, U.S. Patent, 5,1.3.3,942 (1992)... 

Breakup in a highly turbulent field (L/velocity) ". This appears to be the dominant breakup process in distillation trays in the spray regime, pneumatic atomizers, and high-velocity pipehne contactors. 

Lm. The coarseness results from the relatively low power dissipation per mass on distillation trays. This means that it is relatively easy to remove by a device such as a wire mesh pad. Over 50 percent is typically captured by the underside of the next higher tray or by a turn in the piping leaving an evaporator. Conversely, though small on a mass basis, the smaller drops are extremely numerous. On a number basis, more than one-half of the drops in the lower curve are under 5 [Lm. These can sei ve as nuclei for fog condensation in downstream equipment. 

At higher vapor loads, the kinetic energy of the vapor rather than the bubble burst supphes the thrust for jets and sheets of hquid that are thrown up as well as the energy from breakup into spray. This yields much higher levels of entrainment. In distillation trays it is the most common limit to capacity. 

Tray efficiency is one example of the first interaction. Figure 30-6 is a representation of a distillation tray. 

FIG. 30-6 Rep resentation of a distillation tray numbering from the top of the column. 

The American Institute of Chemical Engineer s Distillation Tray Efficiency Research [2] program has produced a method more detailed than the short-cut methods, and correspondingly is believed to produce reliable results. This method produces information on tray efficiencies of new systems without experimental data. At present there is not enough experience rvith the method and its results to evaluate its complete range of application. 

Murphree [85] developed point and overall distillation tray efficiencies, which are examined in detail in Reference 2. The expressions are [59] ... 

Example 8-13 Estimating Distillation Tray Efficiency by Equations 8-7OA and 8-7OB (used by permission of McFarland et al. [86])... 

Figure 8-69B. Nutter float valves in open and closed positions for use on distillation trays. Used by permission, Nutter Engineering, Harsco Corp., Bui. N-2.

Figure 8-90. Distillation tray layout form. (Use with Figure 8-91, not reproduced to scale.) Used by permission, Wyatt Metal and Boiler Worlds, Inc. (1956).

General Purpose Distillation Trays Using 3 in. I.D. Pressed Metal Bell Caps on 5 -in. Centers... 

The packed column has been quite useful in distillation, stripping, and absorptions processes and has become competitive tvith many types of distillation tray designs or types/styles. 

Distillation Tray Features Low AP, High Efficiency, Chem. Engr. Jan. 20 (1975). 

An organic liquid flows across a distillation tray and over a weir at the rate of 15 kg/s. The weir is 2 m long tmcl the liquid density is 650 kg/m3. What is the height of liquid flowing over the weir ... 

Stirred tanks are modeled assuming that both phases are well mixed. Tray columns are usually modeled as well mixed on each tray so that the overall column is modeled as a series of two-phase, stirred tanks. (Distillation trays with tray efficiencies greater than 100% have some progressive flow within a tray.) When reaction is confined to a single, well-mixed phase, the flow regime for the other phase makes little difference but when the reacting phase approximates piston flow, the flow regime in the other phase must be considered. The important cases are where both phases approximate piston flow, either countercurrent or cocurrent. 

Lockett, M. J. (1986) Distillation Tray Fundamentals (Cambridge University Press). 

Figure 9.2 Distillation trays. (From Smith R and Jobson M, 2000, Distillation, Encyclopedia of Separation Science, Academic Press reproduced by permission).

Equation 9.61 is only approximate at best. For distillation trays with long flow paths across the active plate area, Equation 9.61 tends to underestimate the overall efficiency. 

It should be emphasized that the overall stage efficiency from Equation 9.61 should only be used to derive a first estimate of the actual number of distillation trays. More elaborate methods are available but are outside the scope of this text. In practice, the stage efficiency varies from component to component, and more accurate calculations require much more information on tray type and geometry and physical properties of the fluids. 

Engineering Staff, Shell Development Company, Emeryville, California Chem. Eng. Prog. 50 (1954) 57. Turbogrid distillation trays. 

Many of the considerations discussed in the previous section can be applied to vertical bubble flow. Two cases are of interest first, one in which there is no downward or upward liquid flow (Ql = 0), for example, on a distillation tray. With a shallow liquid layer there will be no liquid velocity profile, and hence bubble-rise velocities for uniformly sized bubbles will be the same at each cross-section. It can be shown (see Nicklin, N2) that if the rising velocity of a swarm of bubbles not continuously generated in a still liquid is Vo, then the rising velocity relative to the tube of a swarm of continuously generated bubbles will be, for... 

Later we measured the concentrations of n-propyl, isobutyl, and the combined isoamyl and active amyl alcohols (3-methyl-l-butyl alcohol and 2-methyl-l-butyl alcohol) in distillation tray liquids using a gas chromatographic method with n-butyl alcohol as the internal standard. The distribution of the higher alcohols in the 14-tray concentrating section of a 12-inch pilot column during a run in which the product from tray 7 was 169° proof is shown in the upper portion of Figure 4. The... 

In high pressure distillation, tray operation is usually in the emulsion regime. In small diameter (less than 1.5 m) columns, or at low liquid loads, or the low end of the pressure range (towards 10 bar), however, the froth-and spray regimes can be found. 

M.J. Lockett, Distillation tray fundamentals, Cambridge University Press, Cambridge (1986). 

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