Minimum total trays

Fenske Equation Overall Minimum Total Trays with Total Condenser... 

Example 8-12 Minimum Theoretical Trays/Plates/Stages at Total Reflux... 

The minimum theoretical trays at total reflux can be determined by the Fenske relation as previously given... 

Multichordal downcomers can increase weir length (Fig. 6). Fig. 6 shows a combined multichordal and stepped downcomer. The increased weir length decreases the liquid crest height over the weir. This decreases total tray pressure drop. The stepping is a variation of a sloped downcomer. The step increases the downcomer inlet area with a minimum decrease in tray active area. 

The separation in the distillation column is binary between A and C, so the design of the column is straightforward. Typically, the reflux ratio is set at 1.2 times the minimum, and tray-to-tray calculations give the total number of trays Nt and the optimal feed tray Np. 

Set Total Trays to Twice Minimum Number of Trays... 

In this chapter, a suitable entrainer for this acetic acid dehydration system will be selected from several candidate acetates. Steady-state tray-by-tray column simulation will be used to determine the best entrainer with minimum total annual cost (TAC). Optimum process design and operating conditions will be determined to keep a high-purity bottom acetic acid composition and also to keep a small acetic acid loss in top aqueous draw. The overall control strategy of this column system will also be proposed to hold both bottom and top product specifications in spite of feed rate and feed composition disturbances. In the control study, conventional control strategy using only tray tempaature measurements will be considered so that the result of this study can easily be used directly in industry. 

The conditions of total liquid reflux in a column also represent the minimum number of plates required for a given separation. Under such conditions the column has zero production of product, and infinite heat requirements, and Lj/Vs = 1.0 as shown in Figure 8-15. This is the limiting condition for the number of trays and is a convenient measure of the complexity or difficulty of separation. 

Because a column cannot operate at total reflux and produce net product from the column, a reflux ratio of about 1.1 to 1.5 times the mmmMm reflux will usually give practical results. Be aware that as the reflux ratio comes down approaching the minimum, the number of theoretical and then corresponding actual trays must increase. 

The results indicate that 25 theoretical plates are minimum then by assuming an efficiency of 50%, total actual trays of 50 should be adequate. Choose values of k (see nomenclature) and solve for b and Xj by ... 

UK. = Light key component in volatile mixture L/V = Internal reflux ratio L/D = Actual external reflux ratio (L/D) ,in = Minimum external reflux ratio M = Molecular weight of compound Mg = Total mols steam required m = Number of sidestreams above feed, n N = Number of theoretical trays in distillation tower (not including reboiler) at operating finite reflux. For partial condenser system N includes condenser or number theoretical trays or transfer units for a packed tower (VOC calculations) Nb = Number of trays from tray, m, to bottom tray, but not including still or reboiler Nrain = Minimum number of theoretical trays in distillation tower (not including reboiler) at total or infinite reflux. For partial condenser system,... 

Calculate the total wet tray pressure drop, using an assumed height of clear liquid on the tray of 0.5-in. minimum to 4-in. maximum (1 to 2-in. are usual values). 

Minimum Trays at Total Reflux Fenske Equation ... 

Example 8-25 Scheibel-Montross Minimum Reflux, 80 Minimum Number of Trays Total Reflux — Constant Volatility, 80 Chou and Yaws Method, 81 Example 8-26 Distillation with Two Sidestream Feeds, 82 Theoretical Trays at Operating Reflux, 83 Example 8-27 Operating Reflux Ratio, 84 Estimating Multicomponent Recoveries,... 

Aeration towers are often simply constructed wooden towers with or without the benefit of a forced-air draft, over which the well water is distributed. Typically, the tower holds 8 to 10 trays, each with a 3- to 4-inch (7.6-10.2 cm) bed depth of volcanic lava or coke media to provide the total 30 to 36" (76-91 cm) depth required. The lava or coke acts as a catalyst for the further precipitation of iron and manganese salts. These salts can be readily oxidized provided there is sufficient alkalinity present. If in doubt, ensure a minimum of 120 to 150 ppm total alkalinity (T Aik or M Aik) as CaC03. 

Figure 13.7. Features of McCabe-Thiele diagrams for constant molal overflow, (a) Operating line equations and construction and minimum reflux construction, (b) Orientations of -lines, with slope = ql q — 1), for various thermal conditions of the feed, (c) Minimum trays, total reflux, (d) Operating trays and reflux, (e) Minimum reflux determined by point of contact nearest xD.

The distribution of nonkeys actually depends somewhat on the reflux ratio. For instance, in the case of Example 13.10, the distributions at minimum trays (total reflux) and minimum reflux are substantially different. Often it turns out, however, that the distributions predicted by Eq. (13.119) are close to those at finite reflux whenever R is near 1.2Rm, which is often near the economic value for the reflux ratio. Further discussion of this topic is by Hengstebeck (Distillation, 1961) and Stupin and Lockhart (1968) whose work is summarized by King (1980, p. 434). Knowledge of the complete distribution is needed for estimation of top and bottom temperatures and for determination of the minimum reflux by the method to be cited. 

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